Assessing the Quality of ClinicalProcedures and Technical Standards of Dental Laboratories in Fixed Partial Denture Therapy Zakereyya S. M. Albashaireh, BDS, MSc, PblT Abdulrbman S. Ainegrisb, BDS, à Purpose: This study was conducted to assess the quality of impressions and tooth preparations serif to dental laboratories in iordan and tu determine the technical capabilities of these laboratoriei fo construct fixed partial dentures. Materials and Methods: A sample of I3& impressions and slone casts were examined for clinical errors in 35 laboratories that construct fixed partial dentures. They were sorted into unusable, unsatisfactory, acceptable, or satisfactory categories. The type of impression material and tray, opposing arch impressions, and occlusal records were noted, instructions to technicians were assessed for completeness and clarity. Information regarding laboratory slaff and equipment were collected. Results: Half of fhe specimens inspected were categorized as unusable or unsatisfactory; these were found in commercial laboratories. They showed at least one clinical error such as drags or indefinite finishing lines in impressions and inadequate reduction, undercuts, ot obvious taper on stone casts, Alginate impression material was used for 65% of the cases. Only 27% of specimens were accompanied with instructions; of these 22% were graded poor. No occlusal records were available with 54% of the specimens and no articuiafors were used except in dental school laboratories. The dental schools and some commercial laboratories had the best staff and equipment and were more capable of fabricating fixed partial dentures than Ihose of the Ministry of hHealth and the Royal Medical Services. Conclusion: The quality of abutment preparation and impressions were unsatisfactory or unusable in 50% of cases. Of the 37 available instructions 8 were not clear. The dental schools and some commercial laboratories were technically capable of producing good quality fixed partial dentures. Int J Prosfhodont 1999;! 2:236-241. A s more patients demand fixed partial dentures for the replacement of missing teeth and endure a high cost, the quality of fixed partial denture therapy becomes of increasing professional and public concern,^ Likewise, the quality of fixed prosthodontics provided to patients in Jordan is a cause of worry for professionals in this field. Moreover, the technical standards of fixed prostheses constructed in the Ministry of Health (MOH), the Royal Medical Services (RMS), commercial laboratories, and, to a lesser extent, in dental school laboratories are thought to be disappointing. A fixed partial denture of good quality should be well designed and constructed. It should restore the function and promote the health of the masticatory unit and provide a long service life. These criteria are influenced by the quality of clinical procedures, the standards of the laboratory work, and the oral conReprint requests: Or Z. S. M. Albashaireh, Riyadh Dental Center, ditions prevailing in the patient.' Inadequate reducFast Office Box ! 584, Riyadh ! 1441, Kingdom of Saudi Arabia. tion or imprecise preparation of abutment teeth. 'Assistant Professor and Consultant in Conservative Dsntistry, faculty af Dentistry, Jordan University of Science and Technology, irbid, ¡ordan. ''Specialist in Conservative Dentistry, Royal Medical Seri/ices; and Clinical Supervisor in Conservative Dentistry, Faculty of Dentistry, Iordan Uniyersity of Science and Technology, Irbid, Jordan. The International iourral of Proslhodontii 236 Volume 12, NumbE ' " costs of fixed partial dentures. clear instructions were given and poor if a telephone call to the dental practice was required for further information (eg. Unusable impressions: impressions that displayed obvious drags.'2. and to the equipment and techniques used during laboratory procedures..1999 237 Ttie International journal of Prosthodonticî . which represented the major cities In Jordan. Satisfactory: the impressions or stone casts were free of any of the above errors.AI baîhai reh/AI negri sh Quality of Laboratory. and poor-qualityalloys were used. and experience of the laboratory staff. or demonstrated an i ncreased degree of taper.-" A proficient technician may be able to correct or mask minor faults in a preparation and produce a reasonable restoration. 4. occiusal records should be supplied when applicable. In each commercial and dental school laboratory 4 specimens of impressions and stone casts were examined. Materials and Methods A sample of 60 (75%) dental laboratories. and (2) ascertain the technical capabilities and standards of these laboratories to competently construct fixed partial dentures. As technicians were not required to be registered.^'" The technical quality of fixed prosthodontic work might be compromised in laboratories where old types of equipment and inexperienced staff are involved In the construction of fixed partial dentures. displayed visual undercuts.^ Most (72%) fixed partial denture impressions were taken with flexible plastic trays and 36% showed defects in the recording of the prepared teeth.Procedures for Fixed Partial Dentures particularly the finishing lines. Impressions for anterior crowns' and fixed partial dentures^' made in general dental praaice have been assessed. 5 in the RMS. number.•. such as cleaning blood stains from impressions. and accompanying design prescriptions of impressions and/or stone casts. and training of technicians._. a person was considered a technician for the purposes of this study if they were so recognized by the laboratory owner. :. Unsatisfactory casts: the prepared abutments caused occiusal interferences on pink wax placed between the maxillary and mandibular casts in intercuspai position. Moreover.'iewed and asked to complete the questionnaire during the meeting. Comparatively. was randomly selected from the Register of Dental Laboratories. were detached from the impression tray. 2. . 2 impressions per laboratory were inspected in the MOH and RMS..' Proximal contacts were overbuilt at 65% of the sites studied. Technicians should be provided with a complete and clear prescription of the design and details ofeach restoration or component. Therefore. It included questions related to the qualifications.. A questionnaire was formed following a small pilot study prior to this survey. According to availability." Few investigations have been designed to examine the quality of clinical procedures and to determine the capability of dental laboratories that deal with fixed partial denture technology.. impression techniques. Space was provided for comments regarding fees. ~ = L . They were given a list of laboratory equipment and asked to indicate if this equipment was present and used in their laboratories. The examiner and tbe chief technician assessed details of the practitioner's instruction to technicians and considered them satisfactory if sufficient. pontic tissue contacts were excessive in the majority of cases. They were located as follows: 5 in dental schools.However. abutments that have been prepared and finished carefully require an equally careful and correct impression technique using reliable materials and suitable trays.-. 11 in the MOH.. Over half of the crown impressions exhibited major faults and were recorded to be unacceptable. may have a profound effect on the subsequent fit of the restoration. and 39 commercial laboratories. a sample of dental laboratories was surveyed to: (/) determine the quality of abutment preparation. available occiusal records. The laboratories selected were visited without prior appointment and the chief technicians were inten. Number 3. and showed indefinite and interrupted finishing lines around the circumference of the preparation. blocking minor undercuts. and filling small air bubbles with stone cast material. a few studies have been carried out to determine the quality of clinical procedures undertaken by dentists. the shade details) before the case could be started. Specimens were inspected for defects using magnification loupes (2x) and were categorized by the same examiner according to the following criteria.' Provided that the initial tooth preparation and impression techniques are adequate. The results were analyzed using the Chi-squared test. the esthetics and strength of a fixed partial denture are determined by the skill of the individual technician. the inferior quality of dental prostheses has been attributed largely to errors incurred in laboratories. and opposing arch impressions of the cases selected were noted.' Despite the importance of this broad range of factors. 1.' Metal-ceramic fixed partial dentures have been studied and various technical errors were reported. Acceptable: minor modifications of inspected impressions or stone casts were required. 3.. Factors like the type of impression material and l:ray. Without this tbe impression stage can nullify earlier achievements in the preparation.:. MOH. and dental school laboratories were pooled and shown under "institutions. In contrast. Half of these cases showed clinical errors and were categorized as unusable and unsatisfactory. No statistical differences were found among laboratories in relation to case category (P > 0. the cases inspected in institutionalized dental schools.05). one MOH laboratory and one RMS laboratory did so ¡Table 1 ). and RMS laboratories were of acceptable or satisfactory quality. Tfie internationai Journal of Pro5thoclonti< 238 Volume 12. Numbe . Details of the clinical errors are shown in Table 3. In contrast.Quality of Laboratory Procedures for Fixed Partial Dentures Albasliaireh/Alnegrish Table 1 Number (n) and Percentage ot Surveyed Laboratories that Construot Fixed Partial Dentures Location School Commercial MOH RMS Total Total n % 5 39 11 5 60 4 29 1 1 35 80 74 9 20 53 Table 2 Number (n) and Peroentage of Cases Inspected According to the Factors Studied and Laboratory Location Case category Unusable Unsatisfactory Acceptable Satisfactory Total Impression material Alginate Elastomeric Total Impression tray Rigid plastic Metal Total InstruGlions Available Mot available Total Poor ot available Opposing impressions Available Not available Total Occlusal records Available Not available Total Total Commercial Institutions' n n % n % 0 0 6 U 20 0 0 30 70 100 32 36 16 32 116 28 31 14 28 100 32 36 22 46 136 24 26 16 34 100 2 IB 20 10 90 100 87 29 116 75 25 TOO 89 47 136 65 35 100 16 4 20 80 20 100 88 28 116 76 24 100 104 32 136 76 24 100 17 3 20 1 85 15 100 6 20 96 116 7 17 83 100 35 37 99 136 8 27 73 100 22 16 4 20 80 20 74 42 100 116 64 36 100 90 46 136 66 34 100 16 4 20 80 20 100 47 69 116 41 59 100 63 73 136 46 54 100 'Institutions include school MOH. Consequently. All of the unusable impressions and unsatisfactory stone casts were found in commercial laboratories. Alginate was used for most Results Of the 60 laboratories surveyed 35 (53%] were found to be involved in fixed prosthodontics. The data on MOH." Oniy 4 impressions were available for inspection in the 2 MOH and RMS laboratories (2 impressions each). Impressions and Instructions The distribution of cases inspected according to the factors studied and laboratory location is given in Table 2. the other half of the cases were distributed under the acceptable and satisfactory categories. 136 specimens were examined in the 35 laboratories involved in fixed prosthodontics. RMS. The majority of commercial and dental school laboratories also constructed fixed partial dentures. arid RMS ia bo rato ries A total of 132 impressions and stone casts were examined in the 33 dental school and commercial laboratories (4 specimens each). 50 of these employees (27%) had no dental technology qualifications.rather than cost-dependent. Plastic impression trays of a rigid design (Solo disposable impression trays. programmed vacuum furnaces. Articulators of semiadjustable type were commonly used in the laboratories of the dental schools and were available. while a type of elastomeric impression material was used for the rest. and 22% ofthe available sheets were graded poor and required a telephone call to the dental practice for clarification. A number of commercial laboratories possessed the basic ^ • .AI basha i reVAl negrish Quality of Laboratory Procedures for Fixed Partial Demure Table 3 Number (n) and Percentage of Clinical EiTors in Impressions and Stone Casts Clinical errors n Impressions Drag Detached from tray Indefinite finishing line Stone casts Over reduction Undercut Increased degree of taper Indefinite finishing line Total Table 4 10 17 5 15 25 7 12 9 8 7 68 18 13 12 10 100 Percentages and Locations of Laboratories Using Listed Equipment Type of equipment Schools (n = 5¡ Ccmmereial (n =39) f^OH(n = i i ) RMS(n = Metal work Surveyor 60 Vacuum mixer 100 Gas fumace 20 Electric fumace 100 Sand blaster 100 Casting machines Centrifugal electric muffle 100 Pressure vacuum casting 100 Porcelain furnace Vacuum fired 0 Vacuum automatic 80 Other equipment Die-locating device 60 Ultrasonic cleaner 100 Bench magnifying glass 80 Electric welder 40 Dust extractor unit 100 Compressed air to eacti unit 100 ArticLlators 60 Fume cupboard 100 20 100 20 40 51 39 0 g 0 0 31 44 9 0 20 0 36 87 0 36 0 27 27 44 0 82 0 40 0 60 40 100 0 100 ie 90 0 equipment required for the fabrication of fixed partial denture work. in some commercial laboratories.I r . The majority of the MOH and RMS laboratories had equipment suitable for the construction of removable prosthodontic and orthodontic appliances. The majority of cases were not accompanied by instruction sheets. The fee charged per unit varied from one laboratory to another and was reputation. occlusal records were provided with 53 (70%) ofthem (Table 2).. Cordent) were employed for the majority of cases inspected and metal trays were used for the remainder.X Number 3. g 9 49 62 67 51 85 The total number of technicians was 183. A total of 90 opposing arch impressions were available. They had modern types of equipment such as pressure-vacuum casting machines. but rarely used.. Nonprecious alloys were used extensively in all iaboratoriesbecauseoftheir low cost.1999 100 27 90 26 10 92 95 cases. Laboratory owners considered 22 of the unqualified persons technicians and dealt with the 239 The Inlernatiorial loumäl of Prosthodontics . and die-locating devices. butwerepoody equipped to produce any form of porcelain work (Tabie 4]. -. laboratory Equipment and Techniques Staffing Dental school laboratories were well equipped and capable of performing the widest range of dental work. Quality of laboratory Procedures for Fixed Partial Dentures Albashaireh/Alnegrish remaining 28 persons as laboratory assistants. Some of the impressions were pulling away from the tray. and some porceiain work. Even a skillful and experienced technician would fail to produce a restoration of acceptable strength.^'^'^''^ Such impressions can only lead to distorted working dies and ill-fitting restorations. Consequently. and delivering the finished work to ciinics. One air bubble is sufficient to alter the articulation and result in a faulty restoration.^ ' Many authors have reported the importance of using a rigid impression tray. and RMS laboratories were 2. The experience of 22% of the technicians ranged from 5 to 10 years. and the technician per laboratory ratios for commercial. The 28 laboratory assistants were excluded when these ratios were calculated. They were still using oid types of furnaces for porcelain work and gas furnaces for beating casting rings. The majority of impressions were taken with alginate. They believed that the inferior quality of the products could be attributed in part to their iow salaries. Numbe'i .4. or "seniors" (34%) who had worked in the field for more than 15 years. including design and shade details. • Instructions to technicians.^''^"^^ Although the rigid plastic trays that were used are better than flexible types. orthodontic appiiances.^ The dental schooi and some commercial laboratories had modern types of equipment and were capable of producing ali kindsof dentai work. Fine details ofthe preparation and surrounding soft tissues can be recorded accurately when a suitable elastomeric material is used. some impressions were detached from the trays and showed obvious shrinkage. special or metal trays are recommended.^ An adhesive should be applied to the tray and the manufacturer's instructions should be adhered to while manipulating impression materials. in half of the specimens inspected preparation features were inadequate and the finishing lines were indistinct. full-time training courses at the colleges of dental technology were insufficient. respectively. Clinical procedures of such low quality can only lead to guesswork on the part of the technician and must result in a restoration that will be compromised from the outset. this procedure ensured that the responses ofthe chief technicians themselves were obtained and eliminated any possible interference from laboratory owners. and are therefore a more satisfactory alternative in terms of both cost and accuracy. and esthetics from an impression with such errors. MOH.^''"''^ Moreover. In contrast. This is more than some of the response rates recorded in the literature.36. other reports^'' ' and with the comments of the technicians. and 5. The technicians' experience varied from 1 to 25 years. All technicians were employed on a full-time basis. Discussion The sample was randomly selected and represented the major cities of Jordan. • Impressions should be taken using standard trays and materials. a finding that is in agreement with previous studies. This is in agreement with similar studies. dental school. which is used in the dental schools. These results are in agreement with The International lournal oí Prostliodontii: 240 Volume 12. while the remaining 10% had 10 to 15 years of experience. Laboratory owners empioyed technicians of known inadequate training and paid them iower saiaries. These findings are in accordance with another report. The questionnaires were completed by the chief technician and were collected on the day of the visit to the laboratory. can be reused.44.''^' ' It seems that a standardized prescription form. cierking. Moreover. and inaccurate clinical procedures.6. 2. they empioyed iaboratory assistants presumabiy to perform routine tasks and gênerai work such as cieaning. who thought that some of the preparation and impression procedures were inappropriate. The 2 iaboratories that constructed fixed partiai dentures seemed to be incapable of providing restorations on a large scaie. should be provided and written clearly. those of the MOH and the RMS were mostly equipped for fabricating removable acryiic dentures. Moreover. may contribute to solving this problem. lack of incentives. biologic compatibility. They gave the following suggestions as to how the clinical standards could be raised: • Abutment teeth should be carefully prepared. 2." Many practitioners fail to understand that a "high" restoration is not a result of error by the technician but of defective recording of the occlusa! surfaces of unprepared teeth. Most dentists using commercial laboratories performed unsatisfactory tooth preparation and sent unusable impressions. Some dentists relied on technicians to relate casts in proper occlusion and sent no occiusai records.'^ Dentists supplied no prescriptions of the work requested in the majority of cases. The construction of a good-quaiity Technician Comments The chief technicians thought that the 2-year. This method avoided any problems related to the mailing system and overcame the issue of no response.^-^' The latter are significantly more rigid. with most being either "juniors" (34%) with 1 to 5 years of experience. data on 60 (75%) of the 80 registered dental laboratories at the time of this study were collected and a 100% response rate was achieved. 164. Crowns & Bridges. 7.133:179-184. | Can DentAssoc 198l. 241 14. Kaffe I. Rehberg H|. and RMS laboratories performed satisfactory clinical procedures and sent acceptable impressions. Prosthesis technology in commercial dental laboratories in the United Sfafes. Murphy W M . Crown and bridge technology in the United Kingdom. The International Joumal of Prosthodoniics . 10. . Williams C. 16. 3. The effect of using custom or stock trays on the accuracy of gypsum casts. 3. A Clinical Handhook.9:53-58. which varied depending on the profit of laboratory owners. Miller G D . Northeast SE. Refresher courses for qualified technicians should be organized regularly. Winaanley RB. ShoveKon DS. Naylor |T. Complete denture construction in dental schools and hospitals ot'the United Kingdom and Ireland. Technology courses should be revised and the training period extended.9:367-373. I Prosthet Dent 1985. 1965-74. Bombers "I"). 6. Green |R. these were found in commercial laboratories.56. 175.60:681-684. Clinicians should perform accurate preparation procedures. This made an offer of a better-paid overseas job very attractive to the experienced technicians.172:198-204.^ Technicians were concerned and unhappy with their salaries.27:146-153. 12. Williams GI. Owners should be required to update their laboratory equipment regularly. Oxford: Wright. Bates ]F. The quality ot' impressions for crowns and bridges received at commercial dental laboratories. and supply technicians with complete. Helft M. B. Shortall AC. The changing pattern of dental practice in South Wales. Wilson H|. EdfnundsDH. Br Dent J 1997:133:209-213. Number 3. Half of the fixed partial denture cases inspected were of unacceptable quality. 1993:45-. 5. 13. Conclusion This study implies the following suggestions and recommendations: 1. I Dent 1977^: 133-140. Consideration for adhesion of impression materials to impression frays. Naylor WP. The quality of work will certainly be jeopardized if the duties of the laboratory assistants are extended to include coping with sophisticated types of work. Br Dent 11993:174:235-240. clear instructions. Tjan AHL. and pay them reasonable salaries. Dent Tech 1972:25:163. Comparison of methods of clinical evaluation of fhe marginal fit of complete cast gold crowns. White GE. Hjgget R. Kantorowicz GF. An initial evaluation of faults in commercially manufactured crowns. Impression materials and techniques. 8. Antopolsk. Inlays. The impression tray—An important factor in impression precision. employ technicians with adequate training and experience. Hugget R. J Dent 1977:5:99-106. Stafford GD. Melal ceramic fixed partial dentures from commerciai dental laboratories: Ailoy composition cost and quality of fiL Br DentJ 1992. lohnson A. Eccles ID.Goldfogel M H . Howe LC. Carrotfe PV. van Noort R. The fact that no incentives were paid for skillful technicians may have dampened any enthusiasm for professional development.186. Hunt HH. 4. References 1. Sy-Muñoz JT. 1999 11. Whifehead C. MOH. Rueda LJ.2.187. Johnson A. Women dentists in Wales. Piddock V. Williams |. Murphy W M . 9. Survey of prosthetic technology in commercial denial laboratories. use proper materials and trays for taking impressions. Goodacre Ci. IDenf 1977:5:107-112. A study of the qualify of impressions for anterior crowns received at a commercial laboratory. EcclesID.54:20-24. Dentists using institutionalized dental school. Winstanley RB. Assif D. 2. Regulations including uniform fee charges per unit and reasonable salaries for technicians should be applied to control the establishment of new laboratories and improve the standards of existing ones. Br Den! J1972. 15. Marquis PM. Whang SB. Carrotte PV. Hoffman W . W h y a rigid tray is important to the putty Vfash sMicore impression method. Harrison A. Ir: Kantorowicz CF (ed). Quintessence DentTechnol 1986:10:173-178. Swartz ML. Powell M. Wmstanley RB. Int Dent] 1977. | Prosthef Dent 1988. Inf I Prosthodont 1996.176. 2. Br Dent) 1981:150:215-217.Albashaireh/Alnegrish Quality of Laboratory Procedures for Fised Partial Dentures fixed partial denture needs all the expertise and care of a well-trained and experienced technician. Bomberg SE. The dental schools and some commercial laboratories had the staff and equipment required for producing fixed partial dentures.