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Table of Contents   
ORIGINAL ARTICLE  
Year : 2013  |  Volume : 16  |  Issue : 6  |  Page : 527-531
Effect of dietary solvents on the strength of nanocomposite, compomer, glass ionomer cement: An in-vitro study


1 Reader, Department of Pedodontics and Preventive Dentistry, Kothiwal Dental College and Research Centre, Moradabad, Uttar Pradesh, India
2 Principal and HOD, Department of Pedodontics and Preventive Dentistry, JSS Dental College and Hospital (now a constituent of JSS University), Mysore, Karnataka, India

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Date of Submission20-Jul-2013
Date of Decision23-Sep-2013
Date of Acceptance05-Oct-2013
Date of Web Publication2-Nov-2013
 

   Abstract 

Background: Intraoral degradation of resin restorative materials involves both mechanical and chemical factors. Thus, an in vitro study was conducted to compare the strength of nanocomposite to commonly used esthetic restorative materials in simulated in vivo conditions.
Aim: The aim of this study was to determine the influence of dietary solvents on the strength of nanocomposite and other esthetic restorative materials.
Materials and Methods: Three test groups (nanocomposite, compomer and glass ionomer cement) each containing 60 pre-conditioned samples, divided into four subgroups of 15 samples each and conditioned in different dietary solvents, were subjected to shear punch test in custom designed shear punch apparatus in Instron Universal Testing Machine.
Statistical Analysis: Descriptive statistics, one way analysis of variance (ANOVA), paired t-test were implied.
Results: One-way ANOVA revealed nanocomposite to bear most shear punch strength post-conditioning, as compared with the other two test materials.
Conclusion: Nanocomposite yielded better strength than the other two test materials, indicating its universal application as a restorative material.

Keywords: Compomer; dietary solvents; glass ionomer cement; nanocomposite; shear punch test

How to cite this article:
Kaur H, Nandlal B. Effect of dietary solvents on the strength of nanocomposite, compomer, glass ionomer cement: An in-vitro study. J Conserv Dent 2013;16:527-31

How to cite this URL:
Kaur H, Nandlal B. Effect of dietary solvents on the strength of nanocomposite, compomer, glass ionomer cement: An in-vitro study. J Conserv Dent [serial online] 2013 [cited 2020 Feb 27];16:527-31. Available from: http://www.jcd.org.in/text.asp?2013/16/6/527/120970

   Introduction Top


With the dawn of esthetic dentistry, resin restorative materials are the preferred choice for various applications. These novel restoratives have proved successful due to their ability to match the tooth color and withstand dynamic oral environment. [1] Recent advances in nanotechnology and nanomaterials, have led to the innovation of a restorative material that would be able to retain high polish and surface texture in the anterior region as well as to possess sufficient mechanical properties suitable for high stress bearing restorations.

To circumvent certain perceived inadequacies associated with the dental resin restoratives, a need to develop a material that has the mechanical strength and wear resistance of hybrid composite yet retains the superior polish and gloss retention associated with microfill materials, was substantiated. It was made possible by incorporating nanofill particles (1 nm = 1/1000 μm) in the form of nanomeric (NM) and nanocluster (NC). Summation of two types of nanofillers resulted in the best combination of physical properties along with superior esthetics, long-term polish retention and other optimized physical properties. [2]

The properties and life of these restorations vary from individual to individual. [3] The degree of degradation of restorative materials in the oral environment is directly related to the type of restoration and the biodynamics of the oral cavity. [4] In order to simulate the oral conditions and determine its effect on the performance of resin restorative materials, food simulating liquids as recommended by Food and Drug Administration (FDA) were used in the following comparative study. [5] The purpose of the study was to compare the strength of nanocomposite with the other two commonly used esthetic restorative materials, i.e. compomer and glass ionomer cement after conditioning in dietary solvents. Results of this simulated study would help us understand the efficacy of nanocomposite and other restoratives in the oral environment.


   Materials and methods Top


The test restorative materials used in the study were: Nanofill composite, compomer and reinforced glass ionomer cement. All materials were of the A2 shade. [6]

Shear punch specimens were made by placing the restorative materials into the brass washers (with an inner diameter of 5 mm and outer diameter of 14 mm and 1-mm thick), supported by glass slides in custom made jig. Mylar strip was attached to glass slides attached with the help of colored adhesive tape (color coding shown in [Table 1]). A second glass slide was placed in upper slot of the jig and on the top of the washer, followed by tightening of the screw embedded in the vertical arms of the jig to apply gentle and uniform pressure on the upper slide to extrude the excess material. [9]

The top surface of the compomer and composite resin specimens were cured using the max polymerization unit (light exit window of 8 mm and mean intensity ≥400 mW/cm 2 ) according to manufacturers' instructions. The glass ionomer cement was allowed to set for 5 min with the glass slides in place. Sixty specimens of each test material was made and pre-conditioned in distilled water (DW) in an air tight glass vial, separately, at 37°C for 1 week. The specimens of each of the three groups, together with their washers, were then divided into four sub groups of fifteen each and conditioned in four different dietary solvents [Table 2].
Table 1: Restorative materials used in the study

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Table 2: Groups and subgroups of test restoratives

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At the end of 1 week of conditioning period in the respective solutions, the specimens were washed and blotted dry. Prior to placement in shear punch apparatus, the thickness of each specimen was measured with vernier caliper. Shear punch strength testing was conducted using custom designed shear punch apparatus. Specimens, along with the washers were positioned in the apparatus by means of a self-locating recess. A tool steel punch with the flat end 2 mm in diameter was used to create shear force by sliding through a punch hole with a radial clearance of 0.01 mm. The specimens were subjected to shear punch test in universal testing machine at the crosshead speed of 2.0 mm/min and the maximum load to make punch through the specimen was recorded in Newton's (N) [6] . The peak load values obtained in Newton's (N) formed the basis for computing of shear punch strength (MPa) in accord to the following formula:



Where,
Value of π = 3.14
Punch diameter = 2 mm
Thickness of specimen = 1 mm.


   Results Top


The mean shear punch strength values obtained were subjected to following statistical analysis: One-way analysis of variance (ANOVA) and paired t-test. Descriptive values for test restoratives showed highest strength values for nanocomposite post-conditioning in heptane (82.95 ± 6.93) MPa and lowest value for glass ionomer post-conditioning in citric acid (CA) (36.87 ± 8.61) MPa [Table 3]. One-way ANOVA revealed glass ionomer strength to be significantly (P < 0.001) lower than nanocomposite and compomer [Table 3].
Table 3: Descriptive values and one way ANOVA

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Paired sample t-test within nanocomposite showed a non-significant difference (P > 0.05) among all the pair of dietary solvents except among the pair of DW (distilled water) with heptane and CA (citric acid) with heptane (H) (highlighted in the respective [Table 4]). In case of compomer none of the pair showed a significant difference. However, in glass ionomer cement CA with heptane showed a significant difference [Table 4]. ANOVA showed that in case of test restoratives, all have a significant difference with each other.
Table 4: Paired t-test for three test restoratives

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   Discussion Top


Contemporary restorative techniques are based on the adhesive properties of resin based materials. Despite the significant improvements in adhesive systems, bonded surface remains the weakest area of tooth colored restorations. [10]

These failures can be attributed to the intricate process of disintegration and dissolution in saliva caused by food, chewing and bacterial activity. No in vitro test is capable of reproducing this complex process. Thus, the study was undertaken to highlight the variability in the strength of nanocomposite and other esthetic restorative materials commonly employed in clinical practice after exposing them to simulated in vivo conditions. The specimens of three test materials were pre-conditioned in DW to allow for post-cure of composite and establishment of acid-base reaction in the compomer and reinforced glass ionomer. [6] The dietary solvents used in the study were among those recommended by the FDA guidelines as food simulating liquids (in 1976). [6],[11],[12]

As per FDA guidelines it is predicted that restorative materials exposed to light beverages, candy, fruits, mouth rinses, alcohol and to oils such as butter and fat in the oral environment will be softened in the same manner as those exposed to water, ethanol, citric acid and heptane respectively in-vitro conditions. [13] DW was used as a control to simulate the wet oral environment provided by saliva and water. [11] Water sorption may have a deleterious effect on the properties of composite materials. Absorbed water reacts with either the coupling agent or with the inorganic filler particles leading to debonding of the filler particles and making them to leach out. [14]

It has been demonstrated experimentally that composite restorations are sensitive to the presence of solvent like compounds as cross-linked polymers such as poly(dimethylsiloxane) (PDMS) present in resin restoratives swell in contact with non-polar solvents. [15]

A strength test needs to measure the cohesion within the specimen and its resistance to deformation in order to allow compression between materials and to examine the effects of manipulative variables. The test should also be applicable to a range of materials, should not be technique sensitive and easy specimen preparation. [16] The shear punch test encompasses all these features. [17] The only mandatory requirement for this test is that the two main faces of the disc should be flat and parallel, [18] thereby allowing uniform stress distribution around the punch circumference. [11]

The strength of the three restorative materials in 50% ethanol-water solution was higher than that of control and CA. The values obtained in this study with regards to ethanol solution were in agreement with the previous studies conducted by Yap where ethanol solution resulted in higher values than CA, DW and heptane. In ethanol solution, the strength of nanocomposite (81.80 ± 11.94) MPa was found to be highest among the three restorative groups (compomer [73.73 ± 6.63] MPa; glassionomer [38.15 ± 6.83] MPa). These results were approximating the rank order by Yap study. However, the values computed for the shear punch strength in the present study were in little variation from the Yap study because of the difference in the specimen diameter and testing conditions. [6]

Mean shear punch strength of restorative materials after conditioning in heptane was found to be higher than in ethanol, CA and control, i.e. DW. These results were coinciding with the results obtained by Yap. [19],[20]

Two possible explanations given for this phenomenon are: As heptane reduces oxygen inhibition during post-curing and eliminates leaching out of silica and combined metal in fillers, which may occur after conditioning in aqueous solutions. [17],[19]

In the entire dietary solvents, nanocomposite gave the best performance, followed by compomer and least by glass ionomer cement. These results were in cognizance to the study by Sumitra. Dong Wu, Brian N Holmes and Yap. [2] An in vitro study carried out by Sumitra developed a restorative material, which would be able to retain high polish and surface texture in the anterior region as well to possess sufficient mechanical properties suitable for high stress bearing restorations. It was made possible by incorporating nanofill particles (1 nm = 1/1000 μm) in the form of NM and NC particles. Aqueous colloidal silica sols were used to synthesize dry powders of nanosized silica particles 20 nm and 75 nm in diameter. The silica particles treated with 3-methacryloxypropyltrimethoxysilane using a proprietary method, is a bifunctional material also known as a coupling agent. The use of spheroidal NC fillers with their broad particle distribution enabled to obtain high filler loading, desirable handling characteristics and physical properties comparable with those of commercial hybrid composites. All the strength tests and fracture resistance of these formulations were statistically equivalent to or higher than those of the hybrid or micro hybrid composites and significantly higher than those of the microfill material tested. [2] Studies by Yap and others have also reported a positive correlation between the mechanical properties and volume fraction of the fillers. [20]

The NM particles fill the interstitial spaces between the clusters resulting in densely packed surface. When these materials undergo toothbrush abrasion, only nanosized particles are plucked away, leaving the surfaces with defects smaller than the wavelength of light and consequently display high polish retention. Nanofillers also offer advantages in optical properties, as the size of the NM particles is far below the wavelength of light, making them immeasurable by the refractive index. Summation of two types of nanofillers resulted in the best combination of physical properties along with superior esthetics. [2]

This study, by simulating the oral environment, substantiated the deficiencies of the test restorative materials under various dietary solvents.


   Conclusion Top


In the present study, every effort was taken to duplicate the oral environment. The mean shear punch strength values computed post-conditioning in dietary solvents showed nanocomposite to bear higher strength than compomer and glass ionomer, thereby indicating its better application universally. The conclusion of this in-vitro investigation must be extrapolated to the clinical situation and further in vivo trials are must to confirm the validity of these recommendations.

 
   References Top

1.Söderholm KJ. Leaking of fillers in dental composites. J Dent Res 1983;62:126-30.  Back to cited text no. 1
    
2.Mitra SB, Dong Wu, Holmes BN. An application of nanotechnology in advanced dental materials. J Am Dent Assoc 2003;134:1382-90.  Back to cited text no. 2
    
3.Berg JH. The continuum of restorative materials in pediatric dentistry - A review for the clinician. Pediatr Dent 1998;20:93-100.  Back to cited text no. 3
    
4.Kakaboura AI. Aging of glass ionomer cements. In: Eliades G, Eliades T, Brantley WA, Watts DC, editors. Dental Materials In vivo. Aging and Related Phenomenon. Chicago: Quintessence Publishing Co.; 2002. p. 70-122.  Back to cited text no. 4
    
5.Yap AUJ, Chew CL, Ong LF, Teoh SH. Environmental damage and occlusal contact area wear of composite restoratives. J Oral Rehabil 2002;29:87-97.  Back to cited text no. 5
    
6.Yap AUJ, Lim LY, Yang TY, Ali A, Chung SM. Influence of dietary solvents on strength of nanofill and ormocer composites. Oper Dent 2005;30:129-33.  Back to cited text no. 6
    
7.Literature of Ceram X by Denstply. Scientific Compendium http://www.dentsply.es/Formacion/LiveUpdate1/CeramX/Scientific%20Compendium%20CeramX.pdf  Back to cited text no. 7
    
8.Hegde MN, Hegde P, Bhandary S, Deepika K. An evaluation of compressive strength of newer nanocomposite: An in vitro study. J Conserv Dent 2011;14:36-9.  Back to cited text no. 8
[PUBMED]  Medknow Journal  
9.Dresch W, Volpato S, Gomes JC, Ribeiro NR, Reis A, Loguercio AD. Clinical evaluation of a nanofilled composite in posterior teeth: 12-month results. Oper Dent 2006;31:409-17.  Back to cited text no. 9
    
10.Krithikadatta J. Clinical effectiveness of contemporary dentin bonding agents. J Conserv Dent 2010;13:173-83.  Back to cited text no. 10
[PUBMED]  Medknow Journal  
11.Yap AUJ, Tan DT, Goh BK, Kuah HG, Goh M. Effect of food-simulating liquids on the flexural strength of composite and polyacid-modified composite restoratives. Oper Dent 2000;25:202-8.  Back to cited text no. 11
    
12.Lee SY, Greener EH, Mueller HJ, Chiu CH. Effect of food and oral simulating fluids on dentine bond and composite strength. J Dent 1994;22:352-9.  Back to cited text no. 12
    
13.Ikejima I, Nomoto R, McCabe JF. Shear punch strength and flexural strength of model composites with varying filler volume fraction, particle size and silanation. Dent Mater 2003;19:206-11.  Back to cited text no. 13
    
14.Kao EC. Influence of food-simulating solvents on resin composites and glass-ionomer restorative cement. Dent Mater 1989;5:201-8.  Back to cited text no. 14
    
15.Vinothkumar TS, Deivanayagam K, Ganesh A, Kumar D. Influence of different organic solvents on degree of swelling of poly (dimethyl siloxane)-based sealer. J Conserv Dent 2011;14:156-9.  Back to cited text no. 15
[PUBMED]  Medknow Journal  
16.Roydhouse RH. Punch-shear test for dental purposes. J Dent Res 1970;49:131-6.  Back to cited text no. 16
    
17.McKinney JE, Wu W. Chemical softening and wear of dental composites. J Dent Res 1985;64:1326-31.  Back to cited text no. 17
    
18.Sylesh S, Yohan C, Narayanan LL. Suitability of shear punch test for evaluating dental restorative materials. J Conserv Dent 2004;7:129-31.  Back to cited text no. 18
    
19.Yap AUJ, Lee MK, Chung SM, Tsai KT, Lim CT. Effect of food-simulating liquids on the shear punch strength of composite and polyacid-modified composite restoratives. Oper Dent 2003;28:529-34.  Back to cited text no. 19
    
20.Smisson DC, Diefenderfer KE, Strother JM. Effects of five thermal stressing regimens on the flexural and bond strengths of a hybrid resin composite. Oper Dent 2005;30:297-303.  Back to cited text no. 20
    

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Correspondence Address:
Harsimran Kaur
WZ-11, Ramgarh Colony (Opp. Kirti Nagar Post Office), New Delhi - 110 015
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.120970

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    Tables

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



 

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