In a recent study, an Oral and Maxillofacial Surgery (OMFS) research team at the Faculty of Dentistry of the University of Hong Kong (HKU) revealed that jaw asymmetry is likely to be a causative factor of jaw joint pain, and that surgical correction of facial asymmetry is effective in improving or even curing patients suffering from jaw joint pain.

The research team led by Clinical Associate Professor in OMFS Dr Mike YY Leung, with Dr Aileen Toh as co-investigator, has published the findings in an article titled “Mandibular asymmetry as a possible etiopathologic factor in temporomandibular disorder: a prospective cohort of 134 patients” in academic journal Clinical Oral Investigations.

Facial asymmetry can be a result of the difference in jaws’ growth rate or caused by trauma. Patients with facial asymmetry will see a difference in the length of the left and right side of the jaws, which result in a deviated face as well as a shifted bite. The asymmetric face not only affects the facial appearance of the individual, but also hinders the eating or speech function and lowers the patient’s self-esteem.

Jaw correction surgery, or orthognathic surgery, is the surgical treatment for patients with dentofacial deformities including facial asymmetry. In the surgery, the deformed jaws are surgically corrected in a planned and normalized position so as to improve the patient’s masticatory and speech function, as well as symmetry and facial profile. It is a routine procedure performed by OMFS surgeons and will usually take three to six weeks to recover.

In the study, Dr Leung’s team investigated the prevalence of TMDs in 134 patients. Among them, 82 were with facial asymmetry while 52 with other facial deformities without asymmetry.

It was found that the prevalence of TMD in patients with facial asymmetry was 67.1%, which was significantly higher than those without (40.4%). Of these patients with facial asymmetry, 78.2% are presented with temporomandibular joint (the joint which connects the lower jaw to the skull) (TMJ) disc displacement with reduction, 34.5% have myalgia (muscle pain), and 20% have arthralgia (joint pain) (Note 1). The study shows that patients with dentofacial deformity, in particular facial asymmetry, are much more likely to suffer from TMD than individuals without such deformity.

Since the result suggests TMD could be caused by facial asymmetry, the research team further investigated the effect of orthognathic surgery to correct facial asymmetry and the prevalence of TMD.It was found that the prevalence of TMD in patients with facial asymmetry who underwent jaw correction surgery has reduced by 58.3% at 6 months after the surgery. The finding indicates that surgical correction of facial asymmetry is effective in improving or even curing TMD in these patients.

“We believe patients with facial asymmetry have an imbalanced force to the jaw joints and the masticatory muscles. This may induce chronic trauma to the TMJ and the musculature system in the long-term, which explained the high prevalence of TMD-related symptoms including pain and limited mouth opening in this group.” Dr Aileen Toh said.

“The surgical correction of facial asymmetry allows a normalised masticatory function and a corrected bite, and now we prove it also helps in treating TMDs. Many people misunderstood orthognathic surgery is for aesthetic reasons, in fact the correction of a facial deformity improves the sufferer’s function as well as reduces pain symptoms as a consequence of TMDs.” Dr Mike Leung added.

The research team will further look into the long-term effect of the surgical treatment on TMD and if any relapse will occur.

Note 1: Patients may have more than one symptoms
Journal: Clinical Oral Investigations 2021 July; 25, pages4445–4450.Mandibular asymmetry as a possible etiopathologic factor in temporomandibular disorder: a prospective cohort of 134 patients. Aileen Qiu Jin Toh, Joshua Lue Hang Chan, Yiu Yan Leung.

(Link: https://link.springer.com/article/10.1007%2Fs00784-020-03756-w)

 

For media enquiries:
Ms Melody Tang, Senior Communications Officer of the Faculty of Dentistry, HKU
Tel: 2859 0494
Email: melodytang@hku.hk

For the online press release and photos, please visit: http://www.hku.hk/press/news_detail_23583.html

 

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研究由口腔頜面外科臨床副教授梁耀殷醫生帶領，卓秋槿醫生為共同研究員，結果已於Clinical Oral Investigations期刊一篇名為「下頜不對稱可能是顳顎關節症的病理學因素：134名患者的前瞻性群組研究」的文章發表。

牙骹病患者在進食、說話或張嘴時，他們的顎骨肌肉和關節會感到不適甚至疼痛。全球牙骹病的整體患病率約為5% 至12%。長期慢性疼痛包括牙骹病已知與抑鬱症和情緒病有關。

面部不對稱可能是顎骨生長速率差異的後果，也可能由創傷造成。面部不對稱的患者顎骨左右兩側的長度有差異，導致面部偏歪和咬合不正，影響個人的面部外觀，亦妨礙飲食或言語功能，也會影響患者的自信心。

顎骨矯正手術，或正顎手術，是針對面部畸形，包括面部不對稱的矯型治療手術，屬口腔頜面外科醫生的常規手術，把畸形的顎骨調整至合適的位置，從而改善患者的咀嚼和說話功能，以及重塑面部對稱性和輪廓，術後病人需約三至六周的時間復元。

梁耀殷醫生領導的團隊研究了134名面部畸形患者的牙骹病患病率，當中82人屬面部不對稱，其餘52人有其他面部畸形情況。

研究發現，在面部不對稱患者中，牙骹病的患病率為67.1%，明顯高於沒有面部不對稱的患者（發病率40.4%）。面部不對稱的牙骹病者，有78.2%出現顳下頜關節盤移位，有34.5%表示有肌肉痛，20%表示有關節痛（注一）。研究結果表明，面部畸形患者（尤其是面部不對稱患者）比正常人更容易患有牙骹病。

由於結果顯示牙骹病可能是由面部不對稱引起，團隊於是進一步研究，利用正顎手術矯正患者的面部不對稱，對改善牙骹病的成效。結果發現，接受過正顎手術的面部不對稱患者，牙骹病的患病率在手術後六個月內下降了58.3%，證明正顎手術有助治療面部不均的牙骹病者。

卓秋槿醫生指出：「面部不對稱的患者，他們的下顎關節和咀嚼肌肉承受著不對等的壓力，長遠會對顳下頜關節和肌肉造成慢性創傷，這解釋了研究群組中，出現很多牙骹病包括疼痛和有限的張口度等相關症狀。」

「面部不對稱的矯正手術能改善咀嚼功能和咬合，現在我們證明它也有助於治療顳顎關節症。許多人誤解面部矯形手術是出於美學原因，事實上矯正面部畸形能改善患者的口腔功能，並減輕了顳顎關節症帶來的疼痛症狀。」梁耀殷醫生進一步闡述。

研究小組將進一步研究手術治療對顳顎關節症的長期影響，以及會否復發的問題。

期刊文章: Clinical Oral Investigations 2021 July; 25, pages4445–4450.Mandibular asymmetry as a possible etiopathologic factor in temporomandibular disorder: a prospective cohort of 134 patients. Aileen Qiu Jin Toh, Joshua Lue Hang Chan, Yiu Yan Leung.

(連結: https://link.springer.com/article/10.1007%2Fs00784-020-03756-w)

 

傳媒查詢：
香港大學牙醫學院
高級傳訊主任鄧慧中(Melody Tang)
電話︰2859 0494 / 電郵：melodytang@hku.hk

新聞稿網上版及照片，請瀏覽: http://www.hku.hk/press/news_detail_23583.html

 

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