[Study of three-dimensional anatomical relationship between infrazygomatic crest and maxillary sinus for mini-screw insertion].

PURPOSE: To measure the thickness of the infrazygomatic(IZ) crest above the maxillary first molar and analyze its relationship with maxillary sinus as to derive clinical implications and provide guidance for placements of orthodontic mini-screw.

METHODS: Thirty seven cone-beam CT(CBCT) images of infrazygomatic crest sites were collected from data of 19 adult inter-treatment orthodontic patients. Based on the relationship of maxillary sinus floor and mesiobuccal root of the maxillary first molar, the subjects were divided into high sinus floor group (n=13) and low sinus floor group (n=24). Both lengths of mesial and distal buccal root of the maxillary first molar were measured as a reference for mini-screw positioning. Statistical analysis of the data was conducted using SPSS 20.0 software package.

RESULTS: IZ crest thickness above the maxillary first molar in high sinus group was larger than that in low sinus group, and the thickness decreased as the measurement moved towards the skull base in both groups. Lengths of mesial and distal buccal root of the maxillary first molar were (12.62±0.55)mm and (12.30±0.48)mm respectively in male patients alongside (11.53±0.24)mm and (11.15±0.26)mm respectively in female patients.

CONCLUSIONS: Our data indicated pre-insertion evaluation of the appropriate level of maxillary sinus floor should be performed before placement of mini-screw using CBCT. In order to avoid injury to the mesiobuccal root of the maxillary first molar and enhance the stability of inserted miniscrew, positions for miniscrew implant insertion should be over 13.62 mm in Chinese male patients and 12.53 mm in female patients at the vertical level from buccal CEJ.