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Effect of three different conditioning agents on cavosurface microleakage and bond strength of glass ionomer restorations – An in vitro study
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/jisppd.jisppd_144_22
Keywords: Deproteinization, dye penetration, microleakage, shear bond strength, smear layer How to cite this article: How to cite this URL: The ability of a restorative material to adhere well to the tooth and avoid cavosurface microleakage is one of the most critical needs in restorations. The marginal seal provided by restorative materials is critical for the longevity of the restoration.[1] Adhesive restorative materials currently lack a sufficient marginal seal and hence are unable to prevent microleakage.[2],[3] Close contact between the two substances being linked is required for effective adhesion, and a smear layer, which can be formed during tooth preparation, might disrupt this intimate contact and compromise adhesion quality.[4],[5],[6] Glass ionomer cement (GIC) is the only restorative material that can develop a chemical as well as a micromechanical bond with the tooth substance.[4],[7] Many studies have suggested that pretreatment of the cavity surface before to glass ionomer (GI) application is required to provide better adherence of a restorative material to the remaining structure of the tooth.[8],[9],[10] Prior to GI restorations, conditioning treatments with the etchants of weak mineral or milder organic acid like pyruvic acid (10%), nitric acid (2.5%), polyacrylic acid (20%), citric acid (10%), oxalic acid (1.5%–3.5%) and aluminum chloride were recommended.[5],[11] According to Yilmaz et al.,[12] the objective of conditioning the cavity surface is to eliminate the surface impurities and the smear layer that can impede the adhesion of cements to the surface of the tooth, especially to dentin surface. GIC's acidic nature has also been claimed to partially dissolve the smear layer.[13] Polyacrylic acid has long been used as a pretreatment for GI restorations, and various investigations have confirmed its effectiveness. Charlton and Haveman[8] compared untreated dentin to dentin prepared with 10% polyacrylic acid and discovered that using a conditioner improved the bonding quality to dentin substantially. As a deproteinizing agent beneath resin composites with improved adhesiveness, sodium hypochlorite (NaOCl) has been employed on enamel and dentine.[14] Nassif and El-Korashy[15] studied the effect of a NaOCl/phosphoric acid mixture as a new dentin conditioner under resin composites and found that the etch and rinse single bottle adhesives to dentine had a greater shear bond strength (SBS). Because of its antibacterial activity, inhibition of matrix metalloproteinases (MMPs), and debris removal, chlorhexidine (CHX) digluconate (2%) is advised for use in restorative dentistry following tooth preparation or etching with phosphoric acid and before closing the dentinal tubules.[16],[17] Given that 2% CHX digluconate eliminates debris and the smear layer in addition to its other features, only one study has tested the effect of 2% CHX digluconate as a dentin-GI restoration conditioner.[17] Since the combined conditioning/deproteinization concept has never been tested in GI restorations and there is no study available in the literature comparing the conditioning effects of these three agents, this study was performed to estimate the consequences of H3PO4/5.25% NaOCl deproteinization, 2% CHX digluconate cavity cleanser and 10% polyacrylic acid conditioner, on cavosurface microleakage and bond strength of GI restorations. The institutional ethics committee received the study protocol and gave its approval vide Ref. No. TMDCRC/IEC/19-20/PPD3 dated November 06, 2019.The sample size for this study was calculated using G* power software, version 3.0.1 (Franz Faul universitat, Kiel, Germany), following establishment of power analysis. A sample size of 136 samples–of 68 teeth as 2 samples per tooth (34 in each group) would yield 80% power to detect significant differences, with effect size of 0.29 and significance level at 0.05. A total number of 125 human premolar teeth extracted for orthodontic/periodontal reasons were collected from the Department of Oral and Maxillofacial Surgery. The extracted teeth with the enamel cracks, fracture, malformation, erosion or restoration were then excluded from the study. The extracted teeth were washed under running tap water to clean the blood from it and then hand scaling was performed to remove the adherent tissues from the root surfaces. The teeth were then stored in thymol solution along with the distilled water for 1 week[18] followed by storage of all the extracted teeth in normal saline till further use. Out of 125 collected teeth, 34 teeth were excluded due to enamel cracks, fracture line, carious lesions or erosions. The remaining samples were processed as indicated in Flowchart 1.The samples were grouped in the following manner:
Using a straight fissure bur of tungsten carbide and air-water cooling, a standardized Class-V cavity was prepared on the lingual and buccal surfaces of each tooth. The dimensions of the cavity preparations were 3 mm in width, 3.5 mm in height, and 2 mm in axial depth,[17] and the occlusal and gingival margins were in enamel and dentine, respectively. In Group-1, a 50/50 volume% mixture of 37% H3PO4 and 5.25% NaOCl solution was applied for 60 s before being washed and blot dried.[15] In Group-2, 2% CHX (Bisco, Inc. Irwing Park Rd. Shaumburg, USA) was applied with a micro brush for 20 s before being air dried for 5 s. In Group-3, 10% polyacrylic acid (GC Corporation, Hasunuma-Cho, Tokyo, Japan) was incorporated to the cavity surface using a micro-brush for 20 s before being washed thoroughly with water. In Group-4, no surface pretreatment of the samples was carried out [Figure 1].
After surface treatments, restorative GIC (GC Europe N. V. Interleuvenlaan, B-3001) was filled into the cavities. The exposed root and crown structures were then shielded with 2 coats of nail paint excluding the restoration part and 1 mm around the cavosurface margins of the restoration [Figure 2].The samples were then stored in distilled water for 24 h at room temperature (ISO Test type-I).[19] The samples were then subjected to 500 cycles of thermocycling at 5°C and 55°C (ISO Test type-II),[19] followed by a 5-s water bath and a 5-s dwell time between each bath.[19] All the samples were then dipped in rhodamine B dye solution for 24 h[2] followed by thorough washing under running tap water. After the longitudinal sectioning of the samples in bucco-lingual direction, they were examined under stereomicroscope and the following grading criteria[20] had been used [Figure 3]:
For SBS testing, the roots of all the included samples as shown in Flowchart 1 were removed from 1 mm below the cemento-enamel junction and a flat dentin surface was prepared on lingual/palatal and buccal surfaces of all the samples with a diamond abrasive disc in a slow speed under continuous water cooling. The obtained samples were then submerged in self cure acrylic resin (DPI RR cold cure, Dental products of India, Bombay Burmah Trading Corporation Ltd.) blocks of 1 cm diameter and 2 cm in height. The exposed dentin surface of the samples were then pretreated with conditioning agents the same way as it was carried out in samples for microleakage evaluation in all the four groups [Figure 4]. A round stainless steel split mold[21] with a circular window in the center of 3 mm diameter and of 3 mm height was attached to the tooth's defined surface and stabilized using an adhesive tape.
GIC was mixed as per manufacturer's instructions and condensed on the dentin surface. The split mold was then removed, followed by the adhesive tape with the 3 mm circular window [Figure 5]a. The samples were then subjected to thermocycling, consisting of 500 cycles in a water bath at 5°C and 55°C (Test type-2).[19] Each bath was exposed for 20 seconds, and the time between baths was 5 s. An Instron Universal Testing Machine (Instron Corporation, Canton, MA, USA) was used to evaluate bond strength at a crosshead speed of 0.5 mm/min [Figure 5]b. The unit of measurement of SBS was in mega pascal (MPa). The stereomicroscopic analysis was done for the samples in ×40 magnification and classified into 3 types:
The data for the present study was entered in the Microsoft Excel 2007 and analyzed using SPSS statistical software 20.0 version for windows IBM Statistical Package for Social Sciences statistics, IBM corp., 2018, Chicago, USA. The descriptive statistics included mean, standard deviation. The intergroup comparison for the difference of mean scores between independent groups was done using Kruskal–Wallis test followed post hoc analysis. The level of significance for the present study was predetermined at P ≤ 0.05. [Table 1] shows the mean SBS values (MPa) of all the three groups. The highest SBS was observed in Group 1 and lowest in control group. There were significant differences observed between the groups (P < 0.05). [Table 2] shows the post hoc analysis indicating the superior effectiveness of phosphoric acid/5.25% NaOCl mixture as a pretreatment agent. [Table 3] shows the modes of fracture pattern analyzed under stereomicroscope where maximum cohesive fractures were observed in group 1 and least in group 4. Maximum of adhesive failures was observed in group 4 whereas it was least in group 1. Mixed (cohesive-adhesive) fracture was same in the group 1 and group 2 i.e., 23.52% and for group 3 and group 4 it was 29.4% respectively [Figure 6]a, [Figure 6]b, [Figure 6]c.
For microleakage, group 4 presented the maximum microleakage with a mean of 3.294 ± 0.771 as represented in [Table 4] and [Figure 7]. One way ANOVA revealed statistically significant differences (P < 0.05) for microleakage values also. [Table 5] represents the post hoc analysis for microleakage.
Composite materials and GICs are often used in restorative dentistry for curative treatments.[20] The ionic response of GIC with the tooth surface is thought to be superior, and it can be further improved by using an acid conditioner on the tooth surface. To distinguish it from acid etching, McLean and Wilson coined the term surface conditioning for pretreatment. Conditioning of the surface is used to reduce the amount of alteration in the structures of the tooth surfaces after they have been cut.[10] Residual inorganic and organic components produce a smear layer of debris on the surface of a tooth when it is prepared with the bur or any other instruments.[22] Elimination of the microorganisms in the smear layer should be performed before resin bonding.[22] The smear layer's attachment to the solid dentin and the smear plugs pushed into the dentinal tubules decide whether the smear layer can be bonded to the tooth structure, which is determined by the smear layer's attachment to the solid dentin.[23] Various surface treatment substances have been proposed to eliminate or alter the smear layer before applying GIC to lessen the smear layer's effect and increase bonding.[24] Glasspoole et al.[25] investigated the impacts of numerous surface treatment on BS of several GI cements to tooth enamel and they found that when compared to no pretreatment, phosphoric acid and polyacrylic acid conditioning enhanced the BS of GI materials to enamel. CHX is a widely used antibacterial and disinfectant in dentistry prior to the placement of restorations.[26] In addition to its antibacterial properties, it was observed that applying 2% CHX to the dentin surface for 60 s reduced the collagenolytic activity of the dentin surface and had an inhibitory effect on the MMP enzyme.[27] Lugassy et al.[17] revealed in their study that 2% CHX, with its well-known added benefits, can be used as a dentine conditioning agent as to enhance bond strength of restorative materials. As a deproteinizing agent, the proteolytic action of the NaOCl contains the fragmented long peptide chains and N-chloramines with terminal amine groups.[28],[29] Arias et al.[30] investigated the influence of a 10% NaOCl gel and 10% NaOCl solution on dentine bond strength of 4 different adhesive systems and revealed that the BS was unaffected by the 10% NaOCl gel. When compared to a NaOCl solution (10%), NaOCl gel (10%) was less successful at removing collagen. Nassif and El-Korashy[15] introduced NaOCl/phosphoric acid mixture as a new dentine conditioning agent and observed improved bond strength of adhesive material to dentin. Hypochlorous acid, sodium dihydrogen phosphate and unreacted phosphoric acid are produced when 5.25% NaOCl and 37% phosphoric acid interact. Because hypochlorous acid is unstable, it partially dissociates, releasing chlorine gas during the mixing process. Because of its quick dissociation, the residual hypochlorous acid has a faster deproteinizing impact than NaOCl. At the same time, the mixture's demineralizing capacity is maintained by the unreacted phosphoric acid. As a result, the proposed new conditioning mixture can etch and deproteinize at the same time.[15] It has been emphasized that the stable substrate is not provided by smear layer for restorative material adherence and bonding to the tooth surface. This layer eventually dissolves under restorative material as a result of hydrolysis process, resulting in bacterial penetration, microleakage and pulp irritation.[13] Lugassy et al.[17] concluded in their study that with the use of 2% CHX digluconate there was reduced microleakage when it was compared to other conditioning agents. Many studies have demonstrated that by using various conditioners there is reduction in the microleakage and increases the BS of the GI restoration to tooth surfaces.[25],[31],[32],[33],[34],[35] The findings of the present study indicate that the 50/50 volume% mixture of 5.25% NaOCl and 37% H3PO4 (Group 1) revealed a better bond strength with least microleakage of GIC restoration when it was compared to the other groups. In this study, greater microleakage was seen in the Group 4 (with no pretreatment) followed by Group 3 (pretreated with 10% Peracetic acid) then Group 2 (pretreated with 2% CHX) and then minimum in Group 1. The greater SBS was observed in Group 1 followed by Group 2, Group 3 and least was observed in Group 4. These findings were similar to those of Nassif and El-Korashy,[15] Glasspoole et al.,[25] Yamamoto et al.,[36] Shashirekha et al.[10] and Fernandes et al.[37] as they concluded that preapplication of the conditioning agent improves the bond strength of GIC to dentine, but these findings were different from those of Perdigão et al.,[38] Mostafa and Nadia[39] and Bassi et al.[40] as they concluded that pretreatment of the dentin surfaces with the conditioning agents did not enhanced the bond strength significantly. In the case of microleakage, the findings were similar to those of Lugassy et al.[17] and Fumes et al.,[41] but were different from those of Shinohara et al.[42] as they concluded that the microleakage was increased along the dentin margins with the use of NaOCl as a dentin conditioning agent. Because this was an in vitro study, microleakage and SBS tests are some of the laboratory procedures used to measure marginal adaptation, clinical performance in vivo may differ. In future, long term clinical studies are advocated to confirm the benefits of the above mentioned conditioning agents in the success of GI restorations. Based on the observations of the present study it can be concluded that the 50/50 volume% mixture of 37% H3PO4 and 5.25% NaOCl, as it showed best result in the terms of enhancing SBS and least microleakage of GI restoration in comparison to other conditioning agents, can be used as a pretreatment conditioner before the placement of GIC restorations. The conclusions drawn from the present study are:
Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7] [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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