Cone-beam computed tomography evaluation of palatal bone and soft tissue dimensions for orthodontic miniscrew placement

INTRODUCTION

Orthodontic mini-implants have become an important tool for providing reliable skeletal anchorage without depending on patient compliance or compromising dental units used as anchorage.^[1,2] Palatal mini-implants, in particular, offer advantages such as favorable bone quality, reduced risk of root damage, and the possibility of applying versatile mechanics for anterior and posterior tooth movement.^[3,4] However, the success of palatal mini-implants is strongly influenced by the quantity and quality of available hard tissue and the thickness of overlying soft tissue at the insertion site, which together determine primary stability and long-term survival of the anchorage device.^[5] Cone-beam computed tomography (CBCT) allows three-dimensional evaluation of these parameters and enables site-specific assessment that is not possible with conventional two-dimensional imaging.^[6,7]

Existing literature has evaluated palatal bone thickness in various populations and at different reference points, often focusing on limited regions such as the anterior palate or specific rugae levels.^[8-10] These studies have shown that palatal thickness is not uniform and varies with factors such as age, sex, and sagittal or transverse position within the palate. However, there is limited data on detailed mapping of both hard and soft tissue thickness across multiple coronal planes in defined age groups, especially in specific regional populations. Such information is essential for clinicians to select insertion sites that balance adequate cortical bone support with acceptable soft tissue thickness to minimize soft tissue overgrowth and mechanical complications.^[11] Several foundational studies have established anatomical guidelines for palatal miniscrew insertion. Ludwig et al. provided comprehensive anatomical mapping of palatal sites, identifying safe zones for miniscrew placement based on bone thickness and proximity to neurovascular structures.^[12] Wilmes et al. further refined these recommendations by comparing median versus paramedian insertion in the T-Zone, demonstrating that paramedian sites in the anterior palate offer favorable bone thickness with reduced risk of midpalatal suture interference.^[13] These studies underscore the importance of precise anatomical mapping to optimize miniscrew success rates.

The regional population represents a distinct demographic in which craniofacial and palatal morphology may differ from that reported in other ethnic or geographic groups.^[10,14] Understanding the distribution of palatal hard and soft tissue thickness in this population is clinically relevant for planning miniscrew placement, particularly in adolescents and adults who frequently require maximum anchorage mechanics. There is a need for a systematic, CBCT-based evaluation that compares different coronal planes corresponding to premolar and molar regions, as well as distances from the midpalatal suture, and assesses the influence of age and sex on these measurements.

The objective is to assess the available sites for placement of palatal orthodontic mini-implants in a local population using CBCT. The study aimed to quantify and compare the thickness of palatal hard tissue, soft tissue, and combined hard plus soft tissue at coronal planes in the premolar and molar regions, at 1-mm intervals up to 10 mm from the midpalatal suture, in adolescents and adults of both sexes. The hypothesis was that specific palatal regions would demonstrate greater hard tissue thickness and favorable soft tissue profiles and that these patterns would differ according to age group and sex. By identifying these optimal regions, the study provides clinically applicable guidelines for safe and effective palatal miniscrew insertion in this population.

MATERIAL AND METHODS

This study was a retrospective cross-sectional analysis of CBCT images from patients who presented to the Department of Oral and Maxillofacial Radiology between 2021 and 2024.

Study design

A total of 49 subjects (24 males, 25 females) were randomly selected from the existing database. Subjects were categorized as follows: Adolescents: n = 24 (mean age 17.5 ± 2.8 years; 11 males, 13 females) and adults: n = 25 (mean age 25.6 ± 4.98 years; 13 males, 12 females). Four coronal planes were selected, designated as PM1, PM2, M1,and M2, passing through the mesial-distal midpoints of bilateral first premolars (PM1), second premolars (PM2), first molars (M1), and second molars (M2), respectively. Palatal hard tissue thickness was defined as the distance between the upper edge and lower edge of the palatal bone, palatal soft tissue thickness as the distance between the lower edge of palatal bone and the lower edge of palatal soft tissue, and combined hard plus soft tissue thickness as the distance between the upper edge of palatal bone and the lower edge of palatal soft tissue. Measurements were conducted at 1-mm intervals from the midpalatal suture at distances of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 mm bilaterally. The midpalatal suture itself was designated as point P1, with subsequent lateral points labeled P2 through P10 [Figure 1].

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Figure 1: Cone-beam computed tomography cross-section of the first premolar, demonstrating the measurement protocol.

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All measurements were performed by a single examiner who was calibrated before data collection. To assess intra-examiner reliability, a randomly selected subset of 15 CBCT scans (30% of the sample) was remeasured after a 2-week interval. Intraclass correlation coefficient (ICC) was calculated using a two-way mixed-effects model with absolute agreement to evaluate measurement reproducibility.

RESULTS

Forty-nine subjects were included in this study, comprising 25 adults (mean age 25.6 ± 4.98 years; 13 males, 12 females) and 24 adolescents (mean age 17.5 ± 2.8 years; 11 males, 13 females). No significant differences in palatal thickness were observed between left and right sides (p > 0.05), so bilateral measurements were pooled for analysis.

Palatal hard tissue thickness differed significantly among the four coronal planes (p < 0.001), demonstrating a clear anterior-to-posterior gradient [Tables 1-3]. PM1 Plane demonstrated the greatest hard tissue thickness among all four planes, with a mean of 5.2 ± 1.4 mm averaged across all lateral measurement points (0–10 mm).^[5] In the clinically relevant paramedian zone (1–5 mm lateral to midpalatal suture), mean hard tissue thickness was 4.8 ± 1.3 mm, providing substantial bony support for miniscrew anchorage. The PM1 plane consistently demonstrated adequate hard tissue thickness (≥4 mm) across most measurement sites in both adolescent and adult subjects. PM2 Plane showed the second-highest hard tissue thickness, with an overall mean of 4.8 ± 1.3 mm. In the paramedian zone (1–5 mm), mean thickness was 4.2 ± 1.2 mm, which remained adequate for miniscrew placement though slightly reduced compared to PM1. The V-pattern persisted, with minimum thickness occurring at 2–3 mm lateral and recovery toward 10 mm. M1 Plane and M2 Plane demonstrated progressively thinner hard tissue, with overall means of 4.1 ± 1.2 mm and 3.7 ± 1.1 mm, respectively. In the paramedian zone, M1 averaged 3.6 ± 1.1 mm and M2 averaged 3.2 ± 1.0 mm. At many individual measurement sites in the molar regions, hard tissue thickness was <3 mm, which is insufficient to provide primary stability for standard orthodontic miniscrews.

Statistical analysis (two-way ANOVA, [Table 3]) confirmed significant main effects of both coronal plane (F = 45.32, p < 0.001, η² = 0.18, large effect) and distance from midpalatal suture (F = 28.67, p < 0.001, η² = 0.14, large effect) on hard tissue thickness. The plane and distance interaction was also significant (F = 12.45, p < 0.001, η² = 0.09), indicating that the V-pattern varied slightly in magnitude across different coronal planes, with more pronounced variation anteriorly.

Palatal soft tissue thickness demonstrated a distinctly different pattern from hard tissue. Soft tissue was thinnest near the midpalatal suture (mean 1.8 ± 0.6 mm at 0–1 mm) and increased progressively with lateral distance, reaching 3.5–4.0 mm at 8–10 mm from the midline. This lateral thickening was observed across all coronal planes. At the PM1 and PM2 planes, soft tissue thickness in the paramedian zone (1–5 mm lateral) ranged from 2.0 to 2.8 mm, providing favorable conditions for miniscrew placement with reduced risk of soft tissue complications such as hyperplasia or mechanical interference with oral function. In contrast, at greater lateral distances (6–10 mm), soft tissue thickness increased to 3.2–4.0 mm, which may increase the risk of soft tissue overgrowth around miniscrew heads. Similar patterns were observed at M1 and M2 planes, though overall soft tissue thickness at molar planes was marginally thicker (approximately 0.3–0.5 mm greater) than at premolar planes, further contributing to the unsuitability of molar regions for miniscrew insertion.

Combined hard and soft tissue which determines the appropriate miniscrew length required for adequate bone engagement while avoiding excessive protrusion through soft tissue. Visual patterns are shown in [Figures 2-5].

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Figure 2: Pattern of hard and soft palate thickness in an adult male.

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Figure 3: Pattern of hard and soft palate thickness in an adult female.

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Figure 4: Pattern of hard and soft palate thickness in adolescent male.

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Figure 5: Pattern of hard and soft palate thickness in an adolescent female.

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Clinically significant combined thickness (≥7 mm) was consistently observed at the PM1 plane in the paramedian zone (1–5 mm lateral to midpalatal suture), with mean values ranging from 7.0 to 8.5 mm depending on the specific lateral distance [Tables 1 and 2]. At the PM2 plane, combined thickness in the paramedian zone ranged from 6.5 to 7.8 mm, which remained adequate for placement of commercially available miniscrews (typically 6–10 mm in length with 1.5–2.0 mm diameter).

No statistically significant effects of age (adolescent vs. adult) or sex (male vs. female) were observed on palatal hard tissue, soft tissue, or combined thickness (all p > 0.05) [Table 3]. One-way ANOVA comparing adolescents and adults showed no significant differences in mean palatal thickness at any coronal plane (PM1: p = 0.412; PM2: p = 0.386; M1: p = 0.521; M2: p = 0.467). Similarly, Mann–Whitney U tests comparing males and females revealed no significant sex-related differences (PM1: p = 0.289; PM2: p = 0.325; M1: p = 0.378; M2: p = 0.401). Factorial ANOVA evaluating age and sex interaction effects confirmed no significant interactions (F = 1.23, p = 0.271, r = 0.16, small effect size), indicating that age and sex did not interact to influence palatal thickness patterns.

Post hoc power analysis revealed low statistical power (7.4%) to detect small differences between sexes, with observed effect sizes ranging from r = 0.022 to 0.305 [Table 3]. This low power implies a high risk of Type II error (92.6% probability of failing to detect a true difference if one exists). Therefore, while no statistically significant age or sex effects were detected in this sample, the modest sample size (n = 49) constrains definitive conclusions regarding these demographic factors. The observed effect sizes (predominantly small, r ≈ 0.20) suggest that subtle differences may exist but were not detected due to insufficient sample size.

Recommended sites for miniscrew insertion were mapped as optimal in the anterior premolar regions (P1–P5 at P1 and P2 planes) for both adults and adolescents, with posterior molar regions avoided due to thin hard tissue (<3 mm at many sites).^[7,19]

DISCUSSION

This study systematically assessed palatal hard and soft tissue thickness in the local population across four coronal planes using CBCT, identifying regions suitable for palatal miniscrew insertion in both adolescents and adults. The primary finding was a consistent V-shaped pattern of palatal hard tissue thickness, with maximum thickness at the midpalatal suture and progressive thinning at 2–3 mm lateral distances, followed by gradual thickening toward 10 mm. This pattern was consistent across age and sex groups, suggesting a stable anatomical characteristic in the study population.

The PM1 plane demonstrated significantly greater hard tissue thickness compared to posterior planes, confirming that anterior palatal regions offer superior bony support for miniscrew anchorage. The combined hard and soft tissue thickness of ≥7 mm at the PM1 plane and ≥6 mm at the PM2 plane provided adequate dimensions for safe insertion without risk of palatal soft tissue overgrowth or impingement on underlying neurovascular structures.^[20] Posterior molar planes were found to be inadequate in most subjects, with hard tissue thickness frequently <3 mm, which would compromise primary stability.^[21]

The combined hard and soft tissue thickness measurements obtained in this study have direct clinical implications for miniscrew length selection and insertion planning. At the recommended insertion sites (PM1 and PM2 planes, 1–5 mm lateral to midpalatal suture), the typical combined thickness ranged from 7 to 9 mm, with hard tissue contributing approximately 4–5 mm and soft tissue 2–3 mm. This tissue configuration allows clinicians to select miniscrews of 7–9 mm length that can achieve bicortical engagement or adequate penetration into cortical bone while minimizing excessive protrusion through soft tissue.

Variations in soft tissue thickness across different lateral distances (1–10 mm) influence miniscrew selection. At lateral distances of 1–5 mm, soft tissue thickness remained relatively thin (2–3 mm), providing favorable conditions for miniscrew placement with reduced risk of soft tissue complications such as hyperplasia, inflammation, or mechanical interference with oral function. In contrast, at greater lateral distances (6–10 mm), soft tissue thickness increased progressively, which may necessitate longer screws to achieve adequate bone engagement but also increases the risk of soft tissue overgrowth and patient discomfort. These findings support the recommendation to favor paramedian insertion sites at 1–5 mm lateral to the midpalatal suture, consistent with the anatomical guidelines proposed by Ludwig et al.^[12] and Wilmes et al.^[13]

Wang et al.^[10] reported that the PM1 region provided the thickest bone in adults, consistent with our observations. Chhatwani et al.^[7] similarly demonstrated a V-pattern of bone thickness across the palate, though they focused primarily on anterior regions. Our study extends prior work by providing detailed age and sex comparisons in a specific regional population and including systematic measurements at 1-mm intervals across all four dental planes, offering greater precision for clinical site selection.^[22,23] Our finding that age and sex did not show statistically significant effects on palatal thickness differs from some international studies, which have reported minor sex and age-related variations.^[14,24] This discrepancy may reflect population-specific craniofacial characteristics or genetic diversity in the regional population.^[4,25,26] Our results underscore the importance of conducting CBCT assessments at the population level to guide clinical decision-making. Strengths of this study include systematic CBCT-based measurement at defined anatomical landmarks with 1-mm resolution providing detailed spatial mapping; inclusion of both adolescents and adults, permitting age-related assessment; complete bilateral evaluation with adequate pooling of symmetrical data; application of rigorous statistical methods (two-way ANOVA, factorial analysis) to isolate effects of plane, distance, age, and sex; assessment of intra-examiner reliability demonstrating good reproducibility; post hoc power analysis to evaluate the adequacy of sample size; and clinically applicable outcome providing evidence-based guidelines for miniscrew site selection. The limitations are retrospective design based on existing imaging database, limiting causal inference, and precluding a priori sample size calculation; single-center study, which may limit generalizability to other regions or populations; sample size (n = 49) is modest, cross-sectional design precludes evaluation of temporal changes or long-term stability of miniscrews at recommended sites, including absence of follow-up data on clinical success rates of miniscrews placed at the recommended sites; inter-examiner reliability was not assessed, as all measurements were performed by a single examiner; and long-term clinical follow-up data were not available, as this was a retrospective cross-sectional imaging study. These findings provide evidence-based guidance for selecting palatal miniscrew insertion sites in the regional population.

The PM1 and PM2 planes, particularly at lateral distances of 1–5 mm from the midline, offer optimal bone thickness and soft tissue dimensions for reliable skeletal anchorage.^[27] Clinicians should avoid insertion at molar planes where hard tissue thickness is insufficient (<3 mm).^[28,29] The consistency of these measurements across age and sex groups simplifies clinical decision-making and supports the use of standardized insertion protocols without the need for demographic-specific modifications, though individual anatomical variation should be assessed through CBCT when clinically feasible. The identification of safe insertion zones may reduce complications such as premature miniscrew failure, soft tissue hyperplasia, or neurovascular injury.^[30,31] These recommendations are particularly valuable for cases requiring maximum anterior or posterior tooth movement, where alternative anchorage methods may be less effective.^[32,33]

CONCLUSIONS

This CBCT-based investigation systematically assessed palatal hard and soft tissue thickness in the regional population across multiple anatomical planes and age groups. Palatal hard tissue thickness followed a consistent V-shaped distribution, with maximum thickness at the midpalatal suture and progressive variations with lateral distance. The PM1 plane demonstrated the greatest thickness, followed by the PM2, with molar planes unsuitable for miniscrew placement due to inadequate bone.

No statistically significant effects of age or sex on palatal thickness patterns were detected; however, the study was underpowered to detect small differences, and these findings should be interpreted cautiously in light of the modest sample size and limited statistical power. Based on these findings, the PM1 and PM2 regions at lateral distances of 1–5 mm from the midline are recommended as optimal sites for palatal miniscrew insertion in both adolescent and adult patients from the regional population. These evidence-based recommendations aim to improve the success and safety of palatal miniscrew anchorage in clinical orthodontic practice.