Evaluation of facial hard tissue asymmetry with cone beam computerized tomography

The aim of this study is to determine facial hard and soft tissue asymmetries and the effects of the tissues on each other using cone beam computer tomography (CBCT).Forty nine asymmetric (soft tissue menton [Me?] deviation ? 4 mm) (mean age of study group: 19,9 ± 5,6 years) and 39 symmetric patients (Me? deviation<4 mm) (mean age of control group: 17,8 ± 5,5 years), selected regarding the distance of Me? to facial midline, were included in our study. The CBCT data were exported to MIMICS® software program. The 2D and 3D images of the craniofacial anatomic structures, located in front of external meatus acusticus, were constructed. Using the negative editing function, maxillary complex and mandible were separated from each other. The midsagittal plane was defined as the plane passing through sella and nasion, perpendicular to the horizontal plane. Two dimensional separation of the craniofacial structures into right and left parts were performed. Absolute mandibular midline, passing through the mental spine and menton, was used as a reference line for 3D separation. Thirty eight linear, 4 surface distance, 5 angular, 10 volumetric and 10 surface area measurements were used to evaluate facial asymmetry.Soft and hard tissue menton and upper and lower dental midlines showed more frequently right side laterality and the lower dental midline fit with the absolute mandibular midline in both groups. The upper 1/3 facial measurements demonstrated no differences between right and left side, whereas significant differences were observed at the dentoalveolar level (p<0,001). Lower face height, ramus height, mandibular effective length and corpus length of the deviated side were significantly shorter than that of the opposite side (p<0,001). At the deviation side, volumetric and surface area measurements of the mandible and hard tissue increased (p<0,001), whereas absolute mandibular measurements decreased (p<0,001). In the ramus originated asymmetry group, gonion lateralis was located laterally and in the corpus originated asymmetry group, was located superiorly at the deviated side. Right and left measurement differences in the soft tissue volume were also significant (p<0,01).In conclusion, asymmetry was more frequently identified in the lower third of the face. In asymmetric subjects, significant volumetric measurement differences were found between right and left mandibular segments. Morphological changes at the gonial region were observed. Symmetric subjects with minimum chin deviation showed also mild mandibular asymmetries. Differences in the soft tissue volumetric and surface area measurements pointed out that not only the hard tissue but also the soft tissue is affected from asymmetry. In asymmetric cases, the soft tissue followed the hard tissue to a large extent in chin region, however mandibular skeletal asymmetries seem to be compensated by the soft tissues at different levels.Key Words: Cone beam computer tomography, craniofacial asymmetry, MIMICS® software program, volume, surface area