Flexible thermoplastic denture base materials for aesthetical removable partial denture framework

Flexible Denture: A Literature Review

Careful consideration of material properties used to construct denture base material in removable partial dentures (RPDs) is required for a successful outcome. Because of nylon's flexible nature, nylon denture bases are a widely used alternative material to polymethyl methacrylate (PMMA) in RPDs. Flexible dentures help with retention by creating a seal around the denture's border. In this study, we review current evidence on flexible dentures and provide an overview of their uses, advantages, and disadvantages. We conducted electronic research of English-language articles written between 2018 and 2023 that addressed the different physical and mechanical properties of flexible dentures. Flexible dentures' water sorption did not exceed ISO standards. Other physical properties we investigated, such as color stability and polymerization shrinkage, were lower in flexible dentures than in PMMA. Mechanical properties showed a lower value compared to PMMA, such as surface roughness and hardness, and impact strength. However, flexural strength was controversial. Retention was better in PMMA compared to flexible dentures. Finally, the retention of acrylic teeth compared to flexible dentures was better with the provision of extra mechanical retention means. Therefore, it is important to examine flexible dentures' properties, indications, advantages, and disadvantages when offering patients this solution.

Stress distribution and patient satisfaction in flexible and cast metal removable partial dentures: Finite element analysis and randomized pilot study

Purpose

To compare stress distribution in polyacetyl based flexible RPD (FRPD) with cast metal RPD (CRPD) by using three-dimensional finite element analysis (FEA) and patient satisfaction by using OHIP-14 questionnaire in participants with Kennedy's class I partially edentulous mandibular arch rehabilitated with CRPD and FRPD.

Material and methods

For FEA, 3D models of Kennedy's class I partially edentulous mandibular arch, CRPD in chrome-cobolt alloy, and polyacetyl based FRPD were geometrically modelled and subjected to a vertical load of 100 ​N bilaterally. The in vivo comparison of satisfaction was assessed by enrolling 22 participants with Kennedy's class I partially edentulous mandibular arch. After randomization, 11 participants were rehabilitated by CRPD (group C), and 11 participants by polyacetyl based FRPD (group F). OHIP-14 questionnaire in Hindi language was filled at 1 week and 1 year after denture insertion.

Results

Von Mises stress distribution in CRPD was maximum in mesial rest seat of the primary abutment (100 ​MPa) and minimum for edentulous ridge (7 ​MPa on bone and 6 ​MPa on mucosa). Von Mises stress distribution for polyaccetyl based FRPD was maximum in ridge (25 ​MPa) and minimum in periodontal ligament of the second premolar (3 ​MPa). Patient satisfaction in group F was significantly more than in group C at end of 1 year (P ​= ​.0158).

Conclusion

FRPD is useful in periodontally compromised abutment teeth and CRPD in resorbed ridge conditions. Patient satisfaction is more with polyacetyl based flexible RPD when compared with cast metal RPD at the end of 1 year.

Modern partial dentures - part 2: a review of novel metal-free materials and innovations in polymers

New materials are continuously being developed and advanced for the provision of partial dentures. However, the rate at which they are developing makes it hard for the clinician to discern which would be worth adopting into their practice.This paper looks at some of those materials, including the earlier alternatives to conventional acrylic resins, polyamides and acetal resin, followed by a review of the newer novel polymers that are currently in use, including aryl-ketone-polymers and the polymer group polyaryletherketones.The newer polymers have many similarities, in both properties and aesthetics, such as increased elasticity that allows the dentures to engage deeper undercuts, while maintaining high strength. A significant benefit of the novel polymers is in their ability to fit into a digital workflow. Computer-aided design and manufacture confer a high degree of consistency, efficiency and accuracy in the prosthesis. The ability to use precise digital tools to create frameworks and clasps of accurate parameters limits the introduction of technical error that has the potential to be introduced in the construction of a conventional cobalt-chrome framework.The novel high-performance polymers show great promise. Research is needed on these materials investigating the effects on oral health, longevity and survival of the appliances, as well as studies looking at patient satisfaction and the impact on quality of life.

A Study to Assess the Bond Strength of Acrylic Teeth With Different Retentive Features

Background and Aim:

Flexible denture base has been gaining attention as a denture base material because of its toxicological safety, comfort, and enhanced aesthetics. Debonding of acrylic teeth from the flexible denture base material has posed a great problem to the clinician and patient. This study aimed at comparing the bond strength between flexible denture base with acrylic teeth having different mechanical modifications.

Materials and Methods:

Forty mandibular molar teeth (Combination Acry Rock, Badia Polesine (Ro), Italy) were used in four groups for mechanical modifications on the ridge lap area. The groups were group 1 (no mechanical modifications), group 2 (round groove 2 mm in diameter and 2 mm deep on the ridge lap surface), group 3 (horizontal slot 2 mm deep, 2 mm wide, and 4 mm long prepared on the ridge lap surface of the teeth), and group 4 (T-shaped groove 2 mm deep, 2 mm wide, and length of 4 mm mesiodistally and 2 mm buccolingually prepared with a straight fissure bur). The acrylic teeth were attached to a wax block of dimension 1.2 cm × 1.2 cm × 2.5 cm. These were flasked and dewaxed, followed by injection molding with Valplast flexible denture base material. The bond strength was assessed by attaching the specimens to universal testing machine tested under a tensile load at a cross-head speed of 1 mm/min till it fractured. Data obtained were statistically evaluated by one-way analysis of variance and post hoc test.

Results:

There was significant increase in mean bond strength after various mechanical modifications. Group with T-shaped diatoric hole showed greatest bond strength value compared to other groups.

Conclusion:

Incorporating mechanical retentive features with increased surface area and undercut can improve the bonding of acrylic teeth to flexible denture base.

Nonmetal clasp dentures: What is the evidence about their use?

The aim was to discuss the indications, contraindications, advantages, and disadvantages of Nonmetal clasp dentures (NMCDs), as well as the most relevant properties of its constituent materials. A search was conducted using the keywords: “nonmetal clasp dentures,” “thermoplastic resin,” “flexible resin removable partial denture,” “polyamide,” and “nylon” in databases PubMed/Medline, Lilacs, SciELO, and textbooks between 1955 and 2020. Theses and texts without reliable sources of publication were excluded. Once the analysis instruments were determined, the data were analyzed and discussed. NMCDs present high flexibility, easy adaptation to the abutments, color compatibility and biocompatibility with the oral mucosa, and absence of visible metal clasps. However, they need laboratory relining, grinding, and polishing, do not have criteria for its planning, become rougher and stained over time, and are able to traumatize supporting tissues. The association with metal components seems to be an alternative to increase the success of NMCDs by combining esthetics and biomechanical principles of conventional removable partial dentures. The lack of long-term clinical studies makes the professionals to rely solely on previous experiences or on the manufacturers' recommendations. It suggested that NMCDs must be indicated with caution when not used temporarily.

Attitude of dental professionals toward cast partial denture: A questionnaire survey in India

Aims:

The use of cast partial dentures (CPDs) has been decreased and its importance has been declined in the teaching curriculum. The purpose of this survey was to evaluate the attitudes of dental professionals toward conditions using CPDs in private practice in India.

Settings and Design:

Descriptive survey

Materials and Methods:

This survey consists of eight close-ended questions concerning the use of CPD by dental professionals practicing in India. The URLs of the questionnaire were shared via E-mail to dentists practicing throughout India, to obtain a response of 384 which is a predetermined sample size.

Statistical Analysis Used:

Statistical analysis was done using counts and percentages and the results were further analyzed statistically by the Chi-square test.

Results:

Nearly 42.79% of general dental practitioners (GDPs), 47.26% of prosthodontists, and 9.95% of other specialist dentists responded to the questionnaire. GDPs mostly preferred removable partial dentures (RPDs) (71.87%) and fixed partial dentures (57.22%), whereas prosthodontists preferred mostly implant (60.91%). GDPs mostly preferred flexible dentures (62.42%), whereas prosthodontists preferred CPDs 62.84%. Almost 52.50% of the GDPs mostly raised a cost issue and 63.11% of the prosthodontists had difficulty in adjustment with CPDs. Nearly 63.46% of the dentists told that implant-supported restorations are better options compared to CPDs; still, majority of the dentists (53.23%) were in favor that more importance for teaching CPDs in graduation curriculum should be given.

Conclusions:

This survey shows that in India a significant proportion of GDPs (71.87%) preferred RPDs, mostly flexible dentures (62.42%) due to their low cost compared to CPDs. Prosthodontists mostly preferred implants (60.91%) because they are more confident and better trained in these. It is recommended that more importance be given in teaching implants along with CPDs in graduation curriculum so that practitioners can better educate their patients about implants and their advantages over flexible dentures and their utilization in cases where patients are not willing for CPDs.

Different Materials Used as Denture Retainers and Their Colour Stability

BACKGROUND:

Retainers are of great importance for the longevity of the prosthetic removable partial denture during various functions especially the esthetic one. The key of successful clasp selection is to select a direct retainer that will control tipping and torquing forces on the abutment teeth, provide retention against reasonable dislodging forces and are compatible with both tooth and tissue contour together with the aesthetic desire of the patient.

AIM:

This study aims to compare different clasp material to enhance the choice of the clasp based on the aesthetic point of view.

METHODS:

The colour evaluation of the tested materials had been evaluated by computer aided technique with digital camera with 3 Mega Pixels of resolution.

RESULTS:

In the current research, the technique of colour evaluation was carried out to compare different clasp materials to enhance the choice of the clasp based on the aesthetic point of view. Most commonly, Removable Partial Denture (RPD) retainers are fabricated identically from the metal framework’s alloy as Cobalt Chromium (CoCr) alloy although it is unaesthetic. This esthetic problem has been overcome by other methods and by utilising different materials, these included covering the retainers with tooth-coloured acrylic resin, as well as the introduction of esthetic materials as; Thermoplastic Acetal, Versacryl, and Thermopress.

CONCLUSION:

It has been concluded that the non-metallic Acetal resin clasp shows superior physical properties regarding colour stability.

Flexural strength of hydrogen plasma-treated polypropylene fiber-reinforced polymethyl methacrylate denture base material

Objectives:

The present study aimed to evaluate flexural strength of hydrogen plasma-treated polypropylene fibers-reinforced polymethyl methacrylate (PMMA) polymer composite.

Materials and Methods:

One control group with no fiber reinforcement and 9 polymer composite test groups with varying fiber weight percentage (2.5, 5, and 10 Wt%) and aspect ratio (3/220, 6/220, and 12 mm/220 μm) were prepared. Flexural strength was measured using Instron.

Results:

All hydrogen plasma-treated polypropylene fiber-reinforced test groups obtained significantly higher flexural strength characteristics. Among the test groups, 6 mm long fibers reinforced in 10 Wt% showed superior flexural strength.

Conclusion:

Hydrogen plasma treatment on polypropylene fiber has a significant role in enhancing the adhesion between PMMA polymer matrix and the polypropylene fibers and thereby the flexural strength.

Comparative Study Clarifying the Most Suitable Material to Be Used as Partial Denture Clasps

BACKGROUND

Removable partial denture's clasp is of particular importance as it affects the denture longevity during the function. The key of successful clasp selection is to select a direct retainer that will control tipping and torquing forces on the abutment teeth, provide retention against reasonable dislodging forces and are compatible with both tooth and tissue contour and the aesthetic desire of the patient. In this consideration, different materials employed for the clasp construction were compared mechanically.

AIM

This study aims to compare the most usable esthetic clasps mechanically to clarify the most suitable material to be used as partial denture clasps.

METHODS

Evaluation of surface roughness, retention and deformation has been investigated utilising different in-vitro methods. All these techniques provide valuable information regarding the mechanical properties of the materials tested. However, none of the in-vitro techniques can expose the tested materials to conditions similar to that of the oral environment (in-vivo) such as pH value and temperature variations.

RESULTS

Most commonly, RPD clasps are fabricated from the same alloy of the metal framework, as cobalt-chromium (CoCr) alloy although it is unaesthetic. Other methods consumed to avoid such esthetic mystery have included coating retainers with tooth-coloured resin or introduction of esthetic materials as Thermoplastic Acetal, Versacryl, and Thermopress.

CONCLUSION

It has been concluded that the non-metal Acetal resin retainer reveals superior mechanical properties.

Bacterial Colonization and Tissue Compatibility of Denture Base Resins

Currently, there is minimal clinical data regarding biofilm composition on the surface of denture bases and the clinical tissue compatibility. Therefore, the aim of this experimental study was to compare the bacterial colonization and the tissue compatibility of a hypoallergenic polyamide with a frequently used PMMA resin tested intraorally in a randomized split-mouth design. Test specimens made of polyamide (n = 10) and PMMA (n = 10) were attached over a molar band appliance in oral cavity of 10 subjects. A cytological smear test was done from palatal mucosa at baseline and after four weeks. The monolayers were inspected for micronuclei. After four weeks in situ, the appliance was removed. The test specimens were immediately cultivated on non-selective and selective nutrient media. All growing colonies were identified using VITEK-MS. The anonymized results were analyzed descriptively. A total of 110 different bacterial species could be isolated, including putative pathogens. An average of 17.8 different bacterial species grew on the PMMA specimens, and 17.3 on the polyamide specimens. The highest number of different bacterial species was n = 24, found on a PMMA specimen. On the two specimens, a similar bacterial distribution was observed. Micronuclei, as a marker for genotoxic potential of dental materials, were not detected. This study indicates that the composition of bacterial biofilm developed on these resins after four weeks is not influenced by the type of resin itself. The two materials showed no cytological differences. This investigation suggests that polyamide and PMMA are suitable for clinical use as denture base material.

Flexible Removable Partial Denture Prosthesis: A Survey of Dentists' Attitudes and Knowledge in Greece and Croatia

PURPOSE

The aim of this study was to investigate through a questionnaire the knowledge, attitudes and possible differences in the use of flexible RPDPs among dentists in Greece and Croatia.

MATERIAL AND METHODS

A questionnaire of 16 questions was originally created in English, translated into Greek and Croatian language following a two way translation and tested for apprehension, precision, clarity and homogeneity by a number of native English speaking Greek and Croatian dentists. Following the necessary corrections, the questionnaires replicated in two online surveys and their addresses with an informed consent were sent by emails to nearly 4000 dentists in each country to participate. Collected data were analyzed by chi-square tests at a= .05 level of significance.

RESULTS

378 dentists from Greece and 304 from Croatia participated in the study. 137(36.2%) dentists from Greece and 56(18.4%) from Croatia provided flexible RPDPs to their patients. Statistical analysis for all providers indicated no significant difference between genders (P>.05), significant differences between age groups (P<.01), years of practice (P<.05), specialization (P <.001), and instruction on flexible prostheses (P <.001). The analysis between the two countries showed differences for gender and age groups (P<.01) but no differences between experienced, specialized or instructed groups (P >.05).

CONCLUSION

The survey indicated differences between the two countries in the percentages of dentists using, selecting and providing RPDPs for their patients. Practitioners' age, years in practice and instruction were associated with the provision of the prostheses, while comfort, esthetics and cost were the reasons for deciding to use the flexible RPDPs.

CONCLUSION

Although dentists are not educated in their schools about flexible RPDPs, almost a third of them offer this treatment to their patients. Long term success of these devices depends on clinical education, more experience and definitely more research.

Polyamide as a Denture Base Material: A Literature Review

The purpose of this article was to review the biocompatibility, physical, and mechanical properties of the polyamide denture base materials. An electronic search of scientific papers from 1990-2014 was carried out using PubMed, Scopus and Wiley Inter Science engines using the search terms "nylon denture base" and "polyamide denture base". Searching the key words yielded a total of 82 articles. By application of inclusion criteria, the obtained results were further reduced to 24 citations recruited in this review. Several studies have evaluated various properties of polyamide (nylon) denture base materials. According to the results of the studies, currently, thermo-injectable, high impact, flexible or semi-flexible polyamide is thought to be an alternative to the conventional acrylic resins due to its esthetic and functional characteristics and physicochemical qualities. It would be justifiable to use this material for denture fabrication in some cases such as severe soft/ hard tissue undercuts, unexplained repeated fracture of denture, in aesthetic-concerned patients, those who have allergy to other denture base materials, and in patients with microstomia.  Although polyamide has some attractive advantages, they require modifications to produce consistently better properties than the current polymethyl methacrylate (PMMA) materials. Moreover, since there is a very limited knowledge about their clinical performance, strict and careful follow-up evaluation of the patients rehabilitated with polyamide prosthesis is recommended.