The role of extraction in stability of orthodontic treatment

Impact of third molars on mandibular relapse in post-orthodontic patients: A meta-analysis

BACKGROUND/PURPOSE

Whether third molars contribute to or aggravate relapse, particularly in the mandibular dental arch, after orthodontic treatment remains controversial. Orthodontic clinicians vary widely in their practice regarding prophylactic third molar removal after orthodontic treatment. The present study systematically reviewed and meta-analyzed the available literature, and assessed the impact of third molar removal on the relapse of mandibular dental arch alignment after orthodontic treatment.

MATERIALS AND METHODS

Relevant literature was searched on online databases, namely Pubmed, Embase, and Cochrane. Outcomes of post-orthodontic mandibular relapse were evaluated in terms of the Little's irregularity index, intermolar width, and arch length. Statistical analysis was conducted using the Review Manager software (Version 5.3, The Cochrane Collaboration, Oxford, England).

RESULTS

Our initial search strategy yielded 360 citations, of which three retrospective studies were selected. The Little's irregularity index (weighted mean difference = 0.80, 95% confidence interval = 0.13-1.47, P = 0.02) differed significantly between the erupted third molar extraction group and agenesis third molar group; whereas the arch length and intermolar width did not. No outcome differed significantly between the impacted third molar extraction group and agenesis third molar group.

CONCLUSION

Removal of the mandibular third molars is recommended for alleviating or preventing long-term incisor irregularity.

Long-term development in the mandible and incisor crowding with and without an orthodontic stabilising appliance

In children with dentoalveolar Class II malocclusion with proclined upper incisors treated with extraction of the maxillary first premolars and appliance in the upper jaw only has been reported to increase the lower arch crowding when compared with children with untreated normal occlusion. Stabilising orthodontic appliances might therefore be useful in the lower jaw. A comparison was made of Class II: 1 malocclusion with extraction in the upper arch in 35 individuals in whom a fixed orthodontic appliance was used in the upper arch only and 26 individuals with fixed appliances in both jaws. The mean age at the start of treatment was 12.9 and 12.8 years, respectively. Treatment effects and post-retention changes up to 4 to 5 years out of retention at the age of 20 to 22 years were evaluated from lateral head films and plaster casts. During treatment the orthodontic appliance in the lower arch relieved crowding. The available lower anterior space increased from -0.6 to +0.2 mm, compared, to a decrease from -0.4 to -1.3 mm in the group without mandibular appliances. After 4 to 5 years out of retention the lower arch available space had decreased in both groups, to -1.4 mm in the group where orthodontic appliances had been used in both jaws and to -2.5 mm in the group without an orthodontic appliance in the lower jaw. This difference was significant. But the subjective ranking of the amount of crowding in the lower jaw models showed no significant difference between the 2 groups at the age of 20 to 22 years.

Mandibular incisor stability after bimaxillary orthodontic treatment with premolar extraction in the upper arch

To evaluate long-term changes in the lower incisor region, a comparison was made between children with large overjet treated with extraction of the upper first premolars and fixed appliances in both jaws and untreated children with normal occlusion. The treatment group consisted of 26 children and was studied with plaster models on 5 occasions: before treatment, at the end of active treatment, at the end of retention, after 1 year out of retention and at the last registration 4 to 5 years out of retention. The total time from the start of treatment to the last registration was 9 years and 10 months. Cephalometric registrations were made at the first and last registrations. The group of untreated children, the control group, consisted of 19 individuals. They were also studied with plaster models and lateral headfilms during a period of 10 years. The age of the treatment group and the control group at the last registration was 21.7 years and 20.4 years, respectively. At the first registration there was an available space in the lower anterior region of -0.06 mm (+/- 1.73) in the treatment group and + 0.4 mm (+/- 2.00) in the control group. At the last registration the available space for the treatment group was -1.4 mm (+/- 1.31), an extra space loss of 0.8 mm; in the control group the space loss was 1.3 mm and the available space was thus -0.9 mm. No significant difference in anterior lower jaw crowding could be seen between the treatment and control group at the last registration. Subjective ranking of the plaster models from the final registrations according to the amount of crowding in the lower anterior region showed no significant difference between the treatment and the control group.