Creating the “Perfect” Class V Composite: The Matrix Is Key

INTRODUCTION
Direct composite dentistry presents a variety of placement challenges for a multitude of reasons. The Class V with subgingival margins presents one of the greatest daily concerns and, as a result, the matrix selected to confine the restorative material is paramount to the success of the final restoration. The first successful matrix was introduced to dentistry by Dr. Louis Jack in 1871.¹ In contemporary terms, a dental matrix may be simply defined as a device or piece of properly shaped material that forms the missing wall of the restoration offering special dimension and shape to the restoration during insertion and condensation of restorative material. However, the importance of creating the proper matrix for a direct composite resin cannot be overemphasized based on the complexities that face the practitioner when utilizing these materials to restore a tooth. One of the most critical issues for a successful composite is obtaining and maintaining isolation of the preparation during the entire process of cleansing, treating the enamel and dentinal surfaces, and placement of the composite. Failure to create and maintain an isolated preparation during the bonding and placement procedures, regardless of rubber dam use or other ancillary isolation method, can lead to negative results including microleakage, sensitivity, and potential recurrent caries. Once the proper matrix is in place, the ability to use the concept of “injection molding”—syringing the composite under pressure into the confined matrix mold—allows the operator to more efficiently place the composite in a void-free mass, and more thoroughly seal the margins prior to polymerization.

For years, dentistry has used transparent plastic strips for the majority of the anterior composites placed, many made of the material Mylar, which was developed by DuPont Chemical in the early 1950s. These flat, 2-dimensional strips somewhat confine the resin material and allow for the energy from a curing light to initiate the photoreaction of the composite. One of the underappreciated benefits of the Mylar material is the transference of an ultra-smooth surface to any portion of the composite touching the strip. Research for more than 4 decades has shown that composite cured against Mylar has a more highly polished surface than any diamond or carbide finishing instruments or abrasive polishing systems available.^2-12 However, the ability of the operator to isolate a preparation using the straight or flat strips can be challenging in certain situations. This can lead to a less-than-desirable outcome for both the practitioner and the patient. One specific matrix (Margin Perfect Matrix, or MPM [Margin Perfect Matrix]) has combined the concept of isolating a preparation both apically and interproximally and transferring the surface smoothness of the Mylar to the final restoration. By creating a 270° wrap seal of the tooth preparation, the matrix creates subgingival areas which are smooth, eliminating the need for difficult operator shaping and finishing.

Figure 1. Margin Perfect Matrix (MPM), from Margin Perfect Matrix, is a Mylar film, 0.002 in thick, specifically die-cut to a shape that becomes a universal matrix for all anterior and premolar restorations.

The ability to properly isolate and seal the bonding site of a Class V preparation cannot be underestimated in its contribution to the success of a direct composite. In this article, the authors will outline a protocol using a specifically designed die-cut matrix the dentist can use to create a fixed mold, totally isolating the prepared portions of the tooth, and by syringe pressure-injection of the resin, form a “perfect” seal in the critical gingival areas being restored. As defined by the dictionary, perfect means: Having all the required or desirable elements, qualities, or characteristics; as good as it is possible to be. The technique discussed will utilize a clinical case to illustrate the attributes of having a “system” or protocol to facilitate reproducible results on a daily basis. In the following case report, the authors will present:

1. A demonstration a method of subgingival matrix placement and marginal seal
2. How the MPM is customized, placed, and then secured in place with a light-cured bisphenol A (Bis-GMA) resin instead of a traditional wedge system
3. The use of unit-dose “injection molding” as the ideal method of composite placement.

CASE REPORT
The patient presented with numerous demineralized cervical lesions that would best be treated using minimally invasive direct composite resin restorations.

Clinical Protocol
The first step in this case was to prepare the MPM for use.

The MPM has unique landmarks to identify and become familiar with prior to use in the oral cavity (Figure 1). Following the manufacturer’s directions for use, the matrix is transformed from a 2-dimensional strip into a 3-dimensional mold that can be placed easily around the Class V preparation. As packaged, the matrix is a flat, specifically shaped die-cut system that is molded using finger pressure to form the u-shaped outline of a tooth. In addition, by rolling the interproximal points toward each other, one point at a time, you create a custom-shaped matrix which allows for a 270° wrap of the tooth. The gingival edge of the MPM will guide the matrix under the interdental papillae, forcing the matrix in the sulcus and against the tooth. The MPM is now ready to place around the prepared tooth and into the subgingival space (Figures 2 to 5).

After a local anesthetic was given, the labial carious lesion was removed from tooth No. 21 usin a 330 carbide (Brasseler USA) and an enamel bevel was placed using a 40-μm diamond (889-009-3.5F [Diatech USA]) (Figure 6).

Figure 2. The MPM matrix, prior to shaping by rolling memory bends into it.	Figure 3. Demonstration of forming the initial u-shape tooth shaped matrix.
Figure 4. Rolling the interproximal points toward the long axis, which positions the MPM into the interdental space.	Figure 5. The MPM shaped and ready to place around the prepared tooth.
Figure 6. Incipient carious lesion was removed and an enamel bevel placed using a 40-µm diamond bur.	Figure 7. Once placed around the Class V preparation, the MPM was stabilized using an unfilled bond resin (Heliobond [Ivoclar Vivadent]) on the outside of the matrix and subsequently light cured.

After reviewing the landmarks, the interproximal wings were passed through the contact points and the upper cervical collar was positioned into the sulcus. The matrix should engage the tooth at the base of the sulcus and seat firmly against the root surface. The clinician will notice that the sulcular gingival tissue will be “blanched” if the MPM is properly seated. While holding the matrix firmly in place, a Bis-GMA light-curable resin (Heliobond [Ivoclar Vivadent]) was applied to the outside of the matrix and onto the adjacent (dried) teeth and gingival tissues in a horseshoe pattern, then exposed to an LED light source of 1,000 mW/cm² for 10 seconds (SmartLite Focus [DENTSPLY Caulk]). This acted as a wedge replacement and stabilized the MPM during the remaining clinical steps (Figure 7).

A total-etch technique (Email Preparator [Ivoclar Vivadent]) was used here. Then, after rinsing with a water spray and air-drying, a universal dentin bonding agent (Prime&Bond Elect [DENTSPLY Caulk]) was applied, according to the manufacturer’s instructions (Figure 8). Next, the body composite (Tetric EvoCeram, shade A2 [Ivoclar Vivadent]) was syringed into the matrix using an injection molding technique to minimize voids. This was accomplished by positioning the unit dose nozzle flat on the cervical surface, directly above the prepared margin, then lifting the nozzle so that the occlusal edge of the nozzle was held hard against the tooth surface and the apical edge of the nozzle was open, thus forcing a sheet of composite to slide into the preparation and into gingival area of the matrix (Figure 9). Preheating the body composite to 130°F using a warming device (Calset [AdDent]) greatly facilitates the ease of syringing and also minimizes the chance for voids and air bubbles. Additionally, the use of a small increment of a flowable composite (Heliomolar Flow, shade A1 [Ivoclar Vivadent]) into the preparation (not separately light cured) prior to the “injection” of the warmed body composite can also help create a seamless seal at the tooth-to-restoration interface.

Before curing the restoration, the composite was shaped with a No. 3 brush (Cosmedent), using it as a very thin plastic instrument. The tips of the brush can condense into the matrix-tooth margin and can be used to smooth the juncture of the body composite into the beveled margins (Figure 10).

Figure 8. A total-etch technique was employed here, and after rinsing and air drying, a universal dentin bonding agent (Prime&Bond Elect [DENTSPLY Caulk]) was placed.	Figure 9. The body composite was syringed into the matrix-formed mold created by the MPM. Preheating the composite to 130°F using a warming device (Calset [AdDent]) facilitates application, also decreasing potential for voids and bubbles.
Figure 10. The composite was manipulated with a flat, chisel-shaped brush (No. 3 [Cosmedent]) and ancillary instruments of choice, then light cured using an LED light source with a minimum of 1,000 mW/cm2 for 20 seconds.	Figure 11. Remove the stabilizing resin collar and the MPM.
Figure 12. Note how the smooth surface of the matrix was transferred to the composite restoration, minimizing—if not eliminating—the need to use rotary instruments under the gingival margin.	Figure 13. Final finishing and polishing was accomplished using abrasive cups and points (Astropol [Ivoclar Vivadent]).

Polymerization was accomplished with a high-output LED curing light (SmartLite Focus) with a minimum output of 1,000 mW/cm² following manufacturer’s instructions. Then, the resin-based stabilizing collar was removed with a sickle-shaped instrument (such as a Bates 7/8 scaler [American Eagle Instrument]). Observe how the smooth surface of the matrix was transferred to the composite restoration (Figures 11 and 12). This technique minimizes, if not eliminates, the need to use rotary instruments under the gingival margin.

Final finishing and polishing was accomplished with abrasive cups and points (Astropol [Ivoclar Vivadent]) and the final result can be seen in Figure 13.

CLOSING COMMENTS
Direct composite resins have become a mainstay in today’s contemporary restorative practices. One of the frequent challenges for the practitioner is the isolation of a subgingival Class V. By utilizing a matrix that creates a sealed system, free of crevicular fluids and any blood, coupled with the injection molding of today’s excellent composite materials, one will overcome many of the pitfalls associated with the failures at the gingival margins on Class V restorations. The flexibility of the matrix to conform to the desired shape by the practitioner is a key characteristic of the MPM. This allows the operator to utilize this matrix with success for not only Class V composites, but also for Class III, IV, and full direct resin veneers.

References

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Dr. Belvedere began “injection molding” composite in 1985 and has been teaching continuing education to practicing dentists for more than 40 years. He is a Diplomate of the American Board of Aesthetic Dentistry and an adjunct professor at the University of Minnesota School of Dentistry, where he is the co-director of the University of Minnesota contemporary and aesthetic dentistry level postgraduate course. He can be reached via email at velvytooth@aol.com.

Disclosure. Dr. Belvedere is the creator of the Margin Perfect Matrix and has a financial interest in Margin Perfect Matrix, Ltd.

Dr. Lambert is a Diplomate of the American Board of Aesthetic Dentistry and a Fellow of the American College of Dentists, the Pierre Fauchard Academy, the Academy for Sports Dentistry, and the American Society for Dental Aesthetics. He presents progressive composite dentistry workshops internationally and is a clinical mentor and speaker for the Contemporary Esthetic and Implant Dentistry program at the University of Minnesota School of Dentistry and the Catapult Group. He can be reached via email at ddssmile@aol.com.

Disclosure. Dr. Lambert has a financial interest in Margin Perfect Matrix, Ltd.