journal of prosthodontic research 58 (2014) 3–10Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/jpor Position Paper Clinical application of removable partial dentures using thermoplastic resin—Part I: Definition and indication of non-metal clasp dentures Kenji Fueki DDS, PhDa,d,*, Chikahiro Ohkubo DMD, PhDb,c,e, Masaru Yatabe DDS, PhDb,d,f, Ichiro Arakawa DDS, PhDb,c,g, Masahiro Arita DDS, PhDb,c,h, Satoshi Ino DDS, PhDb,i, Toshikazu Kanamori DDS, PhDb,j, Yasuhiko Kawai DDS, PhDb,c,k, Misao Kawara DDS, PhDb,l, Osamu Komiyama DDS, PhDb,l, Tetsuya Suzuki DDS, PhDb,c,m, Kazuhiro Nagata DDS, PhDb,n, Maki Hosoki DDS, PhDb,o, Shin-ichi Masumi DDS, PhDb,h, Mutsuo Yamauchi DDS, PhDb,p, Hideki Aita DDS, PhDa,q, Takahiro Ono DDS, PhDa,r, Hisatomo Kondo DDS, PhDa,s, Katsushi Tamaki DDS, PhDa,t, Yoshizo Matsuka DDS, PhDa,o, Hiroaki Tsukasaki DDS, PhDa,u, Masanori Fujisawa DDS, PhDa,v, Kazuyoshi Baba DDS, PhDa,u, Kiyoshi Koyano DDS, PhDa,w, Hirofumi Yatani DDS, PhDx a Japan Prosthodontic Society, Clinical Guideline Committee (2011–2012), Japan Japan Prosthodontic Society, Non-Metal Clasp Denture Expert Panel (2011–2012), Japan c Japan Prosthodontic Society, Removable Prosthodontics Expert Panel (2011–2012), Japan d Section of Removable Partial Prosthodontics, Tokyo Medical and Dental University, Japan e Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Japan f Tokyo Branch, Japan g Department of Partial and Complete Denture, School of Life Dentistry at Tokyo, The Nippon Dental University, Japan h Division of Occlusion & Maxillofacial Reconstruction, Department of Oral Function, School of Dentistry, Kyushu Dental University, Japan i Kanagawa Dental University, Yokohama Clinic, Japan j Tohoku & Hokkaido Branch, Japan k Department of Removable Prosthodontics, Nihon University School of Dentistry at Matsudo, Japan l Department of Oral Function and Rehabilitation, Nihon University School of Dentistry at Matsudo, Japan m Section of Oral Prosthetic Engineering, Tokyo Medical and Dental University, Japan n Comprehensive Dental Care, The Nippon Dental University Niigata Hospital, Japan o Department of Fixed Prosthodontics, Institute of Health Biosciences, The University of Tokushima, Graduate School, Japan b * Corresponding author at: Section of Removable Partial Prosthodontics, Department of Masticatory Function Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, 113-8549 Tokyo, Japan. Tel.: +81 3 5803 5514; fax: +81 3 5803 5514. E-mail address:
[email protected] (K. Fueki). 1883-1958/$ – see front matter # 2013 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved. http://dx.doi.org/10.1016/j.jpor.2013.12.002 . . .3. .2. . . . . . .2. . . . . . . . . . Feel during use of NMCDs . . . . . . .2. . . . . . Iwate Medical University. . . . . . Accord- Non-metal clasp denture ing to current prosthetic principles. . . . . . . . . . . . . . . . Showa University. . . . . . . . .1. . . Japan r Department of Prosthodontics. . . . . . . . . . . . . . . . . . . . . . . . .1. . . . Indications and contraindications for NMCDs . . . . . . . . . . . . . . .1. . . . . . . Japan q Division of Occlusion and Removable Prosthodontics. . . . . . . . . Anatomical factors . Design of retentive parts and periodontal condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4. . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. . . . Health Sciences University of Hokkaido. . . . . .2. School of Dentistry. . . . . . . . . . . . . . . . 5. Division of Oral Functional Science and Rehabilitation. . . Japan s Department of Prosthodontics and Oral Implantology. . . . . . . . . . . . . . . . . . 5. . . . .3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1. Advantages and disadvantages of NMCDs . . . . . . . . . . . . . . 5. . . State of oral hygiene. . . . . . . . . . .5. . . . . . . . . . . . . . .1. . . . . . . . . . . . . . . . . . References . . . . . .2. . . 5. 4. . . . . . . . . . . . . . . . . . . . . . . . . . . Kyushu University. . . . . . . . . Acknowledgements . . . . . . . Discoloration and degradation of thermoplastic resin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Published by Elsevier Ireland. . . . . . . . . . . . . . . . .2. . . . # 2013 Japan Prosthodontic Society. . Japan article info abstract Article history: This position paper proposes a definition and naming standard for removable partial Received 11 November 2013 dentures (RPDs) using thermoplastic resin. . . . . . . Disadvantages . . . . . . . . . . . . Metal allergy . . .4 journal of prosthodontic research 58 (2014) 3–10 p Department of Prosthodontics. . 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Japan w Section of Implant and Rehabilitative Dentistry. . . . . . . . . . . . . . . 4. . Non-metal clasp dentures should follow the same design principles as conventional RPDs using metal clasps. . . except for limited cases such as patients with a metal allergy. . . Japan x Department of Fixed Prosthodontics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6 6 6 6 7 7 8 8 8 8 8 9 9 9 9 9 9 9 9 9 10 10 . . . . . . .4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Breakage of resin clasp. . . . . . . . . . 2. . . . . . .3. . . . . . . . . . . . . . . . . . . . . . . . . .1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Japan v Division of Fixed Prosthodontics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contraindications and cases in which use requires caution . . . . . . . . . . . . 4. . . . . . . Rigid Metal allergy non-metal clasp dentures are recommended in cases where patients will not accept metal clasps for esthetic reasons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Osaka University Graduate School of Dentistry. . . . . . . . . . . . difficulty of adjusting retention capacity and repair. . . . . . . . . . . . . Esthetics . . . . Advantages . . . . . . . . . . . . . . . . . . . . . . . .1. . . . . Division of Oral Rehabilitation Faculty of Dental Science. . . . . . Contents 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. . . . . . . . . . . Removable Prosthetics. . . . . . . . . . . . . . . . . . . . . . . . . . . Japan t Department of Oral & Maxillofacial Rehabilitation. . . . . . At a Keywords: with retentive elements (resin clasps) made of thermoplastic resin. . . . . . . . . . . . . . . 4. . . . Accepted 5 December 2013 A panel of 14 experts having broad experience with clinical application of RPDs using Available online 22 January 2014 thermoplastic resin was selected from members of the Japan Prosthodontic Society. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Term and definition. . . . .1. . . . . . Difficulty of polishing . . Ineligibility for insurance coverage . . . . . . . . . . . . ‘‘non-metal clasp denture’’ was referred as the generic name of RPDs Removable partial denture metal clasp dentures into two types: one with a flexible structure that lacks a metal Thermoplastic resin framework and the other having a rigid structure that includes a metal framework. . . . . . . . Kanagawa Dental College. . . 5.2. . . . . . . . . . . flexible non-metal clasp dentures are not recommended Resin clasp as definitive dentures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. 5. . . . . . . . . . . . . . All rights reserved. . . . Japan u Department of Prosthodontics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . .2. . . . . . . . . . . . . . . . . . . . . . Indications . . . . . . . . . . . Asahi University. . . . and presents a guideline for clinical application. . . . . . . . . . Type of partially edentulous arch and occlusal relationship . . . . . . . . . . . . . . . . . . . . . . . Gerodontology and Oral Rehabilitation. . . . . Osaka University Graduate School of Dentistry. . . . . . . . . . . . . . . . . . . 5. . . . . . . . 5. . . . . . . . . . . . . . . . Meikai University. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. . . . . . . . . . . Preparation of position paper . 5. . . . . . . .2. . . . . . . . . . .2. . . . . . . . .2. . School of Dentistry. . . . . . . . . . . . . . . . The panel classified non- meeting of the panel. . . . . . . . . . . . . . but according to the definition in the US GPT-8 Glossary of Prosthodontic Terms [3]. In light of these circumstances. if patients’ demands and desires for a good esthetic appearance are given precedence and such RPDs are used outside the scope of their intended use. If this situation is left unaddressed. and treatment such as reline or repair may be difficult. clasp-free dentures. They first searched the literature in PubMed and Igaku Chuo Zasshi (ICHUSHI. Changes in public awareness have led to increasingly strong demands from patients with respect to esthetic aspects when fitting prostheses. there is a possibility that the inappropriate use of RPDs using thermoplastic resin may become a social issue. the Clinical Guideline Committee responded to a request from the Social Insurance and Dental Service Problem Committee and considered correcting the guideline. whether or not to limit them to thermoplastic resin materials). or discoloration of denture base resin may occur. roughening of the polished surface of the denture base. JPS stated that ‘‘Application of flexible dentures solely from the viewpoint of anterior esthetics is not recommended. Japan Medical Abstracts Society) to collect the latest clinical evidence. The use of RPDs made either from resin alone or a combination of resin and metal is now rapidly gaining popularity among general dentists and is considered to be superior to conventional metal-clasp retained RPDs with metal clasps in terms of both esthetics and comfort [1]. design. and denture design. and their indications should be scientifically verified in the future’’. In a clinical guideline formulated Product name Manufacturer Polyamide BIO PLAST Valplast Flex Star V BIO TONE Lucitone FRS Ultimate HIGH DENTAL JAPAN UNIVAL Nippon Dental supply HIGH DENTAL JAPAN DENTSPLY International Ultimate Polyester EstheShot Bright EstheShot i-Cast i-Cast Polycarbonate Reigning N Reigning JET CARBO-S JET CARBO RESIN Toushinyoukou Toushinyoukou HIGH DENTAL JAPAN HIGH DENTAL JAPAN Acrylic resin ACRY TONE HIGH DENTAL JAPAN Polypropylene UNIGUM WELDENZ in 2008. including abnormal resorption of the residual ridge and increase of movement of the abutment teeth. and metal-free dentures. attachments have been used in patients who place emphasis on esthetics. with an increasing number of patients avoiding RPDs because they are associated with growing old. types of defect. a questionnaire was sent to a panel of prosthodontists on how to formulate a guideline (dentures to be covered. they have the disadvantage that if they are used in the wrong patients they may cause major damage. Given the lack of evidence. polyamide resin (nylon) has been used to fabricate RPDs that do not contain any metal elements. only one original paper had been published based on clinical research on RPDs using thermoplastic resin [4]. nonclasp dentures. the resin part that extends from the denture base to include the abutment teeth and which is responsible for retention is a structural element that should be called a clasp. this is not a generally viable choice. The first issue is that some RPDs using thermoplastic resin do not conform to the principles regarding the standard RPD design in Japan. The objectives of this position paper were (1) to propose an official term and definition for RPDs using thermoplastic resin. . Since 2007. and (2) to provide guidelines for prosthodontists and general dentists on points to note with respect to the indications and contraindications. The need for dentists to respond to this demand from patients may be a cause of the increasing popularity of such RPDs. Generic name Esthetics is a matter of great concern for patients receiving dental treatment. which are commonly known as flexible dentures.5 journal of prosthodontic research 58 (2014) 3–10 1. problems including fracture of the resin clasp. ‘‘non-clasp dentures’’ has become the generally used term. Then. RPDs using thermoplastic resin have some limitations as revealed by prosthodontists [2]. this would be a serious disadvantage for patients. various problems do occur after denture fitting in at least some patients. In practice. The decision was therefore made to select an expert panel from among JPS members who had clinical experience with RPDs using thermoplastic resin in order to form a consensus based on clinical experience. It has also been pointed out that depending on the material. since the 1950s. As this procedure is simple and is not covered by national health insurance. In the United States. Recently. esthetic aspects must be considered to ensure patient satisfaction with dental treatment. In light of this situation. Therefore. it may decrease public trust in dental treatment and dentistry. it was considered that it would be difficult to formulate a guideline for such a wide diversity of patients using standard methods. Patients find the sight of the metal clasp of removable partial dentures (RPDs) in the esthetic area undesirable for both esthetic and psychological reasons. especially prosthetic treatment. stating that ‘‘Although so-called non-clasp dentures have the positive advantage of being effective in restoring external appearance. and while the evidence from clinical trials is limited. the Japan Prosthodontic Society (JPS) has cautioned against the regular clinical use of RPDs using thermoplastic resin. cases in which their use is indicated.’’ The second problem identified by prosthodontists is that there is no set definition or name for RPDs using thermoplastic resin. Introduction Table 1 – Thermoplastic resins available for non-metal clasp dentures in Japan (December 2012). and that the use of such RPDs may seriously affect the periodontal tissues of abutment teeth and the residual ridge. Conventionally. and found that there were a limited number of studies: as of August 2011. and the term ‘‘non-clasp’’ is therefore inappropriate. a number of thermoplastic resins have also been approved for use as denture bases in Japan (Table 1). but the need to remove large quantities of tooth structure and the requirement for specialist skills means that at present. this is one explanation for patients disliking the use of RPDs. and to publish the results as a position paper. The results revealed that most prosthodontists wanted to formulate a guideline on the different types of thermoplastic resin currently in use. and clinical use of such dentures. however. design. Generally it is used to stabilize and retain a removable dental prosthesis. and they are also known as ‘‘resin clasps’’ or ‘‘esthetic clasps’’ [7. The final document was completed after review by the clinical guideline committee. Labour and Welfare. a clasp is defined as ‘‘the component of the clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element. 2. milling dentures. patients for whom esthetics must be given top priority. and it became common to call them by names such as ‘‘non-clasp dentures’’ or ‘‘metal-free dentures. as a material for use in dentures. Preparation of position paper The 21 members selected to serve on the expert panel for 2011– 2012 were requested to complete a questionnaire.’’ Since their approval under the pharmaceutical affairs law in April 2008. NMCDs that do not include a metal structure and are not rigid are indicated as interim dentures or spare dentures for patients with metal allergy. supplier. members discussed the official term and definition for RPDs using thermoplastic resin and the structure of the position paper. The resin retentive elements known as arms. NMCDs with/without overall rigidity according to whether or not they include a metal structure and the elastic modulus of the denture base resin (Table 2) and indications are suggested in each type of NMCD. the name ‘‘non-clasp dentures’’ has taken root among general clinicians.’’ This definition thus includes not only those dentures in which the retentive parts and the denture base are produced as a single whole. and the content was corrected through Internet discussion among the panel as a whole until a consensus was obtained. a total of 14 members prepared the initial draft of this position paper. In this position paper.8]. Thus. 1 – A non-metal clasp denture without metal elements. but also to dentures that incorporate a metal rest or framework (Figs. these dentures were individually imported and used on a trial basis before they were approved by the Ministry of Health. This interpretation therefore indicates that the term ‘‘nonclasp dentures’’ refers only to those that do not incorporate clasps in any form. Indications In this position paper. a type of nylon. however. Information was then gathered from JPS members who had at least 5 years’ clinical experience with RPDs using thermoplastic resin. as they use undercuts to retain and stabilize RPDs. NMCDs have been categorized into two types. in this position paper. and as epitheses for patients in whom the dentures carry no functional burden. Valplast. or laboratories. in general. the US company Valplast developed super-polyamide. Thus. and . but also those dentures in which a resin used for the retentive parts is different from that for denture base (Fig.6]. and reached a consensus. as well as manual search.6 journal of prosthodontic research 58 (2014) 3–10 Fig. patients with few missing anterior teeth. fingers. and patients with few missing teeth with occlusal support. 2 and 3). and wings may thus be regarded as genuine clasps according to this definition. Term and definition In 1956. and five members who had clinical experience with RPDs using thermoplastic resin in several patients were included in our expert panel. 1) [5. The PubMed and ICHUSHI online databases were used to search the literature. and have become widely used worldwide (Fig. In Japan. 4). and is defined as ‘‘the general name for RPDs using denture base resins as the denture retentive parts. such as attachment dentures. or telescope dentures. According to the GPT-8 [3]. 3. but are also called flexible dentures or nylon dentures. Indications and contraindications for NMCDs 4. Fig.1. and these have mistakenly been known by the names of their manufacturer. the resin retentive part of NMCDs is referred to as the ‘‘resin clasp. a ‘‘clasp’’ is not described as being made of metal.’’ 4. and an additional nine members were selected to join the expert panel. the term ‘‘non-metal clasp dentures’’ (NMCDs) is used to refer not only to dentures that do not contain any metal elements. At a panel meeting in August 2012. numerous thermoplastic resins have been developed. Dentures for which all the structural elements other than the artificial teeth are manufactured from this thermoplastic resin without the use of metal have been mostly known by the company name. 2 – A non-metal clasp denture with metal rests. All the members of the expert panel were responsible for writing different sections of the draft position paper.’’ According to this definition. The selection of literature was not carried out systematically. however. Contraindications and cases in which use requires caution Contraindications for NMCDs depend on the type of partially edentulous arch and occlusal relationship. changes in occlusal position. For patients with non-vertical stop occlusion in particular. Fig. . (a) Resin clasp on working cast. patients who do not consent to the preparation of abutment teeth (Fig. rotation and sinking of the denture base.2.journal of prosthodontic research 58 (2014) 3–10 7 Fig. 4 – A non-metal clasp denture using different denture base resins for retentive elements and a denture base. Fig. (b) metal rest and resin clasp.2. 4. (a) Labial view on working cast. and resorption of the residual ridge tend to occur. or a state of oral hygiene that may affect the maintenance and management of RPD treatment. 4. in patients with non-vertical stop occlusion or those with few remaining teeth.1. 2–4). anatomical factors that affect the design and fabrication of RPDs. 5). Type of partially edentulous arch and occlusal relationship NMCDs may be designed with a metal rest or framework to control displacement of the dentures while in use. 5 – A non-metal clasp denture without metal framework replacing missing maxillary bilateral frontal teeth (ValplastW). 3 – A non-metal clasp denture with a framework (Reigning NW). and designs that incorporate metal may be used with almost all types of partially edentulous arches. NMCDs that include a metal structure and are rigid are basically indicated in a wide range of cases (Figs. Their use is difficult. (a) Basal surface of the denture. in whom good treatment results cannot be expected even with the use of metal clasp-retained RPDs. (b) palatal view on working cast. (b) delivered denture. Advantages and disadvantages of NMCDs 5. The resin clasp may lack sufficient retention capacity and strength. or are afraid of surgical treatment. it is possible for the retentive parts to actively utilize a vital tooth. With metal framework. State of oral hygiene Metal clasps are designed in such a way that they do not to come into contact with the gingival margin. Polished surface of the maxillary complete denture (left) was good. both men and women. the artificial teeth may be lost. or fractured. and dentists may be at a loss how to deal with this. . such retainers may be difficult to use.2. and caution is therefore required.2. in whom the distance between the survey line on the abutment tooth and the oral vestibule is inadequate. Denture base of the posterior area was repaired using a cold-cured resin (indicated with arrow).8 journal of prosthodontic research 58 (2014) 3–10 Table 2 – Rigidity of non-metal clasp dentures using thermoplastic resins.1. and caution is therefore required. The cost is also generally high. The stress on the resin clasp may also be high in patients with few remaining teeth. The esthetic appearance of RPDs may be guaranteed by the use of magnetic or precision attachment. are highly concerned about the esthetic appearance. should the dentures sink then the resin clasp compresses the Fig. In patients with a small amount of clearance with opposing teeth at the missing area. its external shape is affected not only by the crown morphology of the abutment tooth but also by the morphology of the alveolar part. 4. As a wide area around the abutment teeth becomes unhygienic. Anatomical factors As the upper margin of the resin clasp of NMCDs is designed to be positioned on the tooth surface and the lower margin on the gingiva. resulting in the concentration of excessive force in the resin clasp. The need for adequate dental plaque control has been emphasized [9]. the thermoplastic denture base resins cannot be chemically bound to the artificial teeth. Although dental implant treatment is effective. this may cause or exacerbate caries and periodontal disease. potentially causing its mechanical damage. however surface of denture base of a mandibular non-metal clasp denture (EstheShotW) has become roughened after a year and 6-month use. suggesting that more careful follow-up is required for patients with metal-free NMCDs. marginal gingiva.1. but if the abutment tooth is a vital tooth. worsening the cleanliness of dentures. they are contraindicated. it may be difficult to design a resin clasp of appropriate shape and width. In most NMCDs. the occlusal position is unstable. high 2000 MPa. and patients with poor oral hygiene and those who do not respond regular repeat appointments are not suitable candidates. 5. 4. cracked. In patients with a clinically short crown length. or poor support is provided by the mucosa of residual ridge at the edentulous area due to severe residual ridge resorption or abnormal mucosa under the denture base. meaning that holes must be made to hold the artificial teeth and they must be mechanically fixed. but the resin clasp of NMCDs covers the tooth structure of the cervical region of abutment teeth. 6 – Deterioration of thermoplastic resin used for nonmetal clasp denture. With NMCDs. It has been reported that NMCDs that contain no metal structures at all tend to sink [9]. In patients who use a NMCD with no support from a metal rest. As there is a high risk that resin clasps may quickly become deformed or break. or telescope dentures.3. but both patients and dentists may hesitate at the thought of a metal clasp visible from the outside. milling dentures. and the labial-buccal mucosa. Although it depends on the location of the remaining teeth and the condition of the opposing dentition. Advantages 5. RPDs may be proposed as an alternative. increasing the opportunities for both patients and dentists to choose RPDs.1.2. Elastic modulusa Generic name Product name Polyamide Valplast Lucitone FRS Ultimate Low Low Low Rigidb Rigidb Rigidb Polyester EstheShot Bright EstheShot Low High Rigidb Rigid Polycarbonate Reigning Reigning N High High Rigid Rigid a b Denture rigidity Low < 2000 MPa. many patients dislike the idea of inserting a metal implant into the bone. As the degradation of resin materials may also increase the adherence of dental plaque. and with an excessive undercut in the alveolar part. particular caution is required if molar occlusal support has been entirely lost. the marginal gingiva. Esthetics Denture wearers. regular oral maintenance is essential. 5. (b) discoloration and decolorization of thermoplastic resin (Lucitone FRSW). Historically.1. non-rigid NMCDs cannot be recommended as definitive . thickness. these materials are regarded as not susceptible to surface loss even when damaged. Their ineligibility for insurance coverage means that patients must pay a greater amount. 5. with the risk of exacerbating periodontal conditions. 5. Nevertheless. Metal allergy Dentures that contain no metal at all eliminate concerns about metal allergy. We will address adhesion to self-curing resin in the context of repair and reline of different materials in Part II. Ineligibility for insurance coverage NMCDs using thermoplastic resin are not covered by national health insurance in Japan. the denture base can be made thinner.4. many people prefer to use NMCDs. There also appears to be no problem with fit [14. 5. 5. 7 – Deterioration of thermoplastic resin used for non-metal clasp dentures. The cost of NMCDs consisting entirely of resin is different from that of dentures that utilize a metal framework for rigidity. but as mentioned in the opening sentences of this paper. Feel during use of NMCDs The resins currently in use have a lower elastic modulus and a softer surface compared with acrylic resin [10–13]. and the heating effect of polishing may also be detrimental. Materials to which self-curing resin does not adhere must be repaired in a laboratory. being designed to be part of the gingiva. the first NMCDs in the 1950s were made of polyamide resin.2. Design guidelines based on differences in materials’ physical properties would therefore be desirable [26].1. the width. As the surface is not as hard as that of acrylic resin.2. 6. although the surface is easily damaged. This means that the area covered by the resin clasp is large.2. within the current restricted scope. difficulty of adjusting retention capacity and repair No guidelines have been indicated for the design of resin clasps of NMCDs. Discoloration and degradation of thermoplastic resin rubbery form. as described above. then the retentive capacity may be recovered to some extent. This advantage has also been utilized subsequently for avoiding metal allergy [17].2. meaning that patients feel better when worn. This makes them lighter and thinner than RPDs using an acrylic resin or metal framework to ensure rigidity. Clasp wires were buried in the retentive parts with the aim of ensuring continued retention and preventing breakage. Meticulous cleaning is therefore essential. Recommendations In this position paper. Disadvantages 5. which was developed to deal with the allergic reaction to residual monomers after the polymerization of acrylic resin [16]. 6 and 7). and a special polish is required.2. the depths and the widths of marks were greater than the acrylic resins by the scratch test [19]. As there is a low risk of breakage of dentures made solely of resin. Breakage of resin clasp.15]. 5. Difficulty of polishing Toothbrush friction experiments (measuring the decrease in volume) on the denture base material used in NMCDs have shown that it loses less than one fifth of the volume lost by acrylic resin [24]. it takes on a Design of retentive parts and periodontal condition In NMCDs. 5. thus the polished surface loses its luster. Therefore. and the undercut and relief regions may easily become dead space.journal of prosthodontic research 58 (2014) 3–10 9 Fig. and this is based heavily on the improved esthetics of RPDs.2.1.2. and length are designed via trial and error. Surface roughening after a few months of denture delivery was identified in all but a few materials [18]. 5. When the glass transition point is exceeded in the non-crystalline portion of a polymer material.3. Candida growth is not a concern as long as denture maintenance is possible. This property means that compared with acrylic resin they may be difficult to polish at the chairside [25]. the resin clasp covers the cervical area of the abutment teeth over a wide area on both the crown and root sides.3. which are highly elastic and not at all rigid.2. but if adequate cleaning cannot be performed then more caution would be required than for acrylic resin [23]. Frequent breakage of the retentive elements in the early years has led to improvement in their physical properties. If the material is one that adheres to self-curing resin. (a) Loss of burnish on polished surface (ValplastW). but if not then it is difficult to adjust. Discoloration and loss of color are also seen [20–22] (Figs. Suzuki H. J Prosthodont Res 2011. Huggett R. Yatabe M. Sato M. Ann Jpn Prosthodont Soc 2011. Kohno S. Ono T. Uchida T. Dhiman RK. Kitahara K.10 journal of prosthodontic research 58 (2014) 3–10 dentures in light of current prosthetic principles. Filho APR.168:1–4 [in Japanese]. Campanha NH. [8] Singh JP. [10] Sano M. Machi H.20:632–863. Wada M. Dent Mater J 2010.21:173–6. Ishikawa S. Progress of EstheShot1 for esthetic denture – report of abrasion losses-. Cury AADB. J Prosthodont 2011. Kanki Y. [11] Yokoyama N. Akita Y. Kimura K. [12] Kawara M. Hojo S. Tamaki Y. Clinical application of removable partial dentures using thermoplastic resin (non-metal clasp dentures). et al. Girish SH. et al. Ino S. Arakawa I.52:577–81. Bedi RP. [26] Taguchi Y.25:80–6 [in Japanese]. Ohkubo C. . JPS does not receive support from any specific group or corporation. Present status and clinical problems of non-metal clasp dentures—can it become one choice for prosthetic rehabilitation? Ann Jpn Prosthodont Soc 2012. Straioto FG.42:140–5 [in Japanese]. Journal of Nippon Academy of Dental Technology 2004. Properties of thermoplastic polymers used for non-clasp dentures. J Nippon Acad Dent Technol 2004. Bellur S. DE 2009. Quintessence 2010. Oguma H. [14] Hayashi K. Members of the expert panel who had contributed to the development of or lectured on a specific resin were not involved in writing about the resin concerned.94:1–85. Characteristics of absorbent and dimensional change. [7] Kaplan P. Shimamura I. [15] Hishimoto M. Efficacy of denture cleansers on Candida Spp. references [1] Suzuki T. Dent Today 2008. Asano T. How to deal with non-clasp denture? Its advantages and problems. Machi H. in Japanese]. Conflicts of interest The preparation of this position paper was funded by JPS. [25] Abuzar MA.3:133 [special issue. J Jpn Soc Dent Products 2009. Characteristics of denture thermoplastic resins for non-metal clasp dentures. J Kanagawa Odont Soc 2007. Questionnaires for patients’ satisfaction with a super-polyamide denture in a clinic. Acknowledgement This paper is the secondary publication of the position paper published in the Annals of Japan Prosthodontic Society [27]. Physical properties of polyester copolymer for denture materials. lto K. Methods of reline and maintenance should be understood with reference to the properties of the different materials used. Iwasaki M. Silva WJ. [6] Meijer GJ. Katou Y. Aysan I. J Prosthet Dent 2005. Non-clasp denture.29:2083–90 [in Japanese]. Physical properties of polyamide resin (nylon group) as a polymeric material for dentures: Part 1.28:161–7 [in Japanese]. Iida S. NMCDs that include a metal framework to provide rigidity may be recommended in cases in which the patient is uncomfortable with a metal clasp running through areas that would affect esthetic appearance. Palfreyman N. biofilm formed on polyamide and polymethyl methacrylate resins.105:51–8. 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