Three-dimensional measurement and analysis of mandibular characteristics in subjects with impacted mandibular second molars

Mandibular second molar impaction: introducing a novel and validated 3D classification system

BACKGROUND

Mandibular second molar (M2M) impaction is a clinically significant manifestation of eruption disturbance in dental development. The primary aim of this study was to investigate the impact of the three-dimensional (3D) characterization on clinical and therapeutic decisions for M2M impaction. The secondary aim was to introduce a validated 3D classification system incorporating both surgical and orthodontic parameters.

METHODS

Bidimensional (2D) and 3D radiological records of 15 impacted M2M were collected and deidentified. Ten experienced clinicians (5 oral surgeons;5 orthodontists) categorized each case, first based on 2D records and then with 3D scans. The degree of orthodontic and surgical difficulty in treating impacted M2M was evaluated using a novel classification system based on anatomical and radiological features. The primary outcome variable was the assessment of differences in diagnosis and decision-making protocol using 2D or 3D records, where clinical relevance ranged from 0 to 4. The secondary outcome variable was the validation analysis of the proposed 3D classification system to determine the concordance among the clinicians. Descriptive statistics and multivariable inferential analysis based on Akaike information criterion (AIC) were performed (α = 0.05).

RESULTS

3D examination allowed a better visualization of M2M impaction with higher clinical relevance for diagnosis of M2M root relationship to alveolar nerve and lingual plate, height to alveolar crest, depth, and inclination relative to the first molar and position relative to the third molar (range:2.69-3.43). The proposed 3D classification of M2M impaction changed clinical decisions regarding surgical-orthodontic approach, biomechanics, patient education, and treatment time estimate (range:2.59-3.33). In the validation analysis of the classification, no evidence of inter- or intra-group (surgeon/orthodontist) bias in score attribution occurred: the model with the minimum AIC was the null model (AIC = 718.04).

CONCLUSION

3D evaluation of impacted M2Ms could enhance diagnostic accuracy, and a classification system was proposed and validated by a group of experienced surgeons and orthodontists with high concordance.

Managing Mandibular Second Molar Impaction: A Systematic Review and Meta-Analysis

PURPOSE

Mandibular second molar (M2M) impaction is a serious eruption disorder. The purpose of this systematic review was to analyze the therapeutic approaches for M2M impaction. The objective of the meta-analysis was to summarize the success of the surgical, surgical-orthodontic, and orthodontic treatment.

METHODS

A PRISMA-guided search strategy was conducted by 2 authors in 5 databases up to January 2023. Randomized and nonrandomized clinical trials were considered. Case reports, case series with<5 patients, and reviews were excluded. Methodological quality was assessed using Newcastle-Ottawa scale and Cochrane Collaboration tool for nonrandomized and randomized clinical trials, respectively. Outcomes were as follows: 1) treatment success rate defined by the repositioning of impacted M2M in the dental arch with normal functional occlusal relationship and periodontal health; 2) time-to-repositioning as time-to-event analysis; and 3) complications. Meta-analysis examined treatment success differences with 3 approaches: orthodontic (uprighting maneuvers/traction), surgical (surgical procedures/strategic extractions), and surgical-orthodontic (combined surgical and orthodontic procedures) as the exposure variable. The quantitative analysis also compared the success rate using third molar removal as the secondary predictor variable. The χ2 test determined the statistical heterogeneity (I2); a cut-off of 70% was used to select the common or random effects model. Odds ratio (OR) and 95% confidence interval (CI) were recorded.

RESULTS

A total of 1,102 articles were retrieved. After full-text reading, 16 articles were included and 1008 M2Ms were analyzed. Nine studies had fair quality, 6 studies had good quality, and 1 had unclear risk of bias. Managing impacted M2Ms showed a moderate to high success rate (66.7 to 100%). Significant differences favoring surgical treatment over orthodontic treatment were observed for M2M uprighting (OR = 4.97; CI: 1.49 to 16.51; P = .01).No differences were detected comparing surgical and surgical-orthodontic treatment (OR = 1.00; CI: 0.03 to 37.44; P = .99), or orthodontic and surgical-orthodontic treatment(OR = 4.14; CI: 0.43 to 40.14; P = .22).Third molar removal showed no significant correlation with M2M uprighting (OR = 1.98; CI: 0.24 to 16.03; P = .5).

CONCLUSION

Despite study limitations, both orthodontic and surgical management of impacted M2M can be effective suggesting that clinicians are able to choose best treatment for most cases.

Introducing surface-to-surface matching technique to evaluate mandibular symmetry: A retrospective study

Objectives

This study introduced a three-dimensional (3D) surface-to-surface matching technique to evaluate the mandibular symmetry of teenagers and adults with unilateral second molar scissor bite.

Methods

The targets came from 73 cone-beam computed tomography (CBCT) images with unilateral second molar scissor bite, including teenagers (n = 30) and adults (n = 43). 73 images without scissor bite and matched in sex and age were selected as controls. The scans were developed into 3D mandible models and seven mandibular functional unit models, including condylar process (Co), coronoid process (Cr), mandibular ramus (Ra), mandibular angle (Ma), alveolar process (Ap), mandibular body (Mb) and chin process (Ch). The surface-to-surface matching technique was introduced. 3D deviation analysis and matching percentages calculation were performed and compared to evaluate the symmetry of the mandible.

Results

Comparisons were made between the study samples and control samples. For teenagers, the matching percentages of the entire mandible (55.31 ± 7.24%), Mb (69.04 ± 9.22%) and Co (65.19 ± 10.67%) in the study group were lower than that of the entire mandible (60.87 ± 6.38%) (P <0.01), Mb (75.0 ± 8.71%) (P <0.05) and Co (70.25 ± 8.20%) (P <0.05) in the control group. While Ap, Ra, Ch, Cr and Ma showed no statistically significant differences (P >0.05). For adults, the matching percentages of the entire mandible (48.88 ± 9.77%), Ap (65.83 ± 11.21%), Mb (64.43 ± 12.03%), Ch (79.17 ± 10.29%), Ra (64.11 ± 9.84%) and Co (61.08 ± 11.64%) in the study group were lower than the entire mandible (59.28 ± 5.49%) (P <0.01), Ap (73.65 ± 9.10%) (P <0.01), Mb (71.66 ± 8.40%) (P <0.01), Ch (83.86 ± 5.59%) (P <0.05), Ra (68.54 ± 7.87%) (P <0.05) and Co (66.20 ± 10.62%) (P <0.05) of the control group. Only Cr and Ma showed no statistically significant differences (P >0.05).

Conclusion

Mandibular asymmetry was observed in both teenagers and adults with unilateral second molar scissor bite. Moreover, compared with teenagers, more mandibular units of adult patients were affected.

Clinical significance

Based on the surface-to-surface matching technique, the symmetric and morphological information of the mandible can be converted into visual color maps and quantitative descriptions. This method can bring convenience to the study of the growth of mandible, orthodontic treatment and orthognathic surgery design.

Surgical Management of Impacted Lower Second Molars: A Comprehensive Review

Impacted lower second molars (ILM2) are rarely reported in the literature, but various studies have been done for its treatment. Apart from solely orthodontic approaches, different surgical management techniques were reported to have successful outcomes. Surgical intervention of ILM2 can help expose the tooth for further orthodontic purposes, simplifying complex treatment methods, and reducing treatment time. This review illustrates the comprehensive evaluation and updated methods of surgical uprighting, repositioning, and transplantation of ILM2 with future directions for better understanding and treatment planning in the clinical setting. The successful outcome of surgical intervention depends on case selection, root development of ILM2, careful surgical manipulation, and adherence to sound biological principles.