Chronic temporomandibular disorders (TMDs) affect the masticatory muscles, the temporomandibular joints (TMJs), and associated structures. Except in cases of trauma, their etiology remains uncertain, debated, and multifactorial. Conservative therapies-including no active intervention-often alleviate symptoms; however, approximately 3% of the population develops persistent forms associated with substantial individual suffering and significant social and economic burden.

At the Unit of Occlusion and Prosthodontics of the University of Santiago de Compostela (USC), Physiologically Oriented Occlusal Equilibration (POOE) has been used for chronic painful TMDs since 1985. POOE aims to correct unilateral mastication patterns and to establish appropriate non-working side contacts in order to protect the temporomandibular joints from mechanical overload. Singh (Cochrane, 2024) emphasized that occlusal interventions should be evaluated with long-term follow-up of at least 3-5 years.

This is a single-blind study: the evaluator remains blinded to treatment allocation during outcome assessment. The aim of this observational study is to assess the long-term effectiveness of POOE treatments for chronic TMDs from 1985 to the present. Treatment effectiveness will be confirmed if the reduction in pain achieved with POOE is statistically significant and clinically meaningful (≥1.5/10 on a 0-10 visual analog scale) compared with sham therapy at ≥3 years post-intervention relative to baseline. Additionally, effectiveness will be supported if the proportion of individuals meeting criteria for chronic TMD ("affected") is lower in the POOE-treated group than in those receiving alternative therapies.

Chronic TMDs constitute a complex syndrome that is currently understood as comprising more than 30 distinct nosological entities. The underlying cause of their pathophysiology has not been fully elucidated. Consequently, treatments are typically empirical and applied simultaneously, including pharmacotherapy, counseling, physiotherapy, occlusal splints (perhaps the most widely used), physical modalities, and other minimally invasive procedures such as arthrocentesis or arthroscopy, extending even to total TMJ replacement. None of these interventions has demonstrated superior efficacy compared with placebo or no treatment. Globally, these patients often consult multiple specialists and undergo numerous treatment modalities, with an unpredictable prognosis.

Physiologically oriented occlusal equilibration (POOE) was shown to be more effective than placebo at 6 months post-treatment. The 2024 Cochrane review indicated that assessing the efficacy of occlusal therapies requires evaluation at least 3 to 5 years after treatment. The treatments performed at USC since 1985 for chronic TMDs represent a valuable source of long-term clinical experience that may clarify whether POOE remains effective many years after treatment (from 1985 to the present), rather than only at 6 months.

Scientific Objectives To evaluate the effect of occlusal adjustment on pain intensity in patients with chronic TMDs during long-term follow-up over several years.

To disseminate the findings-whether positive, negative, or inconclusive-in peer-reviewed scientific journals.

Methods This is an observational study, as no intervention will be applied to participants. It will be open-label or single-blind (outcome assessors will be blinded to the treatment previously received, but participants will not be). The study is cross-sectional, as it will be conducted at a single time point and in a single visit. The study will consist of diagnosing any current TMDs potentially affecting individuals who were previously treated at USC for chronic TMDs. All participating individuals are familiar with the diagnostic procedures, which include extra- and intraoral examination, dynamic recording of mandibular and condylar movements, and the tests recommended in the DC/TMD criteria.

If the participant provides authorization, clinically relevant information from their medical record regarding TMD history will be used to determine the degree of improvement or deterioration relative to the pretreatment baseline.

Inclusion Criteria:

• Previous occlusal equilibration for TMD pain at the University of Santiago.
• Be diagnosed with joint and/or muscle TMD pain according to DC/TMD.
• Be aged 18-85 years.
• Be completely dentate with normal or adequately restored occlusion (fixed crowns/bridges allowed).
• Report pretreatment significant TMD pain (VAS/NRS 4-9 on a 0-10 scale).
• Have actively sought treatment and been referred to the University/Hospital service.
• Have undergone ≥6 months of prior conservative therapy.

Exclusion Criteria:

• Psychosis, major depression, substance abuse, or cognitive impairment.
• Opioid (morphine-derivative) addiction.
• Ongoing litigation or disability claims related to chronic pain.
• Dental professional background.
• Orthodontic treatment within the last 2 years.
• Severe tooth mobility (grade 3).
• Other pain conditions indistinguishable from or more severe than TMD pain.
• Additionally, patients will be excluded if minimally invasive occlusal adjustment cannot achieve equilibration, defined by: 2 mm discrepancy between maximal intercuspation and centric occlusion, and/or 4 mm total interarch discrepancy (≥2 mm on one side) in defined premolar/molars reference points, measured intraorally using a Boley gauge.

All individuals previously treated with occlusal equilibration therapy at the University of Santiago de Compostela for chronic TMD pain who consent to undergo a follow-up diagnostic assessment will be eligible for inclusion. The subgroup that participated in the MAP clinical trial will be analyzed separately.