March 2006, Volume 2, Issue 2
Published by AEGIS Communications
The Adhesive Class IV Design: Minimal Preparation and Biomodification
Douglas A. Terry, DDS, and Ronit Antebi-Hadar, DMD
During the last half of the 20th century, adhesive surface preparation of the enamel and dentin (ie, acid etching, self etching) and composite resin technology have been introduced, which allow minimal invasive procedures without a standard geometric preparation form.1 Currently, the concept “prevention of extension” seeks to minimize the biologic cost to the natural tooth2 by combining prevention, remineralization, and minimal intervention for the replacement of natural tooth structure and/or restorations. This new philosophy has three objectives: to preserve the maximum integrity of the natural dentition, to conserve tooth structure during preparation of a restoration, and to increase the longevity of a restoration between replacements. These three modern dental strategies (preservation, conservation, and longevity) can be applied to the Class IV composite restoration of a fractured anterior tooth. The purpose of this article is to describe a conservative technique for restoring a fractured incisor using a minimal Class IV preparation design with a new-formulation single-component self-etch adhesive system (G-Bond™, GC America, Alsip, IL) and a small-particle composite resin (Gradia® Direct, GC America).
During the past several years, efforts have been made to eliminate the need for acid etching the cavity preparation before application of the dentin bonding agent. Two types (or categories) of bonding agents are used with the self-etching strategy: a two-component system (combined etching/priming solution and a bonding agent) or a single-component system (etching, priming, and bonding material).
The self-etching primer strategy leaves the smear layer in place. These dentin bonding systems are based on the infiltration and modification of the smear layer by an acidic monomer. The objective is to reinforce the bonding of the smear layer to the underlying dentin. These slightly acidic, hydrophilic primers penetrate the smear layer and achieve micromechanical and chemical bonding of the smear layer to the underlying dentin. This technique allows the simultaneous infiltration of the collagen fibers and decalcification of the inorganic component to the same depth in dentin, thereby minimizing the risk of not reinforcing part of the demineralized dentin. Additionally, this prevents the collapse of the collagen fibrils after conditioning and drying. The resin may slightly (0.1µm to 0.5µm) infiltrate the smear layer and the dentin and copolymerize.3
Self-etch materials have been evaluated in numerous studies.4-11 Some of these studies indicate that enamel bonding with self-etch adhesives is as effective as enamel bonding after conventional phosphoric acid etching.6,7 Evidence of enamel leakage has been reported clinically in Class II and Class V composite restorations and in vitro in Class I and Class V restorations when a self-etch adhesive was used as a dentin-enamel adhesive.4,9,10,12 Other studies demonstrate that self-etch adhesives are effective on ground enamel, but less effective on intact enamel.8,13 A study by Perdigao and Geraldeli reported that commercial self-etch adhesives performed better on prepared enamel than on unprepared enamel. This study suggests that for all-in-one self-etch adhesives, instrumentation of unprepared enamel may be critical for their ability to bond to enamel.4 The authors suggest that it may be prudent to acid etch any peripheral enamel margins to minimize the potential of microleakage and enhance bond strength to enamel; however, it is important not to etch the dentin.
Selecting an Adhesive Strategy
The clinical advantages of a self-etch adhesive versus a conventional adhesive technique include the former’s simplicity and reduced postoperative sensitivity. Self-etch systems do not require acid etching or the washing off of acid. The self-etch adhesives are also less technique sensitive than acid-etch adhesives, and this can be seen in four categories.
First, because water is a fundamental ingredient of self-etch systems (allowing ionization of the acidic monomers for demineralization of hard dental tissues), the technique sensitivity associated with substrate hydration is eliminated.5 Second, in comparison to acid-etch adhesives, self-etch adhesives do not allow a discrepancy between the depth of demineralization and depth of resin infiltration because both processes occur simultaneously.4 Third, since the smear plugs are not removed before the application of the adhesive, the potential for postoperative sensitivity is less than with total-etch adhesives.4 Finally, moist bonding is not required for self-etch adhesives as it is for some total-etch adhesive systems.4,5
The goals for future adhesive systems are simplicity of application as well as quality of adhesion. Because clinicians desire restorative materials that are “user friendly,” these simplified self-etch dentin adhesives offer another option. Clinical efficacy and simplicity of application, however, must not be confused with the demands required of the operator’s attention to meticulous detail when considering diagnosis, treatment planning, and the balance of the associated aspects of restorative care.
A 53-year-old woman presented with an oblique, vertical fractureon the maxillary right lateral incisor (tooth No. 7). A previsualized composite mock-up was made with the proper selection of composite restorative materials. The orientation of the restorative materials was charted so that the definitive restoration could be visualized before completion. A 0.5-mm bevel was placed in enamel around the entire margin. The enamel margin was etched for 15 seconds with 37.5% phosphoric acid, rinsed for 5 seconds, and gently air dried for 5 seconds. (The etch should extend several millimeters beyond the bevels.) A single-component self-etch adhesive (G-Bond) was applied to the entire cavity preparation according to the manufacturer’s recommendation and light cured. The tooth was restored using an incremental layering technique with a small particle composite resin (Gradia Direct). This procedure demonstrates that by using a conservative adhesive preparation design in combination with proper adhesive techniques and a methodological protocol of incremental application of composite resins, the clinician can transform a Class IV fracture into a final restoration with an esthetic natural appearance (Figure 1; Figure 2; Figure 3; Figure 4; Figure 5; Figure 6; Figure 7; Figure 8; Figure 9; Figure 10).
Knowledge and a desire to create arelimited by the products available to clinicians for restorative procedures. Advancements in restorative materials and adhesive technology have enabled the development of direct bonding techniques that allow the provision of conservative treatment while allowing clinicians to combine form, function, and esthetics for predictable restorative success.
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About the Authors
Douglas A. Terry, DDS
Assistant Professor, Department of Restorative Dentistry and Biomaterials
University of Texas Health Science Center, Dental Branch
Private Practice, Esthetic and Restorative Dentistry
Ronit Antebi-Hadar, DMD