William W. Brackett

The Effect of Chlorhexidine on Dentin Hybrid Layers In Vivo

This in vivo study evaluated by TEM the degradation of dentin hybrid layers in deep occlusal resin composite restorations. Caries-free premolars scheduled for extraction as part of orthodontic treatment were prepared, restored and evaluated after two and six months. The adhesive used was a single-bottle etch-and-rinse product (Single Bond Plus, 3M ESPE). Control group restorations were placed according to the manufacturers instructions, while the experimental group received application of a 2% solution of chlorhexidine digluconate after etching. No degradation was observed in either group after two months. Slight degradation was found in the control group after six months, but none was observed in the experimental group. In vitro testing showed no significant difference in microtensile bond strength between the control and experimental adhesive protocols.

Durability of Resin-Dentin Bonds to Water- vs. Ethanol-saturated Dentin

Higher 24-hour resin-dentin bond strengths are created when ethanol is used to replace water during wet bonding. This in vitro study examined if ethanol-wet-bonding can increase the durability of resin-dentin bonds over longer times. Five increasingly hydrophilic experimental resin blends were bonded to acid-etched dentin saturated with water or ethanol. Following composite build-ups, the teeth were reduced into beams for 24-hour microtensile bond strength evaluation, and for water-aging at 37°C for 3, 6, or 12 months before additional bond strength measurements. Although most bonds made to water-saturated dentin did not change over time, those made to ethanol-saturated dentin exhibited higher bond strengths, and none of them fell over time. Decreased collagen fibrillar diameter and increased interfibrillar spacing were seen in hybrid layers created with ethanol-wet-bonding. Increases in bond strength and durability in ethanol-wet-bonding may be due to higher resin uptake and better resin sealing of the collagen matrix, thereby minimizing endogenous collagenolytic activities.

In vivo chlorhexidine stabilization of hybrid layers of an acetone-based dentin adhesive.

The current in vivo study evaluated the degradation of dentin hybrid layers in deep occlusal-surface resin composite restorations using TEM. Caries-free premolars scheduled for extraction as part of orthodontic treatment were prepared and restored, then extracted after 12 months. The adhesive used was a single-bottle etch-and-rinse acetone-based product (Prime & Bond NT, Dentsply/Caulk). Control group restorations (n=8) were placed according to the manufacturers instructions, while the experimental group received application of a 2% solution of chlorhexidine digluconate after etching and rinsing and prior to application of the adhesive. Extensive degradation was observed in all of the teeth in the control group after 12 months, while no degradation was observed in the experimental group. In vitro testing showed no significant difference in immediate microtensile bond strength between the control and experimental adhesive protocols.

The critical barrier to progress in dentine bonding with the etch-and-rinse technique

OBJECTIVES The lack of durability in resin-dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin-dentine bonds. The purpose of this study is to examine the integrity of aged resin-dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches. METHODS The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing. RESULTS Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive. CONCLUSIONS The impact was realized by understanding the lack of an inherent mechanism to remove water from resin-dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique.

Comparison of traditional and low sensitivity whiteners.

This placebo-controlled, double-blind randomized clinical trial compared five 10% carbamide peroxide tooth whitening formulations. Three products contained varying concentrations of potassium nitrate as desensitizers. One contained no desensitizers and one was a placebo. During the two weeks of active bleaching, participants used a daily diary to record the number of days of sensitivity from hot, cold, gums, tongue and/or throat. The total number of days of sensitivity experienced by the participants in each group was compared. Participants using the agent with no desensitizers did not experience any more sensitivity than those using the agent containing 3% potassium nitrate. The products that included 0.5% potassium nitrate and 0.5% potassium nitrate and 0.25% sodium fluoride were not associated with any more sensitivity than the placebo group. In addition, the shade tab change from baseline to 11 weeks following cessation of bleaching was compared. Using an active bleaching agent, no difference in color change was noted among the four groups. All four groups were associated with significantly higher color change than the placebo. The addition of a small percentage of potassium nitrate to a 10% carbamide peroxide tooth whitener was shown to significantly reduce postoperative sensitivity without reducing efficacy.

Film thicknesses of recently introduced luting cements.

STATEMENT OF PROBLEM A luting cement must maintain a minimum film thickness over a sufficient period of time to allow seating of indirect restorations. The performance of newer luting cements in this regard has not been evaluated. PURPOSE The purpose of this study was to compare the film thicknesses of 6 luting cements, 2 resin-modified glass ionomer (FujiCEM and RelyX Luting Plus), 2 composite resin (Panavia 21 and RelyX ARC), and 2 self-adhesive resin (Maxcem and RelyX Unicem) cements, over 3 minutes. MATERIAL AND METHODS The film thickness (microm) of each cement (n=7) was determined at room temperature at 1, 2, and 3 minutes after the start of mixing, according to the testing method set forth in ISO Standard 9917. Means of all cements were compared at the 2-minute interval, and means at the 1- and 3-minute intervals for each were compared to the mean for the same cement at 2 minutes, using 1-way analyses of variance (ANOVA) and Tukey-Kramer multiple comparison tests (alpha=.05). RESULTS Except for 1 resin-modified material at 3 minutes, a point beyond its specified working time, all materials produced film thicknesses under 30 microm at 3 minutes and under 26 microm at 2 minutes. CONCLUSIONS All of the materials tested meet the ISO standard of 25-microm maximum film thickness for up to 2 minutes after mixing.

Color differences: Polymerized composite and corresponding Vitapan Classical shade tab

OBJECTIVES This study compared newer composite resin restorative materials to the Vitapan Classical tabs they purported to represent. METHODS Five Vitapan Classical tabs were studied: A3.5, B2, C1, C3, and D2 (n=3). These tabs created a variety of levels of lightness, chroma and hue. Each of these five shade tabs was removed from three different shade guides, and an intraoral spectrophotometer was used to capture CIELAB color coordinates. Three separate readings were made and all nine were averaged. The inter-tab color differences were also calculated. Five specimens approximately 4.0mm thick were fabricated for each of the shades studied using five different composite resin materials. Composite specimens were of the same size and shape as target shade tabs, and three separate recordings were made for each of them. This average was compared to five Vitapan Classical shade tabs to calculate the color differences using both CIELAB and CIEDE2000 color difference formulas. Color differences were compared to thresholds for perceptibility and acceptability reported in other studies. RESULTS CIELAB and CIEDE2000 color differences ranged from 3.9 to 22.8 and from 2.1 to 13.8, respectively. None of the materials proved, an acceptable CIELAB color match to any of the shades tested. CONCLUSION When various shade tabs of Vitapan Classical shade guides were compared with correspondent tabs made of direct restorative composites, no material/shade combination resulted in an acceptable mismatch relative to the used standard of acceptability. Therefore, evaluated resin composites exhibited poor match compared to target Vitapan Classical tabs.

Restoration of proximal contact in direct class II resin composites.

Although this technique performed well in the case presented, it becomes more advantageous with larger restorations. This would be especially true for core build-up restorations of missing cusps, although such cusps must be restored prior to placement of separating rings. Clear plastic matrices are available and permit effective curing of resins, but the authors find the preset contours of these matrices not sufficiently adaptable to differing clinical situations and prefer metal matrices, even though these necessitate additional light curing after matrix removal.

Cytotoxicity of endodontic sealers after one year of aging in vitro

The in vitro cytotoxic response to endodontic sealers was assessed for one year. AH-Plus (AHP), Epiphany (EPH), EndoRez (ER), Guttaflow (GF), InnoEndo (IN), and Pulp Canal Sealer (PCS) were exposed to mouse osteoblasts and human monocytes after curing, 52 weeks of aging, and after resurfacing post-aging; cellular response was estimated by succinate dehydrogenase (SDH) activity. The effect of materials on TNFα secretion from activated (LPS) and inactivated monocytes also was measured. Cell responses were compared with ANOVA and Tukey post hoc analysis (α = 0.05). Initially, all materials except GF suppressed osteoblastic SDH activity compared with Teflon (Tf) controls. SDH activity in cells exposed to some aged sealers improved significantly; but IN and ER remained cytotoxic. When aged materials were resurfaced then tested, AHP, ER, GF, and IN did not change. EPH and PCS were more toxic. Monocytes responded similarly to the osteoblasts. No endodontic sealer activated monocytic TNFα secretion (p > 0.05 vs. -LPS Tf-controls). LPS-activated monocytes exposed to unresurfaced AHP and IN significantly suppressed TNFα secretion. When activated monocytes were exposed to the resurfaced sealers, differential suppression of TNFα secretion was observed for three of the four sealers tested (EPH, IN, and PCS). The results suggest that long-term aging may be a useful adjunct to in vitro assessment of these materials.

Four-year follow-up of the rehabilitation of a mandibular arch with a cementable zirconia-reinforced fixed dental prosthesis: a clinical report.

Implant-supported prostheses have been used extensively to rehabilitate completely edentulous arches. Although combinations of different restorative materials have reportedly been used to fabricate such prostheses, a metal framework is usually chosen for acrylic resin reinforcement. However, cost and the frequent need to section and solder to attain a passive framework fit are disadvantages for using metal. Zirconia has been used widely in restorative dentistry as an alternative to metal. This clinical report describes the fabrication of a zirconia-reinforced cementable fixed dental prosthesis with a 4-year follow-up.