Third Molar Agenesis Is Associated with Facial Size

Does Current Evidence Support the Discussion Around the Guidance Theory? A Systematic Review and Meta-Analysis on the Association Between Maxillary Lateral Incisor Agenesis and Displacement or Impaction of the Permanent Canine

Palatal impaction of the maxillary canine is commonly considered as a genetic condition, while the lateral incisor root has been suggested to guide maxillary permanent canine eruption. This review assessed whether agenesis of the maxillary lateral incisor is associated with eruption disturbances of the maxillary canine (displacement or impaction). Unrestricted searches in six databases for observational case-control human studies until May 2024 assessing eruption disturbances of the permanent maxillary canine in conjunction with permanent maxillary lateral incisor agenesis were performed. Study selection, data extraction and risk-of-bias assessment with the Joanna Briggs Institute's tool were performed in duplicate. Random-effects meta-analyses of odds ratios (ORs) with their 95% confidence intervals (CIs) were performed, followed by meta-regressions and sensitivity analyses. Seventeen reports pertaining to 17 case-control studies were included covering 10,155 patients (11.6 year-old/46% male on average). Maxillary lateral incisor agenesis was associated with eruption disturbance of the maxillary canine (17 studies; OR = 3.88; 95% CI = 2.05-7.34; p < 0.001; I 2 = 58). Lateral incisor agenesis was more associated with canine displacement (7 studies; OR = 7.56; 95% CI = 2.10-27.18; p = 0.008; I 2 = 57) and to a lesser degree with canine impaction (10 studies; OR = 2.39; 95% CI = 1.28-4.48; p = 0.01). No significant effects of patient age or sex were seen, and the results were robust to study design and precision. The quality of evidence was low due to the inclusion of observational case-control studies with methodological issues and residual confounding. Evidence indicates that permanent maxillary lateral incisor agenesis is associated with eruption disturbances of the permanent maxillary canine, including mainly displacement, but also impaction. Trial Registration: PROSPERO database number: CRD42024549898.

Hypodontia as a predictor of third molar agenesis: A comparative cross-sectional study according to sex and tooth type in a French orthodontic population

OBJECTIVES

The aim of this study was to determine the patterns of third molar agenesis and to investigate potential relationships with the agenesis of other permanent teeth, the type of missing teeth, and sex.

METHODS

Panoramic radiographs from 4081 orthodontic patients aged 11 to 21 years were examined to identify non-syndromic tooth agenesis, including third molars. McNemar's Chi-square tests were used to compare the prevalence of third molar agenesis between jaws or sides. Logistic regression analyses were conducted to explore associations between the occurrence or patterns of third molar agenesis and potential explanatory factors.

RESULTS

Third molar agenesis was observed in 19.0% of the sample (19.3% for females and 18.7% for males). The most common patterns of third molar agenesis were bilateral absence of the lower third molars (16.8%) and all third molars missing (16.7%). Third molar agenesis was 3.92 (95% CI=3.07-5.00; P<0.001) times more likely to occur when other permanent teeth were congenitally missing. The congenital absence of maxillary lateral incisors was associated with the agenesis of third molars in the maxilla (OR=3.93; 95% CI=1.07-13.70; P=0.034). At least one missing mandibular third molar was involved in the patterns associated with the agenesis of other permanent teeth. No sexual dimorphism was observed.

CONCLUSION

Third molar agenesis appears to represent a continuum with the agenesis of other teeth, reflecting strong genetic control, affecting both sexes similarly.

Palatal canine impaction is not associated with third molar agenesis

BACKGROUND/OBJECTIVES

Third molar agenesis and palatally impacted canines (PICs) are two independent dental phenotypes with different developmental backgrounds. Isolated reports indicate a common genetic origin for both, however, current data is inconsistent. The aim of this study was to investigate the presence of third molar agenesis in individuals with PICs, compared to individuals without PICs.

MATERIALS/METHODS

This retrospective case-control study comprised 310 individuals (188 females and 122 males), half of whom presented with unilateral or bilateral PICs. Individuals with other dental anomalies of known genetic origin were excluded. The association between PICs and third molar agenesis was assessed using four regression models, with PIC as the dependent variable and sex, age, and third molar agenesis as predictors. One model treated PIC as a nominal variable (pattern) and the other as ordinal (severity), and both were run testing either third molar agenesis severity or third molar agenesis patterns. All statistical tests were performed assuming a type-1 error of 5%.

RESULTS

There was no significant association between canine impaction and third molar agenesis in any of the four regression models. Neither the severity nor the patterns of palatally impacted canines were associated with either the severity or the patterns of third molar agenesis (P > .05).

LIMITATIONS

Due to the common racial background of all participants, the results of this investigation might not be generalizable to the general population.

CONCLUSIONS/IMPLICATIONS

Palatal canine impaction is not associated to third molar agenesis, after accounting for age, sex, and various patterns of PICs and third molar agenesis. These results indicate that these two dental phenotypes do not share a common biological mechanism for their occurrence.

Exploring the Association Between Third Molar Agenesis and Carabelli Traits: A Cross-Sectional Study

Background/Objectives: Dental agenesis is the congenital absence of at least one tooth and has been associated with several other developmental dental conditions, such as morphological dental alterations and Carabelli trait. This study sought to investigate whether third molar agenesis is associated with Carabelli traits in permanent molars. Methods: This was a cross-sectional study that used a convenience sample obtained from the orthodontic records of German patients. Patients with syndromes, oral clefts, congenital alterations including dental agenesis (except agenesis of third molars), and severe cases of bruxism with a loss of tooth tissue were excluded. Teeth with cavitated lesions of dental caries, occlusal wear, restorations, and evident dental deformities were not included in the evaluation. The Carabelli trait was evaluated in the permanent maxillary molars. The Carabelli trait was classified according to its expression for each tooth as either absent, negative, and positive expressions. Third molar agenesis was evaluated only in patients older than 10 years old (based on when initial tooth formation should be visible in the panoramic radiographs). The two-sided Chi-squared test was used to investigate the association between the conditions, using an alpha of 5% (p < 0.05). Results: A total of 155 patients (74 females and 81 males) were investigated; 39 had third molar agenesis and 75 had the Carabelli trait. There was no statistical significance difference between patients with third molar agenesis and those with Carabelli traits in relation to sex (p > 0.05). The Carabelli trait was more common in first molars than in second molars. There was no statistical significant association between third molar agenesis and Carabelli traits (p > 0.05). Conclusions: Third molar agenesis was not associated with the Carabelli trait in the permanent molars in this population.

PITX2 expression and Neanderthal introgression in HS3ST3A1 contribute to variation in tooth dimensions in modern humans

Dental morphology varies greatly throughout evolution, including in the human lineage, but little is known about the biology of this variation. Here, we use multiomics analyses to examine the genetics of variation in tooth crown dimensions. In a human cohort with mixed continental ancestry, we detected genome-wide significant associations at 18 genome regions. One region includes EDAR, a gene known to impact dental features in East Asians. Furthermore, we find that EDAR variants increase the mesiodistal diameter of all teeth, following an anterior-posterior gradient of decreasing strength. Among the 17 novel-associated regions, we replicate 7/13 in an independent human cohort and find that 4/12 orthologous regions affect molar size in mice. Two association signals point to compelling candidate genes. One is ∼61 kb from PITX2, a major determinant of tooth development. Another overlaps HS3ST3A1, a paralogous neighbor of HS3ST3B1, a tooth enamel knot factor. We document the expression of Pitx2 and Hs3st3a1 in enamel knot and dental epithelial cells of developing mouse incisors. Furthermore, associated SNPs in PITX2 and HS3ST3A1 overlap enhancers active in these cells, suggesting a role for these SNPs in gene regulation during dental development. In addition, we document that Pitx2 and Hs3st3a1/Hs3st3b1 knockout mice show alterations in dental morphology. Finally, we find that associated SNPs in HS3ST3A1 are in a DNA tract introgressed from Neanderthals, consistent with an involvement of HS3ST3A1 in tooth size variation during human evolution.

Dental Anomalies and Cranio-Dental Ontogeny in a Captive Wild Boar Population From France

Dental anomalies are frequent in boars and pigs, and they generally affect the first premolar loci. The prevalence of these dental anomalies was investigated in a large number of populations around the world. These studies mainly focused on the influence of domestication, size, sexual dimorphism or food hardness on these anomalies. However, they rarely considered ontogenetic aspects, while these are crucial for understanding their aetiology during animal growth and how the dental row-jaw complex is affected. Here, we studied the incidence of missing first upper and lower premolars in a French population of captive wild boars to discuss the functional and developmental reasons for missing teeth and to assess the impact of missing teeth on the growth of the dental row-jaw complex. Using the CT-scan data of the cranium and mandible of 24 wild boars investigated six times each during their growth, and presenting a balanced sex ratio, we recorded the number of missing teeth. We then quantified the shape of the upper and lower jaws using 3D geometric morphometrics. We found a similar prevalence of missing first premolar (37.5%) between the upper and the lower jaws, which is higher than the frequencies observed in most continental populations of wild boars. The increasing number of anomalies during ontogeny suggests a relaxed constraint on the dentition associated with a different feeding behaviour in captivity. The absence of first premolars does not appear to be associated with size variation or sexual dimorphism, nor does it affect the place of the dentition within the jaw, the latter being more influenced by the dimorphic shape of the canines and the timing of dental eruption.

Palatal canine impaction is associated with craniofacial shape in humans

BACKGROUND/OBJECTIVES

It is unclear whether palatal canine impaction is related to genetic or local/environmental factors. If a genetic origin is assumed, then it could be expected that palatal canine impaction is associated with overall craniofacial development. Within this context, the aim of this study was to evaluate the craniofacial morphology of individuals with palatal canine impaction and compare it to a matched group of normal controls.

MATERIALS/METHODS

The sample for this investigation comprised 404 individuals (232 females and 172 males). Half of these individuals presented with unilateral or bilateral palatal canine impaction confirmed clinically and radiographically. The other half were matched for sex and age with the first half and comprised individuals without tooth impaction, apart from third molars. The shape of the craniofacial structures was outlined on calibrated cephalometric images through 15 curves and 127 landmarks (11 fixed and 116 semi-landmarks). Shape configurations were superimposed using Procrustes Superimposition and the resulting shape coordinates were reduced into principal components for all subsequent analyses. The effect of palatal canine impaction on craniofacial shape was assessed with regression models, separately in females and males. All statistical tests were performed assuming a type-1 error of 5%.

RESULTS

Individuals with palatally impacted canines appear to have a less convex face, a more brachyfacial skeletal pattern, and a sagittally extended premaxilla. In females effect sizes ranged between η2 = 0.136-0.397 (P < 0.05) and in males between η2 = 0.125-0.396 (P < 0.05, apart from the entire craniofacial configuration: P = 0.259).

LIMITATIONS

Palatal canine impaction was not confirmed through cone beam computer tomography images in all patients, however, in those cases, the treatment history confirmed the diagnosis.

CONCLUSIONS/IMPLICATIONS

Palatal canine impaction is related to a distinct craniofacial shape in females and males. These findings allow for speculation that palatal canine impaction is affected by genetic pathways involved in overall craniofacial development.

A prospective randomized study on the efficacy of real-time dynamic navigation in deep horizontal mandibular third molar extractions

PURPOSE

This study aimed to evaluate the clinical efficacy of applying real-time dynamic navigation (RDN) in the extraction of deep horizontal mandibular impacted third molars, hypothesizing that RDN reduces surgical time and minimizes the risk of injury to adjacent anatomical structures.

METHODS

A prospective study was conducted on 160 patients aged between 18 and 37 years with deep horizontal impaction of the mandibular third molar. The participants were randomly assigned to either the experimental group (receiving RDN-assisted extractions) or the control group (undergoing traditional extraction methods). Preoperative planning utilized cone beam computed tomography (CBCT) and Mimics software for the accurate localization and segmentation of impacted teeth. Parametric data were analysed via an independent t test for intergroup comparisons, and significance was set to p < 0.05.

RESULTS

In the experimental group, an average of 11 ± 1 min was required for preoperative planning via RDN, which was not required in the control group. The setup of the navigation system took an average of 4 ± 1 min in the experimental group and 0 min in the control group. The experimental group demonstrated a significantly shorter average surgical time (22 ± 3 min) than did the control group (36 ± 3 min). The differences in the preoperative design time, surgical time, and complication rates between the two groups were statistically significant (p = 0.005). Additionally, the RDN group reported no complications related to adjacent tooth damage or nerve injury.

CONCLUSION

The precision, safety, real-time guidance of RDN supports its use in complicated dental extractions, which would introduce a new era of oral and maxillofacial surgery.

Third molar agenesis in individuals with supernumerary teeth

OBJECTIVES

To explore the association between third molar agenesis and supernumerary tooth formation in a white-European population.

MATERIALS AND METHODS

A record review in various orthodontic clinics identified 380 eligible white-European individuals, half of whom had non-syndromic permanent supernumerary teeth (122 males and 68 females, totalling 244 supernumerary teeth; median age: 13.1, iqr: 1.5 years), and the other half were age- and sex-matched controls with full dentition, excluding the third molars. Tooth sequences were identified in panoramic radiographs.

RESULTS

In the supernumerary group, approximately 80% of the individuals had a single supernumerary tooth, followed by those having two additional teeth. In both groups, there was no sexual dimorphism in third molar agenesis severity. The prevalence of third molar agenesis in the supernumerary group was similar to that of the control group (28/190 = 14.7% in both groups; p = 1.0). In total, 53 third molars were missing in the supernumerary group (n = 190) compared to 67 in the control group (n = 190; p = .862). The ratio of bilateral to unilateral third molar agenesis was significantly lower in the supernumerary group than in the control group (1.0 vs. 3.7, respectively; p = .026).

CONCLUSION

The presence of supernumerary teeth did not significantly alter the likelihood of third molar agenesis or its severity. Bilateral third molar agenesis was considerably less prevalent in individuals with supernumerary teeth compared to controls. The present novel findings have important clinical and developmental implications.

Prophylactic third molar removal: are oral surgeons and orthodontists aligned in preventive approaches?

BACKGROUND

There is a general consensus among dental professionals regarding the extraction of impacted third molars in the presence of clinical symptoms. However, there is less agreement on the management of asymptomatic third molars. The objective of this study is to compare the perspectives of oral surgeons and orthodontists regarding the indications for the extraction of asymptomatic third molars. It is possible that healthcare professionals from different specialties may approach the extraction of these teeth in different ways.

METHODS

In this cross-sectional study, a web-based questionnaire has been employed to collect data by inquiring about the reasons why participants prefer the extraction of asymptomatic third molars. Descriptive statistics were employed to evaluate the data obtained. The level of significance was set at P < 0.05.

RESULTS

Prophylactic extraction of partially impacted molars was more favored among the participants (P < 0.05). The orthodontists preferred prophylactic extraction due to the risk of late anterior dental crowding (LADC); however, the oral surgeons preferred pre-pregnancy extractions (P < 0.05). The extraction decision for partial impaction was higher in females when the risk of distal caries was considered. For fully impacted ones, it was higher in males when the risk of caries and pericoronitis were considered (P < 0.05).

CONCLUSIONS

Orthodontists preferred extraction because of the risk of LADC and caries, while oral surgeons focused on preventing pericoronitis, pathology, focal infection, and symptoms during pregnancy. This divergence between the participants may inform the guidelines for prophylactic management of third molars. These findings may be pertinent in gender medicine.

CLINICAL RELEVANCE

This study has been enlightening for departments to consult each other before the extraction of a patient's asymptomatic third molar.

Agenesis of third molar among the younger population of India born in twenty first century

Objectives

The objective of this study was to find the prevalence of agenesis of third molar among the younger population of India.

Materials and Methods

A cross-sectional study was conducted, and a younger population (13-21 years) born in the twenty-first century were included. Individuals who required an orthopantomogram, for any reason, were recruited in the study.

Results

A total number of 850 orthopantomograms were studied, and 298 (35.05%) individuals showed the agenesis of at least 1 or more third molars. The most common pattern of agenesis was the missing of both maxillary third molars, followed by the agenesis of all third molars. The frequency of agenesis was 18 >28 >48 >38. The study showed a significant predilection in the maxilla as compared to the mandible. There was no statistically significant gender predilection for agenesis of third molar.

Conclusion

The prevalence of third molar agenesis is increasing rapidly with time, with no significant gender predilection and changing trends of patterns of agenesis.

Occlusal characteristics in modern humans with tooth agenesis

Non-syndromic permanent tooth agenesis affects a significant proportion of the population, especially if third molars are considered. Although tooth agenesis has been linked to a smaller craniofacial size, reduced facial convexity and a shorter skeletal face, the occlusal characteristics of individuals with tooth agenesis remain largely unexplored. Therefore, this study investigated potential associations between tooth agenesis and metric occlusal traits in 806 individuals (491 with 4.1 missing teeth per subject, including third molars, and 315 without any tooth agenesis). Dentoskeletal morphology was defined through anatomical landmarks on pre-treatment cephalometric radiographs. Multivariate regression models, adjusted for sex and age, showed that tooth agenesis was significantly associated with a reduced overjet, an increased interincisal angle, and shorter upper and lower dental arch lengths, but not with overbite. Moreover, apart from reduced tooth length and dentoalveolar effects, as the number of missing teeth increased the upper front teeth were progressively retruded according to the craniofacial complex and to the face. Thus, tooth agenesis has a substantial influence on dental and occlusal characteristics, as well as on the sagittal position and inclination of anterior teeth. These findings emphasize the necessity for personalized, multidisciplinary approaches in individuals with multiple agenesis to successfully meet treatment goals.

Supernumerary Tooth Patterns in Non-Syndromic White European Subjects

Supernumerary teeth form at an incidence of about 3% in the population, with differences among races and various clinical consequences. Information on detailed patterns, and especially on white subjects, is scarce in the literature. Therefore, we aimed to investigate the patterns of non-syndromic permanent supernumerary teeth in a white European population. A record review was performed in different orthodontic clinics and identified 207 eligible individuals with 258 supernumerary teeth. Approximately 80% of the subjects had one supernumerary tooth, while 15% had two. Supernumerary tooth formation was more often evident in males (male/female: 1.65). However, there was no sexual dimorphism in its severity. The following pattern sequences, with decreasing prevalence order, were observed in the maxilla: 21 > 11 > 12 > 18 > 28 and in the mandible: 34 > 44 > 35 > 45 > 42. Supernumerary teeth were most often unilaterally present, without sexual dimorphism. In the maxilla, they were more often anteriorly present, whereas in the mandible, an opposite tendency was observed. Supernumerary teeth were consistently more often observed in the maxilla than in the mandible; 74% were impacted, 80% had normal orientation (13% horizontal, 7% inverted), and 53% had normal size. The present thorough supernumerary tooth pattern assessment enables a better understanding of this condition with clinical, developmental, and evolutionary implications.

Sexual Dimorphism in Third Molar Agenesis in Humans with and without Agenesis of Other Teeth

Sexual dimorphism in the human dentition is of interest from a developmental, evolutionary, and clinical point of view. Here, we investigated sexual dimorphism in third molar agenesis patterns and severity in non-syndromic white European individuals with (group A: 303 individuals) and without agenesis (group B: 303 individuals) of teeth other than the third molars. There was no sexual dimorphism in the patterns or the severity of third molar agenesis within groups. Both sexes showed a higher number of third molar agenesis per individual in group A than in group B. The most common third molar agenesis pattern was that of no third molars. For both females and males, bilateral third molar agenesis was approximately three times more frequent in group A than in group B (p < 0.001), whereas no difference was detected for unilateral agenesis. These findings indicate a strong genetic control of the developmental process of tooth formation, with any disruptions affecting both sexes in a similar manner. Overall, the higher vulnerability of third molar formation could be associated with the evolutionary trend in humans towards a reduced number of molar teeth, which seems to show no sex-related differences.

Number of Teeth Is Related to Craniofacial Morphology in Humans

Simple Summary

In modern humans, congenital absence of one or more permanent teeth has a prevalence of 22.6% when considering the third molars and of 6.4% when not. Its high prevalence, in conjunction with evolutionary findings pinpointing to a steady reduction in teeth number, raises the question whether the congenital absence of teeth in modern humans is an evolutionary trend rather than an anomaly. Previous studies have shown that modern humans with less teeth also have smaller faces; however, the association between teeth number and craniofacial morphology remains unclear. Here, we show that less teeth are associated with a flatter profile and a decreased facial height. These findings support the claim of a broader relationship between number of teeth and overall craniofacial development and have evolutionary implications, since face reduction comprises also an evolutionary trend in humans.

Abstract

One of the most common dental anomalies in humans is the congenital absence of teeth, referred to as tooth agenesis. The association of tooth agenesis to craniofacial morphology has been previously investigated but remains unclear. We investigated this association by applying geometric morphometric methods in a large sample of modern humans. In line with previous studies, we report here that a reduced teeth number is linked to a less convex profile, as well as to a shorter face. The effects were similar for males and females; they increased as the severity of the tooth agenesis increased and remained unaltered by the inclusion of third molars and of allometry in the analysis. Furthermore, in cases with tooth agenesis only in the maxilla, there was no detectable effect in mandibular shape, whereas maxillary shape was affected independently of the location of missing teeth. The robustness of the present sample along with the shape analysis and the statistical approach applied, allowed for thorough testing of various contributing factors regarding the presence but also the magnitude of effects. The present findings suggest a relationship between number of teeth and overall craniofacial development and have evolutionary implications.