Effect of Microhardness on Chemical Degradation

Effect of Microhardness on Chemical DegradationAbstractObjective The aim of this study was to judge the effect of chemic degradation media associated with light touch on come on indenture (Ra) and Knoop microhardness (KHN) analyses of incompatible composites. Material and Methods Eighty specimens were prepared for each composite Grandio SO (Voco), Amaris (Voco), Filtek Supreme (3M/ESPE), Filtek LS (3M/ESPE). The specimens were divided into four groups according to the soaking up in chemical degradation media for 7 days artificial saliva (control), heptane, 0.02M citric acid, 70% ethanol. The airfoil of specimens was submitted to 10950 clash cycles (200g load) in an automatic tooth- brushing machine with spotty slurry. ascend roughness and microhardness measurements were obtained at baseline, after immersion in chemical degradation media and after brushing. Data were submitted to three-way repeated measures analysis of variance and Tukeys examine (pResults The KHN style for composites were Grandio (153.535.9)a, Filtek Supreme (87.024.9)b, Amaris (64.524.5)c, LS (69.015.3)c for storage media artificial saliva (97.346.7)a, ethanol (93.349.9)a, citric acid (95.842.1)a, heptane (87.636.7)b and after treatments after chemical degradation (104.849.7)a, baseline (93.842.5)b, after brushing (81.936.5)c. The Ra results for composites were LS (0.150.25)a, Grandio SO (0.190.24)ab, Filtek Supreme (0.200.22)ab, Amaris (0.230.37)b for storage media artificial saliva (0.180.31)a, heptane (0.180.25)a, ethanol (0.200.26)a, citric acid (0.210.28)a and after treatments brushing (0.110.14)a, after chemical degradation (0.230.32)b, baseline (0.240.32)b. Conclusions Brushing after chemical degradation reduced sur memorial tablet roughness values. In general, chemical degradation did not affect composites roughness, but microhardness was signifi standtly reduced. Heptane produced the biggest lessening in composites microhardness.Clinical Relevance The food-simulating s olutions and brushing simulating alter the composites properties, and these alterations are clobber-dependent.Keywords composites, chemical degradation, brushing, Knoop microhardness, surface roughness.IntroductionImprovements on the write up and mechanical properties of rosin-based materials along with increase nice demands draw resulted in the enlarged use of direct composite restorations in anterior and posterior teeth 1,2. These improvements reard more strength and durability to the composite restorations downstairs the conditions of the vocal purlieu. Most of the available composites contain a polymer matrix of dimethacrylate monomers, such as Bis-GMA, UDMA, and TEGDMA (organic chassis), inorganic filler particles (dispersed phase) coated with a methyl methacrylate-functional silane coupling mover to bond the filler to the organic matrix, a photoinitiator system to wholeow photoactivation by light units and early(a) minor additions including polymerization initiato rs, stabilizers and coloring pigments 3-5.However, the critical oral environment conditions (pH changes or humidity) whitethorn increase the composite biodegradation over time 6. Under oral conditions, dental materials may be exposed either intermittently or continuously to chemical agents present in saliva, food and beverages 1. Previous studies have shown that some dietary foods and beverages can cause surface degradation of restorative materials 7-14. Their constituents can soften the organic phase and promotes disintegration of the dispersed phase, altering the surface hardness 1,15.Besides of chemical environment, the toothbrushing is another condition that influences the longevity of composites restorations in vivo. Although toothbrushing plays an burning(prenominal) role in oral hygiene, the effects of abrasion constitutes another important issue on dental materials wear processes, which can result in alterations in surface roughness, loss of contour, staining and plaque ret ention 16.There are several types of composites nowadays, such as nanohybrid, nanofill and microhybrid, which have the similar polymer matrix composition. However, the inorganic phase (size, type and distribution of filler particles) are different. Therefore, the effects of chemical degradation liquids and toothbrushing on surface roughness and microhardness of these types of composites must be reported.Thus, the aim of this study was to evaluate the effects of chemical degradation associated with toothbrushing on surface roughness and microhardness of different composites. The null hypothesis tested was that the immersion in chemical degradation media and brushing are not able to modify the surface roughness and microhardness of the tested materials.Material and MethodsSpecimens preparationEighty cylindrical specimens of each composite were fabricated (shade A3) apply a metallic matrix with 2 mm in height and 3 mm in diameter. A mylar strip was placed over the composite and presse d with a glass plate to provide a flat surface, being re move after curing.The composites were employ in increments of 2 mm and recovered on the top surface using LED photocuring unit (Elipar Freelight 2, 3M/ESPE, St. Paul, MN, USA) at 1200 mW/cm2 power density, activated for 40 s. After curing, they were stored in individual containers with deionized water for 24 h. Then, they were polished using a sequence of 1200, 2400 and 4000 grit aluminum oxide abrasive disks (Extec, Enfield, CT, USA) in a polishing device (DP-10, Panambra, So Paulo, Brazil). After polishing, all the specimens were immersed in deionized water at 37 C for 24 h.Four direct restorative materials were tested, as described in Table 1.Knoop microhardness measurementsThe microhardness measurement was performed with a microhardness tester (FM-700, Future-Tech, Tokyo, Japan), Knoop tip, under 25 g load for 10 s. Three indentations were performed 100 m apart from each other, at the surface of the specimens. The way w ere compulsive as Knoop Hardness Number (KHN).Surface roughness analysisThe mean surface roughness (Ra) was evaluated using a profilometer (MaxSurf XT 20, Mahr, Goettingen, Germany). The diamond stylus moved 2.5 mm long starting the first measurement 0.2 mm from the unkepter area of specimen. Three profile measurements were performed for each specimen at intervals of 0.25 mm and a net average was utilize. The mean Ra values were determined with a cut-off value of 0.8 mm, a transverse length of 0.8 mm, and a stylus speed of 0.1 mm/s.Chemical degradation media immersionThe specimens of each composite were randomly divided according to the food- simulated substances tested (n=20). The solutions tested are mediums recommended by FDA (1976) to be used as food-simulating liquids 17.Heptane P.A. (Synth Labsynth, Diadema, So Paulo, Brazil) was used to simulate butter, fat meals and vegetable oils. Citric acid 0.02M (Synth) simulated beverages, vegetables, fruits and candies. Ethanol 70 % (Zulu Hospitalar 70% Companhia Nacional de lcool, Piracicaba, So Paulo, Brazil) simulated alcoholic beverages and mouthrinses. Artificial saliva was used as control and prepared according to Gohring et al. 18 using 22.1 mmol/l hydrogen carbonate, 16.1 mmol/l of potassium, 14.5 mmol/l sodium, 2.6 mmol/l hydrogen phosphate, 0.8 mmol/l boric acid, 0.7 mmol/l calcium, 0.4 mmol/l thiocyanate and 0.2 mmol/l magnesium.The specimens were kept in individual vials with 2 ml of each solution for 7 days at 37 C. After this period, the specimens were washed thoroughly, and stored in deionized water at 37 C, for 24 h. The microhardness and surface roughness were evaluated.Brushing protocolsSubsequently, the observational units were subjected to brushing abrasion in an automatic toothbrushing (TB) machine (ODEME Biotechnology Joaaba, Santa Catarina, Brazil) which imparted reciprocating motion to 6 soft bristle toothbrush heads (Sanifill Ultraprofissional, Hypermarcas So Paulo, Brazil). This apparatus provides linear brushing movements across the specimens at a speed of 120 cycles per min at 37C, with a double pass of the brush head over the surface. The top surface of resin composites cylinders were submitted to 10950 brushing stokes under a vertical load of 200 g with abrasive slurry, simulating one year of clinical situation 19. The abrasive slurry consisted of fluoridated dentifrice (Colgate Tripla Ao, Colgate-Palmolive, So Paulo, Brazil) and artificial saliva, in a ratio of 13, by weight 20. Toothbrushes were replaced after the completion of each brushing cycles. After brushing, the specimens were kept in deionized water at 37C, for 24 h. At the end of this protocol, the microhardness and surface roughness was obtained.Statistical analysisThis experiment followed a factorial scheme of the 4x3x4 type. The experimental variables under study were composites Grandio, Amaris, Filtek LS, Filtek Supreme, time baseline, after chemical degradation (CD) and after brushing ( TB) and the food-simulating media artificial saliva (AS), heptane (H), citric acid (CA) and ethanol (E). The variable responses were the mean roughness measurement value obtained in profilometer, and the average of three microhardness readings.Data were submitted to statistical analysis using the computer software Statistica for Windows (Statsoft, Tulsa, OK, USA). The inferential statistics consisted of three-way repeated measures ANOVA (composites, time, and chemical degradation media), in which the variable time was considered as a repeated factor, followed by Tukeys test. The level of significance was the conventional value of 5%.ResultsMicrohardness evaluationThe mean KHN values of the composites after chemical degradation media are shown in Figure 1. The application of RM-ANOVA showed significant differences for the factors composites (p=0.0001), time (p=0.0001) and chemical degradation (p=0.0001).Grandio SO composite presented the highest KHN values for all times tested. Amari s and Filtek LS exhibited values significantly lower than Filtek Supreme and Grandio SO (Table 2). For the chemical degradation media factor, the immersion in heptane produced the lowest microhardness manner, compared to the other tested media (Table 3). Regarding the different times, the microhardness (KHN) values significantly increased after immersion in chemical degradation media and decreased after brushing, compared to baseline means (Table 4).Surface roughness analysisThe means of roughness surface (Ra) for the composites are shown in Figure 2. The application of RM-ANOVA showed no significant differences for composite (p=0.034) and time (p=0.626) factors.The roughness means obtained for Amaris composite were significantly higher than Filtek LS. Grandio SO and Supreme exhibited intermediate means (Table 2). For the chemical degradation media, no significant differences were obtained for surface roughness (Table 3). The Ra means after brushing were lower than at baseline and after chemical degradation CD (Table 4).DiscussionThe chemical environment is one aspect of the oral conditions which has an appreciable influence on the in vivo degradation of composites 21. Some chemicals substances from food and drinks can lead to surface degradation of composite restorations, resulting in unaesthetic port and increased surface roughness, accelerating the wear of dental materials 22,23. This degradation is mainly due to the softness of composite matrices with exposure to organic acids and various food and liquid constituents 24,25,12. previously published studies have reported that acidic conditions show a tendency to degrade glass ionomer cements, polyacid modified composite resins, and composite resins 9,26,10,27,11. The present study was performed to check out the Knoop microhardness and surface roughness of four composites, forward and after simulating oral conditions.Hardness is defined as the resistance to permanent indentation or penetration 28,1. It is used to predict the wear resistance of a material and its ability to cause abrasion opposing tooth structure 28. The composites exposed in food-simulating media can suffer chemical softening, reducing their physico-mechanical properties. Changes in the composite hardness usually occur within the first 7 days after exposure to chemical solutions 21. Therefore, this study conducted the initial readings of the hardness in the specimens after post-cure 1, and another reading after the exposure period of immersion.In the present study, specimens stored in heptane showed significantly reduction in microhardness, as also observed previously 14,28. Heptane simulates butter, fatty meals and vegetables oil 14,1 and may damage the resin matrix,12,28 producing cracks in the interface, and consequently, weakening the material.14It is questioned if alcohol-containing beverages may compromise the longevity of composites restorations 29, since it presents the potential of damaging polymers 1,12 , by fully penetrating the resin matrix and promoting the release of unreacted monomers 13. The partial dissolving of the resin matrix may result in the degradation of the filler-matrix interface, thereby impairing the flexural strength and hardness 14. In this study, the concentration of ethanol solution (70%) was used according to previous 28 but it showed no significant effect in the microhardness of composites. The differences in hardness values compared to previous studies could be related to the surface characteristics of the composites, filler distribution and conversion rate 30. Furthermore, the period of 24 h of storage before immersion in ethanol may lead to complete polymerization of the composites, reducing the presence of unreacted monomers on the surface 1,14.The effects of intraoral organic acids, as citric acid, besides producing tooth erosion, can cause surface degradation of composites 9, favoring the breaking of bonds in Bis-GMA molecules of composites 24,11. Desp ite of others studies that citric acid reduced the hardness of composites 7,9, in this study no differences were observed in the microhardness of the composites when immersed in citric acid for 7 days. Nevertheless, the period of storage may have been insufficient to promote differences in the mechanical properties of the specimens surface 7,14.Differences in microhardness means among the composites exposed to the tested solutions were found and are related to their composition and particle limit 14,29. Grandio SO, Filtek Supreme and Amaris have similar matrix composition (Bis-GMA, UDMA, TEGDMA), however, differ in size and amount of filler particles (Table 1). The higher resistance of Bis-GMA to the degradation effects of immersion media can be explained by the fact that bis-acryl resin composite materials contain bifunctional acrylates, which cross-link to provide increased mechanical strength and resistance to weakening in the presence of solvents 28,31.Grandio SO and Filtek Sup reme present nanoscale particles, which provide better mechanical resistance compared to hybrid resins, superior polishing than microfilled resins, higher strength and reduced polymerization shrinkage 32. Due to their nanoscale, these materials showed the highest microhardness values in this study. By the other hand, Filtek LS is constituted of silorane, with quartz and yttrium fluoride as inorganic filler, which increased hydrophobicity and reduced water sorption 33. Differences in microhardness among Filtek LS and others composite could be attributed to the lower filler content (76% w/w), as observed by Yesilyurt et al. 14. Therefore, the differences in composites compositions could have contributed to the differences in hardness.After simulated toothbrushing, there was a reduction in microhardness values. This fact may be due to changes on the surface of the resin matrix when immersed in the solutions before brushing. According to a previous study 2, the immersion in food-simulat ing media increased the exposure of filler particles by softening the matrix. Additionally, toothbrushing can change the surface of composites 2,34,35. In clinical situation, the consumption of food or beverages occurs before brushing habits, reservation this association clinically relevant.Although an increase of the composite surface roughness and degradation after brushing have been previously reported,2 significantly lower roughness means were obtained after brushing in this study. Likewise, previous studies showed that most of composites did not present significant changes by the immersion on chemical degradation media in surface roughness over time 2,9,15.This study found differences on surface roughness of mycrohybid, nanofill and nanohybrid composites, as results of their differences in their compositions. Filtek LS, myycrohybrid composite, had the lowest surface roughness, probably due to low filler content. Filtek Supreme e Grandio SO had an intermediate smoother texture, whereas Amaris showed the roughest surface. Nevertheless, despite of these initial differences, the immersion in chemical solutions did not interfere in the final surface roughness.However, interaction between immersion in food-simulating media and simulated brushing decreased surface roughness, as observed by Turssi et al. 20 This may be attributed to the reaction of the solutions with the polymer matrix. Toothbrushing after the immersion on food-simulating media resulted in the removal of part of the organic matrix around the loosen fillers 2. Then, the softened matrix have become merge with the abrasive slurry, decreasing its abrasive potential 20. Roughness surfaces of composite favors the accumulation of plaque, gingival inflammation, superficial staining and secondary caries.It is noteworthy that the effect of brushing on the composites depends on several factors, such as the type of toothpaste, type and shape of the brush bristles, the proportion of deionized-water solutio n, as well as speed and weight applied during simulation process. As these parameters were standardized for all groups, it can be suggested that the surface roughness varies with the size, hardness and percentage of composite particles, as reported previously 20,36.The different treatments tested resulted in alteration of composite properties, and these alterations were material-dependent thus, the null hypothesis tested was rejected. The present study is important for guiding the improvements of the present composite resins against the challenges they will face during clinical service. It is also relevant to state that esthetics represents only one of the reasons for composite resin restorations failure. Improvements in other areas such as bonding degradation, material deterioration and ability to prevent caries progression/activity should be also considered.ConclusionAccording to the limitations of this study, it can be concluded thatThe microhardness means of the tested composite s were influenced by the materialToothbrushing reduced Ra values of the materials tested, but the solutions used for chemical degradation did not affect the results.Conflict of InterestThe authors declare that they have no conflict of interest.