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

Abstract

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.

Plain language summary

Which is the best place for mini-screws in the chin bone?

Why was the study done? When moving teeth during fixed brace treatment (orthodontics) extra fixation is sometimes needed to prevent teeth moving the wrong way. Small (mini-) screws can be placed into the bone to give this fixation. This study was done to find out how much bone there is in the chin into which the mini-screws can be placed. It looked at how much bone there was at different points, in male and female patients and in different age groups.

What did the researchers do? The researchers measured the height and width of the bone in the chin from three-dimensional X-rays. They measured it in male and female patients who were aged 9–13 years, 14–23 years or 24–50 years.

What did the researchers find? They found that the height and width of the bone increased with age, was greater in male patients and in the front of the chin. The place with the most bone was between the second incisor and the eye (canine) teeth.

What do the findings mean? This means that orthodontists can place mini-screws that are 20–28 mm long at the front of the chin. The ideal place for the mini-screws was between the second incisor and the eye (canine) teeth.