Due to good orthodontic primary care there is only limited number of patients referred for SARME, so our sample is limited, but with some caution the results are significant and led us to some conclusions. 3D imaging with stereometric surface scanners is a frequently used method for a facial soft-tissue evaluation in orthognathic surgery with an already-proven high level of accuracy and reliability (15). The linear-regression model did not manage to obtain any significant results, probably because of the relatively small variance in the maxillary expansion width, and, especially, because of the smaller sample.
The anthropometric analysis of the pre- and post-expansion 3D facial scans demonstrated a statistically significant widening of the nose after expansion at the level of the nasal ala (+ 1.1 mm) and the nasal base (+ 2.2 mm). The consequence of a wider nasal base was a statistically significant increase in the nasal width angle (AcR-Prn-AcL). The width of the mouth remained almost unchanged. It is primarily determined by the orbicularis oris muscle, which lacks the direct origin or insertion with a bony jaw. This could be the reason why the SARME do not seem to have a significant influence on the width of the mouth.
The vertical dimension demonstrated two significant changes. The upper-face-height parameter significantly decreased, indicating the sub-nasale landmark, and the surrounding tissues moved in the superior direction (towards the glabella landmark), while the lower-face height remained unchanged. This superior positioning of the sub-nasale is probably one of the consequences of the complex effect SARME has on the nose morphology, including widening. Conflicting findings were reported by Lagravere and colleagues (16), who concluded that vertical and sagittal skeletal changes following SARME or not clinically significant. The lower-face height remained unchanged, which suggests that no mandibular rotation occurs. In a study by Tong and colleagues (17) a displacement of the chin (pogonion) in a posterior and inferior direction was demonstrated, suggesting the clockwise rotation of the mandible. Also, Oliveira and colleagues (18) reported in their study using CBCT (cone beam computer tomography) scans that a clockwise rotation of the mandible is a transient effect immediately after SARME, but tends to return close to the initial values 6 months after expansion. Secondly, the vertical philtrum height significantly increased, as a result of superior positioning of the sub-nasale area. Contradictory findings were reported by Alves and colleagues (19), who concluded that nasal length and projection and upper-lip length (philtrum height in our study) were not altered by SARME.
A significant increase in the soft-tissue facial profile angle also demonstrates changes in the sagittal direction after SARME. Since the expansion occurs in the middle third of the face, it is clear that anterior repositioning of the sub-nasale landmark occurs. The analysis indeed demonstrated anterior positioning of this area (3C, upper lip area). The facial profile after SARME has, therefore, increased convexity. This is important to consider in treatment planning since some MTD patients also exhibit simultaneous sagittal dento-facial deformity, such as skeletal Class II or III (1). These findings suggest that SARME tends to improve the skeletal Class III malocclusion and worsen the skeletal Class II. Our results contradict the results of Nada and colleagues (10), who found slight retro-positioning of the central part of the upper lip in both groups. Even though our method of 3D facial surface imaging cannot assess bone movements directly, we can still presume that some degree of maxillary advancement occurs following SARME in our patients. This difference could be attributed to the surgical technique, since the posterior part of the lateral nasal wall remained intact in our subjects. Therefore, the forces of the trans-palatinal distractor, besides the transversal expansion, probably move the maxilla slightly anteriorly. Another important sagittal effect that we encountered was a significant increase in the nasolabial angle.
Regional analysis (Fig. 3) showed the small changes after SARME over the whole face. They are the largest immediately over the expanded areas, but also occur in the lower third of the face, below the lower jaw and in posterior parts of the face. It seems that widening of the soft tissues over expanded areas consequently narrows the posterior and lower parts of the face. We observed that the facial soft-tissue mask acts as one unit, as already reported in other orthognathic procedures (20).
Our study objectively evaluates facial changes following SARME in all three dimensions. However, not only do some of our results differ from those of other studies, but the methodology and 3D observation of the whole face also seem to be different. We have confirmed some of the already-known facts, such as widening of the nose and increased projection in the cheek. On the other hand, an increased facial convexity after expansion is a new finding, reflecting the underlying advancement of the maxilla. Furthermore, we observed a reduced upper-face height, while the lower height remained unaffected.
LIST OF ABBREVIATIONS
3D - three-dimensional
SARME - surgically assisted rapid maxillary expansion
MTD - maxillary transverse deficiency
CBCT - cone beam computer tomography