|Year : 2014 | Volume
| Issue : 2 | Page : 86-89
Evaluation of the mechanical properties of conventional glass ionomer cement after the addition of casein phosphopeptide amorphous calcium phosphate: An in vitro study
Shalini Aggarwal, Sanchita T. Bhor, Anita Sanap, Anamika Borkar, Alexis Rego, Vinay Rai
Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Vidyapeeth Society, Dr. D. Y. Patil Dental College and Hospital, Pimpri, Pune, Maharashtra, India
|Date of Web Publication||5-Jun-2014|
Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Vidyapeeth Society, Dr. D. Y. Patil Dental College and Hospital, Pimpri, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
Background: Casein phosphopeptides-amorphous calcium phosphate (CPP-ACP) products have gained much importance in restorative dentistry and minimally invasive dentistry. Addition of CPP into glass ionomer cement (GIC) has been shown to interact with fluoride ions to produce an additive anticariogenic effect through the formation of stabilized amorphous calcium fluoride phosphate phase. Aim: The aim of this study was to determine the additive effect of CPP-ACP on the mechanical properties of conventional GIC. Materials and Methods: The control GIC was prepared with self-curing GIC. The GIC containing CPP-ACP was prepared from the same batch, with 1.56% w/w CPP-ACP incorporated. Compressive strength and microtensile bond strength tests were done. Energy dispersive X-ray (EDX) analysis was used to determine the composition of various structural phases. Results: Incorporation of 1.56% w/w CPP-ACP into the GIC resulted in an increase in compressive strength and microtensile bond strength. The representative EDX spectra taken showed enhanced release of calcium, phosphate, and fluoride ions.
Keywords: Caries inhibition, casein phosphopeptide amorphous calcium phosphate, glass ionomer cement, ion release, material strength
|How to cite this article:|
Aggarwal S, Bhor ST, Sanap A, Borkar A, Rego A, Rai V. Evaluation of the mechanical properties of conventional glass ionomer cement after the addition of casein phosphopeptide amorphous calcium phosphate: An in vitro study. J Dent Res Rev 2014;1:86-9
|How to cite this URL:|
Aggarwal S, Bhor ST, Sanap A, Borkar A, Rego A, Rai V. Evaluation of the mechanical properties of conventional glass ionomer cement after the addition of casein phosphopeptide amorphous calcium phosphate: An in vitro study. J Dent Res Rev [serial online] 2014 [cited 2022 May 21];1:86-9. Available from: https://www.jdrr.org/text.asp?2014/1/2/86/133949
| Introduction|| |
Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) arrests the onset and progression of caries and also remineralizes enamel subsurface lesions.  The anticariogenic potential of CPP-ACP arises from the ability of the CPP to form ACP at the tooth surface, thereby helping attaining and maintaining a state of supersaturation with respect to tooth mineral.  CPP-ACP nanocomplexes show anticariogenic activity in laboratory, animal, and human experiments.
Casein phosphopeptide-amorphous calcium phosphate creates a calcium phosphate reservoir, buffering the free calcium, and phosphate ion activities. This helps to maintain a state of supersaturation with that of the tooth mineral depressing enamel demineralization and enhancing remineralization (Reynolds EC et al, 2008).  It has been shown that CPP has the ability to stabilize calcium phosphate in solution by forming colloidal CPP-ACP complexes. , The CPP molecules contain a cluster of phosphoseryl residues -Ser (P)-Ser (P)-Ser (P)-Glu-Glu-, which significantly increases the apparent solubility of calcium phosphate by stabilizing ACP (Ca 3 (PO 4 ) 2 -nH 2 O) under neutral and alkaline conditions. The multiple phosphoseryl residues of the CPP bind to nanoclusters of ACP in supersaturated solutions, thereby preventing growth to the critical size required for phase transformations (Reynolds, 1997).
Glassionomer cements (GICs) have been clinically established to have certain biological properties, which make them unique as restorative and luting materials. These properties include adhesion to all tooth tissues, anticariogenic properties because of fluoride release, thermal compatibility with enamel, flexural compatibility with dentin, good biocompatibility, and low toxicity to soft tissues. However, poor mechanical properties make it a lesser used material in the stress bearing areas. It has low fracture strength, toughness, and wear.  Microleakage around restorations may occur leading to secondary caries of the adjacent tooth tissues. 
In an approach to further enhance the compressive stress bearing capability of GIC, we incorporated 1.56% w/w CPP-ACP into a selected commercial GIC and investigated the cement's physical properties. Compressive strength and microtensile bond strength to dentin, as well as calcium, phosphate, and fluoride release were determined.
| Materials and Methods|| |
A total of 20 teeth were used for this study 10 samples were used for each study group. Group 1 served as the control group consisting of conventional GIC and Group 2 consisted of incorporating CPP-ACP into GIC in the form of a paste. For the second group, one scoop of powder of GIC with one scoop of CPP-ACP from GC Tooth Mousse was incorporated simultaneously with the liquid.
The study was carried out under three parameters namely:
- Compressive strength
- Micro-tensile strength
- Ion release.
The CPP-stabilized calcium phosphate solutions can re mineralize enamel subsurface lesions at rates of 1.5-3.9 × 10−8 mol hydroxyapatite/m 2 s (Reynolds, 1997). The CPP can stabilize over 100 times more calcium phosphate than is normally possible in aqueous solution at neutral and alkaline pH before spontaneous precipitation (Holt and van Kemenade, 1989).
Each group consisted of 10 samples to test the compressive strength. Cylinders of 4 mm diameter × 6 mm long were made from the GICs. Group 1 consisted of conventional GIC, which was prepared with self-curing GIC (Fuji IX GP, liquid and powder, GC International, Tokyo, Japan) and it served as the control. Group 2 consisted of GIC containing CPP-ACP (Recaldent TM ), which was prepared from the same batch, with 1.56% w/w CPP-ACP incorporated. The CPP-ACP and GIC powder were manually mixed, and the powder: Liquid ratio used was as recommended by the manufacturer. Compressive strength test was performed following ISO method (ISO, 1991).
Each specimen was tested with flat ends between the plates of the mechanical tester and a compressive load was applied at a rate of 0.75 mm/min along the long axis of the specimen. A piece of damp filter paper (Whatman No. 1) was applied to both the top and bottom plates of the mechanical test machine in the area, which will contact the specimens. The maximum force was recorded to the point of failure for each specimen and the compressive strength was calculated.
Microtensile bond strength to dentin
Noncarious human molars were stored in saline solution. The only teeth used were those that had been extracted in the previous 2 months. The teeth were de-coronated followed by the placement of the test materials. Bar-shaped longitudinal specimens, one-half of GIC and one-half of dentin were prepared with GIC (Fuji IX GP, Japan) for Group 1 and the same for GIC containing 1.56% w/w CPP-ACP for Group 2. The micro-tensile bond strength was carried out using a microtensile tester.
Each group consisted of 10 samples. The crown was de-coronated at the cementoenamel junction which was followed by the placement of GIC and GIC containing CPP-ACP in their respective groups. These teeth were then sectioned longitudinally into 3 mm × 15 mm thick slabs, containing half GIC, and half dentin.
The sections were then trimmed to provide a test area and the two ends of the slabs are glued perpendicular to two stainless steel plates with cyanoacrylate. This technique offers simple screening of the regional differences in bond strength of adhesive materials.
The specimens were stressed in tension at a cross-head speed of 1 mm/min until failure occurred. The mean bond strength values were calculated according to the standard formula (ISO, 1991).
The fractured specimens were observed under a scanning electron microscope (SEM) and energy dispersive X-ray analysis was used to determine the composition of various structural phases along the fractured GIC-dentin interfaces.
Data from compressive strength and microtensile bond strength were compared by Student's t-test. Data from the ion release analyses were compared by a one-way classification analysis of variance, with the least significant difference test and comparisons within the groups was done using Mann-Whitney U-test.
| Results|| |
Result: The compressive strength in Group 1 was reported to be 198.80 ± 12.42 MPa compared to Group 2, which has a compressive strength of 212.40 ± 7.99 MPa. There is statistically highly significant difference in mean compressive strength between the study groups (P < 0.05). It is observed that Group 2 has more compressive strength than Group 1.
Micro-tensile bond strength
Result: The micro-tensile bond strength in Group 1 was reported to be 17.10 ± 1.52 MPa compared with Group 2 which has microtensile bond strength of 22.40 ± 1.43 MPa. There is statistically highly significant difference in mean microtensile bond strength between the study groups (P < 0.05). It is observed that Group 2 has more tensile strength than Group 1.
Percentage increase in tensile strengths
Result: The mean percentage increase in microtensile bond strength was 23.57 (±6.14), whereas mean percentage increase in compressive strength was 6.28 (±6.84) from Group 1 to Group 2. The percentage increase in microtensile bond strength was 33.33%, whereas for compressive strength, percent increase was 18.18% [Graph 1].
Elemental analysis for ions present in dentin
Comparison between groups
in Group 1 is 1.47% and Group 2 is 2.13. There is statistically no significant difference in median wt% between the groups.
in Group 1 is 2.77% and Group 2 is 5.77. There is statistically significant difference in median wt% between Group 1 and Group 2 for fluoride.
2 had a mean wt% of 6.2% of calcium as compared to Group 1, which did not show any evidence of calcium.
| Discussion|| |
The success of GICs in restorative dentistry is mainly due to the fact that it has excellent biological properties. Chiefly is its ability to bond to tooth tissue - both enamel and dentin. GICs also interact well with resin composites and hence are used adjacent to resin composites, in atraumatic restorative treatment, in tunnel restorations, and in the restoration of primary teeth.
A cohesive failure was reported in a study carried out by Tanumiharja et al., 2000  which showed that the predominant mode of failure for the CPP-ACP-containing GIC was partial cohesive failure in the GIC and partial adhesive failure between the GIC and the dentin.
The hypothesis of incorporating CPP was based on the fact that CPP-ACP acts as a reservoir for calcium and phosphate and maintains the levels of ACP during surface demineralization of the tooth structure and its ability to channelize the uptake of calcium ions into the demineralized area.
Glass ionomer cements exhibit several clinical advantages compared with other restorative materials. They include physicochemical bonding to tooth structures, long term fluoride release, and low coefficients of thermal expansion. However, their low mechanical strength compromises their use in high-stress-bearing restorations. 
Incorporating CPP-ACP into GIC has shown to contribute to the overall compressive and micro-tensile bond strength of GIC. This could be due to the fact that CPP-ACP nanoparticles may have been physically encapsulated into the set GIC, as has been found with unreacted glass particles in a study carried out by Matsuya et al., (1984), and therefore released as the acid eroded the cement in the acidic buffer. A protective barrier over the dentin by continuous release of CPP-ACP from GIC is created during an acid attack.
Further studies on reaction between CPP-ACP release and saliva buffering capacity to neutralize conditions of low pH in the oral cavity need to be carried out in order better understand the remineralization capabilities of CPP-ACP.
Scanning electron microscope results showed a cohesive failure that was seen within the GIC. It is known that the pores in a solid body act as stress-concentration points where fracture can initiate, and it has been speculated that this explains the frequency of cohesive failure within a GIC. SEM analyses of the fractured surfaces of the different GICs did suggest a greater porosity of the control GIC [Figure 1] relative to the CPP-ACP containing GIC. However, whether this was responsible for the difference in bond strength is unknown. The addition of CPP-ACP to the GIC could have caused increased microtensile bond strength by the incorporating CPP-ACP nanoparticles into the cross linked matrix of the GIC [Figure 2].
|Figure 1: Representative scanning electron micrographs of fractured cement surfaces of the control glass ionomer cement showing porosities and crack propagation|
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|Figure 2: Representative scanning electron micrographs of fractured cement surfaces of the glass ionomer cement (GIC) containing 1.56% w/w casein phosphopeptides-amorphous calcium phosphate showing less porosity as compared to the control GIC|
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Furthermore, the fluoride release was found to be significantly higher in Group 2 (CPP-ACP containing GIC) as opposed to the control group. It is possible that the CPP-ACP caused an elevated release of fluoride ions from the GIC by forming CPP-amorphous calcium fluoride phosphate nanocomplexes, which were released from the cement matrix.
There was a higher release of inorganic phosphate from the CPP-ACP-containing GIC than that was calculated from the control GIC. This was found to be consistent with the addition of the stabilized ACP. Calcium ions were not detected in the control GIC group, but were detected in the CPP-ACP-containing GIC.
| Conclusion|| |
Incorporation of 1.56% w/w CPP-ACP into conventional GIC was shown to increase compressive strength and microtensile bond strength. It was also found to enhance the release of Ca +2 , PO4−2 , and F− ions.
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[Figure 1], [Figure 2]