Composite resins occupy a paramount position as a restorative material of choice because they offer an excellent aesthetic potential and acceptable longevity, with a much lower cost than equivalent ceramic restorations for the treatment of both anterior and posterior teeth (Osborne et al, 1990; Hickel and Mahnart, 2001). In addition, composite restorations allow for minimally invasive preparations or no preparation at all for the replacement of decayed or missing tissues.
The creation of perfect direct restorations has been an elusive goal because of the imperfect optical properties of composite resins and because of improper clinical procedures. The attempt to mimic the shades and layering techniques developed for ceramic restorations lead to complicated application methods, mastered only by highly skilled practitioners.
Consequently, for years this has limited the number of patients who could benefit from the tremendous advantages of direct composite restorations. By using the natural tooth as a model and the identification of respective dentin and enamel optical characteristics (tristimulus L*a*b* color measurements and contrast ratio) has been a landmark in developing better direct tooth coloured materials. (Cook and McAree, 1985; Dietschi et al, 2000).
The “Natural Layering Concept” is a simple and effective approach to the creation of highly aesthetic direct restorations. Since this concept has become a reference in the field of composite restorations, the aim of this paper is to familiarize the practitioner with the features and clinical aspects of this new technique.
OPTICAL CHARACTERISTICS OF HUMAN DENTIN AND ENAMEL AND THEIR INFLUENCE ON COMPOSITE SHADING AND LAYERING CONCEPTS
The dentin L*a*b* color measurements of teeth from the “A” and “B” VITA shade groups have suggested that an ideal dentin replacement material should exhibit the following characteristics:
* single hue
* single opacity
* large chroma scale (beyond the four chroma levels of the VITA system).
The variations of a* and b* values between “A” and “B” VITA shades do not justify the use of distinct dentin colours, at least for a direct composite restorative system. Likewise, the variations of the contrast ratio (opacity-translucency) within a single shade group do not support the use of different dentin opacities (i.e.translucent, regular or opaque dentins). However, chroma (related to a* and b* values) proved to increase from light to dark shades (A1 to A4 or B1 to B3). This supports the concept of a large chroma scale covering all variations of natural dentitions, plus some specific conditions like sclerotic dentin (as found underneath decay, fillings or cervical lesions).
With respect to enamel, differences in tissue lightness and translucency proved to vary in relation with tooth age and therefore confirmed the clinical concept of three specific enamel types (Ubassy, 1983):
* Young enamel: white tint, high opalescence, less translucency
* Adult enamel: neutral tint, less opalescence and intermediary translucency
* Old enamel: yellow tint, higher translucency.
The interpretation of human dentin and enamel by colorimetric data led to the clinical approach named the “Natural Layering Concept,” which embraces a more accurate optical and anatomical characteristic of natural teeth (Dietschi, 1995, 1997 and 2001; Dietschi et al, 2000).
This concept defines the features of an optimal restorative material aimed to replace dentin and enamel, respectively. Dentin shades should be available in one single hue (Vita “A” or Universal dentin shade) with a sufficient range of chroma (covering at least the existing Vita shade range) and presenting opacity close to that of natural dentin. Enamel shades should present different tints and opacity levels, which would replicate all variations found in nature. Typical brand names are Ceram-X duo (Dentsply), Miris (Coltenwhaledent), Enamel HFO (Micerium).
INFLUENCE OF THE NATURAL LAYERING CONCEPT ON SHADE RECORDING
The quality of the final restoration of course depends on a correct shade recording. By using the “Natural Layering Concept” there are only two basic steps involved: 1) selection of dentin chroma in the cervical area, where enamel is the thinnest, 2) selection of enamel tint, often performed by simple visual observation.
In specific and less frequent cases, a third step might be involved in the form of a visual or photographic mapping of the tooth’s special optical effects (such as white hypocalcifications, high opalescence areas or areas with a higher chroma). In this situation, the application of effect materials (white, blue or orange-gold; Miris Effects, Coltenewhaledent, Renamel, Cosmedent) might be recommended.
CASE REPORTS
Case 1
A young patient presented with a large fracture of the left central incisor. In addition, both central incisors present an asymmetrical mesio-distal dimension (Fig. 1A). Shade selection is always performed first, to avoid any interference in chroma and opacity evaluation due to tissue dehydration. Shade selection is done in two basic steps; dentin chroma is first selected with the dentin shade tab next to the cervical region of the reference tooth (Fig. 1B).
The enamel tint is confirmed by placing either the enamel shade tab or a small piece of the light cured material, next to the incisal border (Fig. 1C). Subsequently, a silicone index is fabricated to fix the lingual profile and incisal edge position; the index will be used during the next steps and possibly also at the time of finishing as a control of tooth length (Fig. 1D).
Before proceeding with the restoration, the width of the right incisor is corrected (Fig. 1E). Enamel is applied to the mesial surface of the neighboring tooth. No preparation is required nor is the use of a dentin material, since only a 1mm thick increment needed to be applied (Figs. 1F-G).
The selected enamel composite (CeramX duo, E2) is applied directly on the silicone index, which is then placed against the tooth (Fig. 1H). This allows the lingual build-up of enamel to be performed easily and precisely (Fig. 1I).
The reference of the new incisal edge serves for a precise 3-dimensional placement of dentin (CeramX duo D1) (Fig. 1J). A little increment of blue tinted composite (Miris, Blue effect) was later added on top and in-between dentin peaks to mimic opalescence of natural enamel; this was judged necessary since the intrinsic opalescence of the composite enamel seemed insufficient in this case.
Finally, a last layer of translucent enamel (same as used on the lingual surface) is applied to complete the proximal and buccal profiles and provide desired translucency and brightness (Fig. 1K). Finishing and polishing is complete giving both teeth their final morphology and final dimensions (Figs. 1L-M).
The application of the natural layering concept through a logical application of two separate composite masses which mimic natural tooth anatomy presents clear advantages for the clinician; it makes the whole procedure more efficient and predictable.
Case 2
An adult patient presented defective amalgams which required their replacement (Fig. 2A). A rubber dam is placed before removing the amalgams to prevent inadvertent ingestion of metal powder or inhalation of mercury vapors.
The cavities are prepared and cleaned without the need to follow a specific cavity outline. This represents a major advantage of direct adhesive techniques in posterior teeth (Dietschi and Spreafico, 1997). After the adhesive application (Prime & Bond NT, Dentpsly), the composite was inserted following the horizontal incremental technique (Lutz and Kull, 1980). The proximal ridge is built-up first, usually in two or three increments of about 1mm each (Fig. 2C).
A sectional matrix was used, which is stabi
lized by a metal ring; in addition, the ring creates a slight separation of neighboring teeth and provides a perfect tight proximal contact (i.e.: System Palodent-Dentsply) (Figs. 2C & F).
In addition to this specific incremental technique, the natural layering concept is also followed which will improve the aesthetic appearance of the restoration. It implies the use of dentin masses to replace missing dentin (CeramX-duo D1 to D4) (Figs. 2D & G)) and enamel masses to replace missing enamel (CeramX-duo E1 to E3) (Figs. 2E & H). This supports the simplicity and beauty of this new layering approach. A special sculpting technique is used to develop a natural occlusal anatomy which provides aesthetics and function (Fig. 2I).
Restorations placed with this technique require practically no finishing procedure, except the smoothing of proximal margins and occlusal adjustments. The final views demonstrate the quality of the restorations and their ideal anatomy and function.
CONCLUSION
The natural layering concept has enabled the patient’s aesthetic expectations to be fulfilled in a predictable way by incorporating newly acquired knowledge about natural tissue optical properties into a new composite system. In addition, this has allowed for a significant simplification of clinical procedures, making this technique also accessible to general practitioners. This advance can be regarded as a milestone in operative dentistry, giving a new dimension to free-hand bonding and helping more patients receive conservative and highly aesthetic restorations.
Didier Dietschi is Senior lecturer, Department of Cariology & Endodontics, School of Dentistry, University of Geneva, Switzerland. He is Adjunct Associate Professor, Department for the Practice of General Dentistry, Case Western University, Cleveland, Ohio.
Oral Health welcomes this original article.
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