24 RESTORATIVE Dental Tribune Middle East & Africa Edition | 2/2020 Direct bonding in the smile frame Merging new technologies and human touch for the best By Dr Didier Dietschi, Switzerland Introduction Restorative dentistry has entered a phase of deep conceptual rupture, demarcating two camps, the tradi- tional one, pursuing the convention of human-conceived and fabricated restorations, and the modern one, celebrating new technologies in all aspects and steps of a restorative treatment and limiting tremen- dously the manual contribution of the dentist. However, even the most enthusiastic, modern professionals recognize that no technology can equate to the excellence and perfec- tion of a powerful brain and agile hands acting in synergy, while the most conservative ones also admit that digital dentistry has the poten- tial to elevate the level of mass den- tistry. What is the most reasonable attitude? Probably a position in be- tween the extremes. Freehand direct bonding can then be looked at from different perspectives as well: it will soon be abandoned and replaced by either CAD/CAM and 3-D 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 economy and the quest for an ultraconserva- tive treatment approach. The latter vision is from far the most realistic one, as many restorations cannot be approached simply by new technol- ogies owing to the limits of the cav- ity or restorative geometries and the irrational complexity, preparation imperatives or technology immatu- rity of CAD/CAM and 3-D printing systems if applied unrestrictedly. This report aims then to discuss and illustrate current and future indica- tions and application protocols of direct bonding, as a way to bridge classical and modern dentistry. Overall considerations and indications for direct bonding The use of composite is likely to continue, probably even develop, in the forthcoming decade. Actually, no foreseen new technology seems able to allow soon the intraoral fabrication of highly esthetic and strong restorations in a simple, ef- ficient and cost-effective way. In the case of extraoral 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 (Figs. 1a–e):1, 2 –Class III– V restorations; ––form corrections (tooth shape; proportions and di- mensions); –– esthetic enhancements in young patients; –– diastema and black triangle clo- sure; –– veneering of anterior and lateral teeth (if limited discoloration); –– interceptive approach to tooth wear. The advantages of a direct approach are multifold, including tissue con- servation, use in young patients (aiming for treatment reversibility), reduced execution time and lower cost (as opposed to indirect or CAD/ CAM restorations), providing also satisfactory longevity.3, 4 Conversely, some limits exist, related to the practitioner’s experience, composite shading and layering concept (some systems are still overcomplicated and unreliable in terms of esthetic/ shade outcome) and application of detailed protocols, although the last point or shortcoming is truly a rela- tive one. The use of direct techniques has only few limits in terms of extent, namely nonvital teeth or very large carious lesions, for which crowns or extended bonded porcelain restora- tions are usually preferred. Likely in-between indications for direct or indirect solutions – some cases lie within a gray zone – are resolved mainly according to the operator’s preference rather than any other strong rationale (Figs. 2a–s). Shading and layering concept Overall, layering concepts evolved from a primitive approach to emu- lating natural dental anatomy and optical properties to more reliable protocols for matching tooth color and its many dimensions.5-7 Actually, color integration as per- ceived by patients implies correct hue, opacity, opalescence and fluo- rescence regarding optical deter- minants and surface gloss and light reflection (mainly related to the restorative microanatomy). An op- timal result in terms of esthetic in- tegration is feasible today, although it will rarely be achieved without proper material choice and an ap- propriate layering approach and ap- plication, which are largely product- specific.7 We normally classify composite systems in relation to the number of recommended layers, as well as some selected optical properties, which allow for finer differentiation among brands. In parallel, filler tech- nology has considerably evolved, aiming to offer the practitioner various options, such as universal materials (superfine hybrids or ho- mogeneous nanohybrids), which can be used for both posterior resto- rations, owing to their excellent me- chanical properties, wear resistance and esthetics, or specific composite formulations (spherical or mixed- filler composites) aimed to be used mainly in anterior teeth owing to lower mechanical performance. Our preference today is toward universal composites as far as material tech- nology is concerned and a bilaminar application approach, considered simple, reliable and highly esthetic. The use of the natural tooth as a model has been then a logical evolu- tion of direct restorative materials, leading to an improved shading and layering concept, the natural layer- ing concept (NLC), logically named “An optimal result in terms of esthetic integration is feasible today, although it will rarely be achieved without proper material choice and an appropriate layering approach and application, which are largely product-specific” Fig. 1a: Pretreatment of a 14-year-old patient after a sport trau- ma having resulted in major fractures of both maxillary central incisors, repaired in an emergency department in a public hospi- tal. Fig. 1b: Intraoperative view showing the application of an effect shade (Ice, inspiro) to emulate hypocalcifications. This effect is placed directly over the dentin buildup. Fig. 1c Fig. 1d Fig. 1e (c-e): Post-treatment view showing better smile harmony with proper tooth dimensions and proportions, which would facilitate the scheduled orthodontic treatment as well. after nature’s original model and source of inspiration.8, 9 It resulted from a comprehensive study of nat- ural dentin and enamel optical prop- erties, recognizing the variations in tissue quality related to tooth age and functional maturing. Related findings have logically drawn the lines of this new concept (Fig. 3).6, 7, 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 dentin colors for a direct composite restorative system could be avoided, provided that enamels would offer not only different value/opacity lev- els but also different tints. Likewise, limited natural dentin opacity with- in a given chroma level variation did not support the use of different den- tin opacities (i.e., translucent, regular or opaque dentins).6, 7, 9 Then, a new concept was born, al- lowing the emulation of practically all of the VITA shades by using an appropriate combination of univer- sal dentin shades of a single opacity level and presenting a wide chroma range that extends beyond VITA classical shades and multi-tint/ multi-translucency enamels (typi- cal brands named after their devel- opment period: Miris and Miris 2 [COLTENE], ceram.X duo [Dentsply Sirona], Enamel Plus HFO and HRi [Micerium], and inspiro [Edelweiss DR]). Specific characteristics of NLC dentins and enamels In summary, in an NLC compos- ite system, the specific material optical properties for dentin are a single hue, a single opacity and an extended chroma range (Fig. 3). For enamel, three specific enamel types are needed: to mimic young enamel: white tint and reduced translucency; adult enamel: neutral tint and inter- mediate translucency; and elderly enamel: yellow tint and higher trans- lucency, maintaining a natural opal- escence among the three aforemen- tioned basic enamel types. Various levels of translucency complete the different tints, forming then a multi- tint/multi-translucency system that emulates most natural enamel vari- ations. Effect shades For teeth with richer color compo- sition (strong opalescent halo, no- ticeable dentin mamelons, enamel opacities, etc.), special effect shades produced in a flowable consistency are available in some NLS systems to surpass esthetic boundaries (typical brand: inspiro). Case presentation A patient, aged 16, presented with an esthetic complaint, after orthodontic closure of spaces owing to missing lateral incisors. The functional and ÿPage 26