Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes

Transcription

1 Journal of Oral Rehabilitation ; 586±591 Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes A. KNEZÏ EVICÂ *, Z. TARLE*, A. MENIGA*, J. SÏ UTALO*, G. PICHLER ² & M. RISTICÂ ³ *Department of Restorative Dentistry, School of Dentistry, University of Zagreb, Croatia, ² The Rudjer Boskovic Institute, Zagreb, Croatia and ³ The Institute of Physic, Zagreb, Croatia SUMMARY To ensure an adequate clinical composite lling light source for photopolymerization is of great importance. In everyday clinical conditions commonly used unit for polymerization of composite material is halogen curing unit. The development of new blue superbright light emitting diodes (LED) of 470 nm wavelengths comes as an alternative to standard halogen curing unit of 450±470 nm wavelengths. The purpose of this study was to compare the degree of conversion (DC) and temperature rise of four hybrid composite materials: Tetric Ceram, Pertac II, Valux Plus and Degu ll Mineral during 40 s illulmination with standard halogen curing unit Heliolux GTE of 600 mw cm )2 intensity, Elipar Highlight soft-start curing unit of 100 mw cm )2 (10 s) and 700 mw cm )2 (30 s) intensity and 16 blue superbright LED of minimal intensity of 12 mw cm )2 on the surface and 1 mm depth. The results revealed only a little bit higher DC values in case of polymerization with even 66 times stronger halogen curing units which showed twice higher temperature than blue diodes. Temperature and DC obtained are higher on the surface than on 1 mm depth regardless on the light source used. KEYWORDS: blue superbright light emitting diodes, degree of conversion, temperature, photopolymer- 1 ization, composite resins, halogen curing units Introduction Recently, manufactures have turned their attention to the light source used to convert composite materials from monomers to polymers. Researches have investigated the relationships among curing-source intensity, exposure duration, thickness characteristics of different types of overlaying material and tip-to-tooth curing distance, with the potential to achieve optimal resin cure (Dlugokinski et al., 1998). By light cured composite resins, light source of adequate intensity and wavelength from 400 to 500 nm activates light sensitive substance camphorquinone with maximum absorption at 468 nm. When this molecule is excited at higher energetic level by absorption of adequate quantum of energy (`triplet state') it is able to react with reducing agents. It will result in formation of free radicals which initiate polymerization 2 process (Yoshida & Greener, 1994; Peutzfeldt, 1997; Geurtsen, 1998). Three essential components are required for adequate polymerization: suf cient radiant intensity, correct wavelength of the visible light and curing time. Other factors such as type of composite resin, shade and translucency, temperature of the composite material (Bennett et al., 1994), thickness of the increment, distance of the light tip from the surface of the material (Rueggeberg & Jordan, 1993), curing time (Murchison & Moore, 1992) and post-irradiation time, also in uence the depth, and therefore adequacy of polymerization (Martin, 1998). The number of double carbon bonds which are converted in single bonds determinate the degree of conversion (DC) of composite resins (Lee & Greener, 1994; Tarle et al., 1995a). The DC depends on the material composition, light source properties, distance from light source and illumination time, and ranges from 43á5 to 73á8% when standard curing unit is used (Chung & Greener, 1990; Tarle et al., 1998b). Volumetric shrinkage and heating are two physical phenomena connected with composite resin polymerization (Sakaguchi et al., 1992a,b). The design of ã 2001 Blackwell Science Ltd 586

2 BLUE LEDS PHOTOPOLYMERIZATION 587 the light guides designed to `concentrate' light energy can produce even more heat than a non-constricted design. This heat has been linked to pulpal health risk. Also, guides designed to `concentrate' the energy may produce more heat without necessarily enhancing of composite cure (Blankenau et al., 1999). A small change in curing light intensity causes a signi cant change in DC within a surface zone of the resin composite. The light output of the curing unit may be reduced by many factors in the clinical situations, like a drop in the line voltage, deterioration of the bulb and lter, contamination of the light tip end, and breakage of photo conductive bres as well as distance and the orientation of the light tip end (Myazaki et al., 1996). Using pulsed laser polymerization, higher DC with lower material shrinkage could be achieved (Tarle et al., 1995a). Its use is not yet clinically acceptable and therefore some experiments with blue superbright light emitting diodes (LED) with wavelength of 470 nm are performed. The aim of this study was to compare the DC and temperature rise of four hybrid composite materials after illumination with two standard halogen curing units and blue superbright LEDs on the surface of the composite materials and 1á0 mm depth. Materials and methods In this investigation polymerization effect of standard curing unit Heliolux GTE* of 600 mw cm )2 intensity, Elipar Highlight ² soft-start curing unit intensity of 100 mw cm )2 ( rst 10 s) and 700 mw cm )2 (30 s) and 16 LEDs ³ with light intensity of 12 mw cm )2 (Fig. 1) was analysed. Light intensity was determined with Curing Radiometar Model 100. Blue diodes were connected with stabilized power supply (K.E.R.T. Mod. AT 5D). The temperature was measured using thermometer HC-3500T multimeter. Composite materials used for determination of the DC are shown in Table 1. Determination of the degree of conversion Composite materials samples are prepared in the same way regardless of the light source used. To simulate composite layer on surface and 1 mm depth, 1 mm thick *Vivadent, Schaan, Liechtenstein. ² ESPE, Seefeld, Germany. 3 ³ Nichia, Tokushima, Japan. Demetron Research Corporation, Danbury, CT, USA. 4 Metex, Pirmasens±Winzeln, Germany. Fig. 1. Blue superbright LEDs. overlays and underlays were used to ensure constant `back-re ection'. Over-and underlays were polymerized in Spectramat PM 1831** for 2 min on each side. Uncured composite material samples were placed between two Mylar sheets and pressed by pressure of 10 7 Pa to the 0á1 mm thickness and light cured for 40 s with light source adapted on the upper sheet. In cases of simulating the composite resin at a depth of 1 mm, the cured overlay of appropriate thickness was placed above the upper Mylar sheet and the bre optic tip pressed onto the overlay and also light cured for 40 s. For each material, ve measurements were made for surface and 1 mm depth. After the separation from Mylar sheets Fourier transform infrared spectrometry (FTIR) spectra of polymerized samples were scanned in the transmission mode using Perkin Elmer Spectrometer Model 2000 ²² in infrared spectrum from 4000 to 400 cm )1. Unpolymerized samples were mixed with pure KBr. The spectra were analysed after the subtracting the background and conversion in the absorption mode. Ratios of absorption maximums were calculated according to the F.A. Rueggeberg's base-line method (Rueggeberg et al., 1990). The DC was calculated from equivalent aliphatic/aromatic ratios of cured (C) and uncured (U) samples according to following formula: % conversion ˆ (1 ± (C/U)) 100% Temperature rise measurement The composite material samples are prepared in the same way as for determination of the DC. Temperature was **Ivoclar/Vivadent, Schaan, Liechtenstein. ²² Perkin Elmer, Beacons led, Bucks, UK.

3 588 A. KNEZÏ EVICÂ et al. Table 1. Composite materials used for determining the DC and temperature rise Composite Manufacturer Shade Batch number Expiration date Abbreviation Tetric Ceram Vivadent (Schaan, Liechtenstein) A /2001 TC-A2 Pertac II ESPE (Seefeld, Germany) A /1998 PII-A2 Valux Plus 3M Dental Products (St Paul, MN, U.S.A.) A /1999 VP-A2 Degu ll Mineral Degussa (Hanau, Germany) A /1999 DM-A2 Table 2. The results of the degree of conversion of composite materials illuminated with halogen curing unit Heliolux GTE, Elipar Highlight and 16 blue diodes Degree of conversion (%, 40 s, 0á1 mm thick samples) Heliolux GTE Elipar Highlight 16 blue diodes Composite Surface 1 mm depth Surface 1 mm depth Surface 1 mm depth TC-A2 61á39 1á07 63á11 2á27 61á00 1á10 61á38 1á88 54á58 0á68 53á80 1á88 PII-A2 70á39 1á73 67á33 3á14 68á34 1á05 68á45 1á08 58á89 1á30 59á00 1á52 VP-A2 54á93 1á33 54á03 1á79 55á86 3á03 55á45 1á08 45á93 2á78 46á01 2á39 DM-A2 66á10 2á03 64á97 0á91 65á37 1á06 65á00 1á61 53á85 2á38 54á86 1á41 measured during 40 s polymerization on room temperature using temperature probe with the peek attached to the surface of composite samples. For each material ve measurements were made for surface and 1 mm depth. Results The values of the DC and temperature rise during 40 s polymerization of composite resins samples are shown in tables and graphs as mean and s.d. of ve repetitive measurements. The mean and s.d. are calculated using ANOVA. The results obtained after curing of composite samples by 16 blue LEDs are compared with the results of polymerization values obtained with halogen curing units Heliolux GTE and Elipar Highlight. The results of the DC are shown in Table 2. The DC was higher for all the materials polymerized by halogen curing unit Heliolux GTE and Elipar Highlight. The highest result was obtained for Pertac II ³³ composite material cured by both halogen curing units (70á39 1á73 on the surface, 67á33 3á14 on the 1 mm depth for Heliolux GTE, 68á34 1á05 on the surface and 68á45 1á08 on the 1 mm depth for Elipar Highlight curing unit) and 16 blue LEDs (58á89 1á30 on the surface and 59á00 1á52 on 1 mm depth). The lowest results showed Valux Plus polymerized by ³³ ESPE, Seefeld, Germany. 3M Dental Products, St Paul, MN, USA. halogen curing unit Heliolux GTE, Elipar Highlight and blue LEDs. Graphical representation of the DC in dependence of the material and curing units is shown on Fig. 2. Also, the results of temperature measurement during curing of composite samples by blue LEDs are compared with the results of temperature rise during polymerization with halogen curing units, Heliolux GTE and Elipar Highlight. The results of temperature measurement are shown in Table 3. The highest rise of temperature occurred during polymerization of composite samples with halogen curing unit Heliolux GTE on surface and 1 mm depth. Signi cantly lower rise of temperature occured in case of illumination with blue LEDs compared with two conventional units. Graphical representation of temperature changes in dependence of the material and light sources is shown in Fig. 3. Discussion Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of composite resin restorative materials. Problems associated with inadequate polymerization include inferior physical properties, solubility in the oral environment, and increased microleakage with resultant recurrent decay and pulpal irritation. As light passes through the composite, it is absorbed and scattered, attenuating the intensity and reducing

4 BLUE LEDS PHOTOPOLYMERIZATION 589 Fig. 2. Graph of the DC for the different composite materials in dependence on the light source and depth. Table 3. The results of the temperature rise in composite materials illuminated with halogen curing unit Heliolux GTE, Elipar Highlight and 16 blue diodes Temperature rise ( C, 40 s, 0á1 mm thick samples) Heliolux GTE Elipar Highlight 16 blue diodes Composite Surface 1 mm depth Surface 1 mm depth Surface 1 mm depth TC-A2 15á6 1á82 7á6 0á89 16á2 1á92 7á2 1á09 7á8 0á84 3á8 0á45 PII-A2 17á6 2á17 8á2 1á10 13á8 1á48 7á2 1á09 9á4 0á55 4á8 1á09 VP-A2 14á0 2á0 6á8 0á44 12á6 0á89 7á4 1á14 7á6 1á14 5á4 1á14 DM-A2 16á8 1á92 8á6 1á14 14á2 0á84 8á0 1á0 8á2 0á84 4á2 0á84 Fig. 3. Graph of temperature rise for the different composite materials in dependence on the light source and depth. the effectiveness of the light for resin polymerization as the depth increases. Factors such as ller type, size and loading; light transmission attenuation; type, thickness, and shade of restorative resin; exposure time; distance from light source and light intensity, affects depth of cure of light-activated composite resins (Byne et al.,

5 590 A. KNEZÏ EVICÂ et al. 1994; Devlin et al., 1995). Inadequate power output, long curing times, narrow light tips (<12 mm in diameter) and the degradation of components (bulbs, re ectors, lters and light tips) make it dif cult to adequately cure composite resin, especially in deeper areas (Vargas et al., 1998). The DC as well as temperature rise for all the materials used is higher in case of illumination with standard halogen curing units, Heliolux GTE and Elipar Highlight, than with 16 blue LEDs. The intensity of tested halogen curing unit Heliolux GTE was 600 mw cm )2 and 100 mw cm )2 ( rst 10 s) and 700 mw cm )2 (30 s) for soft-start curing unit Elipar Highlight and for blue LEDs only 12 mw cm )2. This leads us to the conclusion that such difference in the DC values between halogen curing units and blue diodes illumination is not so signi cant because of the great difference of curing intensity. As a result of the low curing energy of blue LEDs slower polymerization reaction in composite material is enabled. It is well known that slower polymerization reaction causes lower temperature increase. It is commonly believed that temperature increase associated with certain dental procedures pose a serious threat to the vitality of the pulp. Pulp temperature increases of 5á5 and 11á1 C in Macaca Rhesus monkeys caused 15 and 60% irreversibile pulpitis, respectively (Zach & Cohen, 1965). Shubert regarded 41á5 C as the threshold beyond which pulp in ammation occurs (Schubert, 1957). In the genesis of thermal damage, the extent of the damage depends on the quality of heat transferred to the biological tissue. The transmission of heat is in uenced by factors such as thermal conductiveness of the target, duration of the thermal impulse, contact surface, temperature and thermal capacity of the source (Baldissara et al., 1997). The effects of heat on biological tissue are usually arteriole vasodilatation, exudation and coagulative necrosis of the cells. Sixteen blue diodes showed twice lower temperature rise than other two standard halogen curing units. The lowest temperature had Valux Plus for all three light sources on the surface (14á2 2á0 for halogen curing unit Heliolux GTE, 12á6 0á89 for Elipar Highlight and 7á6 1á14 for 16 blue LEDs). It can be noticed that on the other side Valux Plus has the lower DC. The highest temperature rise showed Pertac II (17á6 2á17) by illumination with Heliolux GTE and Tetric Ceram (16á2 1á92) by illumination with Elipar Highlight Vivadent, Schaan, Liechtenstein. halogen curing unit on the surface. There is no signi cant difference between DC on surface and 1 mm depth. However, temperature rise on 1 mm depth was twice lower than on the surface of composite samples for all the light sources compared. Illumination with Heliolux GTE curing unit revealed a little higher temperature rise than Elipar Highlight curing unit, while the DC was quite equal for both curing units. The lower temperature rise by illumination with soft-start curing unit Elipar Highlight might be a consequence of lower intensity (100 mw cm )2 ) in rst 10 s of illumination, thus allows slower polymerization reactions and ow of the material during the rst phase, so called pre-gelations phase of polymerization. The temperature rise is a consequence of light source intensity and chemical reaction during setting process of composite materials on the other side (Hansen & Asmussen, 1993; Fujibayashi et al., 1998). Conclusions The results obtained with experimental blue LEDs of minimal intensity and wavelength of 470 nm were promising especially concerning low temperature rise in the composite material samples. To ensure suf cient light intensity for improved curing values it is necessary to use more blue diodes and focusing their light. References BALDISSARA, P., CATAPANO, S.&SCOTTI, R. (1997) Clinical and histological evaluation of thermal injury thersholds in human teeth: a preliminary study. Journal of Oral Rehabilitation, 24, 791. BENNETT, B., PUCKETT, A., PETTEY, D.&ROBERTS, B. (1994) Light source distance and temperature effects on composite polymerization. Journal of Dental Research, 73, 227 (Abstract 1002). BLANKENAU, R., ERICKSON, R.&RUEGGEBERG, F.A. (1999) New light curing options for composite resin restorations. Compendium, 20, 122. BYNE, S.C., HEYMANN, H.D. & SWIFT E.J. Jr (1994) Update on dental composite restorations. Journal of American Dental Association, 125, 687. CHUNG, K.H. & GREENER, E.H. (1990) Correlation between degree of conversion, ller concentration and mechanical properties of posterior composite resins. Journal of Oral Rehabilitation, 17, 487. DEVLIN, H., CASH, A.J. & WATS, D.C. (1995) Mechanical behaviour and structure of light-cured special tray materials. Journal of Dentistry, 23, 255. DLUGOKINSKI, M.D., CAUGHMAN, F.W. & RUEGGEBERG, F.A. (1998) Assessing the effect of extraneous light on photoactivated resin composites. Journal of American Dental Association, 129, 1103.

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