Evaluation of bone depth, cortical bone, and mucosa thickness of palatal posterior supra-alveolar insertion site for miniscrew placement

Abstract

Background: The use of palatal miniscrew offers the possibility to improve the effectiveness of orthodontic expansion devices. Palatal expanders supported by miniscrew can be applied with different clinical protocols. Some authors proposed the use of four palatal miniscrews during miniscrew-supported palatal expansion to maximize skeletal effects in young adults' treatment. However, bone availability decreases in the posterior paramedian palatal regions, making the positioning of the two-posterior paramedian palatal miniscrews challenging, when it is performed avoiding nasal cavities invasion. Some authors proposed miniscrews insertion in a specific region located laterally to the palatal process of the maxillary bone, and apically relatively to the dento-alveolar process. The aim of this study was to evaluate the bone thickness, cortical bone thickness, and mucosae depth of this anatomical site that, in this study, was defined as palatal posterior supra-alveolar insertion site.

Results: The evaluation of bone availability of palatal posterior supra-alveolar insertion site at different antero-posterior levels showed that the maximum amount of total bone thickness was found between the second premolar and the first molar. At this level total bone, thickness is significantly (p < .05) greater compared to the other sagittal sites and it offers on average around 2 mm of extra bone depth for miniscrew placement. Cortical bone thickness is adequate for primary miniscrew stability. Overall, cortical bone thickness considered at different insertion sites showed significant statistically (p < .05) differences. The findings of this study showed that palatal mucosa is particularly thick with average values ranging from 4 to 7 mm, and its extension ultimately affects miniscrew length selection. Palatal mucosa thickness showed no clinically significant differences comparing different sagittal and vertical insertion sites. Data also showed that palatal mucosal thickness slightly significantly increases (p < .05) with the inclination of the insertion axis relative to the occlusal plane. Finally, study findings showed that vertical growth pattern can significantly affect considered outcomes (p < .05).

Conclusions: Palatal posterior supra-alveolar insertion site is an appropriate site for posterior insertion of palatal miniscrews. Considering high anatomical variation preliminary CBCT evaluation is important to achieve optimal miniscrew placement.

Keywords: CBCT; Cortical bone thickness; Orthodontic miniscrew; Palatal bone depth; Palatal expansion; Palatal miniscrew insertion site; Palatal mucosa; TADs.

Fig. 1

CBCT scan and maxillary digital model superimposition

Fig. 2

Outcome evaluation was performed in coronal scans set at different antero-posterior level: interproximal contact point between the second premolar and the first molar (P2-M1), at the upper first molar furcation (M1F) and interproximal contact between the first and the second molar (M1-M2)

Fig. 3

The following outcomes were evaluated: total bone depth (yellow segment), cortical bone thickness (green segment), and palatal mucosa thickness (red segment). Outcomes measurement was performed on three straight lines traced passing through the three landmarks identified on the palatal mucosa profile (− 2P, zeroP, and + 2P). Three sets of lines with different angulation to the occlusal plane were considered: 45° (a), 60° (b), and 75° (c). This evaluation procedure was repeated for the three considered coronal scans. Overall, for each patient 27 insertion sites were evaluated, and 81 outcomes were measured

Fig. 4

Ideal miniscrew position to reach tricorticalism stabilization. Light blue color shows ideal neck dimension extending to the transition zone between palatal mucosa and oral cavity. Gray color represents the miniscrew head interacting with the abutment of the palatal expander