ABSTRACT
BACKGROUND AND OBJECTIVES: The initial size of a root canal is established by progressively introducing K-files according to the increase in the International Organization for Standardization (ISO) size in the apical region. The initial file-fit sensation is caused by coronal interferences rather than always occurring at the apex, as is commonly believed. Flaring the canal at its earliest stages enables the practitioner to accurately assess the size of the canal approaching the apex. This enables more informed judgments on the selection of the master apical file required for shaping and cleaning the apex. The aim of this in vitro study is to examine the impact of cervical flaring on the first estimation of apical file size using three distinct rotary instruments. MATERIALS AND METHODS: Sixty-four extracted permanent maxillary first molars with a curvature of between 10° and 20° were chosen. Conventional access openings were made, and the precise length of the canal was determined, leaving it 1 mm short of the apex. The apical fit was deemed to have materialized when the largest file successfully reached the apex, and further progression beyond that depth was unattainable. An initial file that exhibited tactile resistance both before and following expansion at the designated working length (WL) was observed. The initial file that elicited a sensation of being securely attached was affixed using methacrylate into the root canal. A diamond sectioning disc was used to horizontally cut the apical 0.5 mm of the mesiobuccal root. This was done to expose the canal and the instrument at the WL. The uppermost portions were observed using a 3D optical profilometer, and digital photographs were captured for each sample. RESULTS: The occurrence of coronal interferences and the choice of instruments for flaring had a notable impact on the estimation of the initial apical file (IAF) size. The file size frequency was augmented following flaring using various rotary instruments, namely ProTaper, HyFlex CM, and Endoflare. Group 1, which did not undergo preflaring, exhibited the highest disparity of 257.3 ± 54.4. The variation was substantially different (p<0.01) from all the groups that underwent flaring. The use of HyFlex CM (group 3) for preflaring resulted in the smallest average difference (124.4 ± 29.6) between the maximum diameter of the canal at the apex and the diameter of the initial file used. Endoflare (group 4) exhibited the second lowest mean disparity (178.7 ± 46) between the maximum width of the apical root canal and the diameter of the IAF, with the ProTaper group (211 ± 43.5) following closely behind. Nevertheless, there was no statistically significant discrepancy observed in the average differences between groups 2 and 4 (ProTaper and Endoflare groups, respectively). CONCLUSION: Coronal preflaring significantly contributes to minimizing the variation between the IAF and the diameter of the apical canal. Prior coronal expansion using rotary files enables a more precise identification of the IAF. The choice of equipment used for flaring affects the estimation of the IAF size.
ABSTRACT
Introduction In recent times, finite element analysis (FEA) in the field of dentistry has been employed to assess the mechanical properties of biological materials and tissues, which are difficult to quantify directly within a living organism. Only a limited number of studies have examined the impact of post diameter and length on how stress is dispersed in a maxillary canine tooth. Hence, this in vitro investigation was conducted to analyze the distribution of stress in a maxillary canine tooth that was replaced using metal and fiber posts with different diameters (1.5 mm and 1.8 mm) and lengths (11 mm and 15 mm), applying FEA. Materials and methods A FEA study was performed and all models were grouped as follows: Models 1 and 5 were made of titanium (Ti) and glass fiber posts, respectively, with a diameter of 1.5 mm and a length of 15 mm with composite core and all-ceramic crown; Models 2 and 6 were made of Ti and glass fiber posts, respectively, with a diameter of 1.5 mm and a length of 11 mm with composite core and all-ceramic crown; Models 3 and 7 were made of Ti and glass fiber posts, respectively, with a diameter of 1.8 mm and a length of 15 mm with composite core and all-ceramic crown; and Models 4 and 8 were made of Ti and glass fiber posts, respectively, with a diameter of 1.8 mm and a length of 11 mm with composite core and all-ceramic crown. A force of 200 N was exerted on the ceramic crown at an angulation of 45° to the longitudinal axis of the tooth on the palatal surface above the cingulum. The failure was determined by the correlation between a larger von Mises stress estimate and an increased likelihood of failure. The resulting stresses were then contrasted with the highest possible tensile strength of the material. Results The study demonstrated that fiber posts with a diameter of 1.8 mm and an average length of 11 mm exhibited reduced stress levels in comparison to Ti posts. The largest stresses were seen at the cervical region of the tooth, regardless of the materials employed. There was no discernible alteration in stress when the length and diameter of the post were modified. The highest stress in the composite core was measured in Ti posts measuring 1.5 mm in diameter and 15 mm in length. The highest level of stress on dentin was noted in cases where a fiber post was used, as opposed to cases where a Ti post was used. The measured stress within the fiber post was insignificant. However, the pressures imparted to the dentin were greater and more uniformly distributed in comparison to the Ti post cases. Conclusion It is suggested that a composite resin core be used along with a fiber post that is larger in diameter and smaller in length, within clinical bounds, in order to lessen stress in the radicular tooth, despite the substantial coronal defect. Further clinical trials are required to assess the survival rate of these specific measurements, dimensions, and biomaterials.
