Abstract
Objective
This study aimed to compare the validity of the mental foramen (MF) and gonion (Go) as landmarks for a mandibular horizontal plane by assessing their vertical positions and line angulations.
Methods
Ninety cone-beam computed tomography scans of skeletal Class III adult patients were included. The patients were divided into two main groups: symmetry (n=30) and asymmetry groups (n=60). The asymmetry group was subdivided into the roll (n=30) and non-roll types (n=30). A three-dimensional co-ordinate system was established using the best-fit mirroring superimposition of the mandibular body. Landmark positions of the MF and Go were analysed and line angulations were calculated using their coordinates.
Results
The Go line angulation relative to the x-axis in the mandibular co-ordinate system was significantly greater than the MF line angulation in both groups and asymmetry types (P<0.05). The difference between the Go line and the MF line angulations was significantly greater in the roll type than in the non-roll type. The bilateral vertical discrepancy in Go position was significantly greater than that of MF for both groups and asymmetry types.
Conclusions
The bilateral vertical discrepancy of the MF was significantly smaller than that of Go in symmetrically positioned mandibles. The mandibular roll may be assessed differently when using MF-based versus Go-based mandibular planes.