Exploring root–sinus proximity across varying degrees of transverse maxillary constriction in adolescent patients

Abstract

Background

This study aimed to evaluate linear root–sinus (RS) distances in relation to the severity of transverse maxillary constriction (TMC) severity in adolescents.

Methods

A retrospective analysis of 135 adolescent CBCT scans was performed, including 90 with TMC (study group) and 45 with normal maxillary width (control group). Maxillary width at the mid-alveolar level of the first molars was measured and compared with mandibular width and age-based norms. Patients were classified into four groups: control, mild, moderate, and severe constriction. The shortest distances between roots of the first premolar (1PM), second premolar (2PM), and roots of the first molar (1 M) to the sinus wall were recorded as RS distances. Correlations between TMC severity and RS distances were analyzed.

Results

No significant differences were found among groups for 1 M RS distances. However, 1PM and 2PM RS distances showed significant differences (p < .05), with control groups having greater distances than severe TMC groups. No significant correlation between TMC severity and RS distances was detected (p > .05).

Conclusion

No statistically significant association was observed between TMC severity and RS proximity in adolescents. However, descriptive trends suggest modest differences in premolar RS distances between constriction extremes, while molar root positions appear relatively stable. These findings are hypothesis-generating and may provide clinically relevant anatomical insights for planning maxillary expansion in adolescent patients.

Introduction

Transverse maxillary constriction (TMC) is a common skeletal condition encountered in orthodontic practice, typically characterized by a narrow maxilla and insufficient space for proper dental alignment [1]. In addition to malocclusion, TMC is associated with various functional and aesthetic concerns, including compromised airway function, difficulties in achieving ideal occlusion, and facial asymmetry [2, 3]. Maxillary expansion is among the most effective treatment approaches for TMC in adolescents, as it utilizes the ongoing skeletal growth potential to modify the maxillary arch [4]. In adolescents, during this developmental period, the maxillary sinus (MS) also undergoes significant growth, coinciding with the eruption and positioning of the posterior maxillary teeth [4]. Given the anatomical proximity of the posterior teeth to the sinus floor, changes in maxillary morphology may influence sinus development [5].

Despite the close anatomical relationship between the posterior maxillary teeth and the maxillary sinus, limited research has investigated how maxillary skeletal abnormalities, such as TMC, may influence sinus morphology or pneumatization in adolescents. The position of the sinus floor relative to the posterior tooth roots—commonly referred to as the root-sinus (RS) relationship—is of particular relevance in orthodontic treatment planning, as it may constrain safe tooth movement and increase the risk of complications such as root resorption, cortical bone resistance, or pulpal injury [6–11]. Moving teeth in proximity to the sinus floor is considered one of the most technically challenging procedures due to the anatomical limitations imposed by dense cortical boundaries. It has been hypothesized that more severe cases of TMC may present with increased inferior extension of the sinus floor, further complicating expansion procedures [12, 13].

Although various studies have explored the RS relationship and its variations with age or craniofacial morphology [13–16], to the best of our knowledge, no study has directly assessed the association between the severity of TMC and the proximity of posterior tooth roots to the sinus floor. Therefore, this study aimed to investigate the relationship between TMC severity and root–sinus (RS) proximity in adolescent patients using CBCT.

Material and method

This retrospective study was approved by the Ethics Committee of Istanbul Medeniyet University. (No: 25/455) and included CBCT images of 135 adolescents (mean: 13.23 ± 1.38 range: 11–15 years) selected from the database of the Oral and Maxillofacial Radiology Department of Istanbul Medeniyet University Faculty of Dentistry Hospital. Informed consent for CBCT imaging and the scientific use of anonymized data was obtained from all participants and/or their legal guardians as part of routine clinical intake, prior to image acquisition. Methods were carried out in accordance with relevant guidelines and regulations. The included CBCT scans were obtained from adolescents with full permanent dentition (excluding third molars) and no history of orthodontic or orthognathic treatment. To ensure a homogenous and pathology-free sample, individuals presenting any craniofacial syndromes, skeletal deformities other than TMC, or maxillary bone alterations related to periodontal or endodontic disease were excluded. Scans with maxillary pathology or metallic artifacts that could interfere with image quality or measurement accuracy were also omitted.

Based on transverse maxillary width, the participants were divided into two main groups: the control group, consisting of adolescents with normal maxillary dimensions and no evidence of transverse constriction, and the study group, comprising adolescents diagnosed with TMC. The study group was further subdivided into three equal subgroups according to the severity of constriction: mild (n = 30), moderate (n = 30), and severe (n = 30).

The CBCT images were acquired using a NewTom 5G scanner (QR Verona, Verona, Italy) with the following parameters: 0.57 mA, 110 kV, an exposure time of 3.06 s, voxel size of 0.2 mm, axial slice thickness of 0.2 mm, and a field of view (FOV) of 16 × 18 cm. The images were saved in Digital Imaging and Communications in Medicine format (DICOM) format and reconstructed using NemoFAB software (Nemotec, Madrid, Spain) with continuous 0.2 mm thick slices.

Given that RS distances depended on semi‑automated CBCT segmentation and reconstruction choices, we anchored the workflow in a risk‑averse AI governance approach with human‑in‑the‑loop verification and audit trails. Future iterations should pre‑register a risk checklist and decision‑logging for any AI‑assisted segmentation to minimize harm and hidden bias in adolescent imaging, following the same risk‑averse framework [17].

Assessment of TMC

To assess TMC, the method described by Miner et al. [14] was initially used, comparing the transverse width at the mid-alveolar level of the lingual surfaces of the maxillary and mandibular 1Ms. (Figure 1A and C). In normal occlusion, the maxillary width is approximately 1.2 ± 2.9 mm less than the mandibular width. A maxillary width significantly smaller than this range was considered indicative of TMC. To determine whether the discrepancy originated from a narrow maxilla or a wide mandible, the evaluation was complemented by the method described by McNamara and Brudon [15]. According to this method, the transpalatal width was measured from the gingival margin of the lingual groove of the right first maxillary molar to that of the left molar (Fig. 1B).

Fig. 1.

Coronal CBCT slice illustrating the transverse skeletal measurement used to assess TMC. A Maxillary transverse width-1: Measurement at the mid-alveolar level from the lingual surfaces of the right and left first maxillary molars, based on the method described by Miner et al. [14]. B Maxillary transverse width-2: Measurement of the distance between the gingival margins of the lingual grooves of the right and left first maxillary molars, as described by McNamara and Brudon [15]. C Mandibular transverse width: Measurement at the mid-alveolar level from the lingual surfaces of the right and left first mandibular molars, based on the method described by Miner et al. [14]

To standardize the assessment of TMC in our sample, we utilized normative data reported by McNamara and Brudon for individuals aged 7–15 years. These values were pooled to calculate a single mean (35.0 mm) and standard deviation (1.4 mm), providing a general reference framework for TMC severity, rather than creating age-specific categories. Based on these pooled values, thresholds for TMC severity were defined as follows: Control = within ± 1 SD; Mild = − 1 to − 2 SD; Moderate = − 2 to − 3 SD; Severe = < −3 SD. This age-agnostic approach was applied consistently across all participants to classify TMC severity based on CBCT measurements (Table 1). To our knowledge, no specific reference or validated protocol exists for the Turkish population; therefore, the widely accepted McNamara and Brudon method was adopted to ensure reliable and reproducible assessment of TMC in our cohort.

Table 1.

Classification of TMC Severity Based on Transpalatal Width Using a Pooled Reference Derived from McNamara and Brudon

Constriction Severity	Transpalatal Width (mm)	Interpretation
Normal (1)	33.6–36.4	Within ± 1 SD of the mean
Mild Constriction (2)	32.2–33.5	Between − 1 SD and − 2 SD below the mean
Moderate Constriction (3)	30.8–32.1	Between − 2 SD and − 3 SD below the mean
Severe Constriction (4)	< 30.8	More than − 3 SD below the mean

Evaluation of RS distance

To measure the extent of root–sinus (RS) distance, we followed the method described by Tian et al. [16], evaluating the shortest distance between the maxillary sinus floor and five specific roots: the first premolar (1PM), second premolar (2PM), and the mesial, distal, and palatal roots of the first molar (1 M). For molars, each root (mesiobuccal, distobuccal, and palatal) was evaluated separately. Measurements were taken from both left and right sides, and for each root, the values were averaged per patient prior to statistical analysis—ensuring that each individual was represented by a single value and preserving the independence assumption in the analyses. RS distances were measured on both sagittal and coronal CBCT slices (Fig. 2A and B). For each root, the slice that best depicted the relationship between the root apex and the sinus floor was individually selected, rather than relying on the same slice for bilateral teeth. Measurements were performed using a perpendicular orientation when feasible; when anatomical conditions required, a slightly oblique line was used to ensure accurate identification of the minimal point-to-point distance. For each root, two measurements were therefore obtained—one from the sagittal plane and one from the coronal plane—and the smallest value from these two measurements was recorded as the RS distance. Negative values indicated intrusion of the root apex into the sinus cavity.

Fig. 2.

Measurement of the root–sinus (RS) distance. A Coronal view showing the shortest vertical or oblique distance from the root apex to the sinus floor. B Sagittal view showing the same measurement. ** For two-rooted premolars, the root closest to the sinus floor was measured, as this root is most relevant to evaluating the risk of sinus proximity For molars, each root (mesiobuccal, distobuccal, and palatal) was evaluated separately. The smallest value from the two planes was recorded for each root. Negative values indicated intrusion into the sinus cavity

CBCT planes, using a perpendicular orientation when possible, or a slightly oblique line when necessary to capture the shortest point-to-point distance. This standardized protocol was applied consistently across all roots to ensure measurement reliability. As a result, the control group included N = 90 roots (45 patients), and each TMC severity subgroup included N = 60 roots (30 patients).

CBCT volumes were identified from the institutional database to form the study cohort (90 subjects with normal maxillary size and 45 subjects with TMC). Prior to measurement, each volume was assigned a randomized study code and the coded datasets were mixed. The examiner was blinded to the clinical and demographic information as well as group allocation, and all measurements were performed on these coded images. After completing the measurements, study codes were re-linked to patient identifiers for classification and statistical analysis.

Statistical analysis

All analyses were conducted using the SPSS for Windows statistical software package version 25.0 (IBM Corp., Armonk, NY), with a significance level of p < .05 considered statistically significant. Descriptive statistics (mean and standard deviation for continuous variables, skewness and kurtosis values) were computed. The skewness values for all measurements across groups were within the ± 3.00 range, and the kurtosis values were within the ± 10.00 range, indicating that all variables followed a normal distribution [18]. To preserve the assumption of independence and avoid artificial inflation of the sample size, the mean values of the right and left sides were calculated for each patient. Thus, each individual was represented by a single root–sinus (RS) value per tooth in all analyses. Analyses were conducted separately for each tooth type, ensuring that within each comparison, all observations represent independent patient-level values. By reducing the data to one observation per subject per tooth, parametric tests were considered appropriate for group comparisons.

Specifically, a paired samples t-test was used to confirm the similarity between the right and left root–sinus (RS) distances before averaging. One-way ANOVA was performed to evaluate differences in RS distances and TMC measurements among groups, and the Games-Howell test was applied for post hoc comparisons when significant differences were observed. Correlations between variables were analyzed using the Pearson correlation coefficient.

Results

In this study, all measurements were repeated by the same examiner after a two-week interval to assess intra-examiner reliability. The intraclass correlation coefficient (ICC) was 0.82, indicating a high level of consistency and reliability (ICC = 0.82, 95% confidence interval: 0.76–0.86). Descriptive statistics of the measurements are presented in Table 2.

Table 2.

Descriptive statistics of the measurements

Groups	Variables	Min.	Max.	Mean	SD
Control Group (1)	1. PM	0.67	4.70	2.27	1.22
	2. PM	-0.45	3.49	0.99	0.79
	1. MM	-3.05	2.55	0.23	1.80
	1. MD	-2.09	2.82	0.29	1.45
	1. MP	-2.15	2.15	0.04	1.15
	Max W (1)	30.02	35.00	32.25	1.03
	Mnd W	36.00	40.56	38.42	1.39
	Max W (2)	33.90	43.78	37.51	2.93
Mild Constriction (2)	1. PM	0.80	3.95	1.87	0.87
	2. PM	-0.45	1.71	0.93	0.55
	1. MM	-3.05	2.00	0.18	1.27
	1. MD	-2.09	1.76	0.31	1.05
	1. MP	-1.25	0.83	0.14	0.57
	Max W (1)	28.17	35.48	31.58	2.56
	Mnd W	33.57	41.12	37.26	2.37
	Max W (2)	32.02	33.42	32.77	0.37
Moderate Constriction (3)	1. PM	0.25	3.64	1.91	0.84
	2. PM	-0.51	1.64	0.45	0.67
	1. MM	-3.05	2.06	0.06	0.99
	1. MD	-2.09	1.87	0.11	0.76
	1. MP	-1.25	1.44	0.35	0.50
	Max W (1)	26.53	32.96	30.38	2.09
	Mnd W	38.26	49.89	43.77	4.83
	Max W (2)	30.90	32.00	31.56	0.34
Severe Constriction (4)	1. PM	0.67	3.64	1.56	0.60
	2. PM	-0.48	1.82	0.84	0.69
	1. MM	-2.90	1.88	0.37	1.16
	1. MD	-2.09	1.85	0.45	0.96
	1. MP	-1.60	0.86	0.14	0.53
	Max W (1)	23.23	28.46	26.08	1.34
	Mnd W	30.52	36.52	33.40	1.41
	Max W (2)	27.65	31.23	29.53	0.92

1PM: (1) Premolar, 2PM: (2) Premolar, 1MM: 1. Molar Mesial Root, 1MD: 1. Molar Distal Root, 1MP: 1. Molar Palatal Root, Max W(1): Maxillary Width described by Miner et al., Mnd W: Mandibular Width, Max W(2): Maxillary Width described by McNamara et al. *Values represent per-root averages per patient. The control group included N = 90 roots (45 patients), and each TMC severity subgroup included N = 60 roots (30 patients)

For each root, measurements from the left and right sides were averaged per patient prior to statistical analysis, so that each individual was represented by a single value. This approach preserved the independence assumption in the analyses (Table 3).

Table 3.

Comparison of right and left RS distance values of the patients

Variable	Side	Mean (X)	SD	t	p
1. PM	Right	1.93	1.11	0.50	0.618
	Left	1.96	0.96
2. PM	Right	0.82	0.97	0.08	0.935
	Left	0.83	0.62
1. MM	Right	0.31	2.11	0.64	0.525
	Left	0.23	1.37
1. MD	Right	0.32	1.22	0.86	0.391
	Left	0.26	1.14
1. MP	Right	0.15	0.91	0.01	0.995
	Left	0.15	0.90

1PM: (1) Premolar, 2PM: (2) Premolar, 1MM: 1. Molar Mesial Root, 1MD: 1. Molar Distal Root, 1MP: 1. Molar Palatal Root

RS distances was compared according to the severity of TMC. Accordingly, no statistically significant difference was found among the four groups regarding the RS distance of the mesial, distal, and palatal roots of the 1 M (p > .05). However, the RS distance of the 1PM differed significantly among the groups (p < .05). In Group 1, the RS distance of the 1PM was greater compared to Group 4. Similarly, the RS distance of the 2PM also showed a statistically significant difference among the groups (p < .05), with Group 1 exhibiting a greater distance than Group 3 (Table 4).

Table 4.

RS distances (in mm) of posterior maxillary teeth according to severity of TMC

Variables	Control Group (1)		Mild Constriction (2)		Moderate Constriction (3)		Severe Constriction (4)		P value	Difference
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
1. PM	2.27	1.22	1.87	0.87	1.91	0.84	1.56	0.60	0.020	1 > 4
2. PM	0.99	0.79	0.93	0.55	0.45	0.67	0.84	0.69	0.010	1 > 3
1. MM	0.23	1.80	0.18	1.27	0.06	0.99	0.37	1.16	0.850	--
1. MD	0.29	1.45	0.31	1.05	0.11	0.76	0.45	0.96	0.710	--
1. MP	0.04	1.15	0.14	0.57	0.35	0.50	0.14	0.53	0.441	--

1PM: (1) Premolar, 2PM: (2) Premolar, 1MM: 1. Molar Mesial Root, 1MD: 1. Molar Distal Root, 1MP: 1. Molar Palatal Root *Values represent per-root averages per patient. The control group included N = 90 roots (45 patients), and each TMC severity subgroup included N = 60 roots (30 patients)

No statistically significant correlation was found between maxillary transpalatal width and the RS distances of the 1PM, 2PM, mesial root, distal root, or palatal root of the 1 M (p > .05) (Table 5).

Table 5.

Correlations between RS distances and maxillary transpalatal width in all groups

Variables	1.PM	2.PM	1.MM	1.MD	1.MP	Max W(1)
1. PM	--
2. PM	0.36**	--
1. MM	0.35**	0.42**	--
1. MD	0.30**	0.31**	0.83**	--
1. MP	0.38**	0.25*	0.78**	0.70**	--
Max W (1)	0.11	0.11	0.06	0.07	− 0.03	--

p ˂ 0.05, ** p ˂ 0.001 * 1PM: (1) Premolar, 2PM: (2) Premolar, 1MM: 1. Molar Mesial Root, 1MD: 1. Molar Distal Root, 1MP: 1. Molar Palatal Root

Discussion

This study aimed to investigate the relationship between TMC and RS distance in adolescents using CBCT. All measurements were performed by a single trained examiner using a standardized protocol, and intra-examiner reliability demonstrated high agreement. As multiple observers were not involved in the measurement process, inter-observer variability was not assessed, and intra-examiner reliability was considered the most appropriate indicator of measurement consistency. Although several previous studies have suggested that TMC may be associated with increased maxillary sinus pneumatization (MSP) and altered sinus morphology [19–22], it should be noted that, in the present study, RS distances were evaluated as a linear anatomical indicator of root proximity to the sinus floor rather than a volumetric assessment of sinus pneumatization. Within this context, our study found no statistically significant correlation between RS distances and maxillary transpalatal width. Importantly, the assessment of TMC in our study included both dental and skeletal measurements: transverse widths at the mid-alveolar level of the maxillary and mandibular first molars and transpalatal width [14, 15]. Therefore, potential misclassification due to dental compensation of molars was minimized. The discrepancies between our results and previous reports may instead reflect differences in patient selection, age groups, or diagnostic criteria.

Close proximity of the maxillary posterior tooth roots to the sinus can increase the risk of sinus pathologies, such as sinusitis [23]. Furthermore, surgical interventions involving posterior maxillary teeth may lead to complications such as oroantral communication or displacement of root apices into the sinus [24, 25]. One study reported that, following orthodontic alignment and leveling, posterior roots extended further into the sinus compared to their initial positions, highlighting the potential influence of orthodontic mechanics on RS proximity [26]. Therefore, the anatomical relationship between posterior teeth and the sinus floor is clinically significant across various dental disciplines, including endodontics, prosthodontics, implantology, and orthodontics. The morphology and topography of the sinus floor vary considerably among individuals, which in turn may influence RS relationships [25]. Consistent with previous studies, our findings suggest a tendency for maxillary 1PMs and 2PMs to be farther from the sinus than 1Ms [25–27]. The most prominent variations in RS distances were observed in premolar regions, while molar areas remained relatively stable, suggesting that localized variations in maxillary morphology may differentially influence MSP patterns.

It is well established that factors such as skeletal pattern, sex, and maturational stage can influence both transverse maxillary dimensions and RS proximity [28–30]. In the present study, however, the sample was restricted to adolescents aged 11–15 years to minimize maturational variability, and a clinically representative range of skeletal presentations was included without stratification by sagittal or vertical class, as meaningful subgroup analyses would have required substantially larger sample sizes. While sex differences in sinus dimensions are recognized, evidence suggests that mid-adolescent RS proximities are only modestly affected by sex [31–33]. The primary aim of this study was to examine the association between TMC severity and RS proximity in a real-world adolescent cohort, with a focus on clinically relevant transverse constriction. Despite these constraints, the findings offer preliminary insights into anatomical variations relevant for planning rapid maxillary expansion and underscore the need for future studies incorporating multivariate analyses and larger samples to further explore the influence of skeletal and demographic factors.

Although the trends we observed in our study did not reach statistical significance, they represent preliminary clinical observations, including a tendency for premolar RS distances to vary modestly across TMC severity while molar roots remained relatively stable. In previous studies, Ji et al. [34] suggested that TMC may influence the anatomical relationship between the maxilla and the sinus, potentially contributing to greater MSP, and Baccetti et al. [35] similarly reported a close association between maxillary arch dimensions and sinus morphology. From a clinical perspective, the preliminary trends observed in our cohort may warrant consideration when planning orthodontic or surgical interventions in adolescents with TMC. In such cases, careful preoperative imaging is recommended to evaluate RS relationships and help minimize potential complications. Interventions such as RME, particularly in patients with pronounced TMC, may pose additional risks in the premolar region due to the proximity of root apices to the sinus floor, emphasizing the importance of individualized treatment planning.

Limitations

In this study, TMC classification was based on a single pooled mean and standard deviation rather than age-specific values, which may not fully capture subtle age-related variations in transverse maxillary width; however, the relatively narrow adolescent age range likely minimized this effect. In addition, skeletal pattern was not stratified, which may have influenced root–sinus proximity; future studies with larger cohorts should explore the potential effects of sagittal and vertical skeletal classifications.

Conclusion

This study did not demonstrate a statistically significant relationship between TMC severity and RS distance in adolescents. However, descriptive trends suggest that premolar RS means differ modestly between constriction extremes, whereas molar root positions appear relatively stable. These findings should be considered hypothesis-generating and warrant further investigation with larger samples and refined modeling approaches.

Authors’ contributions

The author is solely responsible for the conception and design of the study, data collection, statistical analysis, interpretation of results, and writing of the manuscript.

Funding

There is no funding for this research.

Data availability

The datasets used in the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This retrospective study was approved by the Ethics Committee of Istanbul Medeniyet University (No: 25/455). Informed consent for CBCT imaging and the scientific use of anonymized data was obtained from all participants and/or their legal guardians prior to image acquisition.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.