The Hierarchy of Bondability

A common misconception of composite shrinkage is that composite moves towards the light source when polymerizing, but it has instead been shown (Cho BH, Et al. Effect of interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations. Oper Dent, 2002, 27, 297-304) that composites shrink towards the most highly bondable surface. While the outcome is often the same in restorative dentistry — gaps under a restoration — understanding why the gap occurs there helped Dr. David Alleman develop his concept of the Hierarchy of Bondability and eliminate gap formation.

Understanding the Hierarchy of Bondability is essential in cases like this with deep defects. Achieving a long-lasting bond to multiple substrates in a tooth is possible, but only with the proper techniques. Case by Dr. Davey Alleman, DMD.

The Hierarchy of Bondability states that different parts of the tooth establish the hybrid layer at different strengths and at different times because of the varying conditions and locations of the dentinal hard tissue. Understanding this concept is essential to adhesive dentistry because gaps from polymerization shrinkage can result in post-operative sensitivity from exposed dentin, crack formation from unsupported tooth structure and restoration failure from large debonded areas of composite.

Why the Hierarchy of Bondability matters in adhesive restorations

Eliminating post-operative sensitivity: As composite shrinks during polymerization, it will create a gap under the composite unless techniques are used to prevent this. Gaps under restorations leave exposed dentin tubules that continue to exude pulpal fluid, which results in pain for the patient (Brannstrom M. The hydrodynamic theory of dentinal pain: sensation in preparations, caries, and the dentinal crack syndrome. Journal of Endodontics. 1986;12(10):453-457). With the development of the Hierarchy of Bondability, gaps and the associated sensitivity can be eliminated by connecting parts of the tooth with the same maximum bondability potential for that part of the tooth to increase bond strength and bonding in small increments to reduce stresses to the developing bond.

Even small restorations can be at risk of debonding and post-operative sensitivity if the correct techniques are not used. Initially case photo by Dr. Davey Alleman, DMD.

Reducing the risk of crack initiation: If a tooth is not bonded side to side, front to back and top to bottom, the tooth structure around the restoration is not supported and at higher risk of crack Initiation . Without a fully bonded restoration, the tooths bends and flexes more than it is designed to do. The Hierarchy of Bondability helps create a complete bond, connecting the tooth like a natural tooth and returning it to normal flexure.

Restored teeth with weak bonds leave the remaining tooth structure at greater risk of fracture, as seen in this slide from the Biomimetic Mastership. As restoration size increases and cusp width decreases, the tooth becomes less resilient.

Longer lasting restorations: Debonded restorations as a result of composite shrinkage increase the risk of total restoration failure. Because of composite shrinkage, many restorations lose their bond before the patient even leaves the office. By using the concept of the Hierarchy of Bondability, Dr. David Alleman solved these issues with adhesive restorations in his Six Lessons Approach to Biomimetic Restorative Dentistry. The solution is Decoupling with Time.

The composite in this old restoration was not fully bonded, likely causing the cusp to fracture. Initial case photo by Dr. Davey Alleman, DMD.

Decoupling with Time to Overcome the Hierarchy of Bondability

The invention of flowable composites saw an increase in bond strength in adhesive restorations. While reviewing this research, Dr. Alleman saw how the same composite materials somehow achieved better outcomes when applied differently. The variable he recognized was time. The time of placing flowable composite allowed the hybrid layer to fully develop without being stressed by polymerization shrinkage.

With techniques to overcome the Hierarchy of Bondability and materials that have been proven to achieve high bond strengths, doctors can achieve ionic bonds in their restorations that stay bonded and symptom-free for decades. Slides from the Biomimetic Mastership.

How understanding the Hierarchy of Bondability improves dental outcomes

Understanding and visualizing the Hierarchy of Bondability allows doctors to restore deep areas of the tooth, including areas where caries is left behind to protect the pulp, without sacrificing the high bond strengths possible with current dental adhesives. As part of Dr. David Alleman’s Six Lessons Approach to Biomimetic Restorative Dentistry, the Hierarchy of Bondability is taught in Lesson 3: Immediate Dentin Sealing and Resin Coating. By using this complete set of protocols, doctors can use the Hierarchy of Bondability to eliminate one of the leading causes of post-operative sensitivity, reduce the risk of crack initiation and create restorations that stay bonded for 20 years and counting.

This case by Dr. Davey Alleman, DMD shows how the Six Lessons Approach to Biomimetic Restorative Dentistry is used to create long-lasting bonds and resolve patient systems by overcoming the Hierarchy of Bondability.

Learn more about the research and techniques behind biomimetic restorative dentistry at Alleman Center biomimetic dentistry training programs.

Learn more about the Hierarchy of Bondability in this Six Lessons Approach Podcast episode.