Vertical incision subperiosteal tunnel access and three-dimensional OBS lever arm to recover a labially-impacted canine: Differential biomechanics to control root resorption

Abstract

A 15-year-old female presented with a chief complaint of unesthetic smile and protrusive lips. Lower facial height and convexity were within normal limits, but the lower lip was protrusive (3mm to the E-Line). Bimaxillary retrusion (SNA 79.5˚, SNB 76˚, and ANB 3.5˚) and a high mandibular angle (SN-MP 38˚) were noted. Lower incisors were prominent (L1 to MP 96˚ and L1 to NB 8 mm). Molars were Class I, but the upper right canine (UR3) was Class II. The upper left deciduous canine (ULc) was retained, and the UL3 was labially impacted. An oblique direction of canine eruption wedged the impaction between the keratinized mucosa and the adjacent incisor, eliciting root resorption on the labial surface of the UL2. The discrepancy index (DI) was 16. Following extraction of all four first premolars and the ULc, all teeth except the UL2 were bonded with a Damon Q® passive self-ligating bracket system. Vertical incision subperiosteal tunnel access (VISTA) technique was performed to produce a submucosal space for retraction and extrusion of the impacted UR3. A button was bonded on the UL3, and a power chain was attached. The elastomer chain exited the mucosa through a more distal incision, and traction was applied with a custom lever arm, anchored by an OBS® inserted into the left infrazygomatic crest. The impaction was retracted into a normal position between the UL2 and UL4. Once the UL3 was extruded to the occlusal plane, the UL2 was bonded and its axial inclination was corrected with a labial root torquing auxiliary. Both arches were detailed and finished. After 24 months of active treatment, the UL3 was well aligned, but the labial gingiva supporting it was immature and only partially keratinized. Follow-up visit 1.5 years later showed its maturation into a stable but relatively thin band of gingiva. In retrospect, this UL3 gingival problem may have been avoided by adjusting the three-dimensional (3D) lever arm for a more palatal emersion of the impaction. There was no change in the preexisting labial root resorption of the UL2, but no additional root resorption on any teeth occurred during active treatment. Final alignment and dental esthetics were excellent as evidenced by an American Board of Orthodontics Cast-Radiograph Evaluation score of 12, and the IBOI Pink and White Esthetic Score of 2. VISTA with an OBS 3D lever arm is an important advance for orthodontic impaction recovery. Submucosal retraction of a labially- impacted, partially transposed maxillary canine permits optimal emergence into the arch. Differential biomechanics of soft and hard tissue explains impaction-related root loss before treatment, as well as the mechanism for protecting an unrestrained lateral incisor while the impacted canine is recovered.