Development of a fiber-reinforced material for fiber posts: Evaluation of stress distribution, fracture load, and failure mode of restored roots.

STATEMENT OF PROBLEM: The biomechanical behavior of post-restored roots with an experimental fiber-reinforced composite resin is unknown. PURPOSE: The purpose of this in vitro study was to investigate the biomechanical behavior of an experimental composite resin (3-mm short glass fiber incorporated in methacrylate matrix with filler particles) used to produce the custom post itself or to reline fiber posts. MATERIAL AND METHODS: Four testing groups (n=10) were created according to the root restoration method: FG, commercially available fiber post; FG+RC, fiber post relined with conventional composite resin; FG+EXP, fiber post relined with the experimental composite resin; and EXP, a custom post made of experimental composite resin. A three-dimensional finite element linear elastic analysis was performed by using geometric representations of groups, and the results were analyzed by von Mises (σvM) and maximum principal stress criteria. In sequence, 40 bovine incisors were assigned to these groups and subjected to a fracture load test (Instron 5965; 0.5 mm/min), and the failure mode was determined. RESULTS: The EXP group showed more homogeneous stress distribution for σvM. ANOVA and the Tukey honestly significant difference (HSD) tests showed significant differences (P<.001) in fracture load (mean ±standard deviation; different superscript letters indicate statistical difference): FG+EXP (669.5 ±107.7)A; FG (620.7 ±59.2)A; EXP (506.5 ±27.0)B; FG+RC (452.7 ±81.6)B. No differences were found for failure mode (P=.595). CONCLUSIONS: The experimental composite resin significantly increases fracture load when used to reline commercially available fiber posts and, irrespective of its use, presented lower stress concentration.

Influence of activation mode of resin cement on the shade of porcelain veneers.

PURPOSE: The aim of this study was to evaluate the influence of resin luting cement's activation mode in the final shade of porcelain veneers after accelerated artificial aging (AAA). MATERIALS AND METHODS: Porcelain veneers (IPS Empress Esthetic) were produced using a standardized shade (ET1) and thickness (0.6 mm). Twenty bovine teeth were collected, prepared, and divided into two groups: group I (n = 10)-light-cured group, only base paste was applied to the veneers; group II (n = 10)-dual-cured group, in which the same base paste used in group I and a transparent catalyst were proportionally mixed for 20 seconds and then applied to the veneers. The specimens were light-cured for 60 seconds each and were next subjected to AAA. They were submitted to color readings with a spectrophotometer in three instances: in the tooth surface (only the substrate), after the cementation and polymerization of the veneers, and after the AAA. The values of L*, a*, and b* were obtained and the total color change was calculated (∆E*). Values obtained were subjected to statistical analysis, with a significance of 0.05. RESULTS: There were no significant differences between dual- and light-cured modes considering ∆E*, L*, a*, and b* values obtained after aging (p > 0.05). Within the dual-cured mode there were no significant differences in ∆E*, L*, a*, and b* values (p > 0.05). CONCLUSION: No relevant differences were found between the two activation modes in color change. When submitted to aging, dual- and light-cured modes of the resin cement showed visually perceptible (∆E* > 1.0) color changes; however, within the threshold of clinical acceptance (∆E* > 3.3).

Influence of preheating and post-curing on a novel fiber-reinforced composite post material.

The aim of this study was to investigate the influence of preheating and post-curing methods on diametral tensile strength (DTS), flexural strength (FS), knoop microhardness (KHN), and degree of conversion (DC) of an experimental fiber-reinforced composite (FRC). Specimens (30 wt% of 3-mm-short E-glass fiber, 22.5 wt% of methacrylated-based resin and 47.5 wt% of filler particles) were subjected to: P - photocuring at 1500 mW/cm2 for 40 s (control); P/M - photocuring and microwave post-curing (540W/5 minutes); P/A - photocuring and autoclave post-curing (120°C/15 minutes); PH-P - preheating (60°C) and photocuring; PH-P/M - preheating, photocuring and microwave post-curing; and PH-P/A - preheating, photocuring and autoclave post-curing. Specimens for DTS (Ø 3 x 6 mm) and FS (25 x 2 x 2 mm) were tested at Instron 5965. KHN employed a 50g load for 30s. DC was measured using FTIR spectroscopy. Statistical analysis employed: factorial analysis, normality test, one-way ANOVA and Tukey's HSD test, independent T-test and the Dunnett test. Interaction between factors was not significant (P>0.05). Preheating promoted significantly higher values of FS and KHN (p = 0.0001). Post-curing promoted significantly higher values for KHN (p = 0.0001). For DTS (p = 0.066) and DC (p= 0.724) no statistical difference was found between groups. SEM images showed that preheating promoted better interaction between glass fibers and resin matrix. Preheating increased FS, KHN and DTS, and post-curing increased KHN. DC was not affected by both methods. Preheating and post-curing methods can be used to improve some mechanical properties of FRCs' but degree of conversion remains unaffected.

Influence of voxel size on cone-beam computed tomography-based detection of vertical root fractures in the presence of intracanal metallic posts.

PURPOSE: This study was performed to evaluate the influence of voxel size and the accuracy of 2 cone-beam computed tomography (CBCT) systems in the detection of vertical root fracture (VRF) in the presence of intracanal metallic posts. MATERIALS AND METHODS: Thirty uniradicular extracted human teeth were selected and randomly divided into 2 groups (VRF group, n=15; and control group, n=15). The VRFs were induced by an Instron machine, and metallic posts were placed in both groups. The scans were acquired by CBCT with 4 different voxel sizes: 0.1 mm and 0.16 mm (for the Eagle 3D V-Beam system) and 0.125 mm and 0.2 mm (for the i-CAT system) (protocols 1, 2, 3, and 4, respectively). Interobserver and intraobserver agreement was assessed using the Cohen kappa test. Sensitivity and specificity were evaluated and receiver operating characteristic analysis was performed. RESULTS: The intraobserver coefficients indicated good (0.71) to very good (0.83) agreement, and the interobserver coefficients indicated moderate (0.57) to very good (0.80) agreement. In respect to the relationship between sensitivity and specificity, a statistically significant difference was found between protocols 1 (positive predictive value: 0.710, negative predictive value: 0.724) and 3 (positive predictive value: 0.727, negative predictive value: 0.632) (P<.05). The least interference due to artifact formation was observed using protocol 2. CONCLUSION: Protocols with a smaller voxel size and field of view seemed to favor the detection of VRF in teeth with intracanal metallic posts.

Influence of the feldspathic ceramic thickness and shade on the microhardness of dual resin cement.

This study evaluated the microhardness of a dual resin cement under the influence of thickness and shade of a feldspathic ceramic. Ninety-five bovine incisors were selected; the crowns, with the roots removed, were embedded in a polystyrene resin and were randomly divided into 19 groups (n=5). On the buccal surface, a standardized cavity, 4.0 mm in diameter and 1.0 mm in depth, was prepared. Ceramic restorations (Noritake Ex 3) were manufactured with 4.0 mm diameter and 1, 2 and 4-mm thicknesses at shades A1, A2, A3, A3.5 and A4. A dual resin cement (Rely X-ARC) was inserted into the prepared cavity. A mylar strip was positioned over the prepared cavity, and light curing was performed for 40 seconds following the protocols: controls-without insertion of the restoration at distances of 0.0, 1.0, 2.0 and 4.0 mm. The remaining groups had the restorations positioned between the resin cement and light source during polymerization. The Vickers hardness test was performed on the cement layer with 50 g of load application for 30 seconds, with 5 indentations for each sample. Two-way ANOVA (5 x 3) and Tukey test (alpha = 0.05) were used to compare the results. The chemical curing of the dual resin cement was not sufficient to compensate for the energy attenuation promoted by the interposition of A3.5 and A4 ceramic material with 4-mm of thickness. The thickness had a greater influence on the cement microhardness than the ceramic restoration shade.

Effect of short glass fiber/filler particle proportion on flexural and diametral tensile strength of a novel fiber-reinforced composite.

PURPOSE: To evaluate the effect of glass fiber/filler particles proportion on flexural strength and diametral tensile strength of an experimental fiber-reinforced composite. METHODS: Four experimental groups (N=10) were created using an experimental short fiber-reinforced composite, having as a factor under study the glass fiber (F) and filler particle (P) proportion: F22.5/P55 with 22.5 wt% of fiber and 55 wt% of filler particles; F25/P52.5 with 25 wt% of fiber and 52.5 wt% of filler particles; F27.5/P50 with 27.5 wt% of fiber and 50 wt% of filler particles; F30/P47.5 with 30 wt% of fiber and 47.5 wt% of filler particles. The experimental composite was made up by a methacrylate-based resin (50% Bis-GMA and 50% TEGDMA). Specimens were prepared for Flexural Strength (FS) (25 mm × 2 mm × 2 mm) and for Diametral Tensile Strength (DTS) (3×6 Ø mm) and tested at 0.5 mm/min in a universal testing machine. RESULTS: The results (in MPa) showed significance (different superscript letters mean statistical significant difference) for FS (p<0.009) and DTS (p<0.001)--FS results: F22.5/P55: 217.24±20.64(B); F25/P52.5: 245.77±26.80(AB); F27.5/P50: 246.88±32.28(AB); F30/P47.5: 259.91±26.01(A). DTS results: F22.5/P55: 21.82±4.42(B); F25/P52.5: 22.00±7.40(B); F27.5/P50: 18.63±4.41(B); F30/P47.5: 31.05±2.97(A). In SEM analysis, areas without fiber reinforcement demonstrated to be more prone to the presence of bubbles and crack development. The group F30/P47.5 showed areas with a great quantity of fibers without empty spaces for crack propagation. CONCLUSION: Increasing fiber content results in higher flexural and diametral tensile strength of an experimental composite reinforced with glass fibers.

Influence of provisional cements on ultimate bond strength of indirect composite restorations to dentin.

PURPOSE: The aim of this study was to evaluate the effect of provisional cements on the adhesion of resin bonded indirect restorations and determine the best method for avoiding adverse effects. MATERIALS AND METHODS: Forty-five bovine incisors were selected, and the enamel removed with a 600-grit SiC abrasive disk to expose superficial dentin. Provisional restorations of acrylic resin were cemented with three different provisional cements: calcium hydroxide cement, Dycal (HC); cement containing zinc oxide-eugenol, Provy (ZOE); zinc oxide eugenol-free cement, TempBond NE (ZNE). The specimens were stored at 100% humidity, 37 degrees C. Then provisional restorations were removed with: (1) hand scaler for 10 s; (2) pumice-water slurry for 10 s; (3) aluminum oxide sandblasting for 10 s. The indirect restorations were subsequently cemented with Single Bond and Rely-X ARC. The teeth were sectioned, 4 slices per tooth (n = 16), and each slice trimmed with a diamond bur to obtain an adhesion area of 1 mm2. The microtensile bond strength test was performed with a universal testing machine (Instron-4411) at a crosshead speed of 0.5 mm/min. The results were analyzed with ANOVA, followed by Tukey's test (p < 0.05). RESULTS: ANOVA showed significant differences in the interaction between provisional cement and dentin cleaning method; in general, aluminum oxide sandblasting provided the highest values of bond strength and calcium hydroxide the lowest. CONCLUSION: The type of provisional cement and its method of removal can affect the adhesion of resin-bonded indirect restorations.

Mechanical properties of light-cured composites polymerized with several additional post-curing methods.

This study determined the microhardness and diametral tensile strength of two hybrid resin composites submitted to conventional light curing, which were post-cured with different methods, and compared these data with the same data collected from one indirect resin composite. Two hybrid composites (TPH Spectrum and Filtek P60) and an indirect one (Solidex) were used. Conventional composites were polymerized with 1) conventional light curing for 40 seconds. Additional curing methods were applied with 2) laboratory multi-focal light curing for seven minutes, 3) microwave curing for five minutes at 500W, 4) oven curing for 15 minutes at 100 degrees C, 5) autoclave curing for 15 minutes at 100 degrees C and (6) were polymerized only with a laboratory light curing unit in three increments for three minutes and post-polymerized for seven minutes. The Solidex group was done following the manufacturers' instructions only. Diametral tensile strength and Knoop hardness tests were applied for all groups of five samples. Data were compared using ANOVA, Tukey and Student t-tests (p < 0.05). Post-curing methods increased the Knoop hardness and diametral tensile strength of conventional composites. In general, Filtek P60 showed higher hardness and diametral tensile strength values than TPH Spectrum resin. The Indirect resin composite showed poorer mechanical properties than conventional composites.

Radiodensity of enamel and dentin of human, bovine and swine teeth.

Several studies have aimed to evaluate the characteristics of hard dental tissues from animal species in order to adequately substitute the usage of human teeth. The purpose of this study was to evaluate the radiodensity of enamel and dentin of human, bovine and swine teeth. Five specimens of 2 mm in thickness were obtained from human, bovine and swine teeth and the radiographic images were taken positioning it on a phosphor plaque digital system, Digora (Soredex, Helsinki, Finland). The radiodensity of each specimen was obtained and data were compared by ANOVA following Tukey test (P < 0.05). The results showed that human and bovine enamel presented similar radiodensity, which was higher than the one from swine enamel; bovine and swine dentin presented similar radiodensity, and only bovine dentin presented greater similarity to human dentin. Bovine teeth seems to be more similar to human teeth in respect to radiodensity.

Effect of glass fiber incorporation on flexural properties of experimental composites.

This study evaluated the effect of fiber addiction in flexural properties of 30 wt% silica filled BisGMA resin (FR) or unfilled Bis-GMA (UR). Ten groups were created (N = 10) varying the resin (FR or UR) and quantity of glass fibers (wt%: 0, 10, 15, 20, and 30). Samples (10 × 2 × 1 mm) were submitted to flexural strength test following SEM examination. Data were analyzed by two-way ANOVA, Tukey, and Student t-test (α = 0.05). Results for flexural strength (MPa) were FR-groups: 0% (442.7 ± 140.6)(C), 10% (772.8 ± 446.3)(ABC), 15% (854.7 ± 297.3)(AB), 20% (863.4 ± 418.0)(A), 30% (459.5 ± 140.5)(BC); UR-groups: 0% (187.7 ± 120.3)(B), 10% (795.4 ± 688.1)(B), 15% (1999.9 ± 1258.6)(A), 20% (1911.5 ± 596.8)(A), and 30% (2090.6 ± 656.7)(A), and for flexural modulus (GPa) FR-groups: 0% (2065.63 ± 882.15)(B), 10% (4479.06 ± 3019.82)(AB), 15% (5694.89 ± 2790.3)(A), 20% (6042.11 ± 3392.13)(A), and 30% (2495.67 ± 1345.86)(B); UR-groups: 0% (1090.08 ± 708.81)(C), 10% (7032.13 ± 7864.53)(BC), 15% (19331.57 ± 16759.12)(AB), 20% (15726.03 ± 8035.09)(AB), and 30% (29364.37 ± 13928.96)(A). Fiber addiction in BisGMA resin increases flexural properties, and the interaction between resin and fibers seems better in the absence of inorganic fillers increasing flexural properties.

Reinforcement of dental methacrylate with glass fiber after heated silane application.

This study evaluated the influence of silane heat treatment and glass fiber fabrication type, industrially treated (I) or pure (P), on flexural and compressive strength of methacrylate resin bars (BISGMA/TEGDMA, 50/50%). Six groups (n = 10) were created: I-sil: I/silanated; P-sil: P-silanated; I-sil/heat: I/silanated heated to 100°; P-sil/heat: P/silanated heated to 100°; (I: I/not silanated; and P: P/not silanated. Specimens were prepared for flexural strength (10 × 2 × 1 mm) and for compressive strength 9.5 × 5.5 × 3 mm) and tested at 0.5 mm/min. Statistical analysis demonstrated the following for flexural strength (P < 0.05): I-sil: 155.89 ± 45.27(BC); P-sil: 155.89 ± 45.27(BC); I-sil/heat: 130.20 ± 22.11(C); P-sil/heat: 169.86 ± 50.29(AB); I: 131.87 ± 15.86(C). For compressive strength, the following are demonstrated: I-sil: 1367.25 ± 188.77(ab); P-sil: 867.61 ± 102.76(d); I-sil/heat: 1162.98 ± 222.07(c); P-sil/heat: 1499.35 ± 339.06(a); and I: 1245.78 ± 211.16(bc). Due to the impossibility of incorporating the stipulated amount of fiber, P group was excluded. Glass fiber treatment with heated silane enhanced flexural and compressive strength of a reinforced dental methacrylate.

Influence of preheating and post-curing on a novel fiber-reinforced composite post material

Abstract The aim of this study was to investigate the influence of preheating and post-curing methods on diametral tensile strength (DTS), flexural strength (FS), knoop microhardness (KHN), and degree of conversion (DC) of an experimental fiber-reinforced composite (FRC). Specimens (30 wt% of 3-mm-short E-glass fiber, 22.5 wt% of methacrylated-based resin and 47.5 wt% of filler particles) were subjected to: P - photocuring at 1500 mW/cm2 for 40 s (control); P/M - photocuring and microwave post-curing (540W/5 minutes); P/A - photocuring and autoclave post-curing (120°C/15 minutes); PH-P - preheating (60°C) and photocuring; PH-P/M - preheating, photocuring and microwave post-curing; and PH-P/A - preheating, photocuring and autoclave post-curing. Specimens for DTS (Ø 3 x 6 mm) and FS (25 x 2 x 2 mm) were tested at Instron 5965. KHN employed a 50g load for 30s. DC was measured using FTIR spectroscopy. Statistical analysis employed: factorial analysis, normality test, one-way ANOVA and Tukey's HSD test, independent T-test and the Dunnett test. Interaction between factors was not significant (P>0.05). Preheating promoted significantly higher values of FS and KHN (p = 0.0001). Post-curing promoted significantly higher values for KHN (p = 0.0001). For DTS (p = 0.066) and DC (p= 0.724) no statistical difference was found between groups. SEM images showed that preheating promoted better interaction between glass fibers and resin matrix. Preheating increased FS, KHN and DTS, and post-curing increased KHN. DC was not affected by both methods. Preheating and post-curing methods can be used to improve some mechanical properties of FRCs' but degree of conversion remains unaffected.

Effect of light sources and curing mode techniques on sorption, solubility and biaxial flexural strength of a composite resin.

UNLABELLED: Adequate polymerization plays an important role on the longevity of the composite resin restorations. OBJECTIVES: The aim of this study was to evaluate the effect of light-curing units, curing mode techniques and storage media on sorption, solubility and biaxial flexural strength (BFS) of a composite resin. MATERIAL AND METHODS: Two hundred and forty specimens were made of one composite resin (Esthet-X) in a stainless steel mold (2 mm x 8 mm Ø), and divided into 24 groups (n=10) established according to the 4 study factors: light-curing units: quartz tungsten halogen (QTH) lamp and light-emitting diodes (LED); energy densities: 16 J/cm² and 20 J/cm²; curing modes: conventional (CM) and pulse-delay (PD); and permeants: deionized water and 75% ethanol for 28 days. Sorption and solubility tests were performed according to ISO 4049:2000 specifications. All specimens were then tested for BFS according to ASTM F394-78 specification. Data were analyzed by three-way ANOVA followed by Tukey, Kruskal-Wallis and Mann-Whitney tests (α=0.05). RESULTS: In general, no significant differences were found regarding sorption, solubility or BFS means for the light-curing units and curing modes (p>0.05). Only LED unit using 16 J/cm² and PD using 10 s produced higher sorption and solubility values than QTH. Otherwise, using CM (16 J/cm²), LED produced lower values of BFS than QTH (p<0.05). 75% ethanol permeant produced higher values of sorption and solubility and lower values of BFS than water (p<0.05). CONCLUSION: Ethanol storage media produced more damage on composite resin than water. In general the LED and QTH curing units using 16 and 20 J/cm² by CM and PD curing modes produced no influence on the sorption, solubility or BFS of the tested resin.

Rehabilitation of periodontally compromised teeth with fiber-reinforced composite resin: a case report.

The rehabilitation of prosthetic spaces resulting from severe periodontitis represents a challenge in terms of functional and esthetic aspects. Generally, tooth extraction is followed by alveolar ridge volume reduction, which increases the esthetic problem. The aim of this article is to report the integration of esthetics and functional parameters in the oral rehabilitation of extracted periodontally compromised mandibular central incisors through the construction of a direct glass fiber-reinforced composite fixed partial denture (DFPD). After periodontal therapy, the patient received a periodontal subepithelial graft, enabling an increase in the thickness and height of the alveolar ridge. The DFPD was fabricated with the use of extracted teeth. Mandibular canines and lateral incisors received cavities 2 mm deep and wide. After fiber insertion, tooth adaptation, and composite resin coverage, the teeth were finished and polished. Results showed an excellent esthetic result with stabilization and function of the remaining periodontally affected teeth.

Inorganic particle analysis of dental impression elastomers.

The aim of this study was to determine quantitatively and qualitatively the inorganic particle fraction of commercially available dental elastomers. The inorganic volumetric fraction of two addition silicones (Reprosil Putty/Fluid and Flexitime Easy Putty/Fluid), three condensation silicones (Clonage Putty/Fluid, Optosil Confort/Xantopren VL and Silon APS Putty/Fluid), one polyether (Impregum Soft Light Body) and one polysulfide (Permlastic Light Body) was accessed by weighing a previously determined mass of each material in water before and after burning samples at 600 ºC, during 3 h. Unsettled material samples were soaked in acetone and chloroform for removal of the organic portion. The remaining filler particles were sputter-coated with gold evaluation of their morphology and size, under scanning electron microscopy (SEM). Flexitime Easy Putty was the material with the highest results for volumetric particle fraction, while Impregum Soft had the lowest values. Silon 2 APS Fluid presented the lowest mean filler size values, while Clonage Putty had the highest values. SEM micrographs of the inorganic particles showed several morphologies - lathe-cut, spherical, spherical-like, sticks, and sticks mixed to lathe-cut powder. The results of this study revealed differences in particle characteristics among the elastometic materials that could lead to different results when testing mechanical properties.

Radiodensity evaluation of dental impression materials in comparison to tooth structures.

UNLABELLED: In the most recent decades, several developments have been made on impression materials' composition, but there are very few radiodensity studies in the literature. It is expected that an acceptable degree of radiodensity would enable the detection of small fragments left inside gingival sulcus or root canals. OBJECTIVE: The aim of this study was to determine the radiodensity of different impression materials, and to compare them to human and bovine enamel and dentin. MATERIAL AND METHODS: Twenty-five impression materials, from 5 classes, were studied: addition and condensation silicones, polyether, polysulfides and alginates. Five 1-mm-thick samples of each material and tooth structure were produced. Each sample was evaluated 3 times (N=15), being exposed to x-ray over a phosphor plate of Digora digital system, and radiodensity was obtained by the software Digora for Windows 2.5 Rev 0. An aluminum stepwedge served as a control. Data were subjected to Kruskal-Wallis and Dunn's method (α=0.05). RESULTS: Different materials and respective classes had a different behavior with respect to radiodensity. Polysulfides showed high values of radiodensity, comparable to human enamel (p>0.05), but not to bovine enamel (p<0.05). Human dentin was similar only to a heavy-body addition silicon material, but bovine dentin was similar to several materials. Generally, heavy-body materials showed higher radiodensity than light-body ones (p<0.05). CONCLUSION: Impression materials' radiodensity are influenced by composition, and almost all of them would present a difficult detection against enamel or dentin background in radiographic examinations.

Influence of powder/liquid ratio on the radiodensity and diametral tensile strength of glass ionomer cements.

UNLABELLED: Clinicians tend to make reductions in glass ionomer power/liquid (P/L) ratios since some materials are difficult to mix and flow into small cavities, grooves or pits. In general, changing the P/L ratio decreases the physical and mechanical properties of conventional glass ionomer cements (GICs) and resin modified glass ionomer cements (RMGICs), but alterations seem to depend on their composition. OBJECTIVE: To determine the influence of P/L ratio on the radiodensity and diametral tensile strength (DTS) of glass ionomer cements. MATERIAL AND METHODS: There were 2 factors under study: P/L ratio (manufacturer's recommended P/L ratio and a 50% reduced P/L ratio), and materials (Vitro Molar, Vitro Fil, Vitro Cem conventional GICs and Vitro Fil LC, Ortho Glass LC RMGICs. Five 1-mm-thick samples of each material-P/L ratio were produced for radiodensity evaluation. Samples were x-ray exposed onto Digora phosphor plate and radiodensity was obtained using the software Digora for Windows 2.5 Rev 0. For DTS, five (4.0 x 8.0 mm) cylinder samples of each material were tested (0.5 mm/min). Data were subjected to one- and two-way ANOVA (5x2) followed by Tukey's HSD test, or Kruskal-Wallis and Dunn's method. For paired comparisons, t-test or Mann-Whitney test were used (α=0.05). RESULTS: There was a significant interaction (P=0.001) for the studied factors (materials vs. P/L ratio). Reduced P/L ratio resulted in significantly lower DTS for the RMGICs, but radiodensity was affected for all materials (P<0.05). CONCLUSIONS: Reduced P/L ratio affected properties of the tested glass ionomer cements. RMGICs were more susceptible to lower values of DTS, but radiodensity decreased for all materials following P/L ratio reduction.

Influence of the powder/liquid ratio and storage time of conventional glass ionomer cements in diametral tensile strength

Introduction: The Glass Ionomer Cements (GICs) are the most versatile dental material with extensive clinical indication. However, the mechanical strength of conventional GICs (C-GICs) is still unsatisfactory under areas of masticatory forces. Objective: To evaluate the influence of C-GIC proportioning system (powder-liquid and encapsulated) and storage period (1h, 24h and 7 days) on Diametral Tensile Strength (DTS). Material and methods: The two variables were tested in relation to C-GIC (Riva Self Cure, SDI, Australia). The following proportioning systems were tested: powder-liquid by weight (g:g) and powder-liquid by volume (flat scoop: drop) and encapsulated system (pre-dosed capsules). Five C-GIC specimens were prepared, according to ISO specification #9917 for each variable to be studied. The specimens were stored in plastic containers containing distilled water and kept at 37ºC and 100% humidity until the mechanical testing in a universal testing machine (Instron Corp., USA) at a speed 0.5 mm/min. The data were submitted to two-way ANOVA and Tukey test for multiple comparisons (α = 0.05). Results: The proportioning system (P < 0.0001) and storage time (P < 0.0001) were significant predictors of DTS, however with no interaction between these factors. Conclusion: The DTS of C-GICs was influenced by storage time (1 hour < 24 hours < 7 days) and by the proportioning system only for the initial period of its setting reaction.

The influence of the cavity preparation design on marginal accuracy of laboratory-processed resin composite restorations.

The aim of this study was to evaluate the influence of different cavity preparation designs on marginal accuracy of laboratory-processed resin composite restored teeth. Eighty mandibular human third molars were selected. There were two experimental factors, occlusal isthmus width (narrow vs wide) and cuspal coverage (inlay, one-cusp onlay, two-cusp onlay, and all-cusp onlay), resulting on eight groups (N = 10). Indirect composite restorations (SR Adoro, Ivoclar-Vivadent) were manufactured and positioned over each respective preparation. Marginal accuracy evaluation was accomplished using a stereomicroscope at three points on buccal, lingual, mesial, and distal regions with 40x magnification. The results showed significant differences (P = 0.00) with wide inlay showing the best overall marginal accuracy and narrow inlay the worst one. Two-way analysis of variance (ANOVA) showed significant differences when considering the factor occlusal isthmus width (P = 0.00). In general, preparations with wide occlusal isthmus presented better results than narrow ones, except for wide all-cusp onlays; however, the test failed to show differences when considering the cuspal coverage (P = 0.42) or the interaction between both factors (P = 0.30). The effect of occlusal width extension on marginal accuracy of indirect composite resin restorations is significant, with lower values of gaps width in wide preparations, but since in a clinical situation this would mean greater removal of sound tooth structure, less-aggressive preparations combined with other restorative procedures seem to be more feasible.

Cavity preparation machine for the standardization of in vitro preparations.

Several in vitro studies employ the confection of cavity preparations that are difficult to standardize by means of manual high speed handpieces. This study presents the development of a cavity preparation machine designed to standardize in vitro cavity preparations. A metal base of 25 mm x 25 mm x 4 mm (length x width x height) was coupled to a small mobile table which was designed to be able to move by means of two precision micrometers (0.01-mm accuracy) in the horizontal directions (right-left, and back-front). A high speed handpiece was coupled to a metallic connecting rod which had an accurate dial indicator enabling control of the vertical movement. The high speed handpiece is also able to move 180 degrees around its longitudinal axis and 360 degrees around its transversal axis. The suggested cavity preparation machine precisely helps in the standardization of cavity preparations for in vitro studies.