The Biomimetic Smile Makeover

Conserving And Strengthening Tooth Structure While Transforming A Smile

Biomimetic dentistry is an interdisciplinary material science that is not only about creating the strongest restoration, but rather creating a restoration that is highly compatible with the structural, functional and biologic properties of underlying dental tissues, thereby reproducing and emulating the original performance and characteristics of the intact tooth. ¹ Literally translated ‘Bio-mimetic’ means to mimic life. We study nature’s properties so that we can better duplicate it. Biomimetic dentistry treats weak, fractured, and decayed teeth in a way that keeps them strong and seals them from the invasion of bacteria.

Biomimetic treatments started with conservative adhesive restorations of the anterior dentition in the 1980’s. Bonded porcelain veneers were shown to restore the functional biomechanics of anterior teeth by Pascal Magne in his 2012 book “Bonded Porcelain Restorations in the Anterior Dentition: A Biomimetic Approach”. Dr. Magne’s mentor at the University of Geneva, Switzerland, Dr. Didier Dietschi, published his book on posterior adhesive restorations in 1997. The University of Geneva and now the University of Southern California, where Dr. Magne teaches, are the leaders in this discipline.

Through biomimetic protocols we are able to develop highly bonded interfaces by utilizing stress reducing and bond increasing techniques. These protocols allow the treatment plans to eliminate full coverage restorations and reduces the need for cutting down sound tooth structure and helps to avoid root canal treatments by keeping the pulp vital whenever possible, since endodontically treated are become brittle and are more prone to fracture due to a lack of pulpal fluid in the dentinal tubules. ² For adhesive direct restorations the goal is to preserve tooth structure and maintain a vital pulp. The conventional cavity preparation, as outlined by G.V. Black, is no longer considered to be conservative or valid. ^{3, 4, 5} Retention form and resistance form have been eliminated because the highly bonded inter-phase of biomimetic protocols reconnects all parts of the tooth which mimics a natural tooth.

The amount of tooth structure removed during initial operative procedures has been demonstrated to have a direct correlation with the longevity of restorative procedures and an inverse relation to the strength of the remaining tooth structure. ^{6, 7, 8} The reduction of occlusal enamel is the first step towards the weakening of the crown portion of a tooth, causing that prepared tooth to behave like a tin can with the top removed, subject to cracks and the potential for interproximal caries. ^{9, 10}

The goals of Biomimetic Dentistry are to (1) eliminate any infection in dentin through the proper diagnosis and removal of caries, (2) prevent gaps or cracks into dentin through the diagnosis and treatment of structural compromises, (3) create a strong connection of all tissues, (4) prevent any internal stresses or strains, (5) to resist attrition, abrasion and erosion through the proper tooth preparation and restoration design, (6) and to function properly within the occlusal envelope of chewing motions. The path to achieving these goals is touched on in this article and referenced in our list of sources. However, a deeper understanding will require further course study and hands on training.

Although the most successful dentistry, in terms of durability and longevity, involve procedures that are the least invasive, the need for ideal esthetics often results in the sacrifice of sound tooth structure in order to achieve the patient’s esthetic desires. This article explores how to work up, stage and execute a biomimetic smile makeover that closely adheres to the principles and fundamentals of biomimetic dentistry without compromising the desired esthetic result.

Adhesive Dentistry – Staying Bonded

It has been stated that adhesive dentistry could be expressed as a simple relationship between bonds and stress. If the bonds can withstand the stress, the restorative technique will be successful. ^{11, 12} This is perhaps the most important concept of Biomimetic Dentistry. We want to increase the bond strength of the materials we use, reduce the stresses on the remaining tooth structure and maintain the seal of the restoration to prevent infection and fracture. Through the evolution and advancement of adhesive dentistry and improved protocols and techniques, we now have the ability to biomimetically reproduce the union between synthetic dental materials and natural anatomic tooth structures. ¹³ Reproducing the original performance of the intact tooth (“biomimetics”) should be the driving force in restorative dentistry. ¹

The protocol that we followed throughout this case includes several very important concepts. The first is the concept of conservative caries treatment that was established by Fusayama. ^{14, 15, 16} Ideal caries removal end points are indicated, including the creation of a peripheral seal zone and the absolute avoidance of pulpal exposure for vital teeth. ^{17, 18, 19} By creating a peripheral seal zone consisting of normal superficial dentin, DEJ and enamel, a bond strength of 45-55 MPa can be generated, to mimic the tensile strength of the DEJ, which has been measured at 51.5 MPa. ¹⁷ This peripheral seal zone will be confirmed by the total absence of caries detector (Kuraray) or Seek (Ultradent). A light pink staining from the dye is acceptable within this area and can still achieve a bondability of about 30 MPa. ^{17, 20} Additionally, studies have shown that the inner carious dentin can become remineralized by a normal biologic process following adhesive resin treatments. ²¹

Our protocol also involved making every effort to avoid cracks and gap formation in dentin. In the absence of dentin fractures or caries, enamel crack lines may not require treatment. However, if there is a crack in dentin, you should go to the bottom of the crack and eliminate the crack if possible, or it will continue to propagate. ²² The polyethylene fibers of Ribbond are proven to increase the fracture strength of teeth, by absorbing and diffusing forces, and help to resist crack opening and to also decrease the resin shrinkage and prevent more catastrophic failures from occurring. ^{23, 24,25} These fibers also help to increase the dentin bond strengths in areas with a high c-factor (configuration factor). ^{26, 27} The c-factor is the ratio of the bonded surface area to the unbounded or free surface area. ^{28, 29} It has been proven that teeth will fracture in a less catastrophic manner when these polyethylene fibers were applied under the direct composite resin restorations. ³⁰

A very important part of our bonding protocol involves using a 2% chlorhexidine solution on exposed dentin after phosphoric acid etching when using a total etch technique (such as with Optibond FL) in order to deactivate endogenous collagenase enzymes called matrix metalloproteinases (MMPs) and preserve the maximum bond strength. ^{31, 32, 33} By deactivating the MMPs a less pronounced water treeing affect can be observed, which means less degradation of resin-dentin bonds. ³⁴ Long-term water exposures are a factor known to promote bond degradation. ^{35, 36} We used Clearfil SE Protect (Kuraray) when bonding mostly to dentin because it contains an adhesive that forms an effective and stable ionic bond with the hydroxyapetite. ³⁷ Addidtionally, Clearfil SE Protect does not require chlorhexidine since it has a unique proprietary component that deactivates the MMPs, while other bonding systems will require the use of a 2% chlorhexidine to achieve the best bond strengths. ^{17, 38} Self-etching primers, such as SE Protect, does very well in deep dentin, and seem to be able to infiltrate through the smear layer into the underlying caries-affected dentin more easily than it would though normal dentin. ^{39, 40, 41, 42} Additionally, the milder acid etching effects of the self-etching primer may help to reduce that outward flow of fluid, resulting in superior dentin sealing. 43 Studies show that reliable dentin adhesive systems render the application of a liner or base unnecessary when it comes to protecting the pulp or to establishing adhesion. ⁴⁴ For our purposes we used Optibond FL (Kerr) and Clearfil SE Protect (Kuraray) because they are the gold standards of bonding, with studies showing the highest bond strengths and that they are least affected by aging. ^{45, 46} Other products would work well for our protocols would be All Bond 3 (Bisco), PQ1(Ultradent), or 3M Universal for adhesives and Vit-l-escence (Ultradent), Herculite (Kerr) or Z-100 (3M) for composite.

It is recommended that the dentin bonding agent be applied and cured onto the freshly cut dentin immediately after the preparation of the tooth, before any temporary cement is used for the indirect restoration. ^{47, 48} Indirect restorations require the immediate dentin sealing (IDS) of the prepared dentin surfaces in order to prevent bacterial contamination, temporary cement contamination and post-operative sensitivity. ^{49, 50, 51} IDS allows the dentin bond time to mature (decoupling time) before it is challenged by the polymerization stress of the resin cement layer or subsequent layers of the composite resin. ⁵² Since the dentin bond strength develops progressively over time, with the free radicals within the resin still available for bonding even after 12 weeks time, a delayed placement of the final restorations can often alleviate some of the residual stresses. ⁵³ During the IDS step it is important to use a substantial thickness of the adhesive layer, in order to partially absorb the composite deformation. Heavily thinned layers of bonding agents are subjected to severe oxygen inhibition and are therefore almost not cured despite being in the presence of the light for 40 seconds. ^{54, 55} The elastic release of the adhesive layer is an appropriate way to limit the intensity of the forces transmitted to the remaining natural tooth tissues. ⁵⁶

We used a 0.5 mm layer of flowable composite to resin-coat the dentin in order to produce a gap-free resin-dentin interface and improve the immediate dentinal sealing (IDS). ⁵⁷ The use of a flowable composite alone or in combination with the polyethylene fibers of Ribbond, significantly reduces leakage at the occlusal margins and at the gingival margins. ^{58, 59} A thick adhesive layer and the use of a flowable resin function as a stress-absorbing layer and helps to improve the effectiveness of the DBA in counteracting the polymerization stress at the resin-dentin interface. ^{60, 61, 62} Resin-coating not only protects the prepared dentin immediately after, but helps to minimize pulp irritation and post-operative sensitivity while also providing a higher bond strength to resin cement. ⁶³

The dentinal bonding systems we used were allowed to mature for 5 minutes in order to allow for more strain relief and decoupling time for the (IDS) technique, so that we could achieve the best bond strength, pulpal protection and minimal postoperative sensitivity. ^{17, 60, 64, 65} Dentin bonds take longer to mature. ⁶⁶ However, if given enough time, the bond to dentin will be higher than that to enamel because the cohesive strength to dentin is greater. ⁶⁷

By using an appropriate layering technique, we can increase the bond strengths, especially in areas with a high c-factor, where the deep cavity floors can affect the dentin adhesion. ^{62, 68} The layering technique is also designed to accommodate the polymerization contraction of composite resins and to partially absorb functional stresses. ⁵¹ Once a layer of resin is light cured, a competition between polymerization shrinkage of the composite and adhesion to the substrate begins. If the bond strength is weaker than the shrinkage stresses between the resin and adhesive system, the tooth-restoration interface may break, forming a gap that will allow for marginal microleakage (and sensitivity). ⁶² With time these residual stresses can be exacerbated under functional loads and may accelerate deterioration of the bond. ⁶⁹

Studies now show that composite does not shrink towards the light, but rather flows towards the most bondable surface, with the contraction stresses developing at the restoration-tooth interface. ^{69, 70, 71} If the polymerization of the resin proceeds gradually, the material may be able to release some of the stress and not be as damaging to the adhesive bonds. ⁷² Small layered increments of resin will lend itself to a more durable restoration, since a stronger composite-dentin bond can be formed when the polymerization contraction is restricted to one direction. ⁷³ It has also been proven that the slower the progression of the curing procedure, the more time is given for stresses to be relieved. ^{74, 75}

CASE PRESENTATION

In June of 2013, a 47 year old man presented to the author’s office with the chief complaint, “I have had 25 years of acid reflux and have lost a lot of enamel. I am interested in protecting and rebuilding my teeth without reducing much more tooth structure.” (Figures 1-9). He was also concerned about trapping food between teeth #’s 2 and 3. The patient had seen an endodontist for a swelling in the upper right area between the molars, which was drained but did not require root canal therapy, and he was advised by us to see the periodontist for a consultation to discuss all esthetic options and treatment plan for an implant to replace his missing upper left first molar. The author decided to take records for an esthetic wax-up in order to determine how much he would need to open up the vertical dimension of occlusion (VDO) in order to be able to create a more ideal smile utilizing the conservative biomimetic principles and achieving better facial harmony.

When viewing his maxillary teeth from an occlusal and lingual view, one can see the erosion and wear of his teeth (Figures 4, 6 and 7), and it becomes evident just how collapsed he actually is. This patient shows more teeth on his left side and less on the right when smiling, and the shortness and color of his teeth contributes to a definite aging of his smile. Additionally, his lips appear less full without the lip support of the lost tooth structure. The patient had a Class I molar relationships on both right and left sides, and a posterior open bite on his Right side in the area of 4-6 (Figures 8 and 9). There was no crowding evident and both arches were found to have lingually inclined teeth, which may have contributed to his wear. It was also noted that his posterior teeth were worn down with a very flat anatomy and lacked proper functional guidance.

CASE WORK-UP

A visual, periodontal and occlusal assessment was completed. Comprehensive records were taken, including: a full mouth series of x-rays, a complete set of photographs, diagnostic impressions, CR and protrusive bite records, and a preoperative facebow record (using the Artex articulator system) in order to take into account the occlusal cant and facial asymmetry that is not perceived in intraoral images or study casts. ⁷⁶ Our lab fabricated an analytic wax-up for the reconstruction of a functionally and esthetically reconstructed VDO, and then we performed an intraoral esthetic evaluation of the wax-up using a diagnostic putty template fashioned from the wax-up to create a matrix for creating an exact replica to be used as a starting point for the provisionals. We filled this template with a bis-GMA-based direct provisional material (luxatemp) and seated it over the isolated preexisting tooth structure. This allowed the patient to “try on” his potential new smile and helped him to envision the possibilities and have realistic expectations about what could be accomplished. The esthetic mock-up also served as a fixed occlusal splint for 2-3 months for the functional evaluation phase. The use of the provisional restorations represents an essential stage in the course of restorative treatment strategies and plays a critical role in preserving or reestablishing masticatory function, phonetics, and esthetic appearance. ⁷⁷ We made modifications in his temporaries to best compensate for any asymmetry and to balance and harmonize his smile. ⁷⁸ We evaluated his case following the requirements for occlusal stability as outlined by Dawson, and adjusted the set-up to create stable stops on all teeth when in centric relation, anterior guidance in harmony with the movements within the envelope of function, full posterior disclusion in protrusive movement, and no posterior interferences on the working or non-working side in canine guidance. ⁷⁹

Our first step included an appraisal of the maxillary central incisors relative to the upper lip, as would normally be done when the treatment planning sequence begins with esthetics. ⁸⁰ We took the time to set up the length and horizontal edge position of the maxillary incisors in the provisional stage to evaluate the envelope of function and to evaluate his speech, especially when pronouncing the “F”, “V” and “S” sounds. ^{79, 81, 82} The author had the curvature of the lower lip be the guide for the ideal smile arc from central incisor to canine. ⁸³ We utilized the additive/reductive technique to balance the harmony of the buccal corridors of his smile. Since most people have some degree of asymmetry, minimizing the buccal corridor space on either side and modifying it to create the illusion of symmetry is a critical feature of smile design. ^{84, 85, 86, 87, 88}

With the patient’s input, we decided to restore the severely damaged dentition with veneers and onlays on conservatively prepared teeth made from an e-max material, and to bond these restorations adhesively after caries excavation and biomimetic reconstruction of deficient tooth structure. We tried to avoid full coverage preparations whenever possible to maintain the integrity of the remaining tooth structure, however, tooth #15 was treatment planned to be prepared for a full coverage e-max crown only because it was replacing an existing crown on a previously prepared tooth. Additionally, an implant will be placed and restored with a PFM crown around a UCLA custom abutment in the area of #14.

THE RESTORATIVE PHASE

The patient’s maxillary temporary luxatemp (DMG America) reconstruction, based on the wax-up, was sectioned distal to tooth #6 so that we could prepare the upper right segment at our first visit. Bite registrations were taken so that the final restorations could be made to the new VDO. Teeth #’s 2 and 3 were structurally compromised but restorable; teeth #4 and 5 had a lot of acid erosion, but were otherwise sound. We had noted that the patient had a large interproximal food trap between 2 an 3, which at one point had caused an abscess to develop prior to our meeting the patient. He had seen an Endodontist to drain it prior to becoming a patient in our office. After removing the old failing bonded restorations and the recurrent deep caries, we performed laser troughing of the tissue surrounding the distal margin of tooth #3 with the NV soft tissue diode laser. We prepared teeth 2 and 3 using Clearfil SE Protect, a Self-Etching Primer and Adhesive system (Kuraray) and then resin coated with 0.5 mm of Clearfil Majesty Flow around any exposed dentin, with Ribbond embedded in the flowable resin. We applied about 1 mm of APX (Kuraray) since it has a modulus of elasticity similar to that of dentin and lower polymerization shrinkage. We then used a warmed Majesty (Kuraray) posterior composite in appropriate small increments to elevate the deeper gingival margin. 51 DME (deep margin elevation) aims to elevate the gingival margin to a level where it can be sealed with a rubber dam during the delivery of the restoration. 89 Additionally, relocating the cervical preparation supragingivally over the existing margin is a non-invasive alternative to a surgical crown lengthening in order to relocate cavity margins supragingivally. 90 Teeth #’s 2 and 3 were prepared for e-max onlays, and teeth 4 and 5 were prepared for e-max onlay/veneers after the palatal cusps were biomimetically reconstructed with incremental layers of bonding to reduce the cuspal strain. 91 Teeth 4 and 5 had IDS (indirect dentinal sealing) after they were prepared.

At his next visit, the temporary restorations were sectioned distal to #11 in order to prepare the upper left segment. Teeth 12, 13 were prepared in the same manner as 4 and 5, after moderate-deep caries was excavated from the facial cervical of #13, and small occlusal pit/fissure caries was excavated from#12 and 13. The palatal cusps of these teeth were also reconstructed in the same manner as 4 and 5 were. Tooth #15 had an e-max crown over a newly reconstructed core to replace his old failing crown, and the dentin was sealed prior to temporization. All of the posterior restorations were inserted using Fusion-Zr dual cure resin cement (Taub Products) and seated using Inlay/Onlay Styx (cosmetic Innovations, Inc.) to position and seat the restorations while using an EMS plastic tip to help vibrate out the excess cement for a more complete seal of the margins.

Teeth whitening had also been performed on his lower arch utilizing a combination of the custom home trays utilizing the Nite White gel for one week to precondition the teeth, followed by four rounds of the in-office ZOOM 2 Advanced Power whitening system (Philips). Initially he was determined to be a D3/C1 shade, and after the in-office procedure he lightened to a B1/040 shade. The patient wanted the final shade of his upper teeth to be a brighter version of A1, looking natural and bright, but not too white.

After the posterior teeth were inserted and his occlusion equilibrated, we performed a structured composite resin build up of the lingual portion of his maxillary anterior teeth 6-11, based off of his mock wax-up and the creation of a clear silicone putty palatal table, in order to allow for enhanced control of the final shape, form, shading and functionality. 92 We were able to relieve or add to the lingual resin in order to achieve better anterior coupling. The shades were layered in small increments to blend and to minimize the polymerization stresses. The teeth were then prepared for veneers instead of full coverage crowns to be more conservative to tooth structure.

Final Impressions were taken using Impregum regular and soft body (3M ESPE) along with a bite registration and counter model. Additionally, a stump shade photo was taken to assist the lab in knowing how to layer the porcelain to attain the desired effects and selected shade.

The veneers were tried in and a Rubber Dam was used to create adequate isolation and to ensure a clean, dry and easily accessible restorative environment. Optibond FL (Kerr Corporation) was subsequently used as our bonding agent, with Chlorhexidine 2 % used on the exposed dentin after etching. The veneers were cleaned and then prepared with silane. The veneers were seated two at a time utilizing Fusion-Zr light cured clear cement (Taub Dental Products), utilizing the Veneer Styx veneer positioning device (Cosmetic Innovations, Inc.) for the final insertion of the veneers (Figures 22-27), and used a plastic EMS tip in conjunction to help vibrate out the excess cement and achieve a complete seating of the restoration. After all veneers were inserted, the rubber dam was removed and we checked his contacts and then occlusion in centric, lateral crossover and protrusive movements. A night guard was made to help protect his investment.

At the conclusion of the planned treatment of his maxillary arch, the patient decided that he also wanted to restore his lower teeth as well to achieve optimum esthetics and protection of his worn dentition. We replaced the old, failing onlay with a new e-max onlay for tooth #18, performed direct biomimetic bonded reconstructions (in the same manner as described previously) for teeth #’s19 and 30 to replace his older inlay and failing onlay respectively. Tooth #31 had an e-max crown over a newly reconstructed core to replace his older failing crown, and the dentin was sealed prior to temporization. Teeth 20-29 were conservatively prepared for veneers. All restorations were sealed, temporized, and subsequently cleaned, isolated, tried-in, seated and adjusted in the same manner as described previously for his the maxillary restorations. His night guard was rechecked and adjusted in centric and excursive movements.

CONCLUSION

Rejuvenating one’s smile has the power to inspire self-confidence and rebuild one’s image. We, as a profession, need to perform our esthetic procedures utilizing the latest in dental materials, techniques and technology to preserve what our patients have, for as long as they have them. Invasive procedures and unnecessary reduction of tooth structure can eventually weaken the teeth and result in stresses and cracks, contributing to bacterial infections and tooth fractures, and the subsequent need for root canals, extractions, implants and bridges. By adhering to the principles and fundamentals of biomimetic dentistry outlined in this article we can achieve uncompromised esthetic results and give our patients the beautiful, healthy and youthful smiles that will help enable them to find new love, land that new job, give that extra edge in business and networking, and to simply just live a happier and healthier lifestyles.

DISCLOSURE

The author is Founder and President of Cosmetic Innovations, Inc. and the inventor of Veneer Styx and Inlay/Onlay Styx; both products were mentioned in this article.

ACKNOWLEDGEMENT

I would like to acknowledge the Alleman-Deliperi Center for Biomimetic Dentistry for helping to move our profession forward and for showing me what it means to stay bonded. In particular, I would like to thank Dr. David Alleman and Dr Simone Deliperi for helping to show me the way. I would also like to thank Dr. David Gerdole for his sharing his knowledge, especially with his Rubber Dam isolation techniques. Additionally, I would like to acknowledge our master ceramist Jason Kim and his entire Dental Laboratory team for their guidance and support throughout the planning and execution of this challenging smile makeover.

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