TMJ symptoms: A rare and useful long-term follow-up.

The association between malocclusion, orthodontic treatment, and TMJ dysfunction has been hotly debated. However, relatively recently, we have reached a near consensus that orthodontics is essentially ‘TMJ neutral’, neither causing nor curing TMJ dysfunction. With rare and obvious exceptions, this is the evidence-informed approach I have adopted over the years. But, of course, many remain unimpressed by the published evidence warning of complex links between malocclusion and TMJ dysfunction.

Notwithstanding this, there are shortcomings in the evidence base, with much of our knowledge limited to cross-sectional research, which fails to account for the longitudinal nature of TMJ dysfunction. Chronic conditions are known to ebb and flow and go through bouts of acute activity and periods of calm. TMJD is similar in this respect. Equally, the static and dynamic occlusion are subject to some change with growth. The means of assessing TMJ function are evolving but also largely subjective. Equally, a clear definition of TMJ dysfunction is often lacking, with a triad of symptoms including pain, click and limited opening required for a definitive diagnosis.

The authors aimed to evaluate whether malocclusions or orthodontic treatment are associated with TMD symptoms. This study was conducted in Finland and published in the Journal of Oral Rehabilitation.

What did they do?

They conducted a prospective follow-up of 200 patients who were all born in 1967 and were examined aged 7, 12, 15 and 32 years as follows:

Participants:

The sample consisted of 200 Finnish children (100 girls and 100 boys) born in Jyväskylä, Finland. The children were selected from seven different primary schools.

Clinical Assessment and Data Collection:

Clinical examinations were conducted four times over 25 years. These included an assessment of the occlusion with a recording of an overjet overbite, crossbite and PAR score. An evaluation of TMJ function, including joint noises, maximum opening, lateral and anterior excursive movements, and related contacts, was also performed. Two experienced orthodontists performed all clinical examinations. Alginate impressions for study models were taken at every time point, and orthopantomograms were obtained as required. Subjects also completed a questionnaire based on the Helkimo index exploring TMJ symptoms, including headache, jaw pain, clicking, and stiffness.

What did they find?

Given the long-term nature of the study, it was unsurprising that the sample was lower at the 25-year follow-up, with 135 participants included at that stage. Fifty-seven subjects (29%) had received orthodontic treatment, with seven having extractions for orthodontic reasons. Overjet and overbite were generally within normal limits reducing slightly over the evaluation period. The prevalence of crossbite was approx. 15% throughout. Most crossbites did not have associated displacement.

Subjective symptoms of TMJD were relatively common, with 43% and 24% reporting clicking and pain, respectively, by 32 years. Pain during mouth opening increased from 3% to 5% from 12 to 32 years. A correlation was found between an increase in PAR score from 12 -15 years and TMJD symptoms. The authors undertook a logistic regression analysis to evaluate the effect of gender, orthodontic treatment, and occlusal features on headache, pain, and TMJ sounds at long-term follow-up.

Females were associated with a higher prevalence of headaches (Odds ratio: 2.4), although gender did not seem to have a specific effect on TMJ symptoms or sounds. Orthodontic treatment had no bearing on headache, TMJ symptoms or sounds. Any crossbite at 12, 15 or 32 years of age, whether treated or untreated, was associated with TMJ sounds at 32 years of age (Odds Ratio: 3.5). However, there was no corresponding effect on the prevalence of either pain or headache.

What did I think?

I think that this was an interesting study. I was impressed that the authors could evaluate the study participants over such a lengthy period. As the authors correctly highlight, much of our knowledge of TMJ symptoms is based on cross-sectional studies only. Given the meandering nature of the condition, a longitudinal assessment is very useful.

I found the results of value but also perhaps a little contradictory in places. My ‘take home’ is that TMJD is common and largely unaffected by occlusion or orthodontics. The association between crossbites (untreated or treated) and TMJ sounds might muddy the waters slightly. However, it is important to note that an isolated click is common and is generally innocent. Importantly, no association between the presence of a crossbite and either TMJ pain or, indeed, headache was observed.

An ongoing issue with the evaluation of TMJD is the subjective nature of the assessment. Furthermore, the questionnaire used in the present study included responses such as ‘sometimes’. When questioned, many of us may admit to experiencing headaches or pain on chewing ‘sometimes’. I wonder whether we may therefore risk overestimating the prevalence of these issues. The authors note that updated tools based on expert consensus have been developed. It would be useful to apply this in similar studies moving forward.

What can we conclude?

TMJ symptoms, including noises and pain, are relatively common and are more prevalent in the fourth decade than in adolescence. However, no consistent association between the occlusion or orthodontic treatment and TMD symptoms seems to be observed. On this basis, I will continue to be reticent in linking orthodontics to beneficial or adverse effects on the TMJ.