a biomimetic approach for achieving esthetic outcomes in ...biomimetic dentistry. 7. in particular,...

18 Winter 2018 • Volume 33 • Number 4

A Biomimetic Approach for Achieving Esthetic Outcomes in Severely Damaged Teeth

David Gerdolle, DMD, MScAndrea Fabianelli, DDS, MSc, PhD

Abstract Encountering severely decayed, damaged, and otherwise compromised vital teeth is commonplace in dai-ly practice. However, when they are located in visible posterior areas, a balance must be reached between achieving biomechanical stability and satisfying esthetic demands. Because there is no singular restorative or adhesive approach that can achieve all clinical, functional, and esthetic goals in all situations, a more open and pragmatic methodology is required. When based on the histo-anatomy of the natural tooth, the clinical protocol undertaken and the indirect restorations delivered can demonstrate natural integration and biomi-metic sustainability. This article describes the application of bio-emulation principles for delivering indirect partial-coverage, adhesively bonded restorations to treat severely damaged premolars.

Key Words: biomimetic dentistry, bio-emulation dentistry, inlays/onlays/overlays, ceramic, lithium disilicate, adhesion

ericaneumann

Sticky Note

Last modified 2/3/18 8:46 am

19 Journal of Cosmetic Dentistry

Gerdolle/ Fabianelli

…in the absence of significant tooth structure, it can be difficult both

clinically and technically to recreate the anatomical form and optical

properties synonymous with intact teeth.“

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Introduction Treating severely decayed, damaged, and otherwise com-promised vital teeth traditionally has been an esthetic challenge for restorative dentists. On the one hand, achieving the clinical goals of such treatment endeavors are predicated on preventing fractures in the weakened teeth, providing a substrate for prosthetic/restorative procedures, and restoring function. On the other hand, it also is of paramount importance to recreate natural es-thetics and optical properties

Historical Treatment Clinically, these concurrent objectives historically have been accomplished by first performing endodontic treat-ment (which may or may not have been necessary), plac-ing a post with core build-up, and ultimately seating a full-coverage crown restoration to help ensure long-term survival. Although the most common and certainly a well-documented prosthetic restorative approach, full-coverage crown restorations do present several drawbacks compared to the more minimally invasive techniques available today. Among potentially detrimental factors are biologic costs (e.g., subgingival margins/invasion of gingival sulcus),1 loss of tooth vitality, and difficulty in checking the restorative substrate.2

Additionally, in the absence of significant tooth struc-ture, it can be difficult both clinically and technically to recreate the anatomical form and optical properties syn-onymous with intact teeth.3 This is particularly true when decay results in interproximal tooth loss and/or presents in combination with Class V or non-carious cervical le-sions.

In fact, the interplay of remaining histo-anatomic structures (e.g., enamel/dentin) and the dimensions of re-maining coronal tooth substance influence strength and seamless optical properties.4 It is universally accepted that the type and amount of remaining tooth structure signifi-cantly affects the survival of restored teeth, improves frac-ture resistance, and contributes to esthetics.5

New ApproachesTherefore, it is not surprising that material and proto-col advances have enabled new and more conservative approaches to the restoration of severely compromised teeth. For example, adhesive resins have helped to pre-vent devitalization, endodontic therapy, and post-and-core placement in teeth where deep caries encroached on the pulp. By enabling bonding of traditional amalgam to dentin, adhesive dentistry has helped to create a “vital core” to preserve dentin and enamel and allow bonding of cast restorations.6

Adhesive dentistry has also allowed dentists to pro-vide significantly longer-lasting and more esthetic resto-rations that preserve greater amounts of dental tissue in

a manner consistent with the principles of bio-emulation and/or biomimetic dentistry.7 In particular, when indirect inlays, onlays, and partial-coverage restorations are planned with consideration of the principles of tooth anatomy, material science, and adhesive dentistry, dentists can deliver treatments that more closely mimic healthy tooth structure.4,5,7

Replacing and Replicating Tooth StructureTo replace and replicate tooth structure, dentists and laboratory technicians must understand the location, thickness, and distribu-tion of different coronal tooth substances; how those structures interact with light to affect esthetics; and how overall tooth anato-my influences strength.4,8 This practical knowledge, when applied to the case at hand, will dictate the type of restoration/coverage, restorative material selection, preparation design, and adhesive bonding and cementation protocol. Although there are multiple clinical indications for adhesively bonded indirect restorations for posterior teeth, there is no singular restorative or adhesive ap-proach that can achieve all clinical, functional, and esthetic goals in all situations. Rather, a more open and pragmatic methodology based on the histo-anatomy of the natural tooth (i.e., concept of bio-emulation) can lead to natural integration and sustainability of biomimetic bonded restorations.4,7,8

Restoration/Coverage and Material Selection <subhead>Biological imperatives (e.g., dentin-pulp complex), biomechanical requirements (e.g., anatomical frailty of premolars, in particular; centrifugal occlusal loads), and esthetic demands must be taken into consideration when determining ideal coverage and restor-ative materials. Overlays and partial coverage restorations fabricat-ed from indirect composites and ceramics are now well-recognized treatments for heavily compromised teeth.9,10 Material options for such restorations that have performed well clinically include com-posites and CAD/CAM-milled blocks (e.g., hybrid resin-ceramic materials). However, the authors’ lengthy clinical experience—and the focus of this article—is with ceramic materials.

Partial-coverage restorations can be fabricated from a number of ceramic materials (e.g., feldspathic porcelain, leucite-reinforced, lithium disilicate, glass-infiltrated ceramic), each of which demon-strates unique advantages and disadvantages. A limiting property of feldspathic porcelain is its weakness compared to other materials.

Among the most promising ceramic material for partial-coverage restorations is a glass ceramic containing lithium disilicate crystals (e.g., lithium disilicate).11 Lithium disilicate demonstrates good chemical stability as well as good clinical and mechanical perfor-mance, even when restorations are fabricated to thin thicknesses.12,13 However, at least 1 mm of occlusal reduction is advisable.

Because lithium disilicate is a glass ceramic, after hot-press or CAD/CAM processing is complete, the glassy matrix of the internal aspect of restorations must be etched with 4.9% hydrofluoric acid for 20 seconds, followed by application of a silane coupling agent (Figs 1a & 1b).14 For luting, a dual-cured adhesive resin cement or heated light-cured composite can be used.



Preparation Design In prosthodontics, universal methodology does not exist; rather, preparations should be based on the histo-anat-omy of the individual teeth being treated. A biomimetic approach to cases involving severely damaged teeth can lead to more conservative tooth preparations and esthetic final outcomes. The latter is of particular importance con-sidering patients’ increasing esthetic demands.

Unfortunately, preparations for premolar inlays, on-lays, and overlays present numerous technical challenges for the practitioner. An example is a situation in which the margins of an overlay invade the buccal area, making it difficult to establish an esthetic, homogeneous transi-tion between the indirect restoration and the tooth. How-ever, placing the overlay margins far from the gingival margins prevents the negative sequelae associated with subgingival margin placement, thereby reducing the risk of iatrogenic periodontal problems.

Practical Esthetic Bio-Emulation Based on these considerations and published literature, the au-thors advocate restoration and preparation designs for severely damaged teeth that not only are more durable and long-lasting, but which also safeguard and preserve as much remaining natural tooth structure as possible. Doing so will enable consideration and delivery of other conservative restorative options in the future, if needed. Therefore, the authors recommend placing full-coverage crown restorations only to replace old crowns and bridges, or in select complex esthetic cases.

Although delivering indirect partial-coverage, adhesively bond-ed restorations in premolars can occasion various clinical challeng-es, the following cases illustrate a specific clinical protocol for pre-dictably restoring severely damaged teeth according to biomimetic and bio-emulation principles.

Figure 1a: Representation of the laboratory steps required for fabricating a hot-pressed lithium disilicate overlay.

Figure 1b: Example of an esthetic lithium disilicate overlay restoration.


Case 1: Minimizing Invasiveness While Maximizing StabilityA patient presented with an asymptomatic mesially fractured vital premolar requiring amalgam replacement (Figs 2a & 2b). Even before undertaking any clinical protocol, the need to overlay the undermined, fissured, secondary decayed cusps was obvious.

Isolation and cleaning were performed first to prevent mois-ture or bacteria from contaminating the dentin wound. Taking into consideration the low elastic modulus of the underlying tissue (mainly dentin), tooth preparation and reduction was guided by 2-mm to 2.5-mm diamond burs (Meisinger Occlu-sal Reduction Kit, Komet; Lemgo, Germany) (Figs 3a-3c). In situations like this, which are typical for pre-restored and/or decayed teeth, such preparation allows adequate thickness for the clinician’s preferred composite or ceramic prosthetic mate-rial to compensate for the dentin’s low elastic modulus.

Additionally, to increase the enamel surface and promote better bonding capabilities (i.e., enamel rods oriented more toward a perpendicular axis) and improve restoration stabil-ity and esthetic integration, the margins were easily designed

Figure 2a: Preoperative buccal view of an asymptomatic mesially fractured vital premolar.

Figure 2b: Preoperative occlusal view of the premolar demonstrating the need to replace the amalgam restoration.

with a long, 30- to 45-degree inclined bevel or a slight cham-fer (Figs 4a & 4b). The high strength of the selected lithium disilicate restorative material (IPS e.max Press HT, ingot A2, Ivoclar Vivadent; Schaan, Liechtenstein), even in thin restora-tions, allowed the margins to be designed with very thin and sharp line angles.

An immediate dentin seal was established after tooth prep-aration to simultaneously protect the dentin-pulp complex and enhance bond strength through maturation of the hybrid layer.15,16 Establishing this essential “bio-base” would simplify overlay placement protocol by essentially separating dentin and enamel bonding, as adhesive bonding to dentin would already have been performed. Therefore, the only substrates the practitioner would need to address adhesively would be enamel and composite (Figs 5a & 5b).

The one-week postoperative view illustrates the mimetic behavior and satisfactory esthetic integration of the selected monolithic lithium disilicate partial-coverage restoration, es-pecially considering the low biological cost of the minimally invasive preparation (Fig 6).

It is universally accepted that the type and amount

of remaining tooth structure significantly affects

the survival of restored teeth, improves fracture

resistance, and contributes to esthetics.

“

“



Figure 3c: Preparations that enable suitable material thickness help compensate for low dentin elastic modulus.

Figure 3b: This type of preparation allows for adequate restorative material thickness.

Figure 3a: Cuspal and occlusal reduction was guided by 2-mm to 2.5-mm diamond burs.

Figure 4b: The margins were easily designed with very thin and sharp margins.

Figure 4b: The margins were easily designed with very thin and sharp margins.


Figure 5a: Buccal view of the final preparation with immediate dentin seal.

Figure 5b: Occlusal view of the completed tooth preparation immediately prior to cementation of the partial-coverage lithium disilicate restoration.

Figure 6: The mimetic behavior and satisfactory esthetic integration of the selected monolithic lithium disilicate partial-coverage restoration was evident at the one-week postoperative follow-up appointment.


Case 2: Balancing Biomechanical and Esthetic Requirements A patient presented with two adjacent mesial-occlusal-distal (MOD) amalgam-restored vital maxillary premolars that were sensitive to cold and during chewing (Fig 7). Typically, cracked and symptomatic teeth are good indications for cuspal cover-age restorations, while the concurrent presence of cervical ab-fractions indicates full-coverage crowns as a valuable treatment option. However, placing such restorations on these premolars would require removal of all the remaining enamel, which is the most ideal natural tooth tissue from a biomechanical perspective. Therefore, in such cases, addressing cervical and occlusal damage in an esthetic, biomimetic, and minimally in-vasive manner can be particularly challenging.

To balance biomechanical and esthetic requirements, the decision was made to restore these premolars with direct composite restorations at the cervical aspect during the first appointment (Figures 8a & 8b) and ceramic overlays on the


Figure 7: A patient presented with two adjacent MOD amalgam-restored vital maxillary premolars that were sensitive to cold and while chewing; abfractions were also present.

Figure 8a: The cervical areas were restored with direct composite restorations during the first appointment.

Figure 8b: Buccal view of the direct composite cervical restorations.

occlusal aspect at subsequent appointments. By preserving a 2-mm high enamel rim, this approach would realize biome-chanical benefits but also present potential drawbacks. These included the esthetic challenge of placing the margin almost in the middle of the buccal surface, and inherent differences among the optical properties of the cervical composite, enam-el stripe, and ceramic. Additionally, the technique is demand-ing, time-consuming, and less profitable. Therefore, the final outcome for this type of preparation and treatment approach must be considered by balancing the importance of biome-chanics and esthetics.

The amalgams were removed during the second appoint-ment. The height-to-width ratio of the remaining dental walls, combined with the presence of multiple dentin cracks, neces-sitated a more invasive preparation involving full cuspal cover-age (Fig 9a). The preparation depth was approximately 2 mm to 3 mm, as described in Case 1. Immediate dentin sealing and composite buildup were also achieved. As in Case 1, at the completion of the preparation appointment, enamel and composite were the only two substrates for the practitioner to address during the cementation appointment (Fig 9b).

At the cementation appointment, a preheated restorative composite (Estelite Sigma Quick A4, Tokuyama Dental; Tokyo, Japan) was used to bond two monolithic lithium disilicate ce-ramic overlays (IPS e.max Press HT, ingot A2). These materials were selected based on their mechanical and optical proper-ties, easy handling, and extended working time (Figs 10a & 10b). A radiograph was taken to verify proper adaptation of the restorations (Fig 11).

Full-coverage crown restorations could have been selected for a patient with high esthetic demands. However, although the treatment approach described here may appear to offer an esthetic compromise for the sake of biomechanical predict-ability, the clinical result after six months proved acceptable (Fig 12).


Figure 10a: A preheated restorative composite was used to bond two monolithic lithium disilicate ceramic overlays.

Figure 10b: Buccal view immediately following cementation.

Figure 17: Following application of the adhesive luting composite, the inlay is inserted into the cavity.

Figure 12: Six-month postoperative view demonstrates acceptable results.

Figure 9a: The amalgam restorations were removed during the second appointment.

Figure 9b: Immediate dentin sealing and composite buildup were accomplished.



Case 3: Ensuring Durable Bonds and Intimate Fit A patient presented with a maxillary second premolar requir-ing restoration. To ensure a large, clear, and comfortable op-erating field, the entire quadrant was isolated (Fig 13). This would also facilitate adhesive cementation and enable easier handling of the luting composite.

However, because hydrophobic resins that are placed di-rectly on dentin as the adhesive bonding layer must be cured separately to achieve a proper hybrid layer, the authors’ proto-col was to immediately seal the dentin during the cavity prepa-ration appointment. Therefore, two substrates—a composite base and peripheral enamel—were prepared. The clinical pro-tocol was initiated by cleaning and roughening the cavity sur-face to promote micromechanical retention.

With the adjacent teeth protected by a metallic matrix band, a hand-held microblaster (CoJet Prep/CoJet Sand, 3M ESPE AG; Seefeld, Germany) was used. Once the composite base (i.e., immediate dentin sealing layer) was complete, the mi-croblaster was used to blast sand particles directly onto the composite surface. During this process, the impact energy pro-duced via tribochemistry a ceramic-like coating on the treated surface.

The ultimate enamel preparation still required etching with phosphoric acid (30% to 37%) for 20 to 45 seconds, even though previous sandblasting improved the enamel surface. Any phosphoric acid overflow did not affect the sandblasted composite surface, with the exception of possibly producing a further cleaning action (Fig 14).

Because adhesive bonding on the tooth surface encom-passes micromechanical and chemical bonds, a subsequent application of silane (Ceramic Primer II, GC Europe; Leuven, Belgium) was required to produce chemical bonds between the treated surface and the luting composite. During silani-zation, plumber’s tape was applied to neighboring teeth and thick floss (SuperFloss, Oral B, Procter & Gamble; Cincinnati, OH) was wedged in between the proximal margins and the rubber dam to facilitate removal of luting composite overflows (Fig 15).

Ideally, the silane layer remained thin. Some heat was ap-plied via a curing unit to improve the silanization reaction (Le Chatelier’s principle)17 and evaporate the resulting water by-product. Significant care was taken to not simultaneously overheat the pulp.18 For this reason, the authors strongly rec-ommend proceeding to cementation without administering local anesthesia19; this will enable the patient to inform the practitioner of any discomfort, including overheating of his or her lips or gingiva.

During the cementation appointment, a thin layer of un-filled hydrophobic adhesive resin (Scotchbond Multi-Purpose, 3M ESPE) was applied to the entire cavity surface (i.e., imme-diate dentin sealing layer) to promote an intimate adaptation between the luting composite and the pretreated surface, as well as improve micro-retention (Fig 16). Regardless of the lut-

ing composite type and its viscosity, none can fully penetrate the micro-irregularities previously produced by airborne parti-cle abrasion. Therefore, to ensure the inlay restoration inserted thoroughly into the cavity for an intimate fit, the unfilled ad-hesive resin was not polymerized.

An adhesive resin cement with ideal mechanical and opti-cal properties was selected. However, despite its high viscosity, pre-heating at 60°C for 15 minutes (Calset composite heater, AdDent; Danbury, CT) was required to reduce the cement’s vis-cosity. This would allow the resin cement to flow gently from the cavity during inlay insertion—first with manual pressure, then via ultrasound (Electro Medical Systems; Nyon, Switzer-land) (Fig 17). The viscosity would increase as the composite cooled.

Although the practitioner has approximately 60 seconds to completely seat the inlay restoration, he or she can enjoy unlimited working time to remove excess luting composite from margins, as the composite is completely light-cured. However, ambient light should be reduced to prevent early and unexpected polymerization. Polymerization is a crucial procedure in the clinical protocol; in this case, it was achieved using two curing units at different angles simultaneously (Fig 18).20 Glycerin gel was applied to cover the entire area to al-low polymerization of the oxygen inhibited layer as well (Fig 19). Following removal of the rubber dam, the occlusion was checked carefully (Fig 20).

…a more open and pragmatic

methodology based on the histo-

anatomy of the natural tooth

(i.e., concept of bio-emulation)

can lead to natural integration

and sustainability of biomimetic

bonded restorations.

“

“


Figure 13: After isolation with a rubber dam, the tooth surface was cleaned and roughened.

Figure 14: The enamel preparation required etching with phosphoric acid.

Figure 15: The composite base was conditioned with silane.

Figure 16: A thin layer of unfilled hydrophobic adhesive resin was applied to the entire cavity surface.

Figure 17: Following application of the adhesive luting composite, the inlay is inserted into the cavity.

Figure 18: Polymerization was achieved using two curing units at different angles simultaneously.


Summary Although treating severely decayed, damaged, and otherwise compromised vital teeth is commonplace in daily practice, do-ing so has traditionally represented an esthetic challenge for restorative dentists. However, if the histo-anatomy of the natu-ral tooth is considered when selecting and executing clinical protocol, indirect partial-coverage restorations can be placed to provide esthetic integration, biomimetic sustainability, and functional durability in visible posterior areas. As illustrated in the three cases presented here, bio-emulation principles can help dentists achieve a balance between biomechanical stabil-ity and esthetics when treating severely damaged premolars in a minimally invasive way.

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Figure 19: Glycerin was used to cover the entire tooth-restoration interface.

Figure 20: After removal of the rubber dam, the occlusion was verified.



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Dr. Gerdolle is an instructor at Garancière University, in Paris,

France. He owns a private practice in Montreux, Switzerland.

Dr. Fabianelli is a visiting lecturer at the University of Genoa, in

Genoa, Italy, and the University of Brescia, in Brescia, Italy. He

owns a private practice in Cortona Arezzo, Italy.

Disclosures: The authors did not report any disclosures.

A biomimetic approach to cases

involving severely damaged teeth

can lead to more conservative

tooth preparations and esthetic

final outcomes.

“

“

a biomimetic approach for achieving esthetic outcomes in ...biomimetic dentistry. 7. in particular,...

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