Evaluation of sorption/solubility, softening, flexural strength and elastic modulus of experimental resin blends with chlorhexidine

Abstract

Objectives

To evaluate physical-chemical properties of experimental diacetate chlorhexidine (CHX)-added resin blends.

Methods

Blends were formulated: G1)TEGDMA; G2)TEGDMA/0.1%CHX; G3)TEGDMA/0.2%CHX; G4)TEGDMA/UDMA; G5)TEGDMA/UDMA/0.1%CHX; G6)TEGDMA/UDMA/0.2%CHX; G7)TEGDMA/BisEMA, G8)TEGDMA/BisEMA/0.1%CHX; G9)TEGDMA/BisEMA/0.2%CHX. Icon ® was the control group. For sorption/solubility (SS), cylindrical specimens (n = 5) were prepared and their weight obtained. The specimens were immersed in deionized water for 7 days at 37 °C and their weight was verified again. SS were calculated using accepted formulas. For softening, cylindrical specimens (n = 10) were prepared and initial Knoop hardness number (KHN) obtained. The specimens were immersed in absolute ethanol for 24 h at 37 °C and final KHN accomplished. Softening values were calculated by KHN reduction percentage. For elastic modulus (EM) and flexural strength (FS) bar specimens were prepared (n = 10) and values obtained with a universal device (three point, 5 mm distance, 0.5 mm/min, load of 50 N). The data was analyzed using one-way ANOVA and Tukey test (α = 5%).

Results

TEGDMA/BisEMA blends and Icon ® showed the lowest sorption from blends (p > 0.05), and Icon ® was the most soluble material (p < 0.01). TEGDMA/UDMA/0.1%CHX showed the highest softening, similar to Icon ® (p > 0.05). For EM, all blends were different than Icon ® (p < 0.01). For FS, TEGDMA blends were similar to Icon ® , showing the lowest averages (p > 0.05).

Conclusions

Monomers chemical characteristics influenced the physical-chemical properties of experimental blends more than CHX. Between the blends tested, UDMA blends presented satisfactory results for assays evaluated.

Clinical significance

Infiltrants CHX-added could arrest and reinforce initial caries lesions, and the antimicrobial effect could prevent new lesions in sound enamel adjacent to the infiltrated area.

Introduction

The main objective of minimal invasive dentistry is to preserve the dental structure with less invasive caries management strategies . Previously studies showed the possibility to infiltrate initial caries lesions with low viscosity materials . The principle of sealing white spot lesions with an unfilled resin was reported as a potential effectiveness method for minimal intervention . Therefore, the infiltrants are a class of dental materials developed to arrest the progression of initial caries lesion and to reinforce mechanically the fragile demineralized enamel . Actually, a TEGDMA (triethylene glycol dimethacrylate) based-material (Icon ® , DMG, Hamburg, Germany) is a resin material available commercially with infiltrant functions. This material was developed from studies with experimental resin blends containing different concentrations of monomers as TEGDMA and BisGMA (bisphenol A diglycidyl methacrylate) with different concentrations of ethanol, and blends containing high amount of TEGDMA with ethanol had high coefficient degrees . Nevertheless, high coefficient of penetration in natural lesions was obtained with solvent-free TEGDMA blends .

The Icon ® effectiveness to penetrate initial caries lesions was evaluated in in vitro studies and clinical trials studies reported it capacity to arrest lesion progression . Studies showed satisfactory esthetic results with Icon ® masking white spots in enamel , the infiltrant also have been studied for controlling enamel erosion progression . Nevertheless, a clinical trial study with 3 years of follow up, comparing the effectiveness of proximal caries infiltration with Icon ® and with a nanofiller fluoride-releasing adhesive system, showed that both materials had similar performance and the infiltration technique was better than the control group, which received only oral health instructions .

Recently, experimental low viscosity monomer blends with infiltrants characteristics containing TEGDMA, UDMA (urethane dimethacrylate) and BisEMA (bisphenol A ethoxylate dimethacrylate) using diluents as ethanol or HEMA (2-hydroxyethyl methacrylate) have been tested in in vitro studies . Concerning physical and mechanical properties, such as degree of conversion, elastic modulus, Knoop hardness and softening ratio, these experimental infiltrants were similar or better when compared to an infiltrant commercially available . These formulations proposed for infiltrant materials seem promising and the addition of an antimicrobial agent could improve their clinical performance decreasing biofilm growth over surfaces and, consequently, avoiding harmful deteriorations.

The advantages of adding antimicrobial agents into resin materials, as composites and dentin bonding systems, to avoid biofilm formation around the restoration had been already discussed in a review , and the use of chlorhexidine (CHX) could be an option. The addition of CHX in dental resin materials was reported in studies that showed the possibility to incorporate 1% CHX into resin materials without considerable changes in their physical-mechanical properties, such as degree of conversion, elastic modulus and bond strength . However, in a humid environment, when the CHX is entrapped in the resin bulk after polymerization, some of the antimicrobial and unpolymerized particles could extrude from the polymer matrix, which could influence the mechanical and physical properties of the material .

The mechanical properties of resin materials could be altered by hydrolysis, and the quality of polymerization could be related to the chemical characteristics of the monomers. The resin materials properties are influenced by water present in oral environment . The monomers as UDMA, TEGDMA and BisEMA have carbon and oxygen or nitrogen in their structures, with hydrolytic susceptible groups, such as ester, urethane, ether linkages, as well as hydroxyl groups . The phenomenon of sorption and solubility may serve as precursors to a variety of chemical and physical processes that include volumetric (such as swelling), physical (such as plasticization), softening and chemical (such as oxidation and hydrolysis) changes . The experimental materials with infiltrants characteristics, as well as other restorative resin dental materials, could be exposed to a wet environment suffering changes. Sorption and solubility properties are important to evaluate the hydrolytic degradation of resin materials. The resistance of water degradation could be associated to the chemical characteristics of the polymers, including quality of cross-link density into bulk matrix and softening ratio .

Therefore, the aim of this study was to evaluate the physical-chemical properties (sorption/solubility, softening and elastic properties) of experimental resin blends with CHX. The first hypothesis tested was that physical-chemical properties could be influenced by different composition of experimental blends and the second hypothesis was that different concentration of CHX would not interfere in the properties evaluated.

Material and methods

Formulation of low viscosity monomers blends

Experimental resin blends were made using the composition shown in Tables 1 and 2 . The monomer TEGDMA was used as a main component for all resin blends. The monomers UDMA or BisEMA were used in some blends in a proportion of 1:4 (wt/wt) ( Table 1 ). The photoinitiator system used in the blends was 1.0 wt% of DMAEMA (2-dimethylaminoethyl methacrylate) and 0.5 wt% of CQ (camphorquinone). The inhibitor BHT (butylated hydroxytoluene) was used in a proportion of 0.1 wt%. Two different concentrations (0.1 wt% and 0.2 wt%) of CHX were tested ( Table 1 ). All chemical components were weight individually at an analytical balance (Mark 210A, BEL Engineering, Piracicaba, SP, Brazil) and the blends were prepared at room temperature in a dark environment. Experimental infiltrants were mixed with a spatula in a beaker. In order to prevent premature polymerization, the resins were stored in the dark and opaque recipients, protected from light, at 4 °C until use. The infiltrant Icon ® (DMG − Hamburg, Germany, Batch 666352), was used as commercial control group.

Table 1
Composition of low viscosity monomer blends with infiltrant characteristics.
Experimental blends Composition
G1 TEGDMA (100 wt.%)
G2 TEGDMA (99.9 wt.%), CHX 0.1 wt.%
G3 TEGDMA (99.8 wt.%), CHX 0.2 wt.%
G4 TEGDMA (75 wt.%), UDMA (25 wt.%)
G5 TEGDMA (74.9 wt.%), UDMA (25 wt.%), CHX 0.1 wt.%
G6 TEGDMA (74.8 wt.%), UDMA (25 wt.%), CHX 0.2 wt.%
G7 TEGDMA (75 wt.%), BisEMA (25 wt.%)
G8 TEGDMA (74.9 wt.%), BisEMA (25 wt.%), CHX 0.1 wt.%
G9 TEGDMA (74.8 wt.%), BisEMA (25 wt.%), CHX 0.2 wt.%
Icon ® TEGDMA, initiators and stabilizers

Table 2
Monomers and photoinitiators used for formulations of resin blends.
Chemical Component CAS Number Molecular Weight g/mol Molecular Formula Manufacturer Batch
TEGDMA 109−16-0 286.32 C 14 H 22 O 6 Sigma-Aldrich, St. Louis, MO, USA 36296HK
UDMA 72869−86-4 470.56 C 23 H 38 N 2 O 8 Sigma-Aldrich, St. Louis, MO, USA MKBD1130
BisEMA 41637−38-1 376.4 C 21 H 28 O 6 Sigma-Aldrich, St. Louis, MO, USA 03514HF
CQ 10373−78-1 166.22 C 10 H 14 O 2 Sigma-Aldrich, St. Louis, MO, USA 083K0014
BHT 128−37-0 220.35 C 15 H 24 O Sigma-Aldrich, St. Louis, MO, USA 04416KD
DMAEMA 2867−47-2 157.21 C 8 H 15 NO 2 Sigma-Aldrich, St. Louis, MO, USA 1437599
CHX 56-95−1 625.55 C 22 H 30 Cl 2 N 10 .2C 2 H 4 O 2 Sigma-Aldrich, St. Louis, MO, USA 083K0014

Sorption and solubility test

Sorption and solubility evaluation were performed according to ISO 4049 , except for specimens dimensions. Five resin disks (n = 5) were made for each material using a polyvinyl siloxane mold (Express XT, 3 M ESPE, St. Paul, MN, US) with 7 mm of diameter and 1 mm of thick. The diameter was used with intention to promote homogeneous polymerization, covering all specimen surfaces with active tip of photocuring device. The mold was completely filled with the blend. After this, a polyester strip was placed over and covered with a glass slide until light curing in order to obtain a smooth and standard flat surface. Each disk was light cured for 60 s with LED VALO device (Ultradent, South Jordan, UT, USA) with power density of approximately 1000 mW/cm 2 . Immediately after polymerization, the disks were stored, individually, in closed Eppendorfs at 37 °C in dry conditions for 24 h. After this period, the Eppendorfs containing the disks were opened and placed in a desiccator containing silica gel in a vacuum environment at 37 °C for 22 h. After this period, the silica gel was changed and the set was kept at 37 °C for more 2 h. When the 24 h of storage at desiccator were completed, each disk was weighed in an analytical balance (Tel Marke, Bel Quimi, São Paulo, SP, Brazil) with an accuracy of 0.001 g. This cycle of drying in silica and weighing in a balance was repeated until a constant mass (M1) of each disk was obtained. For this, the mass of each disk should not have a variation greater than 0.001 g at interval of 24 h period. In this study, after 4 days of consequently weighing, the M1 of disks was established.

Immediately after M1 establishment, the measurements of two diameters of disks were taken using a digital caliper (0.01–150 mm, Product Code 500-144B, Mitutoyo, Tokyo, Japan) with an accuracy of 0.01 mm. The same procedure was done to record thickness values. The mean value of diameter and thickness were obtained to calculate the volume of the cylinder (V), in cubic millimeters (mm 3 ). Then, the disks were immersed, individually, in falcon tubes with 4.66 mL of deionized water at 37 °C for 7 days. The final water volume was calculated taking the proportion suggested by ISO: 10 mL of water for each disk with 15 mm of diameter and 1 mm of depth.

After 7 days, the disks were removed from the water and dried in absorbent paper for 15 s. One minute after removal from the water, each disk was weighed only one time in an analytical balance to obtain the M2 mass. After this, the disks were placed again in a vacuum desiccator with silica gel, and the same cycle already described was done until they kept a constant mass M3. For this study, 5 days of weighing were necessary to obtained the values of M3. The values (in μg/mm 3 ) of water sorption (W sp ) and solubility (W sl ) were calculated using the following equation: W sp = (M 2 M 3 )/V and W sl = (M 1 M 3 )/V .

Softening test

For this test, disks (n = 10) with 5 mm diameter and 1 mm thick were made for each experimental resin blends and the commercial control group ( Table 1 ). A cylindrical mold of polyvinyl siloxane (Express XT, 3 M ESPE, St. Paul, MN, US) was used to make the disks and the procedure of polymerization followed the same requirements used with sorption/solubility disks. After polymerization, the disks were kept in dry environment at 37 °C for 24 h.

The initial Knoop hardness number (KHN1) was taken on superficial surface by five indentations for each disk. Measurements were obtained with the indenter Future-Tech FM-100 (Future-Tech Corp., Kawasaki-City, Japan) automatic procedure with a load of 10 gF applied for 5 s, using 10× magnification lens. The average of five indentations was considered for statistical analysis. After KHN1, the disks were immersed, individually, in 1 mL of absolute ethanol for 24 h at 37 °C. After this period, the final Knoop hardness number (KHN2) was measured following the same procedure previously described. The softening was determined (in percentage) following equation : Softening = 100 − [(KHN2/KHN1) × 100] .

Flexural strength and elastic modulus tests

For these tests, bars specimens (7 mm × 2 mm × 1 mm) of each resin material (n = 10) were prepared using a polyvinyl siloxane mold (Express XT, 3 M ESPE, St. Paul, MN, US). The light curing process followed the same requirements already described. After this, the specimens were kept in a 100% humidity environment at 37 °C for 24 h. The elastic modulus, in GPa, and flexural strength, in MPa, were performed using an universal testing device (Instron 4111, Instron Corp., Dayton, OH, USA) in a three point bending design with a crosshead speed of 0.5 mm/min and a cell load of 50 N until fracture. The distance between supports was 5 mm. The software Bluehill 2 (Illinois Tool Works, Inc., Glenview, IL, USA) was used to calculate the values of the tests.

Statistical analysis

The data of sorption/solubility, softening and flexural strength/elastic modulus were analyzed with the Lilliefors test for the normality distribution. After this, one-way ANOVA and Tukey tests were used to compare the groups at 5% level of significance. The statistical program used was Bioestat 5.3 (Mamirauá Institue, Tefé, AM, Brazil).

Material and methods

Formulation of low viscosity monomers blends

Experimental resin blends were made using the composition shown in Tables 1 and 2 . The monomer TEGDMA was used as a main component for all resin blends. The monomers UDMA or BisEMA were used in some blends in a proportion of 1:4 (wt/wt) ( Table 1 ). The photoinitiator system used in the blends was 1.0 wt% of DMAEMA (2-dimethylaminoethyl methacrylate) and 0.5 wt% of CQ (camphorquinone). The inhibitor BHT (butylated hydroxytoluene) was used in a proportion of 0.1 wt%. Two different concentrations (0.1 wt% and 0.2 wt%) of CHX were tested ( Table 1 ). All chemical components were weight individually at an analytical balance (Mark 210A, BEL Engineering, Piracicaba, SP, Brazil) and the blends were prepared at room temperature in a dark environment. Experimental infiltrants were mixed with a spatula in a beaker. In order to prevent premature polymerization, the resins were stored in the dark and opaque recipients, protected from light, at 4 °C until use. The infiltrant Icon ® (DMG − Hamburg, Germany, Batch 666352), was used as commercial control group.

Table 1
Composition of low viscosity monomer blends with infiltrant characteristics.
Experimental blends Composition
G1 TEGDMA (100 wt.%)
G2 TEGDMA (99.9 wt.%), CHX 0.1 wt.%
G3 TEGDMA (99.8 wt.%), CHX 0.2 wt.%
G4 TEGDMA (75 wt.%), UDMA (25 wt.%)
G5 TEGDMA (74.9 wt.%), UDMA (25 wt.%), CHX 0.1 wt.%
G6 TEGDMA (74.8 wt.%), UDMA (25 wt.%), CHX 0.2 wt.%
G7 TEGDMA (75 wt.%), BisEMA (25 wt.%)
G8 TEGDMA (74.9 wt.%), BisEMA (25 wt.%), CHX 0.1 wt.%
G9 TEGDMA (74.8 wt.%), BisEMA (25 wt.%), CHX 0.2 wt.%
Icon ® TEGDMA, initiators and stabilizers
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Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Evaluation of sorption/solubility, softening, flexural strength and elastic modulus of experimental resin blends with chlorhexidine
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