Practical Biomimetic Restorative Dentistry

Peg Lateral Rejuvenation

Brandon Walker, D.D.S. — Tue, 11 Jun 2024 13:28:45 GMT

Your dental anatomy professors will tell you that undersized lateral incisors, also known as “peg laterals”, are rare. This actually falls in line with a 2013 meta-analysis by Hua et al in which the prevalence of peg laterals was found to be less than 3% across various races. Interestingly enough, this phenomenon is actually seen quite often in practice, particularly in women. It is not uncommon for patients to present with composite veneers placed using traditional methods and materials in their earlier years, though the contours, shade, and polish are less than ideal. Considering the increasing demand for clear aligner orthodontic interventions, learning how to treat undersized lateral incisors in the most conservative way possible is a tremendous service to patients.

Chasing the Red Lizard

Brandon Walker, D.D.S. — Fri, 07 Jul 2023 22:28:24 GMT

Many decisions today are made based on emotion instead of a rational, analytical, and critical mind. It is no question that social media drives much of this unconstrained emotion. After all, users typically scroll quickly with a very limited attention span, and the ‘reply’ or ‘share’ buttons are within closer reach than a well-developed, tempered thought. This is generally true not just for politics, pop culture, and virtually any conceivable topic, but also for dentistry.

It is also true that many treatment decisions are based on antiquated philosophies, lack of advanced training, or even to cater to third-party payers AKA “dental insurance.” I posted a case photo of tooth number 4.6 (30) on Instagram seeking input on how dentists would approach it, and the responses were not surprising.

The post read as follows:

“Your mid-life patient calls and says their amalgam filling came out. This is the crime scene. The tooth is vital. What’s your game plan?”

Is polymerization shrinkage stress a good thing?

Brandon Walker, D.D.S. — Sun, 26 Feb 2023 12:01:04 GMT

In 2004 Versluis et al published an 11 page paper titled Residual Shrinkage Stress Distributions in Molars After Composite Restoration. Within their carefully worded analysis, they emphasized “Calculation of shrinkage stresses in a tooth-restoration complex is not trivial.”

18 years later, Dr. David Clark teamed up with Dr. Richard Young at the Seattle Study Club Symposium and trivialized polymerization shrinkage stress to promote the so-called “Bioclear Method” using 3M Filtek One bulk fill composite and anatomic mylar matrices (Bioclear Matrix). Clark cited a rejected and unpublished study funded by 3M to try and convince the audience that “polymerization stress is a good thing.”

The study involved a series of finite element analysis (FEA) diagrams created by researcher Alex Fok, PhD, MSc and colleagues at the Minnesota Research Center for Biomaterials and Biomechanics. To captivate the audience, Clark made statements like “the bulk of the restoration is going into compression... that dark blue is compression.” He writes off the red “scatter” in areas of higher stress (pulpal floor) where you’re likely to see debonding of composite over dentin.

Courtesy Minnesota Research Center for Biomaterials and Biomechanics

I sent Alex the YouTube video, which has since been removed, and asked him if he agreed with Clark’s analysis of his work and/or use of the diagrams to promote the Bioclear brand:

“I have no financial interest in Bioclear or their partnership with 3M, and I haven't been following David's presentations. But I've seen him misrepresent other people's work, notably the effect of crack length, rather than depth, on the propensity for crack propagation. Hopefully, with our paper published, people can make their own judgement… We only submitted the FEA portion for consideration. It was rejected for lack of experimental results to validate the FEA. That's what I'd need to add to the paper before resubmission.”

Regarding misrepresenting people’s work, Fok is referencing Clark’s popular reference to J.E. Gordon’s book The New Science of Strong Materials: Or Why You Don’t Fall Through the Floor when attempting to explain why teeth crack. Clark is notorious for misinterpreting the Inglis formula in which L represents the length of a crack proceeding inwards from a surface (crack depth), not the length of a crack across a surface, when attempting to corroborate his argument that antiquated tooth preparations cause cracked teeth.

The New Science of Strong Materials: Or Why You Don’t Fall Through the Floor, Crack-stopping, page 109.

It’s unlikely there’s a respected scientist or researcher in adhesive dentistry that agrees with Clark and his elementary idea that “...polymerization shrinkage stresses in these modern preps is a good thing,” even if you “change to a negative c-factor, less than one,” which is conceptually and mathematically impossible. And if that’s not confusing enough, there is no mention of “negative c-factor” in the draft of Fok’s study. Perhaps Clark misspoke, or maybe he simply doesn’t know what he’s talking about. Luckily, there are clinicians and researchers who do.

Residual shrinkage stress distributions in molars after composite restoration. Versluis (2004).

Academic clinician and researcher Alireza Sadr, DDS, PhD, who is Associate Director at Biomimetics Biomaterials Biophotonics & Technology (B4T) laboratory at University of Washington School of Dentistry, has published with colleagues a variety of interesting articles using state of the art Optical Coherence Tomography (OCT) to visualize polymerization shrinkage stress in real-time, and the conclusions are shocking.

In one sample shown below, a 2mm deep cavity is bulk-filled after application of Scotchbond Universal. Dentin delamination or gap formation (white line) occurs after just 12 seconds of curing and continues to increase even after curing ends. This sample closely resembles the bulk placement of composite in Clark’s “Bioclear Method,” though other samples can be viewed and appreciated on the B4T website. The ground-breaking article “Real-time in-depth imaging of gap formation in bulk-fill resin composites” was published in 2019.

It is clear that through a variety of well-documented and peer-reviewed research polymerization shrinkage stress in adhesive dentistry is and never will be a good thing. Uncontrolled polymerization shrinkage causes gap formation at the dentin interface which can lead to post-operative sensitivity, leakage, and recurrent decay over time. Dr. Sadr and colleagues have demonstrated this ad nauseam, as shown by over 60 years of research, and public records obtained from the University of Washington School of Dentistry reveal numerous dental professionals’ continued frustration with Clark’s claims, including fear of being attacked by him if they speak out.

University of Washington Public Records Request - PR_2023_000167. Redactions by Practical BRD.

As of this writing, no peer-reviewed studies supporting Clark’s claims can be found in any reputable journal or repository. Even Clark’s heavily cited FEA analysis, a study funded by 3M OCSD, was rejected after peer-review for “lack of experimental results to validate the FEA”, according to Alex Fok. “I have yet to revise and resubmit the manuscript after it was rejected the first time round. Other projects such as grant writing have taken priority”, said Fok in February 2023, stating he expected to due to so “in the next few months.”

While cavity preparations different from the traditional G.V. Black preparations are more favorable for composite, Sadr and many others have proven that changing the preparation alone does not mitigate the complexities of adhesive dentistry to the degree that Clark and his marketing team might prefer. To learn more, read “Modern Cavity Preparations.”

References

Hayashi J, Espigares J, Takagaki T, Shimada Y, Tagami J, Numata T, Chan D, Sadr A. Real-time in-depth imaging of gap formation in bulk-fill resin composites. Dent Mater. 2019 Apr;35(4):585-596. doi: 10.1016/j.dental.2019.01.020. Epub 2019 Feb 25. PMID: 30819550.

Versluis A, Tantbirojn D, Pintado MR, DeLong R, Douglas WH. Residual shrinkage stress distributions in molars after composite restoration. Dent Mater. 2004 Jul;20(6):554-64. doi: 10.1016/j.dental.2003.05.007. PMID: 15134943.

Oh Snap!

Brandon Walker, D.D.S. — Mon, 20 Feb 2023 03:53:25 GMT

Patients are often surprised when they present to my clinic with a fractured tooth. The typical story involves the patient eating something soft like bread or cheese which is then almost always (wrongly) associated the catastrophic tooth failure. As engineer-minded professionals, we known this is usually not the case.

Fractures are often initiated far earlier. They can be related to the overall design of the tooth involved. For example, upper bicuspids have prominent, uninterrupted grooves spanning from mesial to distal. Just as glass snaps cleanly with a simple score mark, teeth experiencing heavy tensile forces can do the same. Lower second molars have similar occlusal anatomy, leaving them prone to a similar fate. Amalgam fillings on larger teeth tend to cause oblique fractures on the upper buccal cusps and lower lingual cusps. Clinical trends are quite consistent.

The "Liquid Dam" Technique

Brandon Walker, D.D.S. — Tue, 05 Jul 2022 22:31:19 GMT

Clinicians tend to have varying levels of trust for adhesive dentistry. Some clinicians still cut retention slots or grooves in their preps to mechanically retain composite restorations or build-ups. Others create tall build-ups to establish retention and resistance form for their full coverage crowns. And the outlier biomimetic restorative dentists create flat-top biobases trusting nothing but adhesion to retain the partial or full coverage crown come delivery day.

In the case of non-retentive preps, what you do between prep day and delivery can time-consuming and disruptive or quick and predictable. Traditional temporary crowns on non-retentive preps are difficult to keep retained and often result in multiple return visits by the patient when they fall off. In fact, creation of the non-retentive biobase via immediate dentin sealing, deep margin elevation, and/or any necessary “build-up,” can be viewed as the provisionalization step.

Temporary crowns do not just aid in function; they also help maintain the tooth position mesial-distally and occlusally. When traditional temporary crowns aren’t indicated, as with non-retentive preps, another method is necessary to maintain tooth position. When properly sealed with a solid biobase and positionally stable in all dimensions, the 2-3 week provisionalization period can be stress-free for both the patient and doctor. This is why clinicians favor the “liquid dam” technique.

OpalDam™ and OpalDam™ Green courtesy of Ultradent.

OpalDam is a passively adhesive (sealing) methacrylate-based light-cured resin barrier. It is used primarily to protect the gingiva or adjacent teeth during whitening procedures but can also be used to protect the gingiva around a tooth during air-particle abrasion procedures, stabilize sectional matrices, or seal a leaky rubberdam. Since OpalDam was originally developed as a gingival barrier, the material is ideal for provisionalizing non-retentive preps as it is friendly to the soft tissue for hours up to 2-3 weeks. Let’s review a case to see this technique in practice.

Swap It Out

Brandon Walker, D.D.S. — Mon, 07 Mar 2022 14:27:33 GMT

Amalgam replacements in the restorative practice are commonplace. The mistake many clinicians make, however, is thinking one can simply “swap out” the amalgam for composite. If rubber dam isolation is ignored, cavity preparations are not modified, poor adhesive protocols are used, and a “simplified” bulk-fill strategy is employed, there is little argume…

Modern Cavity Preparations

Brandon Walker, D.D.S. — Tue, 25 Jan 2022 03:12:08 GMT

Despite composite resin being in service for over 60 years, there is still much confusion regarding ideal cavity preparations for the material. This is due in part to dental schools throughout the United States teaching standardized, retentive cavity preparations ala G.V. Black which are convenient to teach and grade due to their prescriptive shapes and dimensions. While these cavity preparations are often used interchangeably for both amalgam and composite (particularly in the early pre-clinical years of dental school), they are mostly ideal for the mechanical retention of amalgam and inappropriate for use with bonded composite resin restorative materials.

Cavity preparation design remains both a subjective and sometimes controversial topic today, but it shouldn’t be. In fact, researchers like Alton M. Lacy and Hakon Nordbo had been looking into more compatible cavity preparations for composite resin restorative materials since as early as 1987. Their curiosity was sparked by observations of “a high rate of occlusal wear, a high incidence of microleakage and recurrent caries, difficulties in obtaining suitable proximal contacts with adjacent teeth, isthmus fracture in two- and three-surface restorations, post-operative sensitivity, and lack of radiopacity” with posterior composite restorations (Lacy, 1987).

Comparison of two Class II cavity preparations. Retentive amalgam preparation with sharp cavosurface and internal line angles prepared with a #56 carbide bur (left) and non-retentive composite resin preparation with beveled cavosurface and rounded internal line angles prepared with a super coarse chamfer diamond bur (right). Note the dentin crack in the amalgam preparation (left) resulting from the use of an aggressive carbide bur.

Lacy and Nordbo highlighted in detail the most common issues with early composite resin restorations, and thanks to their efforts along with findings from researchers like Urabe, Unterbrink, Davidson, Fusayama, Tagami, Van Meerbeek, Alleman, Belli, Sadr, Magne, and more, we are now enlightened. Adhesive dentistry has come a long way since the 1980s, yet many general dentists express an unwarranted lack of trust in dental adhesion and still resort to resistance and retention engineering principles when using composite.

Today, tooth substrates are far more understood than ever before through advanced imaging, structural testing, and computer modeling. Modern carbide and diamond rotary instruments along with air-particle abrasion systems are available, caries detecting dye use is more widespread, adhesive systems are far more advanced, flowable and paste composite resins are optimized for better flow and reduced shrinkage, and polyethylene fiber is now available to minimize polymerization shrinkage stresses and facilitate a secure bond at the tooth-restoration interface (Sadr et al, 2019).

Use of these modern advancements or technologies, however, proves futile without first considering a well-designed and engineered cavity preparation. In this article, we’ll discuss enamel and dentin as highly bondable tooth substrates, highlight the concept of hierarchy of bondability, and explore modern cavity preparation considerations to facilitate direct composite tooth restorations built to last.

Bonding Better with Biomimetic Dentistry

Brandon Walker, D.D.S. — Sun, 02 Jan 2022 17:55:33 GMT

One of the most common frustrations expressed by restorative dentists involves the placement and longevity of composite tooth restorations. Tooth restorations, commonly referred to as “dental fillings,” are foundational and arguably the most important treatment in everyday practice. This is especially true in insurance-based practices where reimbursements rates for direct composite procedures are low (and often decreasing) and overhead is a common concern. Adhesive dentistry, however, is highly technique sensitive and should not be rushed, regardless of current industry trends and messaging touting simplified and faster placement methods.

When done without proper isolation, at high speed, and with simplified materials, composite “fillings” can lead to leakage, recurrent caries, and post-operative sensitivity. These preventable adverse outcomes often decrease patients’ trust and confidence in the dental team. However, when executed meticulously using proper isolation, engineering principles, optimal materials, and sound technique, composite restorations are a long-lasting restorative solution that facilitate the preservation of maximum healthy tooth structure and pulp vitality. This is the number one goal of the Biomimetic dentist.

BIOMIMETIC RESTORATIVE DENTISTRY

In the amalgam era, a retentive hole was prepared in a tooth and filled with a self-setting alloy. Though unsightly and relatively aggressive in nature, amalgam fillings have saved countless teeth in the Western world for over 150 years. In contrast, modern adhesion with composite resin enables dentists a far more esthetic and conservative treatment approach. But here’s the kicker: adhesive dentistry is far more complex and technique sensitive than amalgam, and clinicians often fail to recognize the differences between the two materials. Most dental schools in the United States still teach antiquated concepts of retention and resistance form which is necessary for amalgam yet often catastrophic for composite.

Short-lived composite restoration with recurrent caries and cuspal fracture on a teenager girl. Plaque disclosing solution applied to the tooth (far left). Defective composite and caries removal followed by air-particle abrasion (middle left). Immediate Dentin Sealing (IDS) and resin coat (middle right). Incremental cusp replacement with final high-shine polish (far right).

With adhesive dentistry the goal is no longer to simply fill a hole but rather connect the composite restoration to the tooth with virtually zero mechanical retention from bottom to top, side to side, and front to back. This is only possible with a firm understanding of and respect for tooth substrate properties, adhesion principles, material properties, isolation techniques, preparation design, and incremental, stress-reducing material placement techniques. Dentists must learn to trust adhesion. By changing the mentality from simply filling a hole to restoring a tooth defect in a manner that mimics the properties and function of a natural tooth, clinicians can create highly bonded, long-lasting tooth restorations.

Welcome to Biomimetic Restorative Dentistry.

IS FASTER ALWAYS BETTER?

In a modern society that has solidified an addiction to the convenience of fast food, deliveries, and travel, the demand for speedy service in all industries is increasing. Of course, the dental team certainly has incentive to work efficiently. This is driven partially by patient demand for shorter visits to minimize discomfort in the dental setting, but can mostly be attributed to industry pressures such as low insurance reimbursement rates and high overhead. Dental material manufacturers understand these challenges and have responded by offering simplified materials promoted with language that encourages faster placement to reduce treatment times.

In adhesive dentistry, however, faster doesn’t always mean better. In fact, rushing adhesive procedures often results in post-operative sensitivity, reduced longevity, and even catastrophic failure, which translates into return visits, zero-production redos, and increased frustration. While there has been impressive advancements in dental materials such as universal adhesives and bulk fill composites, these products have yet to surpass the quality and performance of two-step, gold standard adhesives and incremental placement techniques (Van Meerbeek et al, 2009). Either way, clinical success, independent of material choices, will ultimately be determined by the skill level and technique of the operator.

ABSOLUTE ISOLATION

There are many “isolation” strategies on the market, but no product offers the level of absolute isolation provided by a rubber dam. A properly placed rubber dam provides the operator and patient a clean surgical field free of moisture from breath, sulcular fluids, and saliva while retracting soft tissue and lips for maximum access and efficiency. Eliminating the need for the clinician or assistant to retract the lips or tongue can also help mitigate hand and wrist fatigue. As such, team members welcome and often favor the use of rubber dam in practice.

Though some patients protest rubber dam initially, they often welcome the idea of increased comfort by not having to endure excess water pooling, tooth and material debris, and risk for iatrogenic injury to soft tissues during treatment, in addition to the procedural benefits mentioned above. A clinician that communicates their intentions to patients not only shows they care about the patient’s comfort, but also that they prioritize the quality of their work.

With proper training, rubber dams can be placed efficiently in a matter of minutes by either the doctor and/or assistant. With a rubber dam employed, the clinician can efficiently prepare teeth, spread load the bonding protocol across multiple teeth, and even leave for hygiene checks or other tasks, giving dentin bonds ample time to mature without risk of contamination. Absent the absolute isolation offered by rubber dam, clinicians must battle multiple intra-oral variables that can prove catastrophic for an otherwise sound bonding protocol.

Anterior sextant therapy prior to air-particle abrasion and adhesive application. Sextant or quadrant strategies afford the clinician an opportunity to spread-load the bonding and restorative protocol across multiple teeth, allowing time for hybrid layer development free of competing stresses from composite placement.

TIME IS ON YOUR SIDE

The Biomimetic Restorative Dentist understands the importance of time in adhesive procedures and strategizes accordingly. Time is crucial particularly in dentin-rich scenarios where formation of a high-quality hybrid layer relies heavily on the ability of dentin bonds to fully mature free of stress. Stacking composite in large increments too quickly on a developing hybrid layer causes delamination at the dentin-adhesive interface as shrinkage stresses in the composite exceed the slowly developing dentin bonds (Alleman et al, 2021). This concept is appropriately referred to as the “adhesive equation” and is not unique to dentistry.

For example, the instructions for use for 3M’s Command Picture Hanging Strips advises users to wait 1 hour after application on a surface for the “adhesive to build” before loading. Given time to set, the load-bearing capability of these strips is still dependent on the surface they’re applied to as well as the surface area of the strip. Similarly, the total surface area of each unique tooth substrate, surface treatment of those substrates, and proper application of the adhesive according to the manufacturer's IFU contribute to the overall bond-ability of the tooth.

One misconception about adhesive dentistry is that enamel bonds are stronger than dentin. However, given adequate time and proper isolation, a two-step, gold-standard bonding system such as Kuraray’s SE Bond, SE Bond 2, or SE Protect can produce a bond to dentin up to twice the strength as the bond to enamel (Van Meerbeek et al, 2003). Respecting time requirements for bond maturation, regardless of the bonding system used, helps mitigate leakage, eliminate post-operative sensitivity without the need for additional desensitizing products (Brannstrom, 1986), and enhance bond performance.

Whether you're applying a Command Strip to the wall or bonding a tooth, the common denominator in achieving a successful outcome is time. Understanding how the adhesive equation applies to composite dentistry and altering one’s restorative protocol to accommodate the concept will help improve clinical outcomes, thus increasing doctor and patient satisfaction. Time is on your side - use it where it matters most.

Immediate Dentin Sealing (IDS) with CLEARFIL SE Protect and 0.5mm flowable resin coat with CLEARFIL Majesty Flow prior to matrix assembly. Dentin bond maturation begins at light cure and continues for 10-20 minutes (Sadr et al, 2019). Time required for matrix assembly mitigates stressing the developing hybrid layer too early, creating a secure bond strategy that prevents leakage and post-operative sensitivity (Krejci, 2000).

KEY TAKEAWAYS

There’s a popular military adage known as the 7 Ps used to emphasize the importance of planning to achieve mission success: Proper Planning and Preparation Prevents Piss Poor Performance. Indeed, success relies heavily on meticulous planning supported by reproducible protocols and the mitigation of any condition or risk that could compromise the mission. This is applicable not just in the military but all aspects of life, including in dentistry. Biomimetic Restorative Dentists seek to deliver the highest quality of care in adhesive dentistry through meticulous, evidence-supported, uncompromised restorative protocols.

Despite messaging from some manufacturers that might suggest otherwise, adhesive dentistry is a highly technique sensitive discipline that cannot be executed in a “simple way” (Van Meerbeek et al, 2001). Clinicians throughout the world routinely express frustrations with short- term longevity, staining, and post-operative sensitivity, while humbly seeking solutions to correct and prevent them. For most, the answer to making adhesive dentistry more enjoyable and predictable lies in developing a deeper understanding of dental adhesion, improving surgical field access and management with rubber dam isolation, and slowing down restorative workflows where time matters most.

Stay tuned for future articles that dive deeper into the biomimetic and adhesion concepts summarized here.

REFERENCES

Alleman, D.S; Alleman, D.S; Deliperi, S; Aravena Diaz, J; Martins, L; Keulemans, F. Decoupling with time. Inside Dentistry. Aug 2021.

Brannstrom M. The hydrodynamic theory of dentinal pain: sensation in preparations, caries, and the dentinal crack syndrome. J Endod. 1986 Oct;12(10):453-7. doi: 10.1016/ S0099-2399(86)80198-4. PMID: 3465849.

Krejci, Ivo and Minos M Stavridakis. “New perspectives on dentin adhesion--differing methods of bonding.” Practical periodontics and aesthetic dentistry: PPAD 12 8 (2000): 727-32; quiz 734.

Van Meerbeek B, De Munck J, Mattar D, Van Landuyt K, Lambrechts P. Microtensile bond strengths of an etch&rinse and self-etch adhesive to enamel and dentin as a function of surface treatment. Oper Dent. 2003 Sep-Oct;28(5):647-60. PMID: 14531614.

Van Meerbeek, B et al. “Adhesives and cements to promote preservation dentistry.” Operative Dentistry (2001): 119-144.

Van Meerbeek B, Peumans M, Poitevin A, Mine A, Van Ende A, Neves A, De Munck J. Relationship between bond-strength tests and clinical outcomes. Dent Mater. 2010 Feb;26(2):e100-21. doi: 10.1016/j.dental.2009.11.148. Epub 2009 Dec 16. PMID: 20006379.