Large Filling vs Crown

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 must be evaluated through structure, force, time, and long-term stability.

The Structural Decision 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 defined by threshold position relative to structure, force, time, and long-term stability.

The next chapter applies the framework to crown versus root canal.