/home/opencode/cpanel/stomaeduj_hacked/uploads/2018/03/Article_5_3_2.pdf DENTAL MATERIALS Original Article THE EFFECT OF CERAMIC LIGHT SCATTERING ON AN INHOMOGENEOUS BEAM PROFILE Jean-François Roulet1a* , Marwah Majid Khudhair1b, Chiayi Shen1c 1 Department for Restorative Dental Sciences, Center for Dental Biomaterials, College of Dentistry, University of Florida, 1395 Center Drive, Gainesville FL 32610, USA a Dr med dent, Dr hc, Professor, Director of Center for Dental Biomaterials b DDS, Preceptor c PhD, Professor ABSTRACT DOI: 10.25241/stomaeduj.2018.5(3).art.2 Aim: The study aimed to measure light scattering of a broad spectrum light curing unit (LCU) as OPEN ACCESS This is an influenced by ceramic type, shade and thickness as well as exposure distance and LCU’s position. Open Access article under the CC BY-NC 4.0 license. Methodology: A broad spectrum LED LCU (ASCENT OL5) was mounted above a spectrometer Peer-Reviewed Article (MARC Resin Calibrator, Blue, Light Analytics) at exposure distances of 1.0, 1.5 or 2.5 mm. The position of the center of the head was aligned with the spectrophotometer’s sensor and then Citation: Roulet J-F, Khudhair MM, Shen C. The effect of ceramic light moved in 1 mm increments in the X-Y plane, while concomitantly recording the irradiance. The scattering on an inhomogeneous beam profile. Stoma Edu J. 2018;5(3):155- process was repeated with lithium disilicate and leucite glass ceramic slabs of similar thicknesses. 160 The loss in irradiance related to the value measured at center position was analyzed by means Academic Editor: Nicoleta Ilie, of linear regressions and multiple ANOVA analysis. Dipl-Eng, PhD, Professor, Ludwig- Results: The regressions showed a good fit (90% - 99%). Moving away from the center showed Maximilians-Universität München, München, Germany decreased irradiance. Values of slope obtained were divided by their respective intercept to eliminate the influence of the irradiance measured at the center. Two three-way ANOVA’s were Received: June 19, 2018 Revised: July 04, 2018 performed. One examined the influence of ceramic slab, direction and translucency/shade. It Acccepted: July 27, 2018 shows only the direction of measurement exhibited significant influence (p < 0.0001) on the Published: August 01, 2018 mean normalized slope values. The other one examined the influence of ceramic slab, direction *Corresponding author: Professor Jean-François Roulet, DMD, PhD, Dr hc and slab thickness. It shows the mean normalized slope values are significantly influenced by Center for Dental Biomaterials, College the direction of measurement and the slab thickness (p < 0.0001). Values of the slopes indicated of Dentistry, University of Florida Room D9-26, 1395 Center Drive, PO the ceramic scattering effect of the light. Thicker samples showed more scattering. Box 100415 Gainesville, FL 32610- Conclusion: The ceramic types, translucency/ shade had no significant effect on the light 0415, USA Tel: +1 352 273 5850; Fax: +1 352 846 scattering. The thicker the ceramic the less irradiance changes were found indicating that the 1643, e-mail: jroulet@dental.ufl.edu ceramics were scattering the light and thus slightly alleviating the effect of the inhomogeneous Copyright: © 2018 the Editorial beam profile. Council for the Stomatology Edu Keywords: light curing, beam profile, glass ceramics, light scattering. Journal. 1. Introduction restoration such as optical behavior, crystalline Bonded ceramic restorations have been used in structure, grain size, defects, intrinsic porosity, thickness dentistry for many decades and the first application and shade [10]. After passing 0.5 mm thick ceramic, the was the resin bonded ceramic veneer [1,2]. A few years irradiance of the light reaching the resin-based luting later, resin bonded ceramic inlays were tested first in agent would be reduced by approximately 75% [7]. vitro [3] and later in vivo [4]. In order to have enough In order to fulfill its function as luting agent, the resin- time for the cementation process, clinicians prefer light- based luting agent must be adequately polymerized. cure resin-based composites (RBC), which usually have This depends on its composition, e.g. the resin mix, a lower viscosity (luting agents) to facilitate the process the refractive index of the filler, the filler size and of bonding veneers to teeth [5]. For inlays, which are size distribution, pigment, and the photo initiators usually thicker, dual-cure resin-based luting agents are used [11,12]. Using microhardness measurements, preferred [5], because it is not clear if the blue light may for Variolink Estetic (Ivoclar Vivadent) the minimum penetrate the ceramic sufficiently to cure the resin- energy required for adequate curing was found to be based luting agent. A clinical study has shown that approximately 5 J/cm2 [13]. after 12 years of observation, glass ceramic inlays and Modern broad spectrum LED light curing units onlays (Empress, Ivoclar Vivadent) luted with dual-cure (LCU), use different types of LEDs, emitting light with resin-based luting agent showed significantly fewer different wavelengths (violet light (380 – 420 nm) bulk fractures than those luted with a light-cured RBC and blue light (420 – 495 nm) [14,15]. Therefore, they (Tetric, Ivoclar Vivadent) [6]. Today we know that glass are able to activate different types of photoinitiators ceramics (leucite and lithium disilicate ceramics) are [16]. Historically, the most used photoinitiator is absorbing the blue light to a considerable amount champhorquinone (CQ) which has an absoption peak [7-9]. The degree of light attenuation by overlying at 470 nm and requires a tertiary amine as co-initiator, ceramics depends on the characteristics of the ceramic which reacts with the activated CQ to create a free Stomatology Edu Journal 155 THE EFFECT OF CERAMIC LIGHT SCATTERING ON AN INHOMOGENEOUS BEAM PROFILE radical used for the polymerization of the resin [17]. Original Article These amines, unfortunately, create a yellowing effect on the material over time [17]. Recently manufacturers started to use alternative photoinitiators, such as phenylbis-(2,4,6-trimethylbenzoyl)-phosphine-oxide (TPO) [18] or bis-(4methoxybenzoyl)diethyl-germane (Ivocerin) [19,20]. These photoinitiators are much more effective than the combination of CQ and tertiary amine, but have absorption peaks below 410 nm (TPO) or 430 nm (Ivocerin), thus requiring broad band LCUs which usually have two different LEDs, (blue and violet light). However, these LED LCUs show more or less pronounced inhomogeneity of the beam profiles [21-24]. This means that not every point on an irradiated surface gets exposed to the same level of irradiation from the Figure 1. Measuring points as related to the position within the light exit different wavelengths, especially in depth [25-27]. window. Blue cross = geometrical center of the light exiting window. Since ceramics scatter the light because its direction is Orange circles =“WEST”, Light blue circles =“EAST”, Purple circles =“North” changed at the grain boundaries, one can assume that and green circles =“SOUTH”(From Roulet et al 2018). the local irradiances may vary less, once the light has Table 1. The ceramics used and their translucency/shade. passed through the ceramic, thus moving the beam profile more towards homogeneity. Furthermore, Material Shade and Translucency since the light is absorbed and scattered more with the IPS Empress A1LT B1LT C2LT D3LT B3HT C2HT thicker ceramic, this should affect the homogeneity of CAD the beam profile as well. IPS e.max The objective of this study was to measure the beam A1LT B1LT C2LT D3LT B3HT C2HT CAD homogeneity of an LCU with known inhomogeneous beam profile after the light had passed ceramic slices Table 2. The ratio of slope to the intercept of linear regression for all of different thickness. ceramics. The null hypothesis tested is that (a) the ceramic has no Empress e.max effect on the beam profile and (b) the thickness of the Direction Translucency /Shade ceramic has no effect on the beam profile as well. 1.0 mm 1.5 mm 2.5 mm 1.0 mm 1.5 mm 2.5 mm HTB3 0.135 0.130 0.115 0.135 0.130 0.115 2. Materials and Methods HTC2 0.129 0.123 0.126 0.129 0.123 0.126 A broad spectrum LED LCU (ASCENT OL5, CAO Group LTA1 0.130 0.136 0.126 0.130 0.136 0.126 South Jordan, UT, USA) was attached to an x-y-z East positioning device mounted on an optical bench LTB1 0.132 0.123 0.123 0.132 0.123 0.123 in order to standardize the positioning of the light LTC2 0.134 0.128 0.123 0.134 0.128 0.123 beam centered above the cosine corrector light signal LTD3 0.130 0.134 0.119 0.130 0.134 0.119 collector of a spectrometer (MARC® Resin Calibrator, Blue light Analytics, Halifax, Canada) with the handle HTB3 0.169 0.165 0.141 0.169 0.165 0.141 towards the right side (“EAST”, Figure 1) at an exposure HTC2 0.163 0.148 0.129 0.163 0.148 0.129 distance of 1.0, 1.5 or 2.5 mm. The diameter of the LTA1 0.129 0.193 0.149 0.129 0.193 0.149 cosine corrector was 3.9 mm. Using the translation West stage, the position of the geometrical center of the LTB1 0.158 0.145 0.142 0.158 0.145 0.142 LCU was first aligned with that of the cosine corrector LTC2 0.172 0.169 0.146 0.172 0.169 0.146 and then moved in 1-mm steps in the x-y plane (“EAST” LTD3 0.159 0.164 0.157 0.159 0.164 0.157 – “WEST” and “NORTH” – “SOUTH”) (Fig. 1). At each position, the irradiance was measured in triplicates. HTB3 0.141 0.140 0.120 0.141 0.140 0.120 The process was repeated with ceramic slabs of 1.0, 1.5 HTC2 0.146 0.132 0.132 0.146 0.132 0.132 or 2.5 mm thickness while applying the LCU directly LTA1 0.156 0.141 0.141 0.156 0.141 0.141 on the ceramic slabs. The ceramics used and their North translucency/shade are listed in Table 1. LTB1 0.145 0.142 0.132 0.145 0.142 0.132 IPS Empress CAD slabs were used as cut from blocks LTC2 0.144 0.137 0.129 0.144 0.137 0.129 with a diamond saw (Isomet 100, Buhler, Lake Bluff, LTD3 0.149 0.143 0.137 0.149 0.143 0.137 USA), IPS e.max CAD slabs were cut from blocks and processed according to manufacturer’s instructions HTB3 0.159 0.154 0.137 0.159 0.154 0.137 in an oven (Programat P-500, Ivoclar Vivadent), under HTC2 0.168 0.148 0.143 0.168 0.148 0.143 vacuum, using the following parameters: heating rate of 90°C/min up to 820 °C, holding time 0:10 min, then LTA1 0.170 0.120 0.124 0.170 0.120 0.124 South heating rate of 30°C/min up to 840°C hold for 7:00 min, LTB1 0.168 0.143 0.140 0.168 0.143 0.140 followed by long-term cooling. LTC2 0.167 0.142 0.150 0.167 0.142 0.150 The irradiance was assessed at each condition described above and related to the highest irradiance LTD3 0.162 0.162 0.147 0.162 0.162 0.147 156 Stoma Edu J. 2018;5(3):155-160. http://www.stomaeduj.com THE EFFECT OF CERAMIC LIGHT SCATTERING ON AN INHOMOGENEOUS BEAM PROFILE Original Article Table 3. The ratio of slope to the intercept of linear regression (pooled shades and translucencies). No ceramic slabs Empress e.max Direction 1.0 mm 1.5 mm 2.5 mm 1.0 mm 1.5 mm 2.5 mm 1.0 mm 1.5 mm 2.5 mm East 0.117 0.122 0.091 0.132±0.002 0.129±0.005 0.122±0.004 0.132±0.020 0.124±0.014 0.116±0.015 West 0.190 0.175 0.141 0.158±0.015 0.164±0.017 0.144±0.009 0.193±0.009 0.187±0.009 0.168±0.009 North 0.163 0.161 0.156 0.147±0.005 0.139±0.004 0.132±0.007 0.155±0.009 0.151±0.008 0.141±0.006 South 0.187 0.172 0.186 0.166±0.004 0.145±0.014 0.140±0.009 0.139±0.015 0.130±0.005 0.114±0.010 (a) (a) (b) (b) Figure 2. Effect of disk thickness on irradiance change in E-W direction Figure 3. Irradiance change from center in E-W direction (a) and N-S (a) and N-S direction (b). direction (b). value which was identified in the present study when normalized slope values with a unit of mm-1. Although positioning the LCU directly and centered on the decreasing irradiance with offset distance yielded sensor. The percentage of irradiance loss was statistical negative value of the slope; to avoid potential confusion of analyzed by means of linear regression for each negative sign in the text absolute value of the normalized material, shade, thickness and direction. The effect of slope is used (Table 2). vertical position (distance between LCU and bottom Two three-way ANOVA’s were performed. One examined of ceramic or sensor surface), horizontal position or the influence of ceramic slab, direction and translucency/ off-set (X-Y plane), glass ceramic type, thickness and shade. It shows only the direction of measurement shade on the irradiance were analyzed using multiple exhibited significant influence (p < 0.0001) on the mean ANOVA’s (SAS 9.4, Cary, NC, USA). normalized slope values. The other one examined the influence of ceramic slab, direction and slab thickness. It shows the mean normalized slope values are significantly 3. Results influenced by the direction of measurement and the slab The numerical data show that there is a linear relationship thickness (p < 0.0001). The mean normalized slope value between the irradiance measured by the MARC unit is in the decreasing order of 1.0, 1.5 and 2.5 mm. For the and the offset distance from the center, excluding effect of direction of measurement, the mean normalized the irradiance value at the center. A total of 144 linear slope value is in the decreasing order of North, West, South regressions (SAS 9.4) were performed from a combination and East. It means the inhomogeneity of the light curing of two ceramic, four directions, three slab thicknesses and depends on the device and the thickness of the ceramic six translucency/shade of each ceramic. The degree of fit slabs. The optical characteristic of the ceramic would have was in general greater than 90% with the majority in the no influence on the inhomogeneity as determined by 99% range. The value of intercept of linear regression is MARC. Figure 2 shows the values of irradiance with respect the calculated irradiance at the center and can influence to the offset distance and direction of measurements for the values of the slope. To normalize the irradiance at the each thickness of the two ceramics. center, each value of slope was divided by the respective The mean and standard deviation of normalized slope value of intercept of the linear regression resulting values by offset distance and slab thickness are pooled Stomatology Edu Journal 157 THE EFFECT OF CERAMIC LIGHT SCATTERING ON AN INHOMOGENEOUS BEAM PROFILE together for each ceramic in Table 3 along with those reduction relative to the offset distance. A flatter slope Original Article when no ceramic slabs were present. The values of no determined from the same experimental configuration ceramic slabs were means of taken from a previous study but with the presence of ceramic slabs would mean that [28]. Figure 3 shows the mean irradiance values measured increased scattering of the light has occurred. As seen in at each location. The values in the figure are means of all Fig. 3, the absolute irradiance values without ceramic were thickness and translucency/shade for both ceramics. substantially higher than those with ceramic interposition. Therefore, for direct comparisons, the slopes must be normalized as described in Materials and Methods. The 4. Discussion ANOVA’s showed that there were no significant differences The LCU used in this study was selected on purpose with respect to the ceramic materials and translucency/ because it is known to have a quite inhomogeneous shade; however, highly significant differences for the beam profile as shown in a previous study [28]. The position (design of LCU) and thickness of the ceramic. objective of this study was to show the effect of ceramics It is known to clinicians that the translucency and the on the inhomogeneity of the beam profile. shade have a high impact on the aesthetical outcome Therefore, it makes sense to use an LCU, where this of a restoration. This is the reason why ceramics are not characteristic is to be expected. As shown in the previous only produced in different shades, but also in different study, the blue range the LCU used was so dominant translucencies. Therefore, it is interesting to see that the (irradiance: blue 1088 mW/cm2 vs violet 71 mW/cm2) shades/translucencies have little effect of scattering the [28], that the observed effects may be mainly for the light in the blue or purple range. This confirms that yellow blue light portion only. However, two factors need to be colors are more important to reach good esthetics with considered, that may influence the outcome. First, it is restorations of teeth. known that the violet light is scattered differently from In Table 2 where the data of all ceramics tested are the blue light by ceramic, which is seen by the different displayed, the slopes with thick slabs are always lower, rate of attenuation [29]. Second, one should remember which means that there is a light scattering effect by the that the sensitivity of photo initiators sensible in the violet thickness of the ceramic; the thicker the ceramic the more range is much higher than the one of camphorquinone light scattering. The same is visible in Table 3, where the for the blue light. Thus, despite the less amount of violet ceramic shades and translucencies were pooled. light reaching the resin-based composite, due to the Based on the outcome of the ANOVA’s, the ceramic had better efficiency, the initiation of the polymerization no effect on the beam profile, which can also be seen is effectively enough to cure the RBC [30], which may in Tab. 3. Therefore, the first null hypothesis must be influence the degree of conversion of an RBC at least accepted. However, one must note that the ceramic had under thin layers of the ceramic [29]. a strong effect when one looks at the attenuation of the In the present study, the LCU was laterally moved in a light, which was not the topic of the present investigation. controlled way in the X- and Y-direction of a coordinated The second null hypothesis can be rejected, since thicker system. This creates a decrease in the irradiance as a ceramic slabs showed more scattering of the light. function of the offset from the center value, which can be determined as a slope, as seen in Figs 2 and 3, and Tab. 2, which is the expression of the inhomogeneity of the 5. Conclusion beam profile. The thicker the ceramic the fewer irradiance changes With the method used (controlled lateral movements), were found as a function of the position indicating that the inhomogeneity of the beam could be roughly the ceramics were scattering the light and thus slightly reproduced. However, the cosine corrector light signal alleviating the effect of the inhomogeneous beam profile. collector used has a diameter of 3.9 mm, which limits the precision. It is suggested for future measurements to use a smaller sensor diameter. Author contributions The ceramics used for the present study (Empress and JFR: Idea, experimental design, wrote the manuscript. IPS e.max) were chosen because they are sufficiently CS: Performed data analysis, substantially contributed translucent for resin-bonded restorations (inlays, onlays, to writing manuscript. MMK: Performed spectrometer veneers and crowns) where light curing of the resin experiment. bonded luting material may be an option [31,32]. Therefore, the scattering behavior of the blue (and violet) light is important if the beam profile is inhomogeneous). Acknowledgement It is known that the irradiance at the target surface The authors have no conflicts of interest. This research received is a function of the exposure distance [21]. did not receive any specific grant from funding agencies Therefore, the decrease in irradiance reported in Fig. 2 is in the public, commercial, or not-for-profit sectors. The not only due to the increased thickness of the ceramic but authors declare that the research was conducted in the also to the increasing distance from the sensor to the light absence of any commercial or financial relationship that exciting window of the LCU. Figure 3 confirms the fact could be construed as a potential conflict of interest. that interposing ceramics in the light beam attenuates a substantive amount of light irradiance [7,33]. The decrease in irradiance as the measuring point moves References farther away from the center is due to the design of the 1. Simonsen RJ, Calamia JR. Tensile bond strengths of etched porcelain. J Dent Res. 1983; 62 (2 Suppl): 297, Abstract #1099. LCU and representative for its beam profile. A steeper 2. 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Jean-François ROULET DDS, DMD, PhD, Dr hc, Prof hc, Professor, Chair Department of Restorative Dental Sciences, Center for Dental Biomaterials College of Dentistry, University of Florida Gainesville, FL, USA CV Jean-François Roulet, DDS, Dr med dent, PhD, is the former chair and current professor of the Department of Restorative Dental Sciences at the University of Florida. Professor Roulet is author/coauthor of more than 180 papers, edited/contributed to 27 textbooks and mentored more than 150 theses. He is a renowned international lecturer with over 800 appearances to date. Dr. Roulet is a member of many professional organizations, has won numerous awards, and holds four patents. He is editor of the Prophylaxe Impuls and Stomatology Edu Journal. His areas of interest include minimally invasive dentistry, dental materials (ie, composites and ceramics), adhesive dentistry, esthetic dentistry, and application concepts in preventive dentistry. Stomatology Edu Journal 159 THE EFFECT OF CERAMIC LIGHT SCATTERING ON AN INHOMOGENEOUS BEAM PROFILE Questions Original Article 1. Why are amine free resin-based composites preferred to bond veneers? qa. They allow for a longer working time; qb. Tertiary amines used in combination with campherquinone tend to discolor over time; qc. Tertiary amines and campherquinone require a broadband light curing unit; qd. Amine free resin-based composites provide a stronger bond. 2. Which ceramics were used for the experiment? qa. Leucite reinforced ceramic and lithium disilicate ceramic; qb. Translucent Zirconium oxide ceramic; qc. Feldspathic ceramic; qd. None of the above. 3. The results were analyzed with: qa. ANOVA and Wilcoxon test; qb. ANOVA and t-test; qc. ANOVA and Kruskal Walls Test; qd. ANOVA and linear regression. 4. Which was the main outcome of the experiment? qa. Ceramic color, shade and type had a significant effect on the scattering of light; qb. Ceramic did not alter the irradiance; qc. All of the above; qd. The thicker the ceramic, the more light-scattering occurred. https://www.gnydm.com/ 160 Stoma Edu J. 2018;5(3): 155-160. http://www.stomaeduj.com