|Year : 2014 | Volume
| Issue : 2 | Page : 70-73
Effect of finishing and polishing procedures on biofilm adhesion to composite surfaces: An ex vivo study
Nishant Vyavahare1, Swarupa Gaikwad2, Srinidhi Surya Raghavendra3, Mohammad Mukhit Kazi4
1 Lecturer, Department of Conservative Dentistry, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
2 Undergraduate Student, Department of Conservative Dentistry, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
3 Professor and Head, Department of Conservative Dentistry, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
4 Lecturer, Department of Microbiology, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||18-Jun-2015|
Dr. Srinidhi Surya Raghavendra
Department of Conservative Dentistry and Endodontics, Sinhgad Dental College and Hospital, STES, Vadgaon Campus, Pune - 411 041, Maharashtra
Source of Support: Indian Council of Medical Research STS Project ID:
2014-03201., Conflict of Interest: None
Introduction: Surface roughness allows plaque accumulation resulting in gingival inflammation, superficial staining and secondary caries. Proper surface finishing and polishing are critical clinical procedures which enhance esthetics and longevity of restorations. This study evaluated adhesion of Streptococcus mutans biofilm on the surface of composite resin discs (nanofilled, Filtek Z350, 3M ESPE, Salt Lake City, UT, USA) after finishing and polishing by different techniques. Methodology: Sixty samples of nanofilled composite resin were prepared in a circular shaped disc- 6 mm × 2 mm and divided randomly in three groups (n = 20) for surface treatments. Control group: composite resin surface in contact with Mylar matrix strips with no finishing or polishing performed, Sof-Lex aluminum oxide disc technique and 30-blade tungsten carbide burs and silicon carbide brushes, Astrobrush. The samples were subjected to biofilm adhesion by inoculation in suitable media. The response variable was the mean CFU/mL present in the Streptococcus mutans biofilms formed on the composite resin surface. Data was statistically analyzed by three-way analysis of variance (ANOVA). Results: The Mean adhesion found in Mylar matrix strip group at 10 dilution was 74.7 ± 3.5, in Sof-Lex group was 147.3 ± 7.0 and in Astrobrush group was 149.4 ± 8.1. This difference in the mean values between the groups was found to be statistically significant (p < 0.01). Conclusion: Mylar matrix strips promoted the least bacterial adhesion, polishing with Sof-Lex aluminium oxide discs provided a smoother surface than Astrobrush and hence less bacterial adhesion than Astrobrush system.
Keywords: Biofilm, composite resin, nanohybrid, polishing discs
|How to cite this article:|
Vyavahare N, Gaikwad S, Raghavendra SS, Kazi MM. Effect of finishing and polishing procedures on biofilm adhesion to composite surfaces: An ex vivo study. J Dent Allied Sci 2014;3:70-3
|How to cite this URL:|
Vyavahare N, Gaikwad S, Raghavendra SS, Kazi MM. Effect of finishing and polishing procedures on biofilm adhesion to composite surfaces: An ex vivo study. J Dent Allied Sci [serial online] 2014 [cited 2020 Jan 25];3:70-3. Available from: http://www.jdas.in/text.asp?2014/3/2/70/159080
| Introduction|| |
The tooth surface is covered with a biofilm - a slime layer consisting of millions of bacterial cells, salivary polymers, and food debris. If uncontrolled, this biofilm reaches a thickness of hundreds of cells on the surfaces of the teeth. This formed biofilm, also called plaque, provides an excellent adhesion site for the colonization and growth of many bacterial species. ,
Various steps are involved in the formation of dental plaque. As soon as a tooth has been cleaned, salivary molecules are adsorbed to the enamel. The enamel is coated with a complex mixture of components, including glycoproteins, acidic proline-rich proteins, mucins, bacterial cell debris, exoproducts and sialic acid which are called as pellicle. The next step is bacterial interaction with this acquired pellicle via specific cell-to-surface interactions.  The biofilm formation is by Streptococcus sanguis and Actinomyces viscosus and is influenced by a number of environmental parameters, such as osmolarity, carbon source and pH.  During the third step, other bacterial species like Streptococcus mutans adhere to the primary colonizers by cell-to-cell interactions. Further bacterial growth on tooth surface leads to the formation of biofilm on the teeth, also called dental plaque. ,
Streptococcus mutans cocci are Gram-positive, facultative anaerobes commonly found in the human oral cavity. They are mesophilic and grow rapidly at temperatures from 18°C to 40°C. They break down sugar for energy and produces an acidic environment, which demineralizes the superficial structure of the tooth. 
The use of composite resins and resin-based materials for anterior and posterior restorations has increased dramatically in the past decade due to the clinical demand for more esthetically acceptable and long-lasting materials. Bacterial adhesion to the surface of composite resins and other dental restorative materials is an important parameter in the etiology of secondary caries formation.  A polished restorative surface ensures adequate esthetics and significantly reduces the risk of initial bacterial adherence and subsequent colonization. It also decreases periodontal disease, marginal discoloration and secondary caries progression promoted specifically by S. mutans and Streptococcus sobrinus. 
The surface of a dental composite restoration normally remains rough. Surface roughness allows plaque accumulation, which may result in gingival inflammation, superficial staining, and secondary caries. Proper surface finishing and polishing are critical clinical procedures, which enhance esthetics and longevity of restorations. Polishing reduces roughness and scratches created by finishing instruments. , The objective of finishing is to contour the composite restoration to its final shape. This process leaves a surface that is still rough and requires polishing to achieve a clinically optimal surface. Studies have shown that composite material surfaces are colonized by oral bacteria, including S. mutans.  Smoother surfaces reduce the biofilm development on restoration and adjacent tooth margins. Care is required during polishing since inappropriate usage can result in greater surface roughness than that existed prior to polishing.  Smoother surfaces and margins reduce the risk of biofilm adhesion and maturation, recurrent caries, gingival irritation, and staining. 
There are various techniques of finishing and polishing composite restorations including diamonds, carbide burs, stones, brushes, rubber wheels, cups, discs, strips, and pastes.
The aim of this study was to evaluate S. mutans biofilm adherence on the surface of nanofilled composite resin subjected to three different finishing and polishing techniques, strips, disks, and brushes.
| Materials and Methods|| |
Samples (n = 60) of nanofilled composite resin (Filtek Z350, 3 M ESPE, St Paul, Minnesota, USA) were prepared in a circular shaped disk -6.0 mm diameter and 2.0 mm in height. The molds were filled with nanofilled composite in a single increment and were covered with Mylar matrix strip to obtain a flat surface. Samples were cured for 40 s with a curing unit (Bluephase C5, Ivoclar Vivadent, Leichtenstein) operating at 500 mW/cm 2 . Samples were retrieved from the mold using a surgical blade and immersed in dark vials containing distilled water at 37°C for 24 h.
Randomly selected samples of nanofilled composite resin were subjected to one of three finishing and polishing techniques:
- Control group - use of Mylar matrix strip with no finishing or polishing procedures (n = 20).
- Aluminum oxide disks (Sof-Lex, 3 M ESPE, St. Paul, MN, USA) (n = 20).
20 samples were polished with disks of grits coarse 100 μm, medium 29 μm, fine 14 μm, superfine 5 μm each unidirectionally for 40 s using contra-angle low speed handpiece (speed up to 20,000 rpm). After the use of each disk, the composite surface was washed and air dried for 5 s. A new polishing disk was used after every third sample.
- 30-bladed tungsten carbide burs (SS White FG-300, Beavers Dental, Morrisburg, ON, Canada) and silicon carbide brushes (Astrobrush, Ivoclar Vivadent, Leichtenstein) (n = 20).
Twenty samples were finished with tungsten carbide for 30 s at a low speed, washed and air dried for 5 s, then polished with silicon carbide brushes for 30 s unidirectionally.
All samples (Group A, B, C) were placed in sterile gamma radiated 24-well tissue culture plates.
A standard suspension of S. mutans (MTCC number 890) was prepared containing 10 6 cells/ml. S. mutans was seeded on brain heart infusion (BHI) agar, incubated at 37°C for 24 h in a CO 2 jar. After incubation, growth was suspended in sterile physiological saline (0.9%), and numbers of cells were counted in a digital spectrophotometer (Equiptronics model EQ 820, Powai, Mumbai, India). The parameters of optical density and wavelength used were 0.620 nm and 398 nm respectively. Adherence testing was done under strict aseptic conditions.
For the adherence testing in laminar flow chamber, Gybbons and Nygaard broth was used. 1.5 ml of broth and 0.1 ml of standardized S. mutans suspension was added to each 24-well polystyrene tissue culture plate. The plates were sealed and incubated at 37°C for 24 h in a CO 2 jar. Samples were then removed and washed thrice with a sterile physiological solution to dislodge loosely bound material. Following this, samples were placed in tubes with 3 ml of sterile physiological saline (0.9%) and sonicated for 30 s to disperse the biofilms. The suspension obtained was diluted at 10, 100 and 1000 times and aliquots were made and 0.1 ml from each aliquot was then seeded on BHI agar to see the number of colonies after 24 h incubation at 37°C and mean values of colony forming units (CFU) were noted. The dilution of S. mutans was done to avoid the false results of biofilm adherence, as the organism has a property of formation of biofilm due to coaggregation.
The response variable was the mean CFU/mL present in the S. mutans biofilms formed on the composite resin surface. Data were statistically analyzed by three-way analysis of variance (ANOVA).
| Observations and Results|| |
[Table 1] shows mean and standard deviation values of the CFU/ml (log10) of S. mutans within the biofilms formed. Mean values of CFU/mL were converted into logarithmic (log10) values and analyzed by three-way ANOVA test for significance.
|Table 1: Mean and SD values of the CFU/ml (log10) of Streptococcus mutans within the biofilms |
Click here to view
The Mylar strip group showed least bacterial adhesion than the Sof-Lex and Astrobrush polishing groups regardless of its dilution [Graph 1]. This difference in the mean values between the groups was found to be statistically significant (P < 0.01). Smoother surface was generated with Sof-Lex aluminum oxide disks when compared to Astrobrush system (Ivoclar Vivadent, Schaan, Leichtenstein), which was seen as higher bacterial adhesion with Astrobrush and a significant mean difference was revealed statistically.
| Discussion|| |
The selection of S. mutans to promote biofilm adhesion is based on the fact that these microorganisms are recognized as the major etiological agent of human dental caries, are present in mature plaque, and represent a significant amount of the oral streptococci in caries lesions. S. mutans adherence to enamel surface and to restorative materials is a preliminary condition to biofilm formation and can eventually promote secondary caries and periodontal diseases. 
Mylar matrix strips (Group A) produced the lowest bacterial adhesion on the nanofilled surface [Table 1]. These results were similar to various previous studies in which the composite surface polymerized against Mylar matrix strips exhibited flatter surfaces compared to finished and polished composites. ,, Although the surface obtained by using the Mylar strip is perfectly smooth, it is rich in resin organic binder. Therefore, removal of the outermost resin by finishing and polishing procedures would tend to produce a harder, more wear resistant, and hence, a more aesthetically stable surface. 
Surface roughness values of Mylar strips are below threshold Ra value of 0.2 μm as suggested by Bollen et al.  Contouring and shaping restorations are performed with finishing and polishing procedures, which are required for optimum periodontal health. This facilitates the removal of the monomer rich surface layer of the composite material, which eventually eliminates the organic matrix, exposing and dislodging the filler particles, thus increasing the surface roughness of polymer-based materials. 
Among the finishing and polishing techniques studied, it was observed that the Sof-Lex aluminum oxide disks provide a smoother surface on composites compared to carbide bur finishing, followed by the Astrobrush. Possible reasons for better surface smoothness with Sof-Lex disks could be due to their inability to displace filler particles in composite resin. Their malleability promotes homogenous abrasion of fillers and resin matrix.  Even though, the Sof-Lex disks had lesser bacterial adhesion than the Astrobrush, the use of disks is limited intra-orally because of the anatomy of the surface to be polished. Aluminum oxide disks are unable to efficiently create, finish and anatomically polish contoured surfaces, especially posterior occlusal surfaces. Thus, both disk and brush polishing techniques have advantages. 
| Conclusion|| |
The initial adherence and subsequent colonization of bacteria on the surface of composite resins are the key of the pathogenesis of the secondary caries promoted particularly by S. mutans. This study observed that S. mutans biofilm adhesion to composite resin surfaces is influenced by finishing and polishing techniques, those performed with Mylar strips allowing least biofilm adhesion. The quality and amount of adhered biofilm are important to the success of the esthetic restorations on a long-term basis.
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