Introduction
Advances in the field of esthetic restorative materials which requires very conservative tooth preparation are in a rapid pace. Moreover clinical and laboratory researches concerning them play an important role because of the patients’ preferences for these materials. 1, 2
Composites are superior in their aesthetic quality and adhesion capability to tooth substrates. The improved mechanical properties of composite forced the clinicians to choose it as a better option for both anterior and posterior restorations.3 Highly viscous GIC (Fuji IX), is widely used in Atraumatic Restorative Technique (ART).4, 5 In this, the powder is modified by replacing calcium with strontium ions which improves its hardness and wear resistance. 1, 6 Cention is an “alkasite” restorative material, like compomer or ormocer and is considered to be a subgroup of the composite. It contains special patented filler (Isofiller) which functions as a shrinkage stress reliever. 7
Two important phenomena that can affect the durability of restorations are water sorption and solubility. Water sorption can increase the volume of the material and thereby can act as a plasticizer resulting in the deterioration of the matrix structure.8 Solubility is defined as the extent to which a material dissolves in a solvent within a given temperature. 9
Nowadays mouthwashes are widely used even without a dental prescription. According to a study by Moran JM et al, frequency of using mouthwashes was up to six times per day. 10 Water, antimicrobial agents, salts, preservatives, and alcohol are the different constituents of mouthrinses.11 It was reported that ethanol in mouthwashes might speed up the degradation of resin based constituents. 12
Periogard mouthwash contains chlorhexidine, which is a bisbiguanide antiseptic having four chlorophenyl rings and two biguanide groups bonded by a hexamethylene bridge. 13 Listerine mouthwash is an essential oil type, which contains thymol, eucalyptol and menthol in an alcohol solvent. 10, 14 Plax mouthwash has Cetyl pyridinium chloride, which is a quaternary ammonium compound. 11
Always there is a concern about effects of mouthwashes on the properties of composite resins like discoloration, staining, and translucency. But only few researchers assessed the influence of mouthwashes on the mechanical and chemical properties of the composites,15 Moreover there is no study till date on comparing the effects of different mouthwashes on Cention N, composite and Type IX GIC.In the light of this,present study was conducted.
Materials and Methods
Restorative materials and solutions used in this study are Cention N (Ivoclar vivadent), Type IX GIC(GC Corporation Tokyo, Japan), Filtek TM Z350 XT(3M ESPE), Listerine, Alcohol based (Johnson and Johnson Healthcare Products), PerioGard with alcohol (Colgate Palmolive Ind.com.Ltda), Colgate Plax, Alcohol free, fluoride containing,(Colgate Palmolive Ind.com.Ltda,)
Preparation of Specimens
For each material, 15 disc-shaped specimens were prepared using a stainless steel mould of of 15+-0.1 mm diameter and 2mm thickness. Products were handled according to the manufacturer’s instructions.
The mould was lubricated with petroleum jelly to facilitate removal of the materials after setting. After proper cleaning and polishing of specimens, they were first stored in a desiccator at 37°C with silica gel for 24 hours(hrs). Later they were transferred to a desiccator at 23°C for 1hrs. They were weighed to an accuracy of 0.1mg in a digital analytic balance and the same process was repeated till a mass of loss not more than 0.1mg in any 24 hrs period is achieved. This is the sample weight before immersion (M1).
Using digital caliper, the diameter of each sample was measured at two points perpendicular to one another and the average diameter was estimated. Then the thickness of each specimen was measured at the center in four equally spaced points and average thickness was estimated. Using the formula, 𝑉 = 𝜋×𝑟2×ℎ, where 𝑟 is the radius (average diameter/2)and ℎ is the average thickness, volume was calculated.
Five samples of each material were immersed in 10ml of three mouthwashes at 37°C for seven days. After seven days, they were removed and washed. The adherent water was removed with a tissue paper. The samples were kept at 37 °C for 15 seconds and weighed (M2). Then the specimens were reconditioned to constant weight in the desiccator using the earlier cycle. The sample weight after immersion (M2) and dessication (M3) were noted. The solvent uptake and solubility were estimated in μg/mm3 using the Oysaed and Ruyter formula as follows:
Sorption = (M2 – M3) ÷V
Where, M1 = Sample weight before immersion
M2 = Sample weight after immersion and
M3 = Sample weight after immersion and desiccation.
Results
Sorption and solubility mean values are given in figure 1 and 2 as graphical representations. ANOVA showed significant difference in sorption and solubility values. Post hoc test was used to compare groups and subgroups. Values of Post hoc test are given in Table 1 and 2 respectively. Sorption is within the permitted values of ISO standard but solubility showed significantly higher values more than permitted limit.
Table 1
Comparison of sorption of restorative materials in mouthwashes usingTukeys Post HocTest
Table 2
Comparison of solubility of restorative materials in mouthwashes usingTukeys Post Hoc Test
Discussion
The resistance against degradation of restorations plays an important role in their clinical longevity.16 Thus increase in the knowledge about sorption and solubility properties should have a critical role in predicting the success of restorations. According to ISO 4049 (2009) standardisation, restorative materials should have water sorption lower than 40µg/mm3 and solubility lower than 7.5 µg/mm3 for 7 days of storage period. 17
Nanofilled composite and Glass-ionomer cements are used in dentistry in a wide manner nowadays.1,2 Cention N is considered to be a good replacement for amalgam as an esthetic posterior bulk fill material. 7
In vitro studies made it clear about the subsurface and surface disintegration of composites while immersing in alcohol.18 At the same time,invivo studies found that mouth rinses with and without alcohol had same effect in plaque control and reducing gingivitis. 13 Thus this study aimed to find out the effect of three different mouthwashes like periogard, listerine and colgate plax on Nanofilled Composite, Type IX GIC and Cention N irrespective of the presence of alcohol.
Variations in values from previous studies might be due to differences in the composition of the mouth washes and restorative materials used. 15
In the present study, tested materials showed maximum sorption and solubility in listerine. This could be due to low pH (4.2) and 30% alcohol content when compared to other two mouthwashes. It may have caused wear of the filler surfaces and finally resulted in debonding. 10, 14
Sorption is a diffusion-mediated process which occurs in the organic resin matrixes. 14 Increased pressure due to change in dimensions by sorption property can constrain the material within the cavity. 19 Resin matrix with hydrophilic HEMA and UDMA showed higher sorption values. Khokhar et al. observed that the UDMA had higher sorption when compared to Bis-GMA because of its urethane groups, which can be correlated with the current study result, that Cention N showed higher values when compared to Composite.20
Mohsen and Craig opinioned that the true sorption values should be more than the reported ones usually since the gain in weight of the samples denotes the water gain, but in fact it is the difference between the weight gain and the release of low molecular weight components. 21, 22
The solubility of restorations may cause surface deformation as well as marginal discrepancies. 10 The effects of chemistry of the oral environment and curing units will be different relying on the type of the material being tested. One more factor that cause variation from previous studies might be due to differences in specimen size, since difference in size will affect time taken for solvent to completely infiltrate within the resin matrix. 9
In composite, alcohol can cause swelling of the resin matrix and thereby release more unreacted monomers and oligomers. 10 In Filtek Z 350, major amount of TEGDMA is replaced by UDMA and BisGMA. This replacement and copolymerization with BisGMA may create more flexible resins having lower water sorption and higher solubility values. TEGDMA can produce the most dense polymer network. But at the same time, it can absorb more water because of its heterogeneous property which creates microporosity and there by release the least amount of unreacted monomer. This might be the reason for lower values of Composite.
Two other possibilities are there to explain sorption of the nanofilled composite. First may be the higher surface area - volume ratio produced from the non-agglomerated silica filler of 20 nm size, which caused more solvent to get accumulated at the filler- resin interfaces where greater amount of silane and the hydrophilic groups available for higher rate of hydrogen bonding. Second, the liquid accumulated at the filler- matrix interzone might diffuse into the aggregates through path already produced by poor impregnation of 5-20 nm-sized primary particles.15
Type IX GIC showed highest sorption and solubility values when compared with other restorative materials. The continuous transferring of the samples to and from the weighing machine during the study was believed to cause minute wear on the surface , this might be the reason for variation in values from earlier studies.10
Sorption as well as solubility can result in hydrolytic degradation of GIC, which in turn affect the mechanical properties of the restorative materials.23 One specific feature of GIC is its water uptake and loss. Ionic interaction is the main bonding mechanism of HVGIC between material constituents and hydroxyapatite of the tooth, which can be hampered by water loss. 24 Thus surface protector medium like petroleum jelly are required. Fluoride releasing property of GIC, which promotes the remineralization, is likely to be related to solubility. Thus, further studies should be required to rule out the effect of solubility on this property of GIC. 9
Improper mixing of the material may cause air voids which in turn result in increased exposure to the solvent and may cause inhibitions zones of unpolymerized materials. This might be the another reason for higher values than expected one. 9
As per Catani-Lorente et al. 25 since clinical scenario is quite different from in vitro conditions, dental practitioners may need to be cautious about the manipulation and application of these restorative materials.
Conclusion
Based on the findings and the results, the following conclusions can be drawn:
Use of alcohol-containing mouth washes having low pH may increase the sorption and solubility of the restorative materials. Thus it is quite reasonable to use alcohol-free mouthwashes especially in patients with extensive restorations even the three mouthwashes used in the current study had effect on sorption and solubility of tested materials irrespective of alcohol content. This might be due to the composition of matrix, nature of filler particles, their hydrophilicity, efficiency of polymerization etc. Thus continuous improvement in the materials’ properties should be required.
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