Maxillo-mandibular Transverse Relationship of Primary Second Molar and Permanent First Molar of Children in Mixed Dentition: A Cone-Beam Computed Tomography Analysis

Suhae Kim; Eungyung Lee; Soyoung Park; Taesung Jeong; Jonghyun Shin

doi:10.5933/JKAPD.2025.52.1.61

J Korean Acad Pediatr Dent > Volume 52(1); 2025 > Article

Kim, Lee, Park, Jeong, and Shin: Maxillo-mandibular Transverse Relationship of Primary Second Molar and Permanent First Molar of Children in Mixed Dentition: A Cone-Beam Computed Tomography Analysis

Original Article

J Korean Acad Pediatr Dent 2025;52(1): 61-75.

Published online: February 21, 2025

DOI: https://doi.org/10.5933/JKAPD.2025.52.1.61

Maxillo-mandibular Transverse Relationship of Primary Second Molar and Permanent First Molar of Children in Mixed Dentition: A Cone-Beam Computed Tomography Analysis

Suhae Kim¹

, Eungyung Lee^1,²

, Soyoung Park^1,²

, Taesung Jeong^1,²

, Jonghyun Shin^1,²

¹Department of Pediatric Dentistry, School of Dentistry, Pusan National University, Yangsan, Republic of Korea

²Dental and Life Science Institute & Dental Research Institute, School of Dentistry, Pusan National University, Yangsan, Republic of Korea

Corresponding author: Jonghyun Shin Department of Pediatric Dentistry, School of Dentistry, Dental and Life Science Institute, Pusan National University, 49, Busandaehak-ro, Mulgeum-eup, Yangsan, 50612, Republic of Korea
Tel: +82-55-360-5183 / Fax:+82-55-360-5174 / Email: jonghyuns@pusan.ac.kr

Received October 20, 2024 Revised November 23, 2024 Accepted November 30, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study examined the transverse relationship between the maxilla and mandible in children with mixed dentition. The study focused on the primary second molar and the permanent first molar in relation to the anteroposterior skeletal patterns using cone-beam computed tomography (CBCT). A total of 102 patients from the Pediatric Dentistry Department at Pusan Dental Hospital were classified into three skeletal groups (Class I, Ⅱ, Ⅲ) based on the ANB angle (angle formed by A-point-nasion-B-point). CBCT scans were analyzed to assess the transverse dimensions of basal bone and dento-alveolar measurements. The results showed that Class Ⅲ patients exhibited a significantly narrower maxillary basal bone compared with Class I and Ⅱ patients. The mandibular basal width was not significantly different between the classes. For primary second molars, Class Ⅲ patients showed significantly narrower maxillary alveolar bone width at the root bifurcation level (51.7 ± 2.5 mm, p < 0.05) compared with Class I and II patients. For permanent first molars, the maxillary occlusal fossa distance was smallest in Class II (45.4 ± 2.4 mm, p < 0.05), and was significantly different from Class I and Class Ⅲ. Maxillary first molar inclination was more lingually inclined in Class Ⅱ patients (99.0 ± 4.2°, p < 0.05) compared with Class Ⅲ patients, whereas Class Ⅲ patients exhibited more buccal inclination. This study highlights the correlation between transverse discrepancies and anteroposterior skeletal classifications, with Class Ⅲ showing a narrower maxillary base and Class Ⅱ patients presenting greater lingual compensation. These findings may aid pediatric dentists in diagnosing transverse relationships in mixed dentition.

Keywords: Transverse discrepancy, Maxillary transverse deficiency, Skeletal classification, Primary second molar, Permanent first molar

Introduction

A maxillary transverse deficiency commonly occurs in the craniofacial region and can sometimes lead to occlusal discrepancy such as posterior tooth crossbites and facial asymmetry [1,2]. Narrow maxilla can also be associated with problems such as upper airway constriction, which increases the airflow resistance and leads the patient to mouth breathing[3]. Mouth breathing, enlarged tonsils, and sleep-disordered breathing are all interrelated and can affect each other [4]. Even without the noticeable problem, such as a crossbite, dental compensation may occur to resolve the transverse discrepancy between the maxilla and mandible, leaving the maxillary discrepancy unnoticed. This suggests that there may be more patients with undiagnosed narrow maxillary arch [5].

In pediatric patients, transverse deficiency of the maxilla may be associated with anteroposterior malocclusion [1]. In Class Ⅲ, the maxilla is retruded and constricted, contributing to maxilla-mandibular disharmony or transverse deficiency of the maxilla in many patients [6,7]. Therefore, phase I treatment involves maxillary expansion with the help of a rapid maxillary expansion (RME) device, followed by forward traction of the maxilla using orthopedic devices such as the facemask. On the other hand, in Class Ⅱ, the maxilla is either anteriorized or the mandible is retruded. In cases where the mandible of a patient with a retracted mandible is guided to Angle Class I, a discrepancy in the upper and lower jaw is observed [8,9]. Maxillary expansion is performed as an initial phase of treatment to correct maxillo-mandibular skeletal disharmony. If a Class II discrepancy remains, orthognathic treatment, such as functional jaw orthopedics, is used to advance the mandible [1,10]

Many diagnostic methods are available for evaluating the transverse relationship of the maxilla and mandible. First is a posteroanterior cephalometric radiograph [11,12]. In the radiograph method, the difference in the width between the left and right jugale points in the maxilla and the width between the left and right antegonial notch in the mandible is defined as an index of the maxillary width difference [13-15]. However, diagnosing transverse deficiency can be difficult due to overlapping structures on radiographs. The second is by using a plaster model [16,17]. This is a relatively easy way to measure the difference in width between the upper and lower teeth. However, dental compensation with narrow maxilla can be masked and go undiagnosed [18]. The third method is the use of cone beam computed tomography (CBCT) which can be used to evaluate the transverse relationship. Several studies have evaluated the transverse length and angle of the left and right first molars in the coronal plane using CBCT [19,20]. The angulation of the teeth on CBCT can be evaluated to diagnose dental compensation and to measure the width of the basal bone [19].

To treat transverse deficiencies, expansion in the maxilla is commonly used. In mixed dentition patients, anchorage of an expansion appliance to the permanent first molar is difficult due to insufficient erupted crown length of the first molar. In this case, using the primary second molar instead of the permanent first molar for anchorage provides adequate expansion and high stability [21,22]. It can also prevent adverse effects on anchored teeth, such as root resorption and thinning of the buccal alveolar bone [23]. Therefore, before using an expansion appliance on a primary second molar, the evaluation of transverse relationships of the primary second molar should be preceded. Based on this, the type of palatal expansion appliance the patient needs and the amount and duration of expansion required can be evaluated. However, studies using CBCT imaging for evaluation of the transverse relationships in mixed dentition patients are few. One previous study compared the transverse relationships in a group of patients with early mixed dentition in Class Ⅲ and the normal group, but that study was based on the permanent first molars that had erupted and reached the occlusal plane [24]. Therefore, this study aimed to compare and evaluate the transverse occlusion of the first molars as well as the primary second molars in children with mixed dentition according to the anteroposterior skeletal relationships.

Materials and Methods

This study was approved by the Institutional Review Board (IRB) of Pusan Dental Hospital (IRB No.: PNUDH 2024-06-015).

1. Study patients

The study included patients who underwent CBCT imaging for orthodontic treatment at the Department of Pediatric Dentistry, Pusan Dental Hospital, between April 2021 and April 2024. After analyzing electronic medical records and applying the inclusion and exclusion criteria, a total of 102 patients were ultimately included in the study.

The inclusion criteria were as follows: 1) Early mixed dentition with fully erupted maxillary and mandibular first permanent molars to the occlusal plane; 2) retained primary molars with at least two-thirds of the molar roots intact; and 3) CBCT done prior to orthodontic treatment.

The exclusion criteria were as follows: 1) Presence of systemic diseases that could affect the oral and maxillofacial regions; 2) history of orthodontic treatment; 3) difficulty in radiographic interpretation due to prefabricated metal crown restorations; 4) cases where the second primary molar had more than one-third of root resorption due to factors such as pulpal treatment or ectopic eruption of the first permanent molar; and 5) presence of posterior crossbite.

Evaluation of anteroposterior occlusion was classified based on the ANB angle (the angle formed by A-point, nasion, and B-point). Class I malocclusion was defined as an ANB between 1.5° and 5°; Class Ⅱ malocclusion was defined as an ANB > 5°; and Class Ⅲ malocclusion was defined as an ANB < 1.5° [25,26]. Our sample included 102 patients; 42 patients (20 males, 22 females) had Class I, 31 patients (16 males, 15 females) had Class Ⅱ, and 25 patients (10 males, 15 females) had Class Ⅲ malocclusion (Table 1). Table 1 shows the sex and age distribution. The number of subjects according to skeletal classification does not differ significantly (p = 0.683). Similarly, age distribution across skeletal classifications is not significantly different (p = 0.273).

2. Study methods

1) Reorientation

CBCT images were captured using the Viso G7 device (PLANMECA, Helsinki, Finland) with a voxel size of 0.3 mm, 110 kV, 11.0 mA, and an exposure time of 3.272 seconds. The acquired CBCT images were stored in Digital Imaging and Communications in Medicine format and analyzed using OnDemand3D imaging software (version 1.0.10.10055; CyberMed, Seoul, Korea) [27]. For skeletal transverse width evaluation, the horizontal plane was set parallel to the Frankfort horizontal (FH) plane and they were assessed from the frontal view. For dentoalveolar width evaluation, the horizontal plane was adjusted to be parallel to the occlusal plane of each tooth (Fig. 1). The coronal plane was observed in four sections, each passing through the buccal grooves of the maxillary and mandibular primary second molars and first permanent molars [19,20]. The sagittal plane was set perpendicular to the horizontal and coronal planes, and passed through the midline of the orbit [28]. The maxilla and mandible were observed in separate planes, and the images were divided into 1 mm slides [29].

2) Measurement

(1) Skeletal transverse width evaluation

The following measurements were measured in the frontal view of the CBCT scan:

① Interjugular width (J-J) was measured as the distance between the left jugale (J) and the right J. The J point refers to the jugal process, located at the most lateral point of the maxillary tuberosity and the intersection of the maxilla and zygomatic buttress. ② Antegonial width (Ag-Ag) was measured as the distance between the left Antegonion (Ag) and the right Ag in the frontal view [14,30].

(2) Dento-alveolar width evaluation

The following measurements were taken where the coronal plane passed through the buccal groove of the maxillary second primary molar (Fig. 2B, Table 2) [19,20,31]:

① MxE1: Distance between the occlusal fossa of the maxillary primary second molar (Mx. E), ② MxE2: Distance between the maximum convex point of the Mx. E, ③ MxE3: Distance between the Mx. E alveolar crests, ④ MxE4: Distance between the line passing through the Mx. E root bifurcation point and the intersection with the buccal alveolar bone.

For the mandibular primary second molar, the following measurements were taken in the section where the coronal plane passed through the buccal groove.

① MnE1: Distance between the occlusal fossa of the mandibular second primary molar (Mn. E), ② MnE2: Distance between the maximum convex point the crowns of Mn. E, ③ MnE3: Distance between the alveolar crests of Mn. E, ④ MnE4: Distance between the line passing through the bifurcation of Mn. E and the intersection with the buccal alveolar bone.

Similarly, the same parameters were measured for the maxillary and mandibular first permanent molars, as shown in Fig. 2C.

① MxM1: Distance between the occlusal fossa of the maxillary permanent first molar (Mx. M), ② MxM2: Distance between the greatest convex point of the crowns of Mx. M, ③ MxM3: Distance between the alveolar crests of Mx. M, ④ MxM4: Distance between the line passing through the bifurcation of Mx. M and the intersection with the buccal alveolar bone.

For the mandibular first permanent molar, the following parameters were calculated:

① MnM1: Distance between the occlusal fossa of the mandibular permanent first molar (Mn. M), ② MnM2: Distance between the greatest convex point of the crowns of Mn. M, ③ MnM3: Distance between the alveolar crests of Mn. M, ④ MnM4: Distance between the line passing through the bifurcation of Mn. M and the intersection with the buccal alveolar bone.

(3) Tooth angulation

The functional occlusal plane was set as the horizontal plane, and tooth angles were measured on the coronal plane passing through the buccal groove of the primary second molar or the permanent first molar. The long axis of the tooth was defined as starting from the deepest point of the occlusal fossa and passing through the bifurcation of the root [5,29]. The angle formed between the long axis of the maxillary primary second molar or permanent first molar and the line parallel to the occlusal plane was measured [9]. For the mandibular second primary molar or first permanent molar, the angle between the long axis of the tooth and a line parallel to the line connecting the lower border of the mandible was measured. The specific definitions of these indicators for the maxillary primary second molar and the maxillary first permanent molar are as follows (Table 3).

For the maxillary primary second molar:

① MxE5: The angle between the long axis of the maxillary right primary second molar and the horizontal plane, ② MxE6: The angle between the long axis of the maxillary left primary second molar and the horizontal plane, ③ MnE5: The angle between the long axis of the mandibular right primary second molar and the plane parallel to the lower border of the mandible, ④ MnE6: The angle between the long axis of the mandibular left primary second molar and the plane parallel to the lower border of the mandible.

For the maxillary first permanent molar:

① MxM5: The angle between the long axis of the maxillary right permanent first molar and the horizontal plane, ② MxM6: The angle between the long axis of the maxillary left permanent first molar and the horizontal plane, ③ MnM5: The angle between the long axis of the mandibular right permanent first molar and the plane parallel to the lower border of the mandible, ④ MnM6: The angle between the long axis of the mandibular left permanent first molar and the plane parallel to the lower border of the mandible.

(4) Maxillo-mandibular transverse discrepancy

For the skeletal measurements, the difference between the distances from Ag-Ag and J-J was calculated. For the dento-alveolar measurements, the difference between the maxillary and mandibular measurements for each length parameter was calculated (Table 4, Fig. 3).

(5) Statistical Analysis

An examiner marked measurement points and calculated the distances and angles in 20 randomly selected samples. This was done two weeks later to assess the intra-examiner reliability. The intraclass correlation coefficient demonstrated high stability (r = 0.879). The normality of the variables was assessed using the Shapiro-Wilk test and the Kruskal-Wallis test was conducted for comparing the non-normal variables. Variables that showed a normal distribution were compared using one-way analysis of variance (ANOVA), followed by a post-hoc analysis using the Bonferroni test. p-values < 0.05 were considered statistically significant. Statistical analyses were conducted using IBM SPSS Statistics version 29.0 (IBM Corp., Armonk, NY, USA).

Results

1. Skeletal transverse width evaluation

The average distance for J-J width was 64.9 mm, and the average distance for Ag-Ag width was 79.1 mm (Table 5). The maxillary width of Class III patients was measured as 62.6 ± 2.4 mm, which was significantly narrower than the maxillary widths of Class I patients (64.9 ± 2.7 mm) and Class II patients (64.8 ± 3.0 mm, p = 0.002). No significant differences were observed in the mandibular width among the groups. The maxillary-mandibular discrepancy was smallest in Class II patients at 13.4 ± 3.9 mm, and was significantly different than Class III patients, who exhibited a discrepancy of 16.2 ± 3.2 mm (p < 0.05).

2. Dento-alveolar width evaluation of the primary second molar

The width of the alveolar bone at the furcation of the maxillary primary second molar was 51.7 ± 2.5 mm in Class III patients, which was significantly smaller than that of Class II patients at 53.6 ± 3.1 mm (Fig. 4, p = 0.026). The distance between the occlusal fossa of the maxillary primary second molar was smaller in Class II patients at 40.2 ± 2.4 mm compared with Class III patients at 41.6 ± 2.0 mm (p = 0.042). No significant differences were observed across the skeletal classifications for the mandibular primary second molar (Table 6).

3. Dento-alveolar width evaluation of the permanent first molar

The distance between the occlusal fossa of the maxillary first permanent molar was 45.4 ± 2.4 mm for Class II, 46.9 ± 2.1 mm for Class I, and 47.0 ± 2.5 mm for Class III. The differences in distance between Class II and Class I and, between Class II and Class III were significantly different (Fig. 4, p = 0.012). In contrast, for the mandibular first permanent molar, there were no significant differences in skeletal classifications, which was similar to the findings for the primary second molar (Table 6).

4. Tooth angulation

Angle differences between the primary second molar and the permanent first molar on the left and right sides were not statistically significant (p > 0.05), and thus, the mean values were used for analysis. The angle of the maxillary primary second molar in Class III was measured to be at 97.3° and exhibited a buccal inclination, compared with an angle of 92.2° in Class II (Table 7, Fig. 4). The angle of the maxillary first permanent molar in Class III was measured to be at 102.9° and exhibited a buccal inclination compared with an angle of 99.0° in Class II. The measured angle in the mandibular primary second molar was at 76.5° and for the first permanent molar, at 69.2°, indicating a lingual inclination when compared with skeletal Classes I and II, but the differences were not statistically significant.

5. Transverse discrepancy of maxillo-mandibular complex

For the alveolar bone length comparison between the maxilla and mandible, Class III exhibited the largest length difference at 16.2mm, followed by Class I at 14.2 mm and Class II at 13.4 mm. At the root bifurcation point of the maxillary and mandibular primary second molars, the alveolar bone length in Class III was 2.9 mm, which was significantly smaller than 4.1 mm in Class II. Additionally, the distance from the occlusal fossa of the permanent first molars in the maxilla and mandible was measured at 2.5 mm and was significantly smaller in Class II (Table 8).

6. Correlation

The angles of the primary second molar were significantly correlated with the angles of the permanent first molar (Table 9). A moderate positive correlation was observed between the angles of the maxillary primary second molar and the maxillary permanent first molars (r = 0.459, p < 0.001). A weak positive correlation was observed between the angles of the mandibular primary second molar and the mandibular permanent first molars (r = 0.342, p < 0.05). Furthermore, as the size of the maxilla and mandible basal bone showed a negative correlation, indicating a decrease in the maxilla relative to the mandible, the maxillary primary second molar displayed a greater inclination (r = -0.361, p < 0.01). In other words, a narrower maxilla compared to the mandible resulted in buccal inclination of the maxillary molars.

Additionally, the narrower the alveolar bone at the root bifurcation of the maxillary primary second molar compared to the mandible, the greater the inclination observed in the maxillary primary second molar and the permanent first molar, demonstrating a weak negative correlation (r = -0.263 for the primary second molar and r = -0.364 for the permanent first molar). Similarly, the narrower the alveolar bone at the root bifurcation of the maxillary permanent first molars compared to the mandible, the greater the inclination observed in the maxillary primary second molar and the permanent first molar, indicating a weak negative correlation (r = -0.203 for the primary second molar and r = -0.315 for the permanent first molar). For the mandibular permanent first molars, a weak positive correlation was found at the same level (r = 0.318).

Discussion

In this study, the alveolar bone length at the root bifurcation point (MxE4) of the maxillary primary second molar in patients with Class Ⅲ was significantly narrower compared with patients in Class I and Class II (p < 0.05). This finding suggested that the narrow basal bone morphology in patients with Class III malocclusion extended to the alveolar bone surrounding the primary second molar. Conversely, the alveolar bone length at the root bifurcation point (MxM4) of the maxillary first permanent molar in Class Ⅲ patients was the narrowest among the groups; however, this difference was not statistically significant. These findings are not consistent with previous studies that reported a reduced alveolar bone thickness in Class III patients compared with normal controls [24]. The discrepancies could be attributed to the fact that in the previous study, alveolar bone thickness was measured in areas located superior to those in this study, as indicated by a significantly smaller antegonial notch width compared to the MxM4 measurements in Class III patients in the present study.

The maxillary primary second molars (MxE5 and MxE6) and the permanent first molars (MxM5 and MxM6) exhibited a greater buccal inclination in Class Ⅲ patients than in Class II patients. Due to a narrow maxillary arch following the eruption of the maxillary permanent first molars, it remains upright and occludes with the mandibular first permanent molar. Miner et al. noted that in the superior convergent group (where the maxillary permanent first molars are buccally inclined while the mandibular permanent first molars are lingually inclined), a significant maxillo-mandibular discrepancy is observed, wherein the mandible appears to be larger than the maxilla [20]. This finding corresponded to the results of the present study. This suggests that even in the absence of observable crossbites, Class III patients with a narrow maxilla and wider mandible undergo dental compensation. Therefore, in clinical practice, resolving dental compensation and maxillary-mandibular discrepancies by expanding a narrow maxilla can be beneficial. Given that the alveolar bone pattern in the maxillary primary second molar is narrow, using the primary second molar as anchorage for expansion can be advantageous. Furthermore, this approach may also facilitate skeletal expansion in the permanent first molar area [21].

In Class II patients, the distance from the maxillary alveolar bone to the root bifurcation of the primary second molar (MxE4) was significantly greater than in Class Ⅲ patients (p < 0.05), while the distance to the occlusal fossa (MxE1) was narrower (p < 0.05). This may be due to the lingual inclination of the maxillary primary second molar (MxE5 and MxE6) and maxillary permanent first molars (MxM5 and MxM6) in Class Ⅱ patients. According to Miner et al., in patients with a larger maxilla compared with the normal group, the maxillary permanent first molars exhibit a lingual inclination and mandibular permanent first molars exhibit a buccal inclination, leading to compensation for skeletal transverse discrepancies. This compensatory mechanism highlights the dynamic relationship between skeletal structures and dental positioning, emphasizing the need for careful evaluation in orthodontic treatment planning for skeletal Class II patients [20]. Similar findings were observed in the present study. To restore the lingual inclination of the maxillary permanent first molars with large maxillary basal bone in skeletal Class II patients, tipping movement of the maxillary permanent first molars is favorable. Along with the expansion appliance, use of an orthodontic device to guide the mandible forward could be a beneficial treatment approach to resolve the maxilla-mandibular discrepancies. In this study, the angles of the mandibular primary second molar and the permanent first molars did not show significant differences among the skeletal classes. Although no significant skeletal differences were observed, the angles of the mandibular primary second molar and permanent first molars in Class III patients were the most lingually inclined, which is similar to findings from previous research. These findings suggest that the inclination patterns in Class III patients can be indicative of underlying skeletal relationships, even though the angles may not differ significantly between skeletal classes. This can assist in clinical evaluation and treatment planning [24]. In case of lingual inclination of the mandibular primary second molar or mandibular permanent first molar, it is necessary to consider the presence, if any, of underlying skeletal discrepancy, such as a large mandible, even in the absence of dental crossbite.

The maxillary basal bone was significantly narrower in Class III patients compared with the other classes (p < 0.05). However, no significant differences were observed in the length of the mandibular basal bone among the skeletal classes. Thus, the maxilla can be relatively narrower than the mandible during the early mixed dentition phase in Class III patients, indicating that the mandibular growth may not yet be pronounced. The mandible tends to show little change at skeletal maturity index (SMI) stages 0 to 1, with gradual increases beginning at stage 2 [12]. These findings highlight the importance of understanding the growth patterns of skeletal classifications. Early interventions can help address discrepancies between the maxilla and mandible before significant growth occurs in the mandible. Recognizing these growth trends can inform treatment planning in orthodontics, particularly for young patients in the mixed dentition stage.

The children included in this study had an average age of 8.1 years, corresponding to SMI stage 0 in terms of skeletal maturity. The mandibular development in these patients was not significantly pronounced, because of which no substantial differences were found among skeletal classes. In Class II patients, the differences in basal bone width between the maxilla and mandible were smaller compared with those in Class III (p < 0.05). This can be interpreted as the maxilla being larger than the mandible during the early mixed dentition phase. These findings suggest that the growth patterns of the maxilla and mandible in young patients may vary significantly based on skeletal classification, and this understanding is crucial for developing appropriate orthodontic treatment plans. Early intervention might be particularly beneficial for Class II patients to maintain balanced growth and development between the maxilla and mandible.

The average J-J distance observed in this study was 64 mm and the average Ag-Ag distance was 79 mm. According to Cortella et al., the average J-J distance for 9-year-olds is 60.6 mm, and the average Ag-Ag distance is 77.1 mm measured from posteroanterior cephalogram radiographs [32]. Wagner and Chung reported that, in 8-year-old female participants, the J-J width ranged from 57.35 to 59.77 mm and the Ag-Ag width ranged from 76.27 to 78.57 mm [33]. The values reported in the present study are slightly larger but are comparable to those reported by Wagner and Chung. It is possible that the study by Wagner and Chung, was conducted exclusively on female participants [33], and this could have contributed to the difference in findings from our study.

CBCT can be used to study various factors such as skeletal asymmetry, airway width, and temporomandibular joint disorders. The American Academy of Oral and Maxillofacial Radiology (AAOMR) recommends the use of CBCT for orthodontic purposes, in cases of anteroposterior, vertical, or transverse skeletal discrepancies [34]. However, clinicians must use CBCT scans only when the benefits of CBCT exposure outweigh the risks in accordance with the ALARA (As Low As Reasonably Achievable) principle. In this study, CBCT was performed on patients who visited for orthodontic purposes, aiming to reduce radiation exposure by not performing additional cephalometric X-rays.

There were some limitations to this study. First, the sample size of the study, particularly for Class III patients, was limited. As this was a retrospective study, the sample size was relatively small. Therefore, future research with a larger sample size is recommended. Second, this study did not investigate the effect of factors such as vertical components or crowding that could affect transverse occlusion. Future research would benefit from assessing transverse occlusion while considering vertical patterns, muscle function activity, and other influencing factors.

Conclusion

In mixed dentition patients with skeletal Class III malocclusion, the maxillary basal bone was notably narrow, while the mandibular basal bone showed no significant enlargement. The alveolar bone at the root bifurcation of the maxillary primary second molar was also narrow and had a buccal inclination. Therefore, using a maxillary expansion appliance anchored to the primary second molar to widen basal and alveolar bone may be beneficial. In Class II patients, the maxillary basal bone was wider, and the occlusal fossa distance between the maxillary and mandibular first molars was narrower, suggesting lingual inclination. Inducing buccal inclination of the maxillary first molar and guiding the mandible forward may be beneficial. These findings may assist pediatric dentists in diagnosing transverse relationships in early mixed dentition.

NOTES

Acknowledgments

This work was supported by a 2-Year Research Grant of Pusan National University.

Conflicts of Interest

The authors have no potential conflicts of interest to disclose.

Funding information

This work was supported by a 2-Year Research Grant of Pusan National University.

Fig 1.

Reorientation of CBCT image using Ondemand software for dentoalveolar measurement. (A) Sagittal section, (B) Axial section, (C) Coronal section. Reoriented as parallel to the occlusal plane (sagittal section), passing through buccal pit of right and left maxillary second deciduous molars (axial section), and parallel to the right and left occlusal plane (coronal section).

Fig 2.

Skeletal transverse evaluation of the frontal view. (A) Measurement of the interjugular width (J-J) (i.e., the distance between the interjugular points bilaterally). Measurement of antegonial notch width (Ag-Ag) (i.e., the distance between the antegonial notch points bilaterally). Indicators for the dento-alveolar width and angulation of (B) the second primary molar and (C) the first permanent molar.

Fig 3.

An example of a transverse discrepancy of the maxillamandibular complex. The difference indicated by the red arrows represents the discrepancy between the maxilla and mandible at the E furcation level (MxE4-MnE4). The blue arrows indicate the difference between the maxilla and mandible at the E occlusal fossa level (MxE1-MnE1).

Fig 4.

Transverse relationship of primary second molar in (A) Class Ⅱ and (B) Class Ⅲ. Transverse relationship of permanent first molar in (C) Class Ⅱ and (D) Class Ⅲ.

Table 1.

Classification of patients according to the skeletal classification

		Class I (n = 42)	Class Ⅱ (n = 31)	Class Ⅲ (n = 25)
Sex (N)	Male	20 (47.6%)	16 (51.6%)	10 (40%)
Sex (N)	Female	22 (52.4%)	15 (48.4%)	15 (60%)
Age (years)	Male	8.4 ± 0.9	8.2 ± 0.9	8.0 ± 0.9
Age (years)	Female	8.5 ± 0.9	7.9 ± 0.7	8.3 ± 1.0
	Total	8.4 ± 1.0	8.0 ± 0.8	8.2 ± 1.0

Age (mean ± SD).

Table 2.

Dentoalveolar linear measurements (widths) of primary second molars (E) and permanent first molars (M)

Linear measurement	Abbreviation	Definition
Primary second molars
		Distance between
Mx E furcation (mm)	MxE4	buccal alveolar bone level equivalent to furcation of UR_E and UL_E roots.
Mx E alveolar crest (mm)	MxE3	buccal alveolar crest level of UR_E and UL_E
Mx E cusp tip (mm)	MxE2	the most convex point of the crown of UR_E and UL_E
Mx E occlusal fossa (mm)	MxE1	the most concave point of the occlusal fossa of UR_E and UL_E
Mn E occlusal fossa (mm)	MnE1	the most concave point of the occlusal fossa of LR_E and LL_E
Mn E cusp tip (mm)	MnE2	the most convex point of the crown of LR_E and LL_E
Mn E Alveolar crest (mm)	MnE3	buccal alveolar crest level of LR_E and LL_E
Mn E furcation (mm)	MnE4	buccal alveolar bone level equivalent to furcation of LR_E and LL_E roots
Permanent first molars
		Distance between
Mx M furcation (mm)	MxM4	buccal alveolar bone level equivalent to furcation of UR_M and UL_M roots
Mx M Alveolar crest (mm)	MxM3	buccal alveolar crest level of UR_M and UL_M
Mx M cusp tip (mm)	MxM2	the most convex point of the crown of UR_M and UL_M
Mx M occlusal fossa (mm)	MxM1	the most concave point of the occlusal fossa of UR_M and UL_M
Mn M occlusal fossa (mm)	MnM1	the most concave point of the occlusal fossa of LR_M and LL_M
Mn M cusp tip(mm)	MnM2	the most convex point of the crown of LR_M and LL_M
Mn M Alveolar crest (mm)	MnM3	buccal alveolar crest level of LR_M and LL_M
Mn M furcation (mm)	MnM4	buccal alveolar bone level equivalent to furcation of LR_M and LL_M

Mx: maxilla; Mn: mandible; UR: upper right; UL: upper left; LR: lower right; LL: lower left; E: primary second molar; M: permanent first molar.

Table 3.

Angular measurements (angle) of primary second molars (E) and permanent first molars (M)

Angular measurement	Abbreviation	Definition
		Angle between
Mx E Rt inclination (°)	MxE5	UR_E axis and occlusal plane
Mx E Lt inclination (°)	MxE6	UL_E axis and occlusal plane
Mn E Rt inclination (°)	MnE5	LR_E axis and inferior border of mandible
Mn E Lt inclination (°)	MnE6	LL_E axis and inferior border of mandible
Mx M Rt inclination (°)	MxM5	UR_M axis and occlusal plane
Mx M Lt inclination (°)	MxM6	UL_M axis and occlusal plane
Mn M Rt inclination (°)	MnM5	LR_M axis and inferior border of mandible
Mn M Lt inclination (°)	MnM6	LL_M axis and inferior border of mandible

Mx: maxilla; Mn: mandible; UR: upper right; UL: upper left; LR: lower right; LL: lower left; E: primary second molar; M: permanent first molar.

Table 4.

Definition of transverse discrepancy of maxillo-mandibular complex

Difference between Mx and Mn at each level	Definitions
Mx (interjugular width) & Mn (antegonial width)	Ag to Ag - J to J
E furcation (mm)	MxE4 - MnE4
E alveolar crest (mm)	MxE3 - MnE3
E cusp tip (mm)	MxE2 - MnE2
E occlusal fossa (mm)	MxE1 - MnE1
M furcation (mm)	MxM4 - MnM4
M alveolar crest (mm)	MxM3 - MnM3
M cusp tip (mm)	MxM2 - MnM2
M occlusal fossa (mm)	MxM1 - MnM1

Mx: maxilla; Mn: mandible; Ag: antegonial notch; J: jugale; E: primary second molar; M: permanent first molar.

Table 5.

Skeletal transverse width evaluation according to skeletal classification

	Class I (Mean ± SD)	Class II (Mean ± SD)	Class III (Mean ± SD)	p-value
Interjugular width (mm)	64.9 ± 2.7^a	64.8 ± 3.0^a	62.6 ± 2.4^b	0.002
Antegonial width (mm)	79.1 ± 3.5	78.1 ± 4.2	78.7 ± 3.7	0.092

Comparisons done using Bonferroni post-hoc analysis.

a,b indicate a significant difference between the three skeletal classifications (p < 0.05).

Table 6.

Dentoalveolar measurements (widths) of primary second molars and permanent first molars according to skeletal classification

	Class I (Mean ± SD)	Class II (Mean ± SD)	Class III (Mean ± SD)	p-value
Primary second molars
Mx E furcation (mm)	53.1 ± 2.2^a	53.6 ± 3.1^a	51.7 ± 2.5^b	0.026
Mx E alveolar crest (mm)	49.6 ± 2.1	49.1 ± 2.6	49.0 ± 2.4	0.494
Mx E cusp tip (mm)	51.5 ± 1.9	50.2 ± 2.6	51.0 ± 2.2	0.144
Mx E occlusal fossa (mm)	41.2 ± 1.9^a	40.2 ± 2.4^b	41.6 ± 2.0^a	0.042
Mn E occlusal fossa (mm)	36.9 ± 3.3	36.6 ± 3.8	36.9 ± 2.8	0.914
Mn E cusp tip (mm)	47.7 ± 3.7	46.7 ± 2.3	47.0 ± 3.5	0.616
Mn E alveolar crest (mm)	46.6 ± 2.1	46.1 ± 1.9	46.4 ± 2.4	0.600
Mn E furcation (mm)	49.0 ± 2.3	48.8 ± 1.9	48.8 ± 2.6	0.953
Permanent first molars
Mx M furcation (mm)	60.1 ± 2.4	60.6 ± 2.7	59.1 ± 2.6	0.082
Mx M Alveolar crest (mm)	56.0 ± 2.2	55.7 ± 2.7	55.5 ± 2.4	0.635
Mx M cusp tip (mm)	56.9 ± 2.0	56.1 ± 2.4	56.4 ± 2.6	0.373
Mx M occlusal fossa (mm)	46.9 ± 2.1^a	45.4 ± 2.4^b	47.0 ± 2.5^a	0.012
Mn M occlusal fossa (mm)	42.2 ± 2.2	42.9 ± 4.9	42.8 ± 4.0	0.687
Mn M cusp tip(mm)	56.1 ± 2.1	54.2 ± 4.8	55.3 ± 3.0	0.058
Mn M Alveolar crest (mm)	57.0 ± 2.2	56.8 ± 3.6	57.4 ± 3.7	0.749
Mn M furcation (mm)	68.6 ± 3.7	69.0 ± 4.1	68.3 ± 2.5	0.790

Mx: maxilla; Mn: mandible; E: primary second molar; M: permanent first molar.

Comparisons done using Bonferroni post-hoc analysis.

a,b indicate a significant difference between the three skeletal classifications (p < 0.05).

Table 7.

Dentoalveolar measurements(angulation) of primary second molars and permanent first molars according to skeletal classification

	Class I (Mean ± SD)	Class II (Mean ± SD)	Class III (Mean ± SD)	p-value
Mx E angulation (°)	95.3 ± 3.9^a	91.7 ± 3.5^b	97.0 ± 3.8^a	< 0.001
Mn E angulation (°)	78.0 ± 3.9	78.7 ± 2.4	76.5 ± 4.8	0.100
Mx M angulation (°)	102.6 ± 4.3^a	99.0 ± 4.2^b	102.9 ± 5.0^a	0.001
Mn M angulation (°)	70.5 ± 4.4	71.1 ± 4.7	69.2 ± 4.2	0.304

Mx: maxilla; Mn: mandible; E: primary second molar; M: permanent first molar.

Comparisons done using Bonferroni post-hoc analysis.

a,b indicate a significant difference in angulation between the three skeletal classifications (p < 0.05).

Table 8.

Maxillo-mandibular transverse discrepancy. Differences between Mx. and Mn. at each level

Difference between Mx and Mn at each level	Definitions	Class I (Mean ± SD)	Class II (Mean ± SD)	Class III (Mean ± SD)	p-value
Mx(interjugular width) & Mn(antegonial width)	Ag to Ag - J to J	14.2 ± 3.7^a	13.4 ± 3.9^a	16.2 ± 3.2^b	0.017
E furcation (mm)	MxE4 - MnE4	4.1 ± 2.1^a	4.8 ± 2.6^a	2.9 ± 3.0^b	0.022
E alveolar crest (mm)	MxE3 - MnE3	3.1 ± 1.9	3.1 ± 1.8	2.5 ± 2.5	0.552
E cusp tip (mm)	MxE2 - MnE2	4.2 ± 2.2	3.8 ± 2.4	4.0 ± 3.0	0.824
E occlusal fossa (mm)	MxE1 - MnE1	4.6 ± 2.5^a	3.6 ± 2.9^b	4.7 ± 2.1^a	0.042
M furcation (mm)	MxM4 - MnM4	-8.4 ± 3.6	-8.3 ± 3.8	-9.2 ± 3.0	0.595
M alveolar crest (mm)	MxM3 - MnM3	-0.9 ± 2.1	-1.1 ± 3.4	-1.9 ± 3.1	0.351
M cusp tip (mm)	MxM2 - MnM2	0.8 ± 1.7	2.0 ± 4.2	1.1 ± 3.1	0.253
M occlusal fossa (mm)	MxM1 - MnM1	4.7 ± 1.8^a	2.5 ± 4.8^b	4.1 ± 3.5^a	0.029

Mx: maxilla; Mn: mandible; Ag: antegonial notch; J: jugale; E: primary second molar; M: permanent first molar.

Comparisons done using the Kruskal-Wallis method.

a,b indicate a significant difference in width between the three skeletal classifications (p < 0.05).

Table 9.

Correlations between the ratio and angular measurements

			Mx E inclination	Mn E inclination	Mx M inclination	Mn M inclination
Mx E inclination		r	-	0.013	0.459^**	-0.025
Mx E inclination		p	-	0.895	0.000	0.809
Mn E inclination		r	0.013	-	-0.193	0.342^*
Mn E inclination		p	0.895	-	0.057	0.001
Mx M inclination		r	0.459^**	-0.193	-	-0.005
Mx M inclination		p	0.000	0.057	-	0.960
Mn M inclination		r	-0.025	0.342^*	-0.005	-
Mn M inclination		p	0.809	0.001	0.960	-
Difference between	Definitions
Mx (J to J) & Mn (Ag to Ag)	Ag to Ag - J to J	r	-0.361^**	0.156	-0.328^*	0.232^*
Mx (J to J) & Mn (Ag to Ag)	Ag to Ag - J to J	p	0.000	0.125	0.001	0.021
E furcation	MxE4 - MnM4	r	-0.263^*	0.163	-0.364^**	0.191
E furcation	MxE4 - MnM4	p	0.009	0.110	0.000	0.059
M furcation	MxM4 - MnM4	r	-0.203^*	0.113	-0.315^*	0.318^*
M furcation	MxM4 - MnM4	p	0.045	0.266	0.002	0.001

Mx: maxilla; Mn: mandible; Ag: antegonial notch; J: jugale; E: primary second molar; M: permanent first molar.

Values presented as Pearson correlation coefficients. A p value less than 0.05 was considered statistically significant.

* : p < 0.05,

** : p < 0.001.

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