Dentin Restoration: How to Trust Your Bond to Dentin

Despite adhesive dentistry entering its fifth decade, many practitioners today still experience frustrations with debonded restorations, fractured cusps and post-operative sensitivity. Is adhesive dentistry really any better than retention form?

Dr. David Alleman experienced these same frustrations when he first incorporated adhesive dentistry into his practice over 25 years ago. Through a five-year literature review, he developed a set of protocols that improved outcomes for adhesive restorations and created bonds to dentin that have lasted over 20 years and counting.

This 2005 case by Dr. David Alleman, DDS shows how poorly bonded composite can negatively impact the tooth. His research into better bonding protocols led to his development of his Six Lessons Approach.

Which bonds better: dentin or enamel?

Adhesive dentistry was originally developed for anterior veneers. These flat preparations with a high percentage of enamel in the bonding surface offered impressive results. But when those same materials and techniques were used for posterior teeth, the result was largely frustration. The difference was dentin bonding. Due to its varying water and hydroxyapatite content within different areas of the tooth, what appears to be bonding to a single substrate, dentin, can actually mean bonding to four or five different substrates (root, intermediate, caries-infected, caries-affected and sound dentin). 

The initial conclusion was that enamel can achieve higher bond strengths than dentin, so adhesive restorations should focus on enamel bonding, even in posterior teeth. Yet research showed other results. By 2000, dentinal bonding systems had been developed that could achieve bonds over 50 MPa to dentin, so why were practitioners still experiencing debonded restorations? The difference was how the bonding systems were applied. Research into dentinal bonding systems bonded to flat surfaces. Most clinicians are treating Class II or MOD restorations that are deep boxes and move through multiple substrates within the tooth. The Six Lessons Approach addressed these variables to achieve more predictable results.

In cases like this one by Dr. Davey Alleman, DMD, bonding to dentin is especially complex due to the varying substrates in the bonding field.

Dentin bonding variables: C-factor, the Hierarchy of Bondability and Time

Dr. David Alleman analyzed how research into dentin bonding was done to identify the variables that could make applying that research inconsistent. 

C-factor: Defined as the ratio of bonded to unbonded surfaces, C-factor relates to stresses in dentinal bonds as composite shrinks towards the center of mass. While bulk-fill composites might seem like an easy solution to adhesive dentistry, using them in a high C-factor preparation means your adhesive restoration will debond in the areas closest to the pulp. Understanding C-factor is key to understanding adhesive dentistry.

Hierarchy of Bondability: Dr. David Alleman coined this term as a way for practitioners to better recognize the varying substrates they are bonding to. Dentinal bonding systems will develop the strongest bonds with the substrates that are easiest to bond to — substrates with lower water content and higher percentages of hydroxyapatite. Creating strong bonds to all substrates in the bonding field creates a longer-lasting restoration.

Time: Adhesive dentistry is a chemical reaction between the dentinal bonding system and the dentin to form the hybrid layer. Every chemical reaction has a beginning, middle and end, so understanding how time affects hybrid layer development ensures the bonds are able to form without stress. Time is not often measured in dental research, but it plays an important role in clinical application.

This case by Dr. David Alleman, DMD shows the different variables that make dentin bonding challenging and how they are addressed with the Six Lessons Approach.

Achieving biomimetic bond strengths to dentin

By understanding the differences between various substrates of the tooth, using a gold-standard bonding system when available and applying techniques that increase bond strengths and reduce stresses, any practitioner can achieve a biomimetic bond to dentin in the peripheral seal zone and most areas close to the pulp — one that mimics the strength at which a natural tooth is connected to itself (30-50 MPa). Dentinal bonds at this strength support natural tooth structure to prevent crack initiation and stay bonded to prevent post-operative sensitivity and pulp inflammation. 

To learn the full set of protocols that achieve predictable bonds to dentin, including immediate dentin sealing and deep margin elevation, view upcoming online and in-person Alleman Center continuing education programs.

Learn more about predictable dentin bonding in this Six Lessons Approach Podcast episode by Dr. David Alleman.