Analysis of primary and permanent molars prepared with high speed and ultrasonic abrasion systems

The aim of this study was to compare high speed and ultrasonic systems with regard to both topography and smear layer formation in the cavity preparations of sound primary and permanent molars. Class I occlusal cavities measuring 2.00 x 2.00 x 2.00 mm were performed in 14 molars, equally divided into two groups (GI = 7 primary teeth and GII = 7 permanent teeth). High speed rotary instruments produced regular layers of enamel and dentin, despite the marked presence of grooves and microfractures on enamel surfaces. On the other hand, ultrasonic abrasion yielded more irregular surfaces in enamel and dentin, with a granular and wavy aspect, but without microfractures in enamel. Both types of dental substrates were found to have an intense smear layer formation, partially or even completely obliterating the dentinal tubules (p>0.05), irrespective of the instrument used. No difference was observed in either primary or permanent teeth as regards the amount of smear layer produced by high speed or ultrasonic abrasion instruments (p>0.05). It was concluded that with regard to the topography of cavity preparations, there were differences between the instruments used, irrespective of the dental substrate. Both systems allowed dense smear layer formation, which completely or partially obliterated the dentinal tubules of primary and permanent teeth.