The effect of finishing sealant augmented margins in

Class V cavities

 
Class V cavities in the buccal and lingual aspects of human posterior teeth were acid etched and restored in one of two ways. In the extended primer technique, the UV polymerized primer coat was extended 2-3 mm beyond the cavity, then finished back. In the butt-joint technique, the primer coat was extended to just below the cavosurface line angle. Eight specimens for each technique were prepared and tested. A surface micro-analyzer capable of detecting one microinch surface roughness was used to determine the variance in marginal smoothness; margins were also examined using a scanning electron microscope. No statistical difference in smoothness was detected between the two techniques.

 
While the use of composite restorative materials is widespread, microleakage at cavity margins and lack of an acceptable smooth marginal finish still exist. Failure to seal the cavities against microleak­ age may be responsible for pulpal irritation and secondary caries. While a smooth margin is essential to minimize staining, plaque accumulation, and calculus formation, it will also contribute to proper marginal seal.
Two finishing methods1-3 have been suggested for enhanced sealing of composite resin restored cavity margins against microleakage. One method consists of conventional finishing of the restorative material in Class V cavities to a butt joint with the primer coat extending just to the cavosurface line angle. Another method involves the application of ultraviolet light activated sealant as a primer coat extending 3 mm beyond the cavosurface line angle. The restorative material is then inserted, extended over the primer coat, and finished to a feather edge.4-5
Since both butt joint and feather edge techniques are currently in use as means of reducing marginal leakage in Class V cavities, the present in vitro study was conducted to determine which of these two techniques result in a smoother margin when finished to clinical acceptability.

 
Posterior teeth were obtained from the oral surgery clinic and were fixed in 10% formalin. Debris and stains were removed using No. 10 and 11 scalpel blades and Nupro coarse polishing paste in rubber prophy cups. The roots were mounted in polyester casting resin. Three mm long and one mm wide Class V cavities were prepared deep enough to extend 0.5 mm into the dentin. All cavities were prepared at the junction between the middle and cervical third of the buccal and lingual aspects of eight teeth with a No. 56 carbide bur. The speci­ mens were kept in water at room temperature at all times between treatments. Adaptic [Johnson & Johnson, New Brunswick, New Jersey 08903, USA] and Nuva-seal [L.D. Caulk, Milford, Delaware 19963, USA] were chosen as the filled com­ posite resin and the cavity sealer, respectively. These materials are in widespread use and perform well in preventing microleakage.6-7 Medium aluminum oxide disks [Minnesota Mining and Manufacturing Co., St. Paul, Minnesota 55101, USA] were used to obtain the final marginal finish3 owing to their ability to smooth down rough filler particles.
Each tooth contained two fillings, one for each of the two sealer application techniques under inves­ tigation. In the butt joint technique, the sealer was placed just below the cavosurface line angle and extended to just beyond the dento-enamel junc­ tion. In the feather edge technique, the sealer was extended 2-3 mm beyond the cavosurface line angle to just beyond the dento-enamel junction. After the sealer was applied and polymerized, the composite restorative material was carried to the cavities and condensed into place using a mylar matrix strip held tightly around the circumference of the tooth for 3 minutes. Initial finishing was accomplished by removing the flash with a No. 10 scalpel blade and rough finish was achieved with a tapered green stone. Final finishing was then accomplished using the medium aluminum oxide disks. A surface analyzer [Model 150, 21 -1410-01, Gould Inc., El Monte, CA, U.S.A.] with the capa­bility of detecting 1 micro-inch of surface rough­ ness was used to determine the variance in margi­ nal roughness between the two methods of sealant application. A traverse speed of 0.01 inch/sec and a chart speed of 0.5 inch/sec was used to provide a clear trace of the interface between the enamel and composite. In order to examine the specimens by scanning electron microscopy [Novascan-30, Carl Zeiss Inc., New York, NY 10018, U.S.A.] they were degassed, and coated with a gold-palladium
alloy film.
To correctly identify the margin, a technique was developed that allowed close correlation between the surface roughness tracing and the electron micrographs of a particular specimen. The technique consisted of placing two pieces of tape along a line on either side of the occlusal margin of the finished cavity and at 45° angle to it.
The specimen was then placed under the traverse bar of the surface micro-analyzer so that the probe traversed from the tape onto the tape over the remaining composite as shown in Figure 1. As the probe traversed the edge of the tape, a clearly identified vertical line appeared on the roughness printout chart corresponding to the drop at the edge of tape. Thus, the surface printout con­ sisted of two distinct vertical lines 3 1/2 inches apart with a clear view of the margin in between. Likewise, the scanning electron micrographs were displayed at such a magnification that the tapes were 3 1/2 inches apart at the center of the photo­ graph and, therefore, showed the same area of the margin traced by the surface analyzer

A: LINE  AND DIRECTION OF PROBE TRAVEL

M:OCCUSAL  MARGIN  OF CLASS V  CAVITY

T:TAPE STRIPS 45° TO  OCCUSAL MARGIN

Fig. 1. A schematic diagram indicating the method used in identifying the cavity margin.

Figure 2(a) is a typical tracing of the butt joint resto­ ration finished to an acceptable margin [denoted by arrow]. Figure 2(b) is a tracing of the feather edge restoration, also finished to an acceptable margin [arrow]. Figures 3(a) and 3(b) are the cor-responding scanning electron micrographs of the two finished occlusal margins. As far as can be determined, there are no qualitative differences between these two types of primer sealer applica­ tion techniques after finishing with the aluminum oxide disks. The photomicrographs of Figure 3 cor­ relate well with the surface analyzer tracings in Figure 2, and enhances our understanding of the characteristics of the two major types of marginal finish. These photomicrographs also allow visual evidence of the nature of the marginal roughness seen in the surface tracings.

 
The statistical analysis showed that the average roughness for the extended primer technique was 3237 ± 535 micro-inches while that for the con­ ventional technique was 2773 ± 434 micro-inches. Analysis of the data, by student t-test [p£0.05] and non-parametric Wilcoxon test8, showed no statistical difference between the two techniques.
Smoothness of the two margins were similar because the sealer, being comparatively softer than the composite, was finished back to the cavosur-face line angle in the feather edge technique. Such a finishing technique seems to leave a feather edge margin very similar in roughness and appearance to the butt joint margin.
Other aspects of the two techniques, such as compressive strength of the feather edge and the wear resistance of the sealer coat placed over the entire preparation, should be examined.

 
Analysis of the surface roughness of margins of Class V cavities restored with a composite filling material was made. Two types of sealer application techniques have been compared. When the butt joint technique, with the sealer placed at the cavosurface line angle, and the feather edge technique, with the sealer placed 2-3 mm beyond the cavosurface line angle, were compared, no vis­ ual, tactile, or statistical differences were detected.

The author wishes to thank Mr. Ron Burrel who served as a laboratory assistant during this study.