Slavkin HC Biomimetics: replacing body parts is no longer science fiction. J Am Dent Assoc. 1996; 127:1254-1257
Magne P, Douglas WH Rationalization of esthetic restorative dentistry based on biomimetics. J Esthet Dent. 1999; 11:5-15
Changqi X, Xiaomei Y, Walker M, Wang Y Chemical/molecular structure of the dentin–enamel junction is dependent on the intratooth location. Calcif Tissue Int. 2009; 84:221-228
Banerjee A, Frencken JE, Schwendicke F, Innes NPT Contemporary operative caries management: consensus recommendations on minimally invasive caries removal. Br Dent J. 2017; 223:215-222
Salis SG, Hood JAA, Kirk EJE, Stokes ANS Impact-fracture energy of human premolar teeth. J Prosthet Dent. 1987; 58:43-48
McDonald A, Setchell D Developing a tooth restorability index. Dent Update. 2005; 32:343-348
Xie KX, Wang XY, Gao J Fracture resistance of root filled premolar teeth restored with direct composite resin with or without cusp coverage. Int Endod J. 2012; 45:524-529
Magne P, Boff LL, Oderich E, Cardoso AC Computer-aided-design/computer-assisted-manufactured adhesive restoration of molars with a compromised cusp: effect of fibre-reinforced immediate dentine sealing and cusp overlap on fatigue strength. J Esthet Rest Dent. 2012; 24:135-146
Magne P, Douglas WH Cumulative effects of successive restorative procedures on anterior crowns flexure: intact versus veneered incisors. Quintessence Int. 2000; 31:5-18
Stokes AN, Hood JAA Impact fracture characteristics of intact and crowned human central incisors. J Oral Rehab. 1993; 20:89-95
Edelhoff D, Sorensen JA Tooth structure removal associated with various preparation designs for posterior teeth. Int J Perio Rest Dent. 2002; 22:241-249
Edelhoff D, Sorensen JA Tooth structure removal associated with various preparation designs for anterior teeth. J Prosthet Dent. 2002; 87:503-509
Porcelain versus composite inlays/onlays: effects of mechanical loads on stress distribution, adhesion and crown flexure. Int J Perio Rest Dent. 2003; 23:543-555
Edelhoff D, Guth JF, Erdelt K Clinical performance of occlusal onlays made of lithium disilicate ceramic in patients with severe tooth wear up to 11 years. Dent Mater. 2019; 35:1319-1330
Buonocore MG A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res. 1955; 34:849-853
Van Meerbeck B, Yoshihara K, Landuyt KV From Buonocore's pioneering acid-etch technique to self-adhering restorations. A status perspective of rapidly advancing dental adhesive technology. J Adhes Dent. 2020; 22:7-34
Nakabayashi N, Kojilma K, Masuhara E The promotion of adhesion by the infiltration of monomers into tooth substrates. J Biomed Mater Res. 1982; 16:265-273
Magne P Immediate dentine sealing: a fundamental procedure for indirect bonded restorations. J Esthet Rest Dent. 2005; 17:144-154
Goulart M, Veleda B, Damin D Preheated composite resin used as a luting agent for indirect restorations: effects on bond strength and resin–dentin interfaces. Int J Esthet Dent. 2018; 13:86-97
Poskus LT, Meirelles RS, Schuina VB Effects of different surface treatments on bond strength of an indirect composite to bovine dentin. Indian J Dent Res. 2015; 26:289-294
Vailati F, Gruetter L, Belser UC Adhesively restored anterior maxillary dentitions affected by severe erosion: up to 6-year results of a prospective clinical study. Eur J Esthet Dent. 2013; 8:506-530
Attin T, Filli T, Imfeld C, Schmidlin PR Composite vertical bite reconstructions in eroded dentitions after 5.5 years: a case series. J Oral Rehab. 2012; 39:73-79
Conrad HJ, Seong WJ, Pesun IJ Current ceramic materials and systems with clinical recommendations: a systematic review. J Prosthet Dent. 2007; 98:389-404
Schlichting LH, Maia HP, Baratieri LN, Magne P Novel-design ultra-thin CAD/CAM composite resin and ceramic occlusal veneers for the treatment of severe dental erosion. J Prosthet Dent. 2011; 105:217-226
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Vailati F, Carciofo S CAD/CAM monolithic restorations and full mouth adhesive rehabilitation to restore a patient with a past history of bulimia: the modified three-step technique. Int J Esthet Dent. 2016; 11:36-56
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Significant changes in prosthodontic considerations, with a movement away from traditional restorations and an emphasis on preservation of tooth structure, have led to the development of the concept of biomimetics in restorative dentistry. The idea of being able to design restorations, which are able to restore accurately the biomechanical, structural and aesthetic integrity of the biomechanically weakened tooth, has been embraced and adopted by clinicians globally. By combining key prosthodontic principles relating to occlusal design and the control of forces on teeth and restorations, together with minimally invasive adhesive dentistry, we are able to predictably restore the function and aesthetics of damaged dentitions without the need for aggressive tooth structure removal. Advances in dental materials science allowing minimal preparations and restorations that are strong and durable in thin section, as well as advances in adhesive dentistry have meant that the biomimetic restoration of teeth is no longer a novel concept, but something that we should all be applying as conservative and restorative dentists.
CPD/Clinical Relevance: This paper describes the rationale and clinical protocols involved in the application of biomimetic restorative dentistry.
Article
The concept of biomimetics was defined by Dr Harold Slavkin in 1996 as ‘the study of biological structures and their functions, providing a strategy to develop synthetic pathways to mimic biological processes'1 essentially, striving to mimic nature. For us as dentists, the model that we aim to recreate is the natural tooth.
The concept of patients being able to regenerate their own body parts would be the ideal. Much research in the field of tissue engineering has been focused on methods to be able to ‘grow’ a natural tooth within the oral environment using the patients’ own cells. However, this is far from being applicable to daily restorative dental practice.
So, what can we do today with the materials and techniques we have available to us right now? Pascal Magne and his team have extrapolated the biomimetic principle into the field of restorative dentistry. They advocate designing a restoration to restore the specific biomechanical, structural and aesthetic properties of the natural tooth.2
The natural tooth has a unique biological configuration, which means it can function in the incredibly demanding oral environment. Teeth are subject to high occlusal loads (compressive, tensile, shearing), fluctuating temperatures, chemical fluctuations, all within a moist environment. The structure of the natural tooth incorporates a hard, brittle and glass-like enamel outer layer, which is supported by a more elastic and resilient dentine. The enamel is characterized as a highly mineralized (96% mineral, 1% organic matrix) prismatic structure that is extremely strong and rigid. The dentine, in comparison, is less mineralized (70% mineral, 20% organic material) and made up of a network of dentinal tubules allowing transmission of various stimuli to the vital pulp. The dentine and enamel are bonded together at the enamel–dentine junction (EDJ) – the critical interface. The EDJ exists as a scalloped border where collagen fibrils extend from the dentine into the enamel allowing deflection of crack propagation through the tooth structure.3 In this way, the EDJ facilitates the dissipation of occlusal loads through the tooth to the periodontal structures, without resultant fracture or deformation. The pulp and periodontal tissues provide the ‘life’ of the tooth allowing reparative and protective responses to occur. The natural tooth, therefore, demonstrates the unmatched compromise between stiffness, strength and resilience, and it is this that we must try to emulate.
When a tooth is subjected to pathological processes (dental caries, traumatic fractures, fractured weakened cusps, tooth wear), the structural integrity and mechanical balance of the tooth is altered. Essentially, we lose much of the hard protective enamel shell. The tooth is weakened as a result of the loss of rigidity imparted by the enamel, the dentine is exposed, risking deformation and wear, and allowing bacterial ingress, placing the pulp at risk. The aims of the restorative procedure are, therefore, to try to return the tooth to its original biomechanical status by using adhesively bonded materials to cover the exposed dentine, restore the tooth rigidity and protect the remaining tooth structure.2
Current restorative materials cannot fully restore the delicate biomechanical balance of the natural tooth. However, the biomimetic restorative approach advocates materials and methods whereby we can come close, especially with the use of adhesively bonded ceramic and composite restorations.
Restoration design for the biomechanically weakened tooth
For small lesions, a minimally invasive approach should be taken. This requires promotion of natural remineralization and lesion arrest, ensuring cavity seal and restoration of tooth form without extensive removal of coronal dentine with invasive operative procedures. Recent consensus recommendations for caries management give evidence that 'supports minimally invasive carious lesion management, delaying entry to, and slowing down, the destructive restorative cycle by preserving tooth tissue, maintaining pulp sensibility and retaining the functional tooth-restoration complex long-term'.4 In those cases where a minimal restoration is required to restore tooth form, the placement of a simple direct composite restoration to ensure cavity seal will suffice to restore the tooth to normal form and function.
The challenge for restoration design comes when more tooth structure is lost, rendering the tooth significantly biomechanically weakened.
In posterior teeth, the loss of substantial coronal tooth structure can significantly weaken the cusps and increase the risk of fracture.5 The cavities are surrounded by tall, thin walls of enamel and dentine, which are unsupported and subject to increased flexure. The key anatomical component seems to be loss of one or more marginal ridges rendering the tooth significantly biomechanically weakened.6 Placement of a direct bonded restoration into such a cavity without cuspal coverage has been shown to be less effective at restoring fracture toughness than when full cuspal coverage is applied.7 Therefore, biomechanically weakened posterior teeth would benefit from full cuspal coverage restorations, to restore tooth rigidity and occlusal form. This has been demonstrated in various studies. Impact loading of weakened posterior teeth showed that restoration with full cuspal coverage onlay restorations (metallic, ceramic or composite) restored the fracture toughness of these teeth.5,7,8
In anterior teeth, the facial and palatal enamel has been shown to be a key contributor for tooth strength and rigidity. Loss of significant facial/palatal enamel can increase tooth flexure. These teeth would benefit from rigid adhesively bonded restorations. Labial ceramic or composite veneers, or all-ceramic adhesively bonded crowns have been advocated in these cases restoring tooth rigidity to 100% and 80%, respectively, of the natural tooth.9,10 Similarly, in cases where a substantial amount of palatal enamel is lost, various authors have advocated the placement of palatal veneers made from composite of gold to restore tooth form. In the same way, we can presume that this restoration design will also restore tooth rigidity.
The final category is, of course, the root-treated tooth – anterior or posterior – where a substantial amount of tooth structure has been lost, as well as tooth vitality, meaning these teeth need strengthening and protection long term.5,7,9
By using the natural tooth as our model, specifically the lost enamel, we can define the optimal characteristics of the ‘biomimetic’ restoration for the biomechanically weakened tooth as follows:
Stiff: resistant to bending under normal loads;
Strong: can withstand high loads in function without fracture;
Adhesive: bonds to underlying tooth structure to allow dissipation of occlusal loads (mimicking the EDJ);
Aesthetic: restores the natural aesthetics of the tooth.
Traditional, indirect restorations using metallic materials and full coverage preparations were designed to envelop and ‘brace’ the weakened tooth. These restorations are very rigid and strong and are successful restorations in most cases, especially if care is taken with restoration design and tooth preparation. However, during the past two decades, the biological cost of traditional crown and bridge preparations – the substantial loss of coronal tooth structure leading to potential loss of pulp vitality – has become a critical aspect to consider.11,12 Indeed, several studies have shown that full coverage preparations on anterior and posterior teeth, using extremely rigid metallic materials can actually weaken the tooth further. Removal of coronal tooth structure at the critical cervical region of the tooth, and the of use metallic restorations with rigidity much higher than the natural tooth, can lead to catastrophic failure (root fracture and decoronation).5,9,10
In comparison, partial coverage restorations are much more conservative, resulting in up to 30% loss of coronal tooth tissue, compared with up to 75% for full coverage preparations.11,12 Partial coverage restorations using ceramics or composite resins have been shown to behave in a more biomimetic manner by restoring tooth rigidity to values similar to the natural tooth, maintaining pulp vitality, demonstrating retrievable fracture patterns and showing good long-term survival rates for anterior and posterior teeth.5,9,10,13,14 The design of the partial coverage restoration is critical (Figures 1 and 2). Biomechanically weakened posterior teeth should, in most instances, receive full cuspal coverage for protection from fracture using adhesively bonded onlay restorations where possible.5,8,13 Weakened anterior teeth, where a substantial amount of tooth structure (facial/palatal enamel) has been lost, should be restored with ceramic or composite veneers, or adhesively bonded all-ceramic crowns to restore tooth rigidity.9,10
Figure 1. (a–c) Ceramic onlay for the biomimetic restoration of the biomechanically weakened posterior tooth. (a) Tooth preparation for an IPS e.max monolithic ceramic onlay with full occlusal coverage. The preparation requires sufficient occlusal reduction for the monolithic lithium disilicate onlay (0.8–1.5 mm). Note the conservation of enamel and dentine at the critical cervical one-third of the tooth. Sufficient enamel is present for predictable adhesive cementation. (b) IPS e.max monolithic onlay cemented restoring occlusal form, tooth rigidity and aesthetics. (c) IPS e.max monolithic onlay cemented restoring occlusal form, tooth rigidity and aesthetics.Figure 2. (a–f) Indirect composite partial coverage crown for biomimetic restoration of the biomechanically weakened anterior tooth. (a) Pre-operative image of the UL2 that has suffered a complex enamel and dentine fracture. (b) Long-cone periapical radiograph shows a vital tooth with no root fractures. (c) and (d) The tooth was prepared for an adhesive indirect composite partial coverage crown. The preparation was minimal, providing a finishing line for the technician, but preserving crucial labial and palatal enamel. Vitality was preserved. (e) Postoperative image after adhesive cementation showing excellent aesthetics. (f) 1-year recall and the tooth is functioning well.
Adhesion
One criterion for biomimetic restoration, is that it is adhesively bonded to the underlying tooth structure. The ‘acid-etch technique’ for bonding to enamel was introduced to the profession by Buonocore in 1955.15 Since then, we have not seen many changes in the protocols to enamel bonding, which means it works, is predictable and provides durable bond strengths of 16–20 MPa between the restorative resin and the etched enamel.16 So, the key to success is to maximize enamel bonding wherever possible. Partial coverage tooth preparations mean that there is often a lot of enamel remaining on the tooth preparation, and at the peripheral margins, which can be bonded to.
Bonding to dentine is not so straightforward and has been the focus of adhesive dentistry since the 1960s. In 1982, Nakabayashi discovered that it is possible to create an intermediary ‘hybrid layer’ whereby resin tags extend into the superficial demineralized collagen matrix providing a micromechanical bond.17 However, simply extrapolating the etch and rinse protocol from enamel to dentine presented some hurdles. Problems with the collapse of the collagen fibrils, trying to achieve ‘wet bonding’ and creating an adhesive bond that is stable over a long time have been challenges.
The primary mechanisms for adhesion have been identified by Van Meerbeck as:
In order to develop a durable bond, each of these principles must be maximized wherever possible. Dentine is an intrinsically wet tissue, and so the bonding agents must initially have an element of hydrophilicity to allow wetting of the etched dentine. The bonding agents must then polymerize into a hydrophobic state to allow long-term bond stability. Many different protocols have been presented to achieve this dentine bond, also with efforts to reduce the technique sensitivity of the protocols. In a recent literature review, Van Meerbeck and co-authors summarized the extensive options available for optimal bonding to dentine and have recommended two ‘gold standard’ approaches for predictable and durable dentine bonding.16
Full etch and rinse protocol
A three-step protocol requiring etching of the enamel and dentine with phosphoric acid for 15 seconds, application of a hydrophilic primer and subsequent application and curing of the unfilled resin.
Recommended system: Optibond FL.
Selective enamel ‘etch and rinse’ and the self-etch protocol
Selective enamel etching for 15 seconds, followed by the self-etch two-step protocol requiring mild etching of the dentine together with priming, followed by application of the resin. Recommended system: Clearfill SE. Additionally, Pascal Magne has documented the protocol of immediate dentine sealing, which has demonstrated superior bond strengths compared with delayed dentine sealing for the adhesive cementation of indirect restorations. The protocol advocates sealing of the freshly cut dentine with a minimally filled resin immediately after tooth preparation. This allows selective etching and wetting of the dentine, formation of a deep hybrid layer with freshly cut exposed dentine tubules, and maturation of the bond prior to cementation. The enamel margins are cleaned of any dentine bonding agent prior to impression making. When it comes to cementation, the bonding agent on the dentine is reactivated by sandblasting, and the preparation etched for enamel bonding. The technique maximizes dentine and enamel bonding and reduces post-operative sensitivity.18
However, as with all dental restorations, no matter how much care is taken with the adhesive bonding protocol, it still remains the weakest link in the system. Therefore, we must not discard the key to prosthodontic success – the control of loads and forces on the tooth, restoration and adhesive bond.19 The design of the occlusal scheme is critical for the loading on the restoration. Partial coverage, adhesively bonded restorations rely almost solely on the adhesive cement for retention due to the reduced retention and resistance form of the tooth preparation. Therefore, care must be taken to load the restoration, and subsequently the cement, in compression wherever possible. Minimizing shear forces on the restorations will aid in the guaranteeing the longevity of the adhesive bond.
Restorative material
Bearing in mind the criteria established earlier in this article for the biomimetic restoration of the biomechanically weakened tooth, there are three materials that we can consider:
Composite resin;
Ceramic;
CAD-CAM hybrid composite resins.
Various studies have documented the use of these materials for the restoration of damaged dentitions, often as a result of tooth wear. There is no clear consensus on which material is superior, and the choice of restorative material can be based on several factors – restorative space, occlusal scheme, differential wear, aesthetic demands, to name a few. What is clear is that all materials are shown to perform well over time periods from 5 to 15 years.
The use of direct and indirect composite resin has been shown to significantly strengthen the biomechanically weakened tooth.9,13Figures 3 and 4 illustrate how single teeth can be restored with direct resin application to provide strong and aesthetic restorations, when carried out by a skilled clinician.
Figure 3. (a, b) Direct composite onlay for the restoration of the biomechanically weakened tooth. (a) Tooth preparation of a heavily broken-down molar. Full occlusal reduction and preservation of cervical enamel, allows adhesive bonding of a direct composite onlay. (b) An aesthetic and functional result, allowing preservation of pulp vitality.Figure 4. (a, b) Direct composite for the restoration of the biomechanically weakened anterior tooth (a) Central incisor suffered enamel and dentine fracture (b) Restoration with a direct composite, restoring tooth rigidity, aesthetics and function without aggressive restorative procedures.
When restoring multiple teeth, the use of indirect laboratory-made restorations can be more predictable, allowing control of the occlusion, contact points and aesthetics. The use of predominantly indirect composite resin for the restoration of the worn dentition is illustrated in Figure 5. The patient has suffered substantial loss of coronal dentine from erosive tooth wear. The dentition was restored using biomimetic principles – partial coverage, adhesively bonded restorations. The teeth were minimally prepared and restorative space was created by increasing the occlusal vertical dimension. The indirect composite restorations were cemented using a preheated composite resin as a luting agent to facilitate seating of the restoration and easier clean up, owing to the decreased viscosity of the luting composite.20 The protocol for surface treatment of the indirect composite that is advocated to provide the most predictable bond is sandblasting with aluminium oxide, and subsequently cleaning the fit surface with ethanol and water, followed by application of a suitable primer.21 The use of silane gives inconsistent results in the literature and, hence, was not used in this case. The key in this case, and arguably in every adhesive case, is the design of the occlusal scheme, allowing all restorations to be loaded in compression as much as possible, reducing the stress on the adhesive bond.
Figure 5. (a–d) Composite resin for the restoration of worn anterior and posterior teeth – a combination of direct and indirect composite restorations restoring function and aesthetics, using biomimetic principles. (a) Pre-operative image of a dentition that has suffered erosive wear resulting in loss of enamel and dentine. Careful planning with a diagnostic wax up allowed additive and adhesive restoration of the case. (b) Restoration of the upper and lower anterior teeth with indirect composite palatal veneers, and direct composite restorations, respectively. (c) Minimal preparation of the worn lower posterior teeth for adhesive composite onlay restorations. (d) Full mouth rehabilitation of the worn dentition with purely additive and adhesive composite resin restorations. The restoration of function and aesthetics has been achieved, using a biomimetic approach.
Restoration of the worn dentition with indirect composite resin has been documented by many authors, showing good success rates up to 10 years.22,23,24 The authors used minimal preparation adhesive restorations to restore both anterior and posterior teeth. Major failures were not noted, but a small number of minor failures was seen in the form of minor chipping/wear and some marginal staining. The restorations affected were easily repaired or replaced. These results are reassuring, advocating indirect composite resin as a material of choice to provide long-term serviceable biomimetic restorations.
At present, we have seen a surge in the application of all ceramic materials for tooth restoration. The most popular ceramic materials are those in which strength and aesthetics have been combined – unique all-ceramic systems combining a strong ceramic core material, which can be layered, with traditional glass-based ceramics for optimal aesthetics, if required. There are various systems available, but in order to achieve a biomimetic restoration, we would require an all-ceramic system that can be adhesively bonded to the tooth – an etchable ceramic. The improved lithium disilicate pressed glass-ceramic material (IPS e.max) was introduced in 2005 and is now available as a milled restoration. This material shows the optimal balance between strength and aesthetics.25 Giving flexural strength values of 350–400 MPa, and showing excellent results in thin section (minimum 0.8 mm), it is ideal for use in the posterior region in its monolithic form.2627 For restoration of the anterior teeth, the veneering ceramic seems to have fewer delamination problems, and excellent optical properties can be achieved with modified cutback procedures to protect it. The high strength core is also etchable, allowing the restoration (monolithic or multi-layered) to be adhesively bonded to the underlying tooth structure. Therefore, the lithium disilicate IPS e.max seems to be the go-to for most clinicians today, and it certainly fulfills the criteria for a biomimetic restoration. The primary concern would be in dentitions where occlusal loads exceed ‘normal’ values – the bruxist. In these cases, there may be a higher risk of crack formation in the ceramic, and so a more rigid and wear resistant traditional material such as gold may be indicated.13
Figure 6 illustrates a case where lithium disilicate pressed ceramic was used for the adhesive biomimetic rehabilitation of a worn dentition. The case is restored with adhesively bonded ceramic onlay restorations on the upper and lower posterior teeth, together with all-ceramic crowns on the upper incisors. Tooth preparation has been kept to a minimum and reorganizing the occlusion and increasing the occlusal vertical dimension provided the necessary restorative space. Function and aesthetics have been restored, with a biomimetic approach, preserving as much tooth structure as possible.
Figure 6. (a–g) Adhesive ceramics for the restoration of the biomechanically weakened dentition. (a) Pre-operative image showing failing anterior composite veneers. (b) Upper arch exhibiting extensive erosive wear on the posterior teeth with a substantial loss of enamel and dentine. (c) Lower arch exhibiting erosive wear affecting the posterior teeth. Removal of amalgam restorations revealed extensive cavities and internal cracks. (d) After increasing the occlusal vertical dimension on the anterior teeth to create restorative space, the upper and lower posterior teeth were prepared for adhesive occlusal onlays. (e) The onlays incorporate full occlusal coverage, crucially retaining the critical cervical enamel and dentine. (f) and (g) The case is restored with adhesive ceramic onlays on the upper and lower posterior teeth, together with all-ceramic crowns on the upper incisors. Function and aesthetics have been restored, with a biomimetic approach, preserving as much tooth structure as possible.
A novel option for the biomimetic restoration of biomechanically weakened teeth is the use of hybrid CAD-CAM composite resin materials – polymer infiltrated ceramics. These have been shown to be effective for the restoration of biomechanically weakened posterior teeth, allowing restoration of fatigue resistance with cuspal coverage occlusal onlays in thin section.26 Their use has also recently been documented for restoration of anterior teeth as partial coverage restorations.28 The material can be used in thin section, has a favourable wear rate, good rigidity and a good chameleon effect allowing for blending of restorative margins. An example is shown in Figure 7, where CADCAM composite resin has been used for the restoration of heavily worn posterior teeth.
Figure 7. (a–e) The use of CAD/CAM composite resins for the restoration of biomechanically weakened posterior teeth. (a) Pre-operative image showing extensively worn upper left molar teeth. Both teeth were vital, but significantly weakened. (b) Lateral view demonstrates the lack of restorative space. (c) Additive and adhesive composite palatal veneers were used to increase the occlusal vertical dimension to provide restorative space. (d) The upper left first and second molars could now be restored with CAD-CAM composite resin and direct composite, respectively (NB lower right worn molar was treated in the same way allowing establishment of full arch occlusal contacts following increase in occlusal vertical dimension). (e) Lateral view showing recovery of occlusal form, aesthetics and tooth rigidity with the occlusal onlays.
There is some debate in the literature regarding the surface treatments required for adhesive cementation of these novel CAD-CAM resin composites. Various treatments have been advocated – sandblasting, hydrofluoric etching, silane treatment and application of a suitable primer. Studies show varied results, but there seems to be a consensus that sandblasting with 50-μm aluminium oxide, followed by treatment with a suitable primer will provide optimal bond strengths. The use of silane surface treatment has conflicting results in the literature.29,30,31 In time, results from clinical studies and cases should hopefully provide more guidance regarding the optimal bonding protocol for these novel materials.
So which material do you choose? The reality is that, for a single tooth, each of the materials is sufficient, provided that restoration is loaded favourably within the occlusal scheme. The challenge for choice of restorative material comes when several teeth are involved, or indeed a full mouth rehabilitation. In these cases, such as those illustrated above, careful ‘top-down’ planning with functional and aesthetically driven diagnostic wax-ups will help the clinician decide which material is suitable for each tooth. Often a full mouth rehabilitation case will require the use of a variety of materials, each fulfilling their role, and each adhering to biomimetic principles. Restorative space can be achieved by increasing the occlusal vertical dimension, again eliminating the need for aggressive removal of tooth structure.
Conclusion
The biomimetic restorative approach is a concept whereby we aim to restore the biomechanical, structural and aesthetic properties of the biomechanically weakened tooth using restorative materials and techniques. The strategies and protocols to achieve this are:
Recover the stiffness of the tooth by choosing restorative materials with mechanical properties similar to the rigid enamel outer shell.
Recreate a system where occlusal loads can be dissipated through the tooth by using adhesive dentistry to bond the restoration to the underlying tooth structure (mimicking the EDJ).
Preserve and protect the remaining tooth structure by adopting a minimally invasive approach using carefully designed partial coverage restorations.
Maintenance of pulp vitality by adopting a minimally invasive approach using carefully designed additive, adhesive and partial coverage restorations.
Recapture the natural tooth aesthetics using tooth-coloured materials with high aesthetics qualities – glass-based ceramic (and composite resin materials).
We have seen a shift in the dental profession towards the practice of minimally invasive dentistry. Developments in material science and clinical protocols have allowed us to expand our horizons and practice functional and aesthetic dentistry, incorporating traditional prosthodontic principles, while still respecting and protecting what nature has provided. In an era where we are seeing many clinicians focusing more on the replacement of teeth, it is important to remember that we are here in the first instance to save teeth, to provide a long-term journey for our patients, allowing them to keep their own teeth into later life.
Recommendations for further research
The biomimetic restorative approach does seem to form the basis of the daily clinical practice of many restorative dentists, especially in Europe and the UK. With the aim of carrying out minimally invasive dentistry, and using adhesive materials, dentists have been applying this approach. We have now been able to provide a name for this approach, together with the provision of some recommended protocols. The recommendation is now to follow up more collective cases in the form of prospective clinical trials, to assess the durability and longevity of this approach, comparison between the various materials and adhesive protocols, and essentially providing an evidence base for the clinical application.
