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Effects of composite restorations on resistance to cuspal fracture in posterior teeth.

A clinically acceptable MOD cavity preparation was used instead of a jig-mounted slot preparation in this investigation. Each preparation was proportional to the tooth dimension. The design of the testing instrument ensured that forces applied to the specimens were applied to tooth structure and not to the restorative material. Prepared unrestored teeth were weaker than restored teeth. No significant difference was noted in fracture resistance between teeth restored with amalgam and with composite resin. The method used in this study is replicable, allowing the possibility of comparison studies by using identical procedures. Future research will focus on issues of polymerization method and modulus of elasticity and their effects on fracture resistance of remaining tooth structure.

Bond strength and durability of glass ionomer cements used as bonding agents in the placement orthodontic brackets

One potential risk of orthodontic treatment is the development of surface decalcification in association with use of brackets and bands. A bonding agent that could render tooth structure more resistant to the caries process clearly would reduce the negative iatrogenic outcomes of orthodontic therapy and thereby benefit the patient. Glass ionomer cement (GIC) bonds chemically to both enamel and dentin. In addition its high fluoride content makes enamel more resistant to caries. The purpose of this study was to evaluate the bond strength and durability of GIC when used as a bonding agent in the placement of orthodontic brackets. The materials tested were three GICs (Ketac-Fil, Ketac-Cem, and Chelon) and a standard bonding agent currently in widespread use (Rely-A-Bond). Brackets were attached to the facial surface of 96 premolar specimens and half the specimens for each bonding agent were thermocycled. Bond shear strength was determined with an Instron testing device by applying a load to the occlusal margin of each bracket to the point of failure. A two-way ANOVA indicated a significant bonding agent by thermocycling interaction (F = 4.78, p less than 0.01). Thermocycling decreased bond strength significantly for all materials, but had the greatest impact on Rely-A-Bond. However, Rely-A-Bond provided the strongest bond with and without thermocycling. Although bond strength for the standard orthodontic bonding agent deteriorates significantly under thermal stress, these results suggest that it is still greater than the bond strength provided by GIC materials.

Effects of incremental versus bulk fill technique on resistance to cuspal fracture of teeth restored with posterior composites

Posterior resin placed with an incremental technique produces greater resistance to cuspal fracture than posterior resin placed with a bulk technique. P-30 composite placed by either a bulk fill or incremental technique produces greater resistance to cuspal fracture than Ful-fil composite.

Shear strength of resin developed by four bonding agents used with cast metal restorations

The evolution of the acid etch technique has made possible a more conservative approach to the fabrication of cast metal restorations. The resin bonding technique, however, places a greater burden for success on the selection of a bonding agent. This study examined the shear bond strength durability of cast metal restorations bonded to tooth structure with one of four metal adhesive bonding agents. Results indicated stronger bonds for restorations cemented with Panavia EX bonding agent than with any of the other bonding agents tested, both with and without exposure to thermal stress. Although it was one of the easier materials with which to work, Panavia EX bonding agent requires the additional step of applying an agent to prevent oxygen contact in the setting process.

Fracture resistance of posterior teeth restored with glass ionomer-composite resin systems

This study compared the fracture resistance of posterior teeth restored with one of four composite resin systems or amalgam. Mesio-occlusodistal cavity preparations were placed in 50 maxillary premolars. Dimensions of the preparation were such that remaining tooth structure was weakened. Five groups of 10 specimens each were designated as follows: I, amalgam; II, Ketac-Bond glass-ionomer base; III, Ketac-Silver glass-ionomer base; IV, GC lining cement glass-ionomer base; and V, Tenure dentinal bonding agent. Specimens in groups II through V were restored with P-30 posterior composite resin. Testing was accomplished by applying an occlusal load to the point of failure for each specimen. Results indicated no significant difference among restorative systems in resistance to cuspal fracture. These findings suggest that neither Tenure nor glass-ionomer cement used in conjunction with posterior composite resin strengthen weakened cusps to any greater extent than does amalgam.

Bond durability between dentinal bonding agents and tooth structure

Glass-ionomer cements and dentinal bonding agents have made possible cavity preparations without mechanical retention. However, durability of bond strength is critical to the longevity of these restorations. This research evaluated the durability of the chemical bond formed by four materials attached directly to tooth structure. Tenure bonding agent recorded the strongest bond at each thermocycling time. In addition, whereas the bond strength remained unchanged for Scotchbond bonding agent, Ketac-Bond glass-ionomer cement, and GC lining cement, bond strength for Tenure bonding agent increased with thermocycling.

Effects of etching time on surface morphology and adhesion of a posterior resin to glass-ionomer cement

This study examined the effects of etching time on surface morphology and adhesion of posterior composite resin to glass-ionomer cement. Three glass-ionomer cements and four etch times were studied. Bond shear strength results revealed significant differences by both cement and etch time. Glass-ionomer surfaces etched for 30 seconds produced the strongest bond to resin. Ketac-Silver cement provided greater shear resistance than either Ketac-Bond cement or GC lining cement. Scanning electron microscopy revealed greater surface roughness for etched versus unetched glass ionomer. However, no subsurface differences were noted with increased etch times. These findings indicate that 30 seconds is the optimal etch time for glass-ionomer cement and that Ketac-Silver cement provides the strongest bond to resin of any of the materials tested. Etched glass-ionomer subsurfaces did not reveal marked differentiation in morphology, suggesting that an alternative method is necessary to detect these differences.

Determination of demand for posterior resin restorations

More specific guidelines in infection control, the CDC pamphlet entitled Preventing the Transmission of Hepatitis B, AIDS, and Herpes in Dent&y can be obtained free of charge by writing to Centers for Disease Control, Center for Preventive Services, Dental Disease Prevention Activity, Atlanta, GA 30333. A beneficial guide that outlines many of the basics of AIDS is entitled AIDS: Reference Guide for Medical Professionals, and can be obtained by sending

Rubber dam usage among practicing dentists.

3.50 to CIRID/Outreach and Education, c/o Dept. of Microbiology and Immunology, UCLA School of Medicine, Los Angeles, CA 90024. Checks should be made payable to: Regents of the University of California.