17 patients (14 female; 3 male) were analysed retrospectively for skeletal and dental relapse before distraction osteogenesis (DO) of the mandibular anterior alveolar process at T1 (17.0 days), after DO at T2 (mean 6.5 days), at T3 (mean 24.4 days), at T4 (mean 2.0 years), and at T5 (mean 5.5 years). Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated. Skeletal correction (T5–T1) was mainly achieved through the distraction of the anterior alveolar segment in a rotational manner where the incisors were more proclined. The horizontal backward relapse (T5–T3) measured −0.3 mm or 8.3% at point B (non-significant) and −1.8 mm or 29.0% at incision inferior ( p < 0.01). Age, gender, amount and type (rotational vs. translational) of advancement were not correlated with the amount of relapse. High angle patients (NL/ML′; p < 0.01) showed significant smaller relapse rates at point B. Overcorrection of the overjet achieved by the distraction could be a reason for dental relapse. Considering the amount of long-term skeletal relapse the DO could be an alternative to bilateral sagittal split osteotomy for mandibular advancement in selected cases.
The principles of distraction osteogenesis (DO) and its clinical application in maxillofacial surgery have opened new horizons in the treatment of facial and skeletal disharmonies. Mandibular DO is still mainly used in patients with syndromes and congenital anomalies and less in non-syndromic adult patients. Many surgeons still prefer to advance the mandible in one step by bilateral sagittal split osteotomy (BSSO) in normal patients than in several steps by DO. Mandibular DO seems to show similar risk factors for skeletal relapse when compared with BSSO for mandibular advancement.
Today there are new surgical approaches to correct mandibular deficiency. DO of the anterior alveolar mandibular process and mandibular wing osteotomy for the correction of the mandibular plane are two of them. Triaca et al. reported that DO of the mandibular alveolar process can be applied in several specific cases: in skeletal Class II patients with crowding to reduce the required sagittal distance to be achieved by an advancement BSSO; in skeletal Class III patients to create space for the decompensation of the lower incisor inclination; in skeletal Class I patients with a dental Class II to create space of one premolar width and overjet normalization, and in skeletal and dental Class I patients with crowding to avoid extraction and the resulting unfavorable profile that often results.
Few studies have been published on the results of DO on the anterior alveolar mandibular process. Recently, the soft tissue, skeletal and dental stability, neurosensory and function after DO of the anterior alveolar process were examined 2.0 years postoperatively. Skeletal relapse at point B was found in 19%. No correlation between the amount of skeletal relapse and the amount of advancement, patient’s age or gender could be demonstrated. Studies on the long-term results of DO of the anterior alveolar process are still lacking. The aims of the present study were to evaluate the amount of skeletal changes and dental changes 5 years after treatment in patients treated with DO of the mandibular anterior alveolar process, and to identify factors related to skeletal and dental stability.
Materials and methods
This study reports the follow-up of an initial sample of 33 patients published previously. Of the 33 patients, 17 patients were available for re-examination. The follow-up group (T1) consisted of 17 Caucasian patients (14 females and 3 males); aged 16.5–56.0 years (mean age 29.8 years, SD 11.9).
They were all treated orthodontically by one orthodontist (MA) and underwent DO of the mandibular anterior alveolar process to correct a skeletal Class II and large overjet with or without incisor crowding at the Pyramide Clinic in Zürich, Switzerland in the years 1998–2004. The female patients in the follow-up group had a mean age of 31.7 years (17.1–56.0 years, SD 12.0 years) and the male patients 21.5 years (16.5–31.4 years, SD 8.6 years) at T1. The surgical procedure was performed by one experienced maxillofacial surgeon (AT) and the technique has been published previously. Patients receiving other surgical procedures simultaneously on the mandible and maxilla such as genioplasty, BSSO, and Le Fort were excluded. Syndromic or medically compromised patients were excluded.
Five cephalograms were taken: the first on average 17.0 days before surgery (T1); and the second (T2) between 0 and 12 days (mean 6.5 days) after the osteotomy and before any distraction was carried out. The third (T3) cephalogram was taken between 13 and 92 days (mean 24.4 days) when the distraction was completed; the fourth (T4) between 0.9 and 3.7 years (mean 2.0 years) at the end of orthodontic treatment; and the fifth (T5) between 2.7 and 8.3 years (mean 5.5 years) after distraction of the mandibular anterior alveolar process. Lower incisors were retained with a bonded canine to canine retainer. The DO procedure has been described previously.
Ethical approval was given by the Ethic Committee of the Kanton Zürich, Switzerland, number 593. All subjects signed written, informed consent.
Skeletal changes were evaluated on profile cephalograms taken with the teeth in the intercuspal position, including a linear enlargement of 1.2%. The cephalograms were taken with the subject standing upright in the natural head position and with relaxed lips. The same X-ray machine and the same settings were used for all cephalograms.
The lateral cephalograms were scanned and evaluated with the program Viewbox 3.1 ® (dHal software, Kifissia, Greece). The cephalometric analysis for T1, T2, T3, T4 and T5 was carried out by one author (CUJ) and included the reference points and lines shown in Fig. 1 . Horizontal ( X -values) and vertical ( Y -values) linear measurements were obtained by superimposing the tracings of the different stages (T2, T3, T4 and T5) on the first radiograph (T1), and the reference lines were transferred to each consecutive tracing. During superimposition, particular attention was given to fitting the tracings of the cribriform plate and the anterior wall of the sella turcica which undergo minimal remodelling. A template of the outline of the mandible of the preoperative cephalogram (T1) was made to minimize errors for superimposing on subsequent radiographs.
Conventional cephalometric variables as well as the coordinates of the reference points ( Table 1 ) were calculated by the computer program. The coordinate system had its origin at point S (sella), and its X -axis formed an angle of 7° with the reference line NSL ( Fig. 1 ). Overjet and overbite were calculated from the coordinates of the points Is (incision superior) and Ii (incision inferior).
|SNA (°)||1.14||IiL-N-point B (°)||1.14||Incision sup.||0.48||0.21|
|SNB (°)||0.82||IiL-N-point B (mm)||0.24||Incision inf.||0.58||0.55|
|ANB (°)||0.48||IiL-A-Pg (°)||1.29||Apex inf.||0.54||0.18|
|NSL/NL (°)||0.86||IiL-A-Pg (mm)||0.49||Point B||0.28||0.45|
|NSL/ML′ (°)||1.01||Holdaway ratio||0.47||Asab||0.35||0.25|
|NL/ML′ (°)||0.84||IsL/IiL (°)||1.63||Pogonion||0.37||1.19|
The lateral cephalograms of T2 were only used to locate the cephalometric point alveolar surgical anterior base (Asab) before postoperative distraction of the alveolar process was carried out. Asab is the most anterior and inferior point of the lower anterior segment resulting from the surgical osteotomy (Figs 2 and 3 ). This cephalometric point was introduced to evaluate the movement (rotation vs. translation) of the lower anterior segment base in comparison to the lower incisors as the ratio (Ii [ X -value; T3–T2]/Asab [ X -value; T3–T2]).
Error of the method
To determine the error of the method, 21 randomly selected cephalograms were re-traced and re-analysed after a 2-week interval. Horizontal ( X -values) and vertical ( Y -values) linear measurements were re-obtained by superimposing the tracings of the different stages (T2, T3, T4, and T5) on the first radiograph (T1). The error of the method (Si) was calculated with the formula
Si = ∑ d 2 2 n
where d is the difference between the repeated measurements and n is the number of duplicate determinations.
The random errors are presented in Table 1 . No systematic errors were found when the values were evaluated with a paired t -test. The drop-out analysis included the unpaired t -test to compare drop-outs with the remaining patients for age and cephalometric features at T1, T2, T3 and T4, and the χ 2 test for sex. Drop-out analysis showed that there were no significant differences between the drop-out and the remaining patients for age and cephalometric features at T1, T2, T3 and T4.
Statistical analyses were conducted using SPSS software (version 19.0, SPSS Inc., Chicago, IL, USA). Normal distribution was confirmed with the Kolmogorov–Smirnov test. The effect of treatment, i.e. the differences between the variables and co-ordinates at T3 and T1 (T3 and T2 for Asab), T5 and T1 (T5 and T2 for Asab), T5 and T4 were tested with a paired t test. The relationships between skeletal variables, age, and gender were analysed with the Pearson’s product moment correlation coefficient.
Table 2 shows the selected variables before surgery (T1) and at 5.5-year follow-up (T5). The mean changes, standard deviations, and ranges for the selected cephalometric parameters before surgery and during the subsequent observation periods are given in Tables 3 and 4 .
|SNA (°)||80.9||3.7||73.1 to 85.7||80.0||2.8||74.0 to 84.4|
|SNB (°)||76.7||4.2||69.8 to 83.8||77.3||3.8||70.7 to 85.5|
|ANB (°)||4.2||2.2||0.3 to 7.1||2.7||3.0||−2.9 to 6.3|
|NSL/NL (°)||7.4||4.1||−1.9 to 15.0||7.6||3.7||0.1 to 13.0|
|NSL/ML′ (°)||33.6||7.9||21.4 to 53.7||34.7||7.1||23.9 to 53.7|
|NL/ML′ (°)||26.2||6.4||16.2 to 44.8||27.1||5.8||19.8 to 45.2|
|Gonion angle (°)||125.9||8.1||115.6 to 145.8||124.3||8.0||111.0 to 143.0|
|Jarabak ratio||64.5||6.5||49.2 to 75.7||63.6||5.4||49.9 to 72.5|
|IsL/NSL (°)||109.3||9.8||81.7 to 120.5||105.0||7.1||91.3 to 117.0|
|IsL/NL (°)||116.7||9.4||91.0 to 126.7||112.6||6.2||99.0 to 121.8|
|IiL/ML′ (°)||91.0||6.8||77.2 to 104.6||96.5||6.6||81.5 to 108.3|
|IiL-N-point B (°)||21.2||8.3||6.2 to 36.3||28.5||6.7||18.1 to 42.3|
|IiL-N-point B (mm)||4.4||3.8||−1.0 to 12.9||7.3||3.7||2.5 to 15.6|
|IiL-A-Pg (°)||20.1||6.5||7.6 to 30.3||26.4||5.7||18.4 to 39.9|
|IiL-A-Pg (mm)||0.1||3.7||−5.3 to 9.0||4.8||2.7||1.3 to 11.9|
|Holdaway ratio||1.0||5.8||−6.1 to 13.6||6.3||4.9||−3.4 to 17.2|
|IsL/IiL (°)||126.2||14.0||106.9 to 157.3||123.8||6.6||81.5 to 108.3|
|Overjet (mm)||7.7||2.1||4.5 to 11.9||2.8||0.9||1.3 to 4.5|
|Overbite (mm)||4.4||1.7||1.0 to 7.3||3.0||1.5||0.2 to 5.5|
|T3–T1 1||T5–T1 2|
|Variable or coordinate||Mean||p||SD||Range||Mean||p||SD||Range|
|Horizontal ( X -value [mm])|
|Point B||3.6||***||2.0||−0.21 to 7.6||3.2||***||2.3||−0.2 to 7.3|
|Asab||2.2||***||2.1||−1.1 to 5.4||1.2||*||2.1||−2.2 to 4.7|
|Pogonion||0.1||ns||1.0||−1.7 to 1.8||0.5||*||1.0||−0.8 to 2.4|
|Go′||−0.6||ns||2.4||−3.5 to 2.5||−0.4||ns||2.7||−5.7 to 2.8|
|Incision sup.||1.1||**||1.4||−1.3 to 3.2||−0.4||ns||1.9||−4.1 to 3.0|
|Incision inf.||6.2||***||2.5||−0.5 to 10.9||4.6||***||3.2||−1.6 to 11.5|
|Apex inf.||4.2||***||1.9||1.7 to 8.8||3.1||***||2.2||−0.6 to 6.7|
|Vertical ( Y -value [mm])|
|Point B||1.4||**||1.7||−1.6 to 4.8||0.0||ns||1.9||−6.0 to 2.3|
|Asab||−0.4||ns||1.4||−4.6 to 1.0||0.1||ns||1.3||−2.5 to 2.1|
|Pogonion||0.2||ns||2.4||−5.1 to 4.8||0.3||ns||1.8||−2.8 to 4.8|
|Menton||0.1||ns||0.5||−0.6 to 1.2||0.0||ns||1.0||−1.5 to 1.5|
|Go′||−0.3||ns||2.4||−3.5 to 2.5||−0.6||ns||1.9||−3.5 to 3.2|
|Incision sup.||−1.8||***||1.7||−6.7 to 0.4||−0.3||ns||1.4||−3.3 to 2.4|
|Incision inf.||1.3||**||1.9||−1.8 to 4.9||1.3||*||1.9||−1.7 to 4.9|
|Apex inf.||0.2||ns||1.2||−2.8 to 2.0||0.1||ns||1.8||−2.8 to 3.4|
|Angular (°), linear measurements (mm), and ratios|
|SNA (°)||−0.4||ns||1.6||−3.0 to 1.7||−0.9||*||1.6||−3.2 to 2.2|
|SNB (°)||0.9||*||1.2||−0.6 to 3.9||0.6||ns||1.6||−1.7 to 3.3|
|ANB (°)||−1.3||***||1.0||−3.9 to 0.9||−1.5||***||1.2||−3.7 to 0.2|
|Wits (mm)||−3.1||***||1.5||−5.3 to 0.4||−2.9||***||2.2||−7.7 to 1.3|
|NSL/NL (°)||0.2||ns||1.3||−2.0 to 2.8||0.2||ns||1.3||−2.1 to 2.1|
|NSL/ML′ (°)||1.3||***||1.3||−0.5 to 3.5||1.1||*||1.6||−2.8 to 3.8|
|NL/ML′ (°)||1.1||**||1.5||−0.4 to 3.7||1.0||*||1.4||−1.6 to 3.6|
|Gonion angle (°)||−2.1||**||2.7||−7.0 to 1.9||−1.6||ns||3.7||−10.2 to 4.5|
|Jarabak ratio||−0.3||ns||1.6||−2.7 to 2.2||−0.9||ns||2.0||−4.0 to 3.4|
|IsL/NSL (°)||1.3||ns||5.9||−5.1 to 22.0||−4.3||**||6.0||−16.7 to 9.6|
|IsL/NL (°)||1.5||ns||5.3||−4.6 to 20.1||−4.1||**||5.7||−14.7 to 8.0|
|IiL/ML′ (°)||7.2||***||4.9||−6.5 to 15.7||5.5||**||5.9||−5.7 to 16.1|
|IiL-N-point B (°)||9.4||***||4.6||−4.2 to 16.1||7.2||***||6.1||−4.3 to 16.5|
|IiL-N-point B (mm)||3.4||***||1.5||−1.7 to 5.2||2.9||ns||2.5||−1.4 to 7.8|
|IiL-A-Pg (°)||6.2||***||4.0||−4.9 to 13.4||6.3||***||5.7||−3.1 to 14.7|
|IiL-A-Pg (mm)||6.0||***||1.9||0.5 to 8.9||4.6||***||2.7||−0.5 to 11.4|
|Holdaway ratio||7.9||***||2.7||1.4 to 12.7||5.4||***||3.3||−1.2 to 13.3|
|IsL/IiL (°)||−9.7||***||7.9||−31.4 to 4.9||−2.4||ns||9.6||−21.9 to 14.5|
|Overjet (mm)||−5.1||***||1.7||−7.8 to −1.1||−4.9||***||1.9||−9.2 to −3.0|
|Overbite (mm)||−3.1||***||1.7||−6.4 to 0.1||1.5||**||1.7||−5.3 to 1.1|
|Ii/Asab||1.8||7.5||−22.4 to 9.7|