The ability of acid etchants to penetrate dentin was tested under simulated clinical conditions. No penetration of the dentinal tubules by acid was detected by use of two different test methods, although pronounced roughening of the treated surfaces was observed.

A method for accelerated testing of dental composite restorative materials is described, and results of these tests are reported. The uniform testing showed considerable variation in the properties of the eight materials included in the study.

SummaryThermal conductivities were determined for five commercial composite restorative materials, one composite crown arid bridge cement, two cavity "bases," arid poly(methy1 methacrylate). In addition, the effect on thermal conductivity of concentration arid type for five resin-reinforcing fillers was investigated. Ilepending upoii type and concentration of filler, the composites ranged in thermal conductivity from somewhat less than that for dentin to slightly over twice that value. Because of their good marginal adaptation, the thermal conductivity of composites must either be closely matched to tooth structiire or a base should be used in deep restorations.

Bovine teeth that were treated with acidulated fluoride before and after etching with phosphoric acid produced adhesive bonds with fissure sealers that were lower than those of untreated controls. Human teeth from an area of high natural fluoridation were shown to be extremely resistant to etching with citric and phosphoric acids.

Seven commercial composite filling materials were studied as regards 1) differences in their ability to take a smooth polish as measured by an electronic roughness gauge and 2) their relative loss in smoothness due to toothbrushing. A series of test formulations indicated that polishability and ability to retain a good polish are interrelated and are functions of filler particle size and filler hardness. Optimization in the filler particles from the point of view of polishability also results in improved wear resistance to toothbrushing.