In-Depth Metallurgical and Microstructural Analysis of Oneshape and Heat Treated Onecurve Instruments.

OBJECTIVE: To define surface, mechanical, microstructural and metallurgical features of conventional One-Shape (OShape) and heat-treated OneCurve (OCurve) nickel-titanium instruments. METHODS: Instruments were analysed by scanning electron microscopy (SEM) on new instruments and after simulated clinical use (SCU). Cyclic fatigue testing was performed and the number of cycles to fracture (NCF) and the length of the fractured instruments were measured (Mann-Whitney test). Fractured instruments during cyclic fatigue testing were then inspected by SEM fractographic analysis. Field emission gun scanning scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy were used to assess alloy surface chemistry. Focused ion beam (FIB) was performed to analyse the oxide layer on the surface of OCurve before and after SCU. X-Ray diffraction (XRD), metallographic evaluation and differential scanning calorimetry (DSC) were used to determine martensitic/austenitic phase transformation temperatures. RESULTS: SEM observations on new instruments revealed a smooth regular surface with flattened milling grooves. No wear features were detected after SCU. OCurve exhibited a higher cyclic fatigue resistance (P<0.05), slower crack propagation and a surface layer of TiO2. Metallographic analysis and XRD showed the prevalence of martensitic grains on OCurve instruments that were stable at body temperature as confirmed by DSC analysis. Furthermore, DSC demonstrated a shift in the temperature transformation ranges suggesting an increase of martensite phase in autoclaved OCurve instruments. CONCLUSION: Heat treatment processes were confirmed as a valid enhancement of the properties of the new generation NiTi instruments. OCurve presented a significant improvement over OShape regarding both mechanical and metallurgical characteristics.

Outcome of secondary root canal treatment filled with Thermafil: a 5-year follow-up of retrospective cohort study.

OBJECTIVES: The aim of the present retrospective cohort study was to assess the 5-year outcome and survival of secondary root canal treatments (2°RCT), exploring the influence of pre-, intra-, and post-operative variables. MATERIALS AND METHODS: One hundred thirty-two endodontically retreated teeth were radiographically and clinically re-examined after 5 years. 2°RCT had been performed during a Masters program following standardized protocols and filled with AH Plus/Thermafil (TF). Pre-, intra-, and post-operative data were collected. The 5-year outcome was blindly evaluated and categorized as healed/diseased on the basis of the periapical index. Bivariate analysis and chi-square test evaluated the association between outcome and 31 demographic/clinical parameters. Multilevel analysis was performed at both patient and tooth level. Statistical significance was calculated at 5% level. RESULTS: At 5-year evaluation, survival rate was 80% with 7.5% lost for endodontic reasons. Eighty-three percent of the teeth were classified as healed. Multilevel analysis identified significant predictors of increased survival: female gender (p = 0.012), absence of a pre-operative metal post (p = 0.017), conservative apical preparation (diameter size < #35) (p = 0.039), teeth restored with a crown (p = 0.009), and final PAI (after 5 years) ≤ 2 (p = 0.001). Multilevel analysis identified as predictor healing: not being a smoker (p = 0.048) and conservative apical preparation < size #35 (p = 0.037). CONCLUSIONS: Outcome of 2°RCT filled with Thermafil was successful at 5 years, showing a high rate of survived and healed teeth comparable to that reported previously for other obturation techniques. CLINICAL RELEVANCE: Present findings confirm 2°RCT as a valid therapeutic option to retain natural teeth.