A comparison of the fitting accuracy of thermoplastic denture base resins used in non-metal clasp dentures to a conventional heat-cured acrylic resin

Description of Poly(aryl-ether-ketone) Materials (PAEKs), Polyetheretherketone (PEEK) and Polyetherketoneketone (PEKK) for Application as a Dental Material: A Materials Science Review

Poly(aryl-ether-ketone) materials (PAEKs), a class of high-performance polymers comprised of polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), have attracted interest in standard dental procedures due to their inherent characteristics in terms of mechanical and biological properties. Polyetheretherketone (PEEK) is a restorative dental material widely used for prosthetic frameworks due to its superior physical, mechanical, aesthetic, and handling features. Meanwhile, polyetherketoneketone (PEKK) is a semi-crystalline thermoplastic embraced in the additive manufacturing market. In the present review study, a new way to fabricate high-performance polymers, particularly PEEK and PEKK, is demonstrated using additive manufacturing digital dental technology, or 3-dimensional (3D) printing. The focus in this literature review will encompass an investigation of the chemical, mechanical, and biological properties of HPPs, particularly PEEK and PEKK, along with their application particularly in dentistry. High-performance polymers have gained popularity in denture prosthesis in advance dentistry due to their flexibility in terms of manufacturing and the growing interest in utilizing additive manufacturing in denture fabrication. Further, this review also explores the literature regarding the properties of high-performance polymers (HPP) compared to previous reported polymers in terms of the dental material along with the current advancement of the digital designing and manufacturing.

Flexural and fatigue properties of polyester disk material for milled resin clasps

To evaluate the flexural and fatigue properties of a polyester disk material used in milled resin clasps of removable partial dentures, experimental polyester disk (mPE), injection-molded polyester (iPE), and polymethyl methacrylate disk (mPMMA) were examined by three-point bending tests and cyclic fatigue tests at 0.75 or 1.50 mm deflection. The mPE exhibited significantly higher flexural strength than the iPE (p<0.05). Meanwhile, the mPMMA displayed higher flexural modulus and strength than the polyesters. The mPE exhibited a significantly lower residual strain than the iPE at the cyclic 0.75 mm deflection (p<0.05); however, microcracks were observed in the mPE at the 1.50 mm deflection. The mPMMA showed a high residual strain at the 0.75 mm deflection and fractured within 1,000 cycles at the 1.5 mm deflection. The higher flexural strength and lower residual strain of the mPE compared with the iPE suggest the advantages of milled resin clasps within a limited deflection.

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.

Evaluation of dimensional accuracy and degree of polymerization of stereolithography photopolymer resin under different postpolymerization conditions: An in vitro study

STATEMENT OF PROBLEM

The appropriate postpolymerization of stereolithography (SLA) resins with the least effect on dimensional accuracy and with optimal polymerization is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the dimensional accuracy and degree of polymerization of a photopolymer resin for SLA with different postpolymerizing times and temperatures.

MATERIAL AND METHODS

Sixty 1.5-mm-thick specimens were made from clear photopolymer resin with a 3D printer to simulate a maxillary complete denture. They were postpolymerized for different periods (15 and 30 minutes) at 3 different temperatures (40 °C, 60 °C, and 80 °C). Both prepolymerization and postpolymerization gap sizes for each specimen were measured at 5 different locations under a stereomicroscope. The tissue surface was scanned before and after polymerization, and the images were superimposed. The deviation was analyzed by using computer-aided design (CAD) software; root mean square estimates (RMSE) and color map data were obtained. Fourier transform infrared spectrometry was used to determine the degree of conversion (DC) of all specimens. The Kruskal-Wallis and Mann-Whitney tests were used to calculate the difference value of the gap sizes (α=.05). One-way ANOVA and the Tukey test were used for RMSE and DC (α=.05).

RESULTS

The smallest average change in gap sizes was found at 15 minutes and 40 °C, and the largest change at 30 minutes and 80 °C. The lowest RMSE was obtained at 30 minutes and 40 °C (P<.05). On the color map, a uniform deposited layer was created at 15 minutes and 40 °C and 30 minutes and 40 °C. The highest DC was found at 30 minutes and 60 °C, which differed significantly from 15 minutes and 40 °C (P<.05). The lowest degree of polymerization was found at 30 minutes and 40 °C.

CONCLUSIONS

The polymerizing temperature exerted a greater effect than polymerizing time, with lower temperatures leading to improved fit and tissue surface accuracy. The recommended parameters for SLA polymerization are 15 minutes and 40 °C. These conditions offered high dimensional accuracy, favorable surface tissue adaptation, and satisfactory DC.

Vertical Displacement in Unilateral Extension Base Flexible Removable Dentures

The need for flexible thermoplastic denture base materials has increased due to patient demand for better esthetic outcomes. Designs aimed at improving esthetic outcomes can cause difficulties for prosthodontists, however, from the viewpoint of function and maintenance. Therefore, the purpose of this study was to investigate vertical displacement in unilateral extension base denture models, comparing that obtained by flexible removable dentures with that by conventional metal clasp dentures. Models of unilateral extension base flexible removable dentures for mandibular defects were prepared. Periodontal ligament and jaw mucosa were simulated using a silicone impression material. Four types of flexible removable denture, with or without a metal rest, and two metal clasp dentures made of acrylic resin as a conventional design were used as dental prostheses. The amount of vertical displacement in the defect areas was measured under a load of 50 N at the first and second molars. Among the 6 types of dentures investigated, the amount of vertical displacement was greater with flexible removable dentures than with metal clasp dentures. This vertical displacement tended to decrease significantly, however, with the use of a metal rest with the flexible removable dentures. Esteshot with a metal rest, in particular, showed the smallest amount of displacement in the flexible removable dentures (first molar, 0.265±0.007 mm; second molar, 0.423±0.008 mm). These results indicate the importance of the application of rests in unilateral extension base flexible removable dentures. It may be useful to employ a metal rest in conjunction with a flexible removable denture to reduce load on the underlying mucosa, as is done with conventional partial dentures.

Effect of photodynamic therapy potentiated by ultrasonic chamber on decontamination of acrylic and titanium surfaces

Photodynamic Therapy (PDT) is an alternative to surface decontamination that is based on the interaction between a non-toxic photosensitizer (PS) and a light source to allow for the formation of reactive oxygen species. The objective of this study was to test a new patented device - the "Ultrasonic Photodynamic Inactivation Device" (UPID) under the patent deposit MU-BR 20.2018.00.9356-3 - for the photodynamic inactivation on contaminated acrylic plates and titanium disk. This new low cost device contains light emitting diodes (LEDs) and was built in a stainless-steel container for better light distribution. In addition, 28 waterproof red LEDs plates, with a wavelength of 660 nm were used, containing three irradiators in each plate, for which the irradiation distribution and the spectral irradiance on all 6 internal faces of this device were calculated. The effect of red LED irradiation (660 nm) methylene blue (MB) (100 μmol/L) diluted in water or 70% alcohol on three types of microorganisms: Candida albicans ATCC 10231, Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922. In order to estimate the effects of PDI, acrylic plates and Titanium disks were contaminated by bacterial suspensions (3 × 10⁸ CFU/mL), then treated with a solution of MB for 30 min, followed by irradiation for 30 min (0.45 J/cm²). Microbial inhibition was evaluated by counting the number of colony forming units (CFU), compared to the control group. The results showed that the UPID promoted significant reduction (p < 0.001) of the microorganism when compared with the positive control. The new device promoted an effective microbial inhibition on the surfaces tested and, thus, makes possible new studies. The perspective is that this new device may be a low-cost and non-toxic alternative to the disinfection of biomedical devices, non-critical instruments and also for use in the food industry.

Patient satisfaction and preference with thermoplastic resin removable partial dentures: a randomised cross-over trial

PURPOSE

This randomised cross-over trial aimed to comparatively investigate patient preference and satisfaction with thermoplastic resin removable partial dentures (TR-RPDs) and conventional metal clasp-retained removable partial dentures (MC-RPDs).

METHODS

Twenty-eight partially dentate subjects were enrolled and randomised to receive MC-RPDs followed by TR-RPDs or vice versa (n=14, each group). The subjects were asked to score overall satisfaction and denture-related parameters 3 months after delivery of each denture. Additionally, they were asked to choose their preferred denture type at the end of the trial.

RESULTS

Of the 28 subjects, 24 (86%; mean age, 67.3 years) completed the trial. The overall satisfaction scores and ratings for oral appearance with TR-RPDs were significantly higher than those with MC-RPDs (P<0.05). Moreover, 75% (18/24) and 83% (20/24) of the subjects reported greater overall satisfaction and better oral appearance with TR-RPDs than with MC-RPDs (P<0.001, both). Scores for mucosal pain and food impaction were significantly better with TR-RPDs than with MC-RPDs (P<0.05). Relative to MC-RPDs, TR-RPDs provided slightly better oral comfort and speech, although the differences were not statistically significant (P>0.05). Scores for chewing ability, denture stability, and ease of denture cleaning were almost identical for both types of dentures.

CONCLUSIONS

These results suggest that TR-RPDs hold an advantage over MC-RPDs in terms of oral appearance and can offer greater satisfaction than MC-RPDs in partially dentate arches with at least an occluding pair in the posterior region.

CLINICAL TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN000007310).

Influence of block-out on retentive force of thermoplastic resin clasps: an in vitro experimental and finite element analysis

PURPOSE

The purpose of this study was to determine the effect of block-out preparation, used to eliminate the undercut area, on the retentive force and stress distribution of resin clasps.

METHODS

A total of 72 polyester and polyamide resin clasps were fabricated on a premolar abutment crown following six block-out preparations. A combination of two types of vertical block-outs and three types of horizontal block-outs (on the missing side) was used on the abutment tooth. Each clasp was subjected to an in vitro removal test using a universal testing machine. The retentive force and traces of the clasp on the abutment tooth were recorded and analyzed with one-way analysis of variance and post hoc comparisons (α=0.05). Non-linear finite element analysis was performed to assess the stress distributions of the resin clasps.

RESULTS

Resin clasps with a vertical block-out of 0.75mm undercut showed significantly higher retentive force than those with the 0.5mm undercut. Resin clasps with horizontal block-out showed significantly lower retentive force than those without horizontal block-out. There was no significant difference between the two thermoplastic resins. The maximum first principal stress of the resin clasp was concentrated under the shoulder of the clasp and strongly influenced by the width of horizontal block-out in the finite element analysis.

CONCLUSIONS

This in vitro experiment suggested that a horizontal block-out is necessary even for a 0.5-mm undercut. The design of the resin clasp should be considered from two aspects: retentive force and deformation risk.

Investigation of the cytotoxicity of thermoplastic denture base resins

PURPOSE

The purpose of this study was to investigate the in vitro cytotoxicity of thermoplastic denture base resins and to identify the possible adverse effects of these resins on oral keratinocytes in response to hot water/food intake.

MATERIALS AND METHODS

Six dental thermoplastic resin materials were evaluated: three polyamide materials (Smile tone, ST; Valplast, VP; and Luciton FRS, LF), two acrylic materials (Acrytone, AT; and Acryshot, AS), and one polypropylene resin material (Unigum, UG). One heat-polymerized acrylic resin (Vertex RS, RS) was chosen for comparison. After obtaining extracts from specimens of the denture resin materials (Φ=10 mm and d=2 mm) under different extraction conditions (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour), the extracts (50%) or serial dilutions (25%, 12.5%, and 6.25%) in distilled water were co-cultured for 24 hours with immortalized human oral keratinocytes (IHOKs) or mouse fibroblasts (L929s) for the cytotoxicity assay described in ISO 10993.

RESULTS

Greater than 70% viability was detected under all test conditions. Significantly lower IHOK and L929 viability was detected in the 50% extract from the VP (70℃) and AT (121℃) samples (P<.05), but only L929 showed reduced viability in the 50% and 25% extract from LF (37℃) (P<.05).

CONCLUSION

Extracts obtained from six materials under different extraction conditions (37℃, 70℃, and 121℃) did not exhibit severe cytotoxicity (less than 70% viability), although their potential risk to oral mucosa at high temperatures should not be ignored.

Effect of fiber content on flexural properties of glass fiber-reinforced polyamide-6 prepared by injection molding

The use of non-metal clasp denture (NMCD) materials may seriously affect the remaining tissues because of the low rigidity of NMCD materials such as polyamides. The purpose of this study was to develop a high-rigidity glass fiber-reinforced thermoplastic (GFRTP) composed of E-glass fiber and polyamide-6 for NMCDs using an injection molding. The reinforcing effects of fiber on the flexural properties of GFRTPs were investigated using glass fiber content ranging from 0 to 50 mass%. Three-point bending tests indicated that the flexural strength and elastic modulus of a GFRTP with a fiber content of 50 mass% were 5.4 and 4.7 times higher than those of unreinforced polyamide-6, respectively. The result showed that the physical characteristics of GFRTPs were greatly improved by increasing the fiber content, and the beneficial effects of fiber reinforcement were evident. The findings suggest that the injection-molded GFRTPs are adaptable to NMCDs because of their excellent mechanical properties.

Evaluation of Three Different Processing Techniques in the Fabrication of Complete Dentures

Aims and Objectives:

The objective of the present study is to compare the effectiveness of three different processing techniques and to find out the accuracy of processing techniques through number of occlusal interferences and increase in vertical dimension after denture processing.

Materials and Methods:

A cross-sectional study was conducted on a sample of 18 patients indicated for complete denture fabrication was selected for the study and they were divided into three subgroups. Three processing techniques, compression molding and injection molding using prepolymerized resin and unpolymerized resin, were used to fabricate dentures for each of the groups. After processing, laboratory-remounted dentures were evaluated for number of occlusal interferences in centric and eccentric relations and change in vertical dimension through vertical pin rise in articulator. Data were analyzed using statistical test ANOVA and SPSS software version 19.0 by IBM was used.

Results:

Data obtained from three groups were subjected to one-way ANOVA test. After ANOVA test, results with significant variations were subjected to post hoc test. Number of occlusal interferences with compression molding technique was reported to be more in both centric and eccentric positions as compared to the two injection molding techniques with statistical significance in centric, protrusive, right lateral nonworking, and left lateral working positions (P < 0.05). Mean vertical pin rise (0.52 mm) was reported to more in compression molding technique as compared to injection molding techniques, which is statistically significant (P < 0.001).

Conclusions:

Within the limitations of this study, injection molding techniques exhibited less processing errors as compared to compression molding technique with statistical significance. There was no statistically significant difference in processing errors reported within two injection molding systems.

Oral health-related quality of life in patients with non-metal clasp dentures: a randomised cross-over trial

We investigated the efficacy of non-metal clasp dentures (NMCDs) with regard to the oral health-related quality of life (OHRQoL) and compare the findings with those for conventional metal clasp-retained dentures (MCDs). This single-centre, randomised controlled, two-phase, open label, cross-over trial included 28 partially dentate individuals. The patients were randomised to receive MCDs followed by NMCDs, or the opposite sequence (n = 14 in each group); each denture was worn for 3 months. OHRQoL was evaluated using the Oral Health Impact Profile-Japanese version (OHIP-J) at entry (T-entry; before treatment with the first denture) and at 3 months after treatment with each denture (T3). An examiner evaluated denture stability, oral appearance and surface roughness before denture delivery (T0) and at T3 and denture hygiene at T3. A total of 24 patients completed the trial. There were no complications related to the dentures, abutment teeth or denture-bearing mucosa during the follow-up periods for both dentures. The mean OHIP summary score was lower for NMCDs than for MCDs, and the difference (9 points) was greater than the minimal important difference (6 points), indicating the difference was clinically relevant. The effect size was medium (0·70). Statistical analyses with linear mixed models found a significant effect of the denture type on the OHIP summary score and scores for the Oro-facial appearance, Oro-facial pain and Psychological impact domains (NMCD < MCD; P < 0·05). The results of our study suggest that NMCDs allow for better OHRQoL compared with MCDs.

Assessment of clasp design and flexural properties of acrylic denture base materials for use in non-metal clasp dentures

PURPOSE

The purpose of this study was to investigate the possibilities of utilizing new acrylic denture base materials in resin clasps using three-point flexural tests and cantilever beam tests.

METHODS

Seven non-metal clasp denture (NMCD) materials and four acrylic denture base materials were used for three-point flexural tests and six NMCD materials and three acrylic denture base materials were used for cantilever beam tests. The flexural strength, elastic modulus, and 0.05% proof stress were measured by three-point flexural tests according to International Organization for Standardization (ISO) 20795-1. And load at 0.5mm deformation, elastic modulus were measured by Cantilever beam tests.

RESULTS

For the three-point flexural tests, only materials that met the conditions for both flexural strength and elastic modulus were the polycarbonate Reigning N (REN) and the acrylics Acron (AC), Pro Impact (PI), Procast DSP (PC) and IvoBase High Impact (HI) which are required in ISO 20795-1, Type 3 denture base materials. And for cantilever beam tests there was no significant difference between PI and either EstheShot (ES), EstheShot Bright (ESB), REN or Acry Tone (ACT) in load at 0.5mm deformation, and no significant difference between PI and either Lucitone FRS (LTF), ES, ESB, REN or ACT in elastic modulus.

CONCLUSIONS

The results thus suggested that some of the acrylic materials used as denture base materials may also be usable for NMCDs, and that the flexural properties of the acrylic material PI resemble those of ES, ESB and ACT, meaning that similar clasp designs may also be feasible.