Midline denture base strains of glass fiber-reinforced single implant-supported overdentures.

STATEMENT OF PROBLEM: The fracture incidence of implant-supported overdentures is more frequent in the area of attachment because of stress concentration and denture deformation in this area. How E-glass fiber reinforcement can address this problem is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the influence of unidirectional E-glass fiber reinforcement on the mid-line denture base strains of single implant-supported overdentures. MATERIAL AND METHODS: An experimental acrylic resin cast was constructed with a single implant placed in the mid-line area and a ball attachment screwed to the implant. Twenty-four experimental overdentures were constructed and divided into 4 groups: group AP fabricated from autopolymerizing acrylic resin without fiber reinforcement, group APF fabricated from autopolymerizing acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix, group HP fabricated from heat-polymerized acrylic resin without fiber reinforcement, and group HPF fabricated from heat-polymerized acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix. A biaxial rosette strain gauge was attached to the incisor areas of each overdenture above the attachment level (Ch1, Ch2) and to a multichannel digital strain meter. A static vertical load of 100 N was applied to the first molar area bilaterally by using a universal testing device during strain measurement procedures. The differences in the mean strain and deflection values among the investigated groups were evaluated for statistical significance using 1-way analysis of variance (ANOVA) with the Tukey post hoc multiple comparison (α=.05). RESULTS: The type of acrylic resin did not have a statistically significant effect on the mean strain values among groups (P=.350), while the reinforcement did significantly affect them (P<.001). The interaction between reinforcement and acrylic resin was not statistically significant (P=.552). Both strain gauge channels in group APF and group HPF recorded significantly lower strain values by almost 50% than those of group AP and group HP (P<.05). CONCLUSIONS: Unidirectional E-glass fiber reinforcement placed over the residual ridge and implant attachment significantly reduced denture base strains and deformation of single implant-supported overdentures.

Assessment of CAD-CAM polymers for digitally fabricated complete dentures.

STATEMENT OF PROBLEM: Information on the mechanical properties of the materials used for manufacturing computer-engineered complete dentures is scarce. PURPOSE: The purpose of this in vitro study was to evaluate the mechanical properties of 3 prepolymerized polymethyl methacrylate (PMMA) resins used in the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) milled complete dentures (CDs), as well as 2 denture base polymers used for conventionally fabricated CDs. MATERIAL AND METHODS: Three CAD-CAM materials were evaluated: Degos Dental L-Temp, IvoBase CAD, and Zirkonzahn Temp Basic Tissue. Two materials used for conventionally manufactured dentures were also included as controls (Palapress and Paladon 65). Each material type was sectioned into bars for flexural strength, nanohardness, elastic modulus, and surface microhardness evaluation (n=8/material). Half of the specimens were stored in water for 30 days, while the other half was dry-stored. A 2-way ANOVA was conducted to detect the effect of material and storage on the evaluated properties (α=.05). Linear contrasts were conducted to compare the differences among the 3 types of CAD-CAM material and the conventional ones. RESULTS: Material type and storage had a significant influence on the flexural strength, nanohardness, elastic modulus, and surface hardness of the materials investigated (P<.001). The post hoc Scheffé test for flexural strength revealed a nonsignificant difference in the interaction between Degos L-Temp and Paladon (P=1.000). In terms of nanohardness, no difference was found when comparing Palapress with Paladon, as well as IvoBase CAD with Zirkonzahn Temp Basic (P=1.000). A nonsignificant interaction in terms of surface hardness was also found between IvoBase CAD and Palapress (P=.575). CONCLUSIONS: The tested materials showed variation in their mechanical properties, with satisfactory behavior of the CAD-CAM materials. However, the results obtained when testing the materials used for the conventional fabrication of complete dentures suggest that their use might still be advisable.

Fatigue resistance of a simulated single LOCATOR overdenture system.

STATEMENT OF PROBLEM: The incidence of fracture in a single-implant overdenture base increases in the region adjacent to the fulcrum implant. PURPOSE: The purpose of this in vitro study was to evaluate the effect of bidirectional woven electrical glass (E-glass) fiber reinforcements on the fatigue resistance of a simulated single LOCATOR-retained overdenture. MATERIAL AND METHODS: Test specimens with a centrally positioned metal housing for a LOCATOR stud attachment were fabricated from autopolymerizing acrylic resin. Specimens for the control group were fabricated without glass fiber reinforcements. The 4L group specimens had 4 layers of E-glass fiber weaves and were divided according to the fiber location into the following 3 subgroups: 4L-A with 4 fiber layers above the metal housing; 4L-N with 4 fiber layers adjacent to the metal housing; and 4L-A+4L-N with 4 fiber layers above and 4 fiber layers adjacent to the housing. Specimens were stored in distilled water for 1 week at 23 °C before cyclic fatigue testing at 10 000 cycles by using a staircase approach (n=12). The results were analyzed with 1-way ANOVA and the Tukey multiple comparisons post hoc analysis (α=.05). A 2-way ANOVA (α=.05) was conducted to detect the effect of fatigue cyclic loading and the position of the fiber layers and their interaction on the fatigue resistance. RESULTS: The results of the investigated compressive fatigue limits for the test groups were 190 ±15.9 N for the control group, 265 ±15.9 N for the 4L-A subgroup, 220 ±15.9 N for the 4L-N subgroup, and 275 ±15.9 N for the 4L-A+4L-N subgroup. A nonsignificant difference was found for creep values between the control group and reinforced subgroups (P>.05). The postfatigue flexural strength values in the 4L-A and 4L-A+4L-N subgroups were significantly higher than those in the control group (P<.001) and the 4L-N subgroup (P=.004 and P=.005). However, no significant difference was found in postfatigue flexural strength between the control group and the 4L-N subgroup (P=.828). CONCLUSIONS: Placing 4 layers of bidirectional E-glass fiber weaves above the metal housing can increase the fatigue resistance and the postfatigue flexural strength of single LOCATOR-retained overdentures.

Load-bearing capacity of simulated Locator-retained overdenture system.

STATEMENT OF PROBLEM: Acrylic resin overdenture bases usually fracture because of stress concentrations at the area of the abutments. PURPOSE: The purpose of this study was to evaluate the reinforcing effect of bidirectional woven electrical glass (E-glass) fiber weaves with a different number of layers and different locations on the load-bearing capacity of simulated Locator-retained overdenture specimens. MATERIAL AND METHODS: Test specimens with a centrally located metal housing for a Locator stud attachment were fabricated from autopolymerizing acrylic resin (polymethylmethacrylate based) and reinforced with bidirectional woven E-glass fiber layers. The control group specimens were fabricated without fiber reinforcement. The 2L group had 2 layers of E-glass fiber weaves and was divided according to the fiber location within the specimens as follows: 2L-A subgroup with 2 fiber layers above the metal housing; 2L-N subgroup with 2 fiber layers adjacent to the housing; and 2L-A+2L-N subgroup with 2 fiber layers above and 2 fiber layers adjacent to the housing. The 4L group had 4 layers of E-glass fiber weaves and was divided according to the fiber location as follows: 4L-A subgroup with 4 fiber layers above the housing; 4L-N subgroup with 4 fiber layers adjacent to the housing; and 4L-A+4L-N subgroup with 4 fiber layers above and 4 fiber layers adjacent to the housing. Dry specimens were submitted to a 3-point static loading test, and the mean flexural strength, flexural modulus, and strain values were analyzed with 1-way ANOVA and Tukey post hoc tests (α=.05). Two-way ANOVA was conducted to detect the influence of the number and location of the reinforcing layers (α=.05). RESULTS: The results revealed a significant difference (P<.001) in flexural strength values between the control group (92.4 ±14 MPa) and the 2 subgroups, 4L-A (116 ±7.3 MPa) and 4L-A+4L-N (117.1 ±6 MPa), with a significant effect only from the number of the reinforcing layers (P<.001) and not the location (P=.153). No significant differences were found with flexural modulus (P=.195) and strain values (P=.174) among the tested groups. CONCLUSIONS: The load-bearing capacity of a Locator-retained overdenture can be significantly increased by placing 4 layers of bidirectional woven E-glass fiber weaves either only above the metal housing or in both locations above and adjacent to the metal.

Effect of different surface treatments on shear bond strength of autopolymerizing repair resin to denture base materials processed with different technologies.

PURPOSE: To evaluate the effect of chemical, mechanical, and combination surface treatments on the shear bond strength (SBS) of autopolymerizing repair resins to conventional heat-cured, computer aided design (CAD)-computer aided manufacturing (CAM) milled, and three-dimensionally (3D) printed denture base materials. METHODS: Specimens were fabricated and divided according to the surface treatment as follows: no surface treatment (control group), monomer treatment (monomer group), resin remover treatment (resin remover group), roughening with 180 FEPA grit abrasive paper followed by monomer treatment (180-grit plus monomer group), and air particle abrasion (air abrasion group). Autopolymerizing resin cylinders were attached before accelerated aging of the specimens in water at 100 °C for 16 h. The SBS was tested using a universal testing machine. Surface roughness was evaluated using a 3D optical profilometer. Scanning electron microscopy (SEM) and stereomicroscopy were used for surface analysis. Data was collected and analyzed using analysis of variance (ANOVA) and Kruskall-Wallis tests (α = 0.05). RESULTS: The denture base material and surface treatment significantly affected the SBS. The milled Temp Basic Tissue demonstrated the highest SBS values across all surface treatments, whereas the two 3D-printed denture base materials exhibited the lowest SBS values. CONCLUSIONS: The bond strength of CAD-CAM-milled denture base resins to autopolymerizing repair resins is comparable to that of heat-cured resins. Surface roughening using air particle abrasion or 180-grit carbide paper can enhance the bond strength of the autopolymerizing repair resin to 3D-printed denture base materials.

Mechanical Properties Evaluation of Three Different Materials for Implant Supported Overdenture: An In-Vitro Study.

Aim: the aim of this study was to compare the flexural strength and elastic modulus of three-dimensionally (3D) printed, conventional heat-cured, and high-impact implant-supported overdenture materials specimens. Materials and Methods: Thirty implant-supported overdenture materials specimens (bar-shaped, 65.0 × 10.2 × 5.1 ± 0.2 mm3) with one central hole were fabricated using 3D-printed, heat-cured conventional, and high-impact denture base resins (n = 10/group). Autopolymerizing acrylic resin was used to attach titanium matrix housings to the central holes of the specimens. A three-point bending test was conducted using a universal testing machine and a model analog with a crosshead speed of 5 mm/min. The indicative flexural strength and elastic modulus were recorded. Data were statistically analyzed using analysis of variance (ANOVA) and the Tukey tests at α = 0.05. Results: One-way ANOVA revealed a significant effect of denture base material on the flexural strength (p < 0.001) but not on the elastic modulus (p = 0.451) of the evaluated materials. The flexural strength of the 3D-printed specimens (95.99 ± 9.87 MPa) was significantly higher than the conventional (77.18 ± 9.69 MPa; p < 0.001) and high-impact ones (82.74 ± 7.73 MPa; p = 0.002). Conclusions: The maximum flexural strength was observed in the 3D-printed implant-supported overdenture material specimens, which might indicate their suitability as an alternative to the conventionally fabricated ones. Flexural strength and elastic modulus of conventional and high-impact heat-cured implant-supported overdenture materials specimens were comparable.

Two-body wear and surface hardness of occlusal splint materials.

The aim of this in vitro study was to evaluate the wear and surface hardness of nine materials for conventional manufacturing, subtractive milling, and 3D printing of occlusal splints, as well as to evaluate the differences in wear and surface hardness between rigid and flexible 3D-printed occlusal splint materials. Two-body wear and Vickers hardness tests were performed. The vertical wear depth and Vickers hardness values were statistically analyzed. Vertical wear depth and surface hardness values were statistically significant among the investigated materials (p<0.05). The lowest vertical wear depth was observed for the heat-cured resin (27.5±2.4 µm), PMMA-based milled material (30.5±2.8 µm), and autopolymerizing resin (36.7±6.3 µm), with no statistical difference (p<0.05). Flexible 3D-printed and CAD-CAM milled polycarbonate-based splint materials displayed lower surface hardness and higher wear than the PMMA-based materials. PMMA-based splint materials displayed the most consistent surface hardness and wear resistance regardless of the manufacturing technology.

Evaluation of the mechanical properties and degree of conversion of 3D printed splint material.

OBJECTIVE: To evaluate the effect of post-curing method, printing layer thickness, and water storage on the mechanical properties and degree of conversion of a light-curing methacrylate based resin material (IMPRIMO® LC Splint), used for the fabrication of 3D printed occlusal splints and surgical guides. METHODS: 96 bar-shaped specimens were 3D printed (Asiga MAX), half of them with a layer thickness of 100 µm (Group A), and half with 50 µm (Group B). Each group was divided in three subgroups based on the post-curing method used: post-curing with light emitting diode (LED) and nitrogen gas; post-curing with only LED; and non-post-curing. Half of the specimens from each subgroup were water-stored for 30 days while the other half was dry-stored (n = 8). Flexural strength and flexural modulus were evaluated. Additional specimens were prepared and divided in the same way for surface hardness (n = 96), fracture toughness, and work of fracture (n = 96). Five specimens were selected from each subgroup for evaluating the degree of conversion (DC). Data were collected and statistically analyzed with 1-way, 2-way ANOVA, and Tukey post-hoc analysis (α = 0.05). RESULTS: The 2-way ANOVA showed that the post-curing method and water storage significantly affected the investigated mechanical properties (P < 0.001). The 1-way ANOVA revealed a statistically significant difference among the tested groups on the investigated properties (P < 0.001). After water storage, the 100 µm subgroup post-cured with only LED showed higher flexural strength (51 ± 9) than the 50 µm and 100 µm subgroups that were post-cured with LED in addition to nitrogen gas atmosphere (38 ± 5, 30 ± 3) (p < 0.05). The 50 µm subgroup post-cured with only LED showed the highest significant flexural modulus values (1.7 ± 0.08) (p < 0.05). However, the 50 µm subgroup post-cured with LED plus nitrogen showed significantly higher surface hardness values (p < 0.05) among the investigated groups. The non-post-cured subgroups showed the lowest values, which were significantly different from the other subgroups (p < 0.05). CONCLUSION: The post-curing method, water storage, and printing layer thickness play a role in the mechanical properties of the investigated 3D Printed occlusal splints material. The combination of heat and light within the post-curing unit can enhance the mechanical properties and degree of conversion of 3D printed occlusal splints. Flexural strength and surface hardness can increase when decreasing printing layer thickness.

3D-Printed vs. Heat-Polymerizing and Autopolymerizing Denture Base Acrylic Resins.

The aim of this work was to investigate the effect of two post-curing methods on the mechanical properties of a 3D-printed denture base material. Additionally, to compare the mechanical properties of that 3D-printed material with those of conventional autopolymerizing and a heat-cured denture base material. A resin for 3D-printing denture base (Imprimo®), a heat-polymerizing acrylic resin (Paladon® 65), and an autopolymerizing acrylic resin (Palapress®) were investigated. Flexural strength, elastic modulus, fracture toughness, work of fracture, water sorption, and water solubility were evaluated. The 3D-printed test specimens were post-cured using two different units (Imprimo Cure® and Form Cure®). The tests were carried out after both dry and 30 days water storage. Data were collected and statistically analyzed. Resin type had a significant effect on the flexural strength, elastic modulus, fracture toughness, and work of fracture (p < 0.001). The flexural strength and elastic modulus for the heat-cured polymer were significantly the highest among all investigated groups regardless of the storage condition (p < 0.001). The fracture toughness and work of fracture of the 3D-printed material were significantly the lowest (p < 0.001). The heat-cured polymer had the lowest significant water solubility (p < 0.001). The post-curing method had an impact on the flexural strength of the investigated 3D-printed denture base material. The flexural strength, elastic modulus, fracture toughness, work of fracture of the 3D-printed material were inferior to those of the heat-cured one. Increased post-curing temperature may enhance the flexural properties of resin monomers used for 3D-printing dental appliances.

Characterization of occlusal splint materials: CAD-CAM versus conventional resins.

AIM: The aim of this in vitro study was to assess the mechanical properties of five commercially available subtractive computer-aided design and computer-aided manufacturing (CAD-CAM) milled splint materials, as well as to compare them with conventional heat-polymerized and autopolymerizing resins used in the construction of conventional splints. MATERIAL AND METHODS: Five CAD-CAM milled (ProArt CAD Splint, Therapon Transpa, Temp Premium Flexible Transpa, Cast, and Aqua), one autopolymerizing (Palapress), and one heat-polymerized (Paladon 65) resin materials were evaluated. Flexural strength, E-modulus, Vickers hardness, fracture toughness, fracture work, water sorption, and water solubility were measured. Samples were evaluated after dry and water storage for 30 days at 37 °C. Data were collected and statistically analyzed. RESULTS: Under both storage circumstances, the flexural strength values of Paladon 65, Therapon Transpa, Temp Premium Flexible Transpa, and Aqua were statistically non-significant (P=0.055). The polycarbonate-based CAD-CAM material Temp Premium Flexible Transpa had the highest statistically significant values of the fracture toughness and fracture work (P<0.001). Moreover, it exhibited the lowest percentages of water sorption and water solubility among the investigated materials (P<0.001). All of the CAD-CAM materials exhibited dry elastic moduli greater than Palapress and lower than Paladon 65. One of the CAD-CAM materials, Cast, had the highest dry Vickers hardness value, which was non-significant when compared to Therapon Transpa (P=0.762). CONCLUSION: CAD-CAM polycarbonate-based splint materials exhibit higher fracture toughness and fracture work as well as lower water sorption and solubility than polymethyl methacrylate-based ones. The mechanical characteristics of the assessed CAD-CAM milled splint materials were not typically superior to those of the conventional heat-polymerized resin. However, some of them outperformed the autopolymerizing acrylic resin in terms of flexural strength, surface microhardness, water sorption, and water solubility.

Effect of potassium hydrogen difluoride in zirconia-to-resin bonding.

The objective of this study was to compare potassium hydrogen difluoride (KHF2) etching for zirconia with commonly used surface roughening and chemical bonding methods (silane, MDP-monomer primer) for resin-based luting cement bonding to zirconia. Zirconia specimens were divided into six groups (n=10) according to surface treatment and bonding procedures, with and without thermocycling (6,000 cycles, 5-55ºC): 1) air-borne particle abrasion with alumina+MDP-monomer (ABP), 2) air-borne particle abrasion with silica-coated trialuminium trioxide+silane (ABPR-S) and 3) KHF2 etching+silane (ETC). Surface roughness and bond strength (SBS-test) for dry and thermocycled specimens were measured. SBS did not vary statistically between the dry groups, but thermocycling decreased the bond strengths of all the tested methods (p<0.05). After thermocycling, ABP had statistically significantly lower bond strength values compared to ABPR-S and ETC (p<0.05). Etching method with KHF2 did not provide better bonding capacity to previously introduced and commonly adopted bonding methods.

Effect of specific retention biomaterials for ball attachment on the biomechanical response of single implant-supported overdenture: A finite element analysis.

PURPOSE: The purpose of this finite element analysis (FEA) was to evaluate the effect of specific retention biomaterials with different elastic modulus on the biomechanical response to the axial and off-axial biting loads of a mandibular midline single implant-supported overdenture (SIO) model. METHODS: Five 3-dimensional (3D) finite element models of an edentulous mandible with SIO were designed as follows: model M with a titanium retentive element for ball attachment, model P with a PEEK retentive element, model S with a silicone resilient liner retentive element, model T with a thermoplastic acrylic resin retentive element made from a CAD-CAM material, and model A with a polyacetal resin retentive element. Posterior bilateral vertical load (PV) at the 1st molar areas and anterior oblique load (AO) at the incisal edge of the mandibular central incisors at a 30-degree angle of 100 N were applied. Stress values were recorded. RESULTS: Stress values were higher for all models under (AO) loading than under (PV) loading. Model M recorded the highest stress values on the implant, its components, cortical, and cancellous bone under both loading conditions. Under (AO) loading condition, the ball abutment von Mises stress value in model S was almost 7 times lower than that of model M (19 and 130 MPa respectively) and the other 3 models (P, T, and A) (119, 121, and 120 MPa respectively). However, model S recorded the highest value of denture base stress at the attachment area. CONCLUSIONS: The elastic modulus of retention materials can affect stresses generated on the implant overdenture components and supporting structures.

Flexural strength and flexural modulus of fiber-reinforced, soft-liner retained implant overdenture.

PURPOSE: To compare the flexural strength and modulus of ball-soft liner­retained overdentures vs ballsocket­ retained overdentures, as well as to evaluate the effect of using glass fiber reinforcement on the mechanical properties of ball-soft liner­retained overdentures. MATERIALS AND METHODS: A total of 80 overdenture specimens were fabricated and divided equally into four groups (n = 20/group): specimens with a metal matrix (group 1); a silicone soft liner matrix (group 2); reinforced with one bundle of unidirectional Stick glass fiber placed above the silicone soft liner matrix (group 3); and reinforced with four weaves of bidirectional Stick Net glass fibers placed above the silicone soft liner matrix (group 4). Half of the specimens from each group were stored in water at room temperature (23°C ± 1°C) for 24 hours, while the other half were stored in water at 37°C for 30 days before being subjected to a static three-point loading test. RESULTS: After 1 day of water storage, the flexural strength and flexural modulus values of groups 1, 3, and 4 were not significantly different from each other (P = .788, P = .084), but were significantly higher than group 2 (P < .05). Water storage for 30 days significantly decreased the flexural strength of group 1 only (P < .001) and not the other three groups (P >.05). CONCLUSION: Overdentures retained with a metal matrix were not significantly different from those retained with a silicone soft liner matrix in terms of flexural strength and modulus after 30 days of water storage. Placing unidirectional and bidirectional glass-fiber reinforcement above soft liner matrices can increase the flexural strength of ball-soft liner­retained overdentures.

Layer structure and load-bearing properties of fibre reinforced composite beam used in cantilever fixed dental prostheses.

This study evaluates the effect of fiber reinforcement quantity and position on fracture load of fixed dental prostheses specimens with different fibre reinforced composite (FRC)/ particulate filler composite (PFC) ratio in a cantilever beam test. Three types of specimen structures where made: Specimens with FRC, PFC, or with a combination of both. Specimen's size was 2.0×2.0×25 mm3 and the thicknesses of the FRC layers were 0, 0.5, 1.0, 1.5 and 2.0 mm. The layers of FRC were placed at the top or at the bottom. Eight groups of specimens were evaluated (n=15/group). The test specimens were statically-loaded until fracture. The fracture loads were linearly dependent on the quantity of the FRC reinforcement when placed at the top (R2=0.941) and bottom (R2=0.896) of the specimens. ANOVA revealed that reinforcement position on the tension side and higher FRC reinforcement volume in the test specimens had positive effect to load bearing capacity (p<0.001).

Characterization of the mechanical properties of CAD/CAM polymers for interim fixed restorations.

This study investigated some mechanical properties of five CAD/CAM materials used for the fabrication of provisional restorations and tooth segments for digitally fabricated dentures. The CAD/CAM blocks were sectioned into bars for flexural strength and elastic modulus testing (n=80), and for surface microhardness (n=80). Half of the specimens were water-stored for 30 days while the other half was dry-stored. Additional specimens were prepared for bond strength (n=40). A 2-way analysis of variance (ANOVA) was conducted to detect the effect of material and water storage (α=0.05). Statistical software (IBM SPSS Statistics v21; IBM) was used for conducting all analyses. Material type and storage significantly affected the flexural strength, flexural modulus and microhardness (p<0.001). The type of material did not have a significant effect on bond strength (p>0.05). The tested materials showed variation in their flexural properties and surface microhardness whereas their bonding properties with resin luting cement were similar.

Dual-curing resin cement with colour indicator for adhesively cemented restorations to dental tissues: Change of colour by curing and some physical properties.

The study was aimed to investigate a color indicator containing dual curing resin composite luting cement and to plot the color change to the time of solidification of the cement. In addition some physical properties were studied. Specimens were made of a dual-cure resin cement (Maxcem Elite™ Chroma, Kerr, Orange, CA, USA) and polymerized by autopolymerization only, or with light initiated polymerization. A spectrophotometer was used to quantify the color change of the cement as plotted with the curing time. The efficacy of the curing process was studied by measuring water sorption and the ultimate flexural properties of the cement. The results showed that the flexural strength of cement after autopolymerization was 27.3 MPa and after light initiated polymerization 48.1 MPa. Young's modulus of bending was 2089.3 MPa and 3781.5 MPa respectively for the same cement samples. Water sorption after two weeks for the autopolymerization cement samples was -1.12 wt% and for the light initiated polymerization samples 0.56 wt%. Non-parametric Spearman's correlation was measured for autopolymerized cement samples between variables for color and solidification load (N), which showed a strong correlation between curing process and color change (p < 0.05). There was a correlation between the color change and degree of monomer conversion of the dual curing resin composite luting cement which contained a color indicator system for polymerization reaction. The study also suggested that autopolymerization only resulted in suboptimal polymerization of the cement. By additional light curing considerably higher flexural properties were obtained.

Surface dissolution and transesterification of thermoset dimethacrylate polymer by dimethacrylate adhesive resin and organic catalyst-alcohol solution.

OBJECTIVES: To evaluate transesterification based dissolution of dimethacrylate and epoxy polymers, the former containing ester groups. Polymer substrates were treated with an adhesive resin (Stick™ Resin) and an organic catalyst-alcohol solution (ethylene glycol and triazabicyclodecene). The surface was chemically and nanomechanically analyzed with Fourier Transform-Infrared (FTIR) spectroscopy, surface profile peak (Rp) and nanohardness and modulus of elasticity. METHODS: A total of 100 specimens each of light-cured dimethacrylate polymer and heat-cured diepoxy polymer were prepared. 20 specimens were randomly selected and used as control group (0s). The remaining specimens were randomly divided into 40 each for treatment with an Stick™ resin and ethylene glycol+triazabicyclodecene. Within each group the 40 specimens were randomly subdivided into 20 each for treatment at 5min and 24h, with 10 specimens for FTIR and nanohardness and modulus of elasticity, and the other 10 for SEM and surface Rp analyses. RESULTS: Dimethacrylate polymer showed a reduction in the nanohardness and modulus of elasticity, Rp values and SEM also showed significant topographical changes after being treated with either Stick™ resin or ethylene glycol+triazabicyclodecene, whereas epoxy resin substrate did not. FTIR analyses affirmed changes in the intensity of ester groups. SIGNIFICANCE: Ester group containing dimethacrylate polymer showed a reduction in NMP within 5min of exposure to the treatment agents with softening by solution ethylene glycol+triazabicyclodecene associated to the reduction of ester groups in the polymer structure by transesterification. Epoxy polymer without ester groups was not affected by surface softening with treatment agents. Adhesive resin caused surface swelling.

Resin adjustment of three-dimensional printed thermoset occlusal splints: Bonding properties - Short communication.

OBJECTIVES: To evaluate the interfacial adhesion of an autopolymerizing acrylic resin to 3D printed thermoset occlusal splints compared to thermoplastic occlusal splints. MATERIALS AND METHODS: Cylinders made of an autopolymerizing acrylic resin were adhered to 3D printed thermoset and also to thermoplastic plates. A different surface treatment and three storage conditions were used: dry, 7 days water-storage and 14 days water-storage. Bond strength test (so-called shear-bond strength test) was afterward performed. RESULTS: ANOVA (R2 = 0.764) revealed significant differences in bond strength according to material (p < 0.001) and storage (p < 0.001) but not for surface treatment (p = 0.202). CONCLUSIONS: The bond strength of autopolymerizing acrylic resin to 3D printed thermoset plates is higher when compared to thermoplastic plates. Bonding between acrylic resin and 3D printed splints was high enough for clinical applications.conclusion CLINICAL RELEVANCE: The bond strength values obtained in this study with 3D printed plates were at the level of generally accepted adequate bonding values for prosthetic materials.

Evaluation of the Effect of Monomer Systems on the Softening of a Composite Resin.

PURPOSE: To measure the softening via swelling of a composite resin by evaluating its surface hardness after the application of four monomer systems. MATERIALS AND METHODS: A total of 40 specimens made of a hybrid composite resin were evaluated. Four monomer systems were used as surface-conditioning primers during five exposure times. Surface microhardness measurements (n = 8) were made after application of the monomer systems. RESULTS: In all exposure times, Scotchbond Universal showed the highest influence on the composite resin surface softening (P < .05), followed by Stick Resin (P < .05). CONCLUSION: Surface softening of composite resins might be achieved with monomer systems, especially with Scotchbond Universal, which may have a positive influence when repairing aged composite resin restorations.

Influence of Monomer Systems on the Bond Strength Between Resin Composites and Polymerized Fiber-Reinforced Composite upon Aging.

PURPOSE: This study examined the influence of different monomer systems on the tensile bond strength between a resin composite and a polymerized fiber-reinforced composite (FRC). The influence of the age (shelf-life) of the FRC prepreg (reinforcing fiber pre-impregnated with a resin system) before preparing the FRC substrate for the bonding test was also assessed. MATERIALS AND METHODS: Semi-interpenetrating polymer network (semi-IPN)-based glass FRC prepregs were aged for various durations (1, 1.5, and 3 years) at 4°C before being used to prepare FRC substrates via light polymerization. Four groups of aged prepregs were prepared through different treatments with: 1. no primer; 2. a dimethacrylate-based adhesive primer; 3. a universal primer; and 4. a specific composite primer. Subsequently, a resin composite luting cement was applied on the treated FRC substrates and cured with light. The water sorption of the FRC-composite specimens was determined. Then, the differences in the tensile bond strength were evaluated using ANOVA (p ≤ 0.05). RESULTS: There were significant differences in the tensile bond strength between the composite cement and the FRC according to the primer used (p < 0.001), aging time (p < 0.001), and their interactive effect (p < 0.001). CONCLUSION: The monomers of the universal primer demonstrated the best ability to diffuse into the semi-IPN structure of the polymer matrix of FRC. This improved the interfacial bond strength between the composite cement and the FRC substrate.