• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Brandt wc lasers med sci 2012
 

Brandt wc lasers med sci 2012

on

  • 220 views

 

Statistics

Views

Total Views
220
Views on SlideShare
220
Embed Views
0

Actions

Likes
0
Downloads
0
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Brandt wc lasers med sci 2012 Brandt wc lasers med sci 2012 Document Transcript

    • Influence of photoactivation method and mold for restoration on the Knoop hardness of resin composite restorations William Cunha Brandt, Lais Regiane Silva-Concilio, Ana Christina Claro Neves, Eduardo Jose Carvalho de SouzaJunior, et al. Lasers in Medical Science ISSN 0268-8921 Lasers Med Sci DOI 10.1007/s10103-012-1184-2 1 23
    • Your article is protected by copyright and all rights are held exclusively by Springer-Verlag London Ltd. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your work, please use the accepted author’s version for posting to your own website or your institution’s repository. You may further deposit the accepted author’s version on a funder’s repository at a funder’s request, provided it is not made publicly available until 12 months after publication. 1 23
    • Author's personal copy Lasers Med Sci DOI 10.1007/s10103-012-1184-2 ORIGINAL ARTICLE Influence of photoactivation method and mold for restoration on the Knoop hardness of resin composite restorations William Cunha Brandt & Lais Regiane Silva-Concilio & Ana Christina Claro Neves & Eduardo Jose Carvalho de Souza-Junior & Mario Alexandre Coelho Sinhoreti Received: 25 October 2011 / Accepted: 6 August 2012 # Springer-Verlag London Ltd 2012 Abstract The aim of this study was to evaluate in vitro the Knoop hardness in the top and bottom of composite photo activated by different methods when different mold materials were used. Z250 (3M ESPE) and XL2500 halogen unit (3M ESPE) were used. For hardness test, conical restorations were made in extracted bovine incisors (tooth mold) and also metal mold (approximately 2 mm top diameter × 1.5 mm bottom diameter × 2 mm in height). Different photoactivation methods were tested: high-intensity continuous (HIC), low-intensity continuous (LIC), soft-start, or pulse-delay (PD), with constant radiant exposure. Knoop readings were performed on top and bottom restoration surfaces. Data were submitted to two-way ANOVA and Tukey’s test (p00.05). On the top, regardless of the mold used, no significant difference in the Knoop hardness (Knoop hardness number, in kilograms–force per square millimeter) was observed between the photoactivation methods. On the bottom surface, the photoactivation method HIC shows higher means of hardness than LIC when tooth and metal were used. Significant differences of hardness on the top and in the bottom were detected between tooth and metal. The W. C. Brandt (*) Department of Dentistry, Implantology Area, University of Santo Amaro, Rua Prof. Eneas de Siqueira Neto, 340, 04829-300 São Paulo, SP, Brazil e-mail: williamcbrandt@yahoo.com.br L. R. Silva-Concilio : A. C. C. Neves Department of Prosthodontics, Dentistry School, University of Taubate, Rua Expedicionário Ernesto Pereira, 110, 12020-330 Taubate, São Paulo, Brazil E. J. C. de Souza-Junior : M. A. C. Sinhoreti Dental Materials Division, Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas, Piracicaba, Brazil photoactivation method LIC and the material mold can interfere in the hardness values of composite restorations. Keywords Dental materials . Composite resins . Surface properties . Hardness test . Dental restoration Introduction Although light-cured resin composites have become the material of choice in directly restoring anterior and posterior teeth, these materials undergo significant volumetric shrinkage when polymerized [1]. Placement and bonding of composites in preparations induce development of mechanical stress inside the material as well as at the bonded interface [2]. Stress is also transmitted via bonded interfaces to tooth structures [3, 4]. The rapid conversion rate in light-cured composites quickly induces an increase in composite stiffness, causing high shrinkage stresses at the bonded interface [3]. This stress may disrupt bonding between the composite and the preparation walls or even cause cohesive failure of either the restorative material or the surrounding tooth tissue [3–5]. This stress development is the main cause of marginal failure and subsequent leakage in resin composite restorations [6]. In order to attenuate the stress generation during the polymerization process, different solutions have been recommended, such as modified filler particle interfaces, cavity lining with flowable composite, and employment of non-shrinking resins. There is also a possibility to decrease the polymerization reaction rates and consecutive mechanical stress transferred. This is achieved by decreasing an irradiance of a light source or by using different photoactivation protocols, such as low-intensity continuous (LIC), soft-start (SS), and pulsedelay (PD) [1–6]. The main goal of these methods is to increase the time for the composite to flow during the earlier
    • Author's personal copy Lasers Med Sci stages of the polymerization and to enable a certain degree of polymer chain relaxation before reaching the rubbery stage [3, 7]. Indeed, previous investigators have described improved marginal adaptation and increased bond strength [3, 7, 8] in comparison to the standard high-intensity continuous (HIC) method. However, a recent study has reported that the degree of conversion (DC) for these methods might be lower when compared to the conventional method [9]. Studies evaluating different curing strategies generally concentrate on the conversion of double bonds. The DC is an important factor because it determines the final properties of composites and can be analyzed indirectly by the hardness test [10, 11]. Regardless of the method as a composite restoration is activated, this should have appropriate properties. However, these properties should not be evaluated only on the surface of the composite, but in the bottom. Because an inadequate polymerization of the composite in the bottom interfere in the properties of the composite restoration causing it to fail [3]. Moreover, many kinds of mold materials (tooth, metal, and silicone) are used to evaluated the hardness of dental composites in vitro. The use of different molds can cause differences in the spread of light within the composite inserted into the mold, which can cause different results of DC and, consequently, in hardness. Then, the results obtained in these studies can be extrapolated for use on teeth and applied in the clinical dentistry. Therefore, the aim of this study was to investigate in vitro the influence of different light-curing methods and mold material used to evaluated the Knoop hardness on the top and bottom of resin composite. The first hypothesis of this study was that different photoactivation methods could produce the same hardness values when the same radiant exposure is used and the second hypothesis was that the mold could influence the hardness of dental composites. Materials and methods Restorative procedures Forty bovine incisors and 40 metal mold were obtained. After extraction, the bovine incisors were cleaned and stored in 0.5 % chloramine-T solution at 4 °C, for a week. After removal of root portions, buccal faces were wet-ground with 400-, 600-, and 1,200-grit SiC abrasive papers to obtain a Table 1 Description of the photoactivation methods flat surface on the enamel. For both molds to be restored (bovine incisors and metal mold), standardized conical cavities (approximately 2 mm top diameter × 1.5 mm bottom diameter × 2 mm in height) were then prepared, using #3131 diamond burs (KG Sorensen, Barueri, Sao Pãulo, Brazil) at high speed, under air–water cooling. A custom-made preparation device allowed standardization of the cavity dimensions. The burs were replaced after every three preparations. In order to expose the bottom surface of the cavities in the bovine incisors, the lingual faces were ground following the same procedure described for flattening the buccal aspects. The specimens were placed onto a glass slab and the restorative procedures were carried out using the resin composite Filtek Z250 (3M ESPE, St. Paul, MN, USA, shade A2), which was bulk inserted into the cavity from its wider side. Different photoactivation procedures, as described in Table 1, were tested. For each method, ten specimens were prepared. Photoactivation was performed only at the top of the molds. Prior to the curing procedures, the output power of the halogen curing unit XL2500 (3M ESPE, St. Paul, MN, USA) was measured with a calibrated power meter (Ophir Optronics, Danvers, MA, USA) and the diameter of the light guide tip with a digital caliper (Mitutoyo, Tokyo, Japan). Light irradiance (in milliwatts per square centimeter) was computed as the ratio of the output power and the area of the tip. Different curing times were used in order to maintain a total radiant exposure of approximately 18.5 J/cm2 for all samples. Irradiance at high light intensity (935 mW/cm2) was carried out with the light guide tip positioned directly onto the restoration, which had been previously covered with a polyester strip. To produce an output of 150 mW/ cm2, a standard black acrylic cylinder separator was used to allow positioning the light guide tip 1.2 cm away from the restoration surface, and the irradiance was confirmed with the power meter. Irradiance measurements were also performed through of the metal mold or tooth mold with the restoration. The purpose of this measurement was to obtain the amount of light (irradiance, in milliwatts per square centimeter) which could cross the resin composite inserted in the molds used (metal mold or tooth mold) after the restoration. Spectral distributions were obtained by using a calibrated spectrometer (USB2000, Ocean Optics, Dunedin, FL, USA). The irradiance and the spectral distribution data were Photoactivation method Exposure protocol High-intensity continuous (HIC) Low-intensity continuous (LIC) Soft-start (SS) Pulse-delay (PD) 935 150 150 150 mW/cm2 mW/cm2 mW/cm2 mW/cm2 for for for for 20 s 125 s 10 s + 935 mW/cm2 for 18 s 5 s + 3mim without light + 935 mW/cm2 for 18 s
    • Author's personal copy Lasers Med Sci integrated using the Origin 8.0 software (OriginLab Northampton, MA, USA). Spectral distributions measurements were also performed through of the metal mold or tooth mold with the restoration. The purpose of this measurement was to obtain the emission spectrum of light which could cross the resin composite inserted in the mold used (metal mold or tooth mold) after the restoration. Irradiance measures between wavelength 450 and 490 nm were performed to evaluated the amount of light available in the region for better absorption of light by the photoinitiator contained in the composite resin: camphorquinone [12]. All these measures were carried out as HIC photoactivation method. Hardness assessment After light-curing procedures, the specimens were dry-stored at 37 °C for 24 h in light-proof containers. Thereafter, both the top and bottom surfaces were wet-polished with 1,200-grit SiC paper to obtain a planar surface. Knoop hardness measurements were taken on both surfaces using an indenter (HMV-2, Shimadzu, Tokyo, Japan), under a load of 490 N (equivalent to 50 gf) for 15 s. Five readings were performed for each surface. The Knoop hardness number (KHN, in kilogram–force per square millimeter) for each surface was recorded as the average of the five indentations. Data were submitted to two-way ANOVA (photoactivation method vs. mold material) followed by Tukey’s test (p00.05). Results Tables 2 and 3 show the means hardness Knoop on the top and bottom when different photoactivation methods and different mold for restoration were used. For top hardness, irrespective of the light-curing method, no significant differences were detected, both for the mold in tooth and in metal. On the other hand, significant differences were detected between tooth and metal when HIC and LIC were used for the photoactivation. The means of hardness Knoop were higher in the metal that in tooth (p<0.05). In the bottom surface, the photoactivation methods HIC, SS, and PD show higher means of hardness Knoop that LIC when tooth was used. When metal was used, HIC shows higher means of hardness Knoop in the bottom than LIC (p<0.05), and SS and PD show intermediated means without statistical difference. Significant differences were detected between tooth and metal when SS and PD were used for the photoactivation. The means of hardness Knoop were higher in the tooth that in metal (p<0.05). Emission spectra of the light-curing unit (LCU) with and without material mold used in this study are shown in Fig. 1. The irradiance of the halogen curing unit XL2500 (3M ESPE) measured with the calibrated power meter was 935 mW/cm2 with emission peak at 485 nm and irradiance between the wavelength 450 and 490 nm of 521 mW/cm2. After restoration of the molds with composite resin, when the bovine incisors was used as mold (tooth mold), the irradiance of 230 mW/cm2 with emission peak at 488 nm across the tooth mold restored with resin composite. Between the wavelength 450 and 490 nm, only the irradiance of 129 mW/cm2 across the tooth mold restored with resin composite. When metal mold was used, only the irradiance of 110 mW/cm2 with emission peak at 487 nm across the metal mold restored with resin composite, and between the wavelength 450 and 490 nm, only 63 mW/cm2 across the metal mold restored with resin composite. Discussion As one of the main disadvantages of dental composite remains in its polymerization shrinkage [1, 4, 5]. Therefore, techniques that reduce the tension caused by the contraction of polymerization are used. Thus, photoactivation methods such as SS and PD are used for this purpose [3, 7–9]. The most usual light unit used for composite resin polymerization is the conventional halogen light. The halogen bulb consists of a filament, which is heated and which emits white light with unwanted wavelengths being filtered out; a polychromatic spectrum of blue light is therefore produced (covering the area from 400 to 500 nm of the visible spectrum). There are, however, some side effects, such as temperature increase during light-curing [13, 14]. However, doubts about the properties of the polymer formed when these photoactivation methods are used remain [10]. Knoop hardness test is widely used to evaluated the properties of dental composites, especially with regard to the DC [10]. Table 2 Means (standard deviations) for top hardness (KHN, in kilograms–force per square millimeter) High-intensity continuous Tooth Metal Low-intensity continuous 61.0 (5.0) B, a 65.2 (2.7) A, a 57.5 (6.4) B, a 63.9 (4.6) A, a Soft-start Pulse-delay 59.7 (3.6) A, a 61.9 (2.1) A, a 58.5 (1.9) A, a 61.9 (1.4) A, a Means followed by distinct capital letters in the same column, and small letters in the same line, are significantly different at p<0.05
    • Author's personal copy Lasers Med Sci Table 3 Means (standard deviations) for bottom hardness (KHN, in kilograms–force per square millimeter) High-intensity continuous Tooth Metal Low-intensity continuous 58.6 (3.3) A, a 55.9 (3.0) A, a 53.1 (3.3) A, b 51.2 (4.2) A, b Soft-start Pulse-delay 57.3 (3.4) A, a 54.5 (2.3) B, a, b 58.4 (2.8) A, a 52.4 (2.1) B, a, b Means followed by distinct capital letters in the same column, and small letters in the same line, are significantly different at p<0.05 Therefore, in the present investigation, hardness was assessed to estimate DC. The present findings show that, for top hardness, no significant differences were observed among the curing methods. This corroborates with the assumption that similar DC can be obtained by different activation strategies, as long as the total radiant exposure is kept constant [15]. However, when assessing the bottom hardness, LIC yielded significantly lower values when compared to all of the other methods when the mold used was the tooth and also showed lower values compared with HIC when the mold was the metal, which is probably a result of a lower DC. Consequently, the first hypothesis was rejected. The irradiance intensity is a critical factor for the in-depth cure of composites, since the incident light is attenuated with increasing distance from the irradiated surface, as a result of absorption and scattering effects [14, 16]. Indeed, Rueggeberg [17] reported that about only 9 % of the light energy hitting the top surface of the composite is available at 2 mm depth. Therefore, during continuous activation at 150 mW/cm2, an intensity reaching the bottom layer around 15 mW/cm2 might be expected. Also, this low light energy would be distributed along the incident electromagnetic spectrum, between 390 and 520 nm. Therefore, as camphorquinone presents an optimal spectral absorbance range between 450 and 490 nm, with an absorbance peak at 470 nm [17], the energy available between 450 and 490 nm might have been insufficient to excite the photoinitiator to the same level than during activation with higher light intensity, Fig. 1 Emission spectra of the LCU with and without material mold leading to poorer polymerization. Indeed, Watts [16] stated that a minimum threshold of light irradiance reaching a specified depth is required to activate effective polymerization. In this study, only 25 % of the light initially available passed through the restoration when the tooth mold was used. When the metal mold was used, a lower amount of light passed through by restoration, only 12 %. Another factor that might be considered is heat generation during the photoactivation procedures. High light intensities result in a high temperature increase within the composite [9, 18], which can account for greater double bond conversion, even at the bottom layer, due to increased monomer mobility in the environment and also increased reaction rate parameters [18, 19]. Additionally, the light guide tip was positioned distant from the cavity surface for producing 150 mW/cm2, in order to approximate the clinical situation. This could also be related to less heat generation. According to the results of this study, we can say that different materials of mold can interfere in the hardness values. In this study, when the tooth was used as a mold for the composite restorations, it produced restorations with lower hardness on the top and higher hardness values in the bottom compared with the hardness values produced when the metal was used as a mold. Consequently, the second hypothesis was accepted. This probably occurred because the amount of light emitted by the LCU when different molds were used was different on the top and bottom of the restorations, due the difference in the material of the mold. The composite restoration made in the metal mold had higher hardness values on the top because some light inside of the cavity was reflected to the top again. The metal has good ability to reflect light, and with the cavities' conical shape, it was possible, unlike the tooth that has no capacity for reflection as good. This was due to higher capacity for reflection of light by the metal mold. Because of this higher capacity for reflection of light, a larger amount of photons are reflected back to the top surface of the sample and increases the curing. However, the composite restorations had higher hardness values in the bottom when the tooth mold was used. Although the tooth has no reflection of light that was as good as the metal, the tooth allows that some light to pass through it. Thus increasing the availability of light at the bottom of the restoration, as opposed to metal that blocks all light. These values are consistent with the results obtained from
    • Author's personal copy Lasers Med Sci analysis of the LCU, for more light passes through the tooth mold (230 mW/cm2) of the metal mold (110 mW/cm2). In addition, the presence of the restoration and mold affected the emission spectrum of light from the LCU because differences existed in peak light output. These results are more evident when the amount of light available in the region for better absorption of light by the photoinitiator contained in the composite resin (camphorquinone) is compared. Between the wavelength 450 and 490 nm, the irradiance of 129 mW/cm2 across the tooth mold restored with resin composite. When metal mold was used, only 63 mW/cm2 across the metal mold restored with resin composite, decreasing the amount of photons available, especially when the metal mold was used; thus, decreasing the cure, and consequently, the Knoop hardness in the bottom surface of restorations made in the metal mold. Much research in dentistry compare in vitro the properties of photoactivated composites into molds made of different materials, such as metals, teeth, and silicones. Then, the results obtained in these studies are extrapolated for use on teeth. But during the photopolymerization, the light must travel a path within the composite, and consequently, into the mold which is inserted in the composite. As the path traveled by light during the photopolymerization may be different when molds made of different materials are used, results with different properties of the composites can be obtained. Therefore, dentists should be careful in the interpretation of these results before applying them in the clinical dentistry. Conclusion Considering the limitations of this study, the hypotheses were partially accepted: The photoactivation method LIC produced lower Knoop hardness values in the bottom of the resin composite restoration made in the tooth mold and metal mold. Different mold materials for restorations, such as tooth or metal, produced resin composite restorations with differences in the Knoop hardness values. References 1. Feilzer AJ, Dooren LH, de Gee AJ, Davidson CL (1995) Influence of light intensity on polymerization shrinkage and integrity of restoration–cavity interface. Eur J Oral Sci 103:322–326 2. Feilzer AJ, de Gee AJ, Davidson CL (1990) Quantitative determination of stress reduction by flow in composite restorations. Dent Mater 6:167–171 3. Brandt WC, de Moraes RR, Correr-Sobrinho L, Sinhoreti MA, Consani S (2008) Effect of different photo-activation methods on push out force, hardness and cross-link density of resin composite restorations. Dent Mater 24:846–850 4. Blažić L, Pantelić D, Savić-Šević S, Murić B, Belić I, Panić B (2011) Modulated photoactivation of composite restoration: measurement of cuspal movement using holographic interferometry. Lasers Med Sci 26(2):179–186 5. Kinomoto Y, Torii M, Takeshige F, Ebisu S (1999) Comparison of polymerization contraction stress between self- and light-curing composites. J Dent 27:383–389 6. Lutz F, Krejci I, Barbakow F (1991) Quality and durability of marginal adaptation in bonded composite restorations. Dent Mater 7:107–113 7. Alonso RC, Cunha LG, Correr GM, Cunha Brandt W, CorrerSobrinho L, Sinhoreti MA (2006) Relationship between bond strength and marginal and internal adaptation of composite restorations photocured by different methods. Acta Odontol Scand 64:306–313 8. Cunha LG, Alonso RC, Correr GM, Brandt WC, Correr-Sobrinho L, Sinhoreti MA (2008) Effect of different photoactivation methods on the bond strength of composite resin restorations by pushout test. Quintessence Int 39:243–249 9. Lu H, Stansbury JW, Bowman CN (2005) Impact of curing protocol on conversion and shrinkage stress. J Dent Res 84:822–826 10. Ferracane JL (1985) Correlation between hardness and degree conversion during the setting reaction of unfilled dental restorative resins. Dent Mater 1:11–14 11. Brandt WC, Cardoso L, Moraes RR, Correr-Sobrinho L, Sinhoreti MAC (2008) Influence of light-curing units on the flexural strength and flexural modulus of different resin composites. Braz J Oral Sci 7:1555–1558 12. Brandt WC, Schneider LF, Frollini E, Correr-Sobrinho L, Sinhoreti MA (2010) Effect of different photo-initiators and light curing units on degree of conversion of composites. Braz Oral Res 24:263–270 13. Tielemans M, Compere P, Geerts SO, Lamy M, Limme M, De Moor RJ, Delmé KI, Bertrand MF, Rompen E, Nammour S (2009) Comparison of microleakages of photo-cured composites using three different light sources: halogen lamp, LED and argon laser: an in vitro study. Lazers Med Sci 24:1–5 14. Rode KM, de Freitas PM, Lloret PR, Powell LG, Turbino ML (2009) Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser. Lasers Med Sci 24:87–92 15. Halvorson RH, Erickson RL, Davidson CL (2002) Energy dependent polymerization of resin-based composite. Dent Mater 18:463–469 16. Watts DC (2005) Reaction kinetics and mechanics in photopolymerised networks. Dent Mater 21:27–35 17. Rueggeberg F (1999) Contemporary issues in photocuring. Comp Cont Educ Dent Suppl 1999:S4–S15 18. Lovell LG, Newman SM, Donaldson MM, Bowman CN (2003) The effect of light intensity on double bond conversion and flexural strength of a model, unfilled dental resin. Dent Mater 19:458–465 19. Souza-Junior EJ, Prieto LT, Soares GP, Dias CT, Aquiar FH, Paulillo LA (2012) The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements. Lazers Med Sci 27:145–151