Fluoride release by restorative materials before and after a topical application of fluoride gel

The release of fluoride from restorative materials (Vitremer, Ketac-Fil, Fuji II LC and Freedom) was evaluated during two 15-day periods, before and after a topical application of acidulated phosphate fluoride gel (APF). For each material, 6 specimens were made, which were immersed in 2 ml of deionized water. The fluoride concentration dosages in the solutions were read at intervals of 24 hours for 15 days. After this period, the specimens of each material received treatment with APF gel for 4 minutes and the fluoride released was analyzed at 24-hour intervals during the following 15 days. The analysis of variance and the Tukey test (p < 0.05) showed that the total mean fluoride released during the initial 15 days was greater for Vitremer and Ketac-Fil and lower for Fuji II LC and Freedom; and in the final 15 days there was a difference in release readings, with the greatest value for Vitremer, followed by Fuji II LC, Ketac-Fil and Freedom. The comparison of the results between the 1st day and the 16th day (after gel application) showed a greater fluoride release on the 16th day for Vitremer, Fuji II LC and Freedom and was equal for Ketac-Fil. Although all the materials evaluated gained fluoride with the application of APF, the data suggest that the resin-modified ionomers are more efficient in releasing fluoride to the medium than the other materials.

Effects of bleaching with carbamide peroxide gels on microhardness of restoration materials

The objective of this in vitro study was to quantitatively assess the effects of bleaching with 10 and 15% carbamide peroxide (CP) on restoration materials by performing superficial microhardness analysis. Acrylic cylindrical containers (4 x 2 mm) were filled with the following restoration products: Charisma (Heraues Kulzer, Vila Santa Catarina, São Paulo, Brazil), Durafill VS (Heraeus Kulzer), Vitremer (3M, Sumaré, São Paulo, Brazil), Dyract (Dentsply, Petrópolis, Rio de Janeiro, Brazil), and Permite C (SDI, São Pauio, São Paulo, Brazil). Sixty samples were prepared of each restoration material. Twenty samples received bleaching treatment with 10% CP, 20 samples received bleaching treatment with 15% CP, and 20 samples were kept submerged in artificial saliva, which was replaced daily. The treatment consisted of immersion of the specimens in 1 cm3 of CP at 10 and 15% for 6 hours per day during 3 weeks, whereupon the test specimens were washed, dried, and kept immersed in artificial saliva for 18 hours. Then the test and control specimens were analyzed using a microhardness gauge. The Knoop Hardness Number (KHN) was taken for each test and control specimen at five different locations by applying a 25 g force for 20 seconds. The values obtained were transformed into KHNs and the mean was calculated. The data were submitted to statistical analysis by analysis of variance and Tukey test, p < .05. The means/standard deviations were as follows: Charisma: CP 10% 38.52/4.08, CP 15% 34.31/6.13, saliva 37.36/4.48; Durafill VS: CP 10% 18.65/1.65, CP 15% 19.38/2.23, saliva 18.27/1.43; Dyract AP: CP 10% 30.26/2.81, CP 15% 28.64/5.44, saliva 33.88/3.46; Vitremer: CP 10% 28.15/3.04, CP 15% 17.40/3.11, saliva 40.93/4.18; and Permite C: CP 10% 183.50/27.09, CP 15% 159.45/5.78, saliva 215.80/26.15. A decrease in microhardness was observed for the materials Dyract AP, Vitremer, and Permite C after treatment with CP at 10 and 15%, whereas no effect on either of the two composites (Charisma and Durafill) was verified. CLINICAL SIGNIFICANCE: The application of the carbamide peroxide gels at 10 and 15% did not alter the microhardness of the composite resins Charisma and Durafill. In situ and clinical studies are necessary to enable one to conclude that the reduction in microhardness of the materials effectively results in clinical harm to the restorations.

Cytotoxicity of denture base resins: Effect of water bath and microwave postpolymerization heat treatments

Purpose: This study compared the effect of two postpolymerization heat treatments on the cytotoxicity of three denture base resins on L929 cells using 3H-thymidine incorporation and MTT assays. Materials and Methods: Sample disks of Lucitone 550, QC 20, and Acron MC resins were fabricated under aseptic conditions and stored in distilled water at 37°C for 48 hours. Specimens were then divided into three groups: (1) heat treated in microwave oven for 3 minutes at 500 W; (2) heat treated in water bath at 55°C for 60 minutes; and (3) no heat treatment. Eluates were prepared by placing three disks into a sterile glass vial with 9 mL of Eagle's medium and incubating at 37°C for 24 hours. The cytotoxic effect from the eluates was evaluated using the 3H-thymidine incorporation and MTT assays, which reflect DNA synthesis levels and cell metabolism, respectively. Results: The components leached from the resins were cytotoxic to L929 cells when 3H- thymidine incorporation assay was employed. In contrast, eluates from all resins revealed noncytotoxic effects as measured by MTT assay. For both MTT assay and 3H-thymidine incorporation, the heat treatments did not decrease the cytotoxicity of the materials tested. Conclusion: Resins were graded by 3H-thymidine incorporation assay as slightly cytotoxic and by MTT assay as noncytotoxic. Cytotoxicity of the denture base materials was not influenced by microwave or water bath heat treatment.

The influence of chemical activation on hardness of dual-curing resin cements.

During the cementation of metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. This study evaluated the influence of chemical activation compared with dual-curing (chemical and light activation), on the hardness of four dual-curing resin cements. In a darkened environment, equal weight proportions of base and catalyst pastes of the cements Scotchbond Resin Cement, Variolink II, Enforce and Panavia F were mixed and inserted into moulds with cavities of 4 mm in diameter and 2 mm in height. Subsequently, the cements were: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated (dual-curing = dual-cured groups). The Vickers hardness number was measured at 1 hour, 24 hours and 7 days after the start time of cements' spatulation. For all the cements, the hardness values of self-cured groups were lower than those of the respective dual-cured groups at 1 hour and 24 hours. At 7 days, this behavior continued for Variolink II and Panavia F, whilst for Scotchbond Resin Cement and Enforce there was no statistical difference between the two activation modes. All cements showed a significant increase in their hardness values from 1 hour to 7 days for both activation modes. Of the self-cured groups, Scotchbond Resin Cement and Variolink II presented the highest and the lowest hardness values, respectively, for all three times tested. Within the limitations of this study, up to the time of 24 h, chemical activation alone was unable to promote similar hardness as to that obtained with dual-curing.

Effect of ceramic surface treatment on the microtensile bond strength between a resin cement and an alumina-based ceramic

Purpose: The objective of this study was to test the following hypothesis: the silica coating on ceramic surface increases the bond strength of resin cement to a ceramic. Materials and Methods: In-Ceram Alumina blocks were made and the ceramic surface was treated: G1 - sandblasting with 110-μm aluminum oxide particles; G2 - Rocatec System: tribochemicai silica coating (Rocatec-Pre powder + Rocatec-Plus powder + Rocatec-Sil); G3 - CoJet System: silica coating (CoJet-Sand) + ESPE-Sil. The ceramic blocks were cemented to composite blocks with Panavia F resin cement (under a load of 750 g/1 min). The cemented blocks were stored in distilled water at 37°C for 7 days and sectioned along the x and y axes with a diamond disk. Samples with an adhesive area of ca 0.8 mm 2 (n = 45) were obtained. The samples were attached to an adapted device for the microtensile test, which was performed in a universal testing machine (EMIC) at a crosshead speed of 1 mm/min. Results: The obtained results were submitted to ANOVA and Tukey's test. Mean values of tensile strength (MPa) and standard deviation values were: (G1) 16.8 ± 3.2; (G2) 30.6 ± 4.5; (G3) 33.0 ± 5.0. G2 and 63 presented greater tensile strength than G1. There was no significant difference between G2 and G3. All the failures took place at the ceramic/resin cement interface. Conclusion: The silica coating (Rocatec or CoJet systems) of the ceramic surface increased the bond strength between the Panavia F resin cement and alumina-based ceramic.

Effect of surface treatments on the resin bond to zirconium-based ceramic

Purpose: This study tested the hypothesis that the tribochemical silica coating on ceramic surfaces increases the bond strength of resin cement to a glass-infiltrated zirconium-based ceramic. Materials and Methods: Fifteen blocks of In-Ceram Zirconia from CEREC InLab (5 per group) and 15 composite blocks (Z-250) 5 mm x 5 mm x 4 mm were made. The ceramic surfaces were polished, and the blocks were divided into three groups: (1) airborne abrasion with 110-μm aluminum oxide particles; (2) Rocatec system, tribochemical silica coating; and (3) CoJet system, tribochemical silica coating. The ceramic blocks were cemented to the composite blocks using Panavia F according to the manufacturer's specifications. All samples were stored in 37°C distilled water for 7 days and later sectioned in two axes using a diamond disk under cooling to obtain specimens with a cross-sectional area of approximately 1 mm2 (n = 45). Each specimen was then attached with cyanoacrylate glue to an adapted device for the microtensile test, which was carried out on a universal testing machine. Results: The results were subjected to ANOVA and Tukey's test. Group 2 (23.0 ± 6.7 MPa) and group 3 (26.8 ± 7.4 MPa) showed greater bond strength than group 1 (15.1 ± 5.3 MPa). There was no significant difference between groups 2 and 3. All failures were in the adhesive zone. Conclusion: The hypothesis was confirmed - the tribochemical systems increased the bond strength between Panavia F and In-Ceram Zirconia.

Influence of activation modes on diametral tensile strength of dual-curing resin cements.

In metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. The effect of the lack of photoactivation on the strength of these cements has been rarely studied. This study evaluated the influence of activation modes on the diametral tensile strength (DTS) of dual-curing resin cements. Base and catalyst pastes of Panavia F, Variolink II, Scotchbond Resin Cement, Rely X and Enforce were mixed and inserted into cylindrical metal moulds (4 x 2 mm). Cements were either: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated through mylar strips (chemical and photo-activation = dual-cured groups) (n = 10). After a 24 h storage in 37 masculineC distilled water, specimens were subjected to compressive load in a testing machine. A self-curing resin cement (Cement-It) and a zinc phosphate cement served as controls. Comparative analyses were performed: 1) between the activation modes for each dual-curing resin cement, using Students t test; 2) among the self-cured groups of the dual-curing resin cements and the control groups, using one-way ANOVA and Tukeys test (alpha = 0.05). The dual-cured groups of Scotchbond Resin Cement (53.3 MPa), Variolink II (48.4 MPa) and Rely X (51.6 MPa) showed higher DTS than that of self-cured groups (44.6, 40.4 and 44.5 MPa respectively) (p < 0.05). For Enforce (48.5 and 47.8 MPa) and Panavia F (44.0 and 43.3 MPa), no significant difference was found between the activation modes (p > 0.05). The self-cured groups of all the dual-curing resin cements presented statistically the same DTS as that of Cement-It (44.1 MPa) (p > 0.05), and higher DTS than that of zinc phosphate (4.2 MPa). Scotchbond Resin Cement, Variolink II and Rely X depended on photoactivation to achieve maximum DTS. In the absence of light, all the dual-curing resin cements presented higher DTS than that of zinc phosphate and statistically the same as that of Cement-It (p > 0.05).

Microtensile bond strength of a resin cement to glass infiltrated zirconia-reinforced ceramic: The effect of surface conditioning

This study evaluated the effect of three surface conditioning methods on the microtensile bond strength of resin cement to a glass-infiltrated zirconia-reinforced alumina-based core ceramic. Thirty blocks (5×5×4 mm) of In-Ceram Zirconia ceramics (In-Ceram Zirconia-INC-ZR, VITA) were fabricated according to the manufacturer's instructions and duplicated in resin composite. The specimens were polished and assigned to one of the following three treatment conditions (n=10): (1) Airborne particle abrasion with 110 μm Al2O3 particles + silanization, (2) Silica coating with 110 μm SiOx particles (Rocatec Pre and Plus, 3M ESPE) + silanization, (3) Silica coating with 30 μm SiOx particles (CoJet, 3M ESPE) + silanization. The ceramic-composite blocks were cemented with the resin cement (Panavia F) and stored at 37 °C in distilled water for 7 days prior to bond tests. The blocks were cut under coolant water to produce bar specimens with a bonding area of approximately 0.6 mm2. The bond strength tests were performed in a universal testing machine (cross-head speed: 1 mm/min). The mean bond strengths of the specimens of each block were statistically analyzed using ANOVA and Tukey's test (α≤0.05). Silica coating with silanization either using 110 μm SiOx or 30 μm SiOx particles increased the bond strength of the resin cement (24.6±2.7 MPa and 26.7±2.4 MPa, respectively) to the zirconia-based ceramic significantly compared to that of airborne particle abrasion with 110-μm Al2O3 (20.5±3.8 MPa) (ANOVA, P<0.05). Conditioning the INC-ZR ceramic surfaces with silica coating and silanization using either chairside or laboratory devices provided higher bond strengths of the resin cement than with airborne particle abrasion using 110 μm Al2O3. © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Weight loss and surface roughness of hard chairside reline resins after toothbrushing: Influence of postpolymerization treatments

Purpose: To evaluate the effect of 2 postpolymerization treatments on toothbrushing wear (weight loss) and surface roughness of 3 autopolymerized reline resins-Duraliner II (D) (Reliance Dental), Kooliner (K) (Coe Laboratories), and Tokuso Rebase Fast (T) (Tokuyama Dental)-and 1 heat-polymerized resin, Lucitone 550 (L) (Dentsply International). Materials and Methods: Specimens (40 x 10 x 2mm) of each material (n = 24) were prepared and divided into 3 groups: control (no postpolymerization treatment); water bath (immersion in water at 55°C); and microwave (microwave irradiation). Specimens were dried until constant weight was achieved and the surface roughness (Ra) was measured. Tests were performed in a toothbrush machine using 20,000 strokes of brushing at a weight of 200 g, with the specimens immersed in 1:1 dentifrice/water slurry. Specimens were reconditioned to constant weight and the weight loss (mg) and surface roughness were evaluated. Data were analyzed by 2-way analysis of variance and followed by Tukey test (α = .05). Results: In the control group, the weight loss of materials D and T was lower (P < .05) than that of L. No differences among materials were found after postpolymerization treatments (P > .05). The weight loss of material T (control = 0.5 mg) was significantly increased (P < .05) after postpolymerization treatments (water bath = 1.9 mg; microwave = 1.8 mg). For materials K and T, the toothbrushed surface roughness was higher (P < .05) after microwave and waterbath postpolymerization treatments. Material L showed increased surface roughness after microwave postpolymerization treatment. Conclusion: The toothbrushing wear resistance of L was not superior to the reline resins. The postpolymerization treatments did not improve the toothbrushing wear resistance of the materials and produced an increased surface roughness for materials L, K, and T.

Effectiveness of microwave irradiation on the disinfection of complete dentures

Purpose: The purpose of this study was to evaluate the effectiveness of microwave irradiation on the disinfection of simulated complete dentures. Materials and Methods: Eighty dentures were fabricated in a standardized procedure and subjected to ethylene oxide sterilization. The dentures were individually inoculated (10 7 cfu/mL) with tryptic soy broth (TSB) media containing one of the tested microorganisms (Candida albicans, Streptoccus aureus, Bacillus subtilis, and Pseudomonas aeruginosa). After 48 hours of incubation at 37°C, 40 dentures were individually immersed in 200 mL of water and submitted to microwave irradiation at 650 W for 6 minutes. Forty nonirradiated dentures were used as positive controls. Replicate aliquots (25 μL) of suspensions were plated at dilutions of 10 -3 to 10 -6 on plates of selective media appropriate for each organism. All plates were incubated at 37°C for 48 hours. TSB beakers with the microwaved dentures were incubated at 37°C for 7 more days. After incubation, the number of colony-forming units was counted and the data were statistically analyzed by Kruskal-Wallis test (α = .05). Results: No evidence of growth was observed at 48 hours for S aureus, B subtilis, and C albicans. Dentures contaminated with P aeruginosa showed small growth on 2 plates. After 7 days incubation at 37°C, no growth was visible in the TSB beakers of S aureus and C albicans. Turbidity was observed in 3 broth beakers, 2 from P aeruginosa and 1 from B subtilis. Conclusion: Microwave irradiation for 6 minutes at 650 W produced sterilization of complete dentures contaminated with S aureus and C albicans and disinfection of those contaminated with P aeruginosa and B subtilis.

Microtensile bond strength between a quartz fiber post and a resin cement: Effect of post surface conditioning

Purpose: To test the bond strength between a quartz-fiber-reinforced composite post (FRC) and a resin cement. The null hypothesis was that the bond strength can be increased by using a chairside tribochemical silica-coating system. Materials and Methods: Thirty quartz-FRCs (Light-Post) were divided into 3 groups according to the post surface treatment: G1) Conditioning with 32% phosphoric acid (1 min), applying a silane coupling agent; G2) etching with 10% hydrofluoric acid (1 min), silane application; G3) chairside tribochemical silica coating method (CoJet System): air abrasion with 30-μ SiO x-modified Al2O3 particles, silane application. Thereafter, the posts were cemented into a cylinder (5 mm diameter, 15 mm height) with a resin cement (Duo-Link). After cementation, the specimens were stored in distilled water (37°C/24 h) and sectioned along the x and y axes with a diamond wheel under cooling (Lab-cut 1010) to create nontrimmed bar specimens. Each specimen was attached with cyanoacrylate to an apparatus adapted for the microtensile test. Microtensile testing was conducted on a universal testing machine (1 mm/min). The data obtained were submitted to the one-way ANOVA and Tukey test (α = 0.05). Results: A significant influence of the conditioning methods was observed (p < 0.0001). The bond strength of G3 (15.14 ± 3.3) was significantly higher than the bond strengths of G1 (6.9 ± 2.3) and G2 (12.60 ± 2.8) (p = 0.000106 and p = 0.002631, respectively). Notwithstanding the groups, all the tested specimens showed adhesive failure between the resin cement and FRC. Conclusion: The chairside tribochemical system yielded the highest bond strength between resin cement and quartz-fiber post. The null hypothesis was accepted (p < 0.0001).

Relationship between the dielectric and mechanical properties and the ratio of epoxy resin to hardener of the hybrid thermosetting polymers

The relationship between the dielectric properties (dielectric constant, ε′, and loss factor, ε; activation energy, E a) and the ratio of epoxy resin (OG) to hardener of the epoxy resin thermosetting polymers was investigated. The amplitude of the ε″ peak decreases with increasing OG content until about 73 wt.% and slightly increases at higher OG content. The temperature of the position of the ε″ peak increases with the increasing of OG content, reaching maximum values for compositions in the range of 67 and 73 wt.%, and then it decreases sharply at higher OG content. The activation energy obtained from dielectric relaxation increased with increasing wt.% OG up to around 70 wt.%. Further increase in concentration of OG up to 83 wt.% reduced E a. The curves of tensile modulus and fracture toughness mechanical properties as a function of OG content presented a similar behavior. ©2006 Sociedade Brasileira de Química.

Biological response of pulps submitted to different capping materials

Pulp capping is a procedure that comprises adequate protection of the pulp tissue exposed to the oral environment, aiming at the preservation of its vitality and functions. This study evaluated the response of the dental pulps of dog teeth to capping with mineral trioxide aggregate (MTA) or calcium hydroxide P.A. For that purpose, 37 teeth were divided into two groups, according to the capping material employed. Two dogs were anesthetized and, after placement of a rubber dam, their pulps were exposed in a standardized manner and protected with the experimental capping materials. The cavities were then sealed with resin-modified glass ionomer cement and restored with composite resin. After sixty days, the animals were killed and the specimens were processed in order to be analyzed with optic microscopy. It was observed that MTA presented a higher success rate compared to calcium hydroxide, presenting a lower occurrence of infection and pulp necrosis.

Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics: The effect of surface conditioning

Purpose: The aim of this study was to evaluate the effect of two surface conditioning methods on the microtensile bond strength of a resin cement to three high-strength core ceramics: high alumina-based (In-Ceram Alumina, Procera AllCeram) and zirconia-reinforced alumina-based (In-Ceram Zirconia) ceramics. Materials and Methods: Ten blocks (5 ×6 × 8 mm) of In-Ceram Alumina (AL), In-Ceram Zirconia (ZR), and Procera (PR) ceramics were fabricated according to each manufacturer's instructions and duplicated in composite. The specimens were assigned to one of the two following treatment conditions: (1) airborne particle abrasion with 110-μm Al2O3 particles + silanization, (2) silica coating with 30 μm SiOx particles (CoJet, 3M ESPE) + silanization. Each ceramic block was duplicated in composite resin (W3D-Master, Wilcos, Petrópolis, RJ, Brazil) using a mold made out of silicon impression material. Composite resin layers were incrementally condensed into the mold to fill up the mold and each layer was light polymerized for 40 s. The composite blocks were bonded to the surface-conditioned ceramic blocks using a resin cement system (Panavia F, Kuraray, Okayama, Japan). One composite resin block was fabricated for each ceramic block. The ceramic-composite was stored at 37°C in distilled water for 7 days prior to bond tests. The blocks were cut under water cooling to produce bar specimens (n = 30) with a bonding area of approximately 0.6 mm2. The bond strength tests were performed in a universal testing machine (crosshead speed: 1 mm/min). Bond strength values were statistically analyzed using two-way ANOVA and Tukey's test (≤ 0.05). Results: Silica coating with silanization increased the bond strength significantly for all three high-strength ceramics (18.5 to 31.2 MPa) compared to that of airborne particle abrasion with 110-μm Al2O3 (12.7-17.3 MPa) (ANOVA, p < 0.05). PR exhibited the lowest bond strengths after both Al2O3 and silica coating (12.7 and 18.5 MPa, respectively). Conclusion: Conditioning the high-strength ceramic surfaces with silica coating and silanization provided higher bond strengths of the resin cement than with airborne particle abrasion with 110-μm Al2O3 and silanization.

Effect of curing regime on the cytotoxicity of resin-modified glass-ionomer lining cements applied to an odontoblast-cell line

Objective: The aim of this in vitro study was to evaluate the cytotoxicity of resin-modified glass-ionomer lining cements submitted to different curing regimes and applied to an immortalized odontoblast-cell line (MDPC-23). Methods: Forty round-shaped specimens of each experimental material (Fuji Lining LC and Vitrebond) were prepared. They were light-cured for the manufacturers' recommended time (MRT = 30 s), under-cured (0.5 MRT = 15 s), over-cured (1.5 MRT = 45 s) or allowed to dark cure (0 MRT). Sterilized filter papers soaked with either 5 μL of PBS or HEMA were used as negative and positive control, respectively. After placing the specimens individually in wells of 24-well dishes, odontoblast-like cells MDPC-23 (30,000 cells/cm2) were plated in each well and incubated for 72 h in a humidified incubator at 37 °C with 5% CO2 and 95% air. The cytotoxicity was evaluated by the cell metabolism (MTT assay) and cell morphology (SEM). Results: Fuji Lining LC was less cytotoxic than Vitrebond (p < 0.05) in all the experimental conditions. However, the cytotoxicity of Fuji Lining LC was noticeably increased in the absence of light-curing while the same was not observed for Vitrebond. The length of light-curing (15, 30 or 45 s) did not influence the toxicity of both lining materials when they were applied on the odontoblast-cell line MDPC-23. Significance: The light-activation plays an important role in reducing the cytotoxicity of Fuji Lining LC. Following the manufacturer' recommendation regarding the light-curing regime may prevent toxic effect to the pulp cells. © 2005 Academy of Dental Materials.