Inferior alveolar nerve block and third-molar agenesis: a retrospective clinical study

Fluctuating asymmetry in third molar agenesis as an aid to estimate socioeconomic status

Traditionally, dental identification techniques are used to establish identity or assist in reconstructing an individual's biological profile. However, other aspects of identity, namely socioeconomic status (SES), can be estimated through teeth. This work aims to evaluate the influence of SES on third molar agenesis in a Portuguese population. X-rays from 448 subjects (223 belonging to a high and 225 to a low socioeconomic status) were assessed and demographic data (age, sex) and dental history were registered. Frequencies and associations between the variables were analyzed using the chi-square test. For each group, differences between third molar agenesis were studied using the Wilcoxon test. The significance level was 5%. X-rays displaying at least one agenesis were more common in females (in both SES groups). Differences between socioeconomic status were found in female subjects' upper right and lower left third molars, with a higher frequency of agenesis in the lower SES group. Agenesis of lower third molars displayed fluctuant asymmetry in both groups, whereas agenesis of upper third molars was also present in the lower SES group. These results suggest that socioeconomic status can affect third molar agenesis prevalence, and fluctuant asymmetry seems more prevalent in the lower SES, as it affects all third molars.

Third Molar Agenesis Is Associated with Facial Size

Simple Summary

Missing third molars is a common occurrence in modern humans with a prevalence of approximately 20% in the general population. The absence of those teeth, however, is not found in other human predecessors. Therefore, there is speculation whether the congenital absence of third molars is part of an evolutionary mechanism that leads to smaller jaws, smaller and fewer teeth, or if their absence is associated with more local developmental factors. In this study, we assessed the size of the cranial base, the maxilla, the mandible and the entire craniofacial complex in individuals missing one or more third molars and compared them with a group with no missing teeth. We showed that in cases with one or more missing third molars, there is a significant decrease in the size of the maxilla, the mandible as well as the entire facial configuration. Additionally, the more missing third molars, the smaller the jaws and the face were. These findings suggest that isolated third molar agenesis is part of a developmental mechanism related to craniofacial size reduction. Whether this mechanism is part of an evolutionary process in humans remains to be seen.

Abstract

Individuals with congenitally missing permanent teeth, other than third molars, present smaller craniofacial configurations compared to normal controls. However, it is not known if agenesis of third molars is part of the same mechanism. Therefore, this study assessed individuals with and without isolated third molar agenesis and tested the relation of this condition to the size of their facial configurations, using geometric morphometric methods. We show that the absence of one or more third molars is associated with a smaller maxilla, smaller mandible and a smaller overall facial configuration. The effect was larger as the number of missing third molars increased. For example, the size of the mandibular centroids in five 16-year-old females with no, one, two, three or four missing third molars showed a size reduction of approximately 2.5 mm per missing third molar. In addition, in cases with third molar agenesis in one jaw only, the effect was also evident on the opposite jaw. Our findings suggest that isolated third molar agenesis is part of a developmental mechanism resulting also in craniofacial size reduction. This might be the effect of an evolutionary process observed in humans, leading to fewer and smaller teeth, as well as smaller facial structures.

Novel PITX2 mutations identified in Axenfeld-Rieger syndrome and the pattern of PITX2-related tooth agenesis

OBJECTIVES

To investigate the mutations in patients with Axenfeld-Rieger syndrome (ARS) and the pattern of PITX2-related tooth agenesis.

METHODS

Whole-exome sequencing (WES) and copy number variation (CNV) array were used to screen the mutations in four ARS probands. After Sanger sequencing and quantitative polymerase chain reaction (qPCR) validation, secondary structure prediction and dual-luciferase assay were employed to investigate the functional impact. Eighteen PITX2-mutated patients with definite dental records were retrieved from our database and literatures, and the pattern of PITX2-related tooth agenesis was analyzed.

RESULTS

A novel de novo segmental deletion of chromosome 4q25 (GRCh37/hg19 chr4:111, 320, 052-111, 754, 236) encompassing PITX2 and three novel PITX2 mutations c.148C > T, c.257G > A, and c.630insCG were identified. Preliminary functional studies indicated the transactivation capacity of mutant PITX2 on Distal-less homeobox 2 (DLX2) promoter was compromised. The maxillary teeth showed significantly higher rate of agenesis (57.94%) than the mandibular teeth (44.05%). The most often missing teeth were upper lateral incisors (83.33%) and upper second premolars (69.44%). Teeth with the least agenesis rate were the lower second molars (19.44%) and lower first molars (8.33%).

CONCLUSIONS

We identified a novel 4q25 microdeletion including PITX2 and three novel PITX2 mutations, and statistically analyzed the PITX2-related tooth agenesis pattern.

Local anesthetics induce autophagy in young permanent tooth pulp cells

Pulp cells are essential for tooth development, and dentin repair and regeneration. In addition these cells have been identified as an important stem cell source. Local anesthetics are widely used in dental clinics, as well as the other clinical disciplines and have been suggested to interfere with human permanent tooth development and induce tooth agenesis through unknown mechanisms. Using pig model and human young permanent tooth pulp cells, our research has identified that the local anesthetics commonly used in clinics can affect cell proliferation. Molecular pathway profiling suggested that LC3II is one of the earliest molecules induced by the agents and p62 is the only common downstream target identified for all the drugs tested. The effect of the drugs could be partially recovered by V-ATPase inhibitor only if early intervention is performed. Our results provide novel evidence that local anesthetics could affect tooth cell growth that potentially can have impacts on tooth development.

A basic review on the inferior alveolar nerve block techniques

The inferior alveolar nerve block is the most common injection technique used in dentistry and many modifications of the conventional nerve block have been recently described in the literature. Selecting the best technique by the dentist or surgeon depends on many factors including the success rate and complications related to the selected technique. Dentists should be aware of the available current modifications of the inferior alveolar nerve block techniques in order to effectively choose between these modifications. Some operators may encounter difficulty in identifying the anatomical landmarks which are useful in applying the inferior alveolar nerve block and rely instead on assumptions as to where the needle should be positioned. Such assumptions can lead to failure and the failure rate of inferior alveolar nerve block has been reported to be 20-25% which is considered very high. In this basic review, the anatomical details of the inferior alveolar nerve will be given together with a description of its both conventional and modified blocking techniques; in addition, an overview of the complications which may result from the application of this important technique will be mentioned.

Morphologic and Demographic Predictors of Third Molar Agenesis: A Systematic Review and Meta-analysis

We aimed to consolidate all available data on worldwide third molar agenesis frequencies, with a particular emphasis on exploring the factors leading authors to find contradictory results for the demographic and morphologic predictors of this anomaly. A total of 12,376 studies were originally identified, then narrowed down to 1,312 for title/abstract screening. On the basis of our inclusion and exclusion criteria, we selected 92 studies, containing 100 effect sizes and 63,314 subjects, for systematic review and metaregression. The worldwide rate of agenesis was found to be 22.63% (95% confidence interval = 20.64% to 24.76%), although the estimates ranged from 5.32% to 56.0%. Our subgroup analyses revealed that women are 14% more likely than men to have agenesis of ≥1 third molars and that maxillary agenesis was 36% more likely than mandibular agenesis in both sexes. Furthermore, we found that having agenesis of 1 or 2 molars was most common, while agenesis of 3 or 4 molars was least common. Finally, we found large differences among agenesis frequency depending on geographic region. This information is expected to be of use not only to clinicians and patients but also to policy makers, given the implications for third molar extraction protocols.