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Bonding Agents and Esthetics
Where science meets art
Gildo Coelho Santos Jr., DDS, MSc, PhD
For more than 40 years, dentists worldwide have been using directly placed resin-bonded composite to restore damaged anterior teeth. While such treatments are invariably more conservative than indirect procedures, operative procedures using direct composite can be challenging and are considered technique sensitive. To provide composite restorations that restore function and aesthetics and blend seamlessly with the residual dentition, clinicians require both technical and artistic skill.1
In order to achieve a lifelike appearance and esthetics, anterior composite restorations often employ advanced multiple layering techniques, using a range of shades, opacities, and translucencies, which remain in the domain of relatively few practitioners. Dentists commonly report that such techniques are time-consuming or complicated and do not offer predictability in terms of aesthetics.2 The main advantage of such procedures is that they require minimal (or no) tooth preparation to enhance resistance and retention form.3
Regardless of the material used, the average survival rate statistics for direct restorations are far from encouraging.4,5 However, the rates for indirect restorations are also poor, averaging approximately 10 years before restorations require total replacement, and when failure occurs, complications are often catastrophic for the tooth.5,6 With an optimum technique, it should be possible to provide direct composite restorations that exceed the average lifespan of indirect restorations.7-8
To achieve this goal, clinicians should keep in mind the science behind the materials selected to restore each clinical case. The foundation for a direct adhesive restoration relies on the preparation of the substrate (ie, enamel, dentin) before the restoration. This preparation requires an understanding of the principles of bonding to enamel and dentin. Selection of the proper bonding technique (eg, self-etch, etch-and-rinse) needs to be assessed on a case-by-case basis. For instance, in Class I, II, III, V, or VI restorations, the preparation has a number of walls and internal areas that contribute to the increased retention. In the case of Class IV restorations, there are no internal areas to increase the retention, so the only method to help maintain the long-term viability of the restoration is bonding to the external walls.
With this principle in mind, when it comes to esthetic and conservative restoration of anterior dentition, specifically Class IV restorations, a quick review of the bond strength values of bonding agents is paramount in order to select the proper adhesive technique (Table 1).9-18
Based on this review, self-etching adhesives are not recommended when restoring Class IV caries. According to Frankenberger and colleagues, these adhesives lack sufficient resistance and retention form because they contain weaker acids that will not sufficiently penetrate enamel to a depth that maximizes resin-tag formation.19 Finally, we need to consider what research has revealed about 4th and 5th generation adhesives as well as universal adhesives. When bonding to enamel, the data indicates that 4th generation adhesives possess bond strengths of around 30 MPa to 33 MPa, 5th generation products have bond strengths in the range of 30 MPa to 48 MPa, and universal bonding agents offer bond strengths ranging from 21.5 MPa to 24 MPa in self-etch mode and 25 to 33 MPa in total-etch mode.
Considering these ranges, a 5th generation bonding agent and an esthetic resin composite system was selected to restore the following clinical case.
A healthy, 21-year-old female presented to the office emergently with a broken central left incisor (No. 9) that resulted from a boating accident (Figure 1). An x-ray scan was taken, and a vitality test was performed. A fractured mesial incisal angle was noted on intraoral and radiographic examination. The patient was provided with restoration options, which included a Class IV resin composite restoration or a porcelain veneer. The patient opted for the Class IV restoration due to its minimally invasive nature and the ease of repair, when needed.
Prior to anesthetic injection, a shade selection was performed. The anterior arch was isolated with a rubber dam from tooth No. 5 to tooth No. 12, and a mock-up restoration was prepared in order to facilitate the construction of a lingual matrix (Figure 2 and Figure 3).
The tooth was prepared to receive a Class IV restoration and beveled in order to promote perfect and seamless margins at the end of the procedure. Before etching, Teflon tape was used to protect the adjacent tooth (No. 8). Next, phosphoric acid (Max-Etch, Clinician’s Choice) was applied, rinsed, and dried (Figure 4 through Figure 6). A bonding agent (MPa MAX, Clinician’s Choice) was selected, applied to the tooth surface, and cured for 20 seconds (Figure 7 and Figure 8).
With the help of the lingual matrix, a nanofilled composite in enamel shade incisal medium (Renamel® NANO™, Cosmedent) was used to build the lingual enamel layer of the restoration (Figure 9). The nanofilled composite was selected due to its mechanical properties, which help it withstand the occlusal (lingual and incisal) forces during mastication.
The dentin mamelons were created with a microfill composite in shade A2 (Renamel Microfill, Cosmedent), and a white opaque tint (Creative Color, Cosmedent) was applied with a No. 1 sable brush (Cosmedent) to replicate white spots present on the adjacent teeth (Figure 10 and Figure 11).
The outer surface (facial) was built with a microfill composite in enamel shade incisal medium (Renamel Microfill, Cosmedent), then the composite surface was smoothed with a No. 3 sable brush (Cosmedent) and cured (Figure 12).
In order to eliminate the oxygen inhibiting layer, hydrosoluble gel was applied on top of the whole composite restoration and it was cured again for 20 seconds on each surface (Figure 13). This process helps improve the esthetics and mechanical properties of the composite surface.
After anatomic adjustments and finishing with a fine diamond bur, a sequence of polishers (ASAP, Clinician’s Choice) was applied to smooth and polish all of the surfaces (Figure 14 and Figure 15).
The initial final result can be seen in Figure 16. At the 24-hour follow-up appointment, a diamond paste (Enamelize, Cosmedent) was applied with a felt point (FlexiPoints, Cosmedent) to achieve a more lifelike result that replicates the surrounding dentition (Figure 17).
Resin composites and bonding agent systems offer a reliable alternative for the restoration of anterior teeth. In this case, the combination of strong bonding agents with highly-esthetic resin composites provided the clinician with outstanding resources to achieve “lifelike” restorations with a long-term life expectancy.
The materials used in this clinical case were provided by Clinician’s Choice and Clinical Research Dental.
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About the Author
Gildo Coelho Santos Jr., DDS, MSc, PhD