Radiographic assessment of lower third molar eruption in different anteroposterior skeletal patterns and age-related groups

Correlation of mandibular third molar orientation and available retromolar space with arch length discrepancy in subjects with different growth pattern

Aim and Objective

To evaluate, compare, and correlate the mandibular third molar orientation and available retromolar space with arch length discrepancy in subjects with skeletal class II malocclusion and different growth pattern.

Material and Method

A total of 250 patients (age >18 yrs) having skeletal class II malocclusion (based on YEN angle and WITS appraisal) were divided into two groups. Both the groups (Group I with erupted mandibular third molars {N = 150} and Group II with impacted mandibular third molars {N = 100}) were subdivided into subgroups IA (n = 71), IB (n = 19), IC (n = 71) and Group IIA (n = 54), IIB (n = 30) and IIC (n = 16) for normo-, hypo- and hyperdivergent growth patterns, respectively (based on Jarabak ratio and Sn-Go-Gn angle). Four parameters, that is, retromolar space, width of third molar, third molar angulation, and mandibular incisor angulation were measured on orthopantomogram whereas arch length discrepancy was calculated with the help of lateral cephalogram and study model. Intragroup, intergroup comparisons (using unpaired Student's 't' test), and Pearson's correlation coefficient for assessed parameters were obtained.

Result

Third molar angulation and retromolar space were significantly higher in Group I than in Group II (hyperdivergent pattern of Group II had highest value). The width of third molar was less than retromolar space in Group II and vice versa for Group I. Mandibular incisor angulation and arch length discrepancy were more in Group II than in Group I, but difference was statistically nonsignificant. Strong positive correlation was observed for mandibular third molar angulation and available retromolar space in normo- and hyperdivergent growth patterns.

Conclusion

Lack of retromolar space along with increased amount of arch length discrepancy and mandibular incisor angulation is responsible for increased chances of third molar impaction in some subjects with class II malocclusion.

Tomographic analysis of relationship of mandibular morphology and third molars eruption

BACKGROUND

Lower third molars (L3M) are the last teeth to erupt in the oral cavity. Uneruption of these teeth still raises questions about its causes, in the literature (1) genetic factors, (2) dental lamina activity and, mainly, (3) insufficient growth and development of the bone bases are included. While the lack of space theory influenced by mandibular morphology and size of L3M was argued to be the main reason for L3M impaction, there is a limitation in the literature in examining such association using more accurate tomographic analysis obtained from CBCT. This work aimed to evaluate the relationship between mandibular morphology and the eruption of L3M.

METHODS

In this regard, 85 Cone Beam Computed Tomographies (CBCT), with 147 L3M, were selected from the archives of the Department of Surgery, Stomatology, Pathology and Radiology, Bauru School of Dentistry, obtained using an Accuitomo® Morita device and using the Dolphin Imaging 11.9 software. L3M eruption was related to linear measurements of jaw length (Co-Gn), retromolar space dimension (D2R), mesiodistal width of the L3M crowns, mandibular first molars (L1M) and mandibular canines (LC) and the angle mandibular (Ar-Go-Me). Independent samples t-test, chi-square tests and logistic regression were performed adopting a significance level of 5%.

RESULTS

The average mandible length of 116.446 mm + 6.415 mm, retromolar space of 11.634 mm + 2.385 mm, mesiodistal size of the L3M of 10.054 mm + 0.941 mm, sum of the mesiodistal widths of the L1M and LC of 15.564 mm + 1.218 mm and mandibular angle of 127.23° + 6.109. There was no statistically significant association between these factors and the eruption.

CONCLUSION

With the results obtained in this study, we conclude that the length and angle of the mandible, teeth size and dimension of the retromolar space are not associated with the L3M eruption.

A 3-dimensional evaluation of available retromolar space for the application of ramal plates

INTRODUCTION

This study aimed to evaluate the available retromolar space for ramal plates in patients with Class I and III malocclusions and compare that space with and without third molars using cone-beam computed tomography.

METHODS

Cone-beam computed tomography images of 30 patients (17 males, 13 females; mean age, 22.2 ± 4.5 years) with Class III malocclusion and 29 subjects (18 males, 11 females; mean age, 24.3 ± 3.7 years) with Class I malocclusion were analyzed. Available retromolar space at 4 axial levels of the second molar root and the volume of the retromolar bone were evaluated. Two-way repeated measures analysis of covariance (repeated measures analysis of covariance) was applied to compare the variables between Class I and III malocclusions and the presence of third molars.

RESULTS

Patients with Class I and III relationships showed up to 12.7 mm of available retromolar space at 2 mm apical from the cementoenamel junction (CEJ). At 8 mm apical from CEJ, patients with Class III malocclusion had 11.1 mm of space, whereas those with a Class I relationship showed 9.8 mm of available space. When patients had third molars, the amount of available retromolar space was significantly greater in patients with a Class I and III relationship. However, patients with Class III malocclusion exhibited greater available retromolar space than those with a Class I relationship (P = 0.028). In addition, the bone volume was significantly greater in patients with Class III malocclusion than in patients with a Class I relationship and those with third molars than in those without them (P <0.001).

CONCLUSIONS

Class I and III groups showed the availability of at least 10.0 mm of retromolar space 2 mm apical to the CEJ for molar distalization. Based on this information, it is suggested that clinicians consider available retromolar space for molar distalization in diagnosing and planning treatment for patients with Class I and III malocclusion.

Evaluation of bone area in the posterior region for mandibular molar distalization in class I and class III patients

OBJECTIVES

The aim of this study was to investigate the bone area in the posterior region, which is important for mandibular molar distalization in skeletal class I and class III individuals with normodivergent and hyperdivergent vertical growth patterns.

MATERIALS AND METHODS

In this retrospective study, cone-beam computed tomography (CBCT) scans of 120 individuals divided into 4 groups as class I normodivergent (group-I), class I hyperdivergent (group-II), class III normodivergent (group-III), and class III hyperdivergent (group-IV). Retromolar area at crown level measurements was performed on CBCT-derived panoramic radiographs and axial sections. Retromolar area at the root level was measured 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm apical to cemento-enamel junction at CBCT axial sections.

RESULTS

Retromolar area decreased towards the root apex in all groups and smallest retromolar area was level of CEJ_10mm in all groups. At any root level, the distal root of the mandibular second molar tooth was in contact with the mandibular inner or outer lingual cortex; 50% in group-I, 46.7% in group-II, 23% in group-III, and 23% in group-IV.

CONCLUSIONS

In normodivergent individuals, the retromolar area length at the root level is observed to be higher in class III than in class I at almost every level. In hyperdivergent individuals, on the other hand, only at CEJ_10mm level, it is higher in length in class III than in class I. Vertical growth pattern has no effect on the root and crown level retromolar area in class I and class III individuals.

CLINICAL RELEVANCE

CBCT provides more useful information than panoramic radiographs for patients who are scheduled for large mandibular molar distalization.

Assessment of mandibular retromolar space in adults with regard to third molar eruption status

OBJECTIVE

The aim of this study was to compare the difference in length and width of the mandibular retromolar space (RMS) stratified by the different eruption and impaction statuses of the third molars in patients with skeletal Class I malocclusion.

MATERIALS AND METHODS

The right mandibular RMS in 186 adult patients categorized according to the different statuses of the third molar was analyzed by using cone-beam computed tomography (CBCT). The shortest distances between the inner lingual cortex of the mandibular body and second molar root were measured parallel to the posterior occlusal line (POL) at depths of 2, 4, 6, 8, and 10 mm (mandibular retromolar space length in root level, RL_in2,4,6,8,10) on the axial slices with the cementoenamel junction (CEJ) as the reference level. The width of the RMS and second molar root was measured vertical to the POL at the terminal point of the molar distalization at depths of 2, 4, 6, 8, and 10 mm (width of the mandibular retromolar space, BW_2,4,6,8,10/ width of the second molar distal root, TW_2,4,6,8,10) from the CEJ.

RESULTS

RL in different measurement planes was 2.72 ± 2.22 ~ 3.74 ± 2.26 for Group A, 5.27 ± 1.68 ~ 9.10 ± 2.04 for Group B, 1.94 ± 2.34 ~ 5.71 ± 4.37 for Group C, 1.83 ± 2.95 ~ 5.05 ± 4.24 for Group D, and 5.93 ± 3.97 ~ 10.52 ± 2.16 for Group E. The BW measurement results for A ~ E group were 9.71 ± 1.41 ~ 10.51 ± 1.81, 9.83 ± 1.39 ~ 12.55 ± 2.11, 9.96 ± 1.21 ~ 12.17 ± 1.62, 9.82 ± 1.47 ~ 12.28 ± 2.77, and 10.02 ± 1.20 ~ 12.75 ± 0.82, respectively. There was no significant difference between men and women in any measurements (P > 0.05). Patients with normal third molars erupted and those vertically impacted possessed larger RMS lengths than those in which the third molars were missing, horizontally impacted or mesially impacted (P < 0.05). In each measurement plane, TW was significantly smaller than BW (P < 0.05).

CONCLUSIONS

Sex had no effect on the length or width of the mandibular RMS. Different statuses of third molars can also differentially affect the mandibular RMS. The mandibular RMS width is not a limit for mandibular molar distalization.

CLINICAL RELEVANCE

When considering the distalization of mandibular molars, more attention should be directed to the lingual cortex of the mandible, and CBCT scans are recommended for patients who require significant mandibular molar distalization. The mandible buccal shelf and retromolar area maybe a safe zone to insert the miniscrew for molar distalization.

Mandibular retromolar space in adults with different sagittal skeletal patterns

OBJECTIVES

To analyze the mandibular retromolar space among normal-divergent adult patients with different sagittal skeletal patterns by cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

CBCTs of a total of 120 normal-divergent adult patients were investigated. Patients were categorized into the following three groups according to their ANB angle: skeletal Class I (48 patients), skeletal Class II (36 patients), and skeletal Class III (36 patients). Four different planes parallel to the mandibular occlusal plane were used to measure the retromolar space. The retromolar space was measured by two reference lines and then compared between different sagittal skeletal patterns groups. The incidence of root contact with the inner lingual cortex was compared among the three groups.

RESULTS

The retromolar space of the Class III patients was significantly larger than that of Class I patients and Class II patients. Compared with Class I and Class III patients, Class II patients had a smaller retromolar space and higher incidence of contact with the inner cortex of the mandible.

CONCLUSIONS

Class III patients had a larger retromolar space than Class I patients and Class II patients in four different planes. The mandibular retromolar space should be evaluated by CBCT in patients who need mandibular molar distalization.

Anatomical limitations and factors influencing molar distalization

OBJECTIVES

To analyze the anatomical limitations and characteristics of maxillary and mandibular retromolar regions affecting molar distalization using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

A total of 120 qualifying patients were classified into equal groups of skeletal Class II and Class III and stratified by vertical growth pattern, age, sex, and third molar presence. The available distance along the axis of distalization and cortical bone thickness (CBT) were measured in the maxillary and mandibular retromolar regions of Class II and Class III patients, respectively. One-way analysis of variance was used to examine the effects of the factors on the measured data.

RESULTS

The minimum available distance of the Class II maxilla was observed at a level 3 mm from the cementoenamel junction (CEJ), while that of the Class III mandible was at a level 9 mm from the CEJ. The average available distance at the limit level was 4.06 ± 1.93 mm in the Class II maxilla, and the average corresponding CBT was 1.00 mm. The average available distance at the limit level in the Class III mandible was 2.80 ± 1.96 mm, and the corresponding CBT was 2.24 mm. In both skeletal Class II and Class III patients, hyperdivergent groups had the least available distance for molar distalization.

CONCLUSIONS

The limit for available distance in the Class II maxilla is closer to the coronal level, while that of the Class III mandible is closer to the apical level. A hyperdivergent growth pattern in a patient is indicative of less potential for molar distalization. Axial slices of CBCT images provide valuable evaluation for molar distalization regarding limit levels.

Mandibular posterior space in class II division 1 and 2 malocclusion in various age groups

PURPOSE

The aim of this study was to compare the mandibular posterior space in subjects with skeletal class II division 1 and division 2 malocclusions in two different age groups.

METHODS

Pretreatment cephalometric radiographs of 160 patients from 9 to 13 years of age (n = 80) and 15 to 18 years of age (n = 80) with class II division 1 or division 2 malocclusion were used for the study. Equal numbers of male and female patients (n = 20) were included in the two age groups in each of the malocclusion groups. Eight linear and six angular measurements were taken for mandibular posterior space evaluation. The data obtained from the study were compared using the independent t-test.

RESULTS

In the present study, the mandibular posterior space was greater in both malocclusion groups in subjects aged 15-18 years than in those aged 9-13 years (p < 0.05). The available posterior spaces behind the mandibular first molars were 4.4 mm and 6.3 mm in females (class II divisions 1 and 2, respectively) and 5.3 mm and 7 mm in males (class II divisions 1 and 2, respectively) in the 9‑ to 13-year-old age group. This space increased significantly by 6.9 mm (p < 0.001) and 3.2 mm (p < 0.01) in females (class II division 1 and 2, respectively) and 3.8 mm (p < 0.01) and 3 mm (p < 0.01) in males (class II division 1 and 2, respectively) in the 15- to 18-year-old age group.

CONCLUSION

Class II division 1 and division 2 malocclusions had similar and inadequate posterior space dimensions for the eruption of the third and an unknown portion of the second molars.