|Year : 2015 | Volume
| Issue : 2 | Page : 73-77
Evaluation of shear bond strength of conventional glass ionomer cements bonded to mineral trioxide aggregate: An in vitro study
Bandu Devrao Napte, Srinidhi Surya Raghavendra
Department of Conservative Dentistry and Endodontics, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||11-Dec-2015|
Srinidhi Surya Raghavendra
Department of Conservative Dentistry and Endodontics, Sinhgad Dental College and Hospital, 44/1, Vadgaon Budruk, Pune - 411 041, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: This study measured the shear bond strength of conventional glass ionomer cements (GICs) (Xtra Fil and Fuji IX) bonded to white mineral trioxide aggregate (WMTA, Angelus) that had been allowed to set for two different time intervals. Materials and Methods: Sixty WMTA specimens were prepared; half were stored for 45 min and the remaining 30 specimens were stored for 72 h at 37°C and 100% humidity. Then, each group was divided into two subgroups of 15 specimens, and each GIC was layered on each of the two WMTA preparations. The GIC-WMTA shear bond strengths were measured and were compared by using one-way analysis of variance. Results: The shear bond strengths with the 45-min and 72-h WMTAs were 7.23 and 7.79 megapascal (MPa), respectively, for Xtra Fil and 7.87 and 8.12 MPa, respectively, for Fuji IX. The GIC-WMTA bond strength was not different between GIC applications to WMTA that had set for 45 min versus 72 h (P > 0.05). Conclusion: GICs might be used over MTA after the MTA has set for 45 min to allow single-visit direct pulp cap procedures.
Keywords: Glass ionomer, mineral trioxide aggregate, shear bond strength, vital pulp therapy
|How to cite this article:|
Napte BD, Raghavendra SS. Evaluation of shear bond strength of conventional glass ionomer cements bonded to mineral trioxide aggregate: An in vitro study. J Dent Allied Sci 2015;4:73-7
|How to cite this URL:|
Napte BD, Raghavendra SS. Evaluation of shear bond strength of conventional glass ionomer cements bonded to mineral trioxide aggregate: An in vitro study. J Dent Allied Sci [serial online] 2015 [cited 2019 Aug 24];4:73-7. Available from: http://www.jdas.in/text.asp?2015/4/2/73/171519
| Introduction|| |
Vital pulp therapy is a critical aspect of all restorative treatments. The goal during the placement of any restoration, whether it is a direct placement composite resin, amalgam restoration, or a full-coverage crown, is to maintain a vital and healthy pulp. In clinical situations where caries, trauma, secondary caries, or old restorations are seen near the pulp, vital pulp treatment is considered. ,,
Mineral trioxide aggregate (MTA) was introduced as a root-end filling material in 1993. It is a mixture of tricalcium silicate and tricalcium aluminate and has been used in furcation repair, internal resorption treatment, pulpotomy procedures, and capping of pulps. ,,,,,,, MTA induces dentinogenesis and cementogenesis and is preferred in the cases of pulp treatment.  In addition, the pulp heals faster with MTA than with calcium hydroxide. 
One of the main disadvantages of using MTA is its long setting time of 2 h 45 min. , Hence, when used as a pulp capping material, MTA requires additional visits. To complete the final restoration in a single visit, a material that is compatible with MTA can be applied over partially set MTA.  Two materials which can be considered are resin composites and glass ionomer cements (GICs). Resin composites cannot be placed directly over freshly mixed MTA because they can affect its setting. Studies recommend a time gap of up to 96 h prior to placing composite resin over MTA.  Furthermore, the etching of freshly mixed or set MTA can lead to impairment of its surface hardness.  Placing GIC over partially set MTA as a part of permanent restoration can be considered.  Studies have shown that conventional Type II GICs can be layered over partially set MTA after 45 min, which makes single-visit pulp capping procedures more feasible. ,
The aim of this study was to measure the shear bond strength of two conventional Type II GICs (Xtra Fil II and Fuji IX) to white MTA (WMTA) which is allowed to set for two different times, 45 min and 72 h. Xtra Fil II is a Type II GIC with setting time of 2.5-5 min and an average compressive strength of 128 megapascal (MPa). Fuji IX is a Type II GIC with setting time of 2.5-4.5 min and a compressive strength of 220 MPa at the end of 1 day.
| Materials and Methods|| |
The materials used in this study were:
- MTA, Angelus, Brazil, Batch No: 30684.
- Fuji IX - high strength posterior restorative (GC Corporation Tokyo, Japan, Batch No: 1403051).
- Xtra Fil II radiopaque glass ionomer restorative cement (Medicept, UK, Batch No: 010902-3).
- TMS-RS temporary filling material (Prime Dental Pvt. Ltd., Thane, Maharashtra, India, Batch No: 131102-01).
The samples were randomly divided into groups as given in [Table 1].
Preparation of mineral trioxide aggregate specimens
Sixty WMTA specimens were prepared by using acrylic block having a cylindrical hole of diameter 4 mm and depth 2 mm. WMTA was mixed according to manufacturer's instructions and placed into the hole of the acrylic block with applicator. It was covered with a moist cotton pellet and temporary filling material (Cavit™ , ESPE, USA) [Figure 1]. Half of the specimens (n = 30) were stored for 45 min and the other half (n = 30) were stored for 72 h at 37°C and 100% humidity. After removing temporary material and moist cotton, WMTA surface was not rinsed or polished. The specimens are further divided into two subgroups of 15 specimens each.
Placement of glass ionomer cement
GICs are placed at the center of WMTA disks after manipulation by packing material into cylindrical plastic tubes of internal diameter 3 mm and height 4 mm. Allowing 10 min for setting, the plastic tube is removed. The specimens are stored for 24 h at 37°C and 100% humidity.
Shear bond strength measurement
The specimens were mounted in a universal testing machine (Star Testing System, India, Model No. STS 248). A crosshead speed of 1 mm/min was applied to each specimen at the interface between conventional GICs and MTA using a knife-edge blade until the bond between the MTA and GIC failed [Figure 2]. The values were calculated in MPas [Table 2]. The mean and standard deviations were calculated. The mean bond strengths of the groups were compared by using one-way analysis of variance and Tukey's honestly significant difference post hoc test (significance level, P ≤ 0.05).
|Table 2: Mean shear bond strength values of glass ionomer cements to mineral trioxide aggregate (n = 15)|
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| Results|| |
The mean and standard deviations of the shear bond strengths are given in [Table 2] and [Table 3]. There were no significant differences among the groups (P > 0.05). The shear bond strength of the conventional GICs (Xtra Fil and Fuji IX) to the MTA was similar after 45 min and 72 h (P > 0.05). The inter group comparisons are given in [Table 4] (95% confidence interval). The shear bond strengths with the 45-min and 72-h WMTAs were 7.23 and 7.79 MPa, respectively, for Xtra Fil and 7.87 and 8.12 MPa, respectively, for Fuji IX. The GIC-WMTA bond strength was not different between GIC applications to WMTA that had set for 45 min versus 72 h (P > 0.05).
|Table 3: Minimum and maximum mean values of shear bond strength between glass ionomer cement and mineral trioxide aggregate|
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|Table 4: Multiple inter-group comparisons shear bond strength (Mpa) of glass ionomer cement to mineral trioxide aggregate (Tukey's honestly significant difference)|
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| Discussion|| |
The term pulp capping refers to protection of the pulp by direct or indirect method. In indirect pulp capping, nonremineralizable carious tissue is removed and a thin layer of caries is intentionally left at the deepest site of the cavity preparation. This is due to the fact that removal of this last layer may expose the pulp. The remaining bacteria will be deprived of its nutrient supply and die.  In direct pulp capping, there is a mechanical exposure of the vital pulp tissue due to trauma or a dental procedure, where the pulp is vital and asymptomatic. A therapeutic base or liner is placed to provide for the maintenance of pulp vitality.
The treatment options for a mechanically exposed pulp in vital permanent teeth, include pulp capping or endodontic therapy.  The American Association of Endodontists glossary of endodontic terms defines pulp cap as treatment of an exposed vital pulp by sealing the pulpal wound with a dental material such as calcium hydroxide or MTA to facilitate the formation of reparative dentin and maintenance of vital pulp. 
Aguilar and Linsuwanont in their review evaluated the evidence regarding clinical and radiographic success in vital pulp therapeutic procedures, including direct pulp capping, partial pulpotomy, and full pulpotomy in vital permanent teeth with cariously exposed pulps using calcium hydroxide or MTA.  The success rates for vital pulp therapy were as follows: 6 months-1 year 87.5%; 1-2 years 95.4%; 2-3 years 87.7%; and >3 years 72.9%. Partial and full pulpotomy had high success rates up to more than 3 years (partial pulpotomy, 99.4%; full pulpotomy, 99.3%). The conclusion was that vital permanent teeth with carious pulpal exposures can be treated successfully with vital pulp therapy.
Materials recommended for pulp capping such as calcium hydroxide, MTA, and bioactive tricalcium silicate mimic growth factors and are used in direct pulp capping of carious and noncarious pulp exposures in asymptomatic teeth. , Stimulation of these growth factors lead to dentin regeneration. 
The setting reaction of MTA results in the formation of calcium hydroxide. Calcium hydroxide has an alkaline nature. This in turn reduces the inflammatory effects of the bacteria on the pulp. , The major disadvantages of calcium hydroxide are its unfavorable physical properties, poor compressive strength, and lack of adhesion. Hence, it needs to be covered with a stronger liner or base. 
The success of the pulp capping procedures is due to the calcium ions from the MTA.  Both MTA and tricalcium silicate during their setting reaction show the release of large numbers of calcium ions, which increases dentin regeneration.  Clinical evaluations have demonstrated success rates between 72.9% and 98%. , One of the main disadvantages of MTA in pulp capping procedures is that it has an extended working and setting time. , Sluyk et al.  reported that MTA required a setting time of 72 h to resist displacement and dislodgement from dentin walls of a preparation. MTA demonstrated insignificant setting within 35 min from placement, and within 24 h it had only 23% of the compressive strength of the material, compared to that seen at 28 days.  Studies have recommended that before restoring the tooth, MTA should be covered with a light-cured glass ionomer liner after placement because of MTA's extended setting time.  Nandini et al. reported that placement of GIC 45 min after placing WMTA does not interfere with MTA setting, and calcium salts can be formed in the interface of both materials.
The strength of the bond between the restorative material and the enamel/dentin, as well as between the restorative material and the cavity liner, is one of the most critical factors for quality dental filling treatment. A bond strength ranging from 17 to 20 MPa has been found to sufficiently resist contraction forces and produce gap-free restoration margins. Shear bond strength gives an estimate of the stress the bonding layer can withstand, and determines the integrity of the materials. Higher values imply better bonding between two interfaces and lesser microleakage. 
In the present study, two materials, conventional GICs and MTA have been used. They have the advantage of working in combination without affecting their properties and gives better results. The mechanism of adhesion of GICs is that it can bind to dental hard tissues via a physicochemical process involving ionic exchange at the interface. The carboxyl groups replace phosphate ions in the tooth structure and forms ionic bonds with the calcium ions of hydroxyapatite. , The shear bond strengths of conventional GICs to conditioned enamel and dentin are relatively low, ranging from 3 to 7 Mpa.  Because of the high percentage of hydroxyapatite in enamel, the bonding to enamel is likely to be stronger than the bonding to dentin. In this study, the mean shear bond strength of both the GICs to WMTA was 8.33 MPa.
Possible reactions which may occur when a GIC is applied on the surface of MTA are: (a) The COO− of the polyacrylic acid could interact with the calcium of the MTA to form calcium salts (b) the silicate hydrate gel of the MTA could condense with the silicate hydrate gel of the GIC to form by-products. Since there are a high percentage of mineral oxides in WMTA, GICs bond strongly to WMTA. 
The adhesion of GIC to enamel and dentin rely mostly on chemical interaction and micromechanical interlocking.  The porous surface of MTA could be a factor that increases the strength of the MTA-GIC bond. The two time intervals used in this study (45 min and 72 h) were chosen on the basis of previous studies. ,,
The physical properties and setting time of MTA materials can be affected by the different liquids used in their preparation.  The critical role of water in the setting of MTA has already been proved.  For GIC layered over partially set MTA, it is necessary to evaluate the influence of the partially set MTA on the setting of the GIC.  Hydration or dehydration of the GIC during its initial setting will alter its physical properties. Therefore, the specimens were stored at 100% humidity. The values of shear bond strength obtained at 45 min and 72 h indicates that there is adequate bond strength between GIC and MTA.
| Conclusion|| |
The combination of GIC with MTA shows great promise in the field of single-visit pulp capping with MTA. The initial low strength and solubility of MTA can be offset by layering Type II GIC which has shown adequate shear bond strength. Further research can be carried out at different time intervals to measure the shear bond strength at the interface between the GICs and MTA, which may suggest further reduction in the time interval for direct pulp capping treatment.
The authors would like to thank Praj Laboratory, Kothrud, Pune, Maharashtra, India, for technical assistance.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]