Beware of Unsupported Conclusions About Occlusal Adjustments

Scientific progress depends not only on publishing research but also on critically evaluating whether the conclusions drawn are justified by the methods used. A recent exchange published in the Journal of Prosthetic Dentistry provides an excellent example of how an interesting clinical observation can generate conclusions that extend beyond what the study design can reliably demonstrate.

• Ohrbach R, Sharma S, Romero M, Almarza A, Cioffi I, Neubert JK, Drangsholt M. Letter to the Editor regarding, "A prospective single arm study of salivary cortisol changes in muscular temporomandibular disorders patients following computer-guided occlusal adjustments". J Prosthet Dent. 2026 Jun 29:S0022-3913(26)00385-9. doi: 10.1016/j.prosdent.2026.04.041.

  
  

• Goud SS, Thumathi P, Poovani SK, Radke J, Kerstein RB. A prospective single arm study of salivary cortisol changes in muscular temporomandibular disorders patients following computer-guided occlusal adjustments. J Prosthet Dent. 2026;136(1):187-195. doi: 10.1016/j.prosdent.2026.02.031.

  
  

What is occlusion?

Occlusion refers simply to the way the upper and lower teeth come together when we bite, chew, or move the jaw. For more than a century dentists have debated whether abnormalities in occlusion contribute to temporomandibular disorders (TMD).

What is an occlusal adjustment?

An occlusal adjustment is a permanent dental procedure in which tiny amounts of enamel are carefully reshaped so that the teeth contact differently during biting and jaw movements. The treatment evaluated in the published study used computerized sensors to identify where teeth touched during side-to-side movements, after which selected contacts were adjusted with the aim of reducing prolonged tooth contact.

The controversy

Some clinicians believe that modifying occlusion can relieve muscular TMD, whereas contemporary evidence generally considers TMD to be multifactorial, involving biological, psychological and social mechanisms. Because permanent occlusal adjustment is irreversible, studies evaluating this treatment require particularly rigorous methodology.

What did the published study do?

The investigators recruited 30 patients diagnosed with muscular TMD. In this research, salivary cortisol (a substance that increases with stress) was measured before treatment and one month after computer-guided occlusal adjustment. The authors also measured disclusion time (the time needed for the upper teeth to seperate when go from side to side) and jaw muscle activity. They observed lower cortisol levels, shorter disclusion times and altered electromyographic activity after treatment.

What conclusions were drawn?

The investigators concluded that modifying the occlusion reduced stress and that prolonged occlusal contacts were responsible for elevated cortisol production. These changes were considered causal because they attribute the observed changes directly to the treatment.

Observation versus causation

One of the most important concepts in clinical research is that observing a change after treatment does not prove that the treatment caused the change. If a patient's symptoms improve after any intervention, several explanations are possible: the treatment worked, the condition improved naturally, symptoms fluctuated over time, placebo effects occurred, or unrelated factors changed.

The Letter to the Editor

A group of internationally recognised researchers in TMD and orofacial pain published a Letter to the Editor arguing that the study should be interpreted with caution because its methodology could not support the strong causal conclusions. The principal concern was that the investigation used a single-arm before-and-after design. Every participant received treatment and there was no randomised comparison group. Therefore, it is impossible to determine whether improvement resulted from the occlusal adjustment itself or from other explanations.

Are there any alternative explanations for this finding?

Natural history: painful TMD frequently improves over time.

Regression to the mean: patients often seek treatment when symptoms are at their worst and subsequently improve regardless of intervention.

Placebo and contextual effects: lengthy clinical procedures often produce substantial non-specific improvements.

Confounding variables: medication use, sleep, stress, diet and other behaviors not measured in this study may all influence outcomes.

Is cortisol the same as stress?

The Letter also argued that psychological stress was never directly measured. Instead, the investigators measured salivary cortisol. Although cortisol is an accepted biological marker, it is influenced by numerous physiological factors and usually requires repeated sampling over several days to characterize reliably.

Diagnostic concerns

The Letter further questioned the diagnostic classification used, noting that internationally accepted DC/TMD criteria were not used and that the term 'occlusomuscular TMD' used by the authors is not part of established scientific nomenclature. WIthout a validated diagnostic system, establishing a diagnosis may be challenging and not reliable.

The authors' response

The original authors responded by defending their conclusions. They argued that previous publications support their treatment approach, that every participant experienced a reduction in cortisol, and that randomised controlled trials should not be viewed as the only valid source of evidence.

What can clinicians learn?

The value of this exchange demonstrates how science progresses. Interesting observations generate hypotheses, other researchers challenge the interpretation, and additional studies are performed. Clinicians should therefore separate the observations reported by a study from the conclusions drawn by its authors.

Practical tips for reading clinical research

·         Separate observations from interpretations.

·         Ask whether the study design can establish causation.

·         Look for randomization and appropriate control groups.

·         Consider alternative explanations before accepting causal claims.

·         Interpret a study within the context of the broader body of evidence rather than in isolation.

Take-home message

This debate is ultimately about critical appraisal rather than occlusion itself. The published study reported interesting findings, while the Letter to the Editor questioned whether the methodology justified the conclusions.

Together, these papers remind us that evidence-based dentistry requires more than reading results. It requires evaluating whether the strength of the conclusions matches the strength of the methods. In this case, the methods used present significant weaknesses that do not support the authors' conclusion.