journal of prosthodontic research 58 (2014) 3–10
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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
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journal of prosthodontic research 58 (2014) 3–10
p Department of Prosthodontics, Division of Oral Functional Science and Rehabilitation, School of Dentistry, Asahi University, Japan q Division of Occlusion and Removable Prosthodontics, Health Sciences University of Hokkaido, Japan r Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Japan s Department of Prosthodontics and Oral Implantology, Iwate Medical University, Japan t Department of Oral & Maxillofacial Rehabilitation, Removable Prosthetics, Kanagawa Dental College, Japan u Department of Prosthodontics, Showa University, Japan v Division of Fixed Prosthodontics, School of Dentistry, Meikai University, Japan w Section of Implant and Rehabilitative Dentistry, Division of Oral Rehabilitation Faculty of Dental Science, Kyushu University, Japan x Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, 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, and presents a guideline for clinical application.
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. At a
Keywords:
with retentive elements (resin clasps) made of thermoplastic resin. The panel classified non-
meeting of the panel, ‘‘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. Accord-
Non-metal clasp denture
ing to current prosthetic principles, flexible non-metal clasp dentures are not recommended
Resin clasp
as definitive dentures, except for limited cases such as patients with a metal allergy. Rigid
Metal allergy
non-metal clasp dentures are recommended in cases where patients will not accept metal clasps for esthetic reasons. Non-metal clasp dentures should follow the same design principles as conventional RPDs using metal clasps. # 2013 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
Contents 1. 2. 3. 4.
5.
6.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of position paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Term and definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indications and contraindications for NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Contraindications and cases in which use requires caution . . . . . . . . . . . . . . . . . . . . 4.2.1. Type of partially edentulous arch and occlusal relationship . . . . . . . . . . . . . . 4.2.2. Anatomical factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3. State of oral hygiene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages and disadvantages of NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1. Esthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2. Feel during use of NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3. Metal allergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1. Discoloration and degradation of thermoplastic resin. . . . . . . . . . . . . . . . . . . 5.2.2. Difficulty of polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3. Breakage of resin clasp, difficulty of adjusting retention capacity and repair. 5.2.4. Design of retentive parts and periodontal condition . . . . . . . . . . . . . . . . . . . . 5.2.5. Ineligibility for insurance coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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journal of prosthodontic research 58 (2014) 3–10
1.
Introduction
Table 1 – Thermoplastic resins available for non-metal clasp dentures in Japan (December 2012). Generic name
Esthetics is a matter of great concern for patients receiving dental treatment, especially prosthetic treatment. Therefore, esthetic aspects must be considered to ensure patient satisfaction with dental treatment. Patients find the sight of the metal clasp of removable partial dentures (RPDs) in the esthetic area undesirable for both esthetic and psychological reasons; this is one explanation for patients disliking the use of RPDs. Conventionally, attachments have been used in patients who place emphasis on esthetics, but the need to remove large quantities of tooth structure and the requirement for specialist skills means that at present, this is not a generally viable choice. In the United States, since the 1950s, polyamide resin (nylon) has been used to fabricate RPDs that do not contain any metal elements. Since 2007, a number of thermoplastic resins have also been approved for use as denture bases in Japan (Table 1). 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]. Changes in public awareness have led to increasingly strong demands from patients with respect to esthetic aspects when fitting prostheses, with an increasing number of patients avoiding RPDs because they are associated with growing old. The need for dentists to respond to this demand from patients may be a cause of the increasing popularity of such RPDs. RPDs using thermoplastic resin have some limitations as revealed by prosthodontists [2]. The first issue is that some RPDs using thermoplastic resin do not conform to the principles regarding the standard RPD design in Japan, and that the use of such RPDs may seriously affect the periodontal tissues of abutment teeth and the residual ridge. As this procedure is simple and is not covered by national health insurance, 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, this would be a serious disadvantage for patients. It has also been pointed out that depending on the material, problems including fracture of the resin clasp, roughening of the polished surface of the denture base, or discoloration of denture base resin may occur, and treatment such as reline or repair may be difficult. In practice, various problems do occur after denture fitting in at least some patients, and while the evidence from clinical trials is limited, there is a possibility that the inappropriate use of RPDs using thermoplastic resin may become a social issue. If this situation is left unaddressed, it may decrease public trust in dental treatment and dentistry. In light of these circumstances, the Japan Prosthodontic Society (JPS) has cautioned against the regular clinical use of RPDs using thermoplastic resin, stating that ‘‘Although so-called non-clasp dentures have the positive advantage of being effective in restoring external appearance, they have the disadvantage that if they are used in the wrong patients they may cause major damage, including abnormal resorption of the residual ridge and increase of movement of the abutment teeth, 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, JPS stated that ‘‘Application of flexible dentures solely from the viewpoint of anterior esthetics is not recommended.’’ The second problem identified by prosthodontists is that there is no set definition or name for RPDs using thermoplastic resin, which are commonly known as flexible dentures, nonclasp dentures, clasp-free dentures, and metal-free dentures. Recently, ‘‘non-clasp dentures’’ has become the generally used term, but according to the definition in the US GPT-8 Glossary of Prosthodontic Terms [3], 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, and the term ‘‘non-clasp’’ is therefore inappropriate. In light of this situation, the Clinical Guideline Committee responded to a request from the Social Insurance and Dental Service Problem Committee and considered correcting the guideline. They first searched the literature in PubMed and Igaku Chuo Zasshi (ICHUSHI, Japan Medical Abstracts Society) to collect the latest clinical evidence, and found that there were a limited number of studies: as of August 2011, only one original paper had been published based on clinical research on RPDs using thermoplastic resin [4]. Then, a questionnaire was sent to a panel of prosthodontists on how to formulate a guideline (dentures to be covered, types of defect, design, whether or not to limit them to thermoplastic resin materials). The results revealed that most prosthodontists wanted to formulate a guideline on the different types of thermoplastic resin currently in use, cases in which their use is indicated, and denture design. Given the lack of evidence, however, it was considered that it would be difficult to formulate a guideline for such a wide diversity of patients using standard methods. 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, and to publish the results as a position paper. The objectives of this position paper were (1) to propose an official term and definition for RPDs using thermoplastic resin, and (2) to provide guidelines for prosthodontists and general dentists on points to note with respect to the indications and contraindications, design, and clinical use of such dentures.
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journal of prosthodontic research 58 (2014) 3–10
Fig. 2 – A non-metal clasp denture with metal rests. Fig. 1 – A non-metal clasp denture without metal elements.
2.
Preparation of position paper
The 21 members selected to serve on the expert panel for 2011– 2012 were requested to complete a questionnaire, and five members who had clinical experience with RPDs using thermoplastic resin in several patients were included in our expert panel. Information was then gathered from JPS members who had at least 5 years’ clinical experience with RPDs using thermoplastic resin, and an additional nine members were selected to join the expert panel. Thus, a total of 14 members prepared the initial draft of this position paper. At a panel meeting in August 2012, members discussed the official term and definition for RPDs using thermoplastic resin and the structure of the position paper, and reached a consensus. All the members of the expert panel were responsible for writing different sections of the draft position paper, and the content was corrected through Internet discussion among the panel as a whole until a consensus was obtained. The final document was completed after review by the clinical guideline committee. The PubMed and ICHUSHI online databases were used to search the literature, as well as manual search. The selection of literature was not carried out systematically.
3.
Term and definition
In 1956, the US company Valplast developed super-polyamide, a type of nylon, as a material for use in dentures. 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, Valplast, but are also called flexible dentures or nylon dentures, and have become widely used worldwide (Fig. 1) [5,6]. In Japan, these dentures were individually imported and used on a trial basis before they were approved by the Ministry of Health, Labour and Welfare, and it became common to call them by names such as ‘‘non-clasp dentures’’ or ‘‘metal-free dentures.’’ Since their approval under the pharmaceutical affairs law in April 2008, numerous thermoplastic resins have been developed, and these have mistakenly been known by the names of their manufacturer, supplier, or laboratories; however, in general, the name ‘‘non-clasp dentures’’ has taken root among general clinicians.
According to the GPT-8 [3], 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. Generally it is used to stabilize and retain a removable dental prosthesis.’’ According to this definition, a ‘‘clasp’’ is not described as being made of metal. The resin retentive elements known as arms, fingers, and wings may thus be regarded as genuine clasps according to this definition, as they use undercuts to retain and stabilize RPDs, and they are also known as ‘‘resin clasps’’ or ‘‘esthetic clasps’’ [7,8]. This interpretation therefore indicates that the term ‘‘nonclasp dentures’’ refers only to those that do not incorporate clasps in any form, such as attachment dentures, milling dentures, or telescope dentures. Thus, in this position paper, the term ‘‘non-metal clasp dentures’’ (NMCDs) is used to refer not only to dentures that do not contain any metal elements, but also to dentures that incorporate a metal rest or framework (Figs. 2 and 3), and is defined as ‘‘the general name for RPDs using denture base resins as the denture retentive parts.’’ This definition thus includes not only those dentures in which the retentive parts and the denture base are produced as a single whole, but also those dentures in which a resin used for the retentive parts is different from that for denture base (Fig. 4). In this position paper, the resin retentive part of NMCDs is referred to as the ‘‘resin clasp.’’
4. Indications and contraindications for NMCDs 4.1.
Indications
In this position paper, NMCDs have been categorized into two types; 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. 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, patients with few missing anterior teeth, and patients with few missing teeth with occlusal support, and as epitheses for patients in whom the dentures carry no functional burden, patients for whom esthetics must be given top priority, and
journal of prosthodontic research 58 (2014) 3–10
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Fig. 3 – A non-metal clasp denture with a framework (Reigning NW). (a) Basal surface of the denture; (b) metal rest and resin clasp.
Fig. 4 – A non-metal clasp denture using different denture base resins for retentive elements and a denture base. (a) Resin clasp on working cast; (b) delivered denture.
Fig. 5 – A non-metal clasp denture without metal framework replacing missing maxillary bilateral frontal teeth (ValplastW). (a) Labial view on working cast; (b) palatal view on working cast.
patients who do not consent to the preparation of abutment teeth (Fig. 5). NMCDs that include a metal structure and are rigid are basically indicated in a wide range of cases (Figs. 2–4).
4.2. Contraindications and cases in which use requires caution Contraindications for NMCDs depend on the type of partially edentulous arch and occlusal relationship, anatomical factors that affect the design and fabrication of RPDs, or a state of oral hygiene that may affect the maintenance and management of RPD treatment.
4.2.1. 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, and designs that incorporate metal may be used with almost all types of partially edentulous arches. Their use is difficult, however, in patients with non-vertical stop occlusion or those with few remaining teeth, in whom good treatment results cannot be expected even with the use of metal clasp-retained RPDs. For patients with non-vertical stop occlusion in particular, rotation and sinking of the denture base, changes in occlusal position, and resorption of the residual ridge tend to occur,
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journal of prosthodontic research 58 (2014) 3–10
Table 2 – Rigidity of non-metal clasp dentures using thermoplastic resins. 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; high 2000 MPa. With metal framework.
resulting in the concentration of excessive force in the resin clasp. As there is a high risk that resin clasps may quickly become deformed or break, they are contraindicated. The stress on the resin clasp may also be high in patients with few remaining teeth. Although it depends on the location of the remaining teeth and the condition of the opposing dentition, particular caution is required if molar occlusal support has been entirely lost, the occlusal position is unstable, 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.
4.2.2.
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, its external shape is affected not only by the crown morphology of the abutment tooth but also by the morphology of the alveolar part. In patients with a clinically short crown length, in whom the distance between the survey line on the abutment tooth and the oral vestibule is inadequate, and with an excessive undercut in the alveolar part, it may be difficult to design a resin clasp of appropriate shape and width. The resin clasp may lack sufficient retention capacity and strength, and caution is therefore required. In most NMCDs, the thermoplastic denture base resins cannot be chemically bound to the artificial teeth, meaning that holes must be made to hold the artificial teeth and they must be mechanically fixed. In patients with a small amount of clearance with opposing teeth at the missing area, the artificial teeth may be lost, cracked, or fractured, and caution is therefore required.
4.2.3.
State of oral hygiene
Metal clasps are designed in such a way that they do not to come into contact with the gingival margin, but the resin clasp of NMCDs covers the tooth structure of the cervical region of abutment teeth, the marginal gingiva, and the labial-buccal mucosa. As a wide area around the abutment teeth becomes unhygienic, this may cause or exacerbate caries and periodontal disease. The need for adequate dental plaque control has been emphasized [9], and patients with poor oral hygiene and those who do not respond regular repeat appointments are not suitable candidates. As the degradation of resin materials may also increase the adherence of dental plaque, worsening the cleanliness of dentures, regular oral maintenance is essential. In patients who use a NMCD with no support from a metal rest, should the dentures sink then the resin clasp compresses the
Fig. 6 – Deterioration of thermoplastic resin used for nonmetal clasp denture. Polished surface of the maxillary complete denture (left) was good, however surface of denture base of a mandibular non-metal clasp denture (EstheShotW) has become roughened after a year and 6-month use. Denture base of the posterior area was repaired using a cold-cured resin (indicated with arrow).
marginal gingiva, potentially causing its mechanical damage. It has been reported that NMCDs that contain no metal structures at all tend to sink [9], suggesting that more careful follow-up is required for patients with metal-free NMCDs.
5.
Advantages and disadvantages of NMCDs
5.1.
Advantages
5.1.1.
Esthetics
Denture wearers, both men and women, are highly concerned about the esthetic appearance. Although dental implant treatment is effective, many patients dislike the idea of inserting a metal implant into the bone, or are afraid of surgical treatment. The cost is also generally high. RPDs may be proposed as an alternative, but both patients and dentists may hesitate at the thought of a metal clasp visible from the outside. The esthetic appearance of RPDs may be guaranteed by the use of magnetic or precision attachment, milling dentures, or telescope dentures, but if the abutment tooth is a vital tooth, such retainers may be difficult to use, and dentists may be at a loss how to deal with this. With NMCDs, it is possible for the retentive parts to actively utilize a vital tooth, increasing the opportunities for both patients and dentists to choose RPDs.
journal of prosthodontic research 58 (2014) 3–10
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Fig. 7 – Deterioration of thermoplastic resin used for non-metal clasp dentures. (a) Loss of burnish on polished surface (ValplastW); (b) discoloration and decolorization of thermoplastic resin (Lucitone FRSW).
5.1.2.
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], meaning that patients feel better when worn. There also appears to be no problem with fit [14,15]. As there is a low risk of breakage of dentures made solely of resin, which are highly elastic and not at all rigid, the denture base can be made thinner. This makes them lighter and thinner than RPDs using an acrylic resin or metal framework to ensure rigidity.
5.1.3.
Metal allergy
Dentures that contain no metal at all eliminate concerns about metal allergy. Historically, the first NMCDs in the 1950s were made of polyamide resin, which was developed to deal with the allergic reaction to residual monomers after the polymerization of acrylic resin [16]. This advantage has also been utilized subsequently for avoiding metal allergy [17].
5.2.
Disadvantages
5.2.1.
Discoloration and degradation of thermoplastic resin
rubbery form, and the heating effect of polishing may also be detrimental.
5.2.3. Breakage of resin clasp, difficulty of adjusting retention capacity and repair No guidelines have been indicated for the design of resin clasps of NMCDs. Therefore, the width, thickness, and length are designed via trial and error. Design guidelines based on differences in materials’ physical properties would therefore be desirable [26]. Frequent breakage of the retentive elements in the early years has led to improvement in their physical properties. Clasp wires were buried in the retentive parts with the aim of ensuring continued retention and preventing breakage. If the material is one that adheres to self-curing resin, then the retentive capacity may be recovered to some extent, but if not then it is difficult to adjust. We will address adhesion to self-curing resin in the context of repair and reline of different materials in Part II. Materials to which self-curing resin does not adhere must be repaired in a laboratory.
5.2.4. Surface roughening after a few months of denture delivery was identified in all but a few materials [18]. As the surface is not as hard as that of acrylic resin, the depths and the widths of marks were greater than the acrylic resins by the scratch test [19], thus the polished surface loses its luster. Discoloration and loss of color are also seen [20–22] (Figs. 6 and 7). Candida growth is not a concern as long as denture maintenance is possible, but if adequate cleaning cannot be performed then more caution would be required than for acrylic resin [23].
5.2.2.
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]. Nevertheless, although the surface is easily damaged, as described above, these materials are regarded as not susceptible to surface loss even when damaged. This property means that compared with acrylic resin they may be difficult to polish at the chairside [25], and a special polish is required. When the glass transition point is exceeded in the non-crystalline portion of a polymer material, it takes on a
Design of retentive parts and periodontal condition
In NMCDs, the resin clasp covers the cervical area of the abutment teeth over a wide area on both the crown and root sides, being designed to be part of the gingiva. This means that the area covered by the resin clasp is large, and the undercut and relief regions may easily become dead space, with the risk of exacerbating periodontal conditions. Meticulous cleaning is therefore essential.
5.2.5.
Ineligibility for insurance coverage
NMCDs using thermoplastic resin are not covered by national health insurance in Japan. The cost of NMCDs consisting entirely of resin is different from that of dentures that utilize a metal framework for rigidity. Their ineligibility for insurance coverage means that patients must pay a greater amount, but as mentioned in the opening sentences of this paper, many people prefer to use NMCDs, and this is based heavily on the improved esthetics of RPDs.
6.
Recommendations
In this position paper, within the current restricted scope, non-rigid NMCDs cannot be recommended as definitive
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dentures in light of current prosthetic principles, with the exception of patients with metal allergies and some others. 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. Methods of reline and maintenance should be understood with reference to the properties of the different materials used.
Conflicts of interest The preparation of this position paper was funded by JPS. JPS does not receive support from any specific group or corporation. No funding from any group or corporation was used for the preparation of this position paper. The members of the expert panel and clinical guideline committee involved in the preparation of this position paper did not receive any support from any specific group or corporation with respect to NMCDs. 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.
Acknowledgement This paper is the secondary publication of the position paper published in the Annals of Japan Prosthodontic Society [27].
references
[1] Suzuki T, Shimpo H, Kitano N, Sato M, Kawai Y, Kanki Y, et al. A questionnaire survey on the thermoplastic dentures. Ann Jpn Prosthodont Soc 2011;3:133 [special issue; in Japanese]. [2] Ohkubo C, Yatabe M, Arita M. Present status and clinical problems of non-metal clasp dentures—can it become one choice for prosthetic rehabilitation? Ann Jpn Prosthodont Soc 2012;4:63–4 [special issue; in Japanese]. [3] Glossary of prosthodontic terms. 8th edition. J Prosthet Dent 2005;94:1–85. [4] Saito M, Oguma H. Questionnaires for patients’ satisfaction with a super-polyamide denture in a clinic. J Esthet Dent 2009;22:60–4 [in Japanese]. [5] Lowe LG. Flexible denture flanges for patients exhibiting undercut tuberosities and reduced width of the buccal vestibule: a clinical report. J Prosthet Dent 2004;92: 128–31. [6] Meijer GJ, Wolgen PJ. Provisional flexible denture to assist in undisturbed healing of the reconstructed maxilla. J Prosthet Dent 2007;98:327–8. [7] Kaplan P. Flexible removable partial dentures: design and clasp concepts. Dent Today 2008;27:122–3. [8] Singh JP, Dhiman RK, Bedi RP, Girish SH. Flexible denture base material: a viable alternative to conventional acrylic denture base material. Contemp Clin Dent 2011;2:313–7. [9] Hosoi T. Non-clasp denture. DE 2009;168:1–4 [in Japanese].
[10] Sano M, lto K, Nomura A, Kohno S. Properties of thermoplastic polymers used for non-clasp dentures. J Jpn Soc Dent Products 2009;23:28–34 [in Japanese]. [11] Yokoyama N, Machi H, Hayashi K, Uchida T, Ono T, Nokubi T. Physical properties of polyamide resin (nylon group) as a polymeric material for dentures: Part 2. Surface hardness and tensile strength. J Nippon Acad Dent Technol 2004;25:87–92 [in Japanese]. [12] Kawara M, Suzuki H, Ishikawa S. Progress of EstheShot1 for esthetic denture – report of abrasion losses-. Ann Jpn Prosthodont Soc 2011;3:E89 [in Japanese]. [13] Ucar Y, Akova T, Aysan I. Mechanical properties of polyamide versus different PMMA denture base materials. J Prosthodont 2012;21:173–6. [14] Hayashi K, Yokoyama N, Machi H, Uchida T, Ono T, Nokubi T. Physical properties of polyamide resin (nylon group) as a polymeric material for dentures: Part 1. Characteristics of absorbent and dimensional change. Journal of Nippon Academy of Dental Technology 2004;25:80–6 [in Japanese]. [15] Hishimoto M, Katou Y, Akita Y, Murakami Y, Iida S. Physical properties of polyester copolymer for denture materials. J Nippon Acad Dent Technol 2008;29:196 [special issue; in Japanese]. [16] Stafford GD, Huggett R. The use of nylon as a denture-base material. J Dent 1986;14:18–22. [17] Kuwahara K, Nagahama F, Kitahara K, Wada M, Makimura S, Kimura K, et al. A case of using non-metalclasp partial denture for the patient with metal allergy. Nichidai Koko Kagaku 2004;30:134–9 [in Japanese]. [18] Yatabe M. How to deal with non-clasp denture? Its advantages and problems. Quintessence 2010;29:2083–90 [in Japanese]. [19] Kawara M, Iwata Y, Iwasaki M, Komoda Y, Iida T, Asano T, et al. Scratch test of thermoplastic denture base resins for non-metal clasp dentures. J Prosthodont Res 2014;58:35–40. [20] Takabayashi Y. Characteristics of denture thermoplastic resins for non-metal clasp dentures. Dent Mater J 2010;29:353–61. [21] Katsumata Y, Hojo S, Ino S, Hamano N, Watanabe T, Kondo N, et al. Color stability of a flexible nylon denture base resin. J Kanagawa Odont Soc 2007;42:140–5 [in Japanese]. [22] Sepu´lveda-Navarro WF, Arana-Correa BE, Borges CP, Jorge JH, Urban VM, Campanha NH. Color stability of resins and nylon as denture base material in beverages. J Prosthodont 2011;20:632–863. [23] Fernandes FSF, Pereira-Cenci T, Silva WJ, Filho APR, Straioto FG, Cury AADB. Efficacy of denture cleansers on Candida Spp. biofilm formed on polyamide and polymethyl methacrylate resins. J Prosthet Dent 2010;105:51–8. [24] Takahashi H, Kawada E, Tamaki Y, Teraoka H, Hosoi T, Yoshida T. Basic properties of thermoplastic resins for denture base material referred to non clasp denture. J Jpn Dent Mater 2009;28:161–7 [in Japanese]. [25] Abuzar MA, Bellur S, Duong N, Kim BB, Lu P, Palfreyman N, et al. Evaluating surface roughness of polyamide denture base material in comparison with poly (methyl methacrylate). J Oral Sci 2010;52:577–81. [26] Taguchi Y, Shimamura I, Sakurai K. Effect of buccal part designs of polyamide resin partial removable dental prosthesis on retentive force. J Prosthodont Res 2011;55: 44–7. [27] Fueki K, Ohkubo C, Yatabe M, Arakawa I, Arita M, Ino S, et al. Clinical application of removable partial dentures using thermoplastic resin (non-metal clasp dentures). Ann Jpn Prosthodont Soc 2013;5:387–408 [in Japanese].
Available 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
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p Department of Prosthodontics, Division of Oral Functional Science and Rehabilitation, School of Dentistry, Asahi University, Japan q Division of Occlusion and Removable Prosthodontics, Health Sciences University of Hokkaido, Japan r Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Japan s Department of Prosthodontics and Oral Implantology, Iwate Medical University, Japan t Department of Oral & Maxillofacial Rehabilitation, Removable Prosthetics, Kanagawa Dental College, Japan u Department of Prosthodontics, Showa University, Japan v Division of Fixed Prosthodontics, School of Dentistry, Meikai University, Japan w Section of Implant and Rehabilitative Dentistry, Division of Oral Rehabilitation Faculty of Dental Science, Kyushu University, Japan x Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, 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, and presents a guideline for clinical application.
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. At a
Keywords:
with retentive elements (resin clasps) made of thermoplastic resin. The panel classified non-
meeting of the panel, ‘‘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. Accord-
Non-metal clasp denture
ing to current prosthetic principles, flexible non-metal clasp dentures are not recommended
Resin clasp
as definitive dentures, except for limited cases such as patients with a metal allergy. Rigid
Metal allergy
non-metal clasp dentures are recommended in cases where patients will not accept metal clasps for esthetic reasons. Non-metal clasp dentures should follow the same design principles as conventional RPDs using metal clasps. # 2013 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
Contents 1. 2. 3. 4.
5.
6.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of position paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Term and definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indications and contraindications for NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Contraindications and cases in which use requires caution . . . . . . . . . . . . . . . . . . . . 4.2.1. Type of partially edentulous arch and occlusal relationship . . . . . . . . . . . . . . 4.2.2. Anatomical factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3. State of oral hygiene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages and disadvantages of NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1. Esthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2. Feel during use of NMCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3. Metal allergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1. Discoloration and degradation of thermoplastic resin. . . . . . . . . . . . . . . . . . . 5.2.2. Difficulty of polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3. Breakage of resin clasp, difficulty of adjusting retention capacity and repair. 5.2.4. Design of retentive parts and periodontal condition . . . . . . . . . . . . . . . . . . . . 5.2.5. Ineligibility for insurance coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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1.
Introduction
Table 1 – Thermoplastic resins available for non-metal clasp dentures in Japan (December 2012). Generic name
Esthetics is a matter of great concern for patients receiving dental treatment, especially prosthetic treatment. Therefore, esthetic aspects must be considered to ensure patient satisfaction with dental treatment. Patients find the sight of the metal clasp of removable partial dentures (RPDs) in the esthetic area undesirable for both esthetic and psychological reasons; this is one explanation for patients disliking the use of RPDs. Conventionally, attachments have been used in patients who place emphasis on esthetics, but the need to remove large quantities of tooth structure and the requirement for specialist skills means that at present, this is not a generally viable choice. In the United States, since the 1950s, polyamide resin (nylon) has been used to fabricate RPDs that do not contain any metal elements. Since 2007, a number of thermoplastic resins have also been approved for use as denture bases in Japan (Table 1). 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]. Changes in public awareness have led to increasingly strong demands from patients with respect to esthetic aspects when fitting prostheses, with an increasing number of patients avoiding RPDs because they are associated with growing old. The need for dentists to respond to this demand from patients may be a cause of the increasing popularity of such RPDs. RPDs using thermoplastic resin have some limitations as revealed by prosthodontists [2]. The first issue is that some RPDs using thermoplastic resin do not conform to the principles regarding the standard RPD design in Japan, and that the use of such RPDs may seriously affect the periodontal tissues of abutment teeth and the residual ridge. As this procedure is simple and is not covered by national health insurance, 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, this would be a serious disadvantage for patients. It has also been pointed out that depending on the material, problems including fracture of the resin clasp, roughening of the polished surface of the denture base, or discoloration of denture base resin may occur, and treatment such as reline or repair may be difficult. In practice, various problems do occur after denture fitting in at least some patients, and while the evidence from clinical trials is limited, there is a possibility that the inappropriate use of RPDs using thermoplastic resin may become a social issue. If this situation is left unaddressed, it may decrease public trust in dental treatment and dentistry. In light of these circumstances, the Japan Prosthodontic Society (JPS) has cautioned against the regular clinical use of RPDs using thermoplastic resin, stating that ‘‘Although so-called non-clasp dentures have the positive advantage of being effective in restoring external appearance, they have the disadvantage that if they are used in the wrong patients they may cause major damage, including abnormal resorption of the residual ridge and increase of movement of the abutment teeth, 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, JPS stated that ‘‘Application of flexible dentures solely from the viewpoint of anterior esthetics is not recommended.’’ The second problem identified by prosthodontists is that there is no set definition or name for RPDs using thermoplastic resin, which are commonly known as flexible dentures, nonclasp dentures, clasp-free dentures, and metal-free dentures. Recently, ‘‘non-clasp dentures’’ has become the generally used term, but according to the definition in the US GPT-8 Glossary of Prosthodontic Terms [3], 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, and the term ‘‘non-clasp’’ is therefore inappropriate. In light of this situation, the Clinical Guideline Committee responded to a request from the Social Insurance and Dental Service Problem Committee and considered correcting the guideline. They first searched the literature in PubMed and Igaku Chuo Zasshi (ICHUSHI, Japan Medical Abstracts Society) to collect the latest clinical evidence, and found that there were a limited number of studies: as of August 2011, only one original paper had been published based on clinical research on RPDs using thermoplastic resin [4]. Then, a questionnaire was sent to a panel of prosthodontists on how to formulate a guideline (dentures to be covered, types of defect, design, whether or not to limit them to thermoplastic resin materials). The results revealed that most prosthodontists wanted to formulate a guideline on the different types of thermoplastic resin currently in use, cases in which their use is indicated, and denture design. Given the lack of evidence, however, it was considered that it would be difficult to formulate a guideline for such a wide diversity of patients using standard methods. 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, and to publish the results as a position paper. The objectives of this position paper were (1) to propose an official term and definition for RPDs using thermoplastic resin, and (2) to provide guidelines for prosthodontists and general dentists on points to note with respect to the indications and contraindications, design, and clinical use of such dentures.
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Fig. 2 – A non-metal clasp denture with metal rests. Fig. 1 – A non-metal clasp denture without metal elements.
2.
Preparation of position paper
The 21 members selected to serve on the expert panel for 2011– 2012 were requested to complete a questionnaire, and five members who had clinical experience with RPDs using thermoplastic resin in several patients were included in our expert panel. Information was then gathered from JPS members who had at least 5 years’ clinical experience with RPDs using thermoplastic resin, and an additional nine members were selected to join the expert panel. Thus, a total of 14 members prepared the initial draft of this position paper. At a panel meeting in August 2012, members discussed the official term and definition for RPDs using thermoplastic resin and the structure of the position paper, and reached a consensus. All the members of the expert panel were responsible for writing different sections of the draft position paper, and the content was corrected through Internet discussion among the panel as a whole until a consensus was obtained. The final document was completed after review by the clinical guideline committee. The PubMed and ICHUSHI online databases were used to search the literature, as well as manual search. The selection of literature was not carried out systematically.
3.
Term and definition
In 1956, the US company Valplast developed super-polyamide, a type of nylon, as a material for use in dentures. 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, Valplast, but are also called flexible dentures or nylon dentures, and have become widely used worldwide (Fig. 1) [5,6]. In Japan, these dentures were individually imported and used on a trial basis before they were approved by the Ministry of Health, Labour and Welfare, and it became common to call them by names such as ‘‘non-clasp dentures’’ or ‘‘metal-free dentures.’’ Since their approval under the pharmaceutical affairs law in April 2008, numerous thermoplastic resins have been developed, and these have mistakenly been known by the names of their manufacturer, supplier, or laboratories; however, in general, the name ‘‘non-clasp dentures’’ has taken root among general clinicians.
According to the GPT-8 [3], 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. Generally it is used to stabilize and retain a removable dental prosthesis.’’ According to this definition, a ‘‘clasp’’ is not described as being made of metal. The resin retentive elements known as arms, fingers, and wings may thus be regarded as genuine clasps according to this definition, as they use undercuts to retain and stabilize RPDs, and they are also known as ‘‘resin clasps’’ or ‘‘esthetic clasps’’ [7,8]. This interpretation therefore indicates that the term ‘‘nonclasp dentures’’ refers only to those that do not incorporate clasps in any form, such as attachment dentures, milling dentures, or telescope dentures. Thus, in this position paper, the term ‘‘non-metal clasp dentures’’ (NMCDs) is used to refer not only to dentures that do not contain any metal elements, but also to dentures that incorporate a metal rest or framework (Figs. 2 and 3), and is defined as ‘‘the general name for RPDs using denture base resins as the denture retentive parts.’’ This definition thus includes not only those dentures in which the retentive parts and the denture base are produced as a single whole, but also those dentures in which a resin used for the retentive parts is different from that for denture base (Fig. 4). In this position paper, the resin retentive part of NMCDs is referred to as the ‘‘resin clasp.’’
4. Indications and contraindications for NMCDs 4.1.
Indications
In this position paper, NMCDs have been categorized into two types; 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. 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, patients with few missing anterior teeth, and patients with few missing teeth with occlusal support, and as epitheses for patients in whom the dentures carry no functional burden, patients for whom esthetics must be given top priority, and
journal of prosthodontic research 58 (2014) 3–10
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Fig. 3 – A non-metal clasp denture with a framework (Reigning NW). (a) Basal surface of the denture; (b) metal rest and resin clasp.
Fig. 4 – A non-metal clasp denture using different denture base resins for retentive elements and a denture base. (a) Resin clasp on working cast; (b) delivered denture.
Fig. 5 – A non-metal clasp denture without metal framework replacing missing maxillary bilateral frontal teeth (ValplastW). (a) Labial view on working cast; (b) palatal view on working cast.
patients who do not consent to the preparation of abutment teeth (Fig. 5). NMCDs that include a metal structure and are rigid are basically indicated in a wide range of cases (Figs. 2–4).
4.2. Contraindications and cases in which use requires caution Contraindications for NMCDs depend on the type of partially edentulous arch and occlusal relationship, anatomical factors that affect the design and fabrication of RPDs, or a state of oral hygiene that may affect the maintenance and management of RPD treatment.
4.2.1. 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, and designs that incorporate metal may be used with almost all types of partially edentulous arches. Their use is difficult, however, in patients with non-vertical stop occlusion or those with few remaining teeth, in whom good treatment results cannot be expected even with the use of metal clasp-retained RPDs. For patients with non-vertical stop occlusion in particular, rotation and sinking of the denture base, changes in occlusal position, and resorption of the residual ridge tend to occur,
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Table 2 – Rigidity of non-metal clasp dentures using thermoplastic resins. 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; high 2000 MPa. With metal framework.
resulting in the concentration of excessive force in the resin clasp. As there is a high risk that resin clasps may quickly become deformed or break, they are contraindicated. The stress on the resin clasp may also be high in patients with few remaining teeth. Although it depends on the location of the remaining teeth and the condition of the opposing dentition, particular caution is required if molar occlusal support has been entirely lost, the occlusal position is unstable, 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.
4.2.2.
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, its external shape is affected not only by the crown morphology of the abutment tooth but also by the morphology of the alveolar part. In patients with a clinically short crown length, in whom the distance between the survey line on the abutment tooth and the oral vestibule is inadequate, and with an excessive undercut in the alveolar part, it may be difficult to design a resin clasp of appropriate shape and width. The resin clasp may lack sufficient retention capacity and strength, and caution is therefore required. In most NMCDs, the thermoplastic denture base resins cannot be chemically bound to the artificial teeth, meaning that holes must be made to hold the artificial teeth and they must be mechanically fixed. In patients with a small amount of clearance with opposing teeth at the missing area, the artificial teeth may be lost, cracked, or fractured, and caution is therefore required.
4.2.3.
State of oral hygiene
Metal clasps are designed in such a way that they do not to come into contact with the gingival margin, but the resin clasp of NMCDs covers the tooth structure of the cervical region of abutment teeth, the marginal gingiva, and the labial-buccal mucosa. As a wide area around the abutment teeth becomes unhygienic, this may cause or exacerbate caries and periodontal disease. The need for adequate dental plaque control has been emphasized [9], and patients with poor oral hygiene and those who do not respond regular repeat appointments are not suitable candidates. As the degradation of resin materials may also increase the adherence of dental plaque, worsening the cleanliness of dentures, regular oral maintenance is essential. In patients who use a NMCD with no support from a metal rest, should the dentures sink then the resin clasp compresses the
Fig. 6 – Deterioration of thermoplastic resin used for nonmetal clasp denture. Polished surface of the maxillary complete denture (left) was good, however surface of denture base of a mandibular non-metal clasp denture (EstheShotW) has become roughened after a year and 6-month use. Denture base of the posterior area was repaired using a cold-cured resin (indicated with arrow).
marginal gingiva, potentially causing its mechanical damage. It has been reported that NMCDs that contain no metal structures at all tend to sink [9], suggesting that more careful follow-up is required for patients with metal-free NMCDs.
5.
Advantages and disadvantages of NMCDs
5.1.
Advantages
5.1.1.
Esthetics
Denture wearers, both men and women, are highly concerned about the esthetic appearance. Although dental implant treatment is effective, many patients dislike the idea of inserting a metal implant into the bone, or are afraid of surgical treatment. The cost is also generally high. RPDs may be proposed as an alternative, but both patients and dentists may hesitate at the thought of a metal clasp visible from the outside. The esthetic appearance of RPDs may be guaranteed by the use of magnetic or precision attachment, milling dentures, or telescope dentures, but if the abutment tooth is a vital tooth, such retainers may be difficult to use, and dentists may be at a loss how to deal with this. With NMCDs, it is possible for the retentive parts to actively utilize a vital tooth, increasing the opportunities for both patients and dentists to choose RPDs.
journal of prosthodontic research 58 (2014) 3–10
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Fig. 7 – Deterioration of thermoplastic resin used for non-metal clasp dentures. (a) Loss of burnish on polished surface (ValplastW); (b) discoloration and decolorization of thermoplastic resin (Lucitone FRSW).
5.1.2.
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], meaning that patients feel better when worn. There also appears to be no problem with fit [14,15]. As there is a low risk of breakage of dentures made solely of resin, which are highly elastic and not at all rigid, the denture base can be made thinner. This makes them lighter and thinner than RPDs using an acrylic resin or metal framework to ensure rigidity.
5.1.3.
Metal allergy
Dentures that contain no metal at all eliminate concerns about metal allergy. Historically, the first NMCDs in the 1950s were made of polyamide resin, which was developed to deal with the allergic reaction to residual monomers after the polymerization of acrylic resin [16]. This advantage has also been utilized subsequently for avoiding metal allergy [17].
5.2.
Disadvantages
5.2.1.
Discoloration and degradation of thermoplastic resin
rubbery form, and the heating effect of polishing may also be detrimental.
5.2.3. Breakage of resin clasp, difficulty of adjusting retention capacity and repair No guidelines have been indicated for the design of resin clasps of NMCDs. Therefore, the width, thickness, and length are designed via trial and error. Design guidelines based on differences in materials’ physical properties would therefore be desirable [26]. Frequent breakage of the retentive elements in the early years has led to improvement in their physical properties. Clasp wires were buried in the retentive parts with the aim of ensuring continued retention and preventing breakage. If the material is one that adheres to self-curing resin, then the retentive capacity may be recovered to some extent, but if not then it is difficult to adjust. We will address adhesion to self-curing resin in the context of repair and reline of different materials in Part II. Materials to which self-curing resin does not adhere must be repaired in a laboratory.
5.2.4. Surface roughening after a few months of denture delivery was identified in all but a few materials [18]. As the surface is not as hard as that of acrylic resin, the depths and the widths of marks were greater than the acrylic resins by the scratch test [19], thus the polished surface loses its luster. Discoloration and loss of color are also seen [20–22] (Figs. 6 and 7). Candida growth is not a concern as long as denture maintenance is possible, but if adequate cleaning cannot be performed then more caution would be required than for acrylic resin [23].
5.2.2.
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]. Nevertheless, although the surface is easily damaged, as described above, these materials are regarded as not susceptible to surface loss even when damaged. This property means that compared with acrylic resin they may be difficult to polish at the chairside [25], and a special polish is required. When the glass transition point is exceeded in the non-crystalline portion of a polymer material, it takes on a
Design of retentive parts and periodontal condition
In NMCDs, the resin clasp covers the cervical area of the abutment teeth over a wide area on both the crown and root sides, being designed to be part of the gingiva. This means that the area covered by the resin clasp is large, and the undercut and relief regions may easily become dead space, with the risk of exacerbating periodontal conditions. Meticulous cleaning is therefore essential.
5.2.5.
Ineligibility for insurance coverage
NMCDs using thermoplastic resin are not covered by national health insurance in Japan. The cost of NMCDs consisting entirely of resin is different from that of dentures that utilize a metal framework for rigidity. Their ineligibility for insurance coverage means that patients must pay a greater amount, but as mentioned in the opening sentences of this paper, many people prefer to use NMCDs, and this is based heavily on the improved esthetics of RPDs.
6.
Recommendations
In this position paper, within the current restricted scope, non-rigid NMCDs cannot be recommended as definitive
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journal of prosthodontic research 58 (2014) 3–10
dentures in light of current prosthetic principles, with the exception of patients with metal allergies and some others. 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. Methods of reline and maintenance should be understood with reference to the properties of the different materials used.
Conflicts of interest The preparation of this position paper was funded by JPS. JPS does not receive support from any specific group or corporation. No funding from any group or corporation was used for the preparation of this position paper. The members of the expert panel and clinical guideline committee involved in the preparation of this position paper did not receive any support from any specific group or corporation with respect to NMCDs. 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.
Acknowledgement This paper is the secondary publication of the position paper published in the Annals of Japan Prosthodontic Society [27].
references
[1] Suzuki T, Shimpo H, Kitano N, Sato M, Kawai Y, Kanki Y, et al. A questionnaire survey on the thermoplastic dentures. Ann Jpn Prosthodont Soc 2011;3:133 [special issue; in Japanese]. [2] Ohkubo C, Yatabe M, Arita M. Present status and clinical problems of non-metal clasp dentures—can it become one choice for prosthetic rehabilitation? Ann Jpn Prosthodont Soc 2012;4:63–4 [special issue; in Japanese]. [3] Glossary of prosthodontic terms. 8th edition. J Prosthet Dent 2005;94:1–85. [4] Saito M, Oguma H. Questionnaires for patients’ satisfaction with a super-polyamide denture in a clinic. J Esthet Dent 2009;22:60–4 [in Japanese]. [5] Lowe LG. Flexible denture flanges for patients exhibiting undercut tuberosities and reduced width of the buccal vestibule: a clinical report. J Prosthet Dent 2004;92: 128–31. [6] Meijer GJ, Wolgen PJ. Provisional flexible denture to assist in undisturbed healing of the reconstructed maxilla. J Prosthet Dent 2007;98:327–8. [7] Kaplan P. Flexible removable partial dentures: design and clasp concepts. Dent Today 2008;27:122–3. [8] Singh JP, Dhiman RK, Bedi RP, Girish SH. Flexible denture base material: a viable alternative to conventional acrylic denture base material. Contemp Clin Dent 2011;2:313–7. [9] Hosoi T. Non-clasp denture. DE 2009;168:1–4 [in Japanese].
[10] Sano M, lto K, Nomura A, Kohno S. Properties of thermoplastic polymers used for non-clasp dentures. J Jpn Soc Dent Products 2009;23:28–34 [in Japanese]. [11] Yokoyama N, Machi H, Hayashi K, Uchida T, Ono T, Nokubi T. Physical properties of polyamide resin (nylon group) as a polymeric material for dentures: Part 2. Surface hardness and tensile strength. J Nippon Acad Dent Technol 2004;25:87–92 [in Japanese]. [12] Kawara M, Suzuki H, Ishikawa S. Progress of EstheShot1 for esthetic denture – report of abrasion losses-. Ann Jpn Prosthodont Soc 2011;3:E89 [in Japanese]. [13] Ucar Y, Akova T, Aysan I. Mechanical properties of polyamide versus different PMMA denture base materials. J Prosthodont 2012;21:173–6. [14] Hayashi K, Yokoyama N, Machi H, Uchida T, Ono T, Nokubi T. Physical properties of polyamide resin (nylon group) as a polymeric material for dentures: Part 1. Characteristics of absorbent and dimensional change. Journal of Nippon Academy of Dental Technology 2004;25:80–6 [in Japanese]. [15] Hishimoto M, Katou Y, Akita Y, Murakami Y, Iida S. Physical properties of polyester copolymer for denture materials. J Nippon Acad Dent Technol 2008;29:196 [special issue; in Japanese]. [16] Stafford GD, Huggett R. The use of nylon as a denture-base material. J Dent 1986;14:18–22. [17] Kuwahara K, Nagahama F, Kitahara K, Wada M, Makimura S, Kimura K, et al. A case of using non-metalclasp partial denture for the patient with metal allergy. Nichidai Koko Kagaku 2004;30:134–9 [in Japanese]. [18] Yatabe M. How to deal with non-clasp denture? Its advantages and problems. Quintessence 2010;29:2083–90 [in Japanese]. [19] Kawara M, Iwata Y, Iwasaki M, Komoda Y, Iida T, Asano T, et al. Scratch test of thermoplastic denture base resins for non-metal clasp dentures. J Prosthodont Res 2014;58:35–40. [20] Takabayashi Y. Characteristics of denture thermoplastic resins for non-metal clasp dentures. Dent Mater J 2010;29:353–61. [21] Katsumata Y, Hojo S, Ino S, Hamano N, Watanabe T, Kondo N, et al. Color stability of a flexible nylon denture base resin. J Kanagawa Odont Soc 2007;42:140–5 [in Japanese]. [22] Sepu´lveda-Navarro WF, Arana-Correa BE, Borges CP, Jorge JH, Urban VM, Campanha NH. Color stability of resins and nylon as denture base material in beverages. J Prosthodont 2011;20:632–863. [23] Fernandes FSF, Pereira-Cenci T, Silva WJ, Filho APR, Straioto FG, Cury AADB. Efficacy of denture cleansers on Candida Spp. biofilm formed on polyamide and polymethyl methacrylate resins. J Prosthet Dent 2010;105:51–8. [24] Takahashi H, Kawada E, Tamaki Y, Teraoka H, Hosoi T, Yoshida T. Basic properties of thermoplastic resins for denture base material referred to non clasp denture. J Jpn Dent Mater 2009;28:161–7 [in Japanese]. [25] Abuzar MA, Bellur S, Duong N, Kim BB, Lu P, Palfreyman N, et al. Evaluating surface roughness of polyamide denture base material in comparison with poly (methyl methacrylate). J Oral Sci 2010;52:577–81. [26] Taguchi Y, Shimamura I, Sakurai K. Effect of buccal part designs of polyamide resin partial removable dental prosthesis on retentive force. J Prosthodont Res 2011;55: 44–7. [27] Fueki K, Ohkubo C, Yatabe M, Arakawa I, Arita M, Ino S, et al. Clinical application of removable partial dentures using thermoplastic resin (non-metal clasp dentures). Ann Jpn Prosthodont Soc 2013;5:387–408 [in Japanese].
