The effect of double adhesive application on the shear bond strength to dentin of compomers using three one-bottle adhesive systems

Tbe development of one-bottle dentin adhesive systems resulted in much opti mism about providing simplified predictable esthetic dentistry. However, la boratory testing of these systems continues to provide significant variatio ns between facilities. A potential effect of the number of applications was noted in this author's laboratory. This study evaluated the effect of doub ling the manufacturer's recommended number of applications on shear bond st rength to dentin. Ninety human molars were divided into groups of 16. The occlusal surfaces w ere finished to 600 grit SiC to provide a flat dentin bonding surface. Prim e & Bond NT-Dyract, Optibond Solo-Elan and One Step-Dyract were evaluated. Each material was tested using: (1) the recommended number of adhesive appl ications and (2) twice the number of applications recommended. All adhesive applications were accomplished before light curing the adhesive. The speci mens were thermocycled after one week of storage and tested in shear after two weeks. Specimens were also fabricated after adding Rhodanzine D to the adhesive to allow for visualization using confocal microscopy. These teeth were sectio ned and viewed 24 hours after fabrication. A t-test was used to compare differences within product groups. The results showed a significant effect (p <0.001) when a double application of Prime & Bond NT was used. No difference was seen with Optibond Solo or One Step. All specimens appeared to have a uniform, glossy appearance of adhesive dur ing fabrication. Therefore, the appearance of the adhesive after applicatio n may not be a reliable predictor of acceptable bonding. Confocal microscop y showed that single application Prime & Bond NT specimens did notexhibit a uniform thickness of adhesive across the entire interface. Tubule penetrat ion and hybridization was apparent for all specimens.