Age-dependent root canal instrumentation techniques: a comprehensive narrative review

Assessment of Anatomical Dentin Thickness in Mandibular First Molar: An In Vivo Cone-Beam Computed Tomographic Study

Aim

To determine the minimum dentin thickness in the mesial and distal walls of the mesiobuccal (MB) and mesiolingual (ML) canals of the mandibular first molars using cone-beam computed tomography (CBCT).

Materials and Methods

CBCT examinations of 624 mandibular first molars from an Indian subpopulation were analyzed. The mesial and distal minimum dentin thickness was evaluated in 1 mm intervals apical to the furcation area. Independent t-test was used to analyze the data (α = 0.05). Using Cohen's kappa coefficient, the interexaminer and intraexaminer reliability was evaluated.

Results

The mesial dentin thickness was significantly higher than the distal dentin thickness for MB and ML canals (P=0.01). The average dentin thickness in the distal and mesial plane of the MB canal was 1.15 ± 0.15 mm and 1.52 ± 0.19 mm at the 1 mm level and 0.83 ± 0.13 and 1.08 ± 0.18 at the 5 mm level, respectively. For the ML canal, the average dentin thickness in the distal plane and the mesial plane was 1.24 ± 0.18 mm and 1.44 ± 0.21 at the 1 mm level and 0.91 ± 0.16 and 1.01 ± 0.17 at the 5 mm level, respectively. Statistical analysis between the MB and ML canals showed significant differences in the dentin thickness at 4 and 5 mm levels in both the distal and the mesial planes (P=0.01). In more than 85% of the cases, the minimum dentin thickness was seen at the 5 mm level in both the distal and mesial planes in MB and ML canals.

Conclusion

The distal planes of the mesiolingual and mesiobuccal canals were thinner in most cases, making the distal surface more prone to iatrogenic perforations. Considerably, at 4 and 5 mm from the furcation, the distal wall was significantly thinner than the mesial walls. Understanding the anatomy of the danger zone in the mesial roots of the mandibular first molars may serve to minimize the risk of endodontic mishaps such as strip perforations.

Endodontic Dentistry: Analysis of Dentinal Stress and Strain Development during Shaping of Curved Root Canals

BACKGROUND

Endodontic shaping causes stress and strain in the root canal dentin. Dentin microcracks have the potential to be later followed by root fractures occurring under the occlusal load. The aim of our research was to theoretically determine the values of such dentinal states of stress and strain during the endodontic shaping of curved root canals using finite element analysis (FEA).

METHODS

To highlight the stress concentrations in dentin, two geometric models were created considering the volume of the curved dental root and the contact between the endodontic file and the root canal walls. The application of forces with different values was simulated both on a uniform curved root canal and on a root canal with an apical third curvature of 25° as they would be applied during the preparation of a root canal.

RESULTS

In the case of the first model, which was acted upon with a force of 5 N, the deformations of the root canal appeared along the entire working length, reaching the highest values in the apical third of the root, although there were no geometric changes in the shape of the root canal. Regarding the second root model, with an apical third curvature of 25°, although the applied force was 2 N, the deformations were accompanied by geometric changes in the shape of the root, especially in the upper part of the apical third. At a higher force of 7 N exerted on the endodontic file, the geometric shape changed, and the deformation reached extreme critical values. The resulting tensile stresses appearing in the experimental structure varied similarly to the deformations.

CONCLUSIONS

Significant stress and strain can develop, especially in the apical third of curved root canals during their shaping, and the risk of cracks is higher for endodontically treated teeth presenting severe curvatures in the apical third of the root.

[Mechanisms of age-related changes in the morphology of the pulp system of the first lower molars]

OBJECTIVE

To study the coupling of age-related systemic changes in inflammation-mediated apoptosis with the features of the anatomy of the pulp system of the first mandibular molars in patients with chronic pulpitis and periodontitis.

MATERIAL AND METHODS

The study included 55 patients of both sexes from 18 to 75 years of age in three age groups - young (18-44 years) (n=17), middle (45-59 years) (n=18), elderly (60-74 years) (n=20) with indications for endodontic treatment. Diagnostic measures were supplemented with New Tom 3G cone-beam tomography. The concentration of anitapoptotic protein Bcl-XL and tumor necrosis factor-a (TNF-a) was determined in the blood, and the level of the nuclear transcription factor NF-KB subunit p65 was determined in the lysates of mononuclear cells.

RESULTS

As a result of the analysis of the sections, significant obliteration of the pulp was revealed throughout and an increase in the frequency of occurrence of slit-shaped channels in the distal root of the first molar of the mandible in elderly patients.

CONCLUSION

The pathogenetic factors leading to a change in the morphology of the pulp system include old age and an imbalance in the system of anti-inflammatory cytokine transcription mechanisms, which contributes to increased apoptosis and the protracted nature of inflammation.