External cervical resorption-part 1: histopathology, distribution and presentation.

External cervical resorption (ECR) is the loss of dental hard tissue as a result of odontoclastic action. It is a dynamic process that involves periodontal, dental and in later stages pulpal tissues. Over the last two decades, ECR has attracted increased interest; this is in part due to novel micro-CT and histopathological techniques for its assessment and also improved radiographic detection using CBCT. This literature review will cover the aetiology, potential predisposing factors, histopathology and diagnosis of ECR. Part 2 will cover the management of ECR.

Comparison of centring ability and transportation between four nickel titanium instrumentation techniques by micro-computed tomography.

AIM: To compare the centring ability and transportation of ProTaper Next (PTN), ProTaper Universal (PTU), Race 123 and RevoS using micro-computed tomography (µCT). METHODOLOGY: Sixty mesial root canals of thirty mandibular molars were divided virtually into coronal, middle and apical thirds, and two reproducible reference points were marked on the external surface of the roots creating 360 measurement points. Samples were randomly allocated to four NiTi instrumentation techniques. Group 1: PTU up to F2 (n = 16), group 2: PTN up to X2 (n = 18), group 3: Race 123 up to T2 (n = 12) and group 4: RevoS up to SU (n = 14). To reproduce a clinical situation, samples were prepared on a phantom head using a surgical operating microscope. Samples were scanned pre- and postoperatively using µCT to compare and calculate the transportation and centring ratio. The data were analysed using parametric statistics. RESULTS: In the coronal and middle third of the root canals, there were significant differences in centring between PTN and PTU (coronal P < 0.001), PTN and RevoS (coronal P < 0.001), Race and PTU (coronal P < 0.01), Race and RevoS (coronal P < 0.01), PTN and RevoS (middle P < 0.01) and Race and RevoS (P < 0.05). Furthermore, there were significant differences in centring between PTN root canal preparations and other instruments in the apical third (PTN and PTU P < 0.01, PTN and Race P < 0.001, PTN and RevoS P < 0.001). In terms of transportation, in the coronal third, there was a significant difference between PTN and PTU (P < 0.05). However, there were no significant differences between the other instruments. In the middle third, significant differences were observed between PTN and PTU (P < 0.05), PTN and RevoS (P < 0.05), Race and PTU (P < 0.05) and Race and RevoS (P < 0.05). However, there were no significant differences between other systems. There was no significant difference in terms of transportation between the four systems in the apical third. CONCLUSIONS: ProTaper Next prepared more centred root canal shapes when compared with Race, PTU and RevoS. In the coronal and middle third of the root canals, the differences in centring between PTN and PTU/RevoS were significant. PTN root canal preparations were more centred than those achieved with all other instruments in the apical third.