Can Resin Cements Be Used Under Metal Castings

Can Resin Cements Be Used Under Metal Castings? A Comprehensive Guide

The use of resin cements under metal castings has become a topic of significant discussion and research in the field of dentistry. While traditional cements have long been the standard, resin cements offer several potential advantages, leading to ongoing evaluation of their efficacy and suitability. This article delves deep into the intricacies of using resin cements under metal castings, examining the benefits, drawbacks, considerations, and best practices to ensure successful and long-lasting restorations.

Understanding Resin Cements and Their Properties

Resin cements are a class of dental materials composed of polymers and monomers that, when polymerized (cured), form a strong, durable bond. They differ significantly from traditional cements like zinc phosphate or glass ionomer in terms of their composition, setting mechanism, and bond strength. Key properties of resin cements that make them attractive for use under metal castings include:

High Bond Strength:

Resin cements exhibit significantly higher bond strengths to various substrates, including metals, compared to traditional cements. This superior bonding is crucial for achieving a long-lasting, retentive restoration. The chemical bonding capabilities are a key differentiator.

Improved Marginal Integrity:

The ability of resin cements to form a strong marginal seal is critical in preventing microleakage, a major cause of secondary caries and restoration failure. The inherent properties of the resin minimize gaps and crevices.

Aesthetic Advantages:

While not directly visible under a metal restoration, the improved marginal integrity contributes to overall aesthetic success by minimizing discoloration and staining around the margins of the metal casting.

Chemical and Physical Properties:

A wide variety of resin cements exist, each with specific physical and chemical properties tailored to different applications. Self-adhesive, dual-cure, and light-cure options offer flexibility in clinical application.

Types of Resin Cements:

Different types of resin cements exist, each with its specific properties and application methods. Understanding these differences is crucial for making informed decisions regarding their use under metal castings:

• Self-adhesive resin cements: These cements do not require a separate etching or bonding agent. Their convenience and time-saving properties make them attractive for many procedures.
• Dual-cure resin cements: These cements initiate polymerization through both chemical and light activation, offering a degree of flexibility and control.
• Light-cure resin cements: These require light activation to complete the polymerization process. They offer precision and control over the setting time.

The Case for Resin Cements Under Metal Castings

Several compelling reasons support the use of resin cements under metal restorations:

Enhanced Retention:

The superior bond strength of resin cements translates into enhanced retention of the metal casting. This is especially important for large restorations or those subjected to significant occlusal forces. Stronger retention minimizes the risk of dislodgement.

Reduced Microleakage:

The improved marginal seal provided by resin cements is a significant advantage in preventing microleakage. This reduction in microleakage contributes to a longer lifespan of the restoration, preventing secondary caries.

Improved Pulp Protection:

Some resin cements offer a degree of pulp protection due to their chemical composition and low-shrinkage properties. This is beneficial, particularly in cases where the pulp is close to the restoration.

Simplified Cementation:

Certain resin cements simplify the cementation process compared to traditional techniques. The ease of use can improve efficiency in the dental practice.

Challenges and Considerations

While resin cements offer many advantages, certain challenges and considerations need to be addressed:

Metal Surface Treatment:

Proper preparation of the metal surface is critical for achieving optimal bond strength with resin cements. This may involve techniques such as air abrasion or chemical etching to create a micro-roughened surface that improves the mechanical interlocking with the cement. Poor surface treatment is a leading cause of failure.

Polymerization Issues:

The complete polymerization of resin cements is crucial for achieving the desired properties. Incomplete polymerization, caused by factors such as insufficient light curing or improper handling, can significantly compromise the bond strength and overall longevity of the restoration.

Film Thickness:

Controlling the film thickness of the cement is essential. Excessive thickness can hinder polymerization and lead to incomplete bonding. Conversely, a film that's too thin might be prone to fracturing. Careful attention to technique and the use of appropriate cement dispensers are necessary.

Cement Selection:

The choice of resin cement is crucial and must align with the specific requirements of the metal casting and the clinical situation. Factors such as the type of metal, the size and location of the restoration, and the patient's medical history all need to be considered.

Moisture Control:

Maintaining a dry field is essential for the successful use of resin cements. Moisture contamination can interfere with the polymerization process and reduce the bond strength significantly.

Best Practices for Using Resin Cements Under Metal Castings

To optimize the success rate when using resin cements under metal castings, adhere to these best practices:

Thorough Surface Preparation:

This includes meticulous cleaning, etching (when appropriate), and rinsing of both the metal casting and the prepared tooth structure. The goal is to create optimal micromechanical retention and chemical bonding.

Accurate Mixing and Dispensing:

Follow the manufacturer’s instructions carefully regarding mixing ratio, mixing time, and application techniques. Accurate dispensing of the cement helps ensure consistent film thickness.

Proper Polymerization:

Ensure adequate light curing time and intensity for light-cure or dual-cure cements. This step is vital for achieving complete polymerization and maximal bond strength. Avoid light interference or shadowing.

Careful Excess Cement Removal:

Remove any excess cement carefully after cementation. Leaving behind excess cement can impede marginal integrity and lead to complications.

Post-Cementation Evaluation:

Following the cementation procedure, perform a thorough clinical evaluation to ensure proper seating and marginal adaptation of the restoration.

Conclusion: Weighing the Benefits and Risks

The use of resin cements under metal castings presents a compelling alternative to traditional cements, offering significant advantages in terms of bond strength, marginal integrity, and aesthetic outcome. However, success is contingent upon careful attention to detail during surface preparation, cement handling, and polymerization. Choosing the appropriate cement type and strictly adhering to best practices are essential to minimize the risks and maximize the long-term success of metal restorations cemented with resin cements. Ongoing research continues to refine our understanding of resin cement behavior and its interaction with various metal alloys, providing more evidence-based guidelines for optimal clinical application. Ultimately, the decision to use resin cement should be based on a comprehensive assessment of the individual case and informed clinical judgment.