Današnji kompozitni materijali polimeriziraju se vidljivim plavim svjetlom valne duljine oko 468 nm. Komercijalni uređaji za polimerizaciju kompozitnih materijala emitiraju plavo svjetlo različite jakosti. Uporaba uređaja za polimerizaciju jačega intenziteta sa svrhom da se postigne veći stupanj konverzije neminovno povećava zagrijavanje i temperaturu u materijalu tijekom stvrdnjavanja te polimerizacijski skuplja materijal. Svrha rada bila je utvrditi postoji li razlika između stupnja konverzije i porasta temperature triju ispitivanih kompozitnih materijala: Amelogen (Akeda Dental, Danska), Pertac II (ESPE, Seefeld, Germany), Z100 (3M Dental Products, St. Paul, Minessotta, USA), polimeriziranih eksponencijskim programom Elipar Trilight (ESPE, Seefeld, Njemačka) polimerizatora i Lux-o-Max (Akeda Dental, Danska) uređajem za polimerizaciju temeljenog na LED (light emitting diodes) tehnologiji. Rezultati su pokazali tek nešto niži stupanj konverzije pri polimerizaciji Lux-o-Max uređajem u odnosu prema eksponencijskome programu Elipar Trilight polimerizatora. Temperaturni porast znatno je niži pri polimerizaciji Lux-o-Max uređajem za sve ispitivane kompozitne materijale u usporedbi s rezultatima dobivenima pri polimerizaciji eksponencijskim programom Elipar Trilight polimerizatora.Today available composite materials are polymerized by blue light, with a wavelength of about 468 nm. Commercially available curing units for composite resin polymerization emit blue light of different intensity. Using curing units of higher light intensity to reach a higher degree of conversion unavoidably leads to higher temperature rise in material during hardening, and also to polymerization shrinkage of material. The aim of this study was to determine if there is any difference between the degree of conversion and temperature rise in three composite materials: Amelogen (Akeda Dental, Denmark), Pertac II (ESPE, Seefeld, Germany) and Z100 (3M Dental Products, St. Paul, Minessotta, USA) polymerized with exponential program of Elipar Trilight curing unit (ESPE, Seefeld, Germany) and Lux-o-Max curing unit (Akeda Dental, Denmark) based on LED (light emitting diodes) technology. The results showed only a slightly lower degree of conversion, in the case of polymerization with Lux-o-Max curing unit. The temperature rise was significantly lower in the case of polymerization with Lux-o-Max curing unit for all tested composite materials

Alena Knežević

Andrej Meniga

Goran Pichler

Jozo Šutalo

Mira Ristić

Zrinka Tarle

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Degree of Conversion and Temperature Measurement of Composite Polymerised with Halogen and LED-Curing Unit

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A S CActa Stomatol Croat, Vol. 37, br. 2, 2003. 165Degree of Conversion andTemperature Measurement ofComposite Polymerised withHalogen and LED-Curing UnitSummaryToday available composite materials are polymerized by blue light,with a wavelength of about 468 nm. Commercially available curingunits for composite resin polymerization emit blue light of differentintensity. Using curing units of higher light intensity to reach a higherdegree of conversion unavoidably leads to higher temperature rise inmaterial during hardening, and also to polymerization shrinkage ofmaterial. The aim of this study was to determine if there is any differ-ence between the degree of conversion and temperature rise in threecomposite materials: Amelogen (Akeda Dental, Denmark), Pertac II(ESPE, Seefeld, Germany) and Z100 (3M Dental Products, St. Paul,Minessotta, USA) polymerized with exponential program of Elipar Tri-light curing unit (ESPE, Seefeld, Germany) and Lux-o-Max curing unit(Akeda Dental, Denmark) based on LED (light emitting diodes) tech-nology. The results showed only a slightly lower degree of conversion,in the case of polymerization with Lux-o-Max curing unit. The temper-ature rise was significantly lower in the case of polymerization withLux-o-Max curing unit for all tested composite materials.Key words: halogen curing units, blue diodes, composite resins,degree of conversion, temperature.Alena KneæeviÊ1Zrinka Tarle1Andrej Meniga1Jozo ©utalo1Goran Pichler2Mira RistiÊ31Department of RestorativeDentistrySchool of Dental MedicineUniversity of Zagreb2Institut of Physics, Zagreb3Institute “Ruer BoπkoviÊ”,ZagrebActa Stomat Croat2003; 165-168ORIGINAL SCIENTIFICPAPERReceived: July 10, 2002Address for correspondence:Alena KneæeviÊDepartment of RestorativeDentistrySchool of Dental MedicineGunduliÊeva 5, ZagrebCroatiaIntroductionVisible light curing composite resins possess (α-1.2 diketone (benzil or camforquinone) as a pho-toinitiator and amine as a reducing agent, usuallydimethylaminoethyl methacrylate. Blue light wave-length from 400 to 500 nm is used for conversionof α-diketone in excited state which is a response tofree-radicals formation (1).The degree and depth of conversion of visiblelight curing composite resins depends on the com-ponents of the material (organic matrix, type andvolume of anorganic filler and size of filler parti-cle), on optic characteristics (colour, translucency,A S C Acta Stomatol Croat, Vol. 37, br. 2, 2003.166Alena KneæeviÊ et al. Composite Resins Polymerizationrefraction index), on intensity and duration of expo-sure to blue light (2). Intensity of halogen curingunits decrease with use, and the maximum poly-merization of composite resin recommended by themanufacturer, ia possible only when the output lightintensity is optimal. Only those wavelengths whichenable activation of (α-diketone enables effectivepolymerization. Most conventional curing units forphotopolymerization have spectrum wavelengths ofbetween 390 and 510 nm and effective wavelengthsare only about 468 nm which is the absorption max-imum of camforquinone. Wavelengths above thisare not useful for composite resin polymerizationand only cause a useless temperature rise (3). To eliminate the useless wavelengths of the con-ventional halogen curing units, which are in daily usein clinical practice, a new unit based on LED-tech-nology has been introduced. This unit emits a wave-length spectrum closely to the wavelength spectrumof camphorquinone. Due to the narrow spectrum ofwavelengths, higher and useless temperature riseduring polymerization is avoided (4-6).The aim of this study was to compare the degreeof conversion and temperature rise of three com-posite resins, polymerized with a halogen curing unitand a unit based on blue diodes.Materials and methodsDegree of conversion measurementThe polymerization effects of the exponentialprogram of the Elipar Trilight halogen curing unitand Lux-o-Max unit based on LED-technology wereanalysed. The exponential program of Elipar Tri-light unit begins with an intensity of 100 mW/cm2and exponentialy increases in 15 seconds to 800mW/cm2 and this intensity remains the same untilthe end of the 40th second. The light intensity for theLux-o-Max unit was 50 mW/cm2 for the first 10 sec-onds and 150 mW/cm2 for the further 30 seconds.The output intensity is determined by Curing Ra-diometer Model 100 (Demetron Research, Danbury,CT, USA). Composite resins used in the experimentwere: Amelogen (A), Pertac II (PII) and Z100(Z100) shade A2.For measuring the degree of conversion five sam-ples for each material were prepared. Compositeresin sample was placed between two Mylar sheetsand pressed with 107 Pa to 0.1 mm thick and ∅1.5cm. The prepared composite resin sample was lightcured with a light tip closed to an upper Mylar sheetfor 40 seconds. FTIR (Fourier transform infraredspectroscopy) the spectra of polymerized sampleswere recorded in transmission mode using PerkinElmer Spectrometer Model 2000 (Perkin Elmer,Beaconsfield, Bucks, England) (4, 5, 7). The ratioof absorption maximum was calculated to the F. A.Rueggeberg (8) baseline. The degree of conversionwas calculated by the following formula:% conversion = (1- (P/N)) x 100where P - molar ratio is of polymerized and N - molar ratio of unpolymerized sample.Temperature measurementFor measuring temperature five samples of eachmaterial were made in a plastic mould, size 4x4x4mm. A Metex multimeter was used for recordingtemperature changes. The multimeter was connect-ed to a personal computer so that the changes in tem-perature during 40 seconds could be seen. The peakof the temperature probe was stuck into the com-posite resin sample 1 mm deep and light cured for40 seconds, with the curing tip close to the surfaceof the composite sample. Temperature rise wasrecorded after 10, 20 and 40 seconds of illumina-tion.Descriptive statistics were used to determinemean value and standard deviation, and ANOVAwas used to determine p-values.ResultsThe results of the conversion degree and temper-ature rise are given in Tables 1 and 2 as medium val-ues and standard deviations. The results of the con-version degree in the case of polymerization withLux-o-Max curing unit are compared with the resultsof composite resin polymerization in the case of Eli-par Trilight halogen curing unit and are presented inTable 1. It can be seen that the degree of conversionin the case of polymerization with Elipar Trilightcuring unit is minimally higher than the degree ofconversion in the case of polymerization with Lux-o-Max. The highest values of conversion degreeAlena KneæeviÊ et al. Composite Resins PolymerizationA S CActa Stomatol Croat, Vol. 37, br. 2, 2003. 167were recorded for Pertac II composite material inthe case of illumination with both curing units(66.74±1.51% by polymerization with the exponen-tial program of Elipar Trilight halogen curing unitand 62.23±3.16% by illumination with Lux-o-Maxunit). The lowest results of conversion degree wasdetermined for Z100 composite material in the caseof polymerization with both curing units (61.04±0.91%by illumination with the exponential program of Eli-par Trilight halogen curing unit and 58.61±0.48%by illumination with Lux-o-Max curing unit). Thereis no significant difference (p>0.05) between poly-merization of composite materials with Lux-o-Maxand Elipar Trilight curing units.The results of temperature measurements aregiven in Table 2. The highest temperature valueswere recorded for Pertac II in the case of illumina-tion with both light sources (13.6±2.88°C by illu-mination with exponential program of Elipar Tri-light unit and 7.2±1.92°C by illumination with Lux-o-Max unit after 40 seconds). The lowest results oftemperature rise were recorded for A composite mate-rial in the case of illumination with Elipar Trilight(12.6±1.14°C) and for Z100 (5.6±0.89°C) in the caseof polymerization with Lux-o-Max curing unit after40 seconds. There is significant difference betweenthe temperature rise by polymerization of compos-ite materials with Elipar Trilight and Lux-o-Maxcuring unit in 20th (p=0.049) and 40th (p=0.005) sec-ond of illumination (Table 3).DiscussionThe light intensity of adequate wavelength whichis emitted during polymerization of composite mate-rials is a very important factor which determines theeffectiveness of the curing unit (9). Recent investi-gations of the conversion degree of composite mate-rial polymerization with standard halogen curingunits have shown that the degree of conversion liesbetween 60% and 75% (4, 5, 7, 10-12). A higherdegree of conversion leads to greater hardness andstiffness of the material and also to higher color sta-bility. The quality of composite resin polymeriza-tion decreased with the distance of the light source.This is very important in deep cavities where appli-cation of composite in thin layers is recommended.Incomplete polymerization has as a consequence ahigher quantity of unreacted monomer which can bedissolved in the mouth. Also, the reactive doublebonds can be hydrolized or oxidized, which leads todegradation of the material and composite filling(13). The results of the conversion degree of all test-ed composite materials in this experiment haveshown a higher degree of conversion in the case ofillumination with the halogen curing unit Elipar Tri-light. A little lower degree of conversion was record-ed only in the case of polymerization of the com-posite material with Lux-o-Max unit based on LED--technology. There is no significant differencebetween the degree of conversion achieved withthese two curing units (p>0.05) which can be con-nected with spectrum distribution.Earlier investigations of the degree of conversionwith blue LED-s which were connected in anotherway have shown slightly lower results of conversiondegree (5, 14-17). This can be caused by unsuitablefocusing of blue diodes and as a consequence theloss of emited blue light.The best values of the degree of conversion werefound for Pertac II (66.74±1.51% in case of illumi-nation with exponential program of Elipar Trilighthalogen curing unit and 62.23±3.16% in the caseof illumination with Lux-o-Max) while the lowestresults of conversion degree were determined forZ100 (61.04±0.91% by polymerization with expo-nential program of Elipar Trilight halogen curingunit and 58.61±0.48% by polymerization with Lux-o-Max curing unit).Polymerization effectiveness depends on the lightsource, although material composition also has sig-nificant influence. Because they all posses cam-phorquinone as a photoinitiator, the difference in thedegree of conversion may be influenced by differ-ent amines which make a complex with cam-phorquinone with different absorption characteris-tics. This is probably one of the reasons why theresults of conversion degree are lower in the case ofcomposite resin polymerization with blue LEDs orplasma curing unit, while they have a narrower spec-trum, i.e. they emit a wavelength of about 468 nm,which is the maximum absorption of camphorqui-none. The complex which camphorquinone makeswith amine or other active components which areadded to the composite material, moves the spec-A S C Acta Stomatol Croat, Vol. 37, br. 2, 2003.168Alena KneæeviÊ et al. Composite Resins Polymerizationtrum of photoinitiators activaction which is no morein wavelengths which emit polymerization curingunits. This results inlower polymerization of thecomposite material (18).Everyday new polymerization units based on dif-ferent technology are introduced on the market: stan-dard halogen curing units with different polymer-ization programs, plazma units, blue superbrightlight emitting diodes. When chosing curing unitsusually most attention is paid to output light inten-sity and illumination time. However, temperaturerise during polymerization of composite resins is avery important factor which can have great influ-ence on vital tooth tissue. Protoplazmatic coagula-tion, expansion and fluid outflow from dentine tubu-li, structural changes in blood vesels and tissuenecrosis are the mean consequence of high temper-ature increase (19).It is known that the higher the degree of con-version the higher the temperature rise. Futhermorethe temperature of the material rises not only becauseof the emitted light influence, but also because ofthe chemical reaction in the material itself duringthe polymerization process. This investigation hasshown that the polymerization of composite resinswith Lux-o-Max unit causes a lower temperature risethan polymerization with exponential program ofElipar Trilight curing unit. The highest temperaturerise, which agrees with the highest results of con-version degree, was determined for Pertac II com-posite material 13.6±2.88°C in the case of illumi-nation with exponential program of Elipar Trilightcuring unit, and 7.2±1.92°C in the case of poly-merization with Lux-o-Max curing unit after 40 sec-onds polymerization). From these results it can beseen that the temperature rises slowly during 40 sec-onds of polymerization with Lux-o-Max curing unit,while in case of polymerization with exponentialprogram of Elipar Trilight halogen curing unit thetemperature rise in the interval of 10 to 20 secondsis higher than in the interval from 20 to 40 secondsbecause of the exponential rise of light intensity.There is significant difference between the temper-ature rise in the 20th (p=0.049) and 40th (p=0.005)second by illumination of composite materials withLux-o-Max and Elipar Trilight curing unit. Thereis no significant difference in the 10th second whichcan be connected with light intensity. During thefirst 10 seconds of illumination, Lux-o-Max hadintensity of 50 mW/cm2, while the exponential modeof Elipar Trilight unit had 100 mW/cm2. In the 20thand 40th second the light intensity for Lux-o-Maxwas 150 mW/cm2 and for Elipar Trilight 800 mW/cm2.The greater difference between the light intensity ofthese two curing units has, as a consequence, greaterdifference between the achieved temperature values.ConclusionQuite an equal degrees of conversion and mar-kedly lower temperature increase were obtained inthe case of polymerization with the blue LED cur-ing unit compared to the conventional halogen unit.It can be assumed that lower heating of the com-posite material will lead to lower heating of vitalpulp tissue. Further development of LED technolo-gy and its clinical use will show its advantages anddisadvantages in comparison with the halogen cur-ing unit.

Degree of Conversion and Temperature Measurement of Composite Polymerised with Halogen and LED-Curing Unit

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