Martha Goël 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.

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.

Quaternary ammonium silane-functionalized, methacrylate resin composition with antimicrobial activities and self-repair potential.

The design of antimicrobial polymers to address healthcare issues and minimize environmental problems is an important endeavor with both fundamental and practical implications. Quaternary ammonium silane-functionalized methacrylate (QAMS) represents an example of antimicrobial macromonomers synthesized by a sol-gel chemical route; these compounds possess flexible Si-O-Si bonds. In present work, a partially hydrolyzed QAMS co-polymerized with 2,2-[4(2-hydroxy 3-methacryloxypropoxy)-phenyl]propane is introduced. This methacrylate resin was shown to possess desirable mechanical properties with both a high degree of conversion and minimal polymerization shrinkage. The kill-on-contact microbiocidal activities of this resin were demonstrated using single-species biofilms of Streptococcus mutans (ATCC 36558), Actinomyces naeslundii (ATCC 12104) and Candida albicans (ATCC 90028). Improved mechanical properties after hydration provided the proof-of-concept that QAMS-incorporated resin exhibits self-repair potential via water-induced condensation of organic modified silicate (ormosil) phases within the polymerized resin matrix.

A Comparison of Human Raters and an Intra-oral Spectrophotometer

Consistently choosing an accurate shade match is far more difficult than it appears. Recently, several electronic shade-matching devices have been marketed. One device is an intraoral spectrophotometer, Easyshade. The current study compared the accuracy and consistency of the Easyshade (ES) device to three clinicians experienced in tooth whitening trials and trained in the use of the Vitapan 3D Master shade. The maxillary anteriors of 16 participants were matched on three separate occasions one month apart. At each appointment, the three clinicians (R1, R2 & R3) and ES independently chose a single 3D Master tab. A trained research assistant used the Easyshade device to record CIE L*, C* and H* and a shade tab. In addition, color differences between shade tabs were calculated using the Delta E 2000 (delta e 00) formula. The CIE L*C*H* data were also used to establish standards for the five lightness groups of the 3D Master. An intrarater agreement was evaluated using an intraclass correlation statistic, and an inter-rater agreement was evaluated using a weighted Kappa statistic. The percentages of exact matches were: ES = 41%; R1 = 27%; R2 = 22% and R3 = 17%. Matches within a half-shade were also calculated. This represents a mismatch that is perceptible but acceptable. The percentages of matches within a half-tab were: ES = 91%; R1 = 69%; R2 = 85% and R3 = 79%. In terms of lightness, the intra-rater agreement was considered to be very good for ES and R2 and good for R1 and R3. For chroma, agreement for ES was considered good, and for the three clinicians, it was considered moderate. The mean color difference for the L*, C*, H* data recorded at each evaluation was 1.5, or only slightly greater than the color difference between the same tab on different guides (1.2). The delta e 00 data were the most accurate data collected, and they were used to establish a standard to which the tab choices of the four raters were compared. A weighted Kappa statistic was performed and, in terms of lightness, agreement was found to be good for all raters. For chroma, agreement was very good for ES and it was good for the clinicians. In terms of the number of exact matches and matches within a half-shade, the performance of ES was at least comparable to, if not better than, the dentists. Statistically, the same was true in terms of consistency and accuracy when making repeated matches of lightness and chroma using the 3D Master shade guide.

In vitro cytotoxicity evaluation of a self-adhesive, methacrylate resin-based root canal sealer.

This study compared the cytotoxicity of MetaSEAL (Parkell Inc, Farmington, NY), a methacrylate resin-based sealer with an epoxy resin-based (AH Plus Jet; Dentsply Caulk, Milford, DE) and a zinc oxide-eugenol-based sealer (Pulp Canal Sealer; SybronEndo, Orange, CA). Five-millimeter diameter disks prepared from the respective sealer and disks prepared from Teflon (negative control) and polymethyl methacrylate (positive control) were placed in direct contact with a rat osteosarcoma (ROS) 17/2.8 rat osteoblast-like cell line at six intervals after setting completely at 72 hours and for 5 succeeding weeks after the disks were immersed in simulated body fluid. Succinate dehydrogenase activity was evaluated by using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide assay. All sealers exhibited severe toxicity at 72 hours, after which toxicity decreased gradually over the experimental period except for Pulp Canal Sealer, which remained severely toxic. MetaSEAL was more toxic than AH Plus Jet during the first week. Both were similar to the toxicity profile of the positive control after the first week, which was probably diffusion controlled.

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.

Cytotoxicity of endodontic materials over 6-weeks ex vivo.

AIM To test the hypothesis that extending the time of a traditional ex vivo cytotoxicity test helps to identify trends in the behaviour of root core materials and sealers, which could ultimately aid in predicting their clinical safety and performance. METHODOLOGY Endodontic sealers and core specimens were initially tested in direct contact with L929 fibroblasts for 72 h. Cell response was estimated by measuring cellular succinate dehydrogenase activity relative to Teflon controls. Cytotoxicity (% of more active cells) was reassessed after 1, 3, 4 and 6 weeks, with the specimens stored in a physiologically balanced salt-solution between tests. RESULTS Distinct trends in cytotoxicity among both core materials and sealers were observed over the 6-week test. Four of the six sealers and two of the three core materials showed cell viabilities of <30% of Teflon after 6 weeks (>70% cytotoxicity). CONCLUSIONS The current results suggest that some endodontic materials have an elevated biological risk for extended intervals.

In vitro osteogenic potential of an experimental calcium silicate-based root canal sealer.

OBJECTIVE This in vitro study compared the cytotoxicity and osteogenic potential of an experimental calcium silicate-based sealer with an epoxy resin-based sealer (AH Plus; Dentsply Caulk, Milford, DE) and a zinc oxide-eugenol-based sealer (Pulp Canal Sealer; SybronEndo, Orange, CA). METHODS Disks prepared from the respective sealer and from Teflon (negative control) were placed in direct contact with a MC3T3-E1 osteogenic cell line at 6 weekly intervals after immersion in a culture medium. Succinic dehydrogenase activities were evaluated using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Extracts from these sealers after the 6-week immersion period were investigated also by MTT assay. Aged sealers were then switched to an osteogenic medium for examination of the alkaline phosphatase activity and mineralization of extracellular matrices produced by the differentiated cells. RESULTS All sealers exhibited severe toxicity after 24 hours, after which toxicity decreased gradually over the experimental period except for Pulp Canal Sealer, which remained severely toxic. Toxicity of the extracts derived from the sealers was concentration dependent, with those derived from the experimental sealer being the least cytotoxic at a 1:10 dilution. Minimal alkaline phosphatase activity and no bone formation were seen with Pulp Canal Sealer. The production of alkaline phosphatase was less intense for the experimental sealer at 7 days. However, both AH Plus and the experimental sealer did not inhibit mineralization of the extracellular matrix after 28 days. CONCLUSION The experimental calcium silicate-based sealer may be regarded as minimally tissue irritating and does not interfere with bone regeneration even when it is inadvertently extruded through the apical constriction.

Water distribution in dentin matrices: bound vs. unbound water.

OBJECTIVE This work measured the amount of bound versus unbound water in completely-demineralized dentin. METHODS Dentin beams prepared from extracted human teeth were completely demineralized, rinsed and dried to constant mass. They were rehydrated in 41% relative humidity (RH), while gravimetrically measuring their mass increase until the first plateau was reached at 0.064 (vacuum) or 0.116 gH2O/g dry mass (Drierite). The specimens were then exposed to 60% RH until attaining the second plateau at 0.220 (vacuum) or 0.191 gH2O/g dry mass (Drierite), and subsequently exposed to 99% RH until attaining the third plateau at 0.493 (vacuum) or 0.401 gH2O/g dry mass (Drierite). RESULTS Exposure of the first layer of bound water to 0% RH for 5 min produced a -0.3% loss of bound water; in the second layer of bound water it caused a -3.3% loss of bound water; in the third layer it caused a -6% loss of bound water. Immersion in 100% ethanol or acetone for 5 min produced a 2.8 and 1.9% loss of bound water from the first layer, respectively; it caused a -4 and -7% loss of bound water in the second layer, respectively; and a -17 and -23% loss of bound water in the third layer. Bound water represented 21-25% of total dentin water. Chemical dehydration of water-saturated dentin with ethanol/acetone for 1 min only removed between 25 and 35% of unbound water, respectively. SIGNIFICANCE Attempts to remove bound water by evaporation were not very successful. Chemical dehydration with 100% acetone was more successful than 100% ethanol especially the third layer of bound water. Since unbound water represents between 75 and 79% of total matrix water, the more such water can be removed, the more resin can be infiltrated.