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The aim of this study was to evaluate the existence of preoperative dentinal defects among differently preserved dentoalveolar bone-blocks (frozen vs. embalmed) and to investigate the effect of varying apical forces (low: <4 N, high: 4-8 N) during root canal preparation on microcrack formation using micro-computed tomography (micro-CT). Thirteen embalmed and seven frozen bone-blocks containing 1-3 single rooted teeth were collected. The teeth were evenly divided into three groups (n = 10): FLow (frozen, <4 N), ELow (embalmed, <4 N), EHigh (embalmed, 4-8 N). After working length determination all specimens were scanned preoperatively. Root canal preparation was performed using nickel-titanium instruments sizes 25/.06 and 40/.06 (F6 SkyTaper; Komet, Lemgo, Germany). A postoperative scan was performed and image stacks were co-registered. All cross-sectional images were screened to identify the presence of dentinal defects. The results were expressed as the percentage of teeth/slices presenting dentinal defects. The statistical analyses were performed with Kruskal-Wallis-Test and Mann-Whitney-U-Test (α = 5%). Embalmed specimens presented a significantly higher percentage of slices with preoperative microcracks (p<0.05) than frozen specimens. No significant difference between groups was observed regarding the induction of microcracks (p>0.05). Root canal preparation does not induce microcracks in dentoalveolar bone-blocks from donors of old age, irrespective of the preservation method and the apically directed forces., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Haupt et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Aim: To evaluate the effect of moisture content in root canal dentine on detection of microcracks using micro-computed tomography., Methodology: Ten roots with and without craze lines or cracks (each n = 5) were selected and scanned six times with different moisture conditions of root dentine using a micro-CT scanner at a high resolution of 10.5 μm. Scanning conditions were as follows: (i) after 30-day wet storage, (ii) after 2-h dry time, (iii) after 48-h wet storage, (iv) after 24-h dry time, (v) after 48-h wet storage, (vi) after 2-h dry time. From each scan, cross-sectional images were obtained at intervals of 1 mm (total n = 708) and evaluated for the presence of dentinal microcracks twice by five calibrated blinded observers. Statistical analysis was performed by nonparametric analysis of variance for longitudinal data (P < 0.05)., Results: Intra-rater percentage agreement ranged between 92% and 98%, whereas inter-rater percentage agreement was 81% and 83%, respectively. No significant differences between all wet groups as well as between both groups with 2-h dry time were detected (P > 0.05). Almost no cracks were observed after wet storage with a significant increase of cracks after 2-h dry time (P < 0.001). Significantly more microcracks were identified after 24 h than after 2-h dry time (P < 0.004)., Conclusions: Moisture content of dentine influenced detection of microcracks when evaluated using micro-CT. Scanning should be performed on dried specimens to allow reliable identification of dentinal defects. Formation of new cracks during dry periods up to 24 h was disproved., (© 2017 International Endodontic Journal. Published by John Wiley & Sons Ltd.)

Purpose: To evaluate the bond strength between two fiber posts (FRC Postec and DT Light Post) and different composite resins following different surface treatments of the posts., Materials and Methods: One hundred sixty extracted teeth were divided into sixteen groups (n = 10). After pretreatment of the post surface with (1) no treatment, (2) silanization, (3) sandblasting + silanization or (4) tribochemical coating, the posts were either luted with the resin cements provided by the manufacturers of the post system or with a core buildup material. Push-out tests were performed in a universal testing machine until the post segment was dislodged from the root section. Data were analyzed using ANOVA. Multiple comparisons were performed using Tukey's test., Results: FRC Postec achieved significantly higher bond strengths than DT Light Post (p < 0.0001). Cementation with the core buildup material showed significantly higher bond strengths than the resin cement provided by the post manufacturers (p < 0.0001)., Conclusion: Post type, type of surface treatment and type of resin cement were significant factors for bond strength. Luting with a core buildup material significantly increased the bond strengths.

Abstract: Aim: To evaluate ex vivo the efficacy of ProTaper Universal Retreatment files (Dentsply Sirona, Ballaigues, Switzerland) in removing Thermafil, GuttaCore (both Dentsply Sirona) or vertically compacted gutta‐percha from curved root canals using micro‐CT. Methodology: Sixty curved molar roots with the same mean canal curvatures and radii in two directions were prepared using ProFile instruments (Dentsply Sirona) to size 30 with .04 taper and obturated with either Thermafil, GuttaCore or vertically compacted gutta‐percha and AH Plus (n = 20). Specimens were retreated using the ProTaper Universal Retreatment files D1, D2 and D3 to working length, and root canal preparation was completed with ProTaper Next (Dentsply Sirona) to size ×4. Percentages of residual filling material and dentine removal were assessed using micro‐CT imaging. Working time and procedural errors were recorded. Statistical analysis was performed using Kruskal–Wallis and Wilcoxon tests. Results: No significant differences between carrier‐based and warm vertical compaction regarding residual filling material (14.2–19.3%) and dentine removal (2.7–3.2 mm3) were detected (P > 0.05). Time to reach working length was significantly faster for canals filled with GuttaCore than that observed for Thermafil and warm vertical compaction (P < 0.05). Five lateral perforations with the D3 file occurred during retreatment, one in the Thermafil and four in the vertical compaction group. Conclusions: Remaining filling material and dentine removal were similar for all canal filling techniques. Regaining working length was significantly faster for GuttaCore compared with Thermafil and vertically compacted gutta‐percha. Procedural errors occurred during retreatment of severely curved root canals with the ProTaper Universal Retreatment files in 5 of 60 canals (8%). [ABSTRACT FROM AUTHOR]

Aim To compare the efficacy of reciprocating and rotary Ni Ti-instruments in removing filling material from curved root canals using micro-computed tomography. Methodology Sixty curved root canals were prepared and filled with gutta-percha and sealer. After determination of root canal curvatures and radii in two directions as well as volumes of filling material, the teeth were assigned to three comparable groups ( n = 20). Retreatment was performed using Reciproc, ProTaper Universal Retreatment or Hedström files. Percentages of residual filling material and dentine removal were assessed using micro- CT imaging. Working time and procedural errors were recorded. Statistical analysis was performed by variance procedures. Results No significant differences amongst the three retreatment techniques concerning residual filling material were detected ( P > 0.05). Hedström files removed significantly more dentine than ProTaper Universal Retreatment ( P < 0.05), but the difference concerning dentine removal between both Ni Ti systems was not significant ( P > 0.05). Reciproc and ProTaper Universal Retreatment were significantly faster than Hedström files ( P = 0.0001). No procedural errors such as instrument fracture, blockage, ledging or perforation were detected for Hedström files. Three perforations were recorded for ProTaper Universal Retreatment, and in both NiTi groups, one instrument fracture occured. Conclusions Remnants of filling material were observed in all samples with no significant differences between the three techniques. Hedström files removed significantly more dentine than ProTaper Universal Retreatment, but no significant differences between both NiTi systems were detected. Procedural errors were observed with ProTaper Universal Retreatment and Reciproc. [ABSTRACT FROM AUTHOR]

Aim To compare the efficacy of hand and rotary nickel-titanium ( Ni Ti) instruments in removing filling material from curved root canals of root filled teeth with unknown preparation parameters. Methodology Ninety mandibular molars with root fillings in curved root canals and homogenous root canal filling extending to 0-2 mm short of the radiographic apex were selected. Root canal curvatures and radii were measured in two directions and microcomputed tomography (micro- CT) scans were used to determine preoperative volumes of the filling material. Subsequently, the teeth were assigned to two identical groups ( n = 14). The root fillings were removed with Hedström files or Flex Master Ni Ti rotary instruments. Postoperative micro- CT imaging was used to assess the percentage of residual filling material as well as the amount of dentine removal. Working time and procedural errors were recorded. Data were compared using analysis of covariance and analysis of variance procedures. Results Root canals retreated with Hedström files were associated with less remaining filling material compared with Flex Master instruments ( P < 0.05). Both retreatment techniques removed similar amounts of dentine with no significant differences ( P > 0.05). Flex Master instruments were significantly faster than Hedström files ( P < 0.05). No procedural errors were detected in the Hedström group, whilst three instruments fractured in the Flex Master group. Conclusions Hand instrumentation resulted in significantly less residual filling material than retreatment with rotary Ni Ti instruments. Dentine removal was not significantly different for both techniques. Flex Master Ni Ti rotary files were significantly faster than Hedström files, but were associated with a higher risk of instrument fracture. [ABSTRACT FROM AUTHOR]