Abstract
The purpose of this study was to examine osseous healing in the cleavage between the bone fragments after sagittal splitting ramus osteotomy (SSRO) utilizing computed tomography (CT). The subjects were 13 patients with mandibular prognathism who underwent bilateral SSRO. CT was used to study the rami immediately after surgery, then 6 months, 1 year, and 2 years after surgery. Many concave type (the angle between the cleavage >90°) anterior borders developed into the stairway type (the angle between the cleavage <90°) 6–12 months after surgery. Few borders changed to the smooth type. Almost all of the stairway and concave posterior borders changed to the smooth type in the 6–12 months after surgery. Regarding the posterior borders 1 year after surgery, the cleavage of distal and proximal bone fragments demonstrated stable osseous healing (smooth type) in cases where the length and width between the bone fragments were large. In conclusion, the authors successfully demonstrated detailed osseous healing in the cleavage between the bone fragments after SSRO. Remodelling between bone fragments is a major mechanism of osseous healing after this procedure.
Sagittal splitting ramus osteotomy (SSRO) is a well-established method of correcting mandibular deformities . Some studies have reported a postoperative relapse of the original deformity when SSRO is followed by rigid fixation of bone fragments using screws and a plate . Few reports have investigated remodelling and osseous healing in the cleavage between the bone fragments . There are few clinical reports regarding the use of computed tomography (CT) to visualize bone formation between the fragments after SSRO for patients with jaw deformity . The authors observed osseous healing in the cleavage space between the bone fragments 1 year after SSRO surgery and remodelling in the cleavage space continued from a previous study . The purpose of this study was to observe long-term osseous healing in the cleavage space between the bone fragments 2 years after SSRO surgery.
Materials and methods
The subjects comprised 13 patients (3 men and 10 women) with mandibular prognathism who underwent bilateral SSRO (26 rami) at the authors’ institution between August 2003 and February 2006. Their ages ranged from 22 to 36 years (mean 28.5 years). The patients underwent rigid fixation by titanium (11 patients) or absorbable (2 patients) plate and intermaxillary fixation between the maxillary and mandible arch brackets for 5–14 days (mean 11.5 days). All patients were instructed to wear elastic bands for as long as possible in order to retain the bone fragments during their hospital stay. Informed consent was obtained from all patients. The project was approved by the Ethics of Human Experiments at the Faculty of Medicine, Kobe University, prior to the start of the study.
CT examinations were carried out on all patients immediately after surgery and at 6 months, 1 year and 2 years postoperatively using Aquilion64 ® (Toshiba Medical Systems, Tokyo, Japan) at the Hakubikai Imaging Support Center (tube current 100 mA; scanning time 3 s; slice thickness 2 mm; slice width 2 mm; field of view 25 cm). The slice plane was parallel to the occlusal plane and the scanned area extended from the floor of the orbit to the inferior border of the mandible.
CT examinations were performed to investigate osseous healing after SSRO. The patients were classified as Deviation cases or Non-deviation cases. Deviation cases displayed more than 3.5 mm of chin (Menton (Me)) deviation from the midline, which markedly affected the postoperative recognition of facial symmetry . The Deviation cases were classified according to the side on which the Me deviation existed prior to SSRO. Non-deviation cases had an Me movement of less than 3.5 mm. The plane passing through the mandibular foramen was designated the upper plane, and the plane passing through the root furcation of the first and second molars of the mandible was designated the lower plane. On examination of the cleavage at the anterior (the measurement points: n = 52) and posterior borders (the measurement points: n = 52) of the distal and proximal bone fragments, the cleaved planes were classified into three types (smooth, stairway, concave) by modifying the methods of N emoto et al. ( Fig. 1 ). The smooth type was stable and smooth between the cleavage at the anterior and posterior borders of the distal and proximal bone fragments. In the stairway type, the angle between the cleavage at the anterior and posterior borders of the distal and proximal bone fragments was 90° or greater. In the concave type, the angle between the cleavage at the anterior and posterior borders of distal and proximal bone fragments was 90° or less ( Fig. 2 ).
The distance, length and width between bone fragments were measured using a micrometer caliper (maximum accuracy 0.05 mm) in the upper and lower planes of a CT taken immediately after surgery (13 patients). The measurements were taken three times and the mean was recorded. The relationship between the classification of osseous healing and the distance between bone fragments was investigated ( Fig. 3 ).
The distance was defined as the diameter between the anterior (or posterior) ends of the distal and proximal bone fragments. The width was defined as the minimum diameter from the anterior (or posterior) end of the distal (or proximal) bone fragment to the proximal (or distal) bone fragment. The length was defined as the diameter from the point of the minimum diameter of the width to the anterior (or posterior) end of the proximal (or distal) bone fragment to the proximal (or distal) bone fragment.
In the upper and lower planes of the CT examinations taken immediately and at 6 months, 1 year, and 2 years postoperatively, the distance of the mandibular ramus was determined using micrometer calipers (maximum accuracy 0.05 mm) and the mean of three measurements was calculated. The ratio of change was calculated using the following equation: the ratio of change of the distance of mandibular ramus (%) = Y − X / X × 100 ( Fig. 4 ) where X was the immediate postoperative value and Y the value at 6 months; or X was the 6 month value and Y the 1 year value; or X was the 1 year value and Y the 2 year value.
Stat-View-J-4.5 software (HULINKS Inc., Tokyo, Japan) was used for the statistical analysis that was carried out on all data for each group by means of one-way analysis of variance (ANOVA) and Fisher’s protected least significant difference (PLSD) method. Data were presented as mean ± standard deviation (SD). A value of p < 0.05 was considered statistically significant.
Results
Distance of the posterior protrusion
The distance of the posterior protrusion was 7.1 ± 2.6 mm in the Non-deviation cases (cases with a Me movement of less than 3.5 mm). The distance of the posterior protrusion was 6.6 ± 2.3 mm on the deviation side of the Deviation cases (cases with a Me movement greater than 3.5 mm). The distance of the posterior protrusion was 10.9 ± 3.0 mm on the non-deviation side of the Deviation cases.
Osseous healing of anterior planes
In the CT examinations of the anterior border of the mandibular ramus taken 6 months after surgery, the Non-deviation cases were classified as 5% smooth type, 15% stairway type and 80% concave type ( n = 20). On the deviation side of the Deviation cases, CT revealed 0% smooth type, 38% stairway type and 63% concave type anterior borders ( n = 16). The non-deviation side of these cases displayed 0% smooth type, 31% stairway type and 69% concave type anterior borders ( n = 16) ( Fig. 5 ).
In the CT examinations of the anterior border of the mandibular ramus taken 1 year after surgery, the Non-deviation cases were classified as 5% smooth type, 30% stairway type and 65% concave type ( n = 20). On the deviation side of the Deviation cases, the CT exams revealed 19% smooth type, 44% stairway type and 38% concave type anterior borders ( n = 16). The non-deviation side of these cases displayed 13% smooth type, 50% stairway type and 38% concave type anterior borders ( n = 16) ( Fig. 5 ).
In the CT examinations of the anterior border of the mandibular ramus taken 2 years after surgery, the Non-deviation cases were classified as 35% smooth type, 55% stairway type and 10% concave type ( n = 20). On the deviation side of the Deviation cases, the CT examinations revealed 44% smooth type, 44% stairway type and 13% concave type anterior borders ( n = 16). The non-deviation side of these cases displayed 56% smooth type, 31% stairway type and 13% concave type anterior borders ( n = 16) ( Fig. 5 ).
A significant number of concave type anterior borders developed into the stairway type between 6 months and 1 year after surgery; few of the concave type changed into the smooth type during this period. Almost all of the concave type anterior borders changed into the smooth or stairway type from 1 to 2 years after surgery.
One year postoperatively, CT examinations of the mandibular rami revealed that the distance between bone fragments was 1.70 ± 0.52 mm in the smooth type of anterior border ( n = 6). The distance between bone fragments was 5.05 ± 2.25 mm in the stairway type ( n = 21) and 4.47 ± 1.92 mm in the concave type ( n = 25). There were significant differences in distance between the smooth type and the stairway type, and between the smooth type and the concave type ( p < 0.05) ( Fig. 6 ).
One year postoperatively, CT examinations of the mandibular rami revealed that the length between bone fragments was 1.58 ± 0.54 mm in the smooth type of anterior border ( n = 6). The length between bone fragments was 4.73 ± 2.31 mm in the stairway type ( n = 21) and 4.21 ± 1.99 mm in the concave type ( n = 25). There were significant differences in length between the smooth type and the stairway type, and between the smooth type and the concave type ( p < 0.05) ( Fig. 6 ).
One year postoperatively, CT examinations of the mandibular rami revealed that the width between bone fragments was 0.87 ± 0.63 mm in the smooth type of anterior border ( n = 6). The width between bone fragments was 1.69 ± 0.90 mm in the stairway type ( n = 21) and 1.45 ± 0.57 mm in the concave type ( n = 25). There was no significant differences in width of all types ( p < 0.05) ( Fig. 6 ).
Osseous healing of posterior planes
In the CT examinations of the posterior border of the mandibular ramus taken 6 months after surgery, the Non-deviation cases were classified as 40% smooth type, 35% stairway type and 25% concave type ( n = 20). On the deviation side of the Deviation cases, the CT examinations revealed 44% smooth type, 44% stairway type and 13% concave type posterior borders ( n = 16). The non-deviation side of these cases displayed 50% smooth type, 44% stairway type and 6% concave type posterior borders ( n = 16) ( Fig. 7 ).
In the CT examinations of the posterior border of the mandibular ramus taken 1 year after surgery, the Non-deviation cases were classified as 80% smooth type, 10% stairway type and 10% concave type ( n = 20). On the deviation side of the Deviation cases, the CT exams revealed 81% smooth type, 19% stairway type and 0% concave type posterior borders ( n = 16). The non-deviation side of these cases displayed 81% smooth type, 13% stairway type and 6% concave type posterior borders ( n = 16) ( Fig. 7 ).
In the CT examinations of the posterior border of the mandibular ramus taken 2 years after surgery, the Non-deviation cases were classified as 90% smooth type, 10% stairway type and 0% concave type ( n = 20). On the deviation side of the Deviation cases, the CT exams revealed 100% smooth type, 0% stairway type and 0% concave type posterior borders ( n = 16). The non-deviation side of these cases displayed 100% smooth type, 0% stairway type and 0% concave type posterior borders ( n = 16) ( Fig. 7 ).
Almost all of the stairway and concave type in the posterior borders changed into the smooth type from 6 months to 2 year after surgery.
One year postoperatively, CT examinations of the mandibular rami revealed that the distance between bone fragments was 4.79 ± 2.68 mm in the smooth type of posterior border ( n = 42). The distance between bone fragments was 7.27 ± 4.06 mm in the stairway type ( n = 7) and 10.77 ± 3.71 mm in the concave type ( n = 3). There were significant differences in distance between the smooth type and the stairway type, and between the smooth type and the concave type ( p < 0.05) ( Fig. 8 ).
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