Soft and hard tissue changes in skeletal Class III patients treated with double-jaw orthognathic surgery—maxillary advancement and mandibular setback

Abstract

The soft tissues of the facial profile may change after skeletal movement in orthognathic surgery. The aim of this study was to evaluate and compare the differences and correlation between hard and soft tissues after double-jaw surgery in skeletal Class III subjects. Radiographs from the following time points were assessed using Dolphin Imaging software: preoperative (T0), 2–4 months postoperative (T1), and 6–12 months postoperative (T2). Eleven hard and soft tissue points of the facial profile were evaluated. The Student’s t -test was used to assess the significance of differences between the time intervals; Pearson’s correlation coefficient was used to assess the significance of correlation existing between these points; significance was set at P < 0.05. In the sample of 58 subjects, the correlation between hard and soft tissues in the mandible was greater than in the maxilla. Similarly, the correlations only between hard tissues and only between soft tissues presented a greater correlation in the mandible. The results are similar to those found in studies on single-jaw surgery for both the maxilla and the mandible. The influence of movements in hard tissues was restricted to the soft tissues of the same jaw, although there were exceptions.

Every treatment plan for orthognathic surgery should take into consideration the functional and aesthetic results and also psychological aspects of the patient. Facial aesthetics has an increasingly relevant role in modern society, and the patient’s perception of their facial profile may influence their submission or not to the surgical procedure.

In 1993, Arnett and Bergman presented a three-dimensional organized analysis of the facial structures, which would later be related to the cephalometry of the soft tissues for diagnosis and treatment planning.

Soft tissue cephalometry enables an evaluation of relationships between objective measurements of important structures. It comprises a method for quantifying facial disharmony and identifying its causes. The true vertical line (TVL) is a vertical line passing through the point subnasale, perpendicular to the horizontal plane of the natural head position (NHP; natural head position assumed when the patient is standing with arms relaxed along the body and looking at the horizon). According to Arnett and Gunson, when landmarks in the skull base are used as a reference line for measuring the profile, erroneous findings may be generated, as the landmarks in the skull base may vary as much as the facial and dental structures measured through it. Thus the TVL is used for assessing the profile because it demonstrates a greater accuracy in relation to intracranial references.

The aim of orthognathic surgery is often aesthetic, in addition to the facial improvement of the occlusion. Therefore, predicting changes in the facial soft tissues after orthognathic surgery is extremely important. Changes in the facial profile in hard and soft tissues have been reported in the literature, and studies assessing these changes in double-jaw surgery are scarcer than those assessing only maxillary or only mandibular surgery. The use of proportions of movement between hard and soft tissues instead of absolute measures is frequent and eliminates the effect of height differences between men and women. However, as Joss et al. remark in their systematic review on the relationship between soft and hard tissues in mandibular setback, many studies have presented the proportion of movement between hard and soft tissues, but are lacking in the exact identification of which hard tissue points are actually correlated to which soft tissue points.

The purpose of this study was to evaluate the changes in the facial profile after skeletal movements in skeletal Class III subjects who underwent double-jaw surgery (maxillary advancement and mandibular setback). The hypothesis of the present study was that skeletal changes (changes in hard tissue points) may affect and are correlated to changes in the soft tissues of the facial profile at different points. The specific aims of this study were as follows: (1) to evaluate the significance of differences between the preoperative and postoperative periods and between two different postoperative periods for each measurement analyzed; (2) to evaluate the significance of the correlation and proportion of movements between hard tissue points and soft tissue points in the short and medium term; and (3) to evaluate the significance of correlation and proportion of movements only between hard tissue points, and (4) only between soft tissue points in the short and medium term.

Materials and methods

This study was conducted in a similar manner to the study of Becker et al., in which radiographs taken 1 week before surgery, between 2 and 4 months after surgery, and between 6 and 12 months after surgery (T0, T1, and T2, respectively) were evaluated. These were cephalometric radiographs of a sample of non-consecutive skeletal Class III subjects who underwent maxillary advancement and mandibular setback. All patients selected were treated in the same way with regard to preoperative, perioperative, and postoperative care. Under general anaesthesia, a Le Fort I osteotomy was performed to allow maxillary movement, and a bilateral sagittal osteotomy of the mandibular ramus was performed to allow mandibular movement. Rigid internal fixation was performed with titanium plates from the same manufacturer; four ‘L’ miniplates were used in the maxilla and one miniplate and one bicortical screw on each side of the mandible of the 2.0 Neoface System miniplate (Neoortho, Curitiba, Paraná, Brazil). The movements of the double-jaw orthognathic surgery were mainly horizontal. The vertical movements were smaller than 3 mm in all cases.

Patients previously treated for maxillofacial deformities by other types of orthognathic surgery (single-jaw surgery, other types of fixation, vertical movement greater than 3 mm) were excluded from the sample, as well as patients who suffered facial trauma or who had other systemic diseases or syndromes. Some patients had incomplete records or X-ray records outside the time ranges necessary for this study. These patients were also excluded from the sample.

Radiographs were taken with a standard length marker of 50.0 mm using a PM 2002 CC Proline panoramic imaging unit (Planmeca, Helsinki, Finland). They were digitalized using an HP ScanJet G4050 scanner (Hewlett-Packard Co., Palo Alto, CA, USA) and afterwards imported into Dolphin Imaging 3D v. 11.5 software (Dolphin Imaging Software, Canoga Park, CA, USA). Cephalometric tracings and measurements of the distances between specific cephalometric points were done with images totally calibrated by Dolphin Imaging 11.5. At this time, the top-most and the bottom-most graduation points were marked on the head-holder nosepiece ruler.

Based on the cephalometric soft tissue points described by Arnett et al., a customized cephalometric analysis was created and then selected in the software for evaluation of the desired measurements. Eleven points (in both hard and soft tissue) were assessed in relation to the TVL, which is a line perpendicular to the horizontal plane of the NHP passing through the subnasale area ( Fig. 1 ). The distance between the TVL and the head-holder nosepiece ruler image set at T0 was established to be the same at T1 and T2 for every subject, and checked by superimposition to ensure that the TVL did not move if the subnasale area changed after surgery.

Fig. 1
Cephalometric points of hard and soft tissues and distances to be measured between them and the true vertical line (TVL): 1, TVL; 2, nasal projection (nasal point); 3, A′ (point A of soft tissue); 4, A (point A of hard tissue); 5, upper lip (most anterior point of upper lip); 6, upper incisor (most incisal point of the upper incisor crown); 7, lower lip (most anterior point of the lower lip); 8, lower incisor (most incisal point of the lower incisor crown); 9, B′ (point B of soft tissue); 10, B (point B of hard tissue); 11, Pog′ (soft pogonion); 12, Pog (hard pogonion).

SPSS v. 18.0 statistical software (SPSS Inc., Chicago, IL, USA) run on the Microsoft Windows operational system was used for the processing and analysis of data.

The level of significance was set at 5%, in which the values of P < 0.05 reject the null hypothesis that there is no difference or significant correlation for each measurement analyzed between the preoperative and postoperative periods and between the two postoperative periods.

The Student’s t -test for paired samples was used in order to assess the presence of significant differences between the preoperative and postoperative periods (T0 with T1, and T0 with T2) and, to evaluate relapse, the differences between the two postoperative periods (T1 with T2).

Pearson’s correlation coefficient was used to assess the existing significant correlation in changes in hard tissue and soft tissue points between the preoperative and postoperative time intervals (T1–T0 and T2–T0), and between the two postoperative time intervals (T2–T1). These tests were used for every measurement.

A single examiner performed all the tracings. Ten percent of tracings were repeated after 2 months by the same examiner and by a more experienced examiner (gold standard). The intraclass correlation coefficient was used to evaluate the intra- and inter-examiner agreements, and the non-parametric Kolmogorov–Smirnov test was used to assess the normality of data.

Results

A strong intra- and inter-examiner agreement was found (intraclass correlation coefficient over 0.900 for both situations for every point assessed).

Lateral cephalometric radiographs were evaluated at T0 (1 week before surgery), at T1 (between 2 and 4 months after surgery, with a mean of 2.8 months), and at T2 (between 6 and 12 months after surgery, with a mean of 9.3 months). A total of 58 skeletal Class III patients submitted to maxillary advancement and mandibular setback constituted the sample. Of these, 38 were women and 20 men. The average age was 27.3 years (range 18–48 years). The average maxillary advancement at point A was 1.5 mm, with a standard deviation of 1.0 mm (range 0.2–6.1 mm) and the average mandibular setback at point B was 7.2 mm, with a standard deviation of 4.2 mm (range 0.9–18.1 mm).

Table 1 shows the minimum and maximum values and the mean and standard deviation obtained in millimetres for each of the points evaluated in relation to the TVL for T0, T1, and T2. Positive values indicate a position in front of the TVL and negative values, a posterior position.

Table 1
Minimum, maximum, mean, and standard deviation in millimetres of the measures evaluated for T0 (preoperative), T1 (2–4 month postoperative), and T2 (6–12 months postoperative) between the lower points and the true vertical line (TVL).
T0 T1 T2
Min/Max Mean ± SD Min/Max Mean ± SD Min/Max Mean ± SD
Nasal projection 10.5/23.3 16.5 ± 2.3 7.8/20.9 15.0 ± 2.3 8.9/21.5 15.2 ± 2.2
A′ −8.4/0.6 −2.3 ± 1.6 −7.4/2.3 −1.3 ± 1.6 −6.9/3.1 −1.2 ± 1.5
A −31.6/−12.9 −18.5 ± 3.2 −30.4/−12.8 −17.0 ± 3.1 −28.4/−12.8 −16.9 ± 2.9
Upper lip −4.4/8.2 1.6 ± 2.1 −1.3/9.2 2.8 ± 2.0 −0.7/9.7 3.0 ± 2.0
Upper incisor −23.7/−5.1 −12.8 ± 4.3 −21.9/−3.3 −11.0 ± 4.2 −20.7/−2.0 −10.9 ± 4.1
Lower lip −5.7/27.6 6.7 ± 5.1 −10.0/11.6 1.1 ± 4.0 −10.7/13.7 1.5 ± 4.2
Lower incisor −19.4/10.3 −7.2 ± 5.6 −28.0/−6.3 −14.9 ± 4.7 −24.2/−4.9 −14.3 ± 4.5
B′ −17.4/17.8 0.5 ± 6.4 −20.6/7.8 −5.8 ± 5.5 −21.5/7.3 −5.8 ± 5.4
B −30.3/3.5 −11.7 ± 6.8 −38.1/−7.1 −18.9 ± 6.2 −39.3/−8.2 −18.8 ± 6.2
Pog′ −16.3/19.7 4.5 ± 7.5 −18.3/9.4 −2.2 ± 6.6 −18.5/9.0 −2.0 ± 6.5
Pog −29.9/12.3 −7.9 ± 8.5 −31.9/−1.0 −15.6 ± 7.3 −31.8/−1.5 −15.3 ± 7.2
Min, minimum; Max, maximum; SD, standard deviation; A′, point A of soft tissue; A, point A of hard tissue; B′, point B of soft tissue; B, point B of hard tissue; Pog′, soft pogonion; Pog, hard pogonion.

Table 2 presents the range of movement and the mean and standard deviation between two periods for every point, for T1–T0, T2–T0, and T2–T1, and the results of the Student’s t -test for paired samples.

Table 2
Range, mean, and standard deviation in millimetres of changes that occurred during the movements between T1 and T0, T2 and T0, and T2 and T1 for lower points evaluated in relation to the true vertical line (TVL).
T1–T0 T2–T0 T2–T1
Range Mean ± SD Range Mean ± SD Range Mean ± SD
Nasal projection −4.2/0.4 −1.5 ± 0.9 c −4.7/0.3 −1.3 ± 0.8 c −2.0/1.2 0.2 ± 0.6 b
A′ 0.0/5.9 1.1 ± 0.8 c 0.0/6.0 1.1 ± 0.8 c −0.8/0.8 0.0 ± 0.4 NS
A 0.1/6.5 1.5 ± 1.0 c 0.1/6.1 1.6 ± 1.1 c −1.1/2.0 0.1 ± 0.7 NS
Upper lip −0.2/3.7 1.2 ± 0.7 c 0.0/3.7 1.4 ± 0.8 c −1.3/1.7 0.1 ± 0.6 NS
Upper incisor 0.2/4.1 1.8 ± 1.0 c 0.0/4.8 2.0 ± 1.0 c −1.6/3.0 0.2 ± 0.8 NS
Lower lip −16.9/−0.2 −5.6 ± 3.2 c −13.9/−0.3 −5.3 ± 3.0 c −1.7/3.0 0.4 ± 0.9 b
Lower incisor −20.5/−0.2 −7.7 ± 4.2 c −16.7/−0.2 −7.0 ± 3.9 c −1.2/3.8 0.6 ± 1.0 c
B′ −16.1/−0.4 −6.3 ± 3.9 c −15.1/−0.5 −6.3 ± 3.7 c −1.6/2.0 −0.0 ± 0.8 NS
B −18.1/−0.9 −7.2 ± 4.2 c −17.5/−0.5 −7.2 ± 4.0 c −1.7/2.0 0.1 ± 0.8 NS
Pog′ −15.7/−0.2 −6.7 ± 4.1 c −16.1/−0.3 −6.4 ± 4.0 c −1.3/3.1 0.2 ± 0.8 a
Pog −19.7/0.8 −7.7 ± 4.9 c −19.7/1.8 −7.4 ± 4.7 c −2.3/2.6 0.4 ± 0.9 b
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Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Soft and hard tissue changes in skeletal Class III patients treated with double-jaw orthognathic surgery—maxillary advancement and mandibular setback
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