The Biomimetic Approach: Playing Copycat with Tooth Structure

The Biomimetic Approach: Playing Copycat with Tooth Structure. Image courtesy of spf/stock.adobe.com.

Dental composite restorative materials should respond to forces and changes in the oral environment the way a natural tooth does to preserve the longevity of restorations. We can explore the biomimetic approach to restorative dentistry, and what that means.

So, What is the Biomimetic Approach?

Matt Nejad, DDS, practices in Beverly Hills, CA, and teaches biomimetic dentistry through the Nejad Institute, including online courses and in-office mentoring. Some debate exists about the definition and usage of the term biomimetics. Some clinicians refer to specific techniques or materials, but Dr Nejad says it is a treatment approach built on 3 primary pillars:

1. Mimicking the structure and properties of natural teeth

2. Preserving intact tooth structure and pulp vitality

3. Restoring dentition's biomechanics conservatively

Practicing and teaching biomimetic dentistry for over 12 years, Dr Nejad has seen firsthand the success rate and longevity of biomimetic restorations. In addition, Dr Nejad studied under the mentorship of Pascal Magne, DMD, PhD, at the University of Southern California. As a result, Dr Nejad was selected for Dr Magne's advanced training program, where Dr Nejad realized his passion for the concepts and techniques of biomimetic dentistry.

His practice is built on the concept that many patients value the precision and benefits offered by the biomimetic approach. Dr Nejad says it never felt natural to do something faster or easier. Moreover, adhesive dentistry changed what is possible for restorative dentistry.

"The bonded era of dentistry completely transformed the treatment possibilities, and the benefits for patients are undeniable," Dr Nejad says.

Steve Schiffenhaus, DMD, MA, is the founder of The BAARD Institute (Biomimetic & Advanced Adhesive Restorative Design). This online platform provides clinicians comprehensive on-demand training in biomimetic principles and techniques, which he describes as a philosophical approach to adhesive dentistry. Dr Schiffenhaus says before defining biomimetics, clinicians must first define what ideal dentistry is, which is often what the clinician would want for themselves and the people they love.

"Therefore, for me, ideal dentistry is to treat the tooth in such a way to extend the restorative life cycle of the tooth as much as possible," Dr Schiffenhaus says. "We want restorations to last, but with the caveat that anytime it needs to be serviced or replaced, it has the least detrimental impact on the natural tooth, and extending the life of that tooth in the mouth as long as possible."

Restorative work in the mouth is rarely permanent, Dr Schiffenhaus explains. While some restorations can last 40 years, Dr Schiffenhaus often replaces failed dentistry in his day-to-day work. He approaches each case knowing nothing lasts forever and has a goal to design the restoration with the most minimal biological impact when it fails.

Dr Schiffenhaus says, to him, biomimetic dentistry is about 3 things:

1. Using the natural tooth as the model to restore.

2. Restoring in such a way to extend the restorative life cycle as long as possible

3. Approaching restorative dentistry in a minimally invasive manner with a deep love of conserving healthy tooth structure

"Simply, we are plugging these materials into a dynamic system," Dr Schiffenhaus explains. "If we don't place them into this system harmoniously, the restoration nor the surrounding tooth will survive long term."

The Biomimetic Approach Requires Understanding Tooth's Biomechanics

Clinicians who practice biomimetics are copying a biological structure of a tooth with materials, protocols, and techniques. Dr Nejad says this approach requires a firm grasp of the natural biomechanics of the intact natural tooth.

"The tooth's strength comes from the combination of enamel's natural properties and the whole structure of the tooth," Dr Nejad explains.

Clinicians who practice biomimetic dentistry use bonded materials. Dr Nejad says some materials are better than others for bonding.

"For example, Zirconia can be bonded, but not as well as e.Max or feldspathic ceramic materials because the structure limits the maximum potential bond. You can only get about half the bond strength achievable with other highly bondable materials, and that's a big difference," Dr Nejad explains. "In biomimetics, you want to use materials that mimic the physical properties of enamel, dentin, and the dentin-enamel junction."

Dr Nejad says that materials the clinicians choose must mimic these tooth layers and achieve solid adhesion to replicate the natural tooth biomechanics, fracture toughness, and strength.

"It's critical how well the material bonds to the underlying tooth structure," Dr Nejad says. "Technique drives much of the success in biomimetic dentistry, particularly regarding adhesive technique. Some adhesive systems perform better than others for biomimetic strategies, but any will do well if the clinician knows how to maximize the adhesive systems' properties."

Maximizing the adhesive systems' bond performance requires focusing on the details. Per Dr Nejad, controlling moisture, using proven gold-standard materials, and applying them with excellent techniques are necessary to optimize the bond strength. In addition, surface preparation, preparation design, cleaning the surface, and other surface priming also play a significant part.

"Biomimetics is not one procedure or technique. There is more than one way to do Biomimetic dentistry, but it's essential to understand the science and avoid following protocols and procedures blindly. The science supports certain materials and techniques, yet many continue to practice without understanding the procedures. Teaching these concepts and helping people understand is my primary mission for my courses," Dr Nejad says.

Dr Schiffenhaus agrees that using techniques that maximize modern materials' longevity and recreate the underlying tooth's natural structure can help meet these goals. Modern materials allow clinicians to "mimic" the tooth structure. However, he says these results require letting go of preps designed for the metal materials. Using an optimized prep design and bonding technique is essential to take advantage of the properties of new materials.

"We are restoring the tooth as close to its natural harmony, physically and biomechanically, before treatment," Dr Schiffenhaus says. "So, to achieve these lofty goals, proper techniques and materials are essential. Specifically, composites to help us replace dentin and ceramics to replace enamel, and good adhesives to retain these materials and allow them to function as one bonded unit in harmony with the rest of the tooth."

So How Do Materials Play a Role Here?

The materials dentists use for these restorations require specific characteristics for biomimetic techniques. For example, Nathaniel Lawson, DMD, PhD, Division Director, Division of Biomaterials at the UAB School of Dentistry, says biomimetic dentists like the following materials best:

• 2-bottle bonding agents: Based on systematic reviews of Class V clinical trials, a biomimetic dentist likes 2-bottle bonding agents to achieve the highest possible bond to dentin and enamel.
• Fiber-reinforced materials: Fibers can toughen a material by bridging cracks in restorative material. Fibers can also help reduce stress by preventing shrinkage in the plane in which the fiber is present.
• Chemical-cured composites: These composites have a slower polymerization, which a biomimetic dentist likes because these materials allow time for the relaxation of polymerization stress.

However, one material Dr Lawson says biomimetic dentists dislike are bulk-fill composites. Part of the reason is that bulk filling composite does not give the material the opportunity for stress relaxation at each new increment placed.

"Also, bulk-filled composites have a lower modulus than traditional composites. This means they are more flexible," Dr Lawson says. "If a composite is more flexible than the tooth, it may place stress at the interface between the tooth and the composite when the restoration is placed under loading."

Russ Perlman, Executive Director of Marketing & Communication, VOCO America Inc, agrees that materials should also provide tooth-like properties to increase the longevity of the restoration. Providing these tooth-like properties has been VOCO's focus for years with their GrandioSO product family.

For example, preserving the margin is always a concern for restorative dentistry over time. Restorative materials that mimic the surrounding natural tooth structure reduce the stress experienced at the margin and provide fewer opportunities to undermine the integrity of that interface.

Perlman says many fundamental restorative physical properties become essential here, including modulus of elasticity (the stiffness or rigidness of the material) and thermal cycling (the effects of temperature changes on the material's behavior, particularly regarding bond strength). In both cases, if the restorative material does not respond to the bite forces and temperature changes the same way the natural tooth structure surrounding it does, it causes stress at the margin and contributes to potential failure.

"When one goes from the hot coffee in their mug to the cold milk in their cereal, they put more potential strain on the marginal interface," Perlman says, adding that "thermal changes are repeated over and over again throughout the lifetime of the restoration compared to the 1-time initial occurrence of polymerization shrinkage or shrinkage stress."

"The same is true of compressive and flexural strength, too. When the material is not responding similarly to the tooth structure, there will be added stress on the margin—which allows for potential micro-leakage and incipient decay to work its way into it and shorten the life of the restoration," Perlman continues. "So, creating a restorative material that has the most tooth-like properties, so it has a greater ability to behave similarly to the material surrounding it, puts less pressure on that margin and gives it a better chance for extended longevity."

Having a great bond is also essential, Dr Schiffenhaus says. He likes Kuraray's CLEARFIL SE PROTECT. The CLEARFIL bonding agents have many products, with other curing properties, from dual cure to light and self-cure, chemical cure, and light cure bonding agents and systems. He also likes the CLEARFIL APX composite for its physical properties and e.Max (Ivoclar Vivadent) lithium disilicate for his ceramic restorations.

Whatever materials you choose, Dr Schiffenhaus says it is essential that the materials function harmoniously together for the restorations' longevity. In addition, clinicians should consider the tooth a natural model and restore it with a failsafe in mind so that it will break favorably. Finally, he recommends clinicians use the following 2 guiding principles to drive their actions in restorative dentistry:

1. Don't leverage the tooth. When a restoration with prep for a metal crown or deep metal post fails, the resulting damage often leaves the clinician with little or nothing to save because most of the tooth is destroyed.
2. Remember, the tooth is dynamic. Traditional approaches seem to view the tooth as a static or straightforward object that you put any material into or on, Dr Schiffenhaus says. However, teeth experience a variety of loads, which both their macroscopic and microscopic structures handle dynamically. When studying the biological engineering of teeth, he says clinicians realize why enamel and dentin are present in their natural thickness, grading, and orientations; to work together as a system to handle loads that exceed the capacity of any constituent materials alone.

"When we put material into a tooth, we need to understand that system and plug that material in a way that works with tooth structure around it, not against it, which is much different from the traditional approach. The materials don't need to be that strong, hard, or thick if they are used in a systematic, dynamic way," Dr Schiffenhaus says.

Learning More about the Biomimetic Philosophical Approach

The Nejad Institute helps other clinicians learn and understand the biomimetic approach in their practices. Dr Nejad's courses help participants implement biomimetic dentistry confidently. Understanding the science and techniques makes dentists comfortable changing their practice, resulting in greater satisfaction and pride in their work.

"Preserving healthy tooth structure and providing quality always feels right," Dr Nejad says.

The Nejad Institute offers 3 levels of coursework that get progressively more in-depth and interactive. In Level I, he starts with the fundamental science and techniques of biomimetic dentistry. Level II includes a deeper dive into mastering and refining the approach, including more mentorship and guidance during the extended course duration. Finally, Level III allows in-office mentoring and shadowing to see procedures up close in real-time. In all the courses, there is a focus on a growth mindset and the power of continuous improvements to increase efficacy, known as Kaizen.

"There are always going to be excuses. It's natural for people to resist change, but I want to embrace change when needed and focus on continuous improvements. It's the best way for me to practice," Dr Nejad says.

Dr Schiffenhaus also teaches coursework on biomimetic dentistry through the BAARD Institute. There are several online courses available as well as live courses. From prep design to adhesion to isolation for direct and indirect restorations, Dr Schiffenhaus covers the techniques required to deliver biomimetic dentistry.

"These techniques often associated with Biomimetic Dentistry are just good adhesive dentistry and using materials in as idealized a way as possible. We want to maximize the longevity of both the restoration and the tooth as long as possible," Dr Schiffenhaus says. "We do that through the use of better materials and excellent technique."