Mini-implant assisted posterior intrusion: A quantification of anterior bite closure in nongrowing subjects.

Introduction: This study aimed to identify the vertical radiographic changes in nongrowing patients after treatment of anterior open bites (AOBs) using mini-implant assisted intrusion and to provide a predictive model to quantify the achievable intrusion.

Methods: This retrospective radiographic study evaluated the dentoskeletal changes in adults using orthodontic mini-implants in 53 treated patients with AOB. Radiographs before and after posterior intrusion were utilized to evaluate the associated changes. Conventional cephalometric analyses provided data for assessment. A paired t test was used to identify significant changes. A regression model (best subsets selection algorithm) was generated to quantify the relationship between mini-implant-assisted intrusion and the resultant change in overbite. A matched, untreated control sample was used for comparison.

Results: One hundred percent of AOBs were corrected using mini-implant-assisted intrusion of the maxillary molars. The overbite increased by an average of 3.6 mm. The average amount of maxillary first molar intrusion was 2.67 mm. The mandibular first molar moved an average of 1.93 mm closer to the palatal plane because of an average clockwise mandibular rotation of 0.78°. The occlusal plane steepened by an average of 3.95°. If all other inputs are held constant, 1 mm of intrusion of the maxillary first molar results in a 0.86 mm increase in overbite.

Conclusions: Mini-implant-assisted intrusion successfully treated AOB in adults with significant dentoalveolar but no significant skeletal changes. An average of 2.67 mm of intrusion of the maxillary first molars is achievable with this method showing that 1 mm of intrusion of the maxillary first molar increased overbite by 0.86 mm. Longer periods of intrusion resulted in greater amounts of bite closure.