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Journal of Dental Research Jul 2021The prophylactic removal of asymptomatic third molars is a common but controversial procedure often rationalized as necessary to prevent future disease on adjacent...
The prophylactic removal of asymptomatic third molars is a common but controversial procedure often rationalized as necessary to prevent future disease on adjacent teeth. Our objective in this retrospective cohort study of adult men was to examine whether second-molar loss differed by baseline status of the adjacent third molar, taking into account the individual's overall state of oral hygiene, caries, and periodontitis. We analyzed data from participants of the VA Dental Longitudinal Study who had at least 1 second molar present at baseline and 2 or more triennial dental examinations between 1969 and 2007. We classified second molars by third-molar status in the same quadrant: unerupted, erupted, or absent. Tooth loss and alveolar bone loss were confirmed radiographically. Caries and restorations, calculus, and probing depth were assessed on each tooth. We estimated the hazards of second-molar loss with proportional hazards regression models for correlated data, controlling for age, smoking, education, absence of the first molar, and whole-mouth indices of calculus, caries, and periodontitis. The analysis included 966 men and 3024 second molar/first molar pairs. Follow-up was 22 ± 11 y (median 24, range 3-38 y). At baseline, 163 third molars were unerupted, 990 were erupted, and 1871 were absent. The prevalence of periodontitis on the second molars did not differ by third-molar status. The prevalence of distal caries was highest on the second molars adjacent to the erupted third molars and lowest on the second molars adjacent to the unerupted third molars. Relative to the absent third molars, adjusted hazards of loss of second molars were not significantly increased for those adjacent to erupted (hazard ratio [HR] = 0.96, 95% confidence interval [CI] = 0.79-1.16) or unerupted (HR = 1.25, 95% CI = 0.91-1.73) third molars. We found similar results when using alveolar bone loss as the periodontitis indicator. Our findings suggest that retained third molars are not associated with an increased risk of second-molar loss in adult men.
Topics: Adult; Dental Caries; Humans; Longitudinal Studies; Male; Molar; Molar, Third; Retrospective Studies
PubMed: 33541172
DOI: 10.1177/0022034521990653 -
International Journal of Oral Science Feb 2024Mammalian teeth, developing inseparable from epithelial-mesenchymal interaction, come in many shapes and the key factors governing tooth morphology deserve to be...
Mammalian teeth, developing inseparable from epithelial-mesenchymal interaction, come in many shapes and the key factors governing tooth morphology deserve to be answered. By merging single-cell RNA sequencing analysis with lineage tracing models, we have unearthed a captivating correlation between the contrasting morphology of mouse molars and the specific presence of PRX1 cells within M1. These PRX1 cells assume a profound responsibility in shaping tooth morphology through a remarkable divergence in dental mesenchymal cell proliferation. Deeper into the mechanisms, we have discovered that Wnt5a, bestowed by mesenchymal PRX1 cells, stimulates mesenchymal cell proliferation while orchestrating molar morphogenesis through WNT signaling pathway. The loss of Wnt5a exhibits a defect phenotype similar to that of siPrx1. Exogenous addition of WNT5A can successfully reverse the inhibited cell proliferation and consequent deviant appearance exhibited in Prx1-deficient tooth germs. These findings bestow compelling evidence of PRX1-positive mesenchymal cells to be potential target in regulating tooth morphology.
Topics: Animals; Mice; Mesenchymal Stem Cells; Molar; Morphogenesis; Tooth Germ
PubMed: 38369512
DOI: 10.1038/s41368-024-00277-0 -
Proceedings of the National Academy of... Jan 2021Identifying developmental explanations for the evolution of complex structures like mammalian molars is fundamental to studying phenotypic variation. Previous study...
Identifying developmental explanations for the evolution of complex structures like mammalian molars is fundamental to studying phenotypic variation. Previous study showed that a "morphogenetic gradient" of molar proportions was explained by a balance between inhibiting/activating activity from earlier developing molars, termed the inhibitory cascade model (ICM). Although this model provides an explanation for variation in molar proportions, what remains poorly understood is if molar shape, or specifically complexity (i.e., the number of cusps, crests), can be explained by the same developmental model. Here, we show that molar complexity conforms to the ICM, following a linear, morphogenetic gradient along the molar row. Moreover, differing levels of inhibiting/activating activity produce contrasting patterns of molar complexity depending on diet. This study corroborates a model for the evolution of molar complexity that is developmentally simple, where only small-scale developmental changes need to occur to produce change across the entire molar row, with this process being mediated by an animal's ecology. The ICM therefore provides a developmental framework for explaining variation in molar complexity and a means for testing developmental hypotheses in the broader context of mammalian evolution.
Topics: Animals; Biological Evolution; Diet; Humans; Mammals; Models, Theoretical; Molar; Morphogenesis
PubMed: 33443174
DOI: 10.1073/pnas.2008850118 -
British Dental Journal Nov 2022Furcation-involved molars are a common presentation in general dental practice. Teeth with increasing degrees of furcation involvement are at a higher risk of requiring... (Review)
Review
Furcation-involved molars are a common presentation in general dental practice. Teeth with increasing degrees of furcation involvement are at a higher risk of requiring extraction. The assessment and management of these teeth may be complicated by difficulties in accessing the furcation for both the clinician and patient. However, with appropriate supportive therapy, these teeth have been shown to have acceptable survival rates. This first article reviews and discusses the classification, assessment and the non-surgical management of furcation-involved molar teeth. An improved understanding of how to appropriately manage these teeth can result in improved outcomes for patients.
Topics: Humans; Prevalence; Molar; Molar, Third; General Practice, Dental
PubMed: 36434224
DOI: 10.1038/s41415-022-5202-x -
Clinical Oral Investigations Dec 2021To evaluate the effect of third molar impaction and impaction-related parameters on third molar development.
OBJECTIVE
To evaluate the effect of third molar impaction and impaction-related parameters on third molar development.
MATERIALS AND METHODS
Panoramic radiographs (N=3972) from 473 males and 558 females between 3.2 and 23.5 years old were analysed. Three parameters of impaction were examined: hindering contact between third and adjacent second molar, retromolar space availability (only in lower third molars), and angulation between the third and adjacent second molar. From the separate parameters, a definition for impaction was derived. Third molars' development was staged according to a modified Köhler et al. staging technique. A linear model was used to compare within-stage and overall age, as a function of hindering contact, retromolar space, and impaction. Furthermore, a quadratic function was used to study the correlation between age and angulation.
RESULTS
Significant differences were found in mean age as a function of hindering contact and retromolar space, depending on third molar location and stage. There was a significant relation between angulation and age, depending on the stage, with all third molars evolving to a more upright position (closer to 0°). Mean ages of subjects with impacted third molars were significantly lower in certain third molar stages, but the differences were clinically small (absolute differences ≤0.65 years). Moreover, after correction for stage differences, no significant differences in age could be demonstrated.
CONCLUSIONS
The development of impacted and non-impacted third molars can be considered clinically equal in our study population.
CLINICAL RELEVANCE
There is no distinction required between impacted and non-impacted third molars for dental age estimation.
Topics: Adolescent; Adult; Child; Child, Preschool; Female; Humans; Infant; Male; Mandible; Molar; Molar, Third; Radiography, Panoramic; Tooth, Impacted; Young Adult
PubMed: 33934201
DOI: 10.1007/s00784-021-03955-z -
Genes Jun 2022This study aims to expand our understanding of the genetic architecture of crown morphology in the human diphyodont dentition. Here, we present bivariate genetic...
This study aims to expand our understanding of the genetic architecture of crown morphology in the human diphyodont dentition. Here, we present bivariate genetic correlation estimates for deciduous and permanent molar traits and evaluate the patterns of pleiotropy within (e.g., m1-m2) and between (e.g., m2-M1) dentitions. Morphology was observed and scored from dental models representing participants of an Australian twin and family study (deciduous = 290, permanent = 339). Data collection followed Arizona State University Dental Anthropology System standards. Genetic correlation estimates were generated using maximum likelihood variance components analysis in SOLAR v.8.1.1. Approximately 23% of deciduous variance components models and 30% of permanent variance components models yielded significant genetic correlation estimates. By comparison, over half (56%) of deciduous-permanent homologues (e.g., m hypocone-M hypocone) were significantly genetically correlated. It is generally assumed that the deciduous and permanent molars represent members of a meristic molar field emerging from the primary dental lamina. However, stronger genetic integration among m2-M1/M2 homologues than among paired deciduous traits suggests the m2 represents the anterior-most member of a "true" molar field. The results indicate genetic factors act at distinct points throughout development to generate homologous molar form, starting with the m2, which is later replaced by a permanent premolariform crown.
Topics: Australia; Humans; Molar; Odontometry; Tooth; Tooth Crown
PubMed: 35741762
DOI: 10.3390/genes13060996 -
ELife Feb 2020Do developmental systems preferentially produce certain types of variation that orient phenotypic evolution along preferred directions? At different scales, from the...
Do developmental systems preferentially produce certain types of variation that orient phenotypic evolution along preferred directions? At different scales, from the intra-population to the interspecific, the murine first upper molar shows repeated anterior elongation. Using a novel quantitative approach to compare the development of two mouse strains with short or long molars, we identified temporal, spatial and functional differences in tooth signaling center activity, that arise from differential tuning of the activation-inhibition mechanisms underlying tooth patterning. By tracing their fate, we could explain why only the upper first molar reacts via elongation of its anterior part. Despite a lack of genetic variation, individuals of the elongated strain varied in tooth length and the temporal dynamics of their signaling centers, highlighting the intrinsic instability of the upper molar developmental system. Collectively, these results reveal the variational properties of murine molar development that drive morphological evolution along a line of least resistance.
Topics: Animals; Biological Evolution; Biological Variation, Population; Embryo, Mammalian; Female; Male; Mice; Molar; Phenotype; Pregnancy; Signal Transduction; Tooth Eruption
PubMed: 32048989
DOI: 10.7554/eLife.50103 -
Journal of Endodontics Jan 2021Targeted Endodontic Microsurgery (TEMS) combines trephine burs and 3D-printed guides to make flapless maxillary palatal root-end surgery possible. This study assessed...
INTRODUCTION
Targeted Endodontic Microsurgery (TEMS) combines trephine burs and 3D-printed guides to make flapless maxillary palatal root-end surgery possible. This study assessed the location of the greater palatine artery (GPA), the relationship of the GPA to maxillary molar root ends, and the feasibility of flapless palatal-approach TEMS.
METHODS
Three endodontists analyzed 250 cone-beam computed tomographic images of maxillary molars for (1) transition morphology between the hard palate and the alveolar process adjacent to first and second molars as an indication of the most likely location of the GPA, (2) the superior-inferior relationship between the GPA and root ends, and (3) the feasibility of palatal-approach TEMS.
RESULTS
Palatal transition morphology included 20% Spine, 72% Bridge, and 8% Smooth. GPA position as related to palatal root ends was classified as 34% superior, 40% adjacent, and 21% inferior. Five percent of classifications were undefined. TEMS was deemed feasible for 47% of maxillary first molars and 52% of second molars, and was significantly more feasible with GPAs superior to palatal root ends. Reasons for infeasibility included GPA proximity and unfavorable resection angle or level. Maxillary first molar palatal roots were 11.13 ± 2.68 mm from the greater palatine foramen (GPF) and 2.37 ± 1.46 mm from the GPA. Second molar palatal roots were 4.94 ± 2.55 mm from the GPF and 2.53 ± 1.77 mm from the GPA.
CONCLUSIONS
Palatal transition morphology and GPA position adjacent to maxillary molars, as manifested in cone-beam computed tomographic coronal views, suggested maxillary palatal root TEMS could be accomplished with a 2-mm safety margin in 47% of first molars and 52% of second molars. Historical paradigms that do not consider flapless palatal surgical approaches may need to be revised.
Topics: Arteries; Cone-Beam Computed Tomography; Maxilla; Microsurgery; Molar; Tooth Root
PubMed: 33091453
DOI: 10.1016/j.joen.2020.10.005 -
Journal of Dentistry Apr 2022The biomechanical response of an autotransplanted tooth and surrounding bone to occlusal loads is not well-known. The aim of the present study was to investigate the...
OBJECTIVE
The biomechanical response of an autotransplanted tooth and surrounding bone to occlusal loads is not well-known. The aim of the present study was to investigate the effect of root form and occlusal morphology on stress distribution in autotransplanted teeth and surrounding bone by using finite element analysis (FEA).
METHODS
Seven FEA models representing different autotransplanted tooth situations were generated: (a) first molar, (b) third molar, (c) root canal-treated third molar, (d) root canal-treated, ankylosed, third molar, (e) crowned third molar, (f) crowned and root canal-treated third molar, (g) root canal-treated, ankylosed, and crowned third molar. Load (200 N) was applied on the occlusal surface, parallel to the long axis of the tooth. Maximum von Mises stress values on dentin and surrounding bone were calculated for each situation.
RESULTS
Differences in stress distribution were observed among models. In ankylosed model, stress was primarily observed at the coronal region of the tooth. The stress was observed more at the coronal region of the tooth in crowned models compared with the non-crowned models. The stress distribution was homogeneous with root canal-treated and crowned autotransplanted tooth.
CONCLUSIONS
The occlusal morphology and root form of the autotransplanted tooth affected the stress in surrounding bone at the transfer site and the biomechanical response of the tooth. The stress was more homogeneous in crowned tooth and primarily observed at the coronal region, which may decrease the risk for root resorption.
CLINICAL SIGNIFICANCE
Root configuration, occlusal form and root canal treatment induce significant changes on the stress distribution on teeth and bone, including characteristic stress concentration and increased stress values. Clinicians can consider crowning autotransplanted teeth for improved stress distribution within the tooth structure.
Topics: Finite Element Analysis; Humans; Molar; Molar, Third; Stress, Mechanical; Tooth, Nonvital
PubMed: 35247471
DOI: 10.1016/j.jdent.2022.104082 -
Journal of Anatomy Jan 2022Molar morphology is shaped by phylogenetic history and adaptive processes related to food processing. Topographic parameters of the occlusal surface, such as sharpness...
Molar morphology is shaped by phylogenetic history and adaptive processes related to food processing. Topographic parameters of the occlusal surface, such as sharpness and relief, can be especially informative regarding diet preferences of a species. The occlusal surface can however be deeply modified by wear throughout an animal's life, potentially obliterating other signals. Age being difficult to assess in wild populations, especially small rodents, experimental studies of wear through age in laboratory populations may constitute a powerful way to assess its impact on molar geometry and topography, and to validate descriptors of molar morphology that could mitigate this issue. Molar morphology was therefore quantified using 3D geometric morphometrics and topographic estimates in four groups of house mice: wild-trapped mice, lab-bred offspring of these wild mice, typical laboratory mice, and their hybrids. Three descriptors of the molar morphology were considered: the surface of the whole molar row, the surface of the first upper molar, and a truncated template of the first upper molar mimicking advanced wear. Increasing wear with age was demonstrated in the different groups, with a more pronounced effect in the wild-trapped population. The geometry of the molar row is not only modified by wear, but also by the relative position of the late developing molars on the jaw due to loading during mastication. As a consequence, the alignment of the molars is modified in wild mice, showing a qualitative difference between wild animals and their lab-bred offspring. Results obtained from the lab should thus be transferred with caution to the interpretation of differences in wild populations. Topographic estimates computed for the first upper molar seems to provide more stable parameters than those based on the whole molar row, because issues related to non-planar occlusal surface along the molar row are discarded. The truncated template was proven efficient in discarding the wear effect to focus on genetic differences, allowing an efficient characterization of the hybridization signature between wild and lab mice. Dominance of the wild phenotype for the first molar shape supports that the lab strain evolved in a context of relaxation of the selective pressures related to nutrition.
Topics: Animals; Diet; Laboratories; Mastication; Mice; Molar; Phylogeny
PubMed: 34333769
DOI: 10.1111/joa.13529