Ni Ti Instruments and Crown-Down Technique to Prepare Dentin Endodontic Walls: a SEM Study

Objectives: the aim of this study was to evaluate the ability to shape apical and medium third of endodontic dentin walls using two different rotary NiTi techniques and one manual crown-down conventional technique. Materials and Methods: thirty extracted human incisors were used for the study. After coronal removal, each root was prepared with a #10 K file. Coronal thirds of all the three groups were then prepared with a Gates no. 5 and 3. Crown-down manual technique and K files (FKG) were used in the first group, rotary technique with NiTi Hero 642 (Micromega)and with NiTi Race (FKG) in the other two groups. Irrigations with 5 ml of NaOCl 5% and EDTA were performed on all specimens. Each sample was split vertically into two halves with a lancet, fixed in 4% glutaraldeyde in 0.2 M sodium-cacodylate buffer, dehydrated in graded concentration alcohol, air dried, then gold sputtered and observed with SEM. Each specimen was evaluated in its three main areas (coronal, middle and apical third), comparing its aspect with four predefined different parameters (smear layer, pulpal debris, inorganic debris, correct surface profile) in order to have a score to all the area of each one. Results: no significant difference was found between the two rotary instrumentations. Crown-down manual technique with K files allows a more precise surface profile, showed a thin not-layered smear layer, the lack of pulpal and inorganic debris and proved better than both rotary instruments. Conclusions: crown-down technique with K file showed better results in comparison with both NiTi rotary instruments (HeRo 642 and RaCe). The use of a large preparation at coronal third and the crown-down technique were responsible for a better control of the apical preparation.