Soft tissue stability in segmental distraction of the anterior mandibular alveolar process. A 2-year follow-up

Abstract

This study evaluated soft tissue changes in adult patients treated with distraction osteogenesis (DOG) of the anterior mandibular alveolar process and related it to different parameters. 33 patients (27 females; 6 males) were analysed retrospectively before surgery at T1 (17.0 days), after surgery at T2 (mean 6.5 days), at T3 (mean 24.4 days), and at T4 (mean 2.0 years). Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated. Statistical analysis was carried out using Kolmogorov–Smirnov test, paired t test, Pearson’s correlation coefficient, and linear backward regression analysis. 2 years postoperatively (T4), the net effect of the soft tissue at point B′ was 100% of the advancement at point B whilst the lower lip (labrale inferior) followed the advancement of incision inferior to 46%. Increased preoperative age was correlated ( p < 0.05) with more horizontal backward movement (T4–T3) for labrale superior and pogonion′. Higher NL/ML′ angles were significantly correlated ( p < 0.05) with smaller horizontal soft tissue change at point B′. Gender and the amount of skeletal and dental advancement were not correlated with postoperative soft tissue changes (T4–T3). DOG of the anterior mandibular alveolar process is a valuable alternative for mandibular advancement regarding soft tissue change and predictability.

The early 21st century saw a paradigm shift in the treatment goal for orthodontic patients. The emphasis on skeletal and dental relationships is changing towards greater consideration of the facial soft tissues . The combination of orthodontic treatment with maxillofacial surgery aims for optimal function and the best aesthetic results. Commonly, when orthognathic surgery is planned, the skeletal tissues are used to determine the amount of change necessary to provide an appropriate soft tissue profile change. The clinician needs precise information to increase the ability to predict the surgical effect of skeletal displacement on the patient’s overlying soft tissue profile.

The changes in shape and position of the overlying soft tissues in retrognathic patients has been evaluated mainly for bilateral sagittal split osteotomy (BSSO) with mandibular advancement and less frequently for mandibular distraction osteogenesis (DOG) . Until now, the evaluation of the soft tissue profile and its change in DOG of the lower anterior mandibular alveolar segment has not been carried out, whereas skeletal relapse has been examined recently . DOG of the lower anterior mandibular alveolar segment was introduced by T riaca et al. . They noted that DOG of the anterior mandibular alveolar process can be applied in the following specific cases: skeletal Class II patients with crowding to reduce the required sagittal distance to be achieved by an advancement BSSO; skeletal Class III patients to create space for the decompensation of the lower incisor inclination; skeletal Class I with dental Class II patients to create space of one premolar width and overjet normalization; and skeletal and dental Class I patients with crowding to avoid extraction and the often resulting unfavourable profile.

The aim of the present study was to evaluate the soft tissue changes in adult patients treated with DOG of the anterior mandibular alveolar process and to relate them to different parameters.

Materials and methods

The sample consisted of 33 Caucasian patients (27 females; 6 males); aged 16.5–56.0 years (mean 30.3 years, SD 10.7). They were treated orthodontically by one orthodontist (MA) and underwent DOG of the mandibular anterior alveolar process to correct a skeletal Class II and large overjet, with or without incisor crowding, from 1998 to 2004 . The female patients had a mean age of 30.8 years (16.8–56.0 years, SD 10.9 years) and the male patients 28.3 years (16.5–43.7 years, SD 10.5 years). The surgical procedure was performed by one experienced maxillofacial surgeon (AT); 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.

Ethical approval was obtained from the ethics committee of the Kanton Zürich, Switzerland, number 593. All subjects signed written, informed consent.

Four cephalograms were taken: the first, on average, 17.0 days before surgery (T1); 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) between 13 and 92 days (mean 24.4 days); and the fourth (T4) between 0.9 and 3.7 years (mean 2.0 years) after distraction of the mandibular anterior alveolar process. The distraction was completed at T3 and the orthodontic treatment at T4. All patients were debonded before T4 and the retention of the lower incisors was achieved with a bonded canine-to-canine retainer.

Cephalometric analysis

The soft tissue changes were evaluated on profile cephalograms taken with the teeth in the intercuspal position, and including a linear enlargement of 1.2%. The cephalograms were taken with the subject standing upright with a natural head position and with relaxed lips. The same X-ray machine and the same settings were used to obtain all cephalograms.

The lateral cephalograms of each patient were scanned and evaluated with the program Viewbox 3.1 ® (dHal software, Kifissia, Greece). The conventional cephalometric analysis for T1, T2, T3, and T4 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, and T4) 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.

Fig. 1
Reference points and lines used in the cephalometric analysis. The coordinate system had its origin at point S (sella), and its x axis formed an angle of 7° with the reference line NSL. G, glabella; S, sella; NSL, nasion-sella-line; N, nasion; x , horizontal reference plane; NL, nasal line; Cm, columella; Sn, subnasale; ILs, upper incisal line; Ans, anterior nasal spine; Pns, posterior nasal spine; As, apex superior; point A; point A′, soft tissue point A; Ls, labrale superior; Ss, stomion superior; Ii, incision inferior; Is, incision superior; Si, stomion inferior; Li, labrale inferior; Go, gonion; ML′, mandibular line prime; Ai, apex inferior; point B; point B′, soft tissue point B; Pg, pogonion; Pg′, soft tissue pogonion; Me, menton; Me′, soft tissue menton; S-line; and y , vertical reference plane.

Conventional cephalometric variables as well as the coordinates of the reference points 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).

The lateral cephalograms of T2 were only used to locate the cephalometric point, called the 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 ( Fig. 2 ). This cephalometric point was introduced to evaluate the movement (rotation versus translation) of the lower anterior segment base in comparison with the lower incisors as ratio (Ii [ x value, T3–T2]/Asab [ x value, T3–T2]).

Fig. 2
Reference points used in the cephalometric analysis of the lower apical base in DOG patients. Ii, incision inferior; point B; Ai, apex inferior; Asab, apical surgical anterior base; Pg, pogonion; and Me, menton. Asab is the most anterior and inferior point of the lower anterior segment resulted by the surgical osteotomy. Asab was introduced to evaluate the movement (rotation versus translation) of the lower anterior segment base in comparison to the lower incisors (Ii); for the ratio see the text.

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–T4) on the first radiograph (T1). The error of the method (si) was calculated with the formula:

<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='si=∑d22n’>si=d22nsi=∑d22n
si = ∑ d 2 2 n
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Soft tissue stability in segmental distraction of the anterior mandibular alveolar process. A 2-year follow-up
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