Effects of three nickel titanium instrument systems on root canal geometry assessed by micro-computed tomography.

AIM: To compare and evaluate the shaping ability of several nickel titanium instrument systems with different motions: two reciprocating single-file systems (Reciproc and WaveOne) and one continuous rotation/reciprocation full-sequence system [Twisted File (TF) Adaptive] using micro-computed tomography. METHODOLOGY: A total of forty-eight mesial canals of mandibular molars with two separate root canals and severe angles of curvature were selected. Canals were divided randomly to one of three experimental groups: group 1, reciprocating instrumentation with Reciproc R25, group 2, reciprocating with the Primary WaveOne file and group 3 'Adaptive Rotary Motion' with Twisted Files. Each group consisted of 16 root canals. Canals were scanned before and after root canal preparation, with a resolution of 20 µm using a micro-computed tomography system. The following parameters were assessed: changes in dentine volume, percentage of unshaped canal walls, degree of canal transportation and centring ability. Data were analysed using analysis of variance and Tukey's post hoc tests test to explore a significant difference in mean dentine removal, mean percentage of noninstrumented canals, mean degree of canal transportation and centring ratio between groups in the apical third and along the entire root canal. The level of significance was set at α = 0.05. RESULTS: Preoperatively, there were no differences regarding root canal curvature and volume between experimental groups (P > 0.05). Overall instrumentation led to enlarged canal shapes with no evidence of preparation errors. None of the three groups was able to shape completely the root canal system. Mean dentine removal along the entire canal and in the apical third was significantly higher with Reciproc when compared with TF Adaptive and WaveOne (P = 0.013). Mean degree of canal transportation was significantly lower with TF Adaptive (P < 0.0001) followed by WaveOne and highest with Reciproc in the apical third and along the entire root canal. CONCLUSIONS: None of the NiTi systems was able to instrument completely the entire root canal. Reciprocation and Adaptive Motions were found to cut dentine efficiently to full working length, with no procedural errors. The TF Adaptive system maintained the original canal anatomy with less canal transportation and better centring ability.

Cyclic fatigue analysis of twisted file rotary NiTi instruments used in reciprocating motion.

AIM: To evaluate the cyclic fatigue fracture resistance of engine-driven twisted file (TF) instruments under reciprocating movement. METHODOLOGY: A sample of 30 size 25, 0.08 taper NiTi TF instruments was tested in a simulated canal with 60˚ angle of curvature and a 3 mm radius. During mechanical testing, different movement kinematics were used at a constant speed, which resulted in three experimental groups (each group n = 10). The instruments from the first group (G1) were rotated until fracture occurred. The instruments in the second (G2) and third group (G3) were driven under reciprocating movement with different angles of reciprocation. The time of fracture for each instrument was measured, and statistical analysis was performed using one-way analysis of variance followed by Tukey's Honestly Significant Different test. RESULTS: Reciprocating movement resulted in a significantly longer cyclic fatigue life (P < 0.0001) when compared with continuous rotation. No difference was found between reciprocation 150° clockwise/30° counterclockwise (CW/CCW) and 30° CW/150° CCW. CONCLUSIONS: The reciprocating movement was associated with an extended cyclic fatigue life of the TF size 0.25, 0.08 taper instruments in comparison with conventional rotation.

Effectiveness of two nickel-titanium rotary instruments and a hand file for removing gutta-percha in severely curved root canals during retreatment: an ex vivo study.

AIM: To evaluate ex vivo the effectiveness of hand files, ProTaper and R-Endo rotary instruments when removing gutta-percha from curved root canals. METHODOLOGY: Ninety severely curved teeth were divided into three groups. The root canals were accessed, prepared and filled with vertically condensed gutta-percha and sealer. Removal of gutta-percha was performed with the following devices and techniques: Hedström files (Vereinigte Dentalwerke, Munich, Germany), ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) and R-Endo (Micro-Mega, Besançon, France). All techniques were used with the solvent eucalyptol. The amount of filling material debris remaining on root canal walls was assessed radiographically from two directions: mesio-distal and bucco-lingual. The images were digitized and analysed with autocad 2000 software. Total canal area, area of the cervical, middle and apical thirds, and area of remaining filling material from both directions were outlined by two different operators and calculated. Statistical analysis of remaining filling material within each third of the canals was performed by the Kruskal-Wallis test. RESULTS: Comparisons of the percentages of remaining filling material in the entire canal did not reveal any significant differences between the methods of removal. However, the canal third was of relevance in all groups; the apical third had the most remaining filling material compared with the middle and cervical thirds (P = 0.0012). CONCLUSION: All instruments left filling material inside the root canal. ProTaper and R-Endo rotary instruments were inadequate for the complete removal of filling material from the root canal system.

Functional interplay between gelatinases and hyperalgesia in endotoxin-induced localized inflammatory pain.

The role of ECM-degrading proteinases in normal developmental processes and in pathological conditions is extensively studied. However, few reports describe the role ECM-degrading proteinases play in modulating hyperalgesia. The goal of this study is to describe the regulation of gelatinases during endotoxin mediated local inflammation, induced by intra plantar endotoxin (ET; 1.25 microg/50 microl) injection in Balb/c mice, and to correlate that with hyperalgesia. ET injections induced hyperalgesia, as determined by hot plate and paw pressure tests, which peaked by 24 h and recovered by 48 h post-injection. Contralateral paw of ET injected mice and saline injected paws in control mice elicited no hyperalgesia. Zymography showed that ET and saline injected paws elicited increased gelatinase activity by 9 h after injection. However, only the former maintained high levels of expression of a 90 kD gelatinase up to at least 96 h post ET injection, while in the latter gelatinase expression was down regulated by 24 h. Interestingly, the 90-kD gelatinase was upregulated in the contralateral paw of the ET-injected mice beyond 48 h post injection. Saline injection in that paw, during a time when gelatinases are upregulated, induced hyperalgesia. Intraperitoneal injection of either ZnCl(2) (100 microM), thymulin (5 microg/100 microl), or morphine (2 mg/kg/100 microl) reversed the ET-induced hyperalgesia and suppressed gelatinase activity. Furthermore, intraperitoneal injection of MPI, an ECM-degrading proteinase inhibitor, reversed ET induced hyperalgesia. Taken together, the above suggests that a functional interplay exists between gelatinase upregulation triggered by ET injections and hyperalgesia. The exact mechanism underlying such correlation remains to be determined.