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Year : 2016  |  Volume : 4  |  Issue : 2  |  Page : 42-47

Evaluation of caries-protective effect of three recent dentin bonding agents on demineralization of root surface: An in vitro study

1 Department of Conservative Dentistry and Endodontics, Career PG Institute of Dental Sciences and Hospital, Lucknow, India
2 Department of Conservative Dentistry and Endodontics, Chandra Dental College, Dharsania, Uttar Pradesh, India

Date of Web Publication21-Apr-2016

Correspondence Address:
Dr. Hena Rahman
Department of Conservative Dentistry and Endodontics, Career PG Institute of Dental Sciences and Hospital, Lucknow - 226 016, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2321-4619.180999

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Objective: To evaluate the caries-protective effect of three recent dentin bonding agents (DBAs) on demineralization of root surface in vitro. Materials and Methods: The root surface of 70 freshly extracted caries-free human teeth was thoroughly cleaned and polished, thereby removing the cementum. The root surfaces were coated with acid-resistant nail polish and 2 mm × 3 mm rectangular window was prepared on the buccal surface. The samples were then divided randomly into three experimental groups; Group 1 (Xeno-V), Group 2 (Tetric N Bond), and Group 3 (Gluma Self-etch) which were further divided into two Subgroups (A and B) with 10 samples each in which second layer of adhesive was cured without air thinning and with air thinning respectively. Subsequently, all specimens were demineralized for 6 days with acidified gel (hydroxyethylcellulose, pH 4.8, 37°C). Each tooth samples were sliced in plano parallel section (80 ± 20 μm) by safe sided diamond disc and examined for caries-like lesions (demineralized area) under a polarized microscope. Data were analyzed using one-way ANOVA, Student's t- and Tukey honestly significant difference tests. Results: All control group specimen exhibited lesions with a mean depth of 86.15 μm. In Group 1–3, the lesion depth was reduced significantly, Subgroup A results were better than B. Conclusion: Demineralization on root surface can be impeded by DBA tested. Gluma Self-etch showed maximum caries-protective effect.

Keywords: Cementum, demineralization, dentine bonding agent, self-etch

How to cite this article:
Aziz A, Rahman H, Chandra R, Loomba K, Singh S. Evaluation of caries-protective effect of three recent dentin bonding agents on demineralization of root surface: An in vitro study. J Res Dent 2016;4:42-7

How to cite this URL:
Aziz A, Rahman H, Chandra R, Loomba K, Singh S. Evaluation of caries-protective effect of three recent dentin bonding agents on demineralization of root surface: An in vitro study. J Res Dent [serial online] 2016 [cited 2020 Sep 25];4:42-7. Available from: http://www.jresdent.org/text.asp?2016/4/2/42/180999

  Introduction Top

In contemporary population, longer lifespan of persons, with the retention of their teeth into the later decades of life, has increased the number of the population exhibiting gingival recession with clinical exposure of cemental surfaces and thereby probably increasing the prevalence of root caries.[1] The root cementum is highly organic with cross-linked collagen structure, is less hard and more permeable to a variety of materials compared with enamel and dentin making it more vulnerable to acid attack.[2] The triad of susceptible root surface, bacteria, and a fermentable carbohydrate provides the necessary ingredients for root caries.

Root lesions occur as primary root caries, recurrent caries, or in areas of abrasion, erosion, or abfraction. Once root lesions are present, several treatment options are available. The most efficient strategy for root caries prevention is based on an assessment of the patient's risk factors, and intervention is to alter the risk.[3] However, once the preventive approach has failed, restorative treatment planning must be carefully individualized to patient need.

Many materials such as silver amalgam, composite resins, conventional and resin-modified glass ionomer cement, compomers, and lasers have been used to restore root-surface caries, but they are far from ideal results. However, recent evidence supports fluoride-releasing materials for the restoration of these defects. With the application of different fluoride preparations, the root caries incidence can be reduced, but not eliminated.[4],[5] Nowadays, self-etch (7th generation) adhesives are widely used as they show reliable bonding to dentin. They are user-friendly and less technique-sensitive compared with etch-and-rinse systems and improves the efficiency in clinical procedures by reducing the chair side time and reduces hypersensitivity on exposed surface.[6] To know the caries-protective effect of these self-etch adhesives on root surface area near the cementoenamel junction (CEJ) three different dentin bonding agents (DBAs) were used in the current study, i.e., Gluma Self-etch, Xeno-V and Tetric N Bond [Table 1]. Thus, the aim of the present study was to evaluate the effectiveness of three recent DBA on demineralization of root surface in vitro.
Table 1: List of the dentine bonding agents, their composition, and manufacturers

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  Materials and Methods Top

A total of 70 freshly extracted single-rooted human teeth were selected and stored in saline solution. This is a preferred procedure as it does not influence the physical properties of dentin.[7] The root surfaces 1 mm apical to CEJ were thoroughly polished using the sof-lex disk (3M), thereby removing the cementum. The root surfaces were then coated with acid-resistant nail paint, thereby exposing a rectangular window of 2 mm × 3 mm on the buccal surface for experimental purpose. The samples were then divided randomly into three experimental groups; Group 1 (Xeno-V), Group 2 (Tetric N Bond), and Group 3 (Gluma Self-etch) which were further divided into two Subgroups (A and B) each with 10 samples in each subgroup and a control group with 10 samples. Subsequently, all specimens were demineralized for 6 days with acidified gel (hydroxyethylcellulose [HEC], pH 4.8, 37°C).

In Subgroup A of all groups, adhesive was applied on the experimental surface of the tooth and light cured for 10 s with air thinning. After this, in the same manner the second layer of adhesive was applied, and light cured for 10 s without air thinning. In Subgroup B of all Groups, adhesive was applied on the experimental surface of the tooth and light cured for 10 s with air thinning. After this, in the same manner, second layer of adhesive was applied and light cured for 10 s with air thinning.

Each 10 samples of each subgroup were placed separately into glass vials with readily available 10 mL solution of 0.9% sodium chloride solution, for a maximum of 8 days before the start of the experiment. Each tooth samples were sliced in plano parallel section by using safe sided diamond disc at 30,000 rpm. Each slices were grounded to sizes 80 μm (±20 μm) using fine grit and paper in three step procedure (400, 600, 800 grit).

Each section was immersed in water and examined for caries-like lesions (demineralized area) with a polarized microscope (Carl Zeiss, 73447 Oberkochen, Germany). Lesion depths were measured using the microscope eyepiece reticle, which was calibrated by placing a 10 micron/unit graticule on the microscope stage. In lesions with irregular advancing fronts, only the deepest measurement was recorded. The statistical analysis was done using one-way ANOVA, Student's t- and Tukey honestly significant difference tests.

  Results Top

Results of the studies are summarized in [Table 2], [Table 3], [Table 4]. [Table 2] depicts that control has maximum demineralization depth (86.15 µm) while the difference between Subgroup 1A and 2A (3.20 µm), between Subgroup 1A and 3A (0.60 µm) and between Subgroup 2A and 3A (3.80 µm) were found to be statistically nonsignificant.
Table 2: Comparison of demineralization depth between Subgroups A of each group (in μm)

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Table 3: Comparison of demineralization depth between Subgroups B of each group (in μm)

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Table 4: Comparison of demineralization depth between the groups (in μm)

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[Table 3] depicts minimum demineralization depth (38.95 µm) was found for Subgroup 3B, and intra-group differences were found statistically significant (P < 0.001).

[Table 4] depicts that maximum difference in demineralization was found between control and Group 3 (49.22 µm) and minimum between Groups 1 and 3 (7.42 µm) which was statistically significant (P < 0.001). The difference between Group 1 and 2 was found to be statistically nonsignificant. Order of demineralization depth found was: Control > Group 2 (Tetric N Bond) ≈ Group 1 (Xeno-V) > Group 3(Gluma Self-etch). The demineralization zones of experimental groups 1-3 were similar to control group concerning the histological structure, but the lesion depth were reduced [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d.
Figure 1: Photomicrograph showing demineralization in (a) control group, (b) Group 1 (Xeno-V), (c) Group 2 (Tetric N Bond) and (d) Group 3 (Gluma Self-etch)

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  Discussion Top

Root caries is an area on the surface of the tooth, at or apical to the CEJ, that has undergone clinically apparent dissolution of mineral of the calcified tissues.[8] Clinically, root caries appears as white (in the earliest stage) or discolored (tan, brown, or black) areas of irregular outline, with or without cavitation, on an exposed root area, along an exposed CEJ, or at a margin of a restoration that is supragingival but within root structure.[9]

Studies have demonstrated that DBA when applied to demineralized dentin surface forms finger - like resin tags protruding into the entrance of the patent dentin tubules. These resin penetrates the superficially demineralized collagen matrix, forming a hybrid layer, and efficiently prevents root surface lesions.[10],[11],[12],[13] Furthermore, DBA can be applied directly on the root surface which is not true for other restorative materials, i.e. it requires minimal invasive procedures.

A wide variety of DBAs is available commercially. In this study, seventh generation DBA, introduced in late 2002 are self-etch, i.e., all-in-one adhesive systems that combine etching, priming and bonding into one step are used.

In single-component adhesives, acidic monomers, hydrophilic monomers, water and/or organic solvents are combined into one solution. The self-etching mechanism of these systems is based on acidic monomers that are able to partially demineralize and infiltrate the dental hard tissues.[6] Unlike etch-and-rinse systems, they use the smear layer as a bonding substrate, by incorporating it into the hybrid layer. As a result of this postoperative sensitivity, a potential risk related to incomplete resin infiltration, is supposed to be limited.[14]

An intact cementum layer has the intrinsic ability to protect the underlying dentin of exposed tooth root against acidic demineralization. Chemical analysis also showed that the removal of cementum, resulted in an initial doubling of the calcium and phosphate, lost from the root surface.[6] In the current study removal of cementum was done before starting the experiment to simulate the clinical condition of root caries. Removing cemental layer facilitated a more standardized demineralization of the remaining dentin with reproducible lesions. The samples which underwent demineralization involve the walls of the dentinal tubules, which significantly increased the initial rate of penetration of acidified gel into the root surfaces. Demineralization of the walls of the individual tubules leads to their confluence; there was loss of root surface tissue. The outline of the dentinal tubules was accentuated and this appearance caused by the loss of the interdentinal tubules was less clear. Subsurface demineralization occurred in all the control groups due to acidic attack on the root surfaces. In the samples which were protected by way of applying DBAs and light cured, without air thinning the dentinal tubules were intact and reached to the surface.

In this study, two coats of DBA was applied on the experimental surface of each tooth as for some all-in-one adhesives, performance may depend on the application method as the number of coats recommended by the manufacturer may not suffice.[15] Application of the all-in-one adhesive in multiple layers may result in higher bond strengths and better infiltration into the hybrid layer.[16] One manufacturer recommends rubbing the adhesive continuously for 15 s, followed by the application of a second coat after gentle air-drying and curing the first coat. This second coat prevents the formation of dry spots on the dentin surface. The single-application produces a porous and fibrous appearance, which is supposed to be over-etched. In the second application, the additional supply of adhesive resin may improve the infiltration of resin monomers into the intertubular demineralised dentin which appears dense.[6] Porosities (or blisters) occur at the enamel and dentin bonding interfaces because most all-in-one adhesives behave as semipermeable membranes. These porosities may be a result of water accumulation either caused by an osmotic gradient or by monomer–solvent phase separation upon evaporation of the acetone. The number and size of these blisters may also depend on the intensity of the air-drying step.[17] Multiple application of adhesives is considered to be effective in preventing the above-mentioned defects and improve the bonding to dentin. Therefore, in the current study double-application of all-in-one bonding systems is again justified.

One study has shown that the strength of the bond is sometimes directly proportional and at other times inversely proportional to the thickness of the bonding material; in other words, it is material-dependent.[18] With those results in mind, we were careful not to thin the adhesive resin excessively. Gentle air blowing for 1–2 s with oil free compressor from a distance of approximately 20 cm was followed.[19],[20]

Bacteria present in the oral cavity metabolize carbohydrates, which results in a reduction of pH. This drop in pH causes demineralization of the root structure initiating the caries process. The critical pH for root surface demineralization is approximately 6.7.[21] Hence, samples of each group were stored in demineralizing solution which was prepared by acidifying sodium hydroxide (0.1n) with lactic acid (0.1n) to pH 4.5, HEC (6% by weight) was added, resulting in a final pH of 4.8.[22] Preliminary experiments with different periods of time proved that the demineralization over a period of 4 days resulted in reproducible lesions of sufficient depth. A longer exposure time did not influence the lesion depth markedly.[23]

Statistical analysis in this study showed that Subgroups A ( first layer cured with air thinning and second layer cured without air thinning) undergone less demineralization compared to Subgroup B (both first and second layer cured with air thinning). The above results can be because shorter drying time attributes to higher bond strength.[24] Dentin collagen collapses easily upon excessive air drying which results in closing of micropores in the exposed intertubular collagen.[19] This might in turn lead to incomplete impregnation of adhesive resin into the underlying dentin and further increase in demineralization.

Statistical analysis in the current study showed that there was no significant difference between Group 1 (Xeno-V) and Group 2 (Tetric N Bond) as compared to Group 3 (Gluma Self-etch), which undergone least demineralization. Gluma Self-etch and Tetric N Bond both have pH > 2 which makes them “mild” self-etch adhesives, whereas Xeno-V has pH < 2 which makes it “intermediary strong” self-etch adhesive. “Mild” self-etching appears most promising, especially with regard to bond stability. In the light of bonding durability, mild self-etch adhesives (Gluma Self-etch) have unique property that all hydroxyapatite are not removed from the interaction zone, and much calcium is available for additional chemical interaction with specific adhesive monomers. Hence, the bonds are stable, even in the aqueous environment, and the mechanism is supposed to prolong the clinical lifetime of the restorations.[10] Furthermore, the preservation of hydroxyapatite around the collagen in mild self-etch adhesives may protect the collagen against hydrolysis and thus prevents the early degradation of the bonds. Presence of glutaraldehyde in Gluma Self-etch also prevents demineralization to some extent.

Acidity of self-etching monomers can be buffered by the mineral components of smear layer. This implies that more the acidic the adhesive, more will be the penetration, resulting in more demineralization.[25] So Xeno-V group being more acidic (pH < 2) resulted in more acidic demineralization of dentin subsurface.

In the present study, Xeno-V group presented no significant difference between single and double coat application of bonding agent over cemental surface. However, it is reported that the bond strength of Xeno-V increased with multi-coating before light curing compared with that of a single coat.[16] The reason for this variation is not clear and needs more clinical trials with longer time periods.

From these results, when adopting new methodology for all-in-one bonding to dentin, practitioners must consider both the characteristics of the adhesives and the original protocols to handle these materials properly. The different thickness of covering layers is related to the viscosity and application procedures. Accordingly, we believe demineralization occurred by penetration of acid through the incompletely covered areas that resulted from the localized loss of the adhesive, possibly as a consequence of local peeling of the adhesive placed on the window, or excessive thinning of the coating due to strong air-blowing.

Although little or no clinical study is available to confirm the efficacy of the dental adhesives in root caries prevention, these materials have suggested to be a potential aid in this matter.[26] This is so because caries process is an accumulation of competing demineralization and remineralization events and not a unidirectional process as performed in the present and most of the other in vitro investigations. Thus, the results of this study must be carefully analyzed and might not be directly translated to clinical situations.

  Conclusion Top

On the basis of the findings of this study, it can be concluded that Gluma Self-etch had the least demineralization depth in vitro as compared to Tetric N Bond and Xeno-V DBAs, which means that of all the 7th generation DBAs tested, Gluma Self-etch has a maximum caries-protective effect.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]

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