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AA - $$$ . /"/"#012" . )*3- +) * . !4 !& 5!6%55787& %) A . 0 @ ! . 9:.567<=8>!<7>.567<=8>!<7>%F?9:. . B & " . /012134. B + AD E $.-.15302/13 - A. G8>78A. . /"/"#012" . )*3- +) ". & 8>78 . NO CONTENTS 1 INTRODUCTION 2-3 2 AIMS & OBJECTIVES 3 REVIEW OF LITERATURE 5-39 4 METHODOLOGY 40-56 5 RESULTS 57-70 6 DISCUSSION 71-75 7 CONCLUSION 76 8 SUMMARY 77-78 9 BIBLIOGRAPHY 79-86 ϭ PAGE NO 4 .TABLE OF CONTENTS SL. 2. lack of toxicity. facility of repair. low water sorption. a certain lack of dimensional accuracy has been accepted as one of the disadvantages of complete denture construction./EdZKhd/KE INTRODUCTION Acrylic processing of waxed-up dentures is considered to be a crucial and technique sensitive procedure.4 Any occlusal discrepancies that result during denture fabrication are disappointing and offset the above advantage. and construction by a simple molding and processing technique. The advantages of PMMA include excellent esthetic properties. low solubility. Polymethylmethacrylate (PMMA) has become the most commonly used material for denture bases since its introduction in 1937. Ϯ . Even after investing a lot of time and clinical skill a definitive movement of teeth during and after processing has long been observed which lead to occlusal discrepancies & disturb the harmonious occlusal scheme achieved earlier.3 Polymerization shrinkage affects the position of the teeth on maxillary and mandibular dentures.1 Since their introduction in Dentistry . adequate strength. resulting from the unavoidable denture base shrinkage during acrylic resin polymerization. and thus the final occlusion of the dentures. Optimum functional occlusion in complete denture prosthesis is one of the basic objectives in Prosthodontic therapy. /EdZKhd/KE The skill and meticulousness of the operator in executing the laboratory procedures is important for successful reproduction of the waxed-trial denture to its completed form. This study was done to investigate the influence and relationship of investing medium on the movements of teeth taking place in two dimensions of space in compression molding technique. when the casts are remounted on an articulator. the more the time consumed in their correction . Compensation is made for opening of vertical dimension by selective spot grinding of teeth until the original occlusion is restored. Shifting of teeth results in an opening of vertical dimension10 and this is indicated by lifting of the incisal guide pin13. careless packing of acrylic resins in the mold space and improper closure of the two flask halves. but in case of more severe opening. Many attempts have been made to minimize the risk of such changes and to improve the accuracy of reproduction of waxed-trial denture in an acrylic resin. it necessitates grinding of the cusps thereby destroying the anatomic features of teeth. The greater the occlusal errors. This grinding process is not only time consuming. The tooth may change in its position as a result of investing procedures (setting expansion will result in movement of the tooth along with the setting dental plaster). ϯ . /DΘK: d/s AIM & OBJECTIVE AIM OF THE STUDY: The aim of this study was to investigate the influence and relationship of investing medium on the movements of teeth taking place in two dimensions of space in compression molding technique. OBJECTIVE OF THE STUDY: To evaluate and compare the movement of artificial teeth in two dimensions of space (anteroposterior & medio-lateral) during processing of the waxed-up dentures using two different gypsum materials for investing. ϰ . d) Flask packed at low pressure entirely with improved dental stone showed no reduction in increase vertical dimension measurement. b) An increased vertical dimension to a minimum of 0. he attributed the heat liberated by setting investment material to the movement of teeth in their wax foundation. Another study was done by Perlowski6 on investment changes during flasking as a factor of complete denture malocclusion. ϱ . On basis of this he concluded: a) The acrylic resins at the final closure of flask had sufficient internal shear resistance or viscosity to allow severe stress distribution in the uncured denture resulting in shifting of some teeth more than others. He used a waxed up ball denture for this purpose.6mm was found to depend on the pressure in the acrylic resin and the material used in the third pour of the flask. iii) Conventional method.Z s/ tK&>/d ZdhZ REVIEW OF LITERATURE A study by Mahler5 was conducted in 1951 on the inarticulation of complete denture processed by compression molding technique. he flasked three identical dentures in three different methods: i) With a stone matrix. The author analyzed the factor of vertical movement of the teeth relative to the investment. ii) With a plaster matrix. c) Absence of pressure during curing cycle had no effect upon the vertical dimension measured. In his experiment. After processing these dentures the indentations of these balls on the investment indicated the presence of pressure in the resin. caused by the pressure applied by the acrylic resin during packing and curing process. followed by during packing of the flask and finally during finishing and polishing procedures.The primary purpose of this study was to measure and to compare the ϲ . c) The close adaptation of the matrix was more important than the hardness of the material used.fabrication of a denture:here they concluded that the first alteration occurs at the time of gypsum cast poured. In an article Woelfel et al 7 on dimensional changes occurring in artificial dentures. b) Plaster matrix aids in the separation of investment from finished denture. A study again by Woelfel et al8 was conducted in 1960 on dimensional changes occurring in dentures during processing. b) Contents of resin base. prevents shifting of teeth during flasking and diminish the internal strains of curing. c) Release of strains. b) The expansion caused by water sorption is about 0. He concluded:a) There was some shifting of the teeth during die investing procedure.2mm and compensates for curing shrinkage.II] Changes during clinical service: And here they came to a conclusion that the dimensional changes during service are due to: a) Sorption on loss of water. d) Flexure fatigue.Z s/ tK&>/d ZdhZ He observed that the use of plaster matrix around the teeth is the most accurate of flasking methods measured. the authors grouped these changes under following:I] Changes during .3mm. They finally concluded that: a) The amount of linear shrinkage occurring in molar-to-molar span is less than 0. D Mirza9 described the degree of dimensional change occurring in dentures and the clinical adaptation of autopolymerized acrylic denture was as good as that exhibited by heat processed dentures. but linear dimensional changes of autopolymerized dentures after 3 months of use was greater than that of heat polymerized dentures ϳ .In this study the authors measured: a) The vertical discrepancies in occlusal relations by comparing the position of incisal guide pin. thus the direction of force should be towards the tongue-cheek side. stainless steel reference pins were inserted in the 2nd molar central fossae and in buccal flange borders measurements were done with the help of Toolmakers microscope. An article by F. For this.The largest part of molar-to-molar on flangeto-flange processing shrinkage occurred when the vertical dentures were removed from the gypsum cast and this was attributed to elastic strain produced when the high-expanding resin was cooled in low expanding mold.00-1. He stated that the average processing shrinkage of autopolymerized dentures after 8 hour of processing was less than that of heat-cured dentures. If the hydraulic force was applied on the tissue borne side of the dentures.b) The linear change in molar-to-molar dimensions from wax model dentures to the polished dentures. The changes in the occlusal relationships as evident by the increase in height of the incisal guide pin before and after curing was from 0.49mm.Z s/ tK&>/d ZdhZ relative accuracy of fit of 186 dentures using recommended processing techniques. then the resin was not adapted properly to the cast. In his experiment he made 80 dentures and divided them into 6 groups. Another study by Atkinsin11 in investigated the movement of teeth during packing and polymerizing of acrylic resin denture base materials their work highlights the importance of a knowledge of the pressure developed during packing and processing and their effect on the denture. and air bubble incorporation. ϴ . at time of final closure reduced the increase of vertical dimension especially when removed from both upper and lower molds. In Group II. He observed the addition of acrylic resin increased the vertical dimension of occlusion while removal of the resin. While in Group VI a small plug of resin was removed from both upper and lower mold. a small plug of resin was removed from the palate region in upper denture before final closure of the flask. In each group he made a single modification in the flasking and packing procedure to study their effect on vertical dimension of occlusion. The authors inferred that the movement of teeth during polymerization is due to several factors namely expansion of the mould during setting of gypsum material. Shrinkage that occurs during polymerization. In Group IV a similar size piece of resin was added to both upper and lower molds.Z s/ tK&>/d ZdhZ A study by Shippee10 was performed in order to evaluate and compare the increase in vertical dimension of compression-molded dentures. Group 1 was the control group. All the dentures were cured under similar condition at 165°F for 8 hours. In Group V a small plug of resin was removed from the lingual flange of lower mold. In Group III a small plug of resin was added to resin in mold for the upper denture. creating strain in the resin. A study was conducted by Peyton & Anthony14 to compare different types of materials as well as techniques of processing a wide range of denture base materials. c) Changes in occlusion are due to release of internal stresses following the polymerization of the acrylic resin base. b) The use of core matrix around the teeth minimized the tooth movement relative to cast. and not by thermal expansion of the wax. Another investigation by Grant13 evaluated the cause and extent of the incisal guide pin elevation following attachment of casts to the articulator by using a sensitive dial gauge attached to the incisal pin of the Hanau articulator. which results in the tilting of teeth. was attached. He concluded: a) During investment the tooth movement is caused by setting expansion of the gypsum. 7cm long. Four different types of self-cure ϵ .Z s/ tK&>/d ZdhZ An investigation by Grant12 described a method. which allowed direct observation of the effect of investment procedure on tooth movement He casted one of the molar tooth of a waxed up complete lower denture in brass and on its occlusal surface a straight vertical metal pin. Both pins were contained in loose plastic sleeves to prevent locking of the pins in the 2nd pour investment. A similar pin was fixed to the surface of cast and the upper end of the pin was bent towards the pin attached to brass tooth. He observed that the elevation of the incisal pin can be limited by delaying the final locking of the articulator pin until the plaster mounting has been in position for at least half hour. Further it was proposed that a layer of wax on the land around the entire border of denture which is subsequently replaced by the layer of resin after packing acts as a cushion and a reservoir. They also compared the total processing time and total working time between the self-cured and heat cured acrylic resin. a Styrene and Vinyl acrylic type. In an article16 on processing complete dentures without tooth movement. The heat-cured dentures did not fit quite as well but were considered good. Another study by Lerner& Pfeiffer15 showed an increase in vertical measurement after processing of complete dentures upto 0. Tilon and Luxene was similar in regard to fit and was slightly less accurate as a group. thus controlling the shrinkage of resin that occurs immediately following polymerization and during the cooling period. The changes during storage were minor and intended to improve rather than detract from the initial fit. He emphasized on few points namely: a) ϭϬ . seven heat cured acrylic materials were used and three special injection products were studied. The authors concluded that the most accurate dentures were invariably of self-cured type. which represents an acrylic resin. apparently as a result of fewer stresses formed during cooling in the moulds. The special injection group comprised of Jectron. when stored in water for an extended period.Z s/ tK&>/d ZdhZ material were included. Rudd gave in depth step-by-step procedure to process complete denture. They also changed relatively little. The total processing time is relatively long (273 minutes) but the working time with both the resins was found to be same (33minutes).5mm by measuring the lift of the incisal pin from the incisal table with the help of modified Vernier Calipers. a = angle of cast orientation). b) There was resultant tooth movement to the left when the cast is depressed to the right and vice versa. An experiment was designed by Lam17 to determine the effects of the 'flash' on the tooth cast relationship. An article by Pera. c) Flash prevents the mold from complete closure.b) He devised a special flask with the central exhaust in which he ϭϭ .Z s/ tK&>/d ZdhZ Investing to be done only in artificial stone. He suggested. d) Repeated trial closures until no flash is evident. c) Minimum packing pressure to be used with maximum flow time.He used a simple photographic method in bodying a double exposure procedure.a) Firstly he emphasized on freezing the mold before packing of the acrylic resin. which revealed the directional patterns of tooth displacement relative to master cast.18 suggested two procedures for avoiding some of the changes that occur in processing acrylic resin dentures.d) Lateral direction is a function of angle of cast orientation and the raised bite (flash thickness) L = d sin a where( L = Lateral direction. He concluded: a) There was posterior movement of the teeth when the anterior part of the cast was placed lower in the flask than the posterior part and vice versa. The amount of displacement of the teeth relative to the cast along with the direction of the displacement that resulted from the various angulations of the cast in the flask was studied. b) Packing should be done for only one denture at a time with only one mix of acrylic resin. d = thickness of flash. freezing helps in slowing down the transformation of the resin from plastic to elastic state. the upper denture should be processed first and the occlusion is corrected against the lower denture in wax and then the lower denture should be processed by the same double-processing technique. Trial closures were done in both group and subsequently after curing the dentures ϭϮ . A study was conducted by Wesley et al 20 that analyzed the relationship between the material used to invest trial dentures and the vertical occlusal changes that occur during curing cycles. and then the teeth and their veneer parts were processed to the bases. The authors used non-anatomic acrylic teeth and arrangement was done in centric occlusion keeping the incisal pin in contact with the table of the articulator. An investigation by Tucker & Freeman19 using double-processing technique for processing complete denture to eliminate some of errors resulting from processing of the acrylic resin in the conventional manner was performed. In the first group -1:1 ratio of Plaster of Paris and artificial stone was used as investment material and the 2nd group the occlusal surfaces of the waxed up dentures was covered with plaster-stone combination. First the base was processed to the cast. He suggested that the exhaust an escape hole should be larger in diameter and short in height to facilitate easy escape of the excess resin.The author suggested.Z s/ tK&>/d ZdhZ allowed the acrylic resin to flow out freely without excess pressure in the flask. to avoid an increase in occlusal vertical dimension. The trial dentures were removed from the articulator and were flasked by using two different investment materials. He observed no change in relation of the pins to each other. it was mounted back on articulator. Then. matching interdigitating tooth aluminum plates were waxed up on the maxillary and mandibular casts and he repeated the experiment with them. First. the mandibular base was processed and after processing. The raise in the incisal pins was measured with vernier calipers.Later an extension of the waxed up maxillary denture onto the posterior aspect of the cast was made. A study by Vig. They came to conclusion that: a) There is no statistically significant difference found between the two investing technique.To simulate a quadrant of posterior teeth.Z s/ tK&>/d ZdhZ along with their cast were transferred back on to the articulators. which compared the shift of the posterior segment of the teeth after processing. The observations were similar to that of the previous experiment. he processed the maxillary dentures and again mounted them on the articulator and found that pins had moved anterior to the corresponding mandibular pins. b) Correction of processing changes should be done before the separation of dentures from the cast. ϭϯ . bases were waxed up and pointed pins were set in maxillary -and mandibular areas to exactly oppose each other.21 proved the hypothesis that the shift of posterior teeth occurred mainly in the maxillary denture. He devised an experiment where by the edentulous maxillary and mandibular casts were mounted on a Hanau articulator. placed in the acrylic teeth and the denture flange. c) Inadequate investing procedures contribute to vertical opening and occlusal discrepancies. An investigation in 1977 by Becker et al 23 used CDC 6400 digital computer for mathematical correction and evaluation of three-dimensional changes in denture teeth and internal surface of denture when the dentures were processed by three different techniques:1) Silicone-gypsum molding technique. The base of these holes formed the reference plane. Eighty trial dentures were fabricated using non-anatomic posterior teeth and the investing materials selected for the study were silicone rubber. artificial stone and plaster of paris. Conventional compression molding technique was used for packing and short curing cycle was employed (1/2 hours at 160°F and 2 !/2 hours at boiling temperature). ϭϰ . The authors placed 3 holes on the crest of ridges. d) Vertical opening of dentures processed by compression molding technique may be due to other factors. 2) Fluid resin technique. which needed further investigation. from which the measurements were done by the movement of metal inserts. one on the crest of incisive papillae and other on the maxillary tuberosities of the cast. The author came to the conclusion that: a) Investing in plaster of paris molds with a stone occlusal matrix can minimize vertical opening in denture processing. b) Tooth movement is minimized by the use of the combination investment. 3) All gypsum pressure molding technique.Z s/ tK&>/d ZdhZ Another study by Zakhari 22 investigated the relationship of investing medium to occlusal changes and the amount of vertical opening in compression molding technique. of 42-gauge diameter. a Hooper duplicator with special vertical posts. a dial gauge and split mounting plates with which they evaluated the tooth movement and dimensional changes of denture base material using 2 investment methods. Another study was done Garfunkel25 to evaluate dimensional changes in complete dentures processed by injection-pressing and the pack and press technique. A study was devised by Mainieri et al 24 consisting of a surveyor. b) Horizontal movement of the teeth was more lingual in silicone investment technique. 2) There was no one processing technique superior to others. which had been processed by the pack and press method. showed greater changes in horizontal and diagonal direction than dentures processed by the injection-pressing method. The author concluded that there are several changes in position of teeth in complete dentures from the wax-up stage until the dentures are processed and polished. Dentures. However. c) The weight of the residual impression between the denture base of acrylic resin and master die was same for both the techniques.Z s/ tK&>/d ZdhZ They came to the conclusion that: 1) All three processing techniques showed three-dimensional changes in position of teeth and internal surface of dentures. vertical changes before decasting are ϭϱ . It emphasized that: a)the amount of vertical opening found in dentures processed with silicone investment was same as for those processed with all gypsum technique. Another study by Shetty &Udani4 measured the movement of artificial teeth in waxed trial dentures in three planes using metal inserts and travelling microscope. A study was conducted by Dukes27 that compared the increase in vertical dimensions of complete dentures after processing with a compression molding technique and with a pour resin technique.Z s/ tK&>/d ZdhZ greater in the injection-pressing method. The authors concluded that the increase in vertical dimension was 6. to evaluate the effect of undercuts. Radiographs made of the lead strip were projected at x 20 magnification and subsequent tracings of the pin inserts were measured and superimposed to evaluate the shrinkage and contour changes. palatal thickness and double curing on the curing changes in acrylic dentures.5 times greater for the pour resin technique than for the compression molding technique. A chrome-cobalt metal base was fabricated over a maxillary cast having a reference point in the center wax up was done over this base and acrylic teeth were placed having metal inserts. which was attached to the pin of articulator. The increase in vertical dimension was measured by calculating the amount of incisal pin opening of a Hanau articulator using a Starett measuring device. Based on the t-test statistics. there was no significant difference between the two methods. involving a precision cast and denture positioner and transfers a lead foil strip from cast to denture. An article by Lechner et al26 gave a simple technique. The movement of these metal ϭϲ . 2. The width of posterior extension was 25mm.The three methods used were: 1. Complete dentures were made for 30 patients. Fabricating complete denture by waxing a layer of base plate wax *the wax-up of the maxillary denture was extended on to the posterior aspect of maxillary cast and 8mm down over posterior edge of master cast. Conventional method of fabricating a complete maxillary denture.The difference between the two methods was highly significant on the basis of t-test statistics. Third method in which six holes were bored before posterior palatal seal in midpalatal area of maxillary cast The authors concluded method 2 and 3 were superior to the conventional method for processing complete maxillary dentures in minimizing induced malocclusion. 7 and 24 hours.Z s/ tK&>/d ZdhZ inserts relative to the central reference pin was evaluated using a travelling microscope at 2. Whereas the processing changes noted with the conventional pack-and-press method were similar to previous studies. In a study by Strovaher29 changes in vertical dimension between the waxed and processed dentures were measured at the incisal guide pin by using a dial indicator. 4. The author concluded the tooth movement in wax trial dentures invariably occurred and has no correlation in direction and time. Fifteen sets were processed by conventional compression molding and 15 sets were processed by using the SR-lvocap injection system. An investigation by Polyzois28 compared three method of waxing denture to minimize tooth shifting in denture fabrication . the ϭϳ . 3. These methods have been attempts to improve the accuracy of fit of the dentures. and light-energy activation. and various combinations (including polymerization under pressure) have been offered as alternative ways to make dentures. but sometimes the goal has also been to provide a more convenient laboratory technique. Comparisons were made before and after polishing the prepared bases to determine if changes occur as a result of this procedure. Chemical-. described by Rupp and others in 1957. An extensive review by Takarnata & Setcos30 covering studies that have investigated the accuracy of acrylic and other types of resins for making dentures using the known range of fabrication methods was published. Traditional compression molding and heat-activation methods for polymerization of denture base resins have been widely used. was used to compare ϭϴ . microwave-.Z s/ tK&>/d ZdhZ injection method produced little or no pin opening. A study by Jackson31 to compare the mucosal surfaces of maxillary complete dentures processed using the SR-lvocap injection technique and the Lucitone heat-polymerized compression molding technique to a metal master impression to determine if one method of denture processing produced a more accurate denture base was performed. The superiority of the injection method before decasting was indisputable. The dental comparator. Studies have shown that stresses introduced during processing can lead to the distortion of denture bases. and the results suggest that the laboratory remount procedure may be unnecessary when this system is used. In another study by Shlosberg et al32 several physical property tests were conducted to compare microwave energy and conventional hot water bath polymerization techniques. No difference found between Lucitone. No porosity was observed in complete or removable partial denture bases polymerized by either technique. Accupak (pack pressed) and SR-Ivocap (injection pressed). and residual monomer content of resin test strips. Another study by Derckx 33 used the Moire topography for measuring the dimensional accuracy of resin complete bases. A study was conducted by Takahashi34 to clarify some of the dimensional change patterns of the denture base of the complete denture following polymerization. density. Dimensional changes of three ϭϵ . Lux-I-dent (injection pressed) found to be well fit to the tissue.Z s/ tK&>/d ZdhZ selected points on the palatal surface of the denture bases. No statistical differences were found in the accuracy of the denture bases processed using either of the two techniques. The two methods of polymerization produced similar dimensional accuracy in complete denture bases. No differences were found in transverse strength. Two methods of evaluating the dimensional accuracy of denture bases were compared using four resin materials and different processing techniques. Knoop hardness. Comparable strength was found between microwave-polymerized and auto-polymerized repairs of resin test strips. The microwave cured resin samples began to enlarge but only slightly and then soon stopped changing. Dimensional changes from the original model immediately after polymerization of complete upper and lower dentures were recorded and all three polymerization methods produced shrinkage on all three axes toward the center. Tooth ϮϬ . The pour-type resin samples began to enlarge until almost all of them reached the original model size within weeks. The complete dentures were measured by using die three dimensional measurement systems. All polymerization method types showed more dimensional change in the lower plate than in the upper plate.Z s/ tK&>/d ZdhZ polymerization method types were compared. The gradual dimensional changes occurring after polymerization up until 4 weeks were also recorded. 3. The heat cured resin samples showed no additional changes but remained in its shrunken state. Heat cured resin samples and microwave cured resin samples showed the same shrinkage with pour type resin samples only showing Vz that amount. In an investigation by Sykora & Sutow35 two base plate waxes and two denture processing techniques were independently compared for dimensional stability. The results obtained were summarized as follows: 1. and a continuous injection system. 2. Occlusion rims were constructed from extra hard and medium soft base plate waxes and teeth were set Acrylic resin bases were processed by a trial packing technique. Z s/ tK&>/d ZdhZ movement was measured in the horizontal and vertical planes to assess wax and denture base dimensional changes at various steps in the process. A study was done by Wakkace et al37 compare the micro-wave processing method to the conventional method. Microwave processing has several time-saving advantages over conventional processing of denture base resins. Another investigation by Dabreo & Herman36 used the reflective surfaces of chrome steel ball bearings to measure the dimensional changes in denture base resins. Little is known about the adaptation of base processed by microwave radiation to the cast and the mouth. incisal pin opening and loss of centric occlusion contacts. In comparison to the trial packing technique. whereas after 8 weeks immersion the continuous injection technique showed smaller dimensional changes relative to the original dimensions at the time of investing. Posterior palatal border adaptation. were also measured. and better adaptation of the posterior palatal border to the cast Measurement of tooth movement in the horizontal and vertical planes showed no significant differences between the two processing techniques for ties prior to immersion in water. the continuous injection system showed significantly smaller changes for incisal pin opening and loss of centric occlusion. 3 and 8 weeks of denture base immersion in water at room temperature. Comparisons were made in five Ϯϭ . and after 1. The authors concluded that the light cured acrylic resins had the least dimensional change. The adaptation of the record bases to a standard cast was measured to determine if there were any statistically significant differences in the fit that could be attributed to the differences in curing methods and the brands of resin. The results demonstrate that base-plates produced by the injection molding procedure exhibit less shrinkage than those produced by the conventional press-pack procedures. Dimensional changes were assessed over a period of 4 months using an optical comparator. The adaptation of artificial dentures made from acrylic resin is clinically acceptable with either microwave curing or the water bath method.Z s/ tK&>/d ZdhZ regions of the palate and ridge. The dimensional accuracy and stability of acrylic resin bases produced by the two molding procedures were compared. The microwave-processed denture bases had equal or better dimensional accuracy than conventionally processed bases. Another study by Huggett et al 39 compared the recently developed injection (dry heat) procedure of processing with press-pack dough molding utilizing three curing cycles. The results indicated a small statistically significant difference in favor of the water bath cure overall. ϮϮ . but clinically there was no appreciable differences in the adaptation of the record bases with either curing method or the resins used. In another study by Sanders et al 38acrylic resin record bases made from three commercial resins were processed by water bath curing and by microwave energy. The specimen cured by the SR-lvocap system exhibited less dimensional change (p less than 0. the SR-lvocap system. The SR-lvocap system might produce a more accurate denture base than the conventional and the microwave curing methods. (perform. The dimensional accuracy was evaluated by the change of the distance vector V. the relative fit of seven denture resins polymerized by different methods to their gypsum casts. and a microwave curing method. which was calculated by means of measurements of the distances between fixed points on specimens. and visible light. Compak and Permacryl 20. 45 degrees C). 100 degrees C). 74 degrees C and Accelar 20. low heat. Relative fit in the molar-to-molar region of the resin bases on their stone casts was evaluated independently by five evaluators at three times (after processing. (Acron MC). after polishing and after storage in water) and ranked using nonparametric statistics.05) than those cured by the conventional and the microwave curing methods. An in vitro study Smith & Powers41 compared. (Triad) fit better after polishing and after storage in water than those resins polymerized at higher temperatures (Lucitone 199. Ϯϯ . The traditional heat-polymerized resin (Lucitone) had an average fit after storage in water. The denture resins polymerized by microwave energy.Z s/ tK&>/d ZdhZ An investigation in 1992 by Salim et al 40 examined the dimensional accuracy of rectangular acrylic resin specimens when they were processed by three methods: a conventional method. Z s/ tK&>/d ZdhZ In a study by Turck et al 42 the Michigan Computer-Graphics Coordinate Measurement System (MCGCMS) was used to determine the dimensional accuracy of dentures processed by three different techniques: conventional heat compression. Twenty-one different polymerization methods were used Ϯϰ . microwave. At specific sites. In a research study by Iibay et al 44 the technique of curing denture base acrylic resins by microwave energy was investigated with respect to polymerization method. All casts 14 dentures for each technique). mechanical and physical properties. and vacuum assisted resin pouring .e. injection pressing. the visible-light-activated technique produced significantly more flange distortion than did either the conventional or microwave techniques. Standardized dentures were fabricated from casts made in an RTV silicone mold. were duplicated with hydrocolloid and 42 dentures were made (i. hardness. and visible-light activation. In yet another study43 the Michigan Computer Graphics Coordinate Measuring System was used to determine the influence of denture teeth on the accuracy of the processed denture bases. however.were used . The MCGCMS measured 22 points on two frontal planes to compare master casts to dentures- The results showed no significant difference in overall dimensional accuracy.The authors concluded that no significant differences were found in injection -pressed dentures. Three different processing methods -compression molding. and 2. Mechanical and physical tests were applied to the samples which were cured by the recommended polymerization method. Water sorption of acrylic resin cured by microwave energy was 0. shedding light on the behavior of base material and the dimensional changes that occurred during processing. almost the same as conventionally cured acrylic.038 mg cm-2. Another study by Abuzar et al 45 investigated tooth movement during processing of acrylic resin compete dentures in relation to palatal form. With respect to a relationship between tooth movement and palatal form. Results conformed with the ADA specification.72 mg cm-2 and the solubility rate in water was 0.Z s/ tK&>/d ZdhZ by varying radiation power and curing time. Radiographs were digitized and the images obtained were processed and analyzed for precise measurement of tooth movement. A palatal form of index was developed. Seven points were located across each cast. Eleven clinical casts were radio graphed at four denture-processing stages. The average transverse load to fracture value was found to be 7. The recommended polymerization method of curing acrylic was 3 min at 550 W in a microwave oven.46 VHN (Vickers hardness number). certain trends were found with varying degree and direction. Ϯϱ . that is. and the transverse deflection value was 1. samples which were polymerized. The Vickers hardness test was applied to the The average value was found to be 22.9 mm at 5000g.5 mm at 3500 g. The finding showed that acrylic resin cured by microwave energy is more resistant to mechanical failure than conventionally cured acrylic and this technique can safely be applied to the production of denture bases.6 kg. Increase in temperature associated with the exothermic nature of the polymerization reaction was recorded. and that the overall dimensional denture base changes are the result of localized changes. war-page. The dimensional changes of the denture base resulting from the two-stage processing technique cannot be considered to be of any clinical significance. Ϯϲ . The temperature of the resin followed the water bath temperature closely.Z s/ tK&>/d ZdhZ An investigation Yeung et al 46 was performed to evaluate the temperature and linear dimensional change of heat-cured acrylic resin in the two-stage processing technique for complete dentures. Temperature differential is excluded as a reason for the warpage of dentures. A study by Sadamori et al 47 examined the influence of thickness on changes (linear dimensions. and water uptake) in a denture base resin following two processing methods (heat polymerization and microwave activation). A high-resolution digital-measuring microscope made measurements between reference marks. Changes were influenced by both processing method and thickness. The total linear shrinkage of the base after two processing cycles was than 1% and compares favorably with studies on the single-stage processing technique. The temperatures recorded at various regions were in phase with each other. Thermocouples were incorporated in the acrylic resin for recording temperatures. both are important factors in the dimensional change of acrylic resin dentures. Z s/ tK&>/d ZdhZ Another study by Kawara et al 48 attempted to verify that the shrinkage of heat-activated acrylic denture-base resin was caused mainly by thermal contraction after processing. The measurement started from the beginning of processing and continued until the specimen was bench-cooled and immediately before and after it was de-flasked. Meanwhile. and compared the results with that of the conventional method. the study examined the degree of distortion resulting from long. Another study by Komiyama & Kawara 49 evaluated the development of residual stress relaxation and clarified how restricted time in the stone mold influenced stress relaxation of heatϮϳ . were identical to the theoretical value of thermal shrinkage. This suggested that polymerization shrinkage was compensated for by thermal expansion during processing by the conventional method. The results revealed quantitatively that the shrinkage of heat-activated acrylic denture-base resin was mainly thermal shrinkage and demonstrated the advantage of the low-temperature method in reducing thermal shrinkage. Furthermore. which they obtained by multiplying the linear coefficients of thermal expansion by temperature differences. as well as during seven-day immersion in water at 37 degrees C. averaged 64% of that in the specimen processed by the conventional method. was observed when the resin was processed by the lowtemperature method. in both die conventional and low-temperature methods. The resin expanded when processed by the conventional method. mild shrinkage. low-temperature processing. possibly polymerization shrinkage. measured from the end of processing to immediately after de-flasking. The strain gauge and thermo-couple were embedded in a specimen at the time of resin packing. Moreover. the shrinkage strains in the period from the completion of processing to immediately after de-flasking. The shrinkage strain in the specimen processed by the low-temperature method. 25 mm thick wax. duplicated to obtain 10 identical casts. Each denture was radiographed immediately before processing after deflasking.Z s/ tK&>/d ZdhZ activated acrylic denture base resin after processing. The dentures were invested. and 10 days from the start of bench cooling. upright. one half for 3 and 5 days restriction. The radiographs were digitized using an Eikonix image digitizer the results showed that there were significant variations in tooth movement between thick and thin denture bases. Flat dumbbell-shaped specimens were used. A maxillary cast from a patient was Base plates were constructed on five casts using 1. Thermocouples and strain gauges were embedded in resin for measuring temperature and strain at the dough-stage of resin packing. Base plates were constructed on the other five casts using 2. 3. In an investigation Jamani et al50 found out the effect of denture thickness on tooth movement during processing of compete dentures was studied. control). finished and polished. and 1 day. in each tooth.5 mm thick wax. Shrinkage strains at deflasking were two thirds for 1 day restriction. Teeth were placed on the ridge of each cast and a TMS pin was placed vertically. decasted. cured.5. The authors suggested that removing a denture base fabricated by heat-activated acrylic denture base resin from the stone mold only after keeping it in stone mold for at least 1 day or more was effective for reducing deformation of the denture base. on removal from the cast and after finishing and polishing using a standard technique. specimens were removed from the mold by deflasking at 4 hours after from the start of bench cooling (immediately after reaching room temperature. Also an increase in the molar-to-molar distance Ϯϴ . as compared with the control. To clarify the stress relaxation in the stone mold. Z s/ tK&>/d ZdhZ was found in both the thin and thick dentures but the magnitude of tooth movement was more in thick dentures. Ϯϵ . as well as one compression-molded methyl acrylate ester copolymer. in general. Ten dentures were fabricated from each resin using monoplane teeth. and 48 hours after a simulated clinical remount. Micro waving of autopolymerizing resin improved mechanical properties and reduced residual monomer. 6. and changes in occlusal vertical dimension for each denture were evaluated at a simulated laboratory remount. Although these two methods were inter-changeable for the conventionally heat cured material. A comparison of some properties51 of denture base polymers processed by both microwave and water-bath methods demonstrated that. 3. and at 0. 24. consistently superior results were produced by following the method recommended by the manufacturer. injection-molded. and fluid poly (methyl methacrylate) resins. The occlusal vertical dimension at the articulator pin was measured at the wax denture stage for each specimen. A study by Swords et al52 measured the effects of commercial resin type on maxillary complete dentures with monoplane teeth by periodically comparing the occlusal vertical dimension of the polymerized dentures with the baseline. water-bath polymerization with a long curing cycle and a 3-hour terminal boil produced superior properties. Commercially available compression-molded. wax trial denture fiducial measurements. were evaluated. individual maxillary dentures from all resin types and at all intervals exhibited dimensional change. Forty-eight virtually identical polymethyl methacrylate dentures were fabricated on master casts with either a deep or shallow palatal vault. Twenty-four hours after polymerization.Z s/ tK&>/d ZdhZ The conclusions were that. the bases on their casts were sectioned at the posterior border and evaluated for degree of adaptation using a traveling microscope. the compression-molded poly (methyl methacrylate) showed no change in mean occlusal vertical dimension from baseline. Another study by Laughlin et al 53 investigated the effects of palatal depth and a resin anchoring system on the adaptation of denture base resin to the master cast after compression molding and heat polymerization. At the last evaluation period. as well as perpendicularly in the midsaggital area. Maladaptation at the interface of the denture base and master cast was measured at predetermined mediolateral locations. Mean gap distances for steep palate dentures were significantly less than shallow palate dentures at vestibule and lateral palate locations. Anchoring holes were made with a #8 round bur to a depth of 5 mm. One half of the master casts of each palate type were altered by the addition of anchoring holes along the posterior land area. and anchoring holes placed in an edentulous master cast along the posterior land area and at the midline significantly improved the adaptation of denture bases. whereas remaining groups exhibited occlusal vertical dimensions significantly less than baseline. ϯϬ . 5 mm. (AC) GC Dent. Groups 1. However. The conclusions were interaction of type of material and cooling procedure had a statistically significant effect on the final adaptation of the denture bases (. water storage was not detected as a source of variance on the final adaptation. 2 and 3 were polymerized with different cycles by microwave radiation and Group 4 was the control and cured by water bath. A heat-cured acrylic resin (CL. Corp.Z s/ tK&>/d ZdhZ An in vitro study by Barbosa et al54 investigated the effect of different microwave curing cycles on the changes in occlusal vertical dimension of complete dentures. Ind. running water (RW) at 20 degrees C for 45 min] on the final adaptation of denture bases was conducted.. Four test groups with 12 maxillary dentures each were evaluated. The average pin opening for all groups was less than 0. Adaptation was assessed by measuring the weight of an intervening layer of silicone impression material between the base and the master die. Clássico Artigos Odontológicos] were used to make the bases. analyses of the vertical dimension changes showed statistically significant differences between groups 2 and 3. ϯϭ . Onda Cryl (OC). The authors concluded that there was no significant difference between the groups polymerized by the microwave method and the control group. Clássico. Clássico Artigos Odontológicos) and two microwave-cured acrylic resins [Acron MC. An investigation by Ganzarolli et al55 evaluating the effect of water storage and two different cooling procedures [bench cooling (BC) for 2 h. No statistically significant difference in change in dimension was observed between the two groups. 12 and 24 h post-pressing times.Z s/ tK&>/d ZdhZ A study by Sinclair & Clark56 investigated the differences in dimension during processing when putty was used. indicating that this is an acceptable method. Two groups of ten standardized dentures. The dough of the acrylic resin was packed in metallic flasks and processed in a water bath curing cycle at 74 masculine C for 9 h. Cross arch measurements were made before and after processing using an eight hour curing cycle followed by slow cooling. in relation to post-pressing times. Another study by Consani et al 57 investigated the dimensional stability of denture bases influenced by packing methods. In each method. 6. The data showed that the RS system had a smaller base distortion compared to conventional packing. The resin base-stone cast sets were transversally sectioned into 3 sections and the base-stone gap measured at 5 points in each section. one group with silicone. Anecdotal evidence suggests that many dental laboratories are surrounding the teeth and gingival margins of the wax patterns for complete dentures with silicone laboratory putty prior to investing in dental stone or plaster to facilitate deflasking and polishing. and one group without were processed. After cooling at room temperature. the bases were removed from the flasks. There was a statistically significant ϯϮ . Forty maxillary wax bases were made and randomly assigned into 2 groups of 20 specimens each according to the conventional and RS system packing methods. finished and fixed on stone casts with instantaneous adhesive. the specimens were subdivided into immediate. with the exception of the 24-h post-pressing time. in the Clássico acrylic resin which was prepared according to manufacturer recommendations. Eight maxillary edentulous casts having U. Flat. the immediate and 6 h times demonstrated values with no statistically significant difference between them. during processing and the effect of water sorption on the processed dentures. dumbbell-shaped specimens were used. F and V configurations of palatal vault were selected and complete dentures were fabricated. In the conventional packing method. To clarify stress relaxation in the ϯϯ . The authors concluded that dimensional changes in frontal and vertical planes were maximum in V shaped palatal vault dentures. Another study Kobayashi et al 59 examined the development of residual stress relaxation in resin denture base samples in the region where shrinkage was restricted. in order to clarify how cooling variations in the stone mould influenced the shrinkage. constructed on the casts having different configurations of the palatal vault. as well as between the 12 and 24 h postpressing times. Water sorption partly compensated for the dimensional changes that occurred during processing.Z s/ tK&>/d ZdhZ difference between the packing methods only in section C (posterior palatal zone). Thermocouples and strain gauges were embedded in the resin for measuring temperature and strain during the dough-stage of resin packing. Dimensional changes occurring in the processed dentures were studied in different regions during processing as well as after water sorption. A study was done by Hegde & Patil58 to evaluate the dimensional changes occurring in the dentures. ambient humidity) for 1 week (while still on the master cast) before anteroposterior and cross-arch measurements were made using the ϯϰ . A maxillary complete denture with acrylic teeth was waxed to full contour on the master cast and replicated to make 40 wax dentures. Ten dentures were allocated to each of 4 groups.Z s/ tK&>/d ZdhZ stone mould.and 24-h experimental groups were 1793. Group 2 used injection-molded PMMA (SR-lvocap). respectively. Another study by Parvizi et al60 compared the linear dimensional changes of 3 injection-molded denture base materials to that of conventionally processed polymethylmethacrylate (PMMA) resin. Group 3 employed injectionmolded nylon (Valplast). and 12. and 12 and 24 h from the start of gradual cooling in a water bath. specimens were removed from the stone mould by de-flasking 4 h after the start of cooling at room temperature (control). All processed specimens were stored at room temperature (25 degrees C. 1354 and 1093 mu epsilon. The authors suggested that a gradual cooling course for 12 h or more after processing a heatactivated acrylic denture base is effective for lessening deformation of the prosthesis. An impression of an aluminum maxillary edentulous arch was made with a condensation silicone impression material (Denture Elasticon) to fabricate a gypsum master cast that was replicated as a silicone mold. and Group 4 used injection-molded styrene (Northern). Group 1 was processed using conventionally processed PMMA (Microlon). The strain differences between before and after removing from the stone mould for the control. ERA attachments cast in metal (Rexillium) with indices milled into the centers were waxed into 3 positions in each denture for recording dimensional measurements of the wax denture. This was particularly evident after removal from the cast after curing (p<0. After polymerization. It was concluded that slow cooling results in less dimensional change.Z s/ tK&>/d ZdhZ ERA reference points with a digital caliper. The results indicated that there was greater change in dimension of dentures with the quenching cooling method than with either overnight cooling in the water bath or bench cooling. Another investigation by Kimoto et al62 examined the effect of bench cooling on the dimensional accuracy of a heat-cured denture base resin .001). and before and after removing the denture from the cast using a computer imaging system. An investigation by Moturi et al 61 compared dimensional changes in poly (methylmethacrylate) complete denture bases resulting from three different cooling regimens following a standard heating cycle. Each material tested also responded differently to the processing stages. A dimensional change of a dumbbellshaped specimen during the fabrication process was measured directly by using the strain gauge method. the specimens were treated in one of the following two processing ϯϱ . After separation from the master cast and following water storage at 37 degrees C for 7 days additional measurements were made. No consistent differences occurred as a result of removing the denture from the cast. Processing the denture base materials produced unequal deformation in different dimensions (anterior-posterior and cross-arch). Changes in three separate dimensions were measured on ten dentures within each cooling regimen after curing. was determined as the total strain. after which. since the internal stress developed by thermal shrinkage will be relaxed during the cooling process. the specimen was removed from the stone mold. A study was done by Turakhia & S.Ram63 to compare the movement of artificial teeth taking place during processing of the denture using various coring material for investing. The strain differential. after processing. Thirty sets of complete dentures were evaluated as follows: 15 sets of complete dentures were arranged in conventional balanced occlusion (control) and 15 sets of complete dentures were arranged in lingualized balanced occlusion. (2) bench cooling: the flask was left to cool in a thermo-stabilized room of 20+/-1 degrees C for 140min. All dentures were ϯϲ . before and after cooling. The strain from deflasking was derived from the difference in the strain. An in vitro study by Basso et al 64 compared the increase in OVD.Z s/ tK&>/d ZdhZ methods: (1) rapid cooling: the specimen was removed from a stone mold within a container of boiling water at 100 degrees C and then left to cool in a thermo-stabilized room of 20+/-1 degrees C. Nowadays many dental laboratories are surrounding the teeth and gingival margins of the wax patterns for complete dentures with silicone laboratory putty prior to investing in dental stone or plaster to facilitate deflasking and polishing so some teeth movement is expected. between complete dentures with teeth arranged in lingualized balanced occlusion and conventional balanced occlusion. Compression molding technique normally requires gypsum mould which is rigid. before and after the removal of the specimen from the stone mold. The flask should be slowly cooled to room temperature. the lingualized balanced occlusion may result in easier occlusal adjustments. Another study by Consani et al 65 investigated the tooth movement of standardized simulated dentures processed by traditional closure or the new Rafael Saide (RS) tension system when cooled in the curing water itself or in curing water followed by bench storage for 3 hours. For traditional closure. the flasks were pressed between the metallic plates of the tension system after the final closure.Z s/ tK&>/d ZdhZ compression molded with a long polymerization cycle. ϯϳ . The denture was deflasked after cooling in the water of the polymerizing cycle (groups A and C) or in the water of the polymerizing cycle and then bench-stored for 3 hours (groups B and D). The occlusal vertical dimension was measured with a micrometer (mm) before and after processing each set of dentures. The distances were measured before and after denture polymerization with an optical microscope. Forty stone casts were formed from a mold of an edentulous maxillary arch. Although the 2 occlusal concepts resulted in similar increases in the OVD after processing. and mesiolabial cusp of the second molars (M). which were afterward placed in spring clamps. as the less complicated occlusal scheme uses a smaller number of centric occlusion contact points. the dentures were flasked conventionally in standard metallic flasks. For the new RS system closure. Metallic pins were placed in the incisal border of the maxillary central incisors (I). The dentures were polymerized in a moist heat-polymerizing cycle for 9 hours at 74 degrees C. The wax denture record bases were made on the casts. dentures set in lingualized balanced occlusion showed an increase in OVD similar to those set in conventional balanced occlusion. labial cusp of the first premolars (PM). After processing. Following deflasking and after each storage period tested. ϯϴ . and RPM-RM (right premolar to right molar) distances were measured with an STM Olympus microscope. 30.Z s/ tK&>/d ZdhZ Tooth movement was similar in dentures processed by traditional closure and by the new RS tension system. The dentures were deflasked after cooling in their own polymerizing water or after cooling in polymerizing water plus bench storage for 3 hours. With exception of the RPM-RM distance after the 30-days water plus bench storage period. with the exception of the anteroposterior distances when the flasks were cooled in their own curing water and bench-stored for 3 hours. and 90 days. and on the mesiolabial cusp of the second molars (M). The final acrylic resin pressing was made in a metallic flask with aid of the RS tension system. There was no statistically significant difference for the PM-PM. the other distances remained statistically stable. M-M (molar to molar). Metallic pins were placed on the labial cusp of the first premolars (PM). A study was performed by Consani et al 66 which assessed the displacement of posterior teeth in maxillary complete dentures stored in water at 37 degrees C. and stored in water at 37 degrees C for periods of 7. and polymerized in a moist-hot cycle at 74 degrees C for 9 hours. the PM-PM (premolar to premolar). Twenty acrylic resin-based maxillary complete dentures were constructed with the anterior teeth arranged in normal overlap and the posterior teeth in Angle class I. LPM-LM (left premolar to left molar). and LPM-LM distances after all storage periods when the flask cooling methods were considered. M-M. and posterior palatal region. Ten bases for each TFC or RSFC method (n=10) were submitted to simulated disinfection (SD) in 150 ml distilled water in a microwave oven at 650 W for 3 minutes. Simulated disinfection by microwave energy improved denture base adaptation when the TFC method was used. control bases for each TFC or RSFC method (n=10) were not disinfected (ND). Measurements were made in the bases using an optical micrometer. Three transverse cuts were made through each stone cast-resin base set. the bases were removed following flask cooling and submitted to conventional finishing with abrasive stones and pumice slurry. Forty stone cast-wax base sets were prepared for flasking by the traditional flask closure (TFC) and Restriction System flask closure (RSFC) methods (n=20).Z s/ tK&>/d ZdhZ Another study by Consani et al 67 determined the effect of simulated microwave disinfection on maxillary denture base adaptation using 2 different flask closure methods. but did not statistically alter base adaptation for the RSFC method. ϯϵ . The RSFC consists of 2 iron plates to hold the flask during definitive flask closure. After polymerization in water at 74 degrees C for 9 hours. mesial of first molars. Acrylic resin (Classico) was prepared according to the manufacturer's instructions. corresponding to the distal of canines. maintaining the flask in a closed position after release of pressure. (FIGURE.Commercially available Dental plaster & Dental stone.2) 3. Vibrator (Confident® Dental Equipments.(FIGURE. India). Acrylizer (KAVO EWL. Hydraulic bench press (SIRIO.4 2. Pyrax Polymars. India).2.D d. Aluminum Foil (K. Type 5509. India). Mentioned below are lists of materials and important equipment used during the study.R. 4. India).3) IMPORTANT EQUIPMENTS USED: 1.Germany). India) (FIGURE. Investing Mediums used . Modelling wax (Modelling wax No.FIGURE. Commercially available cross-linked acrylic teeth (LACTODENTTM.FIGURE-5 3.FIGURE-6 ϰϬ . Commercially available heat polymerized acrylic resin (DPI Heat CureTM.1) 2. MATERIALS USED IN THE STUDY: 1. Hindustan Dental Products. 6. Industries. Dental Products of India).up dentures.KK>K'z METHODOLOGY This study was undertaken to investigate the influence and relationship of investing medium on the movements of artificial teeth taking place in two dimensions of space during the processing of maxillary waxed. Industrial cyanoacrylate adhesive 5. ŝŶĚƵƐƚĂŶŵŽĚĞůůŝŶŐǁĂdž ϰϭ . D d.KK>K'z &/'hZ Ͳϭ͗>ĂĐƚŽĚĞŶƚƌŽƐƐͲůŝŶŬĞĚĐƌLJůŝĐƚĞĞƚŚ &/'hZ ͲϮ͗. D d.KK>K'z &/'hZ Ͳϯ͗W/.ĞĂƚƵƌĞWDD &/'hZ Ͳϰ͗ĐƌLJůŝnjĞƌ;<sKͿ ϰϮ . D d.LJĚƌĂƵůŝĐƉŽǁĞƌƉƌĞƐƐ;^/Z/KͿ &/'hZ Ͳϲ͗sŝďƌĂƚŽƌ;ŽŶĨŝĚĞŶƚͿ ϰϯ .KK>K'z & &/'hZ Ͳϱ͗. 8). This mold was used to make 30 duplicate master casts in type III dental stone on which the complete maxillary dentures could be waxed and processed.KK>K'z INSTRUMENT FOR MEASURING THE SAMPLES: • Traveling Microscope (Garticules Ltd.60 The casts were assigned to the 2 test groups containing 15 casts each & the casts were scored numerically from 1 to 30. A silicone mold (Wirosil®. ϰϰ . thus preventing errors of comparing measurements of one denture with those of other. BEGO.D d. England). a model gypsum cast simulating a maxillary edentulous ridge was used. Bremen.FIGURE.7 Salient features• Magnification 10x • Drum type vernier scale • Capable of travelling in the antero-posterior & medio-lateral direction. Germany) of the model gypsum cast was fabricated (FIGURE. This was to aid in comparing the measurements taken before flasking with those taken after curing of the same denture. PREPARATION OF THE SAMPLESFor the fabrication of the test specimens. KK>K'z &/'hZ Ͳϳ &/'hZ Ͳϴ ϰϱ .D d. D d. before the investing of the specimens (waxed-up dentures).56. ϰϲ . India) were arranged according to basic guidelines and the denture was completely waxed. Bremen.India) were fabricated on the previously poured casts. This maxillary denture was duplicated with RTV silicon duplicating material (Wirosil.69 (FIGURE. Germany) to obtain a mold (FIGURE.linked acrylic teeth (LactodentTM.64.4. two medio-lateral.KK>K'z To fabricate the initial denture. 2 layers of modelling wax (Hindustan dental products) were adapted on a gypsum master cast.23 Bard Parker blade56.56 Each square was scored with a cross using a No.69 (FIGURE. Semi-anatomic cross linked acrylic teeth (Lactodent™. The center point of these crosses served as reference points which were measured with the aid of a Traveling microscope. Using this silicone mold. two antero-posterior and B.60.9).up.68 Small aluminum foil squares were stuck on the occlusal surface of the 1st premolars & 2nd molars using industrial cyanoacrylate adhesive. BEGO. Pyrax Polymars.11 & 12) Four measurements were made: A.Pyrax Polymars .10). 30 maxillary wax dentures with semi-anatomic cross. KK>K'z &/'hZ Ͳϵ &/'hZ ͲϭϬ ϰϳ .D d. D d.KK>K'z &/'hZ ͲͲϭϭ͗DĞĂƐƵƌĞŵĞŶƚďĞŝŶŐ ŵĂĚĞǁŝƚŚĂdƌĂǀĞůŝŶŐŐ ŵŝĐƌŽƐĐŽƉĞ &ŝŐƵƌĞͲϭϮ Ϯ͗ZĞĨĞƌĞŶĐĞĐƌŽƐƐŝŶĂůŝŐŶŵĞŶƚŽĨƚŚĞĐƌŽƐƐͲŚĂŝƌ ŽĨ dƌĂǀĞůŝŶŐŵŽĐƌŽƐĐŽƉĞ ϰϴ . WD ϭ WD ϯ ϯ ϰ ^D Ϯ ^D &/'hZ Ͳϭϯ FOLLOWING INVESTING MEDIUMS M WERE USED: GROUP.1: INVESTING ME EDIUM USED – DENTAL PLASTER ϰϵ .D d.KK>K'z Measurements were made from m: (FIGURE. Maxillary right 1st premolar p (PM) to maxillary left 1st premolar(PM) 2. Maxillary right 2nd molar (SM) to maxillary left 2nd molar(SM) 3. using a Traveling Microscopeand afterwards the specimens (waxed-up denntures) in Group-1 and Group-2 were invested. Maxillary left 1st prremolar(lt PM) to maxillary left 2nd molar(lt S SM). Maxillary right 1st premolar p (rt PM) to maxillary right 2nd molarr (rt SM) 4.13) 1. Dental plaster was mixed according to the manufacturer’s direction.KK>K'z As mentioned above this group contained 15 waxed.up denture) invested in dental plaster. 2. First a thick core of type III dental stone was applied all around the artificial crosslinked acrylic teeth in the shape of a horse. The type III dental stone was mixed with recommended volume of water (100gm:30ml). Later the molds were allowed to cool for 1 hour63 (FIGURE. The rest of the denture processing steps were common to both the groups (Group-1 and Group2). After the initial set of the stone core. 2. Drag part of the flask.specimen (waxed. a pour of dental plaster was done to completely fill the cope as in the conventional method of flasking using dental plaster.The flasks were placed in boiling water for 5 minutes63 to perform wax boil out.15).60 B.D d. The casts & the denture moulds were allowed to cool till room temperature.14). 1.16 & 17 ).specimen (waxed.entirely in dental plaster (FIGURE.shoe (FIGURE. Drag part of the flask. Cope part of the flask.up dentures all of which were invested in dental plaster in the conventional manner.up denture) invested in dental plaster. Separating medium was applied while the dewaxed moulds were warm to get a thin layer of separating medium. GROUP-2: FIRST A CORING OF DENTAL STONE AROUND THE TEETH FOLLOWED BY INVESTING IN DENTAL PLASTER. Cope part of the flaskA.63 1. ϱϬ .22. KK>K'z &/'hZ Ͳϭϰ &/'hZ Ͳϭϱ ϱϭ .D d. KK>K'z &/' 'hZ Ͳϭϲ͗;'ƌŽƵƉͲϭͿĞǁĂdžŝŶŐĚŽŶĞΘ^ĞƉĂƌĂƚŝŶŐ ŵĞĚŝƵŵĂƉƉůŝĞĚ͘ &/' 'hZ Ͳϭϳ͗;'ƌŽƵƉͲϮͿĞǁĂdžŝŶŐĚŽŶĞΘ^ĞƉĂƌĂƚŝŶ ŶŐ ŵĞĚŝƵŵĂƉƉůŝĞĚ͘ ϱϮ .D d. ϱϯ . the difference taken was between the measurement of the later stage and the measurement at the earlier stage. The measurements at the wax stage were used as the baseline readings.D d. and all values were calculated with these measurements as the starting point.48 The flasks were allowed to bench cool for 2 hrs55.Paired and Unpaired ‘t’ test and ANOVA ‘F’ test . In each case. The results were subjected to statistical analysis using parametric tests.KK>K'z Packing was done with Heat Cure Polymethyl methacrylate (DPI Heat CureTM.The flasks were bench cured for 2 hours before placing in the water bath unit and a short curing cycle of acrylic resin was followed for processing.62 & the dentures were divested carefully taking care that the dentures along with the cast were retrieved as a single unit (FIGURE. Measurements were once again made as afore mentioned after the processing of the specimens in Group-1 and Group-2.63. Trial closure was done in a hydraulic power press to ensure complete closure of the flasks48.20 & 21) .18 &19). Dental Products of India) following standardized procedure with a polymer: monomer ratio of 3:1 by Volume66 (approximately 25 ml of polymer and 9ml of monomer) 63 which were mixed in a mixing jar & packed in the dough stage.70 (FIGURE. D d.KK>K'z &/'hZ Ͳϭϴ͗dƌŝĂůůŽƐƵƌĞďĞŝŶŐĚŽŶĞ &/'hZ Ͳϭϵ͗&ůĂƐŬĐůŽƐƵƌĞƵŶĚĞƌ ŚLJĚƌĂƵůŝĐƉƌĞƐƐ ϱϰ . KK>K'z &/'hZ ͲϮϬ͗WƌŽĐĞƐƐĞĚĚĞŶƚƵƌĞƐŝŶ 'ƌŽƵƉͲϭ &/'hZ ͲϮϭ͗WƌŽĐĞƐƐĞĚĚĞŶƚƵƌĞƐŝŶ 'ƌŽƵƉͲϮ ϱϱ .D d. In order to allow for multiple pair wise comparisons within a specimen group a Bonferroni adjustment was employed.D d.05. and statistical significance was accepted at P < 0. when comparing between the two specimen groups.KK>K'z STATISTICAL ANALYSIS: The results for anterior-posterior and medio-lateral dimensions were subjected to a paired t-test when comparing within the same specimen group and to a unpaired t-test with parametric inference. ϱϲ . 6 32.0233 . p=0. ϱϳ . p=0.41983 AFTER 15 21.940 21. HS t (14)=1.9 21.0 34. p=0. Of the 2 Medio-Lateral measurements.607 .Based on the measurements of minimum. as related to the standard deviation .3 21.794 .89 22.811.727 .7 23.972 .1 shows the following: Mean values of all the four measurements for the 15 samples tested in Group 1.the significance was determined(p < than 0.6922 15 46.81 21.9193 15 32.9800 48.8 49.45577 15 46.6900 21.020 Sig t (14)=3.1 MEAN VALUES OF THE FOUR MEASUREMENTS BEFORE & AFTER PROCESSING OF DENTURES IN GROUP-1 Conventional flasking using Dental Plaster Group Type GROUP-I PREMOLAR TO PREMOLAR (PM-PM) BEFORE DENTAL PLASTER N AFTER SECOND MOLAR TO SECOND MOLAR BEFORE (SM-SM) RT PREMOLAR TO RT SECOND MOLAR (rt PM-rt SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) AFTER Minimum Maximum 32. maximum & mean values before & after processing for the 4 measurements.3040 .760 32.020).9800 Mean Std.5783 15 20.05).0 22.87 48. Deviation Paired t test .42 22.115 NS Table.36112 t (14)=0.636.39 15 Median 32.480 47.Z ^h>d^ RESULTS TABLE.the mean value of Second Molar to Second Molar (SMSM) measurement before & after processing were statistically significant (p=0.27 33.7707 . p=0.681.004.43 23.600 21.51605 15 20.6354 BEFORE AFTER t (14)=2.431 NS 32.6466 BEFORE 15 21.3100 22.486.66 47.1 47. 004). ϱϴ .lateral measurement from Premolar to Premolar (PM-PM) & Antero.lt SM) were not so significant.Z ^h>d^ In the Antero-Posterior direction -the mean values of the measurement from Right Premolar to Right Second Molar (rt PM-rt SM) before & after processing were found to be highly significant (p=0. The difference of the mean values of the Medio.Posterior measurement from Left Premolar to Left Second Molar (lt PM. 6827 . HS Table.5300 47.960 32.444.34799 15 21. However the mean values of the Medio-Lateral measurement for teeth movement .3778 t (14) =3.5256 15 21. as related to the standard deviation the significance was determined(p < than 0.42812 15 20. ϱϵ .633 . p=0.7518 15 47.574.093.000.8040 .Second Molar to Second Molar (SM-SM) were highly significant (p=0.30 21.81 15 Median 33.959.2 shows the following: Mean values of all the four measurements using Paired ‘t’ test for the 15 samples tested in Group 2.3000 22. maximum & mean values before & after processing for the 4 measurements.Z ^h>d^ TABLE.022 sig 15 31.Based on the measurements of minimum.2916 15 20.001.1 21. Deviation Paired t test .2247 .440 47.05).Premolar to Premolar (PM-PM) before and after processing were significant (p=0.960 .68588 t (14)=2. HS t (14) =4.710 21.6 22. p=0.7 34.3200 Mean 33.001).95 22.5 22. p=0.00 34.001 HS t (14) =5.5 48.022).66 22.12 48.44682 15 46. The mean values of the Medio-Lateral measurement for teeth movement .41 22.30 47.7 22.426 .7 32.8700 21. p=0.063 .2107 Std.2 MEAN VALUES OF THE FOUR MEASUREMENTS BEFORE & AFTER PROCESSING OF DENTURES IN GROUP-2 Flasking with Dental Stone core around the teeth Group Type GROUP-II PREMOLAR TO PREMOLAR (PM-PM) BEFORE DENTAL STONE N AFTER SECOND MOLAR TO SECOND MOLAR BEFORE (SM-SM) AFTER RT PREMOLAR TO RT SECOND MOLARBEFORE (rt PM-rt SM) AFTER LT PREMOLAR TO LT SECOND MOLARBEFORE (lt PM-lt SM) AFTER Minimum Maximum 32.140 22.5 47. Left Premolar to Left Second Molar (lt PM.lt SM) and Right Premolar to Right Second Molar (rt PM-rt SM) were highly significant (p<0.Posterior measurements for teeth movement.001).Z ^h>d^ And mean values for both the Antero. ϲϬ . 11043 GROUP-I DENTAL PLASTER 15 . 020.2107 .17233 15 .020).lateral measurement .19364 GROUP-II DENTAL STONE 15 . The comparison of mean difference (artificial teeth movement) for the Medio.30911 N GROUP-II DENTAL STONE GROUP-I DENTAL PLASTER 15 .Premolar to Premolar (PM-PM) between the Group-1 and Group-2 were not statistically significant. p=0.4787 . Sig t(28)=3. 234.lateral measurement . p=0.07601 GROUP-II DENTAL STONE GROUP-I DENTAL PLASTER GROUP-II DENTAL STONE t test t(28)=1. NS t(28)=2. HS t(28)=3.Z ^h>d^ TABLE. Whereas the comparison of mean difference (artificial teeth movement) for the Medio. 217.06379 15 .5107 . p=0. 153. 318. p=0. Deviation of difference 15 . 003. ϲϭ .20924 15 .3367 . HS Analysis of the data from the comparison of mean difference for all the 4 measurement between the Group-1 and Group-2 using Unpaired ‘t’ test shows the following. 467.4187 .3640 . 004.1913 .Second Molar to Second Molar (SM-SM) were statistically significant (p=0.25754 15 .3 COMPARISON OF THE MEAN OF DIFFERENCE FOR FOUR MEASUREMENTS BETWEEN GROUP-1 AND GROUP-2 Type PREMOLAR TO PREMOLAR ( PM-PM) SECOND MOLAR TO SECOND MOLAR (SM-SM) RT PREMOLAR TO RT SECOMN MOLAR (rt PM-rt SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) DIFFERENCE DIFFERENCE DIFFERENCE DIFFERENCE group GROUP-I DENTAL PLASTER Mean of difference Std.3933 . Z ^h>d^ The comparison of mean of differences for both the Antero. ϲϮ .Posterior measurements – Right Premolar to Right Second Molar (rt PM-rt SM) and Left Premolar to Left Second Molar (lt PMlt SM) were statistically highly significant (p<0.005). These results are indicative of an appreciable difference in artificial teeth movement in the Antero.Posterior direction between Group-1 and Group-2.In Group-2 artificial teeth movement in the Antero-Posterior direction is statistically less than Group-1. 2107 .717.19364 .4187 .17233 . ϲϯ .20924 .06379 LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) .3640 .56) =1.3933 . HS Analysis of the data for Group-1 using Anova ’F’ test shows that the comparison of mean difference for the Four measurements (Two Medio-Lateral and Two Antero. p=0.11043 RT PREMOLAR TO RT SECOND MOLAR (rt PM-rt SM) .07601 PREMOLAR TO PREMOLAR (PM-PM) SECOND MOLAR TO MOLAR (SM-SM) ANOVA F test F (3.4 COMPARISON OF THE MEAN OF DIFFERENCE FOR THE FOUR MEASUREMENTS WITHIN EACH GROUP Dependent Variable: DIFFERENCE Group GROUP-I DENTAL PLASTER GROUP-II DENTAL STONE To test the effect across the types Type Mean PREMOLAR TO PREMOLAR (PM-PM) SECOND MOLAR TO SECOND MOLAR (SM-SM) RT PREMOLAR TO RT SECOND MOLAR (rt PM-rt SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) Std. ns F (3. However analysis of data for Group-2 shows a statistically significant difference between the Two Medio-Lateral & Two Antero-Posterior mean difference values (p=0.000.56) =8.354.Z ^h>d^ TABLE.107.Posterior).Posterior) was not statistically significant.1913 . p=0.30911 .25754 .4787 .5107 .Lateral and Antero.000).3367 . This result is indicative that artificial teeth movement was uniform in both the dimensions (Medio. Deviation . a. The mean difference is significant at the .018 .126 .047 .002 .047 1. Based on the statistically significant difference between the Two Medio-Lateral & Two AnteroPosterior mean difference values (p=0.047 .000 .000 LT PREMOLAR TO LT PREMOLAR TO * SECOND MOLAR (lt PREMOLAR ( PM-PM) PM SM Based on estimated marginal means *.047 .183* .000 .202* .019 .Lateral dimension for Group-2.145* . Adjustment for multiple comparisons: Bonferroni. Error a p value .000) for Group -2 in TABLE-4 pair wise comparison was done by Bonferroni test across Group-2. d> Ͳϱ Pairwise Comparisons By Bonferroni test Dependent Variable: DIFFERENCE group (I) Type GROUP-II DENTAL STONE PREMOLAR TO SECOND MOLAR TO PREMOLAR ( PM-PM) SECOND MOLAR (SM-SM) RT PREMOLAR TO RT SECOMN MOLAR (rt PM-rt SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) (J) Type Mean Difference (I-J) SECOND MOLAR TO SECOND MOLAR (SM-SM) RT PREMOLAR TO RT SECOMN MOLAR (rt PM-rt SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) RT PREMOLAR TO PREMOLAR TO * RT SECOMN MOLAR PREMOLAR ( PM-PM) (rt PM-rt SM) SECOND MOLAR TO SECOND MOLAR * (SM-SM) LT PREMOLAR TO LT SECOND MOLAR (lt PM-lt SM) Std.Posterior dimension was significantly less than in the Medio.057 .Z ^h>d^ Thus artificial teeth movement in the Antero.05 level. ϲϰ .047 1.047 .056 -. ϲϱ .lt SM). Similarly statistically significant mean difference was seen when Second Molar to Second Molar (SM-SM) value was compared pair wise with Right Premolar to Right Second Molar (rt PM-rt SM) and Left Premolar to Left Second Molar (lt PM.lt SM).Z ^h>d^ The result reveal that a statistically significant mean difference existed when the the Premolar to Premolar (PM-PM) was compared pair wise with Right Premolar to Right Second Molar (rt PMrt SM) and Left Premolar to Left Second Molar (lt PM. Z ^h>d^ ϲϲ . Z ^h>d^ ϲϳ . Z ^h>d^ ϲϴ . Z ^h>d^ ϲϵ . Z ^h>d^ ϳϬ . in spite of the progress in the development of high-polymer materials. This study evaluated and compared the movement of artificial teeth in two dimensions of space (antero-posterior & medio-lateral) during processing of the waxed-up dentures using two different gypsum materials for investing. resulting from the unavoidable denture base shrinkage during acrylic resin polymerization 69 ./^h^^/KE DISCUSSION Heat-activated acrylic denture-base resin has been used for over half a century for completedenture fabrication. Many attempts have been made to minimize the risk of such changes and to improve the accuracy of reproduction of waxed-trial denture in an acrylic resin.72 Even now. A certain lack of dimensional accuracy has been accepted as one of the disadvantages of Heatactivated acrylic resin. The tooth may change in its position as a result of the investing procedures.71. ϳϭ . and thus the final occlusion of the dentures. acrylic resin remains the principal choice. due to its aesthetic and physical properties and plastic manipulability. The setting expansion will result in the movement of the tooth along with the setting dental plaster.Polymerization shrinkage affects the position of the teeth on maxillary and mandibular dentures. Measurements were made at the wax stage before investing and after processing on the master cast. Certain significant findings were brought to notice and these are discussed as follows.lateral and antero-posterior direction in the conventional and the stone core investing methods.2.up dentures were invested in dental plaster in the conventional manner. Four measurements were made: two in the medio-lateral direction and two in the antero-posterior direction between the predetermined reference points. The measurements at the wax stage were used as the baseline readings.68 The waxed-up trial dentures were divided into two groups containing 15 dentures each. ϳϮ . In Group.64.lateral direction.2 first a thick core of type III dental stone was applied all around the artificial cross-linked acrylic teeth & the remainder of the flask was invested in Dental Plaster. In Group.69 and scored with a cross served as reference point which were measure with the aid of a Traveling microscope.60. and all values were calculated with these measurements as the starting point. between right premolar to left premolar (PM-PM) was nearly the same for both Group 1 and Group./^h^^/KE A total of 30 identical maxillary wax dentures were fabricated from a RTV silicon mould of an ideal maxillary denture. waxed. Small aluminum foil squares were stuck on the occlusal surface of 1st premolars & 2nd molars using cyanoacrylate adhesive 56.1. All the reference teeth showed movement in medio. Analysis of the data from the comparison of mean difference for all the 4 measurement between the Group-1 and Group-2 using Unpaired‘t’ test showed that artificial teeth movement in the medio. In this manner the discrepancies in teeth movement were recorded in two dimensions of space. This may be because the artificial teeth are surrounded by fairly uniform volume of dental plaster on all the sides.000) in the dental stone core investing procedure (Group. Therefore the combination of dental stone core & dental plaster in the mould appears to be more effective in reducing artificial teeth movement.63The investment combination of plaster of paris in the mould and an artificial stone cap was superior to other media investigated.1 by ANOVA ‘F’ test shows nearly uniform teeth movement in both medio-lateral and antero-posterior dimensions. In conventional compression molding techniques.73However an earlier study by Vieira74 concluded that the magnitude of the setting expansion of the investing stone had no significant influence on the changes which occurred in the relative positions of teeth.2). Artificial stone core with a low water: powder ratio has been suggested as an investing medium to resist the pressure of the expanding acrylic resin.N.In Group-2 artificial teeth movement in the anteroposterior direction is statistically less than Group-1. ϳϯ .K22 and Turakhia et al. Comparison of the mean of difference for the four measurements within Group. teeth are subjected to considerable pressure during packing and curing of acrylic resin./^h^^/KE Whereas there was an appreciable difference in artificial teeth movement in the antero. Pressure applied on acrylic dough during packing and processing is resisted by the stone core and causes teeth movement in the mediolateral direction as teeth are supported in these regions by relatively weaker materials namely dental plaster.posterior direction between Group-1 and Group-2. Where as artificial teeth movement is least in the antero-posterior dimension (p=0. These findings are in agreement with the findings of earlier studies by Zakhari. Perlowski6 indicated that plaster matrix around the teeth was the most accurate flasking method measured in his investigation. Strohaver29 reported that the injection molding system was more superior in terms of dimensional accuracy.22 Overall the conventional procedure of investing with dental plaster recorded more artificial teeth movement .32 Wakkace37 and Sanders et al38conducted tests to compare microwave energy and conventional hot water bath polymerization techniques. Solution of this problem does not appear to lie in stronger materials to resist this force but it probably lies in restricting and minimizing the forces created or induced with in the flask. which would give adequate physical properties without needing heavy pressure during closure of flask. Jakson et al31.Plaster does not offer sufficient support to the teeth when the pressure of the base material is applied. It appears that pressure induced within a plastic mass of acrylic dough in an enclosed flask is difficult to contain. Baemert et al76. Dirckx33 had conducted studies on injection molding systems and they concluded that there was no significant change in the dimension of cured dentures using this technique in comparison with the compression molding technique. Newer methods of polymerizing acrylic resin have come into existence in order to decrease the amount of distortion that occurs during the processing of the denture. Shlosberg et al. The two methods of polymerization produced similar dimensional accuracy in complete denture bases./^h^^/KE A disadvantage of using stone is that it takes more caution and time to deflask and recover cured dentures. ϳϰ . In other words what we need is a denture base material.73However. Alexander75. Becker et al23. ϳϱ . before & after acrylization.There is a need for further studies to evaluate artificial teeth movement in three dimensions of space serially. In as much as the result of this study. medio-lateral and antero-posterior by comparing measurements at two intervals i./^h^^/KE To summarize. purpose of the this study was to investigate the influence and relationship of investing medium on the movements of teeth taking place in two dimensions of space in compression molding technique. dental stone core method is preferable in view of the minimal movement of the teeth in antero-posterior direction.e. step by step from the wax-up to completion of processing. cooling. SCOPE FOR FURTHER STUDIES: This study focused on the effect of two gypsum investing medium on the movement of artificial teeth in two dimensions of space i. However it should be reiterated that none of the two methods are faultless. deflasking. and after de-flasking.e. 3. 2. when the flask is closed under pressure. Artificial teeth movement in the horizontal plane is minimized by the use of the investment combination of dental stone core and plaster mold. it may be concluded that:- 1. 4.KE>h^/KE CONCLUSION Within the limits of the present study and on the basis of results obtained. The ability of the investing medium to restrict artificial teeth movement might depend on its capacity to resist the pressure induced within the acrylic. The dental Stone core method is superior in view of the fact that it produces significantly less artificial teeth movement than the conventional method. ϳϲ . Neither of the investing methods is successful in completely preventing artificial teeth movement. To increase the parameters. Two groups of 15 maxillary dentures with semi-anatomic acrylic teeth were processed using two different investing mediums. Most of the previous studies conducted have focused on the unidirectional occlusal discrepancies only . taking place in two dimensions of space in the compression molding technique was evaluated. One of the reasons suggested was the difference in the thermal expansion of acrylic resin and gypsum investments when subjected to increase in temperature. two different methods of investing namely conventional and the stone core investing procedure were used. The artificial teeth movement was measured in the medio-lateral ϳϳ .These were observed by the rising of the incisal pin. The occlusal discrepancies during processing of complete dentures were earlier recognized to be due to the movement of teeth in an occlusal direction.Therefore in this investigation the influence of investing medium on the artificial teeth movement. so that the one with least discrepancy can be recommended on a routine basis for clinical application.^hDDZz SUMMARY The processing of complete denture in acrylic resin commonly results in dimensional changes that necessitate occlusal corrections to restore opposing tooth relationships. It is only recently that a few studies have become available to evaluate the artificial teeth movement in the antero-posterior and medio-lateral direction . However the stone core method offers the advantage of reduced teeth movement. ϳϴ . thereby minimizing the need for selective grinding of cusps for interferences in centric occlusion. The findings were statistically analyzed using parametric‘t’ tests and ANOVA ‘F’ test. However neither of the two investment methods was able to prevent artificial teeth movement. The dental stone core method recorded an overall less artificial teeth movement as compared to conventional method of investing with dental plaster. The movement of artificial teeth was measured with the aid of a traveling microscope. it can safely be said that no investing method is totally free of teeth movement .^hDDZz and the antero-posterior directions by taking four measurements between predetermined reference points. two measurements for each direction before processing and again after processing.Whereas the dental stone core method showed the least artificial teeth movement in the antero-posterior direction as compared to the teeth movement in the medio-lateral direction. Therefore in conclusion. 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