The effect of first and second premolar extractions on third molars: A retrospective longitudinal study.

OBJECTIVES: To analyse the effect of first and second premolar extractions on eruption space for upper and lower third molars and on third molar position and angulation during orthodontic treatment. METHODS: The sample consisted of 296 patients of which 218 patients were orthodontically treated without extraction and 78 patients with extraction of first or second premolars. The eruption space for third molars was measured on pre- and posttreatment lateral cephalograms, whereas the angulation, vertical position, the relation with the mandibular canal and the mineralization status of third molars were evaluated using pre- and posttreatment panoramic radiographs. All data were statistically analyzed. RESULTS: The increase in eruption space and the change in vertical position of upper and lower third molars significantly differed between patients treated with and without premolar extractions, whereas the change in angulation, relationship with the mandibular canal and mineralization status of the third molars did not significantly differ between patients treated with and without premolar extractions. CONCLUSIONS: The retromolar space and the position of third molars significantly change during orthodontic treatment in growing patients. Premolar extractions have a positive influence on the eruption space and vertical position of third molars, whereas they do not influence the angular changes of third molars. Due to the retrospective character of the study, these conclusions should be carefully considered. Further prospective research is necessary for better insights into this complex topic. CLINICAL SIGNIFICANCE: This study stresses the importance of considering the possible effects of orthodontic treatment on third molars during treatment planning.

Short-term hard and soft tissue changes after mandibular advancement surgery in Class II patients: a retrospective cephalometric study.

AIM: The aim of this study was to describe hard and soft tissue changes after mandibular advancement surgery and to investigate the possible differences between Class II facial patterns. MATERIALS AND METHODS: Lateral cephalograms of 109 patients who underwent combined orthodontic treatment and bilateral sagittal split osteotomy (BSSO) were studied. Radiographs were taken within 6 weeks before surgery (T0) and at least 6 months postoperatively (T1). Patients were classified into 3 groups according to the preoperative mandibular plane angle. Hard- and soft-tissue changes were analysed with an x-y cranial base coordinate system. Measurements were evaluated statistically. RESULTS: Soft and hard tissues of the chin moved forward and downward. The position of the upper lip remained unchanged, while the lower lip moved forward and upward and decreased in thickness. The soft tissue points of the chin follow their corresponding skeletal points almost completely, while the change of the lower lip was only 76 per cent of the movement of the underlying hard tissue. The increase of SNB was more evident in the low-angle group, as well as improvement of the facial convexity. Stomium superius moved more forward in the low- and medium-angle cases. Ratios of hard and soft tissue changes showed no differences for different facial patterns. LIMITATIONS: Limitations derived from the retrospective study design. Only short-term changes could be addressed. The distinction between surgical changes and changes due to skeletal relapse is difficult to assess. Also, the difficulty to reproduce a relaxed lip position during imaging may influence our results. CONCLUSION: Class II characteristics improved after mandibular advancement. Soft tissues of the chin follow their skeletal structures almost in a 1:1 relationship, while movement of the lower lip was less predictable. The facial pattern of Class II patients should be considered in treatment planning.