Eruption Pattern of Third Molars in Orthodontic Patients Treated with First Permanent Molar Extraction: A Longitudinal Retrospective Evaluation

Spontaneous space closure after extraction of young first permanent molar. Retrospective cohort study

Background

Early compromised first-permanent-molar (FPM) extraction can adversely affect occlusion. However, the current literature does not provide sufficient support for definitive early extraction outcome. This cohort study aimed to evaluate the pattern of post-FPM extraction spontaneous space closure and its pre-extraction indicators.

Methods

Patients of 7-13 years, with compromised FPM at three-tertiary-centers between 2015 and 2019 were retrospectively screened. Pre-extraction indicators were evaluated (extraction location, direction of the second permanent molar (SPM) long-axis, and SPM Demirjian development stage). Spontaneous space closure pattern was evaluated clinically and radiographically using the American Board of Orthodontics (ABO) grading system.

Results

In total, 112 FPMs (73-patients) were identified and five (4.5%) of the extraction sites showed favorable combined-ABO-scores. Distal direction of the SPM long-axis in the maxillary arch significantly decreased the relative risk (RR) of having a SPM rotation/alignment ABO score-1 (P = 0.002; RR = 0.64). For the mandibular arch, Demirjian stage D and E significantly decreased the RR of having ABO score-1 for spacing between the SPMs and second premolars (P = 0.029; RR:0.57, P = 0.004; RR:0.53, respectively) and vertical dimension (P = 0.02; RR = 0.53).

Conclusions

The direction of the SPM long-axis and its developmental stage are key indicators of the favorable outcome pattern of spontaneous space closure after FPM early extraction.

Bilateral distalization of maxillary first molars in a group of adult patients after extraction of maxillary second molars using infra-zygomatic mini-implants: A prospective clinical trial

BACKGROUND

It is now possible to predictably distalize maxillary first molars in nongrowing patients with the infra-zygomatic gear distalizer and to improve malocclusions without having to extract the premolars and regardless of the patient's compliance. The purpose of this study was to investigate the amount and rate of distal movement of the maxillary first molars using our proposed appliance after extraction of maxillary second molars.

METHODS

Ten nongrowing female patients successfully treated with our proposed appliance were the subjects of this study. The amount, rate, and type of distalization, were analyzed through upper jaw cone beam computed tomography (pre- and post-treatment) and scanned casts taken on a monthly interval.

RESULTS

The average amount of distalization of the maxillary first molars was 4.03 mm at the crown level and 2.88 mm at the root level. The rate of distalization had an average of 0.61 mm per month with a maximum of 0.79 mm in the first month because of the regional acceleratory phenomena after extracting the maxillary second molar.

CONCLUSIONS

The maxillary first molars were distalized in a significant manner and all patients reached a Class I relation within an average duration of 6.4 months. The proposed appliance proved to be a viable noncompliance modality to distalize maxillary first molars correcting maxillary Class II malocclusions characterized by maxillary protrusion or maxillary incisor crowding.

Mandibular Posterior Anatomic Limit for Distalization in Patients With Various Patterns of Third Molar Impactions: A Three-Dimensional Cone Beam CT (CBCT) Study

AIM

The aim was to compare and evaluate the variation in the mandible's posterior anatomic limits (MPAL) stratified by different third molar impaction patterns utilizing cone-beam CT (CBCT) in individuals with skeletal Class III malocclusion.

METHODOLOGY

The sample consisted of CBCT records of 80 samples of Class III patients categorized based on the pattern of their third molar impaction. The shortest linear distances from the distal root of the second mandibular molar to the inner cortex of the mandibular body were measured at the crown level, at the cementoenamel junction (CEJ), and at the depths of 4, 6, and 8mm from the CEJ, all parallel to the posterior occlusal line. The MPAL of the four groups were compared. The Shapiro-Wilk test for normality was performed. The Kruskal-Wallis test was performed to compare the MPAL distances between the groups.

RESULTS

Significant differences were noted between the four groups at every level. MPAL distances decreased towards apex in all the groups and was least at the 8mm root level. The greatest MPAL distances were noted in the no-impaction group followed by the horizontal. At 8mm, the MPAL were 4.2+/-1.3 in Group 3 (Control), 3.3+/-0.9 in Group 1 and 2.7+/-0.05 mm in Group 2. Though the amount of space available for distalization was greatest for the mesioangular group at the crown level, it was least at the 8mm level compared to other groups.

CONCLUSION

MPAL distances were shortest at the root level in Class III patients who had mesioangularly impacted third molars and care should be taken before attempting distalization in them.

Criteria for early diagnosis of mandibular third molar agenesis based on the developmental stages of mandibular canine, first and second premolars, and second molar: a retrospective cohort study

BACKGROUND

Permanent first molars with severe dental caries, developmental defects, or involved in oral pathologies are at risk of poor prognosis in children. Accordingly, using the third molar to replace the first molar can be a good treatment option when third molar agenesis is predicted early. Thus, this retrospective cohort study aimed to develop criteria for early detection of mandibular third molar (L8) agenesis based on the developmental stages of mandibular canine (L3), first premolar (L4), second premolar (L5), and second molar (L7).

METHOD

Overall, 1,044 and 919 panoramic radiographs of 343 males and 317 females, respectively, taken between the ages of 6 and 12 years were included. All developmental stages of L3, L4, L5, L7, and L8 were analyzed based on the dental age, as suggested by Demirjian et al. The independent t-test was used to assess age differences between males and females. The rank correlation coefficients were examined using Kendall's tau with bootstrap analysis and Bonferroni's correction to confirm the teeth showing developmental stages most similar to those of L8s. Finally, a survival analysis was performed to determine the criteria for the early diagnosis of mandibular third molar agenesis.

RESULTS

Some age differences were found in dental developmental stages between males and females. Correlation coefficients between all stages of L3, L4, L5, and L7 and L8 were high. In particular, the correlation coefficient between L7 and L8 was the highest, whereas that between L3 and L8 was the lowest.

CONCLUSION

If at least two of the following criteria (F stage of L3, F stage of L4, F stage of L5, and E stage of L7) are met in the absence of L8 crypt, agenesis of L8 can be confirmed.