Effects of orofacial myofunctional therapy on masticatory function in individuals submitted to orthognathic surgery: a randomized trial

Abstract Objectives The esthetic and functional results of orthognathic surgery of severe dentofacial deformities are predictable, however there are differences regarding the effects on stomatognathic system. The aim was to investigate the effects of orofacial myofunctional therapy (OMT) on the masticatory function in individuals with dentofacial deformity submitted to orthognathic surgery (OGS). Material and Methods Forty-eight individuals (18-40 years) were evaluated, 14 undergoing OMT (treated group-TG), 10 without this treatment (untreated group-UTG) and 24 in a control group with normal occlusion; for clinical aspects the data of an individual was missed (n=46). Chewing was performed using the Expanded protocol of orofacial myofunctional evaluation with scores (OMES-E). Muscle tone and mobility were also analyzed before (P0), three (P1) and six months (P2) after OGS. Surface electromyography of the masseter and temporalis muscles was performed, considering the parameters amplitude and duration of act and cycle, and the number of masticatory cycles. The OMT consisted of ten therapeutic sessions along the postoperative period. The results were compared using parametric and non-parametric tests. Results TG showed higher scores in P1 and P2 than P0; for the masticatory type the scores in P2 were significantly higher than P0. In addition, the proportion of individuals with adequate tone of lower lip and adequate tongue mobility for TG increased significantly from P1 and P2 in relation to P0. The EMG results showed a decrease in act and cycle duration in P2 in relation to P0 and P1 for the TG; furthermore the values were close to controls. An increase in the number of cycles from P0 to P2 was also observed, indicating faster chewing, which may be attributed to an improvement of balanced occlusion associated with OMT. Conclusion There were positive effects of OMT on the clinical and electromyography aspects of chewing in individual submitted to orthognathic surgery.


Introduction
Individuals with severe dentofacial deformities (DFD) submitted to orthodontic treatment and orthognathic surgery (OGS) usually are seeking improvements in facial esthetics and function of the stomatognathic system; consequently, better occlusal relations can be achieved 4  Most studies about masticatory function in individuals with DFD submitted to orthodontic-surgical treatment showed that the EMG of masticatory muscles is lower compared to subjects with normal occlusion 16,27 . Moreover, changes in masticatory function or in its components after correction of DFD by OGS are evident. The period of time for occurrence of changes is controversial and may be related to differences in evaluation methods and treatment types 21 .
Regarding the duration of chewing, Ueki, et al. 26 (2009) found no changes in this characteristic after OGS in Class III malocclusion, and the same was found by Youssef, et al. 28 (1997)

in individuals with
Class II and III malocclusion. Conversely, a reduction was observed in the duration of muscle activity in the postoperative period compared to the preoperative in patients with Class III malocclusion 15 . It is relevant to consider the methodological differences between researches, since the knowledge about adaptation of this function with the correction of form still has limitations.
A recent research showed increasing trend of the total number of chewing cycles after 36 months of orthodontic-surgical treatment in patients with Class III malocclusion, determining improvement in the balance of the masticatory muscles after surgery 19 .
Nevertheless, the literature about orofacial myofunctional therapy (OMT) for patients submitted to OGS has been controversial, probably due to methodological differences 15,17,22 . Due to alterations of the orofacial structures in individuals with DFD after OGS, a new proprioceptive scheme must be acquired so the soft structures may satisfactorily perform their functions. Therefore, to complement clinical evaluation and to understand the functional changes in DFD, it is important to study the effect of OMT on the functional aspects of masticatory muscles before and after surgical correction of DFD, to elucidate the adaptation of these muscles after surgery.
In this context, the efficacy of OMT rehabilitation in a short time must be more precisely investigated to know if the functionality of the stomatognathic system and the possible relapses caused by inadequate maintenance of adaptive patterns could be recovered early 15 .
Thus, the aim of this study was to determine the effects of OMT on the clinical and electromyography aspects of masticatory function in individuals with DFD, After OGS, the experimental group was composed of 24 individuals allocated in two sub-groups, namely those who received OMT (Treated group -TG) and those without OMT (untreated group -UTG) ( Figure   1). The allocation was performed by randomization.
The numbers 1-24 were randomized on an Excel worksheet, and the first 14 numbers drawn were part of the TG and the last 10 of the UTG. In evaluations of clinical aspects, data of one individual of TG were missed between the second and third evaluations, who was excluded from the analysis. One individual with class II malocclusion was excluded from the clinical analyses due to the missed data, but included on the instrumental analyses.

Individuals with Class II and III malocclusion
were compared by the t test or Mann Whitney test for all variables according to data normality. Since no significant difference was found, the data were pooled.
TG and UTG were evaluated in three stages: before, one or two weeks before OGS; and post stages, three and six months after OGS. The OMT was applied in the postoperative period, 30 days after surgery, with 10 sessions, one per week. The control group was evaluated in a single period.

Clinical evaluation of chewing
The masticatory function was evaluated using OMES-E 8 , considering that the higher the score, the better the function. The study analyzed the incision, masticatory type, movements of the head or other body parts, altered head posture and food escape.
These assessments were recorded using a Coolpix Following the protocol, mastication was recorded with the individual sitting in a chair with a backrest, the feet resting on the floor at a standardized distance (1 m) from the camera lens, which was mounted on a tripod with focus on the face, neck and shoulders.
The individuals chewed one wafer biscuit and in their habitual manner.
The bite was evaluated during filming and the scores were attributed as following: 1=when the individual did not bite the food but broke it into pieces with his hands before bringing it to his mouth; 2=biting with the molars; 3=biting with the canines and the premolars; 4=biting with the incisors.    Dunnet test for numeric data. The Fisher's exact test was used to compare frequencies. A significance level of 5% was adopted.

Results
The values of the maximum score of OMES-E protocol 8 for TG and UTG in each evaluation period are shown in Table 1. Significant increase was observed in TG from P0 to P1 and P0 to P2. The respective differences were not observed in UTG. Both groups showed significantly lower total scores than their controls in all periods.
The score values for "bite" and "masticatory type" are in Table 2. No significance differences for "bite" were found between periods. For "masticatory type", TG scores in P2 were significantly higher than in P0.
In P0 and P1 the TG and UTG showed lower scores than the CG, whereas in P2 only TG showed lower scores than the CG.
The alterations of head movements and posture, as well as food escape, were recorded as present or absent (Table 2) (Table 3).  The results concerning duration of the masticatory act and cycle of each muscle are presented in      In the analysis of each item in OMES-E protocol in relation to the "masticatory type" before surgery, both sub-groups presented alteration in this aspect compared with the control. A clinical evaluation of masticatory function in individuals with DFD also found changes in the mastication type 17 . In the present study, six months after surgery, the TG showed significant increase in scores of mastication type, suggesting improvement in function, and these results were not observed in UTG. However, comparing the TG and UTG with their counterparts, after surgery, the scores of the TG were significantly lower than the CG; therefore, despite the improvement, the values did not approach the control. In relation to the item "bite", the scores for TG and UTG were similar to their controls at P0.    After surgery, more individuals of TG presented adequate lip mobility, but no differences were found between periods, perhaps due to the small number of subjects. TG presented higher number of individuals with adequate tongue mobility three and six months after surgery compared to the preoperative period, and after surgery only the UTG differed from the control.
Therefore, it could suggest that the OMT contributed to improve muscle mobility. To our knowledge, no studies could be found that describe this aspect in patients undergoing OGS, evidencing the importance of the findings and emphasizing that mobility should be evaluated and treated during OMT.
Regarding EMG of masticatory muscles, the data for muscle activity were analyzed in different periods and no significant difference was found after OGS. After three months TG presented significantly lower EMG values than CG for the right masseter and right temporalis. The UTG did not show similar differences. These findings can suggest that the OMT has little influence on EMG, probably due to the evaluation periods after surgery. Thus, the time needed to obtain improvement of EMG activity after orthognathic surgery can be considered a controversial issue. Some studies found no difference over a period The results confirmed the effect of treatment on the right masseter muscle. In this context, it can be observed that the side of masticatory preference of TG was predominantly the right side mainly in P0, which is in line with masticatory preference side in TG, since The experimental groups showed significantly longer cycle duration in RM and RT at P0 than CG. This probably occurred to compensate dental-occlusal and muscle disorders. According to Engelen, et al. 6