|Year : 2014 | Volume
| Issue : 1 | Page : 2-7
Effect of polishing on the microleakage of two different restorative materials in primary teeth: An in vitro study
Bhagyashree Salunkhe, Gauri Lele
Department of Paedodontics and Preventive Dentistry, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||6-May-2015|
Dr. Gauri Lele
Department of Paedodontics and Preventive Dentistry, Sinhgad Dental College and Hospital, Pune - 411 041, Maharashtra
Source of Support: None, Conflict of Interest: None
Aims and objectives: The aim of this in vitro study was to evaluate the effect of polishing on the microleakage of silorane based Composite (Filtek Z350XT) and Resin modified GIC (Vitremer) restorations in primary teeth. The objectives were to compare the microleakage with and without polishing, and compare the same between the two materials. Materials and Methods: Class V cavities were prepared on 28 retained deciduous anterior teeth, after they were extracted. The prepared teeth were randomly divided into two groups and restored with the respective materials. The restored teeth were then divided into two subgroups (polished and not polished) of seven each. Finishing and polishing for the designated subgroup was done using the Shofu polishing kit. The teeth were then thermocycled and subjected to 1% methylene blue dye penetration, and sectioned buccolingually. Microleakage was evaluated by observing degree of dye penetration under a stereomicroscope, and data subjected to statistical analysis. Statistical analysis was done using Mann-Whitney U test. Results: The results showed that polishing decreased the microleakage in Composite restorations (P<0.05), not in Resin Modified GIC restorations (P>0.05). Intergroup comparison of the microleakage without polishing was not significant (P>0.05) while the intergroup comparison after polishing was significant (P<0.05), with polished composite showing comparatively less microleakage. Conclusions: The conclusions of the study were that unpolished restorations with both materials did not show any significant difference in the microleakage scores. Composite restorations, after polishing, showed significantly less microleakage in primary teeth, while with Resin Modified GIC restorations, there wasn't any difference in microleakage, with or without polishing.
Keywords: Filtek, microleakage, polishing, primary teeth, Vitremer
|How to cite this article:|
Salunkhe B, Lele G. Effect of polishing on the microleakage of two different restorative materials in primary teeth: An in vitro study. J Dent Allied Sci 2014;3:2-7
|How to cite this URL:|
Salunkhe B, Lele G. Effect of polishing on the microleakage of two different restorative materials in primary teeth: An in vitro study. J Dent Allied Sci [serial online] 2014 [cited 2019 Aug 24];3:2-7. Available from: http://www.jdas.in/text.asp?2014/3/1/2/156517
| Introduction|| |
Owing to their morphological and histological characteristics, executing an ideal restoration in primary anterior teeth is often a challenge. Microleakage at tooth-restoration interface is one of the most commonly observed disadvantages of these restorations, leading to secondary caries and often resulting in pulpal involvement.
Various restorative materials have been used to restore cavities in primary anterior teeth, the earlier ones being a silver amalgam, silicates, conventional glass ionomer cement (GIC) and composite resins. The newer materials are typically modifications of these, with improved properties. Many advancements in the restorative materials and techniques for restorations have been done with the aim of reducing microleakage around the restorations.
Two such materials, resin-modified GIC and recently introduced silorane-based composite resin have great potential to be used in the restoration of carious primary teeth due to their definite advantages. However, both are resin-based restorative materials with resultant polymerization shrinkage and hence have a greater chance of microleakage.  Restorative techniques with these materials have also continually been modified over the years to reduce the marginal leakage around restorations diminishing the availability of free-radical monomer at the surface for further reaction and thereby reducing the extent of polymerization shrinkage. One such technique, of polishing the restoration after placement, is advantageous as it reduces the free-radical monomer and provides a smoother and more hygienic surface.
Thus the present study was undertaken with the aim of studying the effect of polishing on microleakage with silorane-based composite restoration (Filtek Z350XT) and resin-modified GIC restoration (Vitremer) for class V cavity in primary anterior teeth.
The objectives of this study were to assess the microleakage of composite (Filtek Z350XT) and resin-modified GIC (Vitremer) restorations in primary anterior teeth, with and without polishing, and compare the same.
| Materials and Methods|| |
The sample was obtained from among the patients reporting to the department with retained anterior teeth, indicated for extraction. After extraction, these teeth were selected for the study based on the following inclusion and exclusion criteria:
- Inclusion criteria
- Extracted primary anterior teeth with the intact labial surface.
- Exclusion criteria
- Teeth having developmental defects.
- Teeth with caries on any surface.
- Extensive loss of tooth structure due to caries or trauma.
Twenty-eight such teeth were selected for the study. The teeth were assigned to two groups I and II by simple random sampling, to avoid bias in the restorative material used. Teeth in group I were to be restored with silorane based composite (Filtek, 3M), while those in group II were to be restored with resin-modified GIC (Vitremer, 3M). Further, these were divided into two subgroups A and B, of seven teeth each, for restorations, which were polished, and not polished respectively, within each group. Thus, samples were divided randomly in four groups.
Hence, for the teeth in group I, restored with Composite (Filtek Z350XT), subgroup IA comprised of seven teeth where the restorations were polished, and subgroup IIA comprised of seven teeth where the restorations were not polished. Similarly, the subgroups were considered for the other group too.
This collected sample of 28 extracted primary anterior teeth was ﬁrst cleaned with an ultra-sonic scaler to remove local factors, disinfected with 10% formosaline for 10 min and then stored in distilled water until required for the next step of the study. The apical end of the teeth was sealed with nail varnish to prevent dye penetration apically. The teeth were then mounted on acrylic resin blocks up to their cemento-enamel junctions leaving the crowns totally exposed. Conventional class V cavities of dimensions 4 mm × 2 mm × 1 mm were prepared on the labial surfaces of the teeth. These were prepared 1.5 mm above the cemento-enamel junction with an ISO size (number 010) straight ﬁssure bur and an inverted cone (number 014). The occlusal margins of the preparation were in enamel, and the gingival margins were in dentin. The shape of the cavity was box shaped with rounded internal line angles. Following the cavity preparation, specimens were restored with the assigned restorative material for that group.
Group I consisted of teeth restored with silorane-based composite (Filtek Z350XT). Group II consisted of teeth restored with resin modiﬁed GIC (Vitremer). Each of the two groups was further divided into two subgroups A and B. Subgroup A, consisted of teeth, which underwent ﬁnishing/polishing. Subgroup B consisted of teeth, which did not undergo ﬁnishing/polishing. The teeth in subgroup B were stored in distilled water at 37°C for 1 week. For subgroup A, immediate ﬁnishing/polishing was done following which teeth were stored in distilled water at 37°C for 1 week. The polishing systems were used as recommended by the manufacturer. A new bur, disk or cup was used after every subgroup.
After a week, the samples were subjected to thermocycling (500 cycles, dwell time: 15 s, 5°C and 55°C Model 051SA) [Figure 1]a and b.
In preparation for dye penetration testing, the surfaces of the teeth were coated with nail varnish, leaving the ﬁnished restorations and 1·5 mm beyond the margins exposed to dye. The restored teeth were then placed in 1% methylene blue dye for 24 h at 37°C. After removal from the dye solution, the teeth were cleaned and sectioned longitudinally through the restorations in a buccopalatal/lingual plane using a diamond disc.
The specimens were then observed under stereomicroscope with a magniﬁcation of 10 X (model number: XTL 3400E) [Figure 2] to check for the presence and degree of microleakage.
The degree of marginal leakage was determined by the criteria described by Khera and Chan (1978)  as follows:
- 0° = No leakage [Figure 3]a.
- 1° = Less than and up to one-half of the depth of the cavity preparation was penetrated by the dye [Figure 3]b.
- 2° = More than one-half of the depth of the cavity preparation was penetrated by the dye, but not up to the junction of the axial and occlusal or cervical wall [Figure 3]c.
- 3° = Dye penetration was up to the junction of the axial and occlusal or cervical wall, but did not include the axial wall [Figure 3]d.
- 4° = Dye penetration included the axial wall [Figure 3]e.
The data thus collected were subjected to statistical analysis using SPSS. The probability value was set as, P < 0.05 as significant. By Kruskal-Wallis test, P value was calculated as <0.002 as significant. Scores were analyzed using Mann-Whitney U test.
| Results|| |
The scores given according to Khera and Chan for degree of dye penetration were tabulated for groups I and II and their subgroups for each of the 7 samples were as shown in [Table 1].
Composite (Filtek Z350XT) restoration: For the subgroup IA, that is, after polishing 14% (1) samples showed no microleakage, 43% (3) samples showed microleakage up to a depth less than half of the prepared cavity, and 29% (2) samples showed microleakage up to the junction of axial and cervical/occlusal wall. None (0) of the samples exhibited microleakage along the axial wall.
From among the unpolished subgroup, that is, IB, none (0) of the samples showed 'no microleakage' or microleakage up to a depth less than half of the prepared cavity. 29% (2) samples showed microleakage up to a depth more than half of the prepared cavity and 43% (3) samples showed microleakage up to the junction of axial and cervical/occlusal wall. Only 29% (2) samples exhibited microleakage along the axial wall.
Vitremer restoration: For subgroups IIA and IIB, none of the samples showed a score of 0°, 1° or 2°. 29% (2) samples showed microleakage up to the junction of axial and cervical/occlusal wall while 71% (5) samples exhibited microleakage along the axial wall.
Comparison was done between the microleakage scores of the teeth samples of the two subgroups (polished and not polished) for each of the two groups using Mann-Whitney U-test, as shown in [Table 2]. For group I (Filtek Z350XT) the value was found to be 0.038, which was signiﬁcant (P < 0.05).
For group II (Vitremer) the value was found to be 1, which was not signiﬁcant (P > 0.05).
Mann-Whitney U-test was carried out to compare the microleakage scores for the two materials in polished and not polished subgroups individually, as shown in [Table 3]. The score for the polished group was found to be 0.002, which was signiﬁcant (P < 0.05). The score for the not polished group was found to be 0.128, which was not signiﬁcant (P > 0.05).
Comparison between two materials
The scores for microleakage were compared for both the restorative materials and 0.001 was the value obtained, which was statistically significant (P < 0.05), shown in [Table 4].
| Discussion|| |
It has been known for many years that conventional restorative materials and techniques might result in dental restorations that do not provide a complete marginal seal. Numerous studies have demonstrated that leakage of fluid will occur between the restoration and the prepared tooth interface.  An impaired marginal seal provides access to bacteria, oral fluids, molecules and ions at the restorative material interface. This in turn leads to staining at the margins of the restorations, breakdown at the margins of the restoration, recurrent caries at the tooth preparation walls and restorative material interface, hypersensitivity of the restored teeth and especially in primary teeth, development of pulpal pathology all of which endanger the longevity of the restoration. 
The development of newer dental materials and operative techniques over the last few years, and a better understanding of dentin substrate characteristics have provided a significant decrease in the marginal microleakage of restorations. However, resin-based restorative materials present polymerization shrinkage and have different linear coefficients of thermal expansion compared to the tooth. These factors affect the clinical performance of resin-based restorations by disrupting the adhesive interface, resulting in microleakage. 
Hence, this study was carried out to assess the difference in microleakage of two restorative materials (Filtek Z350XT and Vitremer) which have a good potential for use in pediatric dentistry. Both the restorative materials selected were resin-based restorative materials (Filtek Z350XT: Silorane-based composite resin; Vitremer: Resin modified GIC) to assess minimal microleakage comparatively and were chosen from the same manufacturer (3M) to avoid any bias.
The microleakage assessment was done by an in vitro method because in vitro tests remain an indispensable method for initial screening of dental materials. However, it is the clinical assessment of the materials that reveals their actual performance levels.  The study was conducted on extracted retained primary anterior teeth, and the sample size was kept at 28 due to the difficulty of getting such teeth fulfilling all the inclusion criteria, that is, noncarious, noncavitated, intact teeth. To rule out any inﬂuence of occlusal loading on microleakage, and owing to the high incidence of cervical presentation of caries in anterior primary teeth, class V cavities were prepared. These were with uniform shape and dimension.
In the oral cavity, the restorations are subjected to both thermal and mechanical stress, and that also contributes to the increase of marginal microleakage. Thermocycling regimens may simulate more appropriately the clinical situation. In the thermocycling method, specimens are submitted to thermal cycles that simulate the intraoral temperature.  The temperature was standardized at 5-55°C and the dwell time was 15 seconds with 500 cycles. These variables seem to be tolerated by the oral tissues and are suitable for clinical conditions. Increases in the dwell times more than 15 seconds exceed real clinical conditions and may hide the thermal isolation characteristics of the restorative material, leaving fatigue to this material.  The low thermal conductivity of resin-based restorative materials suggests that a 15 seconds of dwell time is not sufficient to transfer the temperature through restoration to fatigue the adhesive interface and rupture it, increasing microleakage.
Various techniques have been used to evaluate microleakage such as dye penetration, bacterial leakage, electrochemical method, fluid filtration, radioisotope labeling and scanning electron microscope analysis. Among these techniques, dye penetration is the most widely used method to assess microleakage because of its sensitivity, ease of use and convenience.  Dye penetration was examined under a stereomicroscope at 10 X magnification. Stereomicroscopic examination was chosen for this study as this provides a well-magnified two-dimensional view of the surface to be examined.  1% methylene blue for 24 hours was used for the study as its use is simple, inexpensive and does not require use of complex laboratory equipment. Furthermore, the particle size of this dye is less than the internal diameter of the dentinal tubules (1-4 μm), and hence it is able to show dentin permeability. 
It is generally accepted that a smooth surface has a beneﬁcial effect on the esthetic quality and longevity of the restoration, as well as on its biocompatibility with the oral tissues. Furthermore, the beneﬁts of a smooth restoration are: 
- Minimal irritation of soft and hard tissues.
- Stimulates natural tooth surface esthetics.
- Less likely to trap food debris and plaque.
- Reduced potential for corrosion.
- More hygienic.
It should be noted that the effect of polishing systems on microleakage is material and tissue-dependent. For conventional cements, polishing at ultra-high speeds can decrease microleakage resistance at the dentin margins. For resin-modified cements, systems utilizing wet polishing technique results in better microleakage resistance at the enamel margins. 
Glass ionomer resin composite brings with it the problem of polymerization shrinkage because of inclusion of resin phase. The hybrid materials show curing shrinkage within 5 min after polymerization, increasing over a 24 hours period. This rapid initial shrinkage is the result of free-radical polymerization of resin monomers incorporated in the materials.  Signiﬁcantly higher values of curing shrinkage were found for glass ionomer resin hybrid materials than for conventional ones or resin composites.
Resin composite restorations show signiﬁcant differences in the resin matrix composition as well as in the ﬁller, which inﬂuences the properties of materials, including polymerization shrinkage. Recently, Filtek Z350XT, a silorane based composite has been developed which uses silorane and oxirane to provide a biocompatible, hydrophobic, low-shrinkage silorane base. In these resins, polymerization takes place by cationic "ring-opening" mechanism resulting in minimal polymerization shrinkage.  Silorane-based composites exhibit 0.9% volumetric shrinkage when compared to 2.3-3% for methacrylate based resins. Besides this silorane-based composites have added the advantage of the absence of oxygen inhibition layer. 
In a study by Sengupta et al.  to investigate the effect of polishing on resin modified GIC (Ketac N100) and composite resin (Filtek P90) in permanent teeth, It was found that, difference between microleakage scores of both the restorative materials was not significant. In the present study, designed to assess the same in primary teeth, more microleakage was observed at the restoration-tooth interface of resin modified GIC (group I and group II). Interestingly, no significant difference between microleakage scores was observed between the two sub-groups (Polished IIA and Unpolished IIB) of resin modified GIC in the present study, which was similar to the results of the study conducted by Sengupta et al. in permanent teeth. 
Composite restorations showed a significant difference between the microleakage scores of both polished and unpolished restorations in the present study, similar to that in permanent teeth. 
However, contrary to findings in studies on permanent teeth,  in this study polished surfaces of composite resin showed significantly less microleakage compared to polished surfaces of resin-modified GIC in the present study. This could be attributed to optimal conditions of isolation in an in vitro setting.
More in vitro and in vivo studies are required to be conducted to substantiate the same. Also, study design with larger sample size and follow-up of a longer duration should be carried out to verify the same. Similar studies need to be performed on primary teeth as there is a paucity of literature in this regard.
The results of the study showed that polishing decreased the microleakage in composite restorations and not in resin-modified GIC restorations, and the difference in microleakage scores without polishing was not significant for either material. However, after polishing, composite restorations showed significantly less microleakage in primary teeth.
| Conclusions|| |
- Polishing does provide an optimal seal at the restoration-tooth interface when restored with silorane-based composite (Filtek Z350XT) in primary teeth.
- Polishing does not reduce the microleakage at the interface when restored with resin-modified GIC (Vitremer) in primary teeth.
- Polished restoration of silorane-based composite (Filtek Z350XT) shows less microleakage compared to polished restoration of resin-modified GIC (Vitremer) in primary teeth.
- Unpolished restoration of silorane-based composite (Filtek Z350XT) and resin-modified GIC (Vitremer) shows no significant difference in microleakage in primary teeth.
- Silorane-based composite restoration (Filtek Z350XT) provides better marginal seal compared to resin-modified GIC (Vitremer).
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]