Clinical evaluation of two desensitizing agents for use under Class 5 silver amalgam restorations.

STATEMENT OF PROBLEM: Postoperative sensitivity is sometimes reported to be a clinical problem after placement of silver amalgam restorations. PURPOSE: This study compared postoperative sensitivity of Class 5 caries restored with amalgam restorations and Copalite or DentinBloc cavity liners. MATERIAL AND METHODS: At least 1 pair of amalgam restorations were placed in each of 16 patients and tested for sensitivity at 5 time periods. RESULTS: Sensitivity was significantly less with DentinBloc cavity liner (P < .05) at 24 hours, and 2 and 4 weeks. There was a directional but nonsignificant effect (P > .05) in favor of DentinBloc cavity liner at 1 and 16 weeks. CONCLUSION: DentinBloc cavity liner was more effective than Copalite cavity liner in reducing sort term postoperative sensitivity for amalgam restorations.

Correlative transmission electron microscopy examination of nondemineralized and demineralized resin-dentin interfaces formed by two dentin adhesive systems.

The resin-dentin interface formed by two dentin adhesives, Optibond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M), was ultramorphologically examined by transmission electron microscopy (TEM). Ultrastructural information from nondemineralized and demineralized sections was correlated. It was hypothesized that the different chemical formulations of the two adhesives would result in a different morphological appearance of the hybrid layer. Ultrastructural TEM examination proved that each of the two dentin adhesive systems was able to establish a micromechanical bond between dentin and resin with the formation of a hybrid layer. However, the interfacial hybridization process that took place to produce this resin-dentin bond appeared to be specifically related to the chemical composition and application modes of both systems. OPTI consistently presented with a hybrid layer with a relatively uniform ultrastructure, electron density, and acid resistance. These three parameters were found to be more variable for the hybrid layer formed by SBMP. Characteristic of SBMP was the identification of an amorphous phase deposited at the outer surface of the hybrid layer. Although both adhesive systems investigated follow a total-etch concept, their specific chemical formulations result in different interfacial ultrastructures that are probably related to different underlying bonding mechanisms. The clinical significance of these morphological findings, however, is still unknown.

Demonstration of a focused ion-beam cross-sectioning technique for ultrastructural examination of resin-dentin interfaces.

OBJECTIVES: focused ion-beam (FIB) etching, commonly used as a cross-sectioning technique for failure analysis of semiconductor devices, has recently been applied to biological tissues to expose their ultrastructure for examination. It was the aim of this investigation to determine the practical utility of FIB to cross-section resin-dentin interfaces in order to morphologically evaluate the completeness of resin penetration into the exposed collagen scaffold at the resin-dentin bond interface. METHODS: Two representative commercially available dentin adhesive systems were bonded to mid-coronal dentin. After appropriate fixation and dehydration of the resin-bonded dentin samples, a scanned focused ion-beam of a few tens of nano-meters in diameter was used to cross=section the resin-dentin interface. Examination of the interfacial ultrastructure was accomplished using a field-emission SEM. RESULTS: Results indicate possible artifact production at the cross-sectioned interface, hiding its actual ultrastructure, probably due to a heat-effect with possible recrystallization. Further studies of FIB are needed to optimize its usefulness for resin-dentin interface examinations and other biological tissue applications. SIGNIFICANCE: Complete resin saturation of the demineralized dentin surface-layer has been claimed to be the key factor for a long-lasting resin-dentin bond. A "clean" artifact-free micro-cross-sectioning technique may provide indisputable ultra-structural information about the depth of resin penetration into the demineralized zone. Such a test would be useful in the development of dentin adhesive systems.

Effectiveness of nitric-NPG as a conditioning agent for enamel.

This in vitro study was designed to measure the bond strength of composite resin to enamel treated with various regimes of HNO3-NPG (N-phenylglycine and glycidylmethacrylate) followed by application of PMDM (pyromellitic dianhydride and 2-hydroxyethyl methacrylate). Forty freshly extracted human teeth were prepared with a flat area entirely in enamel on the proximal surface and then divided into five groups. Group 1 was treated with 37% H3PO4, Group 2 with 2.5% HNO3-NPG while rubbing the enamel with the solution, Group 3 with 2.5% HNO3-NPG without rubbing, Group 4 with 37% H3PO4 plus 2.5% HNO3-NPG with rubbing, and Group 5 with 5% HNO3-NPG without rubbing. After drying, PMDM solution was applied to each specimen for 60 seconds. Unfilled resin was applied, cured for 20 seconds, and the composite resin was placed and cured from all sides for a total of 120 seconds. After water bath storage for 7 days, specimens were tested on an Instron machine at a crosshead speed of 2.0mm/min. The highest shear bond strengths measured were for Group 1 (22.7 MPa), followed by Group 2 (20.92 MPa). The lowest bond strength recorded was for Group 3 (14.43 MPa). The results of this study indicate that enamel surfaces treated with 2.5% HNO3-NPG solution, if the solution is rubbed during application, produce a bond strength comparable to that achieved by H3PO4 conditioning.