I-PRF and TMJ disorders: do oral behaviours influence healing?

The treatment of temporomandibular joint (TMJ) disorders by intra-articular injections of injectable platelet-rich fibrin (I-PRF) is gaining traction. However, a question remains for the practitioner: why do some patients respond better than others? This secondary exploratory analysis (NCT05883982), conducted on a cohort of 51 adult patients, addresses this variability by examining the impact of initial oral behaviours on the residual severity of the pathology.

The specific objective of the study was to evaluate whether the habits recorded via the Oral Behaviors Checklist (OBC-21) — such as awake bruxism or singing — are correlated with the Helkimo Index (HI) score, measured on a scale of 0 to 25, during post-therapeutic follow-up. The authors test the hypothesis that these parafunctional behaviours could be associated with the final severity of the disease, after adjusting for the baseline HI score. Beyond the simple mechanical load, these behaviours are explored here as potential indicators of the clinical complexity and biopsychosocial burden of the patient treated with I-PRF.

Methodology: Analysis of a cohort treated with I-PRF

This study is a secondary exploratory cohort analysis conducted as part of a registered clinical trial (NCT05883982). It aimed to assess the predictive factors of the severity of temporomandibular joint (TMJ) disorders after treatment.

• Population: 51 consecutive adult patients presenting with TMJ disorders of articular origin, treated at the Department of Oral and Maxillofacial Surgery in Kielce.
• Therapeutic protocol: Each patient received an intra-articular injection therapy of injectable platelet-rich fibrin (I-PRF), an autologous product derived from centrifuged venous blood.
• Assessment tools:
  • The severity of the pathology was measured via the Helkimo Index (HI), on a scale of 0 to 25, at the beginning (baseline) and at the final follow-up.
  • Oral behaviours were documented using the Oral Behaviors Checklist (OBC-21), including 21 items (awake/sleep bruxism, teeth clenching, unilateral chewing, etc.).
• Statistical analyses: Linear regression models adjusted for the initial HI score were used. The analyses included symptom duration and injection laterality as covariates. To account for multiple testing, a False Discovery Rate (FDR) correction was applied to the p-values.

Evolution of the severity of the pathology (Helkimo Index)

The analysis of this cohort of 51 adult patients shows a significant reduction in the severity of temporomandibular joint (TMJ) disorders following intra-articular I-PRF treatment. The mean Helkimo index (HI) score decreased from 7.0 (SD 6.2) at baseline to 2.5 (SD 3.0) at the final follow-up (p < 0.001).

The adjusted linear regression analysis reveals that the initial HI score is the most robust predictor of severity at follow-up (β = 0.32; 95% CI 0.22 to 0.41; p < 0.001). In contrast, symptom duration (p = 0.70) and injection laterality (p = 0.52) showed no significant association with the final clinical outcomes.

Analysis of oral behaviours (OBC-21)

The central objective of this study was to assess whether baseline oral behaviours (measured by the OBC-21) influenced the response to treatment. After correction for multiple comparisons (FDR), none of the 21 items of the OBC-21 showed a clear statistical association with the follow-up HI score.

Although not significant after rigorous statistical correction, the highest coefficients were observed for awake bruxism (trend towards increased severity at follow-up) and singing (inverse trend). These results suggest that oral behaviours, taken in isolation, are not determining factors of post-therapeutic severity following an I-PRF injection in this cohort.

Observations on the structure of the pathology

The authors note that the residual variability in disease severity could be related to dimensions not captured by the total HI score, such as:

• The structural stage of joint pathology ;
• Pain intensity and psychosocial burden ;
• Other unmeasured clinical severity characteristics.

Clinical interpretation of results

The major finding of this secondary analysis is the observed clinical efficacy of intra-articular I-PRF: the mean Helkimo index (HI) dropped from 7.0 to 2.5 at the final follow-up (p < 0.001). However, the initial severity of the pathology (baseline HI) remains the most robust predictor of the post-therapeutic clinical status (β = 0.32, p < 0.001). Contrary to classical mechanistic hypotheses, baseline oral behaviours (bruxism, clenching, etc.) did not show a statistically significant association with the follow-up score after adjustment. This suggests that I-PRF can be beneficial even in patients presenting with marked parafunctions, as the latter did not hinder the overall reduction in disease severity in this cohort.

Limitations and perspectives

The study presents intrinsic limitations linked to its exploratory design and its sample of 51 patients. Although trends were observed for awake bruxism (β = 0.80) and singing (β = -0.58), they lose their statistical significance after correction for multiple comparisons (FDR-adjusted p > 0.05). Furthermore, unmeasured factors such as the structural stage of the joint or psychosocial burden could influence the results. These data add nuance to the conventional literature that closely links oral behaviours to the persistence of symptoms, suggesting that in the specific context of I-PRF injection therapy, the biological response could take precedence over the behavioural mechanical load.

Implications for practice

For the practitioner, these results indicate that the duration of symptoms or the laterality of the injection are not barriers to the efficacy of I-PRF. The therapeutic decision must not be exclusively conditioned by the presence of specific oral behaviours listed in the OBC-21, as they do not appear to dictate the relative success of the intervention. Emphasis must remain on the initial assessment of dysfunctional severity via the Helkimo index to estimate the post-operative prognosis.

• I-PRF injection shows a significant reduction in the severity of TMJ disorders (decreasing from an HI score of 7.0 to 2.5 on average).
• Relying solely on the presence of bruxism or other oral habits to predict I-PRF failure is not justified by these data.
• The best indicator of the patient's final condition remains their initial severity score: the more severe the condition at baseline, the higher the follow-up score is likely to be despite improvement.

Study summary

This cohort analysis of 51 patients demonstrates a significant reduction in the severity of TMJ disorders following intra-articular injections of I-PRF, with the Helkimo index (HI) dropping from 7.0 to 2.5 (p < 0.001). The main predictor of the final outcome is the initial severity (β = 0.32, p < 0.001), whereas oral behaviours (bruxism, lifestyle habits) assessed by the OBC-21 showed no strong statistical association with the follow-up outcomes after adjustment.

In practical terms, for the practitioner:

• Expand your I-PRF indications: The presence of parafunctions or specific oral behaviours does not appear to limit treatment efficacy; do not consider them as systematic failure factors.
• Ensure a reliable prognosis via the Helkimo score: The more severe the initial impairment, the more likely the final score is to remain high. It is the most robust indicator for managing your patients' expectations.
• Integrate the structural and psychosocial dimensions: Although behavioural habits do not directly influence the post-injection Helkimo score, the assessment of the disease stage and psychological burden remains necessary to refine the overall therapeutic strategy.

Technical Glossary of the Study

I-PRF (Injectable Platelet-Rich Fibrin): Autologous blood product obtained by centrifugation of venous blood, consisting of a liquid fraction rich in platelets and fibrin, used to support intra-articular tissue repair and regeneration processes.

Helkimo Index (HI): Composite clinical measure (scale of 0 to 25) quantifying the severity of temporomandibular joint (TMJ) dysfunction across several domains of symptoms and functional limitations.

OBC-21 (Oral Behaviors Checklist): Self-assessment instrument comprising 21 items that measure the frequency of various oral behaviours, including sleep and daytime habits (parafunctions).

Awake bruxism: Specific oral behaviour (item B3 of the OBC-21) characterised by the clenching or grinding of teeth during the day, studied as a potential factor influencing residual severity after treatment.

Internal derangement: Category of TMJ disorders involving an alteration of the structural relationships between the articular components, considered in the study as one of the initial stages of degenerative joint disease.

Baseline-adjusted analysis: Linear regression model including the initial score (Helkimo Index at T0) as a covariate, allowing the assessment of the association between baseline predictors and the final clinical status independently of the initial severity.

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