Anatomical complexities affecting root canal preparation: a narrative review

A fundamental aspect of the Endodontic field is the knowledge of root canal anatomy. Using a variety of techniques, the internal and external anatomy of teeth have been extensively investigated throughout the past century. Recent improvements in three-dimensional computed tomography have enabled more detailed evaluations of root canal morphology in both clinical and laboratory settings. Essentially, researches have unveiled that the root canal constitutes a complex system, comprising not only the main root canal but also lateral components, including isthmuses, fins, accessory canals and apical ramifications. Undoubtedly, this intricate morphology poses a significant challenge when it comes to the process of shaping, cleaning and disinfecting the root canal system. This article aims to explore the anatomical aspects of the root canal system that impact the chemomechanical procedures.

Exploring the Root Canal Microbiome in Previously Treated Teeth: A Comparative Study of Diversity and Metabolic Pathways Across Two Geographical Locations

AIM

To analyze and compare the root canal microbiome present in root-filled teeth of two different geographical populations, and to study their functional potential using next-a generation sequencing approach.

METHODOLOGY

Sequencing data obtained from surgical specimens from previously treated teeth with periapical bone loss from Spain and USA were included in the study. Taxa were classified using SILVA v.138 database. Differences in genera abundances among the 10 most abundant genera were evaluated using a Kruskal-Wallis test. Alpha diversity indices were calculated in mothur. The Shannon and Chao1 indices were used. Analyses of similarity (ANOSIM) to determine differences in community composition were done in mothur, with Bonferroni correction for multiple comparisons. P values < 0.05 were considered statistically significant. Identification of enriched bacteria function prediction in the study groups (Kegg pathways) was carried out by Linear discriminant analysis Effect Size (LEfSe) via Python 3.7.6.

RESULTS

A greater alpha-diversity (Shannon and Chao1 indices) was observed from samples obtained in Spain (P = 0.002). Geography showed no significant effects on community composition via an ANOSIM using Bray-Curtis dissimilarities (R = 0.03, P = 0.21). Bacterial functional analysis prediction obtained by PICRUSt showed that 5.7% KEGG pathways differed between the Spain and USA samples.

CONCLUSIONS

The taxonomic assessment alone does not fully capture the microbiome's differences from two different geographical locations. Carbohydrate and amino acid metabolism were enriched in samples from Spain, while samples from the USA had a higher representation of pathways related to nitrogen, propanoate metabolism, and secretion systems.

Present status and future directions of intracanal medicaments

Two fundamental goals of endodontic treatment are to prevent or treat apical periodontitis. From a predictive perspective, several variables can affect the outcome of root canal treatment. Some of these variables depend on intraoperative factors, which include irrigation technique, size of the apical preparation, use of intracanal medicaments or the number of appointments necessary to complete the treatment. However, the outcome may also be affected by host and microbial factors. The intensity of periradicular bone loss or tissue damage, the presence of preoperative pain and associated conditions such as mechanical allodynia and central sensitization, the anatomical complexity of the apical portion of the canal, and the virulence and longevity of the bacterial infection can all have a profound influence on the outcome. Furthermore, numerous medical conditions have been reported to decrease the capability of the immune system to heal the periapical tissues. It is the clinician's responsibility to analyse these variables and incorporate them into the disinfection strategy to maximize the chances of healing. This narrative review will focus on the present status of intracanal medicaments, the clinical indications for their use and future directions for research.

Laboratory simulation of longitudinally cracked teeth using the step-stress cyclic loading method

AIM

To simulate in a laboratory setting longitudinal cracking in root filled premolar teeth, using cyclic mechanical fatigue.

METHODOLOGY

Mesial-occlusal-distal (MOD) cavities were prepared in twenty root filled, single-rooted, mandibular premolars restored with fibre posts and resin composites. The samples were randomly divided into two groups based on the loading approaches: static loading with a crosshead speed of 0.5 mm/min and step-stress cyclic loading (1 Hz) with increasing amplitude. The loads and numbers of cycles to failure were recorded. Micro-CT was also used to identify the fracture modes. Statistical analysis was performed using Student's t-test. The level of significance was set at 0.05.

RESULTS

The mean fracture loads for the static loading and cyclic loading groups were 769 ± 171 N and 720 ± 92 N, respectively. There was no significant difference between the two groups (P > 0.05). The proportions of longitudinal, cuspal and mixed-mode fractures under cyclic loading were 50%, 20% and 30%, respectively. Longitudinal fractures occurred with larger numbers of cycles and higher average loads per cycle compared with the other fractures. Static loading produced only cuspal fractures.

CONCLUSIONS

Longitudinally cracked premolar teeth with root fillings were successfully produced using the step-stress cyclic loading method. This provides a more clinically representative methodology for studying cracked teeth in a laboratory setting.

Apical root canal anatomy in the mesiobuccal root of maxillary first molars: influence of root apical shape and prevalence of apical foramina - a micro-CT study

AIM

To determine whether a relationship exists between the apical shape of roots and root canal system complexity by performing a micro-computed tomography analysis.

METHODOLOGY

One hundred extracted permanent maxillary first molars were scanned using a micro-computed tomography device at 19.6 μm voxel size. Two groups of mesiobuccal roots were formed according to the root aspect ratio value in the apical 3-mm cross-sectional level ('<2 and ≥ 2.00'). Data were recorded regarding the number and presence of accessory canals and their location, isthmus, presence of the mesiobuccal canal and dentine thickness. Depending on the analysed variable, Mann-Whitney U test and Z-test for proportions were used to compare groups. The significant level was set at 5%.

RESULTS

Mesiobuccal roots with an aspect ratio ≥ 2.00 at the apical 3-mm cross-sectional level had higher percentages of accessory canals, apical foramina and MB2 root canals in the apical 3 mm. The vertical average distance from the accessory foramina and origin from the anatomic apex was 1.40 and 2.19 mm, respectively. Overall, 21.8% of the accessory canals had their origin coronal to a 3-mm root resection line. There was no difference between the groups regarding dentine thickness.

CONCLUSION

The shape of the apical 3 mm of maxillary first molar mesiobuccal roots was a predictive factor for the presence of complex root canal systems. Roots with a lower aspect ratio had less complex apical anatomy.

Comparative accuracy of the Clearing Technique, CBCT and Micro-CT methods in studying the mesial root canal configuration of mandibular first molars

AIMS

To compare the accuracy of the clearing technique and cone beam computed tomography (CBCT) in the assessment of root canal configurations using micro-computed tomography (micro-CT) imaging system as the reference standard.

METHODOLOGY

Thirty-two mesial roots of mandibular first molars, selected on the basis of micro-CT scans (voxel size: 19.6 μm) and presenting several canal configurations, were evaluated using 2 CBCT scanners (voxels sizes: 120 μm and 150 μm) followed by the clearing technique. Two examiners analysed the data from each method and classified the anatomical configuration of the mesial canal according to Vertucci's system. Data were compared using Fisher's exact and chi-square tests. Reliability for each assessment was verified by the kappa test, and significance level was set at 5%.

RESULTS

Kappa value indicated a high level of agreement between the examiners. Detection of type I configurations was significantly lower in cleared teeth (P < 0.05), whilst type II root canals were detected in all specimens by both tests (P > 0.05). In mesial roots with variable anatomical configurations, CBCT and the clearing method were significantly less accurate than the reference standard (P < 0.05).

CONCLUSION

Within the tooth population studied, accuracy of identifying mesial root canal configuration was influenced greatly by the evaluation method and the type of anatomy. Detection of type I configurations in cleared teeth was significantly lower, whilst type II configurations were detected in all specimens by both methods. In mesial roots with variable anatomical configurations, neither CBCT nor clearing methods were accurate for detecting the actual root canal anatomy.

Prevalence of apical periodontitis detected in cone beam CT images of a Brazilian subpopulation

OBJECTIVES

The aim of this study was to determine the prevalence of apical periodontitis (AP) detected in cone beam CT (CBCT) images from a database.

METHODS

CBCT images of 300 Brazilian patients were assessed. AP images were measured in three dimensions. Age, gender, number and location of total teeth in each patient were considered. AP location was considered according to tooth groups. The extent of AP was determined by the largest diameter in any of the three dimensions. Percentages and the χ(2) test were used for statistical analysis.

RESULTS

AP was found in 51.4% of the patients and in 3.4% of the teeth. Higher prevalence of AP was found in 60- to 69-year-olds (73.1%) and in mandibular molars (5.9%) (p < 0.05). Inadequate endodontic treatment presented higher prevalence of AP (78.1%).

CONCLUSIONS

AP can be frequently found in CBCT examinations. The presence of AP has a significant association with patients' age, and tooth type and condition. CBCT databases are useful for cross-sectional studies about AP prevalence in a population.

Evaluation of the propylene glycol association on some physical and chemical properties of mineral trioxide aggregate

AIM

To evaluate the influence of propylene glycol (PG) on the flowability, setting time, pH and calcium ion release of mineral trioxide aggregate (MTA).

METHODOLOGY

Mineral trioxide aggregate was mixed with different proportions of PG, as follows: group 1: MTA + 100% distilled water (DW); group 2: MTA + 80% DW and 20% PG; group 3: MTA + 50% DW and 50% PG; group 4: MTA + 20% DW and 80% PG; group 5: MTA + 100% PG. The ANSI/ADA No. 57 was followed for evaluating the flowability and the setting time was measured by using ASTM C266-08. For pH and calcium release analyses, 50 acrylic teeth with root-end cavities were filled with the materials (n = 10) and individually immersed in flasks containing 10 mL deionized water. After 3 h, 24 h, 72 h and 168 h, teeth were placed in new flasks and the water in which each specimen was immersed had its pH determined by a pH metre and the calcium release measured by an atomic absorption spectrophotometer with a calcium-specific hollow cathode lamp. Data were analysed by using one way anova test for global comparison and by using Tukey’s test for individual comparisons.

RESULTS

The highest value of flowability was observed with MTA + 20% DW and 80% PG and the lowest values were found with MTA + 100% DW. They were significantly different compared to the other groups (P < 0.05). The presence of PG did not affect the pH and calcium release. The MTA + 100% PG favoured the highest (P < 0.05) pH and calcium release after 3 h. Increasing the PG proportion interfered (P < 0.05) with the setting time; when used at the volume of 100% setting did not occur.

CONCLUSION

The addition of PG to MTA-Angelus increased its setting time, improved flowability and increased the pH and calcium ion release during the initial post-mixing periods. The ratio of 80% DW–20% PG is recommended.