Resin Interim Research Articles

CAD-CAM milled dentures: The Geneva protocols for digital dentures

This technical report describes 2 workflows for fabricating computer-aided design and computer-aided manufacturing (CAD-CAM) milled complete dentures (CDs). The first technique illustrates a manufacturer-independent workflow using conventional clinical steps and a novel, custom modified tray to successfully fabricate CAD-CAM milled CDs. The second technique highlights a nearly digital workflow for manufacturing a CAD-CAM milled CD and a milled resin interim removable partial denture.

Comparison of Fracture Resistance of CAD/CAM Interim Dental Bridge and Conventional Interim Resin Dental Bridge

Comparison of Fracture Resistance of CAD/CAM Interim Dental Bridge and Conventional Interim Resin Dental Bridge

Laboratory workflow to obtain long-term injected resin composite interim restorations from an additive manufactured esthetic diagnostic template.

An analogue and digital workflow for the fabrication of a diagnostic 3D printed polymer template and its duplication for long-term injected composite resin interim restorations is described, because of the lack of scientific evidence in 3-dimensional (3D) printing applied to dentistry in terms of printer technology, printer parameters, postpolymerization processes, and material characteristics. In addition, in the case of 3D printed temporary resins, they cannot be relined successfully and its mechanical properties in the mouth have not been tested yet. The main benefits of this approach relate to the improvement of clinical and laboratory procedures, as conventional waxing is eliminated, conventional master casts are not needed and the process is entirely automatized, improving the workflow, with minimal intervention of the laboratory technician. The additive manufactured diagnostic template represents the materialization of the digital diagnostic waxing and provides a powerful tool to visualize the digital diagnostic waxing in the patient's mouth and face. Furthermore, the diagnostic 3D printed template can be used for multiple applications including interim restorations, radiographical, or surgical guide fabrication. The duplication technique described provides a predictable workflow to obtain long-term injected resin composite restorations from an additive manufactured esthetic diagnostic template, improving the laboratory and chairside procedures.

Physical properties of two bis-acryl interim materials: color stability, flexural strength and shear bond strength to flowable composite resin as add-on material

The objective of this study was to evaluate the mechanical properties of two bis-acryl interim resin materials, such as color stability, flexural strength and shear bond strength to flowable composite resin, simulating clinical situations when this material has to be used for repair as add-on. Two shades of two bis-acryl interim resin materials [Structur 2 SC (shades Bleach and A2); Protemp 4 (shades A1 and A2)] were evaluated. Discs (5 x 1 mm) were fabricated and baseline color was determined after 1 h. Ten specimens were immersed at 37oC in solutions of distilled water (control) and cola-based soft drink (Coca-Cola). Color measurements were performed with a spectrophotometer using CIELab parameters. Color readings were again measured after 2 hours, 4 hours, 24 hours and 7 days. Flexural strength was determined using the three-point bending test (10 x 1 x 2 mm) on a universal testing machine (0.5 mm/min) (n = 10). Discs of bis-acryl resin were embedded in acrylic resin, planned and distributed in 2 groups: G1 - Filtek Z350 Flow/Protemp4 and G2 - Grandio SO Flow/Structure 3 (n = 15). Cylinders (3.5 x 2 mm) were made with the flowable composite resins and polymerized for 20 s. The specimens were stored in distilled water at 37oC for 24 h and subjected to shear bond strength test. Data were analyzed using one-way ANOVA and Tukey’s test ( = 0.05). ΔE values were higher for Structur Bleach (3.08)a compared with Protemp 4 (shade A1, 2.22)b (shade A2, 2.25)b. There were no significant differences between Structur Bleach and Structur A2 (2.62)ab. Coca-Cola presented higher ΔE values (3.08)a than (2.00)b. Regarding time, ΔE values increased from 1.84a after 2 h to 2.31b after 4 h. The higher values were observed after 24 h and 7 days (2.93c and 3.09d, respectively). No significant differences were observed for the flexural strength of Structur (22.05 MPa)a and Protemp 4 (19.01 MPa)a. The repairs executed with Structur/Grandio flow (9.21 MPa)a were similar to those performed with Protemp 4/Z350XT flow (10.71 MPa)a. It can be concluded that the two bis-acyl resins evaluated showed similar physical and mechanical properties.

Cytotoxicity and proinflammatory cytokine expression induced by interim resin materials in primary cultured human dental pulp cells

Statement of problemAcrylic resin materials for interim restoration may adversely affect pulp tissue during the polymerization phase. PurposeThe purpose of this in vitro study was to determine the cytotoxic and proinflammatory cytokine production effects induced by interim resin materials in primary cultured human dental pulp cells (hDPCs). Material and methodsFive interim resin materials were evaluated: 3 types of chemically activated products, 1 light-activated product, and 1 computer-aided design and computer-aided manufacturing (CAD-CAM) product. After obtaining eluates from interim resin materials that either were in the process of polymerizing or were already polymerized, these extracts were cocultured with hDPCs under serially diluted conditions (50%, 25%, 12.5%, 6.25%, and 3.125%) for 24 hours with positive (1% phenol) and negative (distilled water) controls. A cell viability assay with tetrazolium was used to evaluate toxic effects on the cells, and images of both live and dead cells were captured using confocal microscopy. Proinflammatory cytokine levels were measured using cytokine antibody arrays. All experiments were independently repeated 3 times, and data were analyzed using 1-way ANOVA and post hoc Tukey honest significant differences test (α=.05). ResultsCell viabilities less than 70% were observed from the eluates of the 3 chemically activated products under the 50% conditions. Among the chemically activated products, the adverse effects were significantly greater with eluates derived from the polymerizing phase compared than those that had already polymerized, as shown by confocal microscopy images of live and dead cells. However, the light-activated and CAD-CAM-fabricated products did not adversely affect the hDPCs. Significantly increased levels of proinflammatory cytokines were not detected in 12.5% of extract from polymerizing compared with distilled water control. ConclusionsThe 50% eluates derived from chemically activated interim resin during the polymerizing phase were cytotoxic to hDPCs and may adversely affect pulp tissue. Recommendations such as excess washing are necessary during fabrication.

Evaluation of Flexural Strength of Thermocycled Interim Resin Materials Used in Prosthetic Rehabilitation- An In-vitro Study.

Provisional restoration is an analytical component of fixed prosthodontics serving as a ground plan for the design of fixed dental prosthesis. Flexural strength is critical in case of long standing fixed dental prosthesis, to appreciate success of full mouth rehabilitation cases and temporomandibular joint dysfunction therapies. The present study was to evaluate the flexural strength of different provisional restorative resins used for prosthetic rehabilitation. Forty identical samples (n=10 for each material) measuring 25mm×2mm×2mm according to ADA/ANSI specification no. 27 were fabricated using autopolymerizing Poly Methyl Methacrylate (PMMA) (Group A); heat activated PMMA (Group B); autopolymerizing Bis-GMA composite resin (Group C) and light activated Urethane Dimethacrylate Resin (UDMA) (Group D). For 14 days all these samples were stored in artificial saliva. Ten samples from each material were subjected to thermal cycling for 2500 cycles (5°C to 55°C). Later, a standard three point bending test was conducted on all the specimens with a universal testing machine at a crosshead speed of 0.75mm/min. Statistical analysis used included Kruskal-Wallis and Mann-Whitney U test. The mean flexural strength of specimens confirmed higher flexural strength for Group C (102.98 Mpa) followed by Group B (91.86 Mpa), Group A (79.13 Mpa) and Group D (60.01 Mpa). There were significant differences between any two materials tested (p <0.05). Comparison between mean flexural strength values between four groups revealed significant difference between the interim materials (p <0.05). The greatest flexural strength was observed for Bis-GMA composite resins followed by heat cure methacrylate resins, autopolymerizing methacrylate resins and was least for light cure resins. While fabricating provisional restorations, these greater values should be considered for better outcome of the treatment.

Fabricating an Accurate Implant Master Cast: A Technique Report.

The technique for fabricating an accurate implant master cast following the 12-week healing period after Teeth in a Day® dental implant surgery is detailed. The clinical, functional, and esthetic details captured during the final master impression are vital to creating an accurate master cast. This technique uses the properties of the all-acrylic resin interim prosthesis to capture these details. This impression captures the relationship between the remodeled soft tissue and the interim prosthesis. This provides the laboratory technician with an accurate orientation of the implant replicas in the master cast with which a passive fitting restoration can be fabricated.

Evaluation of add-on methods for bis-acryl composite resin interim restorations

Statement of problemInterim restoration materials should allow easy add-on for repair and modification; however, bis-acryl composite resins are reported to have unfavorable performance in this regard. PurposeThe purpose of this study was to find a suitably effective add-on method for bis-acryl interim composite resins. Material and methodsA control group with a new type of bis-acryl material added to the same bis-acryl disks (n=10) was compared to 9 experimental groups (n=20) divided on the basis of their surface conditions: oxygen-inhibited unpolymerized layer preserved; ground; ground and treated with a light-polymerizing bonding agent, with or without a synthetic polyester film (Mylar) cover strip to control oxygen-inhibited unpolymerized layer; with bis-acryl, bis-GMA flowable composite, or poly-methyl methacrylate (PMMA) resins as add-on materials. PMMA specimens added with PMMA resin served as a parallel control group (n=20). Half of the experimental and PMMA control specimens were thermocycled 2000 times at 5 ±2°C and 55 ±2°C. Shear bond strength (SBS) results were then compared using 2-way and 1-way ANOVA and a Tukey honest significant difference (HSD) test (α=.05). ResultsNo significant differences were found between SBS of PMMA and those of bis-acryl controls (21.74 and 17.47 MPa, respectively), with all of the experimental groups exhibiting values comparable to the controls and unaffected by thermocycling. The highest SBS (35.58 MPa) was obtained with the bis-GMA-added group, in which the surface was ground and treated with a bonding agent (P<.05). With the bis-acryl resin and bonding agent group, additional light polymerizing significantly increased the SBS from 15.58 to 23.80 MPa (P<.05). ConclusionsBis-acryl-based interim material has favorable add-on properties, which are improved by additional surface treatment and use of a flowable composite resin.

Comparison of fiber reinforcement placed at different locations of pontic in interim fixed partial denture to prevent fracture: An in vitro study.

Background:The interim restoration is an important phase in fixed prosthodontic therapy. It should provide sufficient durability to withstand the forces of mastication. A fractured interim restoration is damaging to the prosthodontic care and may lead to an unscheduled appointment for repair. Several attempts have been made to reinforce interim fixed partial dentures (FPDs). These have included the use of metal wire, a lingual cast metal reinforcement, a processed acrylic resin interim restoration, and different types of fibers, e.g., carbon, polyethylene, nylon and glass. These fibers can be placed in the occlusal, middle or cervical thirds in the FPD. There is no scientific data to evaluate the effect of fiber placement methods on the fracture resistance of clinical interim FPDs.Purpose of the Study:Hence this study was designed to evaluate fracture load values of interim FPDs with different locations of fiber reinforcement.Materials and Methods:30 interim FPD samples with polymethyl methacrylate (PMMA) reinforced with fibers at three different locations mainly occlusal, cervical and middle (10 samples each) were fabricated using a metal FPD on a master die. They were tested for fracture resistance in universal testing machine.Results:The fracture resistance was recorded and is tabulated and analyzed statistically. The results showed that the placement of the reinforcement in the occlusal third of the pontic resulted in higher fracture resistance which was significantly higher (P < 0.05) than all other locations.Conclusion:The occlusal third of the pontic region from mesial to the distal end of the connector is the best site of placement of the fiber for reinforcing the PMMA interim restorative resin.

Contribution of postpolymerization conditioning and storage environments to the mechanical properties of three interim restorative materials

Because polymer-based interim restorative materials are weak, even well-made restorations sometimes fail before the definitive restoration is ready for insertion. Therefore, knowing which fabrication procedures and service conditions affect mechanical properties is important, particularly over an extended period. The purpose of this study was to evaluate the effect of thermal treatment, surface sealing, thermocycling, storage media, storage temperature, and age on autopolymerizing poly(methylmethacrylate) and bis-acryl interim restorative materials. Outcome measures were flexural strength, Vickers surface microhardness, and impact strength. Flexural strength and microhardness of poly(methylmethacrylate) (Jet Acrylic) and 2 bis-acryl-composite resin (Protemp 3 Garant and Integrity) interim restorative materials were evaluated as affected by storage media, storage temperature, storage time, thermocycling, postpolymerization thermal treatment, or application of a surface sealer. In total, 2880 beam specimens (25×2×2 mm) were fabricated. Mechanical property analyses were made at 10 days, 30 days, 6 months, and 1 year after specimen preparation. Flexural strength was determined by using a 3-point bending test in a universal testing machine with a 1 kN load cell at a crosshead speed of 5.0 mm min(-1). Fracture specimens were recovered and used for determining Vickers microhardness. Measurements were made with a 0.1 N load and 15 second dwell time. Three microhardness measurements were made for each specimen, and the mean was used for reporting Vickers microhardness. Notched impact specimens (64×12.7×6.35 mm) were fabricated from Jet, Protemp 3 Garant, and Integrity interim restorative materials, yielding 288 impact specimens. Impact strengths were assessed at 10 days, 30 days, 6 months, and 1 year with a 2 J pendulum. The effects of the various experimental treatments were determined and rank ordered with analysis of variance, F ratios, and least square means differences Student t tests (α=.05). All experimental treatments investigated had significant effects on flexural strength, with material (P<.001) and thermocycling (P<.001) being dominant. Moreover, all experimental treatments investigated had a significant overall impact on Vickers microhardness with material (P<.001) and Palaseal glaze (P<.001) showing large effects. Material (P<.001) and age (P=.010) had a significant effect on impact strength. Mechanical properties of some interim polymeric materials can be improved by postpolymerization heat treatments or surface glazing. This procedure may extend the useful lifetime of some bis-acryl interim restorations.

Comparison of the flexural strength and marginal accuracy of traditional and CAD/CAM interim materials before and after thermal cycling

Limited information is available concerning the properties of computer-aided designed/computer-aided manufactured (CAD/CAM) interim materials. The purpose of this study was to investigate the flexural strength and marginal accuracy of 2 traditional bis-acryl composite resin interim materials (Protemp 4 and Structur 2 SC/QM) and 2 CAD/CAM interim materials (Teilo CAD and VITA CAD-Temp). Standard specimens (25× 2× 2 mm) of the 4 materials were made (n=20). Each group contained 10 specimens fractured under 3-point loading in a universal testing machine with a cross-head speed of 1 mm/min. The other 10 specimens were subjected to 5000 thermal cycles (5°C and 55°C) before testing. Four groups of interim crowns were fabricated from the 4 materials on models of a prepared left maxillary first molar (n=10). Twenty-four hours after cementing the crowns, margin discrepancies were measured under a stereomicroscope. The crowns then were subjected to 5000 thermal cycles (5°C and 55°C), and the margin discrepancies were measured again. Teilo CAD showed the highest mean flexural strength of the 4 interim materials before and after thermal cycling, and VITA CAD-Temp showed the lowest (P<.05). After thermal cycling, the flexural strength decreased significantly (P<.05). The margin discrepancies were larger for the bis-acryl interim crowns than for the CAD/CAM crowns before and after thermal cycling (P<.05). After thermal cycling, the margin discrepancies in the bis-acryl interim crowns were larger (P<.05); however, no significant differences were found for the margin discrepancies in the CAD/CAM interim crowns (P>.05). CAD/CAM interim materials were stronger and had better marginal accuracy properties than bis-acryl materials, especially after thermal cycling.

Effect of polyhedral silsesquioxane (POSS) on the flexural strength and color of interim materials

Polyhedral silsesquioxane (POSS) nanofillers can reinforce interim materials. However, the interaction between the POSS and the brand and its effect on color are unknown. The purpose of this study was to determine the effect on the flexural strength, color, and color stability of 4 commercially available interim materials modified with 1 wt% POSS. Four commercial interim resin materials were used in this study: Jet, Trim, Temphase, and Protemp. The flexural strength of the interim materials was measured with and without 1 wt% POSS with an Instron universal testing machine. The color of the interim material and the material with 1 wt% POSS were evaluated, followed by the evaluation of the color change after coffee staining. The data were analyzed with a 2-way analysis of variance (ANOVA) followed by the Tukey standardized range test (HSD) to determine statistical significance (α=.05). POSS enhanced the flexural strength of Protemp and Trim but had no effect on Temphase and Jet. POSS had a significant affect on the color (L*, a*, b*), but only 2 pairwise differences (in L* Trim versus Trim POSS and in a* Temphase versus Temphase POSS) were detected. The effect of POSS on color change after coffee staining was minimal. POSS only had a significant effect on ΔL, and only 1 pairwise difference was detected (Temphase versus Temphase POSS). The collapsed means revealed significant differences in color change among brands after coffee staining. The reinforcement effect of POSS on flexural strength depended on the brand, suggesting that the chemistry of the resin affects the ability of POSS to modify mechanical properties. POSS affected the initial color of the interim materials but had little effect on the color change after coffee staining.

Mechanical properties of urethane and bis-acryl interim resin materials

The fracture or dislodgement of an interim prosthesis may result in additional appointments and could negatively affect the outcome of a fixed prosthodontic procedure. The purpose of this study was to evaluate the flexural strength (FS), flexural modulus (FM), work-of-fracture (WOF), and Weibull parameters of 4 bis-acryl (Protemp Plus, Integrity, Turbo Temp 2, Temphase Fast-set) and 2 urethane (NuForm and Tuff-Temp) interim resins after being stored in distilled water for 1 hour and 24 hours. Rectangular beam specimens (25 × 2 × 2 mm) of each resin (n=23) were prepared and stored in distilled water at 37°C. Then 3-point bending tests were performed on 1-hour and 24-hour (wet) and 24-hour (dry and wet) specimens in a universal testing machine at a cross-head speed of 1.0 mm/min. Stress/strain curves were generated and flexural strength, flexural modulus, and WOF values were calculated. Data were subjected to 3-way ANOVA and the Tukey-Kramer pairwise comparison test (α=.05). FS data were also subjected to a 2-parameter Weibull analysis. The 24-hour (wet) mean flexural strength and flexural modulus values were significantly higher than 1-hour values. The urethane Tuff-Temp, chemically and dual-polymerized, showed significantly higher (P<.05) 1-hour FS and FM, while the bis-acryl Protemp Plus showed significantly greater flexural strength and work-of-fracture than the other resins after 24 hours of wet storage. Protemp Plus, NuForm, and Turbo Temp 2 did not decrease in flexural strength and flexural modulus after 24 hours in dry and wet storage conditions. The Weibull modulus values of the flexural strengths of the interim resins at 1 hour and 24 hours ranged from 8.4 to 26.8. Postgelation polymerization plays an important role in the substantial increase in the flexural strength and flexural moduli of the interim resins between 1 and 24 hours. A wide variation in the mechanical properties of the interim resin materials was noted but was, for the most part, not category specific.

Minimally invasive treatment of the atrophic posterior maxilla: A proof-of-concept prospective study with a follow-up of between 36 and 54 months

In the posterior maxilla, tooth loss is usually associated with alveolar bone resorption and sinus pneumatization, limiting the placement of implants without grafting procedures. The purpose of this study was to evaluate a minimally invasive treatment of the atrophic posterior maxilla, with axial and tilted implants and immediate loading. The research hypothesis was that the combination of a guided, minimally invasive approach and the biomimetic features of computer-aided design and computer-aided manufacturing (CAD/CAM) abutments would be an effective alternative to maxillary sinus floor augmentation procedures with reduced bone resorption around implants. Twenty-seven consecutive participants (female=12, male=15) (mean age 54.18 years) with severe atrophy of the posterior maxilla were treated by using guided surgery with immediately loaded axial (39) and tilted (42) implants supporting CAD/CAM zirconia (39) and titanium (42) abutments (81 total) and partial fixed prostheses. Each participant underwent a computed tomography scan, after which 2 or 3 implants were positioned with a flapless or miniflap approach. The drilling protocol was adapted to the bone density of each implant site to obtain an insertion torque ranging between 40 and 50 Ncm. CAD/CAM customized abutments composed of zirconia or titanium were fixed to the implants with prosthetic screws tightened with a torque of 35 Ncm. An acrylic resin interim restoration reinforced with metal was placed immediately. Five to 6 months after initial loading, a zirconia framework was manufactured, and a definitive prosthesis was placed. Clinical and radiological controls were performed at baseline and after 1 and 3 years to assess implant and prosthesis survival and success rate and compare marginal bone remodeling of axial and tilted implants. Inferential statistics for radiological data were acquired by using the Mann-Whitney U-test. All statistical comparisons were conducted at the .05 significance level. The mean follow-up period was 43.3 months (ranging from 36 months to 54 months). The cumulative implant survival rate was 96.3% at 3 years. All prosthetic restorations were stable and in good function, resulting in a cumulative prosthetic survival rate of 100%. Three restorations had chipping of the veneer material; thereafter, the cumulative prosthetic success rate was 91.9%. Treatment of the posterior partially edentulous atrophic maxilla with guided surgery and immediate loading of tilted and straight implants supporting short-span partial fixed dental prostheses is effective.

Evaluation of flexural strength of resin interim restorations impregnated with various types of silane treated and untreated glass fibres

BackgroundFlexural strength is an important mechanical property that determines the long-term prognosis of interim restorations. Studies are lacking regarding the effect of silanation of the various types of glass fibre impregnation on the flexural strength of resin interim restorations. MethodsA customized metal die was milled to simulate the prepared abutments of a three-unit fixed dental prosthesis. A total of seventy five samples of interim fixed dental prostheses were prepared using autopolymerizing tooth colour acrylic resin. Unidirectional and woven forms of glass fibres (Stick and Stick Net), which were silane treated and untreated were used to reinforce the resin matrix. Fifteen samples were prepared for each group along with unreinforced group serving as control. The flexural strength was evaluated with universal testing machine. ResultsThe means and standard deviations of flexural strength for different groups were 13.90 ± 2.96 (control), 61.58 ± 5.26 (unidirectional fibres), 30.89 ± 3.60 (woven fibres), 112.05 ± 5.51 (silane treated unidirectional fibres) and 73.85 ± 4.10 (silane treated woven fibres) respectively. The mean flexural strength of silane treated unidirectional fibres (112.05 MPa) was highest and statistically highly significant (P < 0.0001) compared to all other groups. ConclusionsWithin the limitations of the current study, flexural strength of the reinforced PMMA interim fixed dental prosthesis was significantly higher (P < 0.0001) when compared to the unreinforced PMMA interim fixed dental prosthesis. The use of silane treated unidirectional glass fibres is an effective method of reinforcing interim fixed restorations made of PMMA resins.

Relative fracture toughness of bis-acryl interim resin materials

Fracture of the interim partial denture may cause patient discomfort and result in unplanned appointments and expense. At present, limited information is available concerning the fracture toughness of bis-acryl interim resins, especially immediately following fabrication. The purpose of this investigation was to evaluate the relative fracture toughness and Weibull parameters of 4 commercial chemically polymerized (Protemp Garant 3, Perfectemp II, Integrity, Temphase) and 1 dual polymerizing (Luxatemp Solar) bis-acryl interim resin materials with various filler loading after 1 hour and 24 hours. Disk-shaped, mini-compact test specimens (8.20 × 1.85 mm thick, n=18) with introduced pre-cracks were prepared in a pre-heated split-mold and maintained at 37°C for 5 minutes during polymerization to simulate clinical conditions. Polymerization temperature was measured using an infrared digital thermometer. Specimens were stored in distilled water at 37°C after which the peak load to fracture was recorded at 1 and 24 hours and the fracture toughness (K(1c)) was calculated. An overall Weibull analysis of the fracture toughness was performed incorporating the fracture toughness data with factors polymerization method, time of testing and filler load of the resin. Weibull analysis was performed at (α =.05). Fracture surfaces of representative specimens were examined using scanning electron microscopy. The overall Weibull analysis results showed significant differences (P<.001) in fracture toughness between the times of testing (1 and 24 hours), polymerization method, and as a function of filler loading. The results of the individual Weibull survival analyses showed a significant increase in Weibull Characteristic Strength (σo) values between 1 and 24 hours for all materials. The Weibull moduli (m) for the interim resins ranged between 5.8 and 10.3. SEM analysis of fractured surfaces revealed that crack propagation occurred primarily through the resin matrix between filler particles. Post-gelation polymerization has an important role in determining the fracture properties of both chemical and dual-polymerized bis-acryl interim materials within the first 24 hours. For the materials tested, the higher the filler load, the lower the fracture toughness.

Flexural Strength of Interim Resin Materials for Fixed Prosthodontics

Flexural strength of interim materials is of particular concern with long-span fixed partial dentures (FPDs) or in areas of heavy contact. The purpose of this study was to compare the flexural strength of seven resins used to fabricate interim fixed prostheses. Ten identical 25 x 2 x 2 mm specimens were made from seven interim materials (N = 70) (Trim, Acropars, Protemp 3 Garant, Unifast LC, TempSpan, Tempron, Duralay) according to ADA specification #27. After 14 days' storage in artificial saliva and thermocycling for 2500 cycles (5 C to 55 C), a standard three-point bending test was conducted on the specimens with a universal testing machine at a crosshead speed of 0.75 mm/min. The mean values of flexural strength of each interim material were calculated. Data were analyzed using the Kruskal-Wallis and Mann-Whitney U-test, and the significance level was set at alpha= 0.05. The lowest and highest flexural strengths were found for Trim from ethyl methacrylate resins and TempSpan from bis-acryl resins, respectively. The mean rank of flexural strength of the studied materials was TempSpan = 66.3, Protemp 3 Garant = 53.4, Tempron = 47.5, Duralay = 38.3, Unifast LC = 24.1, Acropars = 17.9, and Trim = 5.9. There was no significant difference between Tempron and Protemp 3 Garant, but the other resins were significantly different. Bis-acryl interim materials exhibited higher flexural strength than the methacrylate resins tested in this study. These higher values should be considered in making interim fixed prostheses, especially when long-term use or long-span FPDs are planned.

Changes in marginal gap size of provisional resin crowns after occlusal loading and thermal cycling

Statement of Problem: Resin materials used for provisional crowns tend to develop enlarged marginal gaps over time. With the advent of new interim resin materials in dentistry that are used for longer clinical periods, controlled comparative analysis of the structural stability of these materials in the oral environment is required. Purpose: This study analyzed marginal gap size changes resulting from occlusal loading and thermal cycling and related these results to material properties. Material and Methods: Groups (n = 10) of provisional crowns were made using 4 resin materials (Jet-relined, Snap-relined, Snap-unrelined, Alike-unrelined). Specimens were first fabricated on a metal master die and fitted with and relined on the master die to standardize pretreatment marginal gap size. Custom die stems were fabricated from a low-fusing alloy (Cerroblend) and cemented with Tempbond cement. The samples were treated with occlusal loading (50,000 cycles, 40 N, 4 Hz) and thermocycling (8,000 cycles, 5°C to 60°C). Measurements of marginal gaps were recorded before and after treatment. Results: The mean changes in marginal gap sizes were Jet-relined, 152.1 μm ± 69.6; Snap-relined, 548.9 μm ± 168.3; Snap-unrelined, 446.6 μm ± 91.8; and Alike-unrelined, 43.9 μm ± 48.7. Two-way ANOVA revealed a significant difference between groups (F=51.758, df 3,1, P≤ .0001). Tukey/Kramer (P ≤.01 level) indicated a significantly larger gap increase for the Snap-relined and Snap unrelined groups. Conclusion: There were significant differences between different brands of resin materials used for provisional crowns. Each must be evaluated individually for stability in the oral environment. (J Prosthet Dent 2000;84:139-48.)