Bonding to old and young dentin – a SEM observation

OBJECTIVES: to verify if there are differences between bonding to old and young dentin.

METHODS: Twelve human molars were donated by patients with 55-to-60 years-old. Other 12 molars from patients with 18-to-22 years-old. The teeth were transversally cut. The occlusal surfaces were grid exposing superficial flat dentin, and polished to 600-grid. All teeth were cut buco-lingually. On the first stage, one of the two equal half occlusal dentin specimens was acid-etched with 35% phosphoric acid (3M ESPE) for 15s. The adhesive system (SingleBond, 3M ESPE) was applied and a hybrid composite resin (Filtek Z250, 3M ESPE) was inserted in increments and light-cured. After 24h, 12-half specimens from young and other 12 from old dentin were cut in perpendicular directions to obtain slices with a low-speed diamond saw (Isomet 1000, Buehler) forming the groups G15Y and G15O. Other 12 half specimens from young and from old dentin were prepared but with the acid-etching applied for 30s. After the cut, the slices were distributed between other two groups: G30Y and G30O. All specimens were fixed, dehydrated, polished to a high-gloss, demineralized, deproteinized and observed under a SEM.

RESULTS: Resin tags on the dentin tubules were formed in all specimens, being larger and more numerous on young dentin. On old dentin (G15O), the HL formed on intertubular dentin was very thin and there were difficult to demineralize peritubular dentin. The duplication of the etching time (G30O) resulted in more homogeneous HL formation on intertubular dentin and formation of HL more predictable on peritubular dentin. The HL on young dentin was thicker when the acid etch was performed for 30s (G30Y).

CONCLUSION: The higher mineral amount on old dentin difficult HL formation on this substrate compared to young dentin. Duplicating the etching time to 30-seconds results in more homogeneous HL formation on old-dentin.