M.F. De Goes

In vivo Preservation of the Hybrid Layer by Chlorhexidine

Host-derived proteases have been reported to degrade the collagen matrix of incompletely-resin-infiltrated dentin. This study tested the hypothesis that interfacial degradation of resin-dentin bonds may be prevented or delayed by the application of chlorhexidine (CHX), a matrix metalloproteinase inhibitor, to dentin after phosphoric acid-etching. Contralateral pairs of resin-bonded Class I restorations in non-carious third molars were kept under intra-oral function for 14 months. Preservation of resin-dentin bonds was assessed by microtensile bond strength tests and TEM examination. In vivo bond strength remained stable in the CHX-treated specimens, while bond strength decreased significantly in control teeth. Resin-infiltrated dentin in CHX-treated specimens exhibited normal structural integrity of the collagen network. Conversely, progressive disintegration of the fibrillar network was identified in control specimens. Auto-degradation of collagen matrices can occur in resin-infiltrated dentin, but may be prevented by the application of a synthetic protease inhibitor, such as chlorhexidine.

Chlorhexidine Preserves Dentin Bond in vitro

Loss of hybrid layer integrity compromises resin-dentin bond stability. Matrix metalloproteinases (MMPs) may be partially responsible for hybrid layer degradation. Since chlorhexidine inhibits MMPs, we hypothesized that chlorhexidine would decelerate the loss of resin-dentin bonds. Class I preparations in extracted third molars were sectioned into two halves. One half was customarily restored (etch-and-rinse adhesive/resin composite), and the other was treated with 2% chlorhexidine after being acid-etched before restoration. Specimens were stored in artificial saliva with/without protease inhibitors. Microtensile bond strengths and failure mode distribution under SEM were analyzed immediately after specimens’ preparation and 6 months later. With chlorhexidine, significantly better preservation of bond strength was observed after 6 months; protease inhibitors in the storage medium had no effect. Failure analysis showed significantly less failure in the hybrid layer with chlorhexidine, compared with controls after 6 months. In conclusion, this in vitro study suggests that chlorhexidine might be useful for the preservation of dentin bond strength.

Polymerization Kinetics of Pre-heated Composite

Temperature affects the polymerization behavior of dimethacrylate-based materials. This study describes the influence of pre-polymerization temperature and exposure duration on polymerization kinetics of a commercial dental photo-activated composite at the top and at 2-mm depth. We used the temperature-controlled stage of a diamond-attenuated-total-reflectance unit to pre-set composite temperature between 3° and 60°C. Composite was light-exposed by a conventional quartz-tungsten-halogen curing unit for 5, 10, 20, or 40 sec. Real-time conversion, maximum conversion rate (R p max), time to achieve R p max, and conversion at R p max were calculated from infrared spectra. Composite pre-warming enhanced maximal polymerization rate and overall monomer conversion (top significantly greater than 2 mm). Time when R p max occurred did not change with temperature, but occurred sooner at the top than at 2-mm depth. Conversion at R p max increased with temperature, allowing more of the reaction to occur prior to vitrification than at room temperature.

Effect of 2% chlorhexidine digluconate on the bond strength to normal versus caries-affected dentin.

This study evaluated the effect of 2% chlorhexidine digluconate (CHX) used as a therapeutic primer on the long-term bond strengths of two etch-and-rinse adhesives to normal (ND) and caries-affected (CAD) dentin. Forty extracted human molars with coronal carious lesions, surrounded by normal dentin, were selected for this study. The flat surfaces of two types of dentin (ND and CAD) were prepared with a water-cooled high-speed diamond disc, then acid-etched, rinsed and air-dried. In the control groups, the dentin was re-hydrated with distilled water, blot-dried and bonded with a three-step (Scotchbond Multi-Purpose-MP) or two-step (Single Bond 2-SB) etch-and-rinse adhesive. In the experimental groups, the dentin was rehydrated with 2% CHX (60 seconds), blot-dried and bonded with the same adhesives. Resin composite build-ups were made. The specimens were prepared for microtensile bond testing in accordance with the non-trimming technique, then tested either immediately or after six-months storage in artificial saliva. The data were analyzed by ANOVA/Bonferroni tests (alpha = 0.05). CHX did not affect the immediate bond strength to ND or CAD (p > 0.05). CHX treatment significantly lowered the loss of bond strength after six months as seen in the control bonds for ND (p < 0.05), but it did not alter the bond strength of CAD (p > 0.05). The application of MP on CHX-treated ND or CAD produced bonds that did not change over six months of storage.

Correlation between light intensity and exposure time on the hardness of composite resin

This study evaluated the correlation between light intensity emitted by the curing units and exposure time on the of degree polymerization of dental composites by measured Knoop hardness. Specimens with 5 mm diameter and 2 mm height were prepared in a copper mold, covered with a mylar strip and polymerized for 30 sec by curing units with 50, 130, 180, 220, 280 and 520 mW/cm2, respectively. The output for all units was measured using a Curing Radiometer (Demetron). Other specimens were polymerized for 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180 sec utilizing units of 130, 220 and 280 mW/cm2. Knoop hardness values of the top and bottom surfaces were measured after 24 h. The results indicate that the curing units with higher light intensity presented improved values of Knoop hardness on the top and bottom regions. As expected, the top surface always presented improved Knoop hardness values in relation to the bottom, after exposure for 30 sec. The values obtained on the surface were statistically superior compared to the values on the bottom (p<0.05) for the intensity of 130, 220 and 280 mW/cm2 after 30, 45 and 60 sec of exposure. ©2000 Kluwer Academic Publishers

Long‐term sealing ability of resin‐based root canal fillings

AIM To evaluate the ability of two resin-based filling materials to provide immediate and long-term sealing of the root canal. METHODOLOGY A total of eighty-two human roots were instrumented and filled with AH Plus/gutta-percha or Epiphany/Resilon. Root filled teeth were sealed coronally either with Coltosol or Clearfil SE Bond/Filtek Z250 or were left unsealed. The quality of root canal sealing was assessed by a fluid filtration method performed at immediate and 180-day time intervals. Mean fluid filtration rates were analyzed by three-way repeated measures anova and Tukey post hoc test. RESULTS Specimens filled with Epiphany/Resilon exhibited higher leakage than specimens filled with AH Plus/gutta-percha (P < 0.05), regardless of the coronal sealing condition and period of evaluation. No difference was detected between coronal restorative materials (P > 0.05), whilst leakage in teeth without any coronal restoration was significantly higher (P < 0.05). After storage, a significant decrease in leakage (P < 0.05) was observed in all experimental groups. CONCLUSIONS AH Plus/gutta-percha provided superior root canal sealing at both immediate and 180-day time periods. The presence of a coronal seal reduced leakage significantly. Storage of root filled specimens did not disturb the sealing ability of the tested materials.

Degree of Conversion and Contraction Stress Development of a Resin Composite Irradiated Using Halogen and LED at Two C-factor Levels

This study verified the influence of curing methods and light sources on contraction stress, stress rate and degree of conversion (DC) of a restorative composite at two C-factor (CF) levels. For the stress test, composite (0.84 mm thick) was applied between two glass rods 5-mm in diameter mounted in a servohydraulic testing machine. Stress rates were calculated as the change in stress vs time at each second. DC was measured by micro-FTIR. Five curing methods were tested at two C-factor levels (1.5 and 3.0): High Intensity LED (LED HI), Continuous Light (QTH CL), Medium Intensity LED (LED MI), Low Intensity LED (LED LI) and Pulse Delay (QTH PD). The results were analyzed by ANOVA and Tukeys test (alpha = 0.05). For the stress test at CF 1.5, QTH PD presented lower values than LED HI, QTH CL and LED LI. At CF 3.0, no difference was observed among the curing methods. For all curing methods, stress values at CF 3.0 were statistically higher than those at CF 1.5. LED HI presented the highest maximum stress rate, followed by QTH CL, LED MI, LED LI and QTH PD for both C-factors. In the DC test, no difference was observed among the methods and between the C-factor levels.

Utilization of occlusal index and layering technique in class i silorane-based composite restorations

PURPOSE This article describes a technique that uses an occlusal index to restore teeth back to their original contour and anatomy with minimal finishing. A new type of ring-opening silorane composite reported to have less than 1% volumetric shrinkage was used in the restoration. For the silorane-based composite, there is no oxygen-inhibited layer to be polished away. The final composite layer is cured under pressure and further minimizes voids and gap formation. The technique can also be used on multiple posterior restorations under rubber dam isolation. Overall, if used properly, this technique helps the clinician produce superb anatomy and reduces time for posterior composite restorations.