Cr co normal value in orthodontics
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CR CO discrepancy normal value orthodontics centric relation centric occlusion
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The library doesn't have a dedicated orthodontics textbook on this topic. The web search results from the peer-reviewed literature give very solid data. Here is a comprehensive answer:
CR-CO Discrepancy: Normal Values in Orthodontics
CR (Centric Relation) is the musculoskeletally stable position of the condyles (forward, upward, centered in the fossa with the disc properly interposed). CO (Centric Occlusion / Maximum Intercuspation / MIP) is the tooth-determined position of maximum bite closure. Almost all patients with natural dentitions have some discrepancy between the two.
Accepted/Normal Values
| Plane | Accepted Value | Considered Significant |
|---|---|---|
| Vertical | ~1.0-1.5 mm | >2 mm |
| Horizontal (AP) | ~0.75-1.25 mm | >2 mm |
| Transverse (lateral) | 0-0.5 mm | Any >0.5 mm |
| Overall slide | Up to 2 mm | >2 mm |
Key reference values from the literature:
- Posselt (classic study): AP distance from retruded contact position to ICP averages 1.25 mm (±1.00 mm) in adults and 0.85 mm (±0.6 mm) in children
- A 2023 JCDR review states: vertical = 1.5 mm, horizontal = 1.5 mm, and transverse = 0.5 mm are acceptable thresholds that do not cause significant pathology
- CR-CO discrepancy >2 mm strains disc ligaments and raises the risk of intracapsular TMJ disorders
Direction of Condylar Displacement (CR to CO)
The condyle moves most commonly:
- Posterior-inferior (~60-70% of subjects) - this is the most common direction
- Anterior-inferior (~11-25%)
- Purely inferior (~2-8%)
The vertical component is larger than the horizontal in most subjects.
Clinical Significance in Orthodontics
- Treatment planning: Cases with >2 mm CR-CO slide can show a different skeletal pattern on CR-mounted study models vs. CO - this can affect ANB angle, overjet, and overbite measurements, potentially changing the diagnosis (e.g., a Class II in CO may appear more severe in CR)
- Deprogramming: A Lucia jig, leaf gauge, or anterior deprogrammer is used before articulator mounting to eliminate muscle engrams and record true CR
- Gnathologic orthodontics (Roth technique): Goal is to finish treatment with CR = CO (zero discrepancy)
- TMJ implications: Large CR-CO slides correlate with higher rates of TMD signs and symptoms
Pre- vs. Post-Treatment Values (Klar study, 200 orthodontic cases)
| Measurement | Pre-treatment | Post-treatment |
|---|---|---|
| Right vertical | 0.90-1.08 mm | 0.56-0.60 mm |
| Right horizontal | 0.73-0.84 mm | 0.50-0.62 mm |
| Transverse | 0.43-0.44 mm | 0.24-0.25 mm |
Orthodontic treatment significantly reduces CR-CO discrepancy across all three planes.
Bottom line: A CR-CO slide of up to 2 mm (vertical + horizontal combined) with no more than 0.5 mm lateral component is generally considered within normal/acceptable limits in orthodontics. Discrepancies exceeding 2 mm warrant careful evaluation for TMD risk and may significantly alter treatment planning when study models are mounted in CR.
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