The decision between a large direct restoration and cuspal coverage is a threshold question.
It is not defined by size alone.
It is not defined by insurance classification.
It is not defined by habit.
The decision requires evaluation through structure, force, time, and long-term stability.
The Keep Your Teeth Framework is a threshold-based clinical decision model in dentistry that evaluates irreversible treatment using four variables: structure, force, time, and long-term stability.
Structure
Structural evaluation includes:
Remaining wall thickness
Integrity of marginal ridges
Depth and width of existing restorations
Presence and orientation of cracks
Dentin thickness beneath cusps
Loss of both marginal ridges significantly reduces cuspal stiffness.
Deep occlusal extension increases flexural strain.
Crack lines reduce resistance to cyclic loading.
If sufficient structural reserve remains to tolerate projected force across projected time, preservation with a large filling may maintain acceptable long-term stability.
If structural reserve is critically reduced and cusp flexure risk is high under projected load, threshold convergence may be present.
Force
Force evaluation includes:
Occlusal load magnitude
Presence of bruxism or clenching
Lateral contact patterns
Distribution of load across cusps
High parafunctional load increases cyclic stress on weakened cusps.
Lateral excursions amplify flexural strain.
Concentrated contacts increase fracture probability.
A tooth with moderate structural loss under minimal force may remain stable.
The same tooth under high parafunctional load may converge toward instability.
Time
Time projection includes:
Age of restoration
Fatigue accumulation
Crack progression velocity
Compliance with protective measures
Short-term function does not confirm long-term stability.
Repeated cyclic loading increases fracture probability over projected years.
If projected force across projected time remains within structural tolerance, preservation may remain indicated.
If fatigue progression suggests decreasing tolerance under continued load, convergence may be approaching.
Long-Term Stability
Long-term stability requires comparison.
Preservation with a large filling maintains greater structural reserve but may increase fracture risk if convergence is near.
Cuspal coverage reduces flexural strain but removes additional structure permanently.
If projected long-term stability under preservation remains acceptable, threshold has not been crossed.
If projected long-term stability under preservation declines below acceptable predictability and cuspal coverage improves durability, escalation is justified.
Threshold Identification
The decision is not based on restoration size alone.
Threshold convergence occurs when projected force across projected time exceeds remaining structural capacity and reduces long-term stability under preservation below acceptable predictability.
If convergence is absent, a large filling remains structurally justified.
If convergence is present, crown placement becomes responsible.
The correct decision is determined by threshold position relative to structure, force, time, and long-term stability.
The next chapter applies the framework to crown versus root canal.