Evaluation of shear bond strength of microwaveable acrylic resins in denture repair: a comparative study

OBJECTIVE: Acrylic denture base fracture is a common mode of failure. Heat-cured, auto-polymerized, visible light-cured, and microwaveable acrylic resins have been used as repair materials. The aim of this study was to evaluate the shear bond strength of two microwaveable resins (Acron MC and Justi) and one auto-polymerizing acrylic resin (ProBase Cold) as denture repair materials as opposed to a heat-cured one using the non-flasking procedure after thermocycling and photoaging. MATERIAL AND METHODS: Ninety cylindrical specimens were made using the Vertex Rapid Simplified heat-cured acrylic resin. Each repair acrylic resin was poured on the specimen's surface using a cylindrical rubber mold with an internal diameter of 8.5 mm. Thirty specimens for each repair material were made. The control group consisted of 10 specimens from each group which were stored in water for 24 h at 37 degrees C; another 10 specimens from each group were subjected to a thermocycling procedure (5-55 degrees C for 1,000 cycles), while the remaining 10 specimens were subjected to a photoaging procedure. Shear bond strength was measured on a universal testing machine and mode of bond failure was examined under a stereomicroscope. Two-way ANOVA and the Bonferroni post hoc test were performed to identify statistical differences at alpha = 0.05. RESULTS: Justi's shear bond values were significantly inferior to those of ProBase Cold (p <0.05) and Acron MC (p <0.05). ProBase Cold and Acron MC acrylic resins exhibited similar values (p >0.05) of shear bond strength. Thermocycling and photoaging did not affect the shear bond values of any of the materials under investigation (p >0.05). CONCLUSIONS: ProBase Cold and Acron MC exhibited similar shear bond values. Justi repair material exhibited inferior bond strength compared with that of ProBase Cold and Acron MC. Aging procedures did not affect the bonding properties of any of the repair materials.     

An evaluation of bond strengths of denture repair resins by a torsional method

Chemical cure resin materials are generally used in the repair of dentures. Different repair resins used may yield different results. The bond strength of three autopolymerizing resins were evaluated using a torsional test method. The results showed that Palapress and Caulk resins had a higher repair strength than Rapid Repair resin.     

Tensile bond strength of four denture resins to porcelain teeth with different surface treatment

PURPOSE

This study evaluated the bond strength between porcelain denture teeth (Bioblend 43D) and four different polymerized denture resins (Lucitone 199, Palapress, Acron MC, Triad) with and without a bonding agent and after four different types of surface treatment (polished, HF etched, sandblasted, air-abraded).

MATERIALS AND METHODS

Central incisor porcelain denture teeth were divided into 32 groups of 5 each. Tensile bond strength (MPa) was determined using a testing machine at crosshead speed of 0.5 mm/min. Mean and standard deviation are listed. Data were analyzed by two-way ANOVA. Means were compared by Tukey-Kramer intervals at 0.05 significance level.

RESULTS

All surface treatment increased bond strength compared to polished surface and the highest bond strength was found with Palapress resin with etched porcelain surface (8.1 MPa). Bonding agent improved the bond strength of all denture resins to porcelain teeth. Superior bonding was found with Palapress and air-abraded porcelain (39 MPa).

CONCLUSION

Resins with different curing methods affect the bond strength of porcelain teeth to denture bases. Superior bonding was found with auto-polymerized resin (Palapress). Application of ceramic primer and bonding agent to porcelain teeth with and without surface treatment will improve the bond strength of all denture resins to porcelain teeth.     

A basic study on newly developed light-curing resins--Fitness, flexural properties and bond strength to self-curing resins

The objectives of this study were to evaluate fitness, bending properties, and bond strength of newly developed light-curing denture base resins (Eclipse, Dentsply) in contrast with conventional heat-curing denture base resins (Acron, GC). These evaluations were performed by fitting tests, bending strength tests, and shear bond strength tests. For the fitting test, 40 resin specimens, 20 for each resin, were made on plaster models, which simulated the maxillae edentulous ridge. The gaps between resin specimens and the plaster model were measured. The bending strength tests were carried out using 16 resin plate specimens (65 x 10 x 2.5 mm). The bending strength and elastic modulus for each denture base resin was calculated. For the shear bond strength test, self-curing resins were bonded to each resin and in total, 32 bonded specimens (20 x 4 x 2.5 mm) were made. The shear bond strength tests were carried out in order to evaluate the bond strength between the self-curing resin and each denture base resin. The results of these tests revealed that Eclipse exhibited better fitness to the plaster model, larger bending strength, and larger elastic modulus than Acron. Furthermore, the bond strength of Eclipse to self-curing resin was equivalent to that of Acron. These results suggest that Eclipse has excellent properties for application in clinical settings.     

Evaluation of the Bond Strength of Denture Base Resins to Acrylic Resin Teeth: Effect of Thermocycling

Purpose: The purpose of this study was to evaluate the thermocycling effects and shear bond strength of acrylic resin teeth to denture base resins.
Materials and Methods: Three acrylic teeth (Biotone, Trilux, Ivoclar) were chosen for bonding to four denture base resins: microwave-polymerized (Acron MC), heat-polymerized (Lucitone 550 and QC-20), and light-polymerized (Versyo.bond). Twenty specimens were produced for each denture base/acrylic tooth combination and were divided into two groups (n = 10): without thermocycling (control groups) and thermocycled groups submitted to 5000 cycles between 4 and 60°C. Shear strength tests (MPa) were performed with a universal testing machine at a crosshead speed of 1 mm/min. Statistical analysis of the results was carried out with three-way ANOVA and Bonferroni's multiple comparisons post hoc analysis for test groups (α= 0.05).
Results: The shear bond strengths of Lucitone/Biotone, Lucitone/Trilux, and Versyo/Ivoclar specimens were significantly decreased by thermocycling, compared with the corresponding control groups ( p < 0.05). The means of Acron/Ivoclar and Lucitone/Ivoclar specimens increased after thermocycling ( p < 0.05). The highest mean shear bond strength value was observed with Lucitone/Biotone in the control group (14.54 MPa) and the lowest with QC-20/Trilux in the thermocycled group (3.69 MPa).
Conclusion: Some acrylic tooth/denture base resin combinations can be more affected by thermocycling; effects vary based upon the materials used.     

The effect of chemical surface treatments of different denture base resins on the shear bond strength of denture repair

STATEMENT OF PROBLEM: Fracture of a repaired denture base often occurs at the junction of the base and repair materials rather than within these materials. PURPOSE: The purpose of the study was to evaluate the shear bond strengths of 4 denture base acrylic resins following the use of 3 chemical solvents and to examine treated acrylic resin surfaces under a field emission scanning electron microscope (SEM). MATERIAL AND METHODS: Forty discs (15 mm in diameter and 3 mm thick) were fabricated for each denture base material (a conventionally molded, heat-polymerized [Meliodent, M], an injection-molded, heat-polymerized [SR-Ivocap, I], and a microwave-polymerized [Acron MC, A]) repaired with an autopolymerizing acrylic resin (Meliodent), for a total of 120 specimens, processed according to manufacturers' instructions, embedded in acrylic resin blocks, and divided into 4 groups of 10. One of the groups served as control and had no surface treatment. In the 3 experimental groups, specimen surfaces were treated with chemical etchants by immersion in acetone (ac) for 30 seconds, in methylene chloride (mc) for 30 seconds, or in MMA (mo) for 180 seconds, respectively. Then autopolymerizing acrylic resin (Meliodent) was placed on the treated surfaces using a brass ring (6 mm in diameter and 2 mm in height) to confine the material to a standardized dimension. After 24 hours of storage at 37 degrees C, the shear bond strength (MPa) of the specimens was measured in a universal testing machine. A 2-way analysis of variance and the Tukey HSD test were performed to identify significant differences (alpha=.05). The nature of the failure was noted as adhesive, cohesive, or mixed. The effect of the chemical treatments on the surface of base resins was examined under an SEM. RESULTS: Chemical treatments increased the bond strength of repair material significantly. Significant differences were found between the control and experimental groups (P<.001). In the control group, M showed the highest (16.7 MPa) bond strength, and A showed the lowest (9.4 MPa). No significant differences were detected between M (18.9 MPa) and A (19.9 MPa) with acetone treatment, or between M (19.3 MPa) and A (20.3 MPa) with methylene chloride treatment. The SEM observations showed that application of chemical etchants produced smoother surfaces than controls. CONCLUSION: Chemical treatment prior to denture base repair showed significant improvement on the bond strength of the base materials. Although the microwave-polymerized acrylic resin, A, showed the lowest shear bond strength compared to the control groups, the highest percentage increase was obtained with A after chemical treatments.     

Tensile bond strength of acrylic resin denture teeth to a microwave- or heat-processed denture base

STATEMENT OF PROBLEM: Fracture of acrylic resin prosthetic teeth from acrylic resin denture bases can be a problem for some patients. The optimal combination of acrylic resin denture tooth, denture base material, and processing method is not known. Purpose. The objective of this study was to compare the tensile bond strengths of heat- and microwave-polymerized acrylic resins among 4 types of acrylic resin denture teeth. MATERIAL AND METHODS: Heat-polymerized (Lucitone 199) and microwave-polymerized (Acron MC) acrylic resins were used. Four types of acrylic resin denture teeth (IPN, SLM, Vitapan, and SR-Orthotyp-PE) were milled to a fixed diameter according to ADA specification no. 15. Ten specimens of each tooth type were processed to each of the denture base materials according to the manufacturers' instructions. Ten additional resin control specimens without teeth also were fabricated. Specimens were thermocycled and tested for strength until fracture with a custom alignment device. Data were analyzed with analysis of variance and Duncan's multiple range test. A scanning electron microscope was used to identify adhesive and cohesive failures within debonded specimens. RESULTS: The mean force required to fracture the specimens ranged from 5.3 +/- 3.01 to 21.6 +/- 5.2 MPa for the microwave-polymerized base and 11.2 +/- 3.0 to 39.1 +/- 5.1 MPa for the heat-polymerized base. The most common failure was cohesive within the denture tooth. With each base material, Orthotyp and IPN teeth exhibited the highest bond strengths; SLM and Orthotyp bond strengths were similar. In general, heat-polymerized groups failed cohesively within the denture base resin or the tooth, and microwave-polymerized groups failed adhesively at either the ridge lap or occlusal surface of the denture tooth. CONCLUSION: Within the limitations of this study, the results suggest that the type of denture base material and denture tooth selected for use may influence the tensile bond strength of the tooth to the base. Selection of more compatible combinations of base and resin teeth may reduce the number of prosthesis fractures and resultant repairs.     

Denture base resins: comparison study of color stability.

Several denture base resins have been recently introduced that provide easier or faster processing. Although these materials have adequate strength properties, the color stability is also of interest. This study evaluated the color stability of five denture base acrylic resins and one denture base repair resin. The samples were subjected to conditions of accelerated aging to test color stability. Five samples of each material were processed and aged for 100 and 300 hours. The color stability was quantitatively measured using the Minolta Chroma Meter II. Color measurements were made before weathering and at 100 and 300 hours the color difference delta E was calculated for all samples. At 300 hours the color change of the materials was significantly different at p less than 0.01. It was found that: (1) the color of Lucitone Hy-pro and Acron was least affected by conditions of accelerated aging; (2) Triad, Accelar 20, and Perm demonstrated noticeable color changes; and (3) Compak-20 had an appreciable color change and was the least color-stable of the materials tested.     

Repair of denture base resins with visible light-polymerized reline material: effect on tensile and shear bond strengths

STATEMENT OF PROBLEM: Triad visible light-polymerized (VLP) reline resin has the potential to repair denture bases from other resin systems with the elimination of flasking/deflasking procedures. PURPOSE: This study measured the tensile and shear bond strengths of Triad VLP, PMMA, and glass-fiber-reinforced PMMA (GF-PMMA) acrylic resins before and after repair with Triad VLP reline material. MATERIAL AND METHODS: Fifty-six specimens were fabricated from Triad VLP, PMMA, and GF-PMMA denture base resins. Both Triad VLP reline material and autopolymerizing acrylic resins were used to repair identical laboratory fabricated resin joints. Twenty-eight rectangular specimens (in 4 different groups of 7 each) were prepared to study the shear bond strength of Triad reline material used to repair different denture base resin joints. RESULTS: Statistically significant differences (P< .0001) were found between the tensile strengths of specimens repaired with the Triad VLP reline resin used as a repair agent and those repaired with the autopolymerizing resin. The tensile strength of the Triad VLP denture base resin was found to be higher than that of both the PMMA and GF-PMMA acrylic resins. CONCLUSION: The low tensile and shear bond strengths found after the repair of PMMA and GF-PMMA acrylic resins with Triad VLP reline material were attributed to a lack of cohesion/adhesion between the Triad VLP reline material and the interfaces of the treated sites. The use of Triad VLP reline material to repair Triad VLP denture base resin produced the highest strengths.     

Effect of polyaramid fiber reinforcement on the strength of 3 denture base polymethyl methacrylate resins

Purpose The interactive effects of synthetic polyaramid reinforcement fibers on the transverse strength of intact and repaired heat‐polymerized denture base acrylic resins were investigated. Materials and Methods Three polymethylmethacrylate (PMMA) polymers were tested: Acron MC (GC International Corp, Scottsdale, AZ), Lucitone 199 (Dentsply International Inc, York, PA), and Microlon (The Hygienic Corp, Akron, OH). With each polymer, there were 2 controls and 4 experimental groups (n = 9 per group). The treatment groups were intact heat‐polymerized PMMA control, PMMA with unreinforced repair, PMMA with polyaramid reinforced repair, intact polyaramid reinforced heat‐polymerized PMMA control, polyaramid reinforced PMMA with unreinforced repair, and polyaramid reinforced PMMA with polyaramid reinforced repair. The transverse fracture strengths of the samples were measured with a 3‐point bending test on a Zwick Universal Testing Machine (Zwick of America, Inc, East Windsor, CT). Results The highest mean strength at fracture was recorded with intact polyaramid reinforced heat‐polymerized PMMA controls for all resins. Analysis of variance showed significant differences in transverse strength (p < .05 ) by experimental group, by material, and by interaction of group and material. Tukey HSD (honestly significant difference) Multiple Comparisons Test (α= 0.05) showed that intact polyaramid reinforced heat‐polymerized PMMA controls were significantly stronger than intact heat‐polymerized PMMA controls and all the other treatment groups. Use of polyaramid reinforcement in repair of unreinforced PMMA or polyaramid reinforced PMMA did not result in significantly increased transverse strength. Conclusions Polyaramid reinforcement significantly increased the transverse strength of intact heat‐polymerized PMMA. Polyaramid fibers did not significantly increase strength to reinforce PMMA repairs.     

Strength of relined denture base polymers subjected to long-term water immersion

PURPOSE: This study was undertaken to characterize the long-term equilibrium flexural strength at proportional limit (FSp) of 4 denture reline polymers processed onto 4 denture base polymers. MATERIALS AND METHODS: A 3-point flexural test was applied on rectangular specimens of each denture base polymer-denture reline polymer. Each specimen was immersed in water for 4 months prior to and 4 months after reline. RESULTS: Significant differences existed among the relined specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P < 0.05). The descending order in FSp according to the denture base polymer, arranged in terms of statistical significance was: Acron approximately Acron MC > Triad > Palapress Vario, where approximately denotes no significant difference between Acron and Acron MC. The descending order in FSp according to the denture reline polymer, arranged in terms of statistical significance was: Triad > Rebaron > Rebaron LC > Tokuso Rebase. Significant difference existed among all of the denture reline polymers. CONCLUSION: The present study showed that the long-term equilibrium strengths of 4 denture reline polymers processed onto 4 denture base polymers were different. The strength of the relined specimen of a denture base is dependent on the strength of the denture base polymer and that of the reline polymer.     

Impact strength and fracture morphology of denture acrylic resins

STATEMENT OF PROBLEM: Microwave-polymerization cycles may affect the impact strength and fracture morphology of denture base acrylic resin, and the microstructural effects of these processes have not been fully determined. PURPOSE: This study evaluated the impact strength and fracture morphology of denture base acrylic resins processed by microwave energy and hot water bath. MATERIAL AND METHODS: Twenty specimens measuring 65 x 10 x 2.5 mm were fabricated from each of 4 acrylic resins processed according to the manufacturers' recommendations: Lucitone 550 (control; 9 hours at 74 degrees C); Onda Cryl (3 minutes at 360 W + 4 minutes pause + 3 minutes at 810 W); Acron MC (3 minutes at 500 W); and Vipi Wave (20 minutes at 180 W + 5 minutes at 540 W). The impact strength was evaluated in an impact testing machine using the Charpy method with a load (impact action) of 3.95 J. Mean values of impact strength were compared by Tukey honestly significant difference test (alpha = .05). Fractures were classified as brittle or intermediate. Fractographic analysis was performed for all fragments by angle analyses of crack propagation, and the microstructural morphology characterization was accomplished with scanning electron microscopy (SEM). Data from the fractography analysis were submitted to the Kruskal-Wallis test for angles and radius (alpha = .05). RESULTS: Significant differences (P < .001) were found in the impact strength for Vipi Wave and Acron MC acrylic resins, which demonstrated the lowest values (0.19 +/- 0.04 and 0.21 +/- 0.02, respectively). Most fractures were classified as brittle (Lucitone 55%; Onda Cryl 75%; Acron MC 90%; Vipi Wave 65%). Fractographic angle analysis of brittle fractures showed no differences among acrylic resins studied; however, angle values of intermediate fractures for Onda Cryl were lower in comparison with those from Lucitone 550 and Vipi Wave (P = .03). The SEM observations revealed that brittle fractures showed defined and organized crystallographic planes, whereas the intermediate fractures had a disorganized appearance. CONCLUSION: Within the limitations of this study, it was observed that impact strength in microwave-polymerized acrylic resins varies according to the period of irradiation. Acrylic resins exhibited a high number of brittle fractures, irrespective of the processing technique.     

Shear bond strengths for composite and autopolymerized acrylic resins bonded to acrylic resin denture teeth

Statement of problem. Composite has been used to modify acrylic resin denture teeth. Purpose. This in vitro investigation examined the shear bond strengths between composite and autopolymerized acrylic resin bonded to acrylic resin denture teeth. Material and methods. The surface treatments used for the denture teeth included wetting with methyl methacrylate (MMA), vinylethyl methacrylate monomer (VEMA), unfilled liquid resin, composite bonding agent, and composite color modifier. Nonhydrated and hydrated denture tooth groups were included. A commercial composite was bonded to the denture teeth. The control group consisted of autopolymerized PMMA resin bonded to the acrylic resin denture teeth, and another group consisted of polyvinylethyl methacrylate bonded to acrylic resin denture teeth. The samples were thermocycled and tested in shear. Results. Acrylic resin denture teeth prewetted with MMA and treated with unfilled resin or a bonding agent had bond strength values comparable to the control group. VEMA was not as effective in promoting the bond. Composite color modifier did not produce a significantly weaker bond between the acrylic resin teeth and added composite. No prewetting of the teeth with MMA resulted in the lowest bond strength. Mean shear bond strengths for corresponding hydrated and non-hydrated groups were not significantly different. Conclusion. Bond strength of composite-to-acrylic resin denture teeth was comparable to the bond strength of autopolymerized acrylic resin.     

A Study on Effect of Surface Treatments on the Shear Bond Strength between Composite Resin and Acrylic Resin Denture Teeth

Visible light-cured composite resins have become popular in prosthetic dentistry for the replacement of fractured/debonded denture teeth, making composite denture teeth on partial denture metal frameworks, esthetic modification of denture teeth to harmonize with the characteristics of adjacent natural teeth, remodelling of worn occlusal surfaces of posterior denture teeth etc. However, the researches published on the bond strength between VLC composite resins and acrylic resin denture teeth is very limited. The purpose of this study is to investigate the effect of five different methods of surface treatments on acrylic resin teeth on the shear bond strength between light activated composite resin and acrylic resin denture teeth. Ninety cylindrical sticks of acrylic resin with denture teeth mounted atop were prepared. Various treatments were done upon the acrylic resin teeth surfaces. The samples were divided into six groups, containing 15 samples each. Over all the treated and untreated surfaces of all groups, light-cured composite resin was applied. The shear strengths were measured in a Universal Testing Machine using a knife-edge shear test. Data were analyzed using one way analysis of variance (ANOVA) and mean values were compared by the F test. Application of bonding agent with prior treatment of methyl methacrylate on the acrylic resin denture teeth resulted in maximum bond strength with composite resin.     

Comparative bond strengths of autopolymerising denture resin and light cured composite resin to denture teeth

AIM: To investigate the shear bond strengths between light cured composite and autopolymerised acrylic resin bonded to acrylic resin denture teeth. METHODS: Surface treatments were used for the denture teeth included wetting with methylmethacrylate (MMA) monomer, composite bonding agent and acid etching. The samples were divided into seven groups. Two groups of specimens were immersed in distilled water for 30 days to hydrate the teeth. Five other groups of embedded denture teeth were stored in air at room temperature for 30 days. RESULTS: Analysis of variance indicated statistically significant differences between groups (P < 0.001). CONCLUSION: The greatest bond strengths to denture teeth were in acrylic resins polymerised with pressure and wetted with monomer. The bond strengths of hydrated and unhydrated samples gave similar results both with acrylic resins and composites.     

Heat-cured acrylic resin repaired with microwave-cured one: bond strength and surface texture

This study evaluated the influence of chemical surface treatments in the repair strength of a heat-cured acrylic resin (Lucitone 550, (LU)). A total of 70 specimens were made with LU according to American Dental Association (ADA) specification No. 12. Of these, 14 remained intact and were used as a control group (GI). A total of 56 specimens were selected randomly. These specimens were cut in the middle (10 mm), repaired with a microwave acrylic resin (Acron MC (AC)), and processed in a microwave oven for 3 min at 500 W. Prior to the repair, the surface of the cut ends received different chemical treatments (GIII = AC monomer dipping/30 s; GIV = acetone dipping/30 s; GV = acetone dipping/15 s + blast of air + AC monomer dipping/15 s; GVI = no wetting treatment). However, 14 intact specimens made with AC formed a second control group (GII). The effect of the chemical treatments on the surface texture of LU was observed with scanning electron microscopy. Flexural test results were submitted to paired t-test and showed statistical differences (P < 0.05) only between the pairs GIV-GV and GIV-GVI. Strength mean values of repaired specimens were statistically lower (79-90%) than GII mean values. Strength mean values of GVI and GIV were 93 and 106%, respectively, of GI mean, showing no statistical differences. Scanning electron microscopic observations revealed various effects of the chemical treatments on the denture base resin surface. In conclusion, the wetting surface treatments affected the bond strength between the two acrylic resins, and no statistical differences in strength were observed between intact heat-cured denture base material and the same material repaired with microwave acrylic resin.     

Comparison of shear bond strengths of different types of denture teeth to different denture base resins

PURPOSETo determine the shear bond strengths of different denture base resins to different types of prefabricated teeth (acrylic, nanohybrid composite, and cross-linked) and denture teeth produced by computer-aided design/computer-aided manufacturing (CAD/CAM) technology.MATERIALS AND METHODSPrefabricated teeth and CAD/CAM (milled) denture teeth were divided into 10 groups and bonded to different denture base materials. Groups 1–3 comprised of different types of prefabricated teeth and cold-polymerized denture base resin; groups 4–6 comprised of different types of prefabricated teeth and heat-polymerized denture base resin; groups 7–9 comprised of different types of prefabricated teeth and CAD/CAM (milled) denture base resin; and group 10 comprised of milled denture teeth produced by CAD/CAM technology and CAD/CAM (milled) denture base resin. A universal testing machine was used to evaluate the shear bond strength for all specimens. One-way ANOVA and Tukey post-hoc test were used for analyzing the data (α=.05).RESULTSThe shear bond strengths of different groups ranged from 3.37 ± 2.14 MPa to 18.10 ± 2.68 MPa. Statistical analysis showed significant differences among the tested groups (P<.0001). Among different polymerization methods, the lowest values were determined in cold-polymerized resin.There was no significant difference between the shear bond strength values of heat-polymerized and CAD/CAM (milled) denture base resins.CONCLUSIONDifferent combinations of materials for removable denture base and denture teeth can affect their bond strength. Cold-polymerized resin should be avoided for attaching prefabricated teeth to a denture base. CAD/CAM (milled) and heat-polymerized denture base resins bonded to different types of prefabricated teeth show similar shear bond strength values.     

Comprehensive Analysis of Repair/Reinforcement Materials for Polymethyl Methacrylate Denture Bases: Mechanical and Dimensional Stability Characteristics

Fracture of complete denture is a common problem as acrylic resins hold inherent limitations. This necessitates affirmation of a selection criterion by evaluating the critical requirements of repair materials. The study intended to evaluate mechanical properties and dimensional stability of common denture base repair and reinforcement materials under standard experimental protocol. Seven types of denture reinforcement materials were chosen. Forty cuboidal samples were made in accordance with ISO 178 for three point bending test and divided to eight groups of five samples each. One group acted as control and samples of seven groups were sectioned and repaired with chosen materials. Five mechanical properties—fracture load, deflection, flexural strength, fracture toughness and elastic modulus were evaluated for all groups. Forty mandibular complete denture specimens were utilized for evaluating fracture load and deflection under loading. Dimensional stability after repair with seven different repair materials was analyzed in two planes (Linear and curvilinear) utilizing separate set of denture samples. Heat cure polymethyl methacrylate with polyethylene fiber was affirmed as material of choice based on this study as it accomplishes the most critical norms of requirement.     

Some variables influencing the bond strength between PMMA and a silicone denture lining material

PURPOSE: The purpose of the present study was to investigate the effect of roughening the denture base surface on the tensile and shear bond strengths of a poly(dimethylsiloxane) resilient lining material (Molloplast-B) bonded to a heat-cured acrylic resin denture base material. These measured bond strengths were compared to those obtained by packing the soft lining material against poly(methyl methacrylate) (PMMA) denture base acrylic resin dough. MATERIALS AND METHODS: Three groups of 10 specimens each were constructed for both tensile and shear tests. In the first group, Molloplast-B was packed against cured PMMA denture base surface. In the second group, Molloplast-B was packed against cured PMMA denture base whose surface had been roughened with an acrylic bur. In a third group, Molloplast-B was packed against PMMA denture base acrylic resin dough. RESULTS: Molloplast-B exhibited significantly higher tensile and shear bond strengths when packed against acrylic resin dough. Roughening the denture base surface prior to the application of Molloplast-B had a statistically significant weakening effect on tensile bond strength compared with the smooth surface and the acrylic resin dough. For the shear bond strength, roughening the surface produced a nonsignificant increase compared with the smooth surface, but the bond was weaker than when packed against acrylic resin dough. CONCLUSION: Significant differences in tensile and shear bond strength were recorded between the three methods used to bond Molloplast-B to denture base material.     

Color stability: Denture base resins processed with the microwave method

Several quick heat-cured denture base resin systems and microwave processing resins have been introduced to provide easier and faster processing. The microwave processing method is the fastest of the heat-cured processing methods. Conventional acrylic resins processed with the microwave method seem to possess adequate physical properties, and one study indicated that a microwave acrylic resin was reasonably color stable under conditions of accelerated aging, although manufacturers do not recommend using them for microwave processing. The purpose of this study was to evaluate the color stability of seven conventional and one microwave heat-cured denture base materials processed with the microwave method. The samples were subjected to conditions of accelerated aging to test for color stability. The color stability was quantitatively measured and color measurements were made before weathering and at 300, 600, and 900 hours. The mean color change for each sample group was statistically analyzed with polynomial regression to determine the pattern of color change over time. The differences in color change for the acrylic resins were significant for all materials, but the color change for Lucitone Hy-pro was not noticeable on visual examination. The results of this study revealed that color changes occurred after accelerated aging in heat-cured denture base resins and Acron GC microwave acrylic resins processed with the microwave method. Hy-pro and TruTone materials exhibited the least color change; Hy-pro material was the most color stable material.