Fatigue Resistance of New and Used Nickel-Titanium Rotary Instruments: a Comparative Study.

OBJECTIVES: Aim of the present study was twofold. First, to evaluate in vitro, the performance of two different NiTi rotary instruments in one molar case; then, to evaluate their resistance to cyclic fatigue, compared to new ones. MATERIAL AND METHODS: 25 ProTaper Next (PTN) nickel-titanium (NiTi) instruments (Maillefer-Dentsply, Baillagues, CH) for each of the following two sizes: X1 (17.04 ) and X2 (25.06) were randomly divided into two groups. The first group (n = 10) immediately under- went to a cyclic fatigue test. The second group (n = 15) was initially used to prepare 15 extracted molar teeth and then subjected to a cyclic fatigue test. Same was done for 25 Horizen (HZ) instruments (Kerr Endodontics, Orange, Ca) for each of the following two sizes: 20.04 and 25.06. Instruments were rotated in curved artificial canal until fracture occurred and times to fracture were recorded. All data were collected and statistically analyzed using a variance test (confidence interval CI = 95%). RESULTS: HZ reached working length more rapidly than PTN, and with less deformations. For the fatigue tests, all the new instruments were significantly more resistant than the used ones. The HZ instru- ments were significantly more resistant in all sizes than PTN, both when new and used instruments were tested. CONCLUSIONS: Since in previous studies ProTaper Next demonstra- ted a better resistance to cyclic fatigue than most of nickel-titanium instruments, Horizen's performance put them in a high rank amongst the most resistant nickel-titanium rotary instruments.

Two clinical cases of prosthetical rehabilitation after a tumor of the upper maxilla.

The most frequent type of treatment for patients diagnosed with a malignant neoplasia of the oral cavity is surgical removal of the tumor. As a result of the resection performed, it is difficult to obtain satisfactory results in the oral rehabilitation of these patients. When possible, fixed prostheses are the best option, because they guarantee stability, but they should be made so that the operator can remove them periodically to check the health of the oral tissues underneath and to intercept any relapse of the tumor. This study analyses two cases of patients surgically treated for a tumor of the upper maxilla at the Oral and Maxillo-Facial Surgery of Sapienza University, in Rome. In the first case the surgical site was covered with local flaps, and the patient was rehabilitated with an implant-supported removable prosthesis. In the second case the maxilla was reconstructed with a fibula vascularized free flap, and the patient was rehabilitated with an implant-supported prosthesis screwed to a titanium bar solidarizing the implants. Therefore, this prosthesis was fixed, but could be removed by the dentist. The different approach to these two cases was influenced by the different anatomic situations after the reconstruction. It is important for the dentist to approach these patients knowing the kind of surgery they received because this aspect will influence rehabilitative choices. Rehabilitation should be planned, when possible, before surgical treatment, in order to cooperate with the maxillo-facial surgeon in choosing the most appropriate restorative treatment.