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.

No abstract

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.

The potential for maximizing conversion of room-temperature, photoactivated resin composite in the oral environment is limited. Pre-heating composite prior to light-curing is hypothesized to increase monomer conversion and reduce the duration of light exposure. Composite temperature was controlled at between 3 degrees C and 60 degrees C prior to exposure with a conventional quartz-tungsten-halogen curing unit: 5, 10, 20, or 40 sec. Monomer conversion was calculated from infrared spectra at 0 mm (top) and 2-mm-deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r(2) = 0.999, 2 mm r(2) = 0.998. Conversion ranged from 31.6% (3 degrees C) to 67.3% (60 degrees C). The duration of light exposure, reduced by 50 to 75% with pre-heated composite, yielded the same or significantly higher conversion (p = 0.001) than with control (22 degrees C, 20 sec). Both hypotheses were accepted: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light exposure than with room-temperature composite.

No abstract

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 degrees and 60 degrees 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.

Preheating composite has potential benefits, but should be used with knowledge of its limitations. Reheating of unused composite does not affect its degree of conversion, thus decreasing material waste. Heating of the composite preloaded in the delivery syringe enhances the temperature of extruded composite.

SUMMARY 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. Flat surfaces of two types of dentin (i.e. ND and CAD) were prepared with a water-cooled high speed diamond disc, and then acid-etched, rinsed and air-dried. In control groups, dentin was re-hydrated with distilled water, blot-dried and bonded with a three-step (Scotchbond Multi-Purpose-MP) or a two-step (Single Bond 2-SB) etch-and-rinse adhesive. In experimental groups, dentin was re-hydrated with 2% CHX (60 s), blot-dried and bonded with the same adhesives. Resin composite build-ups were made. Specimens were prepared for microtensile bond testing in accordance with the non-trimming technique and then tested either immediately or after 6-month storage in artificial saliva. Data were analyzed by ANOVA/Bonferroni tests (α = 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 6 months seen in control bonds for ND (p<0.05), but it did not alter the bond strength of CAD (p>0.05). Application of MP on CHX-treated ND or CAD produced bonds that did not change over 6 months of storage.