Impact of Gastric Acid Induced Surface Changes on Mechanical Behavior and Optical Characteristics of Dental Ceramics.

PURPOSE: To test the impact of exposure to artificial gastric acid combined with toothbrush abrasion on the properties of dental ceramics. Earlier research has indicated that immersion in artificial gastric acid has caused increased surface roughness of dental ceramics; however, the combined effects of acid immersion and toothbrush abrasion and the impact of increased surface roughness on mechanical strength and optical properties have not been studied. MATERIALS AND METHODS: Three commercially available ceramics were chosen for this study: feldspathic porcelain, lithium disilicate glass-ceramic, and monolithic zirconium oxide. The specimens (10 × 1 mm discs) were cut, thermally treated as required, and polished. Each material was divided into four groups (n = 8 per group): control (no exposure), acid only, brush only, acid + brush. The specimens were immersed in artificial gastric acid (50 ml of 0.2% [w/v] sodium chloride in 0.7% [v/v] hydrochloric acid mixed with 0.16 g of pepsin powder, pH = 2) for 2 minutes and rinsed with deionized water for 2 minutes. The procedure was repeated 6 times/day × 9 days, and specimens were stored in deionized water at 37°C. Toothbrush abrasion was performed using an ISO/ADA design brushing machine for 100 cycles/day × 9 days. The acid + brush group received both treatments. Specimens were examined under SEM and an optical microscope for morphological changes. Color and translucency were measured using spectrophotometer CIELAB coordinates (L*, a*, b*). Surface gloss was measured using a gloss meter. Surface roughness was measured using a stylus profilometer. Biaxial flexural strength was measured using a mechanical testing machine. The data were analyzed by one-way ANOVA followed by Tukey's HSD post hoc test (p < 0.05). RESULTS: Statistically significant changes were found for color, gloss, and surface roughness for porcelain and e.max specimens. No statistically significant changes were found for any properties of zirconia specimens. CONCLUSIONS: The acid treatment affected the surface roughness, color, and gloss of porcelain and e.max ceramics. The changes in translucency and mechanical strength for all materials were not statistically significant. Zirconia ceramic showed resistance to all treatments.

Post-prophylaxis gingivitis prevention with two-step stannous fluoride dentifrice plus whitening gel sequence or chlorhexidine gluconate mouthrinse.

PURPOSE: To assess use of a two-step dentifrice/gel sequence versus chlorhexidine gluconate mouthrinse on gingivitis prevention after dental prophylaxis. METHODS: A 12-week, randomized controlled trial was conducted to compare the effectiveness and safety of a two-step dentifrice/gel sequence to a positive control in healthy adults with established gingivitis. After informed consent, gingivitis and stain levels were assessed by clinical examination. Eligible subjects received a dental prophylaxis and were randomly assigned to twice daily unsupervised use of either (1) two-step oral hygiene sequence:0.454% stannous fluoride dentifrice followed by 3.0% hydrogen peroxide whitening gel for the test group; or (2) 0.12% chlorhexidine gluconate oral rinse and 0.76% sodium monofluorophosphate dentifrice for the control group. Clinical measurements of gingivitis bleeding sites and tooth stain area/intensity were collected after 4, 8 and 12 weeks use, while safety was assessed via clinical examination and oral status interview of the subjects. RESULTS: A total of 44 subjects were enrolled and 35 completed the 12-week study. At baseline, bleeding sites ranged from 10-33. After prophylaxis and assigned treatment, both groups exhibited significant (P≤ 0.0001) reductions in bleeding sites. Responses were directionally better in the two-step sequence at all post-baseline timepoints, with groups differing significantly (P < 0.05) at Week 8. Tooth stain measurements demonstrated that the two-step dentifrice/gel sequence did not contribute to any significant (P> 0.13) stain accumulation. In contrast, stain accumulation was evident (P< 0.003) in the chlorhexidine group beginning at the Week 4 visit. Adverse events were more common in the positive control, and contributed to early termination. CLINICAL SIGNIFICANCE: Twice daily use of a two-step stannous fluoride dentifrice and peroxide whitening gel sequence after prophylaxis provided comparable or superior gingivitis benefits to chlorhexidine gluconate rinse without the concomitant side effect of staining.

Effect of Two-minute Application of 35% Sodium Ascorbate on Composite Bond Strength following Bleaching.

AIM: The aim of this study is to assess the effect of 35% sodium ascorbate on microtensile bond strength of dentin immediately after bleaching with 35% hydrogen peroxide. MATERIALS AND METHODS: A total of 25 sound human 3rd molars were collected. Teeth were randomly divided into five groups for different treatments: Group I [bleaching + immediate bonding (i.e., restoration)], group II (bleaching + delayed bonding), group III (bleaching + sodium ascorbate + immediate bonding), group IV (bleaching + sodium ascorbate + delayed bonding), and group V (bonding only). After bleaching, but before bonding, groups II and IV were stored for 1 week in deionized water at 37°C. All samples were bonded using OptiBoned FL (Kerr) and Filtek Supreme (3M/ESPE). Teeth were sectioned into 1 × 1 mm 2 bars, and microtensile bond strength was tested with a universal testing machine (Instron 8841) at a cross-head speed of 0.5 mm/minute. RESULTS: Microtensile bond strength differed significantly across the five groups, with a significant reduction in microtensile bond strength observed for samples in group I relative to samples in any of the other treatment groups (p < 0.05). CONCLUSION: The application of a high concentration of sodium ascorbate for a shorter time reversed the negative effect of 35% hydrogen peroxide bleaching on composite bonding strength to dentin. CLINICAL SIGNIFICANCE: The negative effects of bleaching on composite bonding can be neutralized by the application of the reversing agent sodium ascorbate thus, increasing the efficiency of clinic chair time. This is clinically relevant for those patients requiring restorative treatment immediately after in-office bleaching.

Hoxb13 knockout adult skin exhibits high levels of hyaluronan and enhanced wound healing.

In contrast to adult cutaneous wound repair, early gestational fetal cutaneous wounds heal by a process of regeneration, resulting in little or no scarring. Previous studies indicate that down-regulation of HoxB13, a member of the highly conserved family of Hox transcription factors, occurs during fetal scarless wound healing. No down-regulation was noted in adult wounds. Here, we evaluate healing of adult cutaneous wounds in Hoxb13 knockout (KO) mice, hypothesizing that loss of Hoxb13 in adult skin should result in enhanced wound healing. Tensiometry was used to measure the tensile strength of incisional wounds over a 60-day time course; overall, Hoxb13 KO wounds are significantly stronger than wild-type (WT). Histological evaluation of incisional wounds shows that 7-day-old Hoxb13 KO wounds are significantly smaller and that 60-day-old Hoxb13 KO wounds exhibit a more normal collagen architecture compared with WT wounds. We also find that excisional wounds close at a faster rate in Hoxb13 KO mice. Biochemical and histochemical analyses show that Hoxb13 KO skin contains significantly elevated levels of hyaluronan. Because higher levels of hyaluronan and enhanced wound healing are characteristics of fetal skin, we conclude that loss of Hoxb13 produces a more "fetal-like" state in adult skin.

Potential surface alteration effects of laser-assisted periodontal surgery on existing dental restorations.

OBJECTIVE: Laser-assisted gingivectomies are performed in proximity to teeth, existing restorations, and implants. In case of accidental exposures, a detrimental surface defect may cause failure. Surface interactions should be evaluated for safety margin determination of certain laser-material combinations. The purpose of this in vitro study was to assess the microscopic and visible effects of CO2, Nd:YAG, and 810-nm diode laser irradiations on various dental materials and tooth tissue. METHOD AND MATERIALS: Study samples were fabricated (10 x 7.5 mm irradiation surface area, 1 mm thickness) from eight material groups (amalgam, base metal, gold, palladium-silver, composite, ceramic, titanium, and extracted tooth slices). Laser irradiations were performed with CO2, Nd:YAG, and 810-nm diode lasers using the manufacturer's recommended settings for gingivectomy at a 45-degree angle for 30 seconds. Irradiated surfaces were evaluated under SEM at 200x and 1,000x magnifications. Standardized photographs were obtained using a camera mount system (10x high-definition macro lens). The SEM images and photographs were correlated to determine surface interactions. RESULTS: Nd:YAG detrimentally affected all metallic materials and tooth structures. CO2 altered amalgam, gold, and palladium-silver slightly, whereas composite, ceramic, and tooth surfaces were detrimentally altered. The 810-nm diode altered amalgam, gold, titanium, palladium-silver, and composite but only gold and palladium-silver surfaces were barely traceable. CONCLUSION: Within the limitations of this in vitro study, surface effects were all instant; therefore, even a short accidental exposure may be destructive in some laser-material combinations. During gingivectomies, CO2 near tooth-colored restorations and Nd:YAG near metallic restorations and implants should be used carefully. The 810-nm diode was found to be safer due to its reversible alterations in only some materials. Further in vivo studies are necessary to clinically apply the outcomes of this study.

Long-term microtensile bond strength of surface modified zirconia.

OBJECTIVE: To compare long-term microtensile bond strength of zirconia, surface-modified via a novel treatment, to current surface conditioning methods for zirconia, when resin bonded to dental composite. METHODS: Two ProCAD (porcelain) and 10 sintered ZirCAD (ZrO(2)) blocks (18 mm × 14 mm × 12 mm) were obtained from manufacturers. Twelve Herculite XRV composite blocks were fabricated (18 mm × 14 mm × 12 mm). Bonding surface of blocks was polished through 1200-grit SiC and air-abraded (50 µm alumina, 0.28MPa, 20s). Blocks were then separated into six groups: (1) porcelain (control), HF-etched/silane-treated, (2) ZrO(2), tribochemical-coated/silane-treated, (3) ZrO(2), primer-treated, (4) ZrO(2), modified via novel 3.2 nm silica layer/silane-treated, (5) ZrO(2), modified via novel 5.8nm silica layer/silane-treated, and (6) ZrO(2), modified via novel 30.4 nm silica layer/silane-treated. Blocks were bonded to composite using Clearfil Esthetic cement. Blocks were stored in distilled water (37°C, 24h), then cut into microtensile bars (n=8/gp), then bond strengths were measured using a universal testing machine at 0, 1, 3, and 6 months. All groups were statistically analyzed (ANOVA, Tukey's, p<0.05). RESULTS: At 6 months (aging), all silica seed layer specimens displayed microtensile bond strength similar to CoJet specimens but less than that of silane-modified dental porcelain. CONCLUSION: The deposition of a silica layer on zirconia resulted in similar or superior long-term resin bond strength when compared to traditional silanation and bonding techniques for zirconia but lower than that for silane-treated dental porcelain.