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Year : 2019  |  Volume : 10  |  Issue : 2  |  Page : 127-130  

Microhardness of coronal dentin adjacent to resin-modified glass ionomer and compomer in Class V restorations

Department of Conservative Dentistry and Endodontics, Bapuji Dental College and Hospital, Davangere, Karnataka, India

Date of Web Publication18-Jul-2019

Correspondence Address:
Prakash Lokhande
Department of Conservative Dentistry and Endodontics, Bapuji Dental College and Hospital, M.C.C B Block, Davangere - 577 004, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jnsbm.JNSBM_8_19

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Aims: The objective of this in vitro study was to compare the microhardness values of coronal dentin adjacent to resin-modified glass-ionomer cement (RMGIC) and compomer. Materials and Methods: Standardized Class V preparation was performed for 30 extracted human permanent molars affected by Class V caries. The samples were divided into three groups as follows: specimens before restoration (Group 1) (n = 10), samples restored using RMGIC (Group 2) (n = 10), and specimens treated with compomer (Group 3) (n = 10). Dentinal discs with 2-mm diameter were obtained after embedment into acrylic resin. Vickers microhardness measurements were performed using a digital microhardness tester (Zwick/Roell) immediately after the 10th, 20th, and 30th day by applying a load of 25 g for 15 s at a distance of 100, 200, and 300 μm from the cavity floor. Statistical Analysis Used: One-way analysis of variance and post hoc Tukey tests (P < 0.05) were conducted for all groups of specimens. Results: Group II demonstrated higher microhardness values as compared to those obtained for Group I and Group III. Conclusion: The results of the present study showed that the microhardness of the dentin adjacent to RMGIC was higher than that of the dentin adjacent to the compomer.

Keywords: Compomer restoration, remineralization rate, resin-modified glass-ionomer cement, Vickers microhardness

How to cite this article:
Lokhande P, Mangala T M. Microhardness of coronal dentin adjacent to resin-modified glass ionomer and compomer in Class V restorations. J Nat Sc Biol Med 2019;10:127-30

How to cite this URL:
Lokhande P, Mangala T M. Microhardness of coronal dentin adjacent to resin-modified glass ionomer and compomer in Class V restorations. J Nat Sc Biol Med [serial online] 2019 [cited 2021 Jul 29];10:127-30. Available from:

   Introduction Top

Microhardness is one of the most important physical properties of dental materials. In particular, microhardness measurements allow the evaluation of the mineral content in the tissue and assessment of possible mineral losses due to the dissolution of their inorganic part (which is typically observed during the caries process) as well as quantification of the density increase caused by the ion incorporation (remineralization) process.[1]

Hardness is the resistance of a material to plastic deformation that is typically measured under an indentation load. Various hardness-testing procedures have been developed, including Barcol, Brinell, Rockwell, Shore, Vickers, and Knoop ones. Among these methods, Brinell and Rockwell macro-hardness tests, as well as Vickers and Knoop microhardness tests (conducted underloads not exceeding 9.8 N), represent the most widely used techniques. The resulting indentations are relatively small, and their depths are <19 μm. Hence, these methods can be used for conducting hardness measurements in small regions of thin objects.[1] Furthermore, the hardness of carious dentin is strongly correlated with its relative infectivity, which can help a dentist to distinguish between the infected (soft) and affected (hard) dentin.[2] Thus, microhardness represents one of the most important physical characteristics utilized in the comparative studies of various dental materials.[3]

Dental caries is an infectious disease which causes local destruction of the tooth hard tissue and is related to diet, microorganism accumulation, and salivary conditions. Due to the ion loss from the tooth to the environment during demineralization, a decrease in the dentin microhardness is usually observed. When the pH of the oral environment reaches a critical value of 5.5, the subsaturation of Ca 2+ and PO43− ions occurs. After its magnitude exceeds 5.5 through the buffering action of the saliva, these ions in the environment become supersaturated. In the latter case, the affected tooth tends to incorporate them through a so-called remineralization process.[4] In addition, high concentrations of fluoride and other ions were detected in the dentin adjacent to glass-ionomer cement (GIC) restorations, which resulted in the hypermineralization of the previously demineralized dentin.[5]

Resin-modified glass-ionomer (RMGI) cements and polyacid-modified resin composites (compomers) are often used to improve the mechanical properties of dental restorations while retaining the esthetics, adhesion, and fluoride-releasing properties of conventional GIC.[6] In this study, RMGI cement is utilized due to its low sensitivity, high fluoride release rate, relatively high strength (as compared to those of traditional glass ionomers), and ability to be cured with light. On the other hand, compomer possess the advantage of both their composite and glass ionomer constituents (including fluoride release).[7]

Enamel, dentin, cementum, and bone are natural composites. With ion exchange, there is variation in apatite properties, magnesium substitute inhibits the crystal growth, carbonate increases solubility, and fluoride exchange decreases the solubility. Demineralization and remineralization are dynamic processes which are dependent on various factors such as saliva flow, pH, oral health, medication, restorative materials, eating, and drinking habits. Saliva, fluoride therapy, and probiotic bacteria can be used to prevent tooth demineralization. Glass ionomer and resin-modified GIC were used to inhibit demineralization and promote remineralization through fluoride. Apart from resin-modified GIC (RMGIC) and glass ionomer, other smart materials have been introduced such as composite-containing Amorphous Calcium Phosphate (ACP) and composite-containing Hydroxy Apatite (HA), but they have not been used wide.[8]

The main purpose of this study is to evaluate the changes in the hardness of dentin adjacent to RMGI and compomer restoration taking the benefit of remineralizing property due to the presence of fluoride.

   Materials and Methods Top

Thirty extracted human mandibular molars affected by Class V caries and free of any abnormalities such as cracks, fracture, and discoloration have been examined in this work. Standardized Class V preparations with occlusocervical widths of 2 mm, mesiodistal widths of 5 mm, and depths of 2 mm (measured with respect to the cavity margins) were prepared using round and straight carbide bur.

The samples were divided into the following three equal groups (n = 10) according to a particular restoration type: Group I contained the specimens without restorations, Group II consisted of the samples restored with RMGIC (Vitremer, 3M ESPE, USA), and Group III contained the specimens restored with a compomer (Dyract flow, Dentsply, India) according to the manufacturer's instructions. After being stored in normal saline for 10 days, the samples were blotted dry and embedded into acrylic resin. Dentinal sections (cross sections) with 2-mm thickness were made at the cavity floors and roofs using a microtome, after which the specimens were ground and polished with an abrasive paper (100 grit). Vickers microhardness (VHN) measurements were performed using a digital microhardness tester (Zwick/Roell) immediately after the 10th, 20th, and 30th day of testing by applying a load of 25 g for 15 s at distances of 100, 200, and 300 μm from the cavity floor. The obtained results were reported in the form of a mean ± standard deviation. The one-way analysis of variance tests were performed for multiple comparisons, whereas the post hoc Tukey tests were conducted for group comparisons using the SPSS software (version. 16, SPSS Inc., Chicago, USA). The data points with P ≤ 0.05 were considered statistically significant.

   Results Top

The VHN values of coronal dentin obtained for Group II at a distance of 100 μm from the cavity floor were significantly higher (P < 0.01) than the magnitude obtained for Group I (P > 0.05) and III (P > 0.05) [Table 1], [Table 2], [Table 3].
Table 1: Vickers microhardness values of coronal dentin obtained for Group I, II, and III after 10, 20, and 30 days of testing at 100 μm from the cavity floor

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Table 2: Vickers microhardness values of coronal dentin obtained for Group I, II, and III after 10, 20, and 30 days of testing at 200 μm from the cavity floor

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Table 3: Vickers microhardness values of coronal dentin obtained for Group I, II, and III after 10, 20, and 30 days of testing at 300 μm from the cavity floor

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The VHN for Group 1 and 3 with respect to depth and days, there was no statistically change in hardness value [Table 1], [Table 2], [Table 3].

   Discussion Top

There is no specific standardized condition for dentin microhardness testing; therefore, it mainly depends on the researcher. Microhardness test is used to check the hardness of the material, which evaluate the loss or gain of minerals from the dentin substrate.[9],[10]

In previous studies, the teeth used for hardness measurements were either fixed or stored in physiologic saline solution, deionized water, phosphate buffer saline, or distilled water since no dehydration of the tested specimens occurred after sectioning.[11]

The microhardness values of the prepared samples were measured immediately after the 10th, 20th, and 30th day because of the relatively high rate of fluoride release within 6–12 weeks observed for glass ionomer-based restorations. The measurements were conducted at distances of 100, 200, and 300 μm from the cavity floor, owing to the ion exchange between the restoration and the tooth structure and remineralization of the adjacent teeth.[12]

Vickers tests are preferable techniques used by the majority of researchers in this area.[13] The corresponding VHN measurements were conducted using a Zwick/Roell digital microhardness tester by applying a load of 25 g through an indenter at a dwell time of 15 s.[14]

The importance of using RMGIC is mainly because of its low sensitivity to water dehydration, rapid setting, relatively high strength, good esthetics, and bonding as compared to conventional GIC.[15],[16],[17],[18],[19]

Compomer was used in this study because of its structure and physical properties similar to composite, fluoride release, bonding to dentin, good marginal adaptation, higher compressive, and flexural strength.[19],[20],[21]

Group I demonstrated no significant changes in VHN after 30 days of testing regardless of the distance from the cavity floor that is from 100, 200, and 300 μm [Table 1], [Table 2], [Table 3]. This may be due to the loss of mineral content through carious process, and mineral content is directly proportional to microhardness. The peripheral dentin has lower microhardness values as compared to that of coronal dentin and the lowest near pulpal dentin.[22],[23]

The results obtained for Group II show that its VHN values increase after 30 days of testing [Table 1], [Table 2], [Table 3]. Fluoride interferes with the carious process reducing demineralization and enhancing remineralization of the enamel and dentin. There is an increase in microhardness value after 30th day this is because the amount of fluoride release gradually increases over 6 weeks. The microhardness value at 100, 200, and 300 μm was almost same. This might be due to effect of remineralization effect more at 1 mm from the application site and it extends up to 3 mm. Increase in mineral content may be due to the presence of fluoride which forms fluorhydroxyapatite, presence of enzyme alkaline phosphatase in dentin which, in turn, yields in formation of calcium hydroxyapatite, and also due to leached out ions from GIC restoration such as calcium and strontium.[24],[25],[26],[27]

The data obtained for Group III exhibited no significant changes in VHN values measured at the 10th, 20th, and 30th day of testing and at all distances from the cavity floor that is 100, 200, and 300 μm [Table 1], [Table 2], [Table 3]. While their magnitudes were significantly lower than those determined for Group II. In addition, the rate of fluoride release from the compomer gradually decreased with time [15] and was systematically lower than the rates obtained for RMGI cement and GIC.[6],[17],[20]

   Conclusion Top

The results obtained in this study revealed that the microhardness of the dentin adjacent to RMGI cement was larger than those of the dentin adjacent to the compomer and control group (which consisted of the specimens without restorations). Hence, it can be concluded that the use of biomaterials with improved mechanical properties (such as flexural strength) and greater fluoride release rate enhances the structure and microhardness of dentin.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Table 1], [Table 2], [Table 3]


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