The optimal site for orthodontic mini-screw placement in the mandibular symphysis: A cone-beam computed tomography study.

OBJECTIVE

To determine the ideal site for mini-screw (MS) insertion in the mandibular symphysis by obtaining total, intraosseous and extraosseous height and depth measurements in this anatomical region in relation to the mandibular anterior teeth and further categorise the results by sex and age.

DESIGN

Cross-sectional study.

SETTINGS: Cone-beam computed tomography (CBCT) images were analysed from existing clinical records.

METHODS

CBCT images of 90 patients were examined from a single centre at UniCIEO University. The sample was divided into three age groups: G1 = 30 patients aged 9-13 years; G2 = 30 patients aged 14-23 years; and G3: 30 patients aged 24-50 years. Total, intraosseous and extraosseous height and depth measurements of the mandibular symphysis were obtained at the lower central incisor (LCI), lower lateral incisor (LLI) and lower canine (LC), along the long axis of each respective tooth, by a calibrated operator. For statistical analyses, t-tests and Mann-Whitney U-test, analysis of variance (ANOVA) and Kruskal-Wallis test were used. Two-way ANOVA was applied for variables with significant differences (P <0.05).

RESULTS

Sex-related differences were observed, with male patients presenting greater measurements than female patients, including total height at LCI (mean difference = -2.54, 95% confidence interval [CI] = -3.93 to -1.17) and LC (mean difference = -3.12, 95% CI = -4.71 to -1.54), as well as intraosseous height at LCI (mean difference = -3.00, 95% CI = -4.32 to -1.68) and LLI (mean difference = -2.24, 95% CI = -3.39 to -1.08).

CONCLUSIONS

An age-related increase in mandibular symphysis height and depth was observed. With respect to the ideal MS dimensions and the optimal site for orthodontic skeletal anchorage, MSs with a length of 20-28 mm may be placed vertically and deep in the lower vestibule of the mandibular symphysis, in the region of the lateral incisor and canine.