Effects of tooth quality, tooth structure, and cement mixing ratios on dental adhesion

Experiments were performed on a number of bovine dentin specimens with the intent of understanding the effects of dentin quality and preparation on dentinal adhesion. Dentin quality was evaluated by measuring its wetting characteristics and hardness properties. The effects of chemical treatment, thermal dehydration and rehydration on dentin quality were examined. The contribution of enamel to adhesion was evaluated by comparing the adhesion of dentin samples that had the enamel ground off prior to bonding with dentin samples that retained the enamel wall. Sulfuric acid and tannic acid etching of dentin were performed for both ground and unground teeth. Unground dentin specimens were also exposed to thermal aging at 65° C. The torsional bond strength of the dental tissues under these modified processing conditions was evaluated using a commercial glass-ionomer cement. The same procedure has been repeated on unground and ground teeth by changing several different cement mixing ratio. The chemical, thermal, and mechanical properties of the cement mixing ratios were evaluated separately to provide a better understanding of adhesion. Acid etching treatment was found to improve dentin wetting characteristics and roughened the dentin surface leading to improve dental adhesion. Thermal treatment renders the dentin surface more hydrophobic and subsequently reduces adhesion. Weaker strengths were measured for untreated and ground teeth. This is related to lower mechanical interlocking and lower chemical adhesion when the smear layer covers the dentin. Mixed failure modes were detected during dentin debonding while cohesive failure within the cement were observed during enamel debonding indicating that enamel bonded better to the cement than dentin did. Improper cement mixing decreased the bond strength of enamel and dentin.