Oral Health Group
Feature

The Concealed Margin Restoration: Anterior Margin Placement for Optimum Aesthetics

April 1, 2003
by William E. Turner DMD Cert Esth. FAGD


Leonardo daVinci wrote that ‘most people see without looking, listen without hearing, and touch without feeling’.1 Dentists are as guilty of this as anyone else. We all have a practice full of large anterior composite restorations that if we were to look at them closely, we would see that they are far from invisible. We accept this as the standard of care only because it has always been this way. In the days of silicate materials, it was reasonable to accept compromised aesthetics, but with a myriad of excellent composite materials at our disposal, it is time to reexamine what constitutes acceptable aesthetics.

Placement of margins in large anterior composite restorations has traditionally been dictated by the extent of the caries and/or the previously existing restoration, plus the enamel bevel for retention and blending of the composite.2-6 This typically results in the margin being located somewhere on the labial surface of the tooth, in a highly visible area. We can often blend the composite into the existing tooth structure to create a margin that is almost invisible.

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The anatomy of the surrounding tooth can often be simulated in the restoration. Still, the restoration may not be truly invisible. Metamerism is the phenomenon where the spectrum of light reflected from the tooth is different from that reflected by our restorative material. This results in the colour of the restoration appearing different under different lighting conditions.

As well, the polishability of the material can make it difficult to blend our restoration into the surrounding tooth. We would always prefer to use hybrids for their strength, but they are difficult to polish to a sufficient shine to match some teeth.7 If we choose a microfil because we require a high shine, we must accept compromised strength and longevity.8

With large anterior composites, the biggest problem with achieving a truly invisible result is the margin between the restorative material and the natural tooth structure. It is very challenging to consistently create margins that not only disappear, but remain invisible for many years. Over time, the high polish we place on our restorations tends to degrade, and margins begin to break down and collect stain. Despite our best efforts, patients do things like smoke and drink coffee, tea, and red wine. Eventually that margin we so carefully designed and executed becomes unsightly.

How many restorations do we all have in our practices that would be perfectly serviceable were it not for the highly visible demarcation between the composite and the natural tooth structure? Teeth do not remain the same colour for a lifetime, and while the manufacturer may argue otherwise, the colour stability of many composites is not perfect either.9 This shifting of colour can result in restorations becoming more visible over time.

Conservation of tooth structure is a fundamental tenet of dentistry. Nothing we can make is as good as natural tooth structure. Most dentists agree it is a laudable goal to conserve as much natural tooth structure as possible. With that said, placing margins in the aesthetic zone frequently requires that we sacrifice a small amount of valuable tooth structure in order to place our margins in concealed areas.

When placing large anterior restorations in the aesthetic zone, simply placing the traditional bevel at the margin often results in a restoration that becomes aesthetically inadequate in a few years. Placement of the margins of such restorations in hidden areas results in a restored tooth that has uniform surface colour and anatomy. When the margins deteriorate as they usually do, they are still invisible because they have been placed in concealed areas.

If there is a change in colour of the tooth or the restorative material over time, it is far less noticeable when that difference is between the colour of adjacent teeth, than when it is between the incisal half and the gingival half of the same tooth.

Traditionally it was desirable to avoid placing margins interproximally and in the gingival sulcus primarily because of the difficulty in maintaining an isolated field for placing the restorative material.10-14 In this age of dentin bonding the need for isolation is more important that ever. Fortunately, with the development of the Belvedere matrix, this is no longer a problem.15 (See sidebar.)

TECHNIQUE

In placing a large anterior restoration in the aesthetic zone, we must include the patient in the decision making process. The choice is between placing the margins in order to conserve as much natural tooth structure as possible and risk creating a restoration that will become aesthetically unacceptable within a few years, or sacrificing a small amount of tooth structure to increase the aesthetic longevity of the restored tooth.

Once the decision is made to place the margins in concealed areas, the initial preparation of the tooth is no different from traditional cavity preparation. Resistance and retention form are created, and caries is fully excavated (Figs. 1 & 2). The difference comes when it is time to bevel the margins of the preparation. Instead of the traditional two or three mm. bevel, the visible surfaces of the tooth are marked to a depth of 0.3 mm. with a 834.31.016 depth cutting diamond (Brasseler, Savannah, GA) (Fig. 3).

A medium grit diamond is then used to reduce the visible tooth structure to the depth of the marks. Fine chamfer finishing lines are created just within the gingival sulcus, and in the interproximal areas (Fig. 4). A good choice for both reduction and creation of the chamfer is a two grit diamond 6844.31.014 (Brasseler, Savannah, GA).

Following completion of the preparation, a Belvedere matrix is placed (Contour strip, Ivoclar-Vivadent, Amherst N.Y.), and stabilized with unfilled resin (Heliobond, Ivoclar-Vivadent, Amherst, NY) The Belvedere matrix is designed to isolate the labial surface of the tooth fully against saliva and crevicular fluid.

When properly placed, the Belvedere matrix provides total isolation of the prepared tooth to facilitate bonding. Further, the smoothly finished surface of the band produces a smooth finish to the composite, which is well tolerated by the gingival sulcular epithelium (Fig. 5).

Once the tooth is properly isolated, it is cleansed of organic debris and disinfected with 2.5 % sodium hypochlorite. An appropriate solution is made by diluting Javex bleach (Colgate-Palmolive, New York NY) with an equal volume of water.

Fresh solution should be prepared weekly to ensure an effective solution.16 Mixing the solution with flour of pumice to create a thin paste helps to control the solution and prevent it from running where it isn’t wanted. The tooth is rinsed thoroughly with water, dried, and etched for fifteen to twenty seconds with 35% phosphoric acid. Dentin bonding adhesive is applied according to the manufacturer’s recommendations.

The author prefers to apply a thin layer of flowable composite over the adhesive layer, and cure it. This helps to stabilize the hybrid layer and prevent polymerization shrinkage from pulling the dentin adhesive away from the tooth, which will result in postoperative sensitivity. It also promotes the initiation of the polymerization process in contact with the tooth, and since polymerization shrinkage must take place toward composite, which is already set, the composite is prevented from pulling away from the bond interface with the tooth.

Composite is placed and cured in layers until full contour or slight overcontour is achieved. The complexity of the composite placement procedure will of course vary according to the operator’s preference. For the ultimate in aesthetics, hybrid composite is placed to provide a strong structure, which is then layered with microfil to provide a surface, which is highly polishable. Many modern microhybrid composites are polishable to the point that one has to question the need for microfil composites. Hybrids will never have the same shine that is possible with a microfil, but some can be polished to shine that is more than acceptable fo
r routine use.

Regardless of the composite system selected, an opaquer should be placed within the composite in any area where the composite is thick or extends through the full thickness of the tooth. The uniform translucency of composite tends to give a large class 4 composite a lower value than the surrounding tooth, which results in a grey appearance. Placement of a small amount of composite opaquer in the appropriate shade blocks light transmission through the tooth and creates a much better shade match with the tooth.

The area of coverage of the opaque layer should approximate the area occupied by dentin in the natural tooth. The opaquer is normally applied in a thin and even discontinuous layer (Fig. 6). Excessive opaquer often results in a ‘headlight’ effect similar to that often seen in porcelain fused to metal crowns. The goal is simply to break up the light to prevent it from being transmitted directly through the tooth. The opaquer should be covered with 0.3-0.5 mm. of the final composite shade, either hybrid or microfil (Fig. 7).

Once the restoration is built to full contour and fully cured, the matrix band can be removed (Fig. 8). The restoration is trimmed using spiral-fluted carbide finishing burs such as an H46.31.012 (Brasseler, Savannah, GA). The composite should not be disturbed below the crest of the gingiva. The smooth surface of the mylar matrix band creates a highly polished surface which is well tolerated by the gingival tissues in contact with it.6 The restoration is then polished with the system of choice (Figs. 9 & 10).

The author prefers the Astropol system (Ivolcar Vivadent, Amherst, NY) or other systems of points, cups and discs. Such systems permit the operator to maintain appropriate surface anatomy throughout the polishing process. Disc systems tend to remove all surface anatomy and result in an unnaturally smooth surface to the restoration. Interproximal surfaces are trimmed and polished using diamond finishing strips (Brasseler, Savannah, GA) and Sof-lex polishing strips (3M Espe, St. Paul, MN).

CONCLUSION

In his principles for cavity preparation G. V. Black advocated the placement of restoration margins in self-cleansing areas to prevent restoration failure from recurrent decay.2 Today most of our patients can maintain oral hygiene and dietary control sufficient to eliminate the need for ‘extension for prevention.’ However for restorations in the aesthetic zone, placement of margins in concealed areas is the contemporary interpretation of Black’s principle.

In the same way restoration longevity was enhanced by minimizing recurrent decay in Black’s day, the longevity of modern aesthetic restorations is enhanced by placing margins in areas where their inevitable deterioration will not result in cosmetic failure, and consequently the requirement for premature replacement.

William E. Turner, DMD, Cert. Esth. FAGD, is a 1981 graduate of the University of Manitoba and maintains a full-time general and aesthetic dental practice in Thunder Bay, ON. He holds a Certificate of Proficiency in Aesthetic Dentistry from the State University of New York at Buffalo, and is a fellow of the Academy of General Dentistry, the Academy of Dentistry International, and the International Academy of Dental-Facial Aesthetics.

The author would like to thank Dr. William Hettenhausen for his assistance in the preparation of the illustrations for this article.

Oral Health welcomes this original article.

REFERENCES

1.Gelb M J. How to think like Leonardo daVinci. New York, 1998, Dell Publishing Co.

2.Black G V. A work on operative dentistry, Vol. 2, ed. 5, Chicago, 1924, Chicago Medico-Dental Publishing Co.

3.Jordan R E. Aesthetic Composite Bonding: Techniques and materials. Burlington, Ontario, 1988, B C Decker Inc.

4.Eid H. Retention of composite resin restorations in class IV preparations. J Clin Pediatr Dent 2002 Spring;26(3):251-6.

5.Donly K J, Browning R. Class IV preparation design for microfilled and macrofilled composite resin. Pediatr Dent 1992 Jan-Feb;14(1):34-6.

6.Tan D E, Tjan A H. Margin designs and fracture resistance of incisal resin composite restorations. Am J Dent 1992 Feb;5(1):15-8.

7.Berastegui E, Canalda C, Brau E, Miquel C. Surface roughness of finished composite resins. J Prosthet Dent 1992 Nov;68(5):742-9.

8.Kim K H, Park J H, Imai Y, Kishi T. Fracture behaviour of dental composite resins. Biomed Mater Eng 1991;1(1):45-57.

9.Hosoya Y. Five year colour changes of light-cured resin composites: influence of light-curing times. Dent Mater 1999 Jul;15(4):268-74.

10.Gwinnett A J. Bonding factors in technique which influence clinical success. NY State Dent J 1982; 48:223.

11.Hormati A A, Fuller J L, Denehy G E. Effects of contamination and mechanical disturbance on the quality of acid-etched enamel. J Am Dent Assoc 1980; 100:34.

12.Cox C F. Microleakage related to restorative procedures. Proc Finn Dent Soc 1992:88 Suppl 1:83-93.

13.Sasafuchi Y, Otsuki M, Inokoshi S, Tagami J. The effect on pulp tissue of microleakage in resin composite restorations. J Med Dent Sci 1999 Dec;46(6):155-64.

14.Spahr A, Schon F, Haller B. Effect of gingival fluid on marginal adaptation of class II resin-based composite restorations. Am J Dent 2000 Oct;13(5):261-6.

15.Belvedere P C, Lambert D L. Advancing your direct composites through the use of a specialized matrix. Oral Health April 2002; 92(4):75-83.

16.Johnson B R, Remeikis N A. Effective shelf-life of prepared sodium hypochlorite solution. J Endod 1993 Jan;19(1):40-3.

Belvedere Matrix Preparation and Placement

The Belvedere matrix was developed by Dr. Paul Belvedere to isolate the buccal surface of teeth during the placement of composite, indirect and direct veneers. They are available as Contour Strips from Ivoclar Vivadent (Amherst NY) (Fig. 11). They are supplied inside a plastic container, which seems like a good idea until you realize that it is easy for the end of the roll of Contour Strips to become lost inside their container. An elastic band should be placed around the container to retain the end of the roll and prevent it from being lost inside. If this happens the only recourse is to cut a large hole in the container to retrieve the end.

The parts of the Contour Strip are identified as the interproximal point (IP), the cervical collar (CC), and the interproximal leg (IL) (Fig. 12). When the strip is removed from the roll, it is left with a natural curvature (Fig. 13). The strip is first rolled between the fingers in the direction of this curvature, to form it into a ‘U’ shape (Fig. 14). By varying the pressure exerted by the fingers on the matrix, and the distance that it is rolled, the curvature can be controlled to accommodate a variety of teeth. A strip can be rolled tightly for a mandibular incisor, or less tightly for a maxillary cuspid (Fig. 15).

Next the interproximal points are rolled inward in a similar manner as was done to create the initial ‘U’ shape of the strip (Fig. 16). Finally the cervical collar of the matrix is flared with a round shafted instrument (Fig. 17). This allows the cervical collar to seal tightly against the gingival portion of the tooth, and creates an excellent emergence profile when properly placed in the gingival sulcus.

The formed matrix is then placed on the tooth by slipping the interproximal points through the contact areas from the labial toward the lingual (Fig. 18). It may be necessary to separate the teeth slightly by torquing an instrument between them. The flared cervical collar is gently guided into the labial sulcus. When properly positioned, the gingiva will blanch slightly (Fig. 19). The tissue and the strip are dried with a gentle stream of air, a generous drop of unfilled bond resin (Heliobond, Ivoclar Vivadent, Amherst, NY) is applied to the outside of the matrix, and cured for ten to twenty seconds.

Once the basics are mastered, there are numerous variations and tricks to adapt the technique to a variety of situations. When properly placed, the Belvedere matrix will effectively seal out saliva and crevicular fluid while the tooth is c
leansed, disinfected, etched, bonded, and restored (Fig. 20). Once placement of the restoration is complete, the matrix and the cured bond resin can be gently removed with a large sickle scaler, such as a U15 or 7/8 Bates (Fig. 21). The restoration is then trimmed to final contour and polished to a high shine. Subgingival finishing should be avoided to maintain the smooth finish created by the matrix strip.