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Evaluation of palatal bone depth, cortical bone, and mucosa thickness for optimal orthodontic miniscrew placement performed according to the third palatal ruga clinical reference.

OBJECTIVES
This retrospective CBCT study aimed to evaluate the palatal anatomical characteristics using the third palatal ruga as a reliable clinical reference for miniscrew placement.


METHODS
Thirty-six subjects (mean age17.1 y.o. ± 4.1) were randomly selected and their records (CBCT volume and maxillary digital models) were included.BlueSkyPlan CBCT software viewer (BluSkyBio, V4.7) was used to measure the following outcomes at the level of third palatal ruga, 2 mm anteriorly and 2 mm posteriorly: total bone depth, cortical bone thickness, and mucosa thickness. The outcomes were evaluated on lines perpendicular to the palatal mucosa laying on different sagittal planes: the mid-palatal plane, 2 and 4 mm paramedian planes.


RESULTS
The maximum mean amount of bone depth was registered 2 mm posteriorly to the third ruga and 4 mm paramedian (9.7 mm). No significant difference was observed between the third ruga insertion site and its corresponding 2 mm posterior site. Cortical bone of palatal vault did not change significantly in anteroposterior direction for all the considered sites. Significant differences were found comparing cortical bone at the suture level with cortical bone 2-mm and 4-mm paramedian at all anteroposterior levels. Palatal mucosa increases its thickness in paramedian insertion sites, and it decreases in posterior insertion sites.


CONCLUSIONS
Both third palatal ruga and 2 mm posteriorly to third ruga (4 mm paramedian) could be the optimal insertion site for palatal miniscrew placement, depending on individual anatomic conditions. The thickness of the cortical palatal bone showed, at 4 mm paramedian, optimal characteristics for miniscrew primary stability. Palatal mucosa thickness values suggest miniscrew neck extension of 2.0-2.5 mm for optimal mucosa adaptation.