Introduction of Direct Bonding in the Smile Frame
Restorative dentistry has entered a phase of deep conceptual rupture, demarcating two camps, the traditional one pursuing the tradition of human comprehended and fabricated restorations and the modern one, celebrating new technologies in all aspects and steps of a restorative treatment, limiting tremendously the manual contribution of the dentist. However, even the most enthusiastic, modern professionals recognize that no technology can meet the excellence and perfection of a powerful brain and agile hands acting in synergy, while the most conservative ones also admit that digital dentistry has potential to elevate the level of mass dentistry. What is the most reasonable attitude?
Probably a position in-between the extremes! Free-hand direct bonding in the smile frame can then be looked at from different perspectives as well; it shall be soon abandoned and replaced by either CAD-CAM and 3D printed restorations or on the contrary, even further developed, using some new digital technologies to improve its outcome and practicality, fueled worldwide by a slowing down economy and quest for ultra-conservative treatment approach. The later vision is from far the most realistic one, as many restorations can’t be approached simply by new technologies due to the limits of cavity or restoration geometries and the irrational complexity, preparation imperatives or technology immaturity of CAD-CAM and 3D printing systems if applied unrestrictedly.
Overall Considerations & Indications for Direct Bonding
The use of composite is likely to further exist, probably even develop in the forthcoming decade. Actually, no 3D printing or any foreseen technology will allow soon the intra-oral fabrication of highly esthetic and strong restorations in a simple, efficient and cost- effective way. In case of extra-oral fabrication, tapered cavities or at least different cavity designs are required, generating as well undesired complications and costs. Keeping this in mind, direct composite application has unique advantages in the following, precise indications (Fig. 1)
- Class III to V restorations
- Limited to moderate form corrections (tooth shape, tooth proportions & dimensions), especially in post-orthodontic cases.
- Esthetic enhancements in young patients.
- Diastema and black triangle closure.
- Veneering of anterior and lateral teeth (if limited discoloration).
- Interceptive approach of tooth wear.
The advantages of a direct approach are multifold, including tissue conservation, use in young patients (aiming for treatment reversibility), execution time and lower cost (as opposed to indirect or CAD/CAM restorations), providing also satisfactory longevity. Conversely, some limits exist, related to practitioner’s experience, composite shading and layering concept (some systems still are overcomplicated and poorly reliable in term of esthetic/shade outcome) and application detailed protocols, although the later point or shortcoming is truly a relative one.
The use of direct techniques has only few limits in term of extent. namely non-vital teeth or very large decays for which crowns or extended BPR (Bonded Porcelain Restorations) are usually preferred. In-between likely indications for direct or indirect solutions, some cases lay within a “grey zone”, being resolved mainly according to operators preference rather than any other strong rationale. (Fig.2)
Shading & Layering Concept
Overall, layering concepts evolved from a primitive approach to emulate natural dental anatomy and optical properties to more reliable protocols to match tooth color and its many dimensions. Actually, “color” integration as perceived by the patients implies a correct hue, opacity, opalescence and fluorescence in regard to optical determinants and also surface gloss and light reflection (mainly related to the restoration micro-anatomy). An optimal result in term of aesthetic integration is feasible today although it will rarely be achieved without proper material choice and appropriate layering approach and application, which are largely product specific (Dietschi & Fahl, 2016)
We normally classify composite systems in relationship to the number of recommended layers and as well as some selected optical properties, which allow for finer differentiation among brands. In parallel, filler technology also considerably evolved, aiming to offer the practitioner various options such as universal materials (super fine hybrids or homogeneous nano-hybrids) which can be used both for posterior restorations, owing to their excellent mechanical properties and wear resistance, and esthetics or specific composite formulations (spherical or mixed filler composites) aimed to be used mainly in anterior teeth due to lower mechanical performances
Our preference goes today toward universal composites as material technology is concerned and a bi-laminar application approach, considered simple, reliable and also highly esthetic. The use of a natural tooth as a model has been then a logical evolution of direct restorative materials, leading to improved shading and layering concept (NLC) logically named after nature’s original model and source of inspiration. It resulted from a comprehensive study of true natural dentin and enamel optical properties, recognizing the variations in tissue quality related to tooth age and functional maturing. Related findings have logically drawn the lines of this new concept (Dietschi et al, 2000; Dietschi et al, 2006) (Fig.4).
Interestingly, spectrophotometric measurements (tristimulus L*a*b* color and opacity values)of natural teeth belonging to various VITA shade groups led to the conclusion that the use of distinct dentine colors for a direct composite restorative system could be avoided, providing that enamels would offer not only different value/opacity levels but also different tints. Likewise, limited natural dentin opacity within a given chroma level variation did not support the use of different dentin opacities (i.e.: translucent, regular or opaque dentins).
Then, a new concept was born, allowing the emulation of practically all usual VITA shades by using a proper combination of universal dentin shades of a single opacity level and presenting a wide chroma range that
extends beyond Vita Classic shades) and multi-tint/multi-translucency enamels (typical brands named after their development period: Miris and Miris2 (Coltène/Whaledent), Ceram-X du (Dentsply), Enamel HFO Plus and Hri (Micerium), and Inspiro (EdelweissDR). .
Specific Characteristics of NLC Dentins and Enamels
In summary, in an NLC composite system, the specific material optical properties for dentin are a single hue, a single opacity and an extended chroma range (Fig 5). For enamel, three specific enamel types are needed to mimic young enamel: white tint and reduced translucency, adult enamel: neutral tint and intermediary translucency and for elderly enamel: yellow tint and higher translucency, maintaining a natural opalescence among the 3 aforementioned basic enamel types. Various levels of translucency complete the different tints, forming then a multi-tint/multi-translucency system that emulates most of natural enamel variations.
Conclusion
As said, the free-hand application of composite is to stay and even likely to further develop while we don’t foresee new techniques challenging their simplicity and efficiency. Actually, on one hand, 3D intra-oral printing of composite restorations with a high filler load seems unlikely to happen soon due to such material viscosity, while on the other hand, an extra-oral fabrication would require tapered cavity design with a significant, non-conservative alteration. In short, there isn’t any innovative technology that can replace direct composites yet. Having said that, achieving optimal forms, smile configuration and color isn’t so simple and improved clinical protocols are needed to obtain high esthetic results with direct bonding in a predictable manner. This is where existing technologies can bring a significant contribution in the form first of digital diagnostic (Digital Smile Design) and 3D printed mockup to support treatment planning, constrain clinical difficulties and therefore expand its successful use. The next milestone in treatment reliability is the use of a highly effective and simple layering approach such as the Natural Layering Concept. The later 2 improvements in Direct Bonding application are keys to success for the modern practitioner, specialist or not.
