The ratio of soft and hard tissue changes after bilateral sagittal split ramus osteotomy (BSSRO) setback in skeletal class III deformity
Kaewalin Chanasapjaroen
Resident of residency training program in Oral and Maxillofacial Surgery, Faculty of Dentistry, Khon Kaen UniversityWilawan Weraarchakul
Associate Professor, Department of Preventive Dentistry, Faculty of Dentistry, Khon Kaen UniversitySupaporn Kongsomboon
Assistant Professor, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Khon Kaen UniversityKeywords :
skeletal class III deformity, orthognathic surgery, BSSRO, ratio of soft and hard tissue
Abstract :
The patients with skeletal class III deformity who underwent bilateral sagittal split ramus
osteotomy (BSSRO) setback procedure have the variability changes of the hard tissue and soft
tissue. Knowing the change ratio can improve the prediction outcomes after surgery. The purpose
of the study was to compare the change ratio of soft to hard tissue and to evaluate and determine
the possible factors, e.g., gender, age, mandibular setback distance, lip and chin thickness following
BSSRO. This was a retrospective analytical study, evaluating the ratio of soft tissue to hard tissue
changes at upper lip, lower lip and chin from lateral cephalometric radiographs. Cephalometric
analyses of all samples were performed and classified into 3 categories including preoperative (T0)
postoperative 6 months (T1) and postoperative 12 months (T2). Thirty-five subjects with completed
data for analysis were included. The average amount of mandibular setback distance was 5.80
mm, soft tissue thickness of lip and chin were 14.5 mm and 12.3 mm, respectively. The ratios of
soft tissue to hard tissue changes after 12 months BSSRO setback were as follows; at upper lip
(Sn : A = 0.55, Ls : U1 = 0.73), lower lip (Li : L1 = 0.94, Mlf : B = 0.98), chin (Pg’ : Pg = 0.94, Me’ : Me = 1.01).
Comparison of mean difference of the ratio soft to hard tissue changes between 6 and 12 months
after BSSRO setback, only Me’: Me was significantly different (p = 0.005). For the analysis of correlation co-
efficients between gender, age, amount of mandibular setback and lip and chin thickness relation
to ratio of soft to hard tissue changes after 12 months BSSRO setback, a significant correlation was
found between lower lip thickness and the ratio of soft to hard tissue changes at Li : L1 (p = 0.02)
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