As we progress through the TMJ Series—having examined dislocation cases, muscle dysfunction, occlusal instability, bruxism, and splint therapy—we now reach a critical junction in understanding the masticatory system: how do we evaluate structural occlusion after symptomatic stabilization? In Part 6, we discussed what happens after splint therapy and identified signs that indicate a patient is ready for functional reevaluation.
This brings us naturally to Part 7, where we address one of the most nuanced diagnostic puzzles in occlusion: Why do centric relation (CR) and centric occlusion (CO) often fail to align, even after muscle relaxation and joint decompression?
When patients complete TMJ splint therapy and show signs of stabilization, the next clinical dilemma often emerges: What if centric relation (CR) and centric occlusion (CO) still don’t match? This post—Part 7 in our TMJ Series—dives into the biomechanical, neurological, and clinical reasons why CR and CO may remain divergent, and what that means for long-term occlusal health.
What Are CR and CO? A Quick Recap
Centric Relation (CR) is a maxillomandibular relationship where the condyles are in their most anterior-superior position against the articular eminence, independent of tooth contact. It is a repeatable, joint-based position.
Centric Occlusion (CO) is the position of the mandible when the teeth are in maximum intercuspation—essentially, where the patient bites down naturally. This is a tooth-guided position and may not align with CR.
In a healthy system, CR and CO ideally coincide. But for many patients, particularly those recovering from TMJ dysfunction or bruxism, there is a measurable CR-CO discrepancy.
Why Don’t CR and CO Always Align?
There are several contributing factors:
- Neuromuscular compensation: Patients with chronic dysfunction often adapt their mandibular posture to avoid pain or clicking, resulting in habitual CO that veers away from CR.
- Occlusal interference: Premature contacts or dental asymmetries can deflect the mandible during closure.
- Muscular imbalance: Hyperactivity or weakness in specific muscle groups (like the lateral pterygoid) shifts mandibular pathing.
- Condylar displacement or remodeling: Long-term joint dysfunction may alter the condylar shape or position, changing the natural CR.
Clinical Signs of CR-CO Discrepancy
Clinicians should be alert to these indicators post-splint:
- Slide from CR to CO >2mm
- Asymmetrical wear patterns
- Repeatable contact only in CO, not CR
- Shifting centric stops after muscle fatigue tests
- Inconsistent bite registrations on wax or silicone
These signs suggest that the system has adapted around a structural fault, not resolved it.
CR-CO Discrepancy and Occlusal Instability
A persistent CR-CO discrepancy can have long-term consequences:
- Accelerated wear on guiding cusps
- Mandibular postural fatigue
- Periodontal stress from non-axial loading
- Muscle pain due to chronic compensation
- Increased risk of relapse in orthodontic or prosthodontic cases
Therefore, post-TMJ splint therapy is a key diagnostic window. The discrepancy becomes unmasked once muscle hyperactivity subsides and the patient bites in a “truer” pattern.
Diagnostic Tools to Evaluate CR-CO
- Leaf gauge or Lucia jig: Deprogram the muscles and recapture CR.
- Articulated diagnostic casts: CR-mounted models show occlusal relationships in a joint-based reference.
- Joint Vibration Analysis or MRI: Evaluate condylar positioning or disk status.
- T-Scan or pressure mapping: Analyze real-time occlusal force distribution.
Each tool adds insight into whether CR-CO discrepancy is muscular, dental, or skeletal in origin.
Case Snapshot: Post-Splint CR-CO Shift
A 43-year-old male completed 12 weeks of splint therapy for anterior disc displacement without reduction. Joint clicking resolved, and ROM normalized. Upon CR mounting, a 2.5mm slide to the right was observed during closure. The habitual CO contact was on tooth #16, while CR centric stop was evenly shared.
This shift is clinically significant because it reveals the true mandibular rest position after muscular deprogramming—often exposing hidden disharmonies masked by parafunctional adaptation. Recognizing and correcting this shift can prevent premature wear, periodontal overload, and further dysfunction.
The final treatment plan included occlusal adjustment and fabrication of an anterior deprogrammer to guide mandibular stability.
Clinical Decisions: When to Adjust vs. Accept
A mild discrepancy (<1mm) may be physiologically tolerable. However, larger discrepancies—especially those causing muscular or periodontal symptoms—often require intervention:
- Selective grinding
- Occlusal equilibration
- Full-mouth rehabilitation (in complex cases)
- Orthodontic or orthognathic coordination
Always balance the treatment plan against the patient’s functional demands and adaptive capacity.
Internal & External Links
Previous posts in the TMJ Series:
- 1: TMJ Dislocation Case Study
- 2: Muscle Dysfunction Overview
- 5: TMJ Splint Therapy
- 6: Post-Splint Evaluation
Further Reading:
Stay with us in the TMJ Series as we explore occlusal rehab protocols based on CR mounting, parafunctional risk mapping, and interdisciplinary coordination.
