Journal of investigative and clinical dentistry 2010
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    Journal of investigative and clinical dentistry 2010 Journal of investigative and clinical dentistry 2010 Document Transcript

    • Journal of Investigative and Clinical Dentistry (2010), 1, 151–155ORIGINAL ARTICLEDental BiomaterialsInfluence of extended light exposure time on the degreeof conversion and plasticization of materials used as pitand fissure sealantsBoniek Castillo Dutra Borges1, Eduardo Jose Souza-Junior1, Anderson Catelan1, ´ ´Jose Roberto Lovadino1, Paulo Henrique dos Santos2, Luıs Alexandre Maffei Sartini Paulillo1 ´ ´& Flavio Henrique Baggio Aguiar1 ´1 Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil2 Department of Dental Materials and Prosthodontics, Aracatuba School of Dentistry, Aracatuba, Brazil ¸ ¸Keywords Abstractflowable composite, hardness test, in vitro, Aim: To evaluate the conversion and plasticization of fissure sealer materials,light-emitting diode, pit and fissure sealant. as influenced by extended curing time.Correspondence Methods: Twenty specimens (n = 5) of a pit and fissure sealant and a flowableDr Boniek Castillo Dutra Borges, composite at two curing times (20 and 60 sec) were photocured with the Blue-Rua Minas Novas, 390, cs 18, Natal, phase 16i light-emitting diode. The conversion was determined by FourierRN CEP 59088-725, Brazil. transform infrared/attenuated total reflection spectroscopy 24 h after polymeri-Tel: +55-84-3207-2981 zation. Hardness was measured, and samples were stored in absolute ethanolFax: +55-84-3207-2981 for 24 h. A second hardness measurement was executed after storage to assessEmail: plasticization by the percentage of hardness decrease. Data were analyzed byReceived 5 March 2010; accepted 5 June analysis of variance and Pearson’s correlation (a = 0.05).2010. Results: The pit and fissure sealant showed lower degree of conversion than the flowable composite. The 60-sec curing time increased the conversion onlydoi: 10.1111/j.2041-1626.2010.00015.x for the flowable composite. Plasticization was lower for the flowable composite than for the pit and fissure sealant. The 60-sec light exposure time showed a similar percentage of hardness decrease of 20 sec. A low correlation between the conversion and plasticization was found. Conclusion: Extended curing time improved the conversion only for the flow- able composite. The pit and fissure sealant presented lower conversion and higher plasticization than the flowable composite. it has been shown that enamel sealing on dentin non-Introduction cavitated occlusal lesions could arrest their progression,Recently, minimally invasive dentistry approaches have since the sealant is attached to the pits and fissures.5been raised in scientific and clinical dentistry worldwide.1 These points instigate the investigation of factors thatIn this sense, pit and fissure sealants are recognized as an might contribute to prolonging the period of contact ofeffective method in preventing caries initiation and sealants with occlusal pits and fissures.arresting caries progression, providing a physical barrier Light-activated, resin-based materials, such sealants andthat inhibits microorganisms and food particles from flowable composites, can be used as pit and fissure seal-collecting in pits and fissures.2 ants.6 Because the physical properties of restorative mate- However, the efficacy of sealants is directly related to rials influence their mechanical behavior under clinicaltheir long-term retention.3 The loss of sealants is associ- loading conditions, the physical strength of resin-basedated with subsequent caries development.4 Moreover, dental materials is important for maximizing their clinicalª 2010 Blackwell Publishing Asia Pty Ltd 151
    • Physical properties of sealing materials B.C.D. Borges et al.performance.7,8 Therefore, better physical properties of clinical longevity could be increased. The present studythese materials can increase their retentive performance tested the hypothesis that extended light exposure wouldafter curing. increase the DC and decrease the plasticization of materi- The degree of conversion (DC) is one of the most als used as pit and fissure sealants.investigated physical properties of resinous materials indentistry, since it has been shown that an insufficient Materials and methodsDC of resin composites can facilitate the proliferation ofcariogenic bacterial species,9 and it has also been associ- Experimental designated with the increased solubility of these materials.10 It The factors under study were materials at two levelsis rational to assume that increased light exposure time (a pit and fissure sealant and a flowable composite) andcan improve the DC of composite resins.11 Subse- curing time at two levels (20 sec, following manufac-quently, an increased DC of resinous pit and fissure turer’s instructions; 60 sec, extended exposure time). Thesealants is expected by extending the light exposure DC and plasticization after ethanol storage were used totime, although the literature is scarce in studies that characterize the effect of extended light exposure time onhave tested this. the polymeric network of both materials tested. The However, the DC is not sufficient for characterizing the materials’ composition, batch numbers, and radiance3-D structure of resin-based materials, since polymers (mW/cm2) of the light-curing unit used in the studywith the same DC might present differences in the linear- are shown in Table 1.ity of the chains generated after light curing.12 Insufficientcross-linking of the polymer matrix might make resin- Specimen preparationbased materials more sensitive to the plasticizing effect ofexogenous substances that contain a variety of chemicals, Square-shaped silicone matrices (4 mm2 · 1 mm height)for example, acids, bases, salts, alcohols, and oxygen, that were used to fabricate 40 sealant specimens (n = 5). Seal-enter the oral environment during eating and drinking,13 ing materials were injected into the center of the matrixand might have a degradative effect on the polymer net- using the disposable tip supplied by the manufacturework and compromise its clinical efficacy. under controlled temperature and relative humidity con- Thus, it is important to investigate whether or not ditions. Material surfaces were covered with a Mylar stripextended exposure time can improve physical properties, and then photoactivated for 20 or 60 sec with the light-such the DC, and decrease plasticization of resin-based emitting diode (LED) Bluephase 16i unit (Vivandent,materials used as pit and fissure sealants, since their ¨ Burs, Austria) under a 3-mm distance.Table 1. Composition and batch number of the sealants, and radiance (R) (mW/cm2) of the light-curing unit used in the study CommercialMaterial name (manufacturer) Shade Batch CompositionPit and fissure sealants Fluroshield (Dentsply, Opaque white 142812B Urethane-modified Bis-GMA ´ Niteroi, RJ, Brazil) (<40%); resins (<10%), PENTA phosphate (<5%), Bis-GMA (<5%); glass filler (<30%), silica amorphous (<2%); TiO2 (<3%), NaF (<5%)Flowable composites Permaflo (Ultradent Products, A2 182017B Bis-GMA (8.5%), South Jordan, UT, USA) TEGDMA (20%), sodium monofluorophosphate (0.3%), zirconium filler (68%)Light-curing unit Manufacturer R at 3-mm distance R, as informed by the manufacturerBluephase 16i Vivandent, Burs, Austria ¨ 990 1400Bis-GMA, bisphenol A-glycidyl methacrylate; PENTA, dipentaerythritol pentaacrylate monophosphate; TEGDMA, triethylene glycol dimethacrylate.R was measured with a curing radiometer (model 100; Demetron Research, Danbury, CT, USA); 3-mm distances were established through adigital caliper coupled to a metallic support.152 ª 2010 Blackwell Publishing Asia Pty Ltd
    • B.C.D. Borges et al. Physical properties of sealing materials under study on the DC and plasticization. The level ofDC analysis correlation between the DC and plasticization was studiedAfter polymerization, the specimens were removed from using Pearson’s correlation test. All statistical proce-the matrices and stored dry in light-proof containers at dures were performed by Assistat 7.5 Beta software37°C for 24 h. The DC measurements were recorded in (Federal University of Campina Grande, Campinaabsorbance mode with a Fourier transform infrared ´ Grande, Paraıba, Brazil).(FTIR) spectrometer (Spectrum 100 FTIR, PerkinElmer, ˜Sao Paulo, Brazil), coupled to a zinc selenide multiple Results(six) reflection, attenuated total reflection accessory, witha refraction index of 2.4 at 1000 cm)1 (PerkinElmer), DCoperating under the following conditions: 650–4000 cm)1 There were statistically significant differences betweenwavelength, 4 cm)1 resolution, and 32 scans. The percent- light-curing times (P = 0.007) and materials (P < 0.001).age of unreacted carbon–carbon double bonds (C = C) The flowable composite had a higher DC than the pitwas determined from the ratio of absorbance intensities and fissure sealant at 20 sec (P = 0.02) and at 60 secof aliphatic C = C (peak at 1638 cm)1) against the inter- (P < 0.001). Extended light-curing exposure time (60 sec)nal standard (aromatic C–C, peak at 1608 cm)1) provided a higher DC for the flowable compositebefore and after curing the specimen. The DC was deter- (P < 0.001) (Table 2).mined by subtracting the percentage of the C = C from100%. Plasticization There were statistically significant differences betweenPlasticization analysis materials (P < 0.001). The pit and fissure sealant andIn the plasticization analysis, the percentage of hardness flowable composite had a similar %HD after ethanol stor-decrease (%HD) after ethanol storage was considered.12 age at all curing times tested (P > 0.05). However, atAfter the DC measurement, an initial microhardness 60 sec, there was a lower %HD for the flowable compos-(MHi) reading was undertaken on the top surface of each ite (Table 3).specimen using a microhardness tester (HMV-2T E; Shi-madzu, Tokyo, Japan) with a Knoop diamond indenter DC versus plasticization correlationunder a 50-g load for 15 sec. Five Knoop hardness mea-surements were made on the top surface of each speci- There was a low negative correlation between the DC andmen: one at the center, and the other four at a distance %HD (r = 0.65, P = 0.002) (Figure 1).of approximately 200 lm from the central location. Theaverage of the five values was calculated as the Knoop Table 2. Degree of conversion (%) means (standard deviations)hardness number (KHN) value for each specimen. After according to the factors testedthe MHi reading, all of the specimens were immersed inabsolute ethanol (100%) at room temperature for 24 h. Curing timeFollowing this period, a second microhardness reading Material 20 sec 60 sec(MHf) was conducted. Five Knoop measurements weremade on the top surface of each specimen as previously Fluroshield 65, 20 (2, 55) Ab 67, 33 (1, 08) Ab Permaflo 70, 62 (0, 98) Aa 74, 04 (0, 58) Badescribed. The MHi and MHf analyses were done bythe same operator. The results were tabulated, and the Uppercase letters in the rows and lowercase letters in the columns%HD was calculated using the following equation: indicate statistically significant differences (P < 0.05).%HD = 100 ) ([MHf · 100]/MHi]), where MHf repre-sents the final KHN value (after absolute ethanol storage), Table 3. Percentage of hardness decrease means (standard deviations)and MHi represents the initial KHN value (before abso- according to the factors testedlute ethanol storage). Curing timeStatistical analysis Material 20 sec 60 secThe data explanatory analysis indicated that the data met Fluroshield 52, 31 (1, 89) Aa 54, 82 (2, 97) Aa Permaflo 44, 13 (1, 47) Ab 45, 68 (2, 67) Abthe presuppositions of a parametric test. The two-wayanalysis of variance and Tukey’s test at 5% significance Uppercase letters in the rows and lowercase letters in the columnswere executed to evaluate the effect of two factors indicate statistically significant differences (P < 0.05).ª 2010 Blackwell Publishing Asia Pty Ltd 153
    • Physical properties of sealing materials B.C.D. Borges et al. 70 tion of light energy occurs in opaque sealants in compari- 60 son with clearer materials as a result of opacifying agents present in opaque resin-based ones.14 The polymerization 50 reaction was possibly more attenuated Fluroshield than in 40 Permaflo, decreasing the DC in Fluroshield.% HD It is well known that an extended light exposure time 30 increases heat generation by light sources and the DC in 20 composite resins.18,19 Since only Permaflo had increased 10 DC by a 60-sec curing time, factors other than the heat generated by the LED-curing unit used in the present 0 60 62 64 66 68 70 72 74 76 study might have influenced the DC of the materials. This DC flowable composite might contain higher a concentrationFigure 1. Correlation between degree of conversion (DC) and per- of polymerization initiator in comparison with Fluro-centage of hardness decrease (%HD). r = )0.65; P = 0.02. shield. It was demonstrated that an increased concentra- tion of initiator (camphorquinone) results in greater hardness of experimental composites due to higher mono-Discussion mer conversion.16 Consequently, increased light activationThe clinical success of pit and fissure sealants is well doc- time could prolong the excitation of photoinitiator mole-umented in the literature and is directly related to its cules in Permaflo, resulting in an increased DC.capacity of remaining bonded to occlusal pits and fis- Although a 60-sec curing time increased the DC of Per-sures.3 The hardened material forms a strong micro- maflo, plasticization was not decreased. The cross-linkmechanical bond to etched tooth enamel, thus physically density (CLD) of resinous materials can be indirectlyobliterating susceptible areas of the tooth surface and pre- measured by composite softening on organic solvents,venting dental caries.14 Therefore, the physical properties such as absolute ethanol.12 The low correlation foundof pit and fissure sealants after polymerization have a between the DC versus plasticization in this investigationdirect implication on their long-term clinical success in confirms that polymers with the same DC might presentthe oral cavity and should be investigated. differences in the linearity of the chains generated after In this study, the hypothesis that extended light expo- light curing.12 As 20 and 60 sec resulted in a similarsure would increase the DC and decrease the softening of %HD for Permaflo, one can affirm that the polymericthe pit and fissure sealant and flowable composite was matrix in these groups had a similar CLD.partially accepted. A 60-sec photocure time provided a However, in comparison with Permaflo, Fluroshieldhigher DC only for the flowable composite, while the suffered higher plasticization. It is generally accepted that%HD was maintained in both materials. Since the DC is highly cross-linked polymers are more resistant to degra-a critical element in the physical properties of the resul- dation and solvent uptake, whereas linear polymers pres-tant polymers and their bond to enamel,14 an increased ent more space and pathways for solvent molecules tocuring time can improve the mechanical strength of the diffuse within their structure,13 resulting in increased soft-flowable composite in an oral environment. ening, which can be assessed by a hardness test.20 There- Factors, such as material translucency, filler content, fore, Permaflo presented a higher CLD than Fluroshield.and monomer composition, besides the concentration of In addition, since plasticization occurs in the polymerizeda photoinitiator contained in the resin-based material, resin phase, the fact that Permaflo presents a lowercan influence DC.10,15,16 It was shown that the greater the amount of resinous matrix than Fluroshield can also jus-content of triethylene glycol dimethacrylate (TEGDMA) tify lower plasticization after 24 h of ethanol experimental dimethacrylate-based polymeric matrixes, The results of this study confirm that multiple labora-the greater the conversion of monomers.17 Since Permaflo torial tests are important to correctly characterize thehas a higher TEGDMA content in comparison with effect of curing protocols on a polymeric network ofFluroshield, monomer conversion (DC) was higher for resin-based dental materials. Extended light exposure timeflowable composites. only improved the DC of the flowable composite tested. Moreover, Fluroshield is an opaque shade, and Perma- The pit and fissure sealant used presented a lower DCflo presents different compositions regarding monomer and higher plasticization than that of the flowable com-and filler type and shade. Therefore, differences between posite. The flowable resin composite tested in this studythe DC of these materials are also supported because of and extended light exposure time should be encouragedopacifying agents contained in Fluroshield. It is believed to be used as pit and fissure sealants, since it can reach athat a more substantial reflection, scattering, and absorp- higher DC compared to conventional sealant materials.154 ª 2010 Blackwell Publishing Asia Pty Ltd
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