| Abstract: Introduction: Orthodontic mini-implants have been incorporated into orthodontic treatment modalities. Adequate
bone at mini-implant placement site can influence the success or failure of anchorage. The present study was to determine
the thickness of cortical bone in the maxillary mid-palatal area at predetermined points for the placement of orthodontic
mini-implants using Cone Beam CT technique in order to evaluate the relationship of these values with the facial
height. Materials and Methods: A total of 161 patients, consisting of 63 males (39.13%) and 98 females (60.87%),
were evaluated in the present study; 38% of the subjects had normal facial height, 29% had short face and 33% had long
face. In order to determine which patient belongs to which facial height category, i.e. normal, long or short, two angular
and linear evaluations were used: the angle between S-N and Go-Me lines and the S-Go/N-Me ratio. Twenty points were
evaluated in all the samples. First the incisive foramen was located. The paracoronal cross-sections were prepared at distances
of 4, 8, 16 and 24 mm from the distal wall of the incisive foramen and on each cross-section the mid-sagittal and
para-sagittal areas were determined bilaterally at 3- and 6-mm distances (a total of 5 points). The thicknesses of the cortical
plate of bone were determined at the predetermined points. Results: There was a significant relationship between the
mean cortical bone thickness and facial height (P<0.01), with significantly less thickness in long faces compared to short
faces. However, the thickness of cortical bone in normal faces was similar to that in long and short faces. Separate evaluation
of the points showed that at point a16 subjects with short faces had thicker cortical bone compared to subjects with
long and normal faces. At point b8 in long faces, the thickness of the cortical bone was significantly less than that in short
and normal faces. At point d8, the thickness of the cortical bone in subjects with short faces was significantly higher than
that in subjects with long faces. Conclusion: At the point a16 the cortical bone thickness in short faces was significantly
higher than normal and long faces. The lower thickness of the cortical bone in the palatal area at points b8 and d8 in subjects
with long faces might indicate a lower anchorage value of these points in these subjects. |