The Effect of Chemical Surface Treatments on the Flexural Strength of Repaired Acrylic Denture Base Resin

Purpose: To investigate the effect of the selected chemical surface treatment agents on the flexural strength of heat‐polymerized acrylic resin repaired with autopolymerized acrylic resin. Materials and Methods: Ninety heat‐polymerized acrylic resin specimens (Meliodent) were prepared according to ISO1567 and randomly divided into nine groups: positive and negative control groups (groups I and II), and seven experimental groups (groups III to IX). Specimens in groups II to IX were cut in the middle and beveled 45°. Group III was then treated with methyl methacrylate (the liquid part of Unifast TRAD) for 180 seconds. Group IV was treated with Rebase II adhesive according to the manufacturer's instructions. Groups V to IX were treated with methyl formate, methyl acetate, and a mixture of methyl formate–methyl acetate at various concentrations (75:25, 50:50, 25:75% v/v, respectively) for 15 seconds. They were then repaired with autopolymerized acrylic resin (Unifast TRAD). A three‐point loading test was performed using a universal testing machine. One‐way ANOVA and post hoc Tukey's analysis at p < 0.05 were used for statistical comparison. Failure analysis was then recorded for each specimen. The morphological changes in untreated and treated specimens were observed by scanning electron microscopy. Results: The flexural strengths of groups III to IX were significantly higher than that of group II (p < 0.05). The flexural strengths of groups IV to IX showed no significant difference among them (p > 0.05). All specimens in groups V to IX showed 100% cohesive failure, while groups II, III, and IV showed cohesive failure of 10%, 60%, and 60%, respectively. From scanning electron micrographs, the application of methyl formate, methyl acetate, and a mixture of methyl formate–methyl acetate solutions on heat‐polymerized acrylic resin resulted in a 3D honeycomb appearance, while specimens treated with methyl methacrylate and Rebase II adhesive developed shallow pits and small crest patterns, respectively. Conclusion: Treating surfaces with methyl formate, methyl acetate, and a mixture of methyl formate–methyl acetate solutions significantly enhanced the flexural strength of heat‐polymerized acrylic denture base resin that had been repaired with autopolymerized acrylic resin.     

Effect of Chemical Disinfectants and Repair Materials on the Transverse Strength of Repaired Heat-Polymerized Acrylic Resin

PURPOSE: The purpose of this study was to evaluate both the effects of immersion in different chemical disinfectant solutions and the type of repair material on the transverse strength of repaired heat-polymerized acrylic resin. MATERIALS AND METHODS: A total of 110 rectangular specimens (65 x 10 x 3 mm) of heat-polymerized acrylic resin (Triplex) were fabricated. After polymerization, the specimens were polished, then stored in distilled water at 37 degrees C for 1 week. The specimens were divided into 11 groups (n = 10) coded A to K. Specimens of Group A remained intact (control). The specimens of Groups C to F and Groups H to K were immersed in the following chemical disinfectant solutions (1%, 2.5%, and 5.25% sodium hypochlorite and 2% glutaraldehyde, respectively) for 10 minutes. The specimens of all groups except those of Group A were sectioned in the middle to create 10 mm gaps and repaired with the same resin (Groups B to F) and autopolymerizing acrylic resin (Groups G to K). The specimens of Groups C to F and Groups H to K were again immersed in the disinfectant solutions in the same sequence. The transverse strength (N/mm(2)) was tested for failure in a universal testing machine, at a crosshead speed of 5 mm/min. Two-way analysis of variance (ANOVA) was performed to evaluate the effects of both the disinfectant solutions and repair materials on the transverse strength of repaired specimens. All data were statistically analyzed using one-way analysis of variance followed by Tukey's test at 95% confidence level. RESULTS: The repaired specimens treated with/without disinfectant solutions showed similar (p > 0.05) transverse strength values. No differences (p > 0.05) were detected among the repaired specimens either with heat-polymerized or autopolymerizing acrylic resins. The intact specimens showed transverse strength values (86.9 +/- 11.8) significantly higher (p < 0.05) than the values of the repaired specimens. CONCLUSIONS: Among the repaired specimens, transverse strength was not affected after immersion in the disinfectants for the immersion period tested (10 min). The repair material, either heat-polymerized or autopolymerizing acrylic resin, had no effect on the transverse strength of the repaired acrylic resin specimens.     

Flexural Strengths of Denture Base Resin Repaired with Autopolymerizing Resin and Reinforcements After Thermocycle Stressing

PURPOSE: Fracture of an acrylic denture base is a common problem in prosthodontic practice. Although various reinforcement methods have been used, when a fractured denture base is repaired with autopolymerizing resin recurrent fractures frequently occur at the repairing interface or adjacent areas. The purpose of this study was to evaluate the maximum flexural load of denture base resin repaired with autopolymerizing resin and several reinforcement systems after thermocycle stressing. MATERIALS AND METHODS: Rectangular (10 x 70 x 3 mm) flexural specimens were fabricated by repairing a pair of heat-cured denture base resin specimens using autopolymerizing resin and a series of reinforcement materials. The materials included 4 metal wires and a woven glass fiber. Each reinforcement was embedded in the center of the specimens. Flexural specimens repaired without reinforcement were prepared as controls. Specimens were subjected to 50,000 thermocycles (4 approximately 60 degrees C, 1-minute dwell time). A 3-point flexural test was carried out by loading the center of the repaired site at 5 mm/minute crosshead speed with 50 mm span jig supports. The load necessary to cause fracture was recorded for each specimen. All data were statistically analyzed using ANOVA and the Bonferroni/Dunn test (alpha < 0.05). RESULTS: The average load to fracture of specimens repaired with nonreinforced autopolymerizing resin was 68.4 N after 50,000 thermocycles. Specimens reinforced with 1.2 mm diameter stainless steel wire exhibited the highest value (89.8 N). The value for specimens reinforced with 1.2 mm diameter Co-Cr-Ni wire was 86.6 N. These fracture loads were significantly higher than those for specimens without reinforcement (p < 0.05). Low elasticity reinforcement, such as pure titanium wires, woven metal wire, and woven glass fiber were not effective in increasing the load to fracture values of flexural specimens. CONCLUSIONS: Specimens reinforced with 1.2 mm diameter stainless steel wires or Co-Cr-Ni wires resulted in significantly higher loads to fracture as compared to specimens without reinforcement. The use of pure titanium wire, woven metal wire, and woven glass fiber did not improve the fracture loads.     

Effect of Surface Preparation Using Ethyl Acetate on the Shear Bond Strength of Repair Resin to Denture Base Resin

Purpose : This study evaluated the effect of using ethyl acetate as a surface preparation agent on the shear bond strength of repair resin to denture base resin.
Materials and Methods : The flat surfaces of a heat-processed denture base resin were prepared with one of the following: (1) without preparation, (2) 60-second application of ethyl acetate, (3) 120-second application of ethyl acetate, (4) 180-second application of ethyl acetate, and (5) 5-second application of dichloromethane. An autopolymerizing repair resin was applied. The specimens were then immersed in 37°C distilled water for 24 hours. The specimens in groups 1, 3, and 5 were thermocycled up to 10,000 times in water between 5 and 55°C with a 1-minute dwell time at each temperature. The shear bond strengths were determined at a crosshead speed of 1.0 mm/min (n = 10). The morphological changes in the repair surfaces after preparation were observed with a scanning electron microscope.
Results : The shear bond strengths of groups 3 and 5 were significantly higher than the other groups before thermocycling ( p < 0.05). The shear bond strengths of group 3 were significantly lower than those of group 5 after thermocycling ( p < 0.05). The scanning electron microscope (SEM) views showed that the dissolution progressed deeper with the preparation duration.
Conclusions : The 120-second surface application of ethyl acetate enhanced the shear bond strength between the repair resin and the denture base resin, although the bond durability was inferior to that of the conventional surface preparation.     

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.     

A Review of Fiber-Reinforced Denture Base Resins

Purpose One method of reinforcing denture base material is to use fiber composite reinforcement. Different types of fibers, such as glass (GF), carbon/graphite, aramid, and ultrahigh-modulus polyethylene (UHMP) fibers have been tested for this purpose. Materials and Methods This article reviews the studies conducted on the fiber-reinforced denture base resin systems. Results The literature has reported that the fiber concentration and its adhesion to polymer matrix influences the transverse strength of the fiber composite. The highest transverse strength value (265 MPa) with polymethyl methacrylate (PMMA) was obtained by incorporating 58 wt% GF into the resin. UHMP fibers incorporated into PMMA resin yielded the highest impact strength value (134 kJm^-2) of the fiber-PMMA composites. Conclusions Despite the improved mechanical properties of fiber-reinforced denture materials, further research is required to show the clinical usefulness of the fiber reinforcement.     

Hardness,Flexural Strength,and Flexural Modulus Comparisons of Three Differently Cured Denture Base Systems

Purpose: This study compared the surface hardness, flexural strength, and flexural modulus of a light‐ and heat‐cured urethane dimethacrylate (UDMA) to two conventional polymethyl methacrylate (PMMA) denture base resins. The effect of less‐than‐optimal processing condition on the hardness of internal and external surfaces of UDMA specimens was also investigated. Materials and Methods: The materials tested were Eclipse (light‐ and heat‐cured UDMA), Meliodent (heat‐cured PMMA), and Probase Cold (auto‐cured PMMA). Eclipse specimens were prepared by adapting the material onto the master cast and light curing in the processing unit for 10 minutes. Meliodent and Probase Cold specimens were prepared according to the manufacturers' instructions. Twenty rectangular specimens measuring 65 × 10 × 2.5 mm³ were prepared for each material. They were stored in water at 37°C for 30 days before testing. The surface hardness was measured using Vickers Hardness (VHN) test, and flexural strength and flexural modulus were measured using a 3‐point bending test. Twenty‐five additional Eclipse specimens were similarly prepared and were processed at various times of less than 20 minutes of curing. Vickers Hardness was determined on both the external and internal surfaces of specimens. Data were analyzed using a one‐way ANOVA for comparisons of hardness, flexural strength, and flexural modulus between the three denture base materials and for hardness values of both the internal and external surface of Eclipse specimens with curing times. Post hoc analyses (Scheffé test) determined the difference between the groups. Student t‐test was used for comparison of hardness between the external and internal surfaces of Eclipse specimens. Results: The hardness (VHN) values were 19.4 ± 0.7, 17.0 ± 0.4, and 16.0 ± 0.4; the flexural strengths (MPa) were 103 ± 4, 78 ± 3, and 63 ± 4; and the flexural moduli (MPa) were 2498 ± 143, 1969 ± 55, and 1832 ± 89 for Eclipse, Meliodent, and Probase Cold materials, respectively. A comparison among the three polymers showed there were significant differences in surface hardness, flexural strength, and flexural modulus (p < 0.05). No significant difference in surface hardness (VHN) between the internal (19.1 ± 0.6 to 19.4 ± 0.7) and external surfaces (18.9 ± 0.4 to 19.2 ± 0.6) of irradiated Eclipse specimens was observed at 10‐, 12‐, and 14‐minute polymerization times. Conclusion: The surface hardness, flexural strength, and flexural modulus of light‐ and heat‐cured UDMA (Eclipse) were significantly higher than the values obtained for heat‐only cured (Meliodent) and auto‐cured (Probase Cold) PMMA denture base systems.     

可见光固化基托树脂研究

研究了可见光固化基托树脂的基质树脂、多功能单体和光引发体系的合成工艺以及粘度调整剂、基托树脂、处理剂、空气遮蔽剂的制备工艺;讨论了基质树脂结构、交联剂结构、光引发体系、光照时间以及不同光源照射等因素对光固化基托树脂物理性能的影响;还讨论了光固化基托树脂的色泽稳定性以及空气遮蔽剂、气泡对光固化基托树脂表面形态的影响。     

In Vitro Tensile Bond Strength of Denture Repair Acrylic Resins to Primed Base Metal Alloys Using Two Different Processing Techniques

Purpose: Approximately 38% of removable partial denture (RPD) failures involve fracture at the alloy/acrylic interface. Autopolymerizing resin is commonly used to repair RPDs. Poor chemical bonding of repair acrylic to base metal alloys can lead to microleakage and failure of the bond. Therefore, ideal repair techniques should provide a strong, adhesive bond. This investigation compared the tensile bond strength between cobalt‐chromium (Super Cast, Pentron Laboratory Technologies, Llc., Wallingford, CT) and nickel‐chromium (Rexalloy, Pentron Laboratory Technologies, Llc.) alloys and autopolymerized acrylic resin (Dentsply Repair Material, Dentsply Int, Inc, York, Pa) using three primers containing different functional monomers [UBar (UB), Sun Medical Co., Ltd., Shiga, Japan: Alloy Primer (AP) Kuraray Medical Inc., Okayama, Japan; and MR Bond (MRB) Tokyuyama Dental Corp., Tokyo, Japan] and two processing techniques (bench cure and pressure‐pot cure). Material and Methods: One hundred and twenty eight base metal alloy ingots were polished, air abraded, and ultrasonically cleaned. The control group was not primed. Specimens in the test groups were primed with one of the three metal primers. Autopolymerized acrylic resin material was bonded to the metal surfaces. Half the specimens were bench cured, and the other half were cured in a pressure pot. All specimens were stored in distilled water for 24 hours at 37°C. The specimens were debonded under tension at a crosshead speed of 0.05 cm/min. The forces at which the bond failed were noted. Data were analyzed using ANOVA. Fisher's PLSD post hoc test was used to determine significant differences (p < 0.05). Failure modes of each specimen were evaluated under a dissecting microscope. Results: Significant differences in bond strength were observed between combinations of primers, curing methods, and alloys. Primed sandblasted specimens that were pressure‐pot‐cured had significantly higher bond strengths than primed sandblasted bench‐cured specimens. The pressure‐pot‐curing method had a significant effect on bond strength of all specimens except Co‐Cr alloy primed with UB. The highest bond strength was observed for both Co‐Cr and Ni‐Cr alloys that were sandblasted, primed with MRB, and pressure‐pot cured. Co‐Cr alloys primed with UB had the lowest bond strength whether bench cured or pressure‐pot cured. Primed specimens generally experienced cohesive bond failures within the primer or acrylic resin. Nonprimed specimens generally experienced adhesive bond failures at the resin/metal interface. Conclusions: Within the limitations of this study, MRB provided the highest bond strength to both Ni‐Cr and Co‐Cr alloys. Generally, bond strength improved significantly when specimens were primed. Pressure‐pot curing, in most cases, resulted in higher bond strength than bench curing. The results of this in vitro study suggest that MRB metal primer can be used to increase bond strength of autopolymerized repair acrylic resin to base metal alloys. Curing autopolymerized acrylic under pressure potentially increases bond strength.