---
title: "Mandibular incisor alveolar housing and IA-PAMD alignment in untreated skeletal Class III: CBCT an"
id: "plos-one-22-mandibular-incisor-alveolar-housing-and-incisor-alveolar-axis-relationship-in"
canonical_url: "https://medichelpline.com/clinical-feed/plos-one-22-mandibular-incisor-alveolar-housing-and-incisor-alveolar-axis-relationship-in"
content_type: "clinical_feed_article"
specialty: "Dentistry"
source_name: "PLOS ONE (Medicine)"
source_url: "https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358261"
published_at: "2026-09-15T14:00:00.000Z"
evidence_level: "Journal Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Mandibular incisor alveolar housing and IA-PAMD alignment in untreated skeletal Class III: CBCT an
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/plos-one-22-mandibular-incisor-alveolar-housing-and-incisor-alveolar-axis-relationship-in
- **Specialty:** [Dentistry](https://medichelpline.com/clinical-feed/dentistry.md)
- **Primary Source:** PLOS ONE (Medicine)
- **Source URL:** [Original Journal Publication](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0358261)
- **Published At:** 2026-09-15T14:00:00.000Z
- **Evidence Rating:** Journal Feed
## Executive GIST (TL;DR)
- This cross-sectional CBCT study analyzed 320 mandibular incisors from 80 untreated patients with skeletal **Class III** malocclusion (signed ANB < 0°) to quantify labial and lingual alveolar bone thickness at three root levels and to evaluate the relationship between incisor axis and local alveolar axis (signed **IA-PAMD**). - Scans were acquired with a Planmeca ProMax 3D Max unit (0.20-mm voxel) and images oriented in a standardized coordinate system. Four mandibular incisors per patient (FDI 32, 31, 41, 42) were measured at cervical, middle, and apical root levels. - Mean labial thicknesses were 0.36 mm (cervical), 0.49 mm (middle), and 2.40 mm (apical). Mean lingual thicknesses were 0.59 mm (cervical), 1.39 mm (middle), and 4.01 mm (apical). **Labial bone** was consistently thinner than **lingual bone** (P < 0.001). - Labial cortical thickness was below 0.5 mm in 80.3% of cervical observations and 63.4% of middle-root observations, indicating a high frequency of minimal labial cortical plate presence in this cohort. - Signed IA-PAMD correlated positively with labial apical thickness and negatively with lingual apical thickness; there was no correlation with total apical width. In adjusted multivariable models, each 1° increase in signed IA-PAMD was associated with +0.084 mm labial apical thickness (95% CI, 0.053–0.115) and −0.092 mm lingual apical thickness (95% CI, −0.141 to −0.043), with a near-zero effect on total apical width. - The mirrored labial and lingual coefficients and near-zero total-width coefficient support interpreting signed IA-PAMD as reflecting **root-apex eccentricity within the symphysis** rather than overall apical bone volume or safety threshold. - The authors caution that signed IA-PAMD should not be used as a treatment target or safety threshold. The absence of a Class I comparator restricts conclusions specific to Class III morphology. - The study adhered to STROBE, used retrospective CBCT and cephalometric records from June 2024–June 2025, and included 80 eligible patients after screening 1,522 records. Ethical approval and de-identification procedures were reported.
## Clinical Analysis & Structured Key Points
Mandibular incisor alveolar housing and incisor-alveolar axis relationship in untreated skeletal Class III malocclusion: A cross-sectional CBCT study | PLOS One Browse Subject Areas ? Click through the PLOS taxonomy to find articles in your field. For more information about PLOS Subject Areas, click here . Article Authors Metrics Comments Media Coverage Reader Comments Figures Figures Abstract Patients with skeletal Class III malocclusion may have limited alveolar support around the mandibular incisors, but conventional cephalometric measures do not directly describe the root-alveolus relationship. This retrospective cross-sectional study quantified labial and lingual alveolar bone thickness and examined whether signed IA-PAMD indicated apical root position within the symphysis. Pretreatment cone-beam computed tomography and lateral cephalometric records from 80 untreated patients (320 incisors) with signed ANB < 0° were analyzed. Bone thickness was measured at three root levels. Correlations and cluster-robust multivariable models adjusted for tooth, age, sex, signed ANB, GoGn-SN, and incisor mandibular plane angle. Mean labial thickness was 0.36, 0.49, and 2.40 mm at the cervical, middle, and apical levels; corresponding lingual values were 0.59, 1.39, and 4.01 mm. Labial bone was thinner than lingual bone (all P < 0.001), and labial thickness was below 0.5 mm in 80.3% of cervical and 63.4% of middle-root observations. Signed IA-PAMD correlated positively with labial apical thickness, negatively with lingual apical thickness, and not with total apical width. In adjusted models, each 1° increase in signed IA-PAMD was associated with 0.084 mm greater labial apical thickness (95% CI, 0.053–0.115), 0.092 mm lower lingual apical thickness (95% CI, −0.141 to −0.043), and no difference in total apical width (−0.008 mm; 95% CI, −0.082 to 0.065). The mirror-image labial and lingual coefficients, together with the near-zero total-width coefficient, support interpretation of signed IA-PAMD as a measure of root-apex eccentricity within the symphysis rather than aggregate apical bone support. It should not be interpreted as a treatment target or safety threshold, and the absence of a Class I comparator limits conclusions specific to skeletal Class III morphology. Citation: Nguyen TH, Nguyen HL, Dao TD, Vu TTT (2026) Mandibular incisor alveolar housing and incisor-alveolar axis relationship in untreated skeletal Class III malocclusion: A cross-sectional CBCT study. PLoS One 21(9): e0358261. https://doi.org/10.1371/journal.pone.0358261 Editor: Eman Allam, UCLA School of Dentistry, UNITED STATES OF AMERICA Received: July 16, 2026; Accepted: August 28, 2026; Published: September 15, 2026 Copyright: © 2026 Nguyen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All relevant data are within the manuscript and its Supporting Information files. Funding: The author(s) received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. Introduction Skeletal Class III malocclusion combines sagittal jaw disharmony with dentoalveolar compensation. Mandibular incisors commonly incline lingually, reducing the clinical severity of anterior crossbite but potentially placing their roots close to the cortical boundaries of the symphysis. Lower-incisor position is therefore relevant to camouflage treatment and presurgical decompensation, in which further tooth movement may alter periodontal support [ 1 , 2 ]. The incisor mandibular plane angle (IMPA) remains a convenient two-dimensional measure, but its reference is the mandibular plane rather than the local alveolar housing. The same IMPA can occur in symphyses with different width, inclination, and cortical distribution. Cone-beam computed tomography (CBCT) can directly depict the labial and lingual alveolar boundaries when three-dimensional imaging is already clinically indicated [ 3 ]. Previous CBCT studies have consistently reported reduced mandibular anterior alveolar dimensions or increased dehiscence and fenestration in skeletal Class III malocclusion, particularly in hyperdivergent subjects and during presurgical decompensation [ 4 – 17 ]. These studies differ in sampled teeth, skeletal subgroups, root levels, and defect definitions. Recent work has also emphasized that mean thickness alone may obscure the large proportion of sites at which the cortical plate is minimally detectable [ 10 , 11 , 16 , 17 ]. Thus, the present study is primarily confirmatory with respect to thin labial bone, but extends the evidence by examining all four mandibular incisors at three root levels in an untreated cohort and by reporting both patient-level asymmetry and tooth-level frequency distributions. The angle between the lower-incisor long axis and the principal axis of the mandibular dentoalveolar bone (IA-PAMD) has been proposed as a local alternative or complement to IMPA [ 18 ]. Because IA-PAMD is referenced to the symphyseal alveolus rather than to the mandibular plane, it may capture information about root-alveolus alignment that IMPA does not. However, an unsigned angle can merge clinically opposite configurations, whereas a signed angle can distinguish whether the incisal portion of the tooth axis lies labial or lingual to the local symphyseal axis. A cross-sectional association should also not be interpreted as a biological limit for orthodontic movement. This study aimed to quantify labial and lingual alveolar bone thickness around the four mandibular incisors in untreated skeletal Class III malocclusion, describe the frequency of measurements below 0.5 and 1.0 mm, and evaluate whether signed IA-PAMD was associated with the distribution of apical bone around the root apex beyond IMPA and skeletal covariates. The descriptive expectation that labial bone would be thinner than lingual bone preceded the current peer-review revision. The signed-angle three-outcome comparison was added during peer review to distinguish root-apex eccentricity from greater total apical support. Materials and methods Study design, setting, and ethics This retrospective cross-sectional imaging study was reported according to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. Pretreatment wide-field CBCT and lateral cephalometric records acquired between June 2024 and June 2025 were identified among patients attending the Department of Orthodontics, Hanoi National Hospital of Odonto-Stomatology, Hanoi, Vietnam. The records were accessed for research purposes from June 1, 2025, to November 30, 2025. Only images acquired for clinical diagnosis or treatment planning were used; no additional imaging was performed for research purposes. The authors had access to information that could identify individual patients during record screening and data extraction. Direct identifiers were subsequently removed and replaced with study codes before statistical analysis, and no identifying information was included in the analytical dataset. The study was approved by the Institutional Review Board for Ethics in Biomedical Research, VNU University of Medicine and Pharmacy, Hanoi, Vietnam (study code 1820; May 16, 2025). The Institutional Review Board waived the requirement for individual informed consent because the study involved retrospective analysis of existing diagnostic records that were de-identified before analysis. Participants The imaging archive contained 1,522 paired records acquired between June 2024 and June 2025. During the first-round revision, all 1,522 records were re-screened from the first record in the chronological archive using the revised final Class III definition, and screening continued until all records in the period had been reviewed. Of these, 1,442 records were excluded or not included for the primary reasons summarized in Fig 1 , leaving 80 eligible patients for analysis. The current sample therefore reflects complete revision-stage re-screening and was not obtained by stopping once a target number had been reached. Download: PNG larger image TIFF original image Fig 1. Participant screening flow. During the first-round revision, all 1,522 paired imaging records were re-screened consecutively using the revised final skeletal and clinical Class III definition. Each excluded record was assigned one primary final reason. Failure of the final Class III definition required consideration of signed ANB < 0° together with the specified clinical Class III occlusal criteria. The final analysis included 80 patients and 320 mandibular incisors. https://doi.org/10.1371/journal.pone.0358261.g001 As a post hoc study-size justification for the secondary association analysis, a previously reported correlation of r = 0.463 between lower-incisor inclination and buccal apical alveolar bone thickness [ 19 ] was used. A minimum of 45 independent participants would provide 90% power at a two-sided alpha of 0.05 for a correlation of this magnitude. This calculation was added during peer review, was not used to stop enrolment, and did not determine which records were included; all eligible patients in the study period were retained. Eligibility criteria were: pretreatment wide-field CBCT and lateral cephalometric images acquired at the same diagnostic stage; 28 permanent teeth excluding third molars, with the teeth required to be present on the images rather than necessarily fully erupted; adequate image quality and a field of view of 13 x 13 cm; complete apical closure of all four mandibular incisors; and skeletal Class III diagnosis defined by signed ANB < 0° together with a clinical Class III canine or molar relationship and anterior edge-to-edge bite or anterior crossbite. The source master’s-thesis cohort had originally used sex-specific Wits appraisal criteria. For the first-round revision, however, Wits appraisal was removed from the case definition and the revised skeletal and clinical criteria just described were applied uniformly during re-screening of all 1,522 records. Wits values were not retained in the revised analytic dataset and were therefore not used in the revision-stage re-screening or the current analysis. Exclusion criteria were previous or ongoing orthodontic treatment; restorations, proximal caries, or endodontic treatment affecting mandibular incisors; abnormal incisor morphology or position that precluded standardized measurement; congenital craniofacial anomalies; previous orthognathic surgery; and maxillofacial trauma. CBCT acquisition and image orientation CBCT examinations were obtained in the hospital imaging department with a Planmeca ProMax 3D Max unit (Planmeca, Helsinki, Finland). All scans used a single acquisition protocol performed by trained technicians: 96 kV, 5.6 mA, 12.08-second scan time, 13 x 13 cm field of view, and 0.20-mm voxel size. Digital Imaging and Communications in Medicine data were imported into InVivo Dental 6/6.5 (Anatomage, San Jose, CA, USA). Images were oriented in a standardized coordinate system using the midsagittal plane and a horizontal plane based on bilateral orbital landmarks. For each incisor, the sagittal section was adjusted to pass through the center of the crown and root and was checked in the axial and coronal views before measurement. Alveolar bone and axis measurements The mandibular incisors were coded according to the FDI system (32, 31, 41, and 42). The long axis of each tooth was defined from the incisal midpoint to the root apex. A reference segment extending from the intersection of the tooth axis with the cementoenamel-junction level to the root apex was divided into three equal parts. The cervical and middle measurement levels were located at the first and second division points from the cementoenamel-junction level, respectively. At the cervical and middle levels, labial and lingual alveolar bone thicknesses were measured from the root surface to the outer cortical boundary along lines perpendicular to the tooth axis. Apical thickness was measured from the root apex to the labial or lingual cortical boundary along the corresponding apical line, which was perpendicular to the tooth axis and parallel to the cervical and middle measurement lines. A value of 0 mm indicated that a cortical plate could not be resolved at the measurement point. Signed IA-PAMD was constructed on the same standardized sagittal section ( Fig 2 ). IA was the incisor long axis. A line was drawn between the labial and lingual alveolar crests adjacent to the measured incisor, and point A was defined as the midpoint of this alveolar-crest line. Point D was operationally defined as the visual geometric center of the mandibular symphyseal bony outline on that sagittal section. PAMD was the line joining point A to point D. Signed IA-PAMD was recorded in degrees. Positive values indicated that the incisal portion of the tooth axis lay labial to PAMD, corresponding to relative proclination and a root apex displaced toward the lingual cortex. Negative values indicated that the incisal portion of the tooth axis lay lingual to PAMD, corresponding to relative retroclination and a root apex displaced toward the labial cortex. The PAMD construction followed the published local-axis concept [ 18 ], with the present protocol adding the signed convention and explicit operational definitions of points A and D. The term principal axis is used here in this operational sense rather than as a mathematically derived principal component. Download: PNG larger image TIFF original image Fig 2. Signed IA-PAMD and alveolar bone thickness measurements. (A) IA is the mandibular incisor long axis; point A is the midpoint of the line joining the labial and lingual alveolar crests; point D is the visual geometric center of the mandibular symphyseal bony outline; and PAMD is the line joining A and D. Signed IA-PAMD is positive when the incisal portion of the tooth axis lies labial to PAMD and negative when it lies lingual to PAMD. (B) The reference segment from the tooth-axis intersection at the cementoenamel-junction level to the root apex is divided into three equal parts. The cervical and middle levels are the first and second division points, and the apical line passes through the root apex. All three bone-thickness measurement lines are perpendicular to the tooth axis and parallel to one another. https://doi.org/10.1371/journal.pone.0358261.g002 Conventional cephalometric variables were SNA, SNB, signed ANB calculated as SNA minus SNB, GoGn-SN, and IMPA. All measurements were performed without access to treatment outcomes because the images were pretreatment records. Measurement reliability Two calibrated examiners independently repeated the measurement protocol in the same 10 randomly selected CBCT scans (40 incisors) and were blinded to each other’s results. For intra-rater reliability, Examiner 1 repeated measurements on those same 40 incisors after a 2-week interval while blinded to the first measurements. The same image-orientation rules, landmark definitions, calibration procedure, and analysis unit were used for the inter- and intra-rater comparisons. Inter-rater reliability was assessed using a two-way random-effects, absolute-agreement, single-measure intraclass correlation coefficient (ICC). Intra-rater reliability was assessed using a two-way mixed-effects, absolute-agreement, single-measure ICC. The 95% confidence intervals for both sets of ICCs were obtained with the same tooth-level bootstrap procedure. Absolute disagreement was summarized as mean absolute difference and Bland-Altman limits of agreement. Reliability analyses were reported separately for labial and lingual thickness at the cervical, middle, and apical levels and for signed IA-PAMD. The small numerical differences between inter- and intra-rater estimates were not interpreted as a ranking of reproducibility. Statistical analysis Continuous data are presented as mean and standard deviation or as median and interquartile range, as appropriate, and categorical data as frequency and percentage. Tooth-level measurements were summarized by tooth and root level. Because four incisors were nested within each participant, labial and lingual thicknesses were first averaged across the four teeth for each participant; these patient-level averages were compared using two-sided Wilcoxon signed-rank tests. Medians and interquartile ranges were reported together with Wilcoxon test statistics and effect sizes, calculated as the absolute value of the standardized Wilcoxon z statistic divided by the square root of the number of paired observations. Tooth-level thicknesses were additionally categorized as <0.5 mm and <1.0 mm to describe the frequency of minimal radiographically detectable bone and thin bone, respectively. These cutoffs were used as descriptive imaging categories and were not treated as validated biological safety thresholds. Tooth-specific Spearman rank correlations assessed the associations between signed IA-PAMD and three apical outcomes: labial apical thickness, lingual apical thickness, and total apical width (labial plus lingual). For each outcome, the four tooth-specific correlation P values were adjusted with the Holm method. Multivariable analyses used each apical outcome as the dependent variable and signed IA-PAMD as the main independent variable. Models adjusted for tooth, age, sex, signed ANB, GoGn-SN, and IMPA. Ordinary least-squares coefficients were estimated with participant-clustered robust standard errors. To examine whether signed IA-PAMD improved explanatory fit within this dataset beyond the conventional covariates, model R-squared was compared before and after inclusion of signed IA-PAMD, and partial R-squared was calculated. The adult-only sensitivity analysis had been specified before the current peer-review revision. The signed-angle three-outcome correlations and models, the stricter signed ANB<=−2° sensitivity subset, and the correlation-based study-size justification were added during peer review to address interpretation and case-definition questions. These revision analyses were therefore treated as secondary or sensitivity analyses rather than as prospectively specified confirmatory tests. All tests were two-sided with alpha = 0.05. Analyses were performed in Python 3.11 using SciPy and statsmodels. No values were imputed. Data were double-entered. The de-identified analysis dataset used for the revised analyses is provided as S1 File . Results Participant characteristics The final sample included 80 untreated patients and 320 mandibular incisors. The sample comprised 38 males (47.5%) and 42 females (52.5%), with a mean age of 18.31 years (standard deviation 4.77; range 11−33). Thirty-nine participants (48.8%) were adults aged at least 18 years. The mean signed ANB was −3.83 degrees; values ranged from −12.31 to −0.52 degrees, with a median of −3.69 degrees and interquartile range of −5.15 to −2.19 degrees. Sixty-three participants had signed ANB<=−2° ( Table 1 ). Download: PNG larger image TIFF original image Table 1. Participant characteristics (n = 80). https://doi.org/10.1371/journal.pone.0358261.t001 Alveolar bone thickness Across the four incisors, the labial plate was thinnest at the cervical and middle root levels. Tooth-specific mean labial cervical thickness ranged from 0.34 to 0.40 mm, whereas labial middle thickness ranged from 0.46 to 0.52 mm. At the apex, mean labial thickness ranged from 2.18 to 2.59 mm. The lingual plate increased more markedly from the cervical level to the apex, where tooth-specific means ranged from 3.92 to 4.14 mm ( Table 2 and Fig 3 ). Download: PNG larger image TIFF original image Table 2. Tooth-specific alveolar bone thickness. ht
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