Applicatioin of micro-screw for mandibular incisors intrusion: a clinical and cephalometric study

Abstract

Objective To evaluate the effects of micro-screw on the intrusion of lower incisors and the leveling of curve of Spee in the process of orthotherapy.Methods Fifteen patients (5 males,10 females) with deep-bite were selected,aged from 11.3 to 28.8 years,with average of 17.2 years.All of them were Angle Class Ⅱ Classification 1 malocclusion and had a curve of Spee larger than 3 mm.Orthotherapy of extraction was adopted for the first premolars of two upper mandible and second premolars of two lower mandible.All these patients had micro-screws implanted at root apex area between lower lateral incisor and canine bilaterally,and when the 0.457 mm× 0.635 mm (0.018 in ×0.025 in) Ni-Tisquare wire was internalized,the strength of intrusion from micro-screws was used.Lateral cephalometric radiographs were taken before loading the micro-screw and immediately when the curve of Spee was leveled.Two linear and two angular measurements were selected for cephalometric analysis.Results The following results were noted: the lower incisors were significantly intruded for a mean of (4.10±0.98) mm; the mandibular molars were not significantly extruded for a mean of (0.91±0.69) mm; some lower incisors proclined and some lower incisors retroclined for a mean of (-0.09±4.12)°.After bite opening,the mandibular plane angle was minimally altered for a mean of (0.25±0.70)°; the ratio of lower incisor intrusioin to lower molar extrusion was 4.5: 1.0.Conclusions The combined use of micro screw with Ni-Ti wire is capable of enhancing the intrusion of lower incisors and leveling the curve of Spee,and it has minimal side effects on the posterior teeth. Key words: Curve of Spee; Micro-screw; Intrusion; Extrusion