Composite and Adhesive Dentistry: A Conservative Approach
Material advancements increase the options for direct restorations
The revival of direct adhesive dentistry is on. With advances in the physical and optical properties of dental resins and the predictability of dental adhesives, restorative dentists have rediscovered the virtues of composites as a conservative approach in the replacement of tooth structure.
It has always remained the charge of restorative dentists to be advocates for their patients and to thoroughly understand their needs to reestablish the health and function of the smile. Recommendations based upon the most conservative treatment possible that achieve the goals of health are always in the best interest of the patient. The predictability of successful restoration is predicated upon the dentist’s mastery of the fundamentals of color, dental physiology, and function.1
The Restorative Process
The success of any mechanical system is directly related to the engineering and design of how forces are introduced and distributed. In the masticatory system, we are introducing restorative solutions in an incredibly inhospitable environment.2 These attempts to emulate natural tooth structure are subjected to extreme thermal changes, caustic acids, staining agents, and hundreds of pounds of force. What is even more amazing is that we expect success where what God created has failed.
The dynamic design of this sophisticated system, which incorporates an omnipresent understanding of biology, structure, function, and esthetics, is recognized as the Functional Matrix.3 By using proper positioning and creating restorations that mimic natural tooth contours, we can provide an environment that is cleansable and maintainable for our patients, and promotes the best opportunity to obtain optimal health. The Functional Matrix relates the management and direction of forces to the optimal contours of the anterior teeth and subsequently to the temporomandibular joint (TMJ) and the muscles of mastication. It teaches us the importance of every contour of the anterior teeth and how they are designed for a specific function. A compromise in any of these contours will inescapably influence the muscles, the TMJ, and the health of the system.
As restorative dentists, we need to be comprehensive in our evaluation of these success or failures and recognize that 90% of failures are not attributed to the materials or techniques, but rather to our failure to plan.4 Our vision of failure is often narrowed to the single criteria of the fracture of the restoration, when in truth we need to also appreciate failure to represent all of the signs and symptoms of occlusal disease, including tooth mobility or migration, gingival recession, sensitivity, muscle symptoms, and the potential for breakdown of the TMJs. In our assessment of restorative materials, therefore, bulletproof is not necessarily better. It may be seductive, but the reality lies in our mastery of the orchestration of all of the parameters of health and engineering.5
Responsible esthetics predicates the conservation of tooth structure. Over-aggressive tooth preparation often necessitates indirect restorations and limits our treatment options in the future. Our anecdotal experience has deepened our appreciation for conservation. Restorations do not last forever, and we need to weigh the consequences of the latent effect of removing tooth structure. The quality and quantity of the remaining enamel significantly affects the flexural strength of the teeth, as well as the durability and strength of the bond of the restoration.6 The inherent parameters of direct resin restorations often provide the restorative dentist with the most conservative treatment option. The application of direct resins does not require additional preparation for retention or resistance form or for the elimination of undercuts. Material advancements in nanotechnology have enhanced handling, polymerization shrinkage, fracture/wear resistance, polishability, and color stability, and have therefore expanded our treatment indications. Many of the parameters of fracture/wear resistance have approached the indirect solutions of leucite-reinforced glass that revolutionized restorative dentistry in the 1980s. Direct resins used within a comprehensively managed environment provide a great opportunity for a minimally invasive solution.7
Esthetically, when faced with the challenges of replacing missing tooth structure, the key concept is to recognize the optical properties of the structures to be restored.8 This concept is can be described as replacing enamel with enamel and dentin with dentin, but it is not so simple in clinical application. Enamel is a crystalline structure with a unique and varying orientation of enamel rods. It is innately devoid of chroma, but is intimately involved in the reflection and refraction of light. Changes in the structure of the enamel due to thinning, aging, and attrition can further introduce areas of maverick inclusions and artifacts. Dentin is a very amorphous layer that absorbs light and contributes the chroma we experience in the visual appearance of teeth. Dentin will undergo progressive and continual changes influenced by the pulp and the formation of sclerotic dentin. With these inherent nuances that are found in nature, there is not a single restorative material that can replicate this dynamic optical challenge.
Stratification is an attempt to recreate these idiosyncrasies. Using a protocol of layering resins to reestablish the varying chroma, opacities, maverick artifacts, and values, we can build restorations that can blend harmoniously into the surrounding tooth structure with polychromatic characteristics. This 3-dimensional (3D) color effect is what we see in nature.9
Composite systems are designed to facilitate this process. Although the nomenclature may vary within systems, dentin replacement resins are typically more opacious and provide the chroma for the restoration. Options for enamel replacement have evolved with our understanding of color. Initially, chromatic enamels attempted to simplify the shade-matching process, achieving a chameleon effect with the surrounding tooth structure. In areas of greater volume of tooth loss, the clinician would find it necessary to supplement the restoration at deeper layers with a chromatic dentin resin. In the 1990s, non-VITA (Vident, www.vident.com) shade, achromatic enamel resins were introduced with a natural layering concept of stratification, which enabled clinicians to develop more 3D depth of color. These surface layers of achromatic enamel resins contained no pigment, but influenced the chroma and value of the underlying foundations depending on their thickness and opacity.10
At deeper layers, localized additive or neutralizing effects can also be considered. Tints and opaquers can help to achieve localized effects. Opaquers are typically effective at blocking out discolorations, but also can raise the value of the color in their area of application. Tints can introduce hues, but will often lower the value of the color.11 Deeper discolorations often need to be neutralized to ovoid the bleed-through into the surrounding restoration. Pink opaquers can be effective in accomplishing this without the unbalancing effects of raising the value.
This post-orthodontic patient presented with the objective of improving her smile with the upgrade of a deteriorating restoration on a previously damaged anterior tooth (Figure 1). Although the solutions for the patient’s esthetic needs may seem obvious, it is important to first assess the patient’s overall dental health and the relationship of this anterior tooth with the balance of the smile. In a young patient, the signs and symptoms of occlusal imbalance may be subtle, but significant nonetheless. Without a comprehensive evaluation, the introduction of any restorative treatment mitigates the opportunity for predictability.
In this patient’s case, a discrepancy between centric relation and maximal intercuspation potentiated unfavorable force vectors that would influence the longevity of any restorative solution. A model analysis provided the opportunity to eliminate these risk factors, test out potential treatment solutions, and make modifications to tooth contour before treatment was recommended. Stents could then be fabricated on the bench top that would clinically facilitate the restorative techniques (Figure 2).
In this case, a nanohybrid direct resin system, Filtek™ Supreme Ultra (3M ESPE, www.3mespe.com) was used for its physical properties of strength, handling, and polishability, and its chromatic and achromatic dentin/enamel resins. A great advantage that a direct chairside system offers is the ability to complete a mock-up or trial shade tab, using a natural layering technique with varying opacities and shades to refine the formula to create an invisible restoration. Clinically, care must be taken when designing this custom shade tab to ensure that the teeth to be matched do not dehydrate. Dehydration of tooth surfaces can happen quickly, and can dramatically alter the shade and surface maverick colors, which are not otherwise visible in a naturally hydrated condition. In this case, a simplified stratification technique was selected with four layers: a lingual white enamel, dentin shade, enamel chromatic shade, and a final veneering achromatic enamel.
From the model study and diagnostic wax up, a restorative stent was fabricated to copy the intended lingual, incisal, and proximal contours of No. 9. Clinically, the failing composite restoration was removed. On the lingual cavosurface, a chamfer finish line was prepared in sound enamel, which allows for an additional bulk of resin, providing adequate resistance form in areas of direct functional contact. On the facial aspect, two bevels are created. The primary bevel extends beyond the cavosurface 2 mm. The secondary bevel has an infinity finish to the extent that the facial surface will be covered. The surface of the tooth was then conditioned with a total-etch technique and sealed with Scotchbond™ Universal Adhesive (3M ESPE) (Figure 3). The proximal surfaces of the adjacent teeth are protected from this conditioning with a clear Mylar strip.
The lingual putty matrix is then used to fabricate a thin 0.4-mm shell of the achromatic enamel (Figure 4) directly against the adjacent unprepared, unconditioned cavosurface, engaging and filling the lingual chamfer margin. If a halo effect is desired, addition resin may be elected in the incisal aspect. This will refract light, creating the halo. Once this lingual shell has been polymerized, the matrix can be removed and all subsequent layers will be developed upon this framework.
A dentin shade resin, which typically has the highest opacity, is then applied to the framework and shaped to mimic the naturally occurring histological portion of missing dentin. It is important for the clinician to appreciate that the incisal and proximal areas are typically dominated by enamel, and therefore limit the more opacious dentin to this outline form, as can be observed in the adjacent teeth. Achromatic enamel is then layered from the primary bevel and feathered to the incisal and proximal limits of the tooth (Figure 5). The use of a brush is effective in placing this layer. The final layer of achromatic enamel is placed to extend from the infinity bevel to the final facial contours of the tooth (Figure 6).
When developing the final facial contours of the tooth, it is important to balance the facial line angles and reflective zones to create visual balance. The use of a pencil can be helpful in identifying and modifying these line angles (Figure 7). The restoration is then polished with a series of silicon polishers in a wet state, creating a slurry that aids in progressive development of the surface finish and ultimately polishes with a diamond paste.
Surface texture is the final fingerprint that enables a restoration to harmonize with the balance of the dentition. Over-polishing and smoothing the surface of a restorative material can disturb the reflection of light and thwart this attempt at emulating nature. If additional texture is desired, it can be created with the use of a green stone in a slow speed handpiece that is allowed to “walk over” the surface of the resin, mimicking the idiosyncrasies identified on the adjacent surfaces. This can then be re-buffed with the tertiary polishers and pastes to regain the luster without removing the desired texture (Figure 8).
Comprehensive care is about the complete understanding of patients’ needs and serving as their advocate in recommending solutions. The advancement in direct resin materials and adhesives has expanded our ability to provide restorative solutions or even transition patients as an interim service. Although a majority of our complex reconstruction cases may require indirect materials for the time being, the key concept is that comprises the protocol of the Functional Matrix remains unchanged, whether the solution is to be accomplished in resin or ceramic.12
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About the Author
Scott W. Finlay, DDS, FAGD, FAACD
The Dawson Academy
St. Petersburg, Florida