To the best of author’s knowledge, there are only few similar studies that have evaluated the effects of BTX-A injection on click severity and these studies were mostly limited to case series. (24). The present study was designed according to the promising preliminary results of Bakke et al.(8) and Emara et al. (7)
They reported successful use of BTX-A injection as a treatment for TMJ clicking, however these studies were case reports and case series. On the other hand, our study was designed as a randomized clinical trial and we compared the effects of BTX-A injection on TMD with normal saline.
Results showed that although BTX-A decreased the click severity in 3 months in compare to the placebo group, there was no significant difference in resolving click between the two groups. It was also seen that both BTX and normal saline injection had reduced the click sound in 1 month; but in month 3 there was a decrease in click severity only in BTX group (however not significant) which can possibly indicate the effectiveness of BTX in our study.
It is also notable that maximum opening and lateral and protrusive movements have been increased in BTX-A group, when comparing results in month 3 with baseline; however, the differences were not statistically significant (Table 2).
The difference between our results and other similar studies (7, 8) could be due to several reasons. First, those studies were case series and did not compare the result with placebo. It could also be due to different methods, amount (BTX dosage) and frequency of injections. These studies used intra oral route for access to lateral pterygoid muscle, but we used extra oral method based on Kai-Yuan Fu study (28). Volume of injection was also lower than other studies due to the probable risk of hemorrhage as a result of proximity to the maxillary artery and the pterygoid venous plexus. The other cause of this insignificant result might be unilateral injection. It should also be mentioned that as mean age of BTX-A group was 4 years younger than control group (Table 1); it can be expected that in control group, the problem diminishes as self-limit in comparison with BTX-A group. Above all, larger sample size can result in more specific results.
Based on the present study, pain severity (VAS) was reduced significantly after one week following the injection. The mean VAS in BTX group was lower than in the placebo group, but it was not significantly different. Normal saline may wash joint space and decrease inflammatory mediators and act as joint lavage. Similar to our results, kurtoglu (29) Emara and bakke (7, 8) reported that pain was decreased and psychological statues improved during the time. On the other hand, psychological effects might have an impact on our results (the so-called placebo effect). This might confirm that despite decreasing click sound during the first week, it returns after one month in the placebo group. Overall, patients were satisfied with the treatment, especially during the first month. It should also be noted that all patients had received medicine (NSAIDs and muscle relaxants) for two weeks before intervention, and were trained to follow approaches such as eating soft foods and chew bilaterally, using warm pack etc.; hence it can itself have a role in decreasing the symptoms in both groups.
In VON Lindern study 200U BTX was used for all masticatory muscle such as masseter, temporalis and lateral pterygoid for treatment of painful hyperactivity, parafunctions and hypermobility of jaw and result were satisfactory due to pain reduction (30). Muscles act as a team and relaxation in all of them results in noticeable decrease of pain. Also Karacalar (31) used BTX in both medial and lateral pterygoid muscle and good result have been obtained, use of this two muscle as a one unit might be better to release pain faster. Though, we aimed to paralysis only the lateral pterygoid because of its role in anterior disk displacement (click) due to its attachment to the disc.
Dosage of BTX for injection varied in different studies, which depends on muscle bulk and site of injection. For masticatory muscles (temporalis and masseter) the recommended amount of BTX for each muscle ranges from 40 to 60 U each at several injection points (29). Since the lateral pterygoid is a small muscle and located deeply and adjacent to several vital structures that may be affected by seepage, it requires a lower amount and the injection is made at a single point. In some studies (7, 8), 35 U was injected intraoral and other researcher had used 50 U in the lateral pterygoid, but this was accompanied by a higher percentage of side effects such as dysphagia (32). We selected 15 units BTX for injection in lateral pterygoid.
We implemented the extra oral approach like Fu KY and Ziegler CM in our study (12, 28) because the access for injection was more comfortable than intraoral injection. 15U was injected in the lateral pterygoid and patients were followed up as mentioned in the method section. Based on our result; it seems intraoral approach may have better results for paralysis of lateral pterygoid in treating clicking.
Similar to other studies, maximum jaw opening did not change (7, 8), but mean of lateral movement and protrusion increased gradually in BTX group. Lateral pterygoid relaxation is a cause that patients can move their jaw more comfortably without pain, although statistically was not different with the placebo group.
The initial diagnosis of click was obtained by clinical examination and complains of patients, and based on American Academy of Orofacial pain criteria. One of the benefits of present study, was the using of different measurements such as helkimo index, VAS and all of movement separately for better evaluation. Helkimo-index was measured before and after treatment and it was a positive point, previous researches did not measure it. This index was used to roll out the psychology effects. (hajian 2016) TMJ series radiography also was obtained and pathologic problems were excluded from the study.
In this study we had some limitation, it was better to evaluate disk position before and after treatment with MRI because it shows the disk position better and can detect it more properly. Electromyography is a useful devise that can be used with injection to assure that needle enters into muscle properly and not into space. In this study, like alveolar nerve block injection, we used anatomic points.