How to Improve PFM Crown Fit and Avoid Marginal Discrepancy & High Occlusion

How to Improve PFM Crown Fit and Avoid Marginal Discrepancy & High Occlusion

A Practical Guide for Dentists and Dental Laboratories

Porcelain-fused-to-metal (PFM) crowns remain one of the most widely used restorative solutions in modern dentistry. However, PFM crown fit issues, including marginal discrepancy and high occlusion, continue to be the leading causes of clinical failure and costly remakes.

Understanding the root causes—and how to prevent them—can significantly improve restoration success rates and reduce chairside adjustments.

What Causes Poor PFM Crown Fit?

In many cases, marginal misfit and high occlusion occur together, often indicating incomplete crown seating. These issues typically arise from a combination of clinical and laboratory factors.

Clinical Factors Affecting Crown Fit and Occlusion

1. Tooth Preparation Errors

Improper tooth preparation is one of the most common causes of poor crown fit.

Rough or uneven surfaces can create interference points

Irregular shoulder margins reduce marginal accuracy

An inconsistent path of insertion prevents full seating

Ensure smooth preparation, clearly defined margins, and a uniform insertion path.

2. Inaccurate Impression Techniques

Without proper gingival management, achieving an accurate margin is extremely difficult.

Lack of gingival retraction leads to unclear margins

Low-precision materials increase distortion risk

Use gingival retraction (cord or paste) in conjunction with high-precision materials, such as silicone impressions.

3. Model Inaccuracy

The accuracy of the working model directly affects the final restoration.

An incorrect water-to-powder ratio alters expansion.

Non–high-strength stone reduces dimensional stability

Delayed pouring causes impression shrinkage

Use Type IV dental stone and follow strict mixing protocols. Pour models immediately after impression taking.

4. Bite Registration Errors

Incorrect bite records are a major contributor to high occlusion in crowns.

Wax bites are prone to deformation.

Transportation can distort occlusal records.

Use silicone bite registration materials or rigidly protect wax records during transport.

5. Lack of Temporary Crowns

Without provisional restorations:

Teeth may drift or over-erupt

Occlusion becomes unstable

Always provide well-fitted temporary crowns.

 

Laboratory Factors in PFM Crown Accuracy

1. Die Preparation and Stability

Unstable or poorly repositioned dies can cause both marginal gaps and occlusal errors.

Ensure:

Accurate die seating

Secure and parallel die pins

Proper base stone hardness

2. Margin Integrity During Fabrication

Marginal discrepancy often occurs during:

Die trimming

Wax pattern fabrication

Metal coping and porcelain finishing

Key Point:

Even minor damage at the margin can compromise the entire restoration.

3. Occlusion Transfer and Adjustment

Errors in occlusal interpretation lead directly to high crowns.

Incorrect articulation

Wear of opposing models

Inaccurate lateral movement simulation

Use semi-adjustable or fully adjustable articulators for better accuracy.

How to Reduce Remakes and Improve Quality

Improving PFM crown quality control requires collaboration between clinicians and dental laboratories.

Standardize workflows

Improve communication between the clinic and the lab

Use high-quality materials

Follow strict technical protocols

Why It Matters

Poor crown fit not only affects function and comfort but can also lead to:

Secondary caries

Periodontal complications

Patient dissatisfaction

Increased remake costs

By minimizing marginal discrepancy and occlusal errors, both clinicians and labs can achieve more predictable and efficient outcomes

Our Approach at HYC Dental Laboratory

At HYC Dental Laboratory, we focus on delivering consistent, high-precision restorations through:

Advanced CAD/CAM technology

Strict quality control protocols

Experienced technicians with over 20 years of expertise

Reliable turnaround times

Our goal is to help our partners reduce chairside adjustments and improve patient satisfaction.