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Van Ankum EM, Majcher KB, Dolovich AT, Johnston JD, Flegel KP, Boughner JC. Food texture and vitamin D influence mouse mandible form and molar roots. Anat Rec (Hoboken) 2024; 307:611-632. [PMID: 37702738 DOI: 10.1002/ar.25315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Revised: 08/16/2023] [Accepted: 08/17/2023] [Indexed: 09/14/2023]
Abstract
Industrialization influenced several facets of lifestyle, including softer nutrient-poor diets that contributed to vitamin D deficiency in post-industrzialized populations, with concomitantly increased dental problems. Here we simulated a post-industrialized diet in a mouse model to test the effects of diet texture and vitamin D level on mandible and third molar (M3) forms. Mice were raised on a soft diet with vitamin D (VitD) or without it (NoD), or on a hard diet with vitamin D. We hypothesized that a VitD/hard diet is optimal for normal mandible and tooth root form, as well as for timely M3 initiation. Subsets of adult NoD/soft and VitD/soft groups were bred to produce embryos that were micro-computed tomography (μCT) scanned to stage M3 development. M3 stage did not differ between embryos from mothers fed VitD and NoD diets, indicating that vitamin D does not affect timing of M3 onset. Sacrificed adult mice were μCT-scanned, their mandibles 3D-landmarked and M3 roots were measured. Principal component (PC) analysis described the largest proportion of mandible shape variance (PC1, 30.1%) related to diet texture, and nominal shape variance (PC2, 13.8%) related to vitamin D. Mice fed a soft diet had shorter, relatively narrower, and somewhat differently shaped mandibles that recapitulated findings in human populations. ANOVA and other multivariate tests found significantly wider M3 roots and larger root canals in mice fed a soft diet, with vitamin D having little effect. Altogether our experiments using a mouse model contribute new insights about how a post-industrial diet may influence human craniodental variation.
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Affiliation(s)
- Elsa M Van Ankum
- Department of Anatomy, Physiology & Pharmacology, University of Saskatchewan, Saskatoon, Canada
| | - Kadin B Majcher
- Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, Canada
| | - Allan T Dolovich
- Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, Canada
| | - James D Johnston
- Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, Canada
| | - Kennedy P Flegel
- Department of Anatomy, Physiology & Pharmacology, University of Saskatchewan, Saskatoon, Canada
| | - Julia C Boughner
- Department of Anatomy, Physiology & Pharmacology, University of Saskatchewan, Saskatoon, Canada
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2
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Huang Y, Chen Y, Yang D, Tang Y, Yang Y, Xu J, Luo J, Zheng L. Three-dimensional analysis of the relationship between mandibular retromolar space and positional traits of third molars in non-hyperdivergent adults. BMC Oral Health 2023; 23:138. [PMID: 36894923 PMCID: PMC9999568 DOI: 10.1186/s12903-023-02843-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 02/27/2023] [Indexed: 03/11/2023] Open
Abstract
BACKGROUND The anatomical position of the mandibular third molars (M3s) is located in the distal-most portions of the molar area. In some previous literature, researchers evaluated the relationship between retromolar space (RS) and different classifications of M3 in three‑dimensional (3D) cone-beam computed tomography (CBCT). METHODS Two hundred six M3s from 103 patients were included. M3s were grouped according to four classification criteria: PG-A/B/C, PG-I/II/III, mesiodistal angle and buccolingual angle. 3D hard tissue models were reconstructed by CBCT digital imaging. RS was measured respectively by utilizing the fitting WALA ridge plane (WP) which was fitted by the least square method and the occlusal plane (OP) as reference planes. SPSS (version 26) was used to analyze the data. RESULTS In all criteria evaluated, RS decreased steadily from the crown to the root (P < 0.05), the minimum was at the root tip. From PG-A classification, PG-B classification to PG-C classification and from PG-I classification, PG-II classification to PG-III classification, RS both appeared a diminishing tendency (P < 0.05). As the degree of mesial tilt decreased, RS appeared an increasing trend (P < 0.05). RS in classification criteria of buccolingual angle had no statistical difference (P > 0.05). CONCLUSIONS RS was associated with positional classifications of the M3. In the clinic, RS can be evaluated by watching the Pell&Gregory classification and mesial angle of M3.
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Affiliation(s)
- Yumei Huang
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Yunjia Chen
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Dan Yang
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Yingying Tang
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Ya Yang
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Jingfeng Xu
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Jun Luo
- Stomatological Hospital of Chongqing Medical University, Chongqing, China.
| | - Leilei Zheng
- Stomatological Hospital of Chongqing Medical University, Chongqing, China. .,Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China. .,Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China.
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Assessment of mandibular retromolar space in adults with regard to third molar eruption status. Clin Oral Investig 2023; 27:671-680. [PMID: 36374353 DOI: 10.1007/s00784-022-04782-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 11/06/2022] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The aim of this study was to compare the difference in length and width of the mandibular retromolar space (RMS) stratified by the different eruption and impaction statuses of the third molars in patients with skeletal Class I malocclusion. MATERIALS AND METHODS The right mandibular RMS in 186 adult patients categorized according to the different statuses of the third molar was analyzed by using cone-beam computed tomography (CBCT). The shortest distances between the inner lingual cortex of the mandibular body and second molar root were measured parallel to the posterior occlusal line (POL) at depths of 2, 4, 6, 8, and 10 mm (mandibular retromolar space length in root level, RLin2,4,6,8,10) on the axial slices with the cementoenamel junction (CEJ) as the reference level. The width of the RMS and second molar root was measured vertical to the POL at the terminal point of the molar distalization at depths of 2, 4, 6, 8, and 10 mm (width of the mandibular retromolar space, BW2,4,6,8,10/ width of the second molar distal root, TW2,4,6,8,10) from the CEJ. RESULTS RL in different measurement planes was 2.72 ± 2.22 ~ 3.74 ± 2.26 for Group A, 5.27 ± 1.68 ~ 9.10 ± 2.04 for Group B, 1.94 ± 2.34 ~ 5.71 ± 4.37 for Group C, 1.83 ± 2.95 ~ 5.05 ± 4.24 for Group D, and 5.93 ± 3.97 ~ 10.52 ± 2.16 for Group E. The BW measurement results for A ~ E group were 9.71 ± 1.41 ~ 10.51 ± 1.81, 9.83 ± 1.39 ~ 12.55 ± 2.11, 9.96 ± 1.21 ~ 12.17 ± 1.62, 9.82 ± 1.47 ~ 12.28 ± 2.77, and 10.02 ± 1.20 ~ 12.75 ± 0.82, respectively. There was no significant difference between men and women in any measurements (P > 0.05). Patients with normal third molars erupted and those vertically impacted possessed larger RMS lengths than those in which the third molars were missing, horizontally impacted or mesially impacted (P < 0.05). In each measurement plane, TW was significantly smaller than BW (P < 0.05). CONCLUSIONS Sex had no effect on the length or width of the mandibular RMS. Different statuses of third molars can also differentially affect the mandibular RMS. The mandibular RMS width is not a limit for mandibular molar distalization. CLINICAL RELEVANCE When considering the distalization of mandibular molars, more attention should be directed to the lingual cortex of the mandible, and CBCT scans are recommended for patients who require significant mandibular molar distalization. The mandible buccal shelf and retromolar area maybe a safe zone to insert the miniscrew for molar distalization.
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Singh GD, Lee S. Midfacial development and the wisdom of teeth: A case series. Clin Case Rep 2022; 10:e05133. [PMID: 36034603 PMCID: PMC9400035 DOI: 10.1002/ccr3.5133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 11/08/2021] [Accepted: 11/10/2021] [Indexed: 11/11/2022] Open
Abstract
The alignment of third molars has largely been overlooked by orthodontists. Since difficulties arise during their eruption, a plethora of surgical procedures is advocated for their management, including prophylactic extraction. This case series describes the use of midfacial development in 4 patients and illustrates successful patterns of third molar eruption.
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Affiliation(s)
- G. Dave Singh
- Vivos Therapeutics, Inc. and School of Medicine Stanford University Stanford California USA
| | - Sangmin Lee
- Shiningyou Dental Office Pusan Republic of Korea
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Aoun Y, Husseini B, Younes R, Ghosn N, Bouserhal J. Assessment of lower third molar space: A comparative radiographic study. Dentomaxillofac Radiol 2022; 51:20220049. [PMID: 35466682 PMCID: PMC10043605 DOI: 10.1259/dmfr.20220049] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Objective: The aim of this study was to assess lower third molar space using four different radiographic reconstructed Cone Beam Computed Tomography (CBCT) images: orthopantomogram, lateral cephalogram, multiplanar CBCT and a newly introduced three-dimensional (3D) simulation technique. Methods: The CBCT scans of 32 individuals (20.97 ± 2.152 years) with a total of 50 lower third molars were collected and analyzed. The ratio between the necessary space and available space for lower third molars was calculated on each radiographic reconstructed image. Repeated-measure analysis of variance followed by multiple comparison tests were used. Results: The mean ratio was significantly smaller with cephalograms (0.611 ± 0.263), followed respectively by orthopantomograms (0.756 ± 0.221), multiplanar CBCT (0.789 ± 0.191) and 3D simulation technique (0.807 ± 0.193) (p < 0.001). The lowest mean difference was recorded between multiplanar CBCT and 3D simulation technique (0.017). Intra class correlation coefficient was strong (>0.90) for all techniques except cephalograms. Conclusions: The assessment of the lower third molar space differs according to the adopted imaging technique. 3D simulation technique is a useful novel technology that allows an exploration of the crown in many different dimensions and orientations, giving more predictable results than the conventional methods.
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Affiliation(s)
- Yasmina Aoun
- Craniofacial Research Laboratory, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
| | - Bachar Husseini
- Craniofacial Research Laboratory, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
- Department of Oral Surgery, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
| | - Ronald Younes
- Craniofacial Research Laboratory, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
- Department of Oral Surgery, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
| | - Nabil Ghosn
- Craniofacial Research Laboratory, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
| | - Joseph Bouserhal
- Craniofacial Research Laboratory, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
- Department of Orthodontics, Faculty of Dental Medicine, Saint-Joseph University of Beirut, Beirut, Lebanon
- Department of Orthodontics, Henry M. Goldman School of Dental Medicine, Boston, United States
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6
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Boughner JC, Marchiori DF, Packota GV. Unexpected variation of human molar size patterns. J Hum Evol 2021; 161:103072. [PMID: 34628299 DOI: 10.1016/j.jhevol.2021.103072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 08/15/2021] [Accepted: 08/16/2021] [Indexed: 11/17/2022]
Abstract
A tenet of mammalian, including primate dental evolution, is the Inhibitory Cascade Model, where first molar (M1) size predicts in a linear cline the size and onset time of the second (M2) and third (M3) molars: a larger M1 portends a progressively smaller and later-developing M2 and M3. In contemporary modern Homo sapiens, later-developing M3s are less likely to erupt properly. The Inhibitory Cascade Model is also used to predict molar sizes of extinct taxa, including fossil Homo. The extent to which Inhibitory Cascade Model predictions hold in contemporary H. sapiens molars is unclear, including whether this tenet informs about molar initiation, development, and eruption. We tested these questions here. In our radiographic sample of 323 oral quadrants and molar rows from contemporary humans based on mesiodistal crown lengths, we observed the distribution of molar proportions with a central tendency around parity (M1 = M2 = M3) that parsed into 13 distinct molar size ratio patterns. These patterns presented at different frequencies (e.g., M1 > M2 > M3 in about one-third of cases) that reflected whether the molar row was located in the maxilla or mandible and included both linear (e.g., M1 < M2 < M3) and nonlinear molar size ratio progressions (e.g., M1 > M2 < M3). Up to four patterns were found in the same subject's mouth. Lastly, M1 size alone does not predict M3 size, developmental timing, or eruption; rather, M2 size is integral to predicting M3 size. Our study indicates that human molar size is genetically 'softwired' and sensitive to factors local to the human upper jaw vs. lower jaw. The lack of a single stereotypical molar size ratio for contemporary H. sapiens suggests that predictions of fossil H. sapiens molar sizes using the Inhibitory Cascade Model must be made with caution.
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Affiliation(s)
- Julia C Boughner
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan S7N 5E5, Canada.
| | - Denver F Marchiori
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan S7N 5E5, Canada.
| | - Garnet V Packota
- College of Dentistry, University of Saskatchewan, 105 Wiggins Road, Health Sciences Building, Saskatoon, SK, S7N 5E5, Canada
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Evaluation of Vitamin D (25OHD), Bone Alkaline Phosphatase (BALP), Serum Calcium, Serum Phosphorus, Ionized Calcium in Patients with Mandibular Third Molar Impaction. An Observational Study. Nutrients 2021; 13:nu13061938. [PMID: 34200107 PMCID: PMC8228145 DOI: 10.3390/nu13061938] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/27/2021] [Accepted: 05/29/2021] [Indexed: 01/17/2023] Open
Abstract
The aim of this study was to evaluate the levels of vitamin D (25OHD) and other bone biomarkers in patients with third molar impaction (TMI). Thirty males and 30 females with unilateral or bilateral impacted mandibular third molar, and 15 males and 15 females as a control group (CG) were recruited. Rx-OPT was used to evaluate dental position and Pederson index to measure the difficulty of the intervention. Bone biomarkers were measured through blood venous sample in TMI group and CG. Mann-Whitney test, Pearson’s correlation coefficient, linear regression model were used to compare the different parameters in the two groups. 25OHD showed lower values in TMI group than in CG (p < 0.05) with values significantly lower in bilateral impaction (p < 0.05). Pearson’s coefficient for 25OHD presented a negative correlation with the Pederson index (ρ = −0.75). Bone alkaline phosphatase (BALP) showed significantly lower dosage in TMI group than CG (p = 0.02), Pearson’s coefficient for BALP presented a negative correlation with the Pederson index. Serum calcium, serum phosphorus, ionized calcium levels in TMI and CG groups were similar and Mann-Whitney test did not significantly differ between TMI and CG. TMI could be a sign of vitamin D deficiency and of low BALP levels that should be investigated.
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Ko D(J, Kelly T, Thompson L, Uppal JK, Rostampour N, Webb MA, Zhu N, Belev G, Mondal P, Cooper DML, Boughner JC. Timing of Mouse Molar Formation Is Independent of Jaw Length Including Retromolar Space. J Dev Biol 2021; 9:jdb9010008. [PMID: 33809066 PMCID: PMC8006249 DOI: 10.3390/jdb9010008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 02/18/2021] [Accepted: 03/01/2021] [Indexed: 11/30/2022] Open
Abstract
For humans and other mammals to eat effectively, teeth must develop properly inside the jaw. Deciphering craniodental integration is central to explaining the timely formation of permanent molars, including third molars which are often impacted in humans, and to clarifying how teeth and jaws fit, function and evolve together. A factor long-posited to influence molar onset time is the jaw space available for each molar organ to form within. Here, we tested whether each successive molar initiates only after a minimum threshold of space is created via jaw growth. We used synchrotron-based micro-CT scanning to assess developing molars in situ within jaws of C57BL/6J mice aged E10 to P32, encompassing molar onset to emergence. We compared total jaw, retromolar and molar lengths, and molar onset times, between upper and lower jaws. Initiation time and developmental duration were comparable between molar upper and lower counterparts despite shorter, slower-growing retromolar space in the upper jaw, and despite size differences between upper and lower molars. Timing of molar formation appears unmoved by jaw length including space. Conditions within the dental lamina likely influence molar onset much more than surrounding jaw tissues. We theorize that molar initiation is contingent on sufficient surface area for the physical reorganization of dental epithelium and its invagination of underlying mesenchyme.
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Affiliation(s)
- Daisy (Jihyung) Ko
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Tess Kelly
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Lacey Thompson
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Jasmene K. Uppal
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Nasim Rostampour
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Mark Adam Webb
- Canadian Light Source, University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, SK S7N 2V3, Canada; (M.A.W.); (N.Z.); (G.B.)
| | - Ning Zhu
- Canadian Light Source, University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, SK S7N 2V3, Canada; (M.A.W.); (N.Z.); (G.B.)
| | - George Belev
- Canadian Light Source, University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, SK S7N 2V3, Canada; (M.A.W.); (N.Z.); (G.B.)
| | - Prosanta Mondal
- Clinical Research Support Unit, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada;
| | - David M. L. Cooper
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
| | - Julia C. Boughner
- Department of Anatomy, Physiology & Pharmacology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada; (D.K.); (T.K.); (L.T.); (J.K.U.); (N.R.); (D.M.L.C.)
- Correspondence:
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Billet G, Bardin J. Segmental series and size: clade-wide investigation of molar proportions reveals a major evolutionary allometry in the dentition of placental mammals. Syst Biol 2021; 70:1101-1109. [PMID: 33560370 DOI: 10.1093/sysbio/syab007] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 01/27/2021] [Accepted: 02/05/2021] [Indexed: 11/14/2022] Open
Abstract
Iterative segments such as teeth or limbs are a widespread characteristic of living organisms. While their proportions may be governed by similar developmental rules in vertebrates, there is no emerging pattern as regards their relation to size. Placental mammals span eight orders of magnitude in body size and show a wide spectrum of dietary habits associated with size and reflected in their dentitions, especially molars. Although variation in size constitutes an important determinant for variation in biological traits, few major allometric trends have been documented on placental molars so far. Molar proportions have been intensively explored in placentals in relation to developmental models, but often at a small phylogenetic scale. Here, we analyzed the diversity of upper molar proportions in relation to absolute size in a large sample of placental species (n = 286) encompassing most of the group's dental diversity. Our phylogenetically informed analyses revealed a twofold pattern of evolutionary integration among upper molars: while molars covary in size with each other, their proportions covary with the absolute size of the entire molar field. With increasing absolute size, posterior molars increase in size relative to anterior ones, meaning that large-sized species have relatively large rear molars while the opposite is true for small-sized species. The directionality of proportional increase in the molar row exhibits a previously unsuspected allometric patterning among placentals, showing how large-scale variations in size may have influenced variation in dental morphology. This finding provides new evidence that processes regulating the size of individual molars are integrated with overall patterns of growth and calls for further testing of allometric variation in the dentition and in other segmental series of the vertebrate body.
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Affiliation(s)
- Guillaume Billet
- Centre de Recherche en Paléontologie - Paris, CR2P, Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, 8 rue Buffon 75005 Paris, France
| | - Jérémie Bardin
- Centre de Recherche en Paléontologie - Paris, CR2P, Sorbonne Université, Muséum national d'Histoire naturelle, CNRS, T.46-56, E.5, case 104, 4 place Jussieu, 75252 Paris cedex 05, France
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