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Table of Contents   
ORIGINAL RESEARCH  
Year : 2020  |  Volume : 31  |  Issue : 3  |  Page : 470-474
The effect of leachable components of resin cements and its resultant bond strength with lithium disilicate ceramics


Department of Conservative Dentistry & Endodontics, SRM Kattankulathur Dental College and Hospital, SRM University, SRM Institute of Science and Technology, Kancheepuram, Tamil Nadu, India

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Date of Submission11-May-2019
Date of Decision09-Jul-2019
Date of Acceptance29-Aug-2019
Date of Web Publication06-Aug-2020
 

   Abstract 


Objectives: To evaluate the leachable components of resin cements in oral simulating fluids using high performance liquid chromatography and its resultant shear bond strength with ceramics. Methods: Forty extracted permanent human mandibular molar teeth were sectioned horizontally with a disc beneath the dentino-enamel junction to expose the coronal dentin surface and later finished with 600-grit silicon carbide paper to create a uniform flat surface. Forty Lithium Di-silicate Ceramic block cylinders were sliced in a saw cutting machine at 250 rpm under water-cooling to obtain the discs. The teeth and the ceramic discs were then randomly assigned to two groups on the basis of material used for luting the ceramic disk. Group I: Ceramic disc luted with tooth surface using Variolink II Dual cure Resin Cement, Group II: Ceramic disc luted with tooth surface using multilink speed self-adhesive self-curing resin cement. All ceramic discs were etched with 5% HF acid (IPS Ceramic Etching Gel, Ivoclar, Schaan, Liechtenstein) for 20 seconds, then rinsed thoroughly for 20 seconds and dried for 20 seconds. Ceramic specimens were luted on dentin surfaces with the application of 5 kg load. The samples were stored in 75% ethanol solution for 2 weeks at 37 degree Celsius for chemical aging. HPLC Analysis were performed to analyze the eluted monomer. After HPLC Analysis, Samples were then loaded using universal testing machine for the evaluation of shear bond strength between ceramic discs and the resin cements before and after the elution of monomers. Results: Under HPLC analysis, results showed that the peak release of monomer is Bis-GMA in both the groups. The shear force required to break the bond between the ceramic luted to tooth surface with the resin cements were more for Group I. Statistical results: The statistical analysis was done using ANOVA and paired t-test and it shows P value ≥0.05, hence the null hypothesis is rejected. Conclusion: The monomer eluded from all the groups are identified as Bis-GMA, The eluded monomer decreases the bond strength between the resin cement and the ceramic due to water sorption, The Variolink II (dual cure) resin cement shows improved bond strength than the Multilink (self-cure self-adhesive) resin cement.

Keywords: Bond strength of lithium di-silicate ceramics with tooth surface, dual cure resin cement, elution of monomers, high performance liquid chromatography, analysis, self-cure resin cement

How to cite this article:
Mavishna M V, Venkatesh KV, Sihivahanan D. The effect of leachable components of resin cements and its resultant bond strength with lithium disilicate ceramics. Indian J Dent Res 2020;31:470-4

How to cite this URL:
Mavishna M V, Venkatesh KV, Sihivahanan D. The effect of leachable components of resin cements and its resultant bond strength with lithium disilicate ceramics. Indian J Dent Res [serial online] 2020 [cited 2020 Sep 23];31:470-4. Available from: http://www.ijdr.in/text.asp?2020/31/3/470/291486



   Introduction Top


Resin composites and ceramic materials have broadened the choices for aesthetic restorations. The long-term success of ceramic restorations not only depends on the structure of material, but also depends mainly on the strength and durability of the bond of the luting composite to the tooth and the ceramic substrates.[1]

Dual cure resin-based adhesive luting materials are extensively used for cementation of indirect esthetic restorations.[1] Self-adhesive self-cure resin cements were introduced in the past few years to simplify the adhesive luting procedures by eliminating the multiple steps for bonding.[2]

Some of the components, such as unreacted monomers, are released from self-adhesive self-cure resin cements when the material is immersed in saliva. The biocompatibility of the restorations may be affected due to the elution of components from Self-Adhesive Self-Cure Resin Cement. Release of substances is a critical issue for dental materials. It can lead to important loss of material and probably also to failure of the restoration.[3],[4] Unreacted monomers can be measured by numerous techniques including Gas Chromatography (GC), High Performance Liquid Chromatography (HPLC), gas chromatography mass spectrometry, and electrospray ionization mass spectrometry. The most common method used for the determination of these monomers is the HPLC method.[5]

Various investigations have shown that using adhesive cements increases the fracture resistance of ceramic restorations. With contemporary adhesive cements and the new generation of bonding systems, achieving a strong and durable bond to both the tooth structure and the indirect restoration could be feasible.[6]

Shear stresses are believed to be major stresses involved inin vivo bonding failures of restorative materials.[1] Bond strength measurements are among the methods used to evaluate the effectiveness of adhesive systems, hence predicting their performance in the oral environment.[6]

Thus, the aim of this study is to analyze the leachable components of resin cements in oral simulating fluids and its resultant bond strength with ceramics.

The null Hypotheses were: 1. The eluted monomer in the resin cements does not have any effect in the shear bond strength of ceramics to tooth; 2. The degree of conversion of both dual cure and the self-cure resin cements does not have significant difference.


   Materials and Methods Top


Forty extracted permanent human mandibular molar teeth without any defect were chosen. The teeth were then sectioned horizontally with a disc beneath the dentino-enamel junction to expose the coronal dentin surface and later finished with 600-grit silicon carbide paper to create a uniform flat surface.

Forty Lithium Di-silicate Ceramic blocks were rounded to 9 mm in height, 6 mm in length, and 6 mm in breadth using a diamond-impregnated drill mounted on a cutting machine. The cylinders were sliced in a saw cutting machine (Iso Met Low Speed, Buehler, IL, USA) at 250 rpm under water-cooling to obtain the discs. All the discs were ultrasonically bathed in 99.8% isopropanol for 380 s and stored dry at room temperature.

The surfaces that would be in contact with the cement were etched with 5% HF acid (IPS Ceramic Etching Gel, Ivoclar, Schaan, Liechtenstein) for 20 seconds, then rinsed thoroughly for 20 seconds and dried for 20 seconds.

The teeth and the ceramic discs were then randomly assigned to two groups on the basis of material used for luting the ceramic disc.

Total of 40 samples of ceramic disc luted with tooth surface using resin cements were divided into 2 groups.

Group I: Eluded samples of luted Ceramic discs with tooth surface using Variolink II dual cure resin cement. (Variolink Esthetic – Ivoclar vivadent, Schaan, Liechtenstein (n = 10)) Group II: Eluded samples of luted Ceramics discs with tooth surface using Multilink Speed Self Adhesive Self Cure resin cement. (Ivoclar multilink N system pack resin cement; Ivoclar vivadent, Schaan, Liechtenstein) (n = 10).

Silanization was done using Monobond N. Ceramic specimens were luted on dentin surfaces with the two luting systems in accordance with the manufacturers' instructions. During cementation period, static load (5 kg) is applied to the specimens. Excess luting cements were removed using “flicking-off” with a hand instrument.[7] Light polymerization was applied for 40 second (Blue phase C5, Ivoclar Vivadent AG, Schaan, Liechtenstein).

The samples were stored in water and 75% ethanol solution and for 2 weeks at 37 degree Celsius for chemical aging.

The analysis of extracts from the resin cement in ethanol and water as well as reference solutions of the monomers was carried out by high performance liquid chromatography (HPLC) (Agilent Technologies) with the following conditions:

  1. Column: steel column (Waters Corporation, Milford, MA, USA), 2 mm thickness of ceramic disc bonded to tooth surface using resin cements
  2. Mobile phase: 75% CH3 CH2 OH (Ethanol)
  3. Flow speed: 1 mL/min
  4. Detection: UV, 205 nm for Bis-GMA and 208 nm for TEGDMA, Bis-EMA, UDMA and Bis-DMA
  5. Injection: 10 mL loop at constant room temperature.


All the measurements were performed three times for each of the extracts. Calibration curves were made relating the eluted peak area to known concentrations of Bis-GMA, TEGDMA, Bis-EMA, UDMA, and Bis-DMA. Standard chromatograms of Bis-GMA, TEGDMA, Bis-EMA, UDMA, and Bis-DMA were obtained. The concentrations of the leaching monomers from composite resins for per storage periods were calculated by using the coefficients obtained by linear regression analysis of the results from the standard series. After HPLC analysis, all the samples were then subjected for shear bond strength analysis.

For the Shear Bond strength Analysis, all the 40 samples such as both pre and post eluded samples of Ceramic disc luted with Tooth Surface using Variolink II dual cure Resin cement and Multi link Self Adhesive Self Cure Resin cement were used.

All the samples were loaded using universal testing machine (Model 3382, Instron Industries, USA) for the evaluation of shear bond strength between ceramic discs and the resin cements before and after the elution of monomers at a cross head speed of 0.5 mm/sec.

Statistical analysis

The statistical analysis was done using ANOVA and paired t-test.

The statistical analysis results shows P value ≤ 0.05, hence the null hypothesis is rejected.


   Results Top


1. Evaluation of the leaching component:

In the presence study, the amount of eluted monomer from two different resin cements in the immersion media (75% of ethanol) at a time period of 2 weeks at 37° C were evaluated using HPLC.

(I) SPECIFICITY

A baseline reference values were analyzed using HPLC.

BisGMA – 4.141

TEGDMA – 3.446

UDMA – 3.828

BiSEMA – 3.003

BiSDMA – 9.236

(II) LINEARITY, RANGE, AND SPECIFICITY

The ceramic discs were luted with resin cements which were immersed into the immersion medium for 24 hours. After 24 hrs the solution prepared for the immersed resin cements were analyzed for the release of Bis-GMA, TEGDMA, UDMA, BiS-EMA, BiS-DMA were calculated directly from the regression equation of the calibration curve obtained by the methods proposed by the HPLC.

All the values were analyzed for each extract. Calliberation curves were made relating the eluted peak area to the concentrations of Bis-GMA, TEGDMA, UDMA, Bis-EMA, Bis-DMA, and standard chromatograms were obtained and taken as reference.

Under HPLC analysis, results showed that the peak release of monomer is Bis-GMA in both the groups [Figure 1].
Figure 1: Cementation of ceramic disc with tooth surface, HPLC Analysis and calibration curve and Bond strength analysis

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2. Shear bond strength analysis

For evaluation of shear bond strength samples were subjected to bond strength analysis using Universal Testing Machines. Pre and post eluded samples were subjected to shear bond strength analysis at a cross head speed of 0.5 mm/sec. The force required to break the bond between the ceramic luted to tooth surface with the resin cements were analyzed using an inbuilt software with the UTM.


   Discussion Top


The long-term success of ceramic restorations not only depends on the structure of material, but also depends mainly on the strength and durability of the bond of the luting composite to the tooth and the ceramic substrates.[8] Bond strength measurements are among the methods used to evaluate the effectiveness of adhesive systems.[9] Shear and tensile strength tests are the most widely used.[9] However, various investigations have reported that the mode of failure, occurring after shear bond testing is often cohesive within the substrate rather than adhesive at the interface.[10],[11],[12] Failures of cemented restorations may be explained by water sorption, solubility, and microleakage of resin cements.[13] It causes reduction of bond strength of restoration with dental substrate. Several factors contribute to the process of elution from resin based dental materials.[13] According to Ferracane, the first relates to the amount of components released, and this should be directly related to the extent of the polymerization reaction. Second, the chemistry of the solvent has a significant effect on the elution, and third, the chemical nature and the size of the released components play a role.[14],[15] 75% Ethanol is used as an extraction medium as it is a food stimulator and aging accelerator aggressive medium verified by FDA (1976, 1988) of USA and therefore it is considered to be clinically relevant. Ethanol 75% has a softening effect on composite materials after attacking their cross-linked network, affecting this way with the release of substances.[16] Schneider et al. showed in their study that one of the main effects of ethanol 75% is the weakening of the mechanical properties of the composite materials.[17] High performance Liquid Chromatography [HPLC 1260 Infinity series Aglient USA] was used to analyze the eluted monomers as it gives a greater level of control over the separation process since the monomers are soluble in mobile phase.[18] It uses reference standard of monomers in order to evaluate the amount of eluted substances through the use of calibration standard curves of peak areas versus monomer concentration of each substance.[19] Present study showed that Bis-GMA was shown to be released in higher rates, an average of 30% area of Bis-GMA monomer is released within the time period of 4 minutes. This might be due to the Bis-GMA is a larger, rigid and highly viscous monomer with high transition temperature. That resulted the lower degree of conversion during polymerization. Shear bond strength showed that, there is increased bond strength in non-eluded monomer group than eluded monomer group. Hence, the first null hypotheses is rejected. The dual cure resin cements showed higher bond strength than self-adhesive self-cure resin cements. This indicates that the dual cure resin cement group had more degree of conversion than self-adhesive self-cure resin cements. Hence, the second null hypotheses is rejected. The composition of both material given in [Table 1] and [Table 2]. The hydrolytic degradation is due to either the breaking of chemical bonds in the resin or softening through the plasticizing action of immersion medium.[20],[21],[22] Reduction of Flexural strength as well as modulus of elasticity are critical for thicker areas of resins. Scientific evidences shows that absorbed water acts as a plasticizer for the resin cements, creating unsupported areas underneath restorations and increases chance of fracture of restoration under masticatory forces.[23],[24] In addition to pretreatment, the composition of the dual cure resin cements unquestionably contributed to cementing quality. These resin cements contains crosslinking monomers such as Bis-GMA, which produce polymers of high mechanical quality because of their high molecular weight, low polymerization contraction and rapid hardening. Dual cure resin cements also contains the monomer diluent TEGDMA, which has high flexibility and low polymerization contraction. TEGDMA also provides a high degree of conversion and has hydrophobic properties that prevent substantial water uptake after curing.[25] Compared to Bis-GMA, TEGDMA allows better clinical handling owing to its low viscocity. A redox reaction of benzoyl peroxide of dual cure resin cements with aromatic tertiary amines underlies the better setting mechanism.[25] In a study by Moraes et al. 2011, they evaluated the dual and self curing potential of self adhesive resin cements as thin films and found that the rate and the extent of conversion were lower for the self adhesive resin cement as compared with the conventional cement, also in Self Adhesive Self Cure Resin Cements, water is formed during the neautrilization reaction between the acidic monomers and basic inorganic fillers, this process being necessary to increase the PH of the filler. Any unconsumed or free water may interfere with the properties of Self Adhesive Self Cure Resin cement.[2] Loss of bond strength using Self Adhesive Self Cure Resin Cements may be due to usage of acidic primer. Because the acid is not rinsed off after application, residual acids can partially neautrilizes the high PH in the self cured component of the adhesive making them less effective in chemical polymerization process.[26]
Table 1: Evaluation of leaching components using HPLC

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Table 2: Evaluation of Shear bond strength

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Clinical significance

Water sorption of resin cements causes elution of monomers that reduces the mechanical properties of resin cements that in turn decreases the bond strength between tooth and ceramic interface.


   Conclusion Top


Within the limitation of the study it can be concluded that,

  1. The monomer eluded from all the groups is identified as Bis-GMA
  2. The increase in elution of monomer causes decrease in mechanical properties of resin cements.
  3. The Variolink II (Dual cure) resin cement shows improved bond strength than the Multilink Speed (Self-Adhesive Self-Cure resin cement)


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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24.
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Correspondence Address:
Dr. M V Mavishna
Mavishna Bhavan Mothiram Madakki Neduvanvila, Parassala PO, Trivandrum, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.IJDR_398_19

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