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J Am Dent Assoc, Vol 136, No 8, 1106-1112.
© 2005 American Dental Association
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RESEARCH

Surface roughness of new microhybrid resin-based composites



RÜSTÜ GEDIK, D.D.S., Ph.D., FERIDUN HÜRMÜZLÜ, D.D.S., Ph.D., AKIN COSKUN, D.D.S., Ph.D., ÖZDEN ÖZEL BEKTAS, D.D.S. and ALI KEMAL ÖZDEMIR, D.D.S., Ph.D.


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
Background. Rough, poorly polished resin-based composite (RBC) surfaces contribute to staining, plaque accumulation, gingival irritation and recurrent caries. Proper finishing and polishing enhance both the esthetics and the longevity of restored teeth.

Methods. The authors evaluated the influence of various finishing and polishing techniques on the surface roughness of four microhybrid RBCs. Thirty samples of each material were cured under Mylar matrix strips (Yates and Bird/Motloid, Chicago). All microhybrid RBC specimens were finished with multifluted carbide burs, except for the Mylar matrix strip samples, and then were polished using one of four finishing systems: Sof-Lex contouring and polishing disks (3M ESPE, St. Paul, Minn.); Enhance Finishing System (Dentsply-Caulk, Milford, Del.) followed by Prisma Gloss (Dentsply-Caulk) polishing paste application; Astropol finishing, polishing and high-gloss polishing system (Ivoclar Vivadent, Schaan, Liechtenstein); and Astrobrush polishing system (Ivoclar Vivadent). The authors tested the samples to obtain average surface roughness and analyzed the values.

Results. The use of the Astrobrush technique caused the greatest roughness on all RBC specimens. The smoothest surface was produced with a carbide bur followed by aluminum oxide disks, Astropol technique and Enhance technique. Overall, there were differences in surface quality among the materials. InTen-S (Ivoclar Vivadent) had statistically lower surface roughness values after finishing and polishing with the Astrobrush technique, compared with the other RBCs.

Conclusion. The highest surface roughness values were achieved after the Astrobrush technique was used. The Sof-Lex aluminum oxide disks, and Enhance and Astropol techniques provided the smoothest surface.

Clinical Implications. The Sof-Lex, Enhance and Astropol techniques produced a smooth surface after the finishing and polishing of materials, while the Astrobrush technique yielded the least favorable results.

Key Words: Microhybrid resin-based composite; surface roughness; finishing; polishing

Smooth, highly polished restorations have been shown to be more esthetic and more easily maintained than restorations with rougher surfaces.1,2 All resin-based composites (RBCs) should be polished after polymerization because rough, unpolished restorations increase the coefficient of friction and may increase the rate of wear.3 In addition, a smooth surface can reduce plaque retention, thereby minimizing possible gingival irritation, surface staining, patient discomfort and secondary caries.2,4

A smooth surface can reduce plaque retention, minimizing possible gingival irritation, surface staining, patient discomfort and secondary caries.

RBC surfaces can be finished and polished using various techniques. Burs, disks and pastes have all been used to achieve a smooth surface.5–7 Unfortunately, there usually is a problem during the finishing and polishing of RBCs because the resin matrix and inorganic filler differ in hardness and, thus, do not abrade uniformly. Apparently, the finishing and polishing procedures contribute to the appearance of the color and glass of a composite restoration.8

Since the introduction of RBCs, studies have been conducted to develop a finishing and polishing procedure that would produce a smooth-surfaced restoration. Frequently, however, newer, different materials had replaced the RBC and finishing and polishing materials by the time the study was completed. This indicated a need for continuous research. In recent years, manufacturers have improved RBCs by reducing particle size, increasing filler quantity, improving adhesion between the filler and the organic matrix, and using low-molecular-weight monomers to improve handling and polymerization.9 By experimenting with particle size, shape and volume, manufacturers have introduced RBCs with differing physical and handling properties (Table 1Go).


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  		TABLE 1 RESIN-BASED COMPOSITES TESTED.

 
With the development of new microhybrid composites, updated evaluations of polishing procedures are necessary. We conducted a study to compare the effect of four polishing systems on the surface roughness of four microhybrid composites.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
We tested four microhybrid resin-based composites—Esthet-X (Dentsply-Caulk, Milford, Del.), Venus (Heraeus Kulzer, Dormagen, Germany), InTen-S (Ivoclar Vivadent, Schaan, Liechtenstein), Point 4 (Kerr, Orange, Calif.) (Table 1Go)—and four finishing techniques—Sof-Lex contouring and polishing disks (3M ESPE, St. Paul, Minn.); Enhance Finishing System (Dentsply-Caulk) followed by Prisma Gloss (Dentsply-Caulk) polishing paste application; Astropol finishing, polishing and high-gloss polishing system (Ivoclar Vivadent); and Astrobrush polishing system (Ivoclar Vivadent) (Table 2Go). We calculated the sample size for the study protocol using the range and standard deviations from data presented in the literature.10,11 Based on those published values—a significance level of {alpha} = .05 with a power of 80 percent—we calculated a sample size of three units per cell. To prevent type II errors, we increased the final sample size to six samples per group, with five groups for each of the four materials.


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  		TABLE 2 FINISHING AND POLISHING SYSTEMS TESTED.

 
To reduce variability, a research assistant prepared, finished and polished all of the samples. She made 30 cylindrical specimens of each material using a mold (4-millimeters thick and 10 mm in diameter). She placed the mold on Mylar matrix strips (Yates and Bird/Motloid, Chicago) and a glass slide and inserted the RBCs into the mold in two increments. She inserted the first increment into the mold and polymerized it with a light-curing unit (Elipar Curing Light 2500, 3M ESPE, St. Paul. Minn.) for 40 seconds. When she inserted the second increment, she laid another Mylar matrix strip and glass slide on top of it and placed a 2,000-gram axial load over it for 30 seconds to extrude the excess material. After she removed the load and the upper glass slide, she cured the samples with a light-curing unit for 40 seconds. After light curing was completed, she placed the samples in 10 milliliters of artificial saliva at 37 C for one week. The research assistant removed the samples with tongs and randomly assigned the samples to one of the five test groups: Group I, Mylar matrix strip only (control); Group II, Sof-Lex; Group III, Enhance Finishing System; Group IV, Astropol; Group V, Astrobrush.

In an attempt to mimic the clinical situation, the research assistant first contoured all of the samples, except for those in Group I, with a multifluted carbide bur. She treated Group II samples with aluminum oxide disks at coarse (55 micrometers), medium (40 µm), fine (24 µm) and ultra fine (8 µm). She treated Group III samples with aluminum oxide–impregnated polymer points, followed by fine (1 µm) and extra fine (0.3 µm) polishing paste using a foam polishing cup. She treated Group IV samples with Astropol F gray finishing cup (40 µm), Astropol P green polishing cup (20–40 µm) and Astropol HP pink high-gloss polishing cup (10 µm). She treated Group V samples with a silicon carbide–impregnated polyamide bristle brush (Astrobrush). To remove debris after each step of the finishing and polishing procedures, the research assistant rinsed all of the samples with water and air-dried them before the next step. She finished and polished specimens with a slow-speed handpiece. She applied disks and points with light pressure in a low-speed handpiece with water spray and discarded the disks and points after use.

We selected representative samples from each group for microscopic examination. We sputter-coated the samples with gold, and examined them using a scanning electron microscope (JSM-5600, JEOL, Tokyo). We took photomicrographs at a magnification of (x1,000) for surface topography comparisons. To obtain the average surface roughness of the samples in micrometers, we used a surface profile measuring instrument (Surtronic 3+, Rank Taylor Hobson, Leicester, England), taking into consideration the mean value of the height of the surface profile above and below a center line throughout a prescribed sampling length roughness. We took three successive measurements at different locations for each sample. Then we recorded the roughness value for each sample as the average of these three readings. Using two-way analysis of variance (ANOVA) and Tukey test, we compared the mean surface roughness values.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSION
 REFERENCES
 
The average surface roughness for combinations of RBCs and polishing systems are shown in Table 3Go and Figure 1Go, respectively. When we analyzed the results using two-way ANOVA, we found significant effects of both the finishing and polishing techniques (F = 127.01; P < .05) and the different composites (F = 4.22; P < .05) on surface roughness. Sof-Lex disks, Astropol cups and Enhance points followed by the Prisma Gloss application techniques exhibited fewer roughness values on the outer surfaces of materials tested, and there were no significant differences among these techniques. The use of Astrobrush system resulted in the highest roughness values on all composite materials. InTen-S had statistically lower surface roughness values after finishing and polishing when the Astrobrush technique was used, compared with the other RBCs. Representative scanning electron microscopy photomicrographs of samples finished with the procedures we describe, as well as the matrix surface, are shown in Figures 2Go through 6GoGoGoGo (Figures 2Go, 3Go and 4Go appear on page 1110 and Figures 5Go and 6Go appear on page 1111), and which also correlated with the surface roughness as measured with the surface profile measuring instrument.


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  		TABLE 3 SURFACE ROUGHNESS FOR FOUR MATERIALS AND FIVE FINISHING PROCEDURES.

 


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  		Figure 1. Mean surface roughness of microhybrid resin-based composites and the control. Esthet-X is manufactured by Dentsply-Caulk, Milford, Del. Venus is manufactured by Heraeus Kulzer, Dormagen, Germany. InTen-S is manufactured by Ivoclar Vivadent, Schaan, Liechtenstein. Point 4 is manufactured by Kerr, Orange, Calif. Mylar matrix strip is manufactured by Yates and Bird/Motloid, Chicago. Sof-Lex is manufactured by 3M ESPE, St. Paul, Minn. Enhance is manufactured by Dentsply-Caulk. Astropol is manufactured by Ivoclar Vivadent. Astrobrush is manufactured by Ivoclar Vivadent.

 


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  		Figure 2. Scanning electron microscopic photomicrograph (x1,000) of the Esthet-X (Dentsply-Caulk, Milford, Del.) surface after removal of the Mylar matrix strips (Yates and Bird/Motloid, Chicago).

 


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  		Figure 3. Scanning electron microscopic photomicrograph (x1,000) of the Esthet-X (Dentsply-Caulk, Milford, Del.) surface after finishing with the carbide bur followed by the Astropol (Ivoclar Vivadent, Schaan, Liechtenstein) technique.

 


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  		Figure 4. Scanning electron microscopic photomicrograph (x1,000) of the Point 4 (Kerr, Orange, Calif.) surface after finishing with the carbide bur followed by the Enhance (Dentsply-Caulk, Milford, Del.) technique.

 


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  		Figure 5. Scanning electron microscopic photomicrograph (x1,000) of the InTen-S (Ivoclar Vivadent, Schaan, Liechtenstein) surface after finishing with the carbide bur followed by the Sof-Lex (3M ESPE, St. Paul, Minn.) technique.

 


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  		Figure 6. Scanning electron microscopic photomicrograph (x1,000) of the Venus (Heraeus Kulzer, Dormagen, Germany) surface after finishing with the carbide bur followed by the Astrobrush (Ivoclar Vivadent, Schaan, Liechtenstein) technique.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSION
 REFERENCES
 
Finishing refers to gross contouring or reducing of the restoration to obtain the desired anatomy. Polishing reduces the roughness and scratches created by finishing instruments.12 Proper finishing and polishing are important steps that enhance both the esthetics and longevity of restored teeth.13,14 Rough, poorly polished surfaces contribute to staining, plaque accumulation, gingival irritation and recurrent caries.2 In our study, as well as in others,10,12,15–18 we found that the Mylar matrix strip formed the smoothest surface. Nevertheless, as certain studies have shown,19,20 the surface layer, which is rich in resin, needs to be eliminated; thus, finishing is indispensable. In this study, the research assistant used carbide burs to finish the outer surfaces of the samples and then used different polishing techniques.

There are, however, some new agents in the dental market that remove the resin-rich (air-inhibited) layer before finishing is performed on the RBCs. Diamond and carbide burs also are necessary for contouring anatomically structured and concave surfaces such as the lingual surface of anterior teeth or the occlusal surfaces of posterior teeth. Jung21 suggested that carbide finishing burs would be best suited for smoothing and finishing, owing to their low cutting efficiency on hybrid composites. Ferracane and colleagues22 reported that finishing using diamond burs tended to leave a more irregular surface when compared with finishing using carbide bur. Moreover, studies have reported that using finishing burs alone provided a rough composite surface.23–25 The use of finishing burs followed by polishing paste alone did not provide the same level of smoothness achieved using abrasive-impregnated disks or aluminum oxide disks.10 On the other hand, aluminum oxide disks have limitations due to geometry. When using disks, it often is difficult to efficiently create, finish and anatomically polish contoured surfaces, especially in the posterior regions of the mouth. In concave areas, differently shaped abrasive instruments are required.1,10 For these reasons, after we used carbide burs to finish all of the specimens in our study, we chose to study the Astrobrush technique, the Astropol cups technique and the Enhance points followed by the Prisma Gloss application technique.

Our study showed that the use of carbide finishing burs followed by the Astropol cups technique provided a smoother surface than did the use of the Astrobrush technique. Furthermore, in other studies, as well as in ours, a smoother surface was produced with the use of the Sof-Lex aluminum oxide disks technique15,26 and by using Enhance points followed by the Prisma Gloss application technique,27,28 which produced similar results. Other studies, as well as ours, have shown that there is no significant difference between RBCs after finishing and polishing using the Sof-Lex system and the Enhance system followed by application of Prisma Gloss.12,29

In our study, the highest roughness values were achieved after the research assistant used the Astrobrush technique. This may have occurred because the composite’s inorganic filler, which has a tendency to absorb energy, avoided or softened the formation and propagation of surface microcracks in the material.30 Among the materials tested, InTen-S had statistically lower surface roughness values after finishing and polishing when the Astrobrush technique was used, compared with the other RBCs. The surface roughness of the composite is dictated by the size, hardness and amount of filler, which enhance the mechanical properties of the RBCs, and by the flexibility of the finishing material, the hardness of the abrasive and the grit size.11,31

The results of our study indicate that abrasive instruments can be chosen on the basis of the tooth’s anatomy and the accessibility of the restorations. However, rubber polishing instruments and aluminum oxide disks provided a smooth finished surface on tested materials. In addition, the correlation to clinical practice may be limited26; however, our in vitro study correlates only to clinical situations in which there are accessible and relatively flat surfaces. Since there are several physiological and biological processes that may be related to the increase in surface roughness,32 further studies are needed to determine which finishing techniques are best suited to clinical situations in which access is limited and restoration surfaces are complex. Therefore, future studies should attempt to simulate concave and convex surfaces.


   CONCLUSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
REFERENCES
 
Use of the Sof-Lex aluminum oxide disks, Enhance points followed by Prisma Gloss application technique and Astropol cups provided the smoothest surface for all the composites tested. The highest roughness values were achieved after use of the Astrobrush technique. Overall, there were differences in surface quality among the materials. InTen-S had statistically lower surface roughness values after finishing and polishing when the Astrobrush technique was used, compared with the other RBCs.


   FOOTNOTES
 

Dr. Gedik is an assistant professor, Cumhuriyet University, Faculty of Dentistry, Department of Oral Diagnosis and Radiology, Sivas, Turkey.


Dr. Hürmüzlü is an assistant professor, Cumhuriyet University, Faculty of Dentistry, Department of Restorative Dentistry, Sivas, Turkey, e-mail "fhurmuzlu{at}cumhuriyet.edu.tr". Address reprint requests to Dr. Hürmüzlü.


Dr. Coskun is an assistant professor, Cumhuriyet University, Faculty of Dentistry, Department of Prosthodontics, Sivas, Turkey.


Dr. Bektas is a resident, Cumhuriyet University, Faculty of Dentistry, Department of Restorative Dentistry, Sivas, Turkey.


Dr. Özdemir is an associate professor, Cumhuriyet University, Faculty of Dentistry, Department of Prothodontics, Sivas, Turkey.


   REFERENCES
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 

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