A Study on the Influence of the Osteotomy Slope on Bony Changes after Advancement Genioplasty.

[INTRODUCTION] The slope of the osteotomy used for the genioplasty dictates the vertical change. The horizontal bony changes after advancement genioplasty are not identical to the intercortical bony changes, because the variety of osteotomy slopes result in different vertical changes.

[MATERIAL AND METHODOLOGY] Ten of these patients had additional osteotomies as follows: five maxillary, three mandibular and two both maxillary and mandibular. Pre-operative and post-operative (at least 6 months) lateral cephalograms were retrospectively analyzed to assess horizontal and vertical movements of the chin. The following landmarks were used, Hard tissue pogonion (Pog), Occlusal plane (OPL), Menton (Me), Menton plane (MePL). The following parameters were calculated: ΔH = H-H, ΔV = V-V, The ratio between ΔH and ΔV equals tangent α, Calculated α = inverse tangent α .

[RESULTS] The Mean Horizontal bony movements was 3.75 mm (SD 1.4 mm, range -6 to 15 mm). The Mean Vertical bony movements was 1.4 mm (SD 0.8 mm, range 0.5-2 mm). The Mean Measured Osteotomy slope angle was 82.2 (SD 7.4, range 75-91). The Calculated Mean Slope Angle based on the ΔH/ΔV ratio was 82.3 (SD 7.0, range 74-95).

[DISCUSSION] The slope of the osteotomy used for the genioplasty dictates the vertical change. The osteotomy slope angle was defined as the angle between the osteotomy and a line perpendicular to the occlusal plane. The measured angle was compared with the calculated angle deduced from the horizontal and vertical genial post-operative changes.