THE MARGINAL FIT OF MILLED-CERAMIC INLAYS A COMPARATIVE THREE DIMENSIONAL AND MICROSCOPIC RESEARCH

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1 Prosthetic dentistry THE MARGINAL FIT OF MILLED-CERAMIC INLAYS A COMPARATIVE THREE DIMENSIONAL AND MICROSCOPIC RESEARCH Sorana BACIU 1, Cristian BERCE 2, Alexandru Victor BURDE 3, Marius MANOLE 4, Adrian FLOREA 1 1 Assoc. Prof. PhD, Iuliu Hatieganu University of Medicine and Pharmacy, Cluj-Napoca, Romania 2 Scientific Researcher, PhD, University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca, Romania 3 Univ. Assist., PhD Student, Iuliu Hatieganu University of Medicine and Pharmacy, Cluj-Napoca, Romania 4 Assist. Prof. PhD, Iuliu Hatieganu University of Medicine and Pharmacy, Cluj-Napoca, Romania Corresponding author: Sorana Baciu; soranav@yahoo.com Abstract 1. INTRODUCTION Objective: The main goal of the present study is to compare two methods for evaluating the marginal fit of fixed prosthetic restorations. For this purpose we used a milled ceramic material, out of which we obtained class I inlays. The marginal gap was analyzed using micro CT and electronic microscopy. Materials and methods: After extraction of four caries-free mandibular first molars, first class inlay cavities were prepared. The marginal gap was analyzed circumferentially at the occlusal margin using a Bruker micro CT, by measuring the distance at the occlusal limit of the cavities, between the restoration and the tooth in several points for every surface of each tooth before cementing. For the second method SEM technology was used, and measurements were made at the occlusal limit of the cavities, between the restoration and the tooth in 50 microns steps. The data were compared with One way ANOVA with Tukey s Multiple Comparison Test performed using 5.00 for Windows (GraphPad Prism 5.00 Software, San Diego, California USA). Results and discussion: For both methods we obtained clinical acceptable values of the marginal gap for the milled ceramic inlays. The null hypothesis was rejected. We obtained statistical significant differences of the measured gaps using the two above mentioned methods. Conclusions: Both evaluation methods are reliable for measuring the marginal gap of fixed prosthetic restorations, each method having specific indications, advantages and disadvantages. They offer indispensable information which lead to improvement of the restorative treatments. Keywords: marginal fit, milled ceramic inlay, pressed resin inlay, micro CT, SEM. The need for a constant improvement of the various parameters of restorative treatments (aesthetics, ergonomics, mechanical properties, number of appointments) led, during the last decades, to the replacement of classical fillings in premolar-molar area with different aesthetic inlays. The most commonly used materials are ceramics and composite resins cured trough different techniques. A research performed on 2,328 chairside milled inlays and onlays showed a surviving rate of 95.5% after 9 years [1], while another study, made on 1,011 milled inlays and onlays, showed a 84.4% surviving rate after 18 years [2]. Ceramic inlays obtained through milling techniques have gained a leading place between these types of restorations because of the aesthetics and longevity assured by a precise marginal fit [3]. Different ceramic materials utilize various fabrication methods and therefore result in distinct degrees of aesthetic quality and strength [4]. Table 1. Properties of various ceramic inlays obtained through different techniques Restorative material Fabrication method Aesthetics Strength Feldspathic porcelain Fired on refractory die Excellent Weak Reinforced leucite Lost wax-pressed ceramic Excellent Moderate Milled ceramic block Excellent Moderate Aluminous core Slip cast; glass infiltrated Good Strong core; weak veneer Lithium disilicate Lost wax-pressed ceramic Moderate Strong Milled ceramic block Moderate Strong 62 Volume 7 Issue 1 January / March 2017

2 THE MARGINAL FIT OF MILLED-CERAMIC INLAYS A COMPARATIVE THREE DIMENSIONAL AND MICROSCOPIC RESEARCH Milled ceramic restorations offer a very good marginal fit which, along with other factors (periodontal integration, biocompatibility of ceramics) is a crucial factor for a successful prosthetic treatment. Improvement of the different parameters of milled inlays is due to constant upgrading of various parts intake, such as: high resolution of the intraoral acquisition unit (25 µm), 5 axis milling, as well as reproducible results of the milling unit (up to ±30 µm). The main advantage of the CAD CAM is a diminished intervention of the dental technician through conventional techniques, which reduces the chances of human errors. As shown in our previous studies [5-6], the accuracy of restorations depends on many factors: a precise impression, a correct pouring technique of the dies, an accurate wax pattern - when included, as well as a flawlessly cementation technique. Empress CAD are feldspathic monochromatic blocks reinforced with leucite (mainly SiO 2 and Al 2 O 3, K 2 O, Na 2 O) with a lower degree of translucency than other ceramic blocks, yet higher brilliance, which recommends them for restoration in the frontal and lateral area [7]. The KAlSi 2 O 6 leucite crystals, formed by a controlled process, assure an increased strength of the material, while propagation of cracks is slowed down or deflected. In this process, the crystalline phase absorbs fracture energy. As a result, cracks propagation is arrested or decelerated [8]. The aim of our study was to determine the marginal discrepancy of milled leucite glassceramic inlays (obtained by the CAD CAM technology) and to compare the results using two different evaluating methods: SEMelectronic microscopy and micro CT. 2. MATERIALS AND METHODS The ceramic inlays were made on healthy upper molars extracted and stored in artificial saliva for less than 6 months at 4 C. As part of a larger study, we standardized the preparation method and used the same preparation steps, following the general guidelines for inlay preparations, as in previous studies [5-6]. First class inlay cavities were prepared using a high speed carbide bur FG271 (ismile, Sacramento, Canada) with a 0.3 mm tip, which was used for entrance and for establishing the pulpal floor at a depth of 2.5 mm. Then, a FG169L (SS White, New Jersey, USA) high speed bur with a tip thickness of 0.5 mm was used to extend the occlusal outline mesio-distally along the central groove, at a 3-5 degree divergence to the facial and lingual walls, as well as to accomplish final extension in the triangular grooves. The final step of cavity preparation was performed with a 6862 (Komet Dental, Lemgo, Germany) high speed diamond bur used to correct the enamel margins and to perform rounding of the internal edges. All preparation steps were made under constant water-cooling. For each tooth, two inlays were manufactured - one inlay was made of pressed thermoplastic resin (n=4) (BredentGmbh&Co.KG, Senden, Germany), the other - of milled leucite glass-ceramic (n=4) (Empress CAD). Fig. 1. Laboratory steps for fabricating milled inlays; milled inlays inserted into the cavities For milled Empress inlays, the impression was made using duplicating silicone Duplicast. The dies were made of a scanable die material - Shera Hard Rock, which prevents an uneven reflection of the structured light used during scanning. For image aquisition we used an InEos X5 (Sirona Gmbh, Germany) scanner, equipped with a light source with structured blue light, which provides an International Journal of Medical Dentistry 63

3 Sorana BACIU, Cristian BERCE, Alexandru Victor BURDE, Marius MANOLE, Adrian FLOREA automatic emission of the incident light beam at 45º. HDR scanning mode was used to make multiple exposures and to enable shot selection. The design of inlays was established with the InLab software (Sirona Gmbh, Germany). The restoration parameters were: spacer 80 µ, occlusal milling offset = 0, minimal radial and occlusal thickness 800 µ, marginal thickness 70 µ. Morphology was re-established using the biogeneric individual function. For the milling phase, a HT - B2- I8 Empress CAD block and a 4-axis In Lab MCXL milling unit were used. Normal milling mode was applied with a cilindric pointed bur 12s and a step bur 12. The steps for investigating marginal gaps were standardized as in previous studies, being made on pressed lithium dilisicate inlays compared to Bio HPP inlays and milled inlays. The obtained reconstructions were placed into the cavities without cementation and the marginal gap was analyzed using a Skyscan 1172 desktop µct scanner (SkyscanBruker, Kontich, Belgium). Scanning was carried out at 80 kv, 100 µa using an aluminium and copper filter. The specimens were rotated 180º with a rotation step of 0.4º and an exposure time of 500 ms. The overall scanning time was approximately 75 min per specimen. The x-ray beam was irradiated perpendicularly to the preparation long axis, and the image pixel size was 6.92 μm. The x-ray projections were reconstructed using SkyScan s volumetric reconstruction software (Nrecon) that uses the set of acquired angular projections to create a set of cross section slices through the object. Reconstructed slices were saved as a stack of BMP-type files. The CTAn software (Skyscan, Aartselaar, Belgium) was used to obtain cross-section images through the center of the teeth (Z-axis) and also to perform measurements using the line measurement tool. The images were inspected and the marginal gap of each inlay was analyzed in horizontal sections, at the occlusal margin of each restoration, circumferentially, by measuring the distance between the restoration and the tooth in 100 µm steps. For electronic microscopic scanning, aluminium holders of 10 mm/ø9 mm (from Bio- Rad, USA) were covered with carbon bioadhesive tabs (from Electron Microscopy Sciences, USA) on which the four molars were positioned vertically, keeping all 4 samples at a sufficient distance from the lens of the microscope. Next, a drop of colloidal silver (Agar Scientific, Austria) dropped with an automatic pipette (200 μl) Brand (Brand GmbH, Wertheim, Germany) was used to establish the electric conductivity between the surface of the coverslips and the metallic holders. The colloidal silver was dried and the holders were introduced into a Polaron E-5100 sputter coater. In the chamber of the sputter coater, under high vacuum and argon atmosphere, the teeth were covered with a thin layer of several nm of gold atoms (at 2400 V and 20 ma for 45 sec) [9]. Fig 2a. Samples fixed on holders moistured with colloidal silver. 2b samples sputterd with gold 64 Volume 7 Issue 1 January / March 2017

4 THE MARGINAL FIT OF MILLED-CERAMIC INLAYS A COMPARATIVE THREE DIMENSIONAL AND MICROSCOPIC RESEARCH Table 2. Measurement number: MicroCT and SEM technique on teeth restored with milled inlays Sample MicroCT milled inlays SEM milled inlays M M M M SEM examination of the metalized samples was carried out with a Jeol JSM-25S scanning electron microscope operating at 25 kv, and magnifications of 45 x. For the milled inlays between 245 and 383, measurements were made, depending on the volume of each sample. Olympus MicroImage Programme was used to analyze the obtained data, which were subsequently included in the statistical study. Figure 3a. SEM image and measurements 3b. Comparison of the number of measurements milled inlays using 3b SEM and MicroCT image-horizontal section For both types of materials on each tooth there were measured: the lowest and the highest values with both analyzing methods, and the average values and standard deviation were calculated for each of the four inlays. Statistical analysis was carried out on 8 columns of values (in two sets of 4). The results for the ceramic inlays on the 4 molars were compared with One way ANOVA with Tukey s Multiple Comparison Test performed using 5.00 for Windows (GraphPad Prism 5.00 Software, San Diego, California USA). The statistical program also expressed values by comparing each molar with others, displaying data for the same and for different evaluation methods. 3. RESULTS The lowest and highest values of the gaps are listed in the tables below for CAD CAM analyzed by both methods. Sample Table 3. Minimal and maximal gaps CAD CAM measured with SEM and micro CT SEM CAD CAM Minimal gap MicroCTCAD CAM minimal gap SEM CAD CAM Maximal gap MicroCT CAD CAM Maximal gap M1 21, M M M International Journal of Medical Dentistry 65

5 Sorana BACIU, Cristian BERCE, Alexandru Victor BURDE, Marius MANOLE, Adrian FLOREA We calculated de average and standard deviation on all 4 teeth, examined by the two different evaluation methods. Table 4. Comparison of average and standard deviation for CADCAM measured by microct and SEM µ CT M1 Cad Cam SEM M1 µct M2 SEM M2 µct M3 SEM M2 µct M4 SEM M4 Average Std dev Statistical analysis was carried out for each method employed. The statistics was realized on 8 columns of values (in two sets of 4). The results for the 8 inlays on the 4 molars were compared with One way ANOVA with Tukey s Multiple Comparison Test performed using 5.00 for Windows (GraphPad Prism 5.00 Software, San Diego, California USA). Table 5. Statistical analysis of ANOVA and Tukey s test for CAD CAM Analyzed table Data 1 One-way analysis of variance P value P< P value summary *** Are the mean values signifcantly different? (P < 0.05) Number of groups 8 Yes F 15.4 R squared Bartlett s statistics (corrected) 75.3 P value P< P value summary *** Do variances differ significantly (P < 0.05)? Yes ANOVA Table SS df MS Treatment (between columns) Residual (within columns) Total Tukey s Multiple Comparison Test Mean Diff. q Significant? P < 0.05? Summary 95% CIofdiff CADCAM MCT1 vs CADCAM SEM Yes *** t-4.53 CADCAM MCT1 vs CADCAM MCT No ns CADCAM MCT1 vs CADCAM SEM No ns CADCAM MCT1 vs CADCAM MCT No ns CADCAM MCT1 vs CADCAM SEM Yes *** CADCAM MCT1 vs CADCAM MCT No ns CADCAM MCT1 vs CADCAM SEM Yes * CADCAM SEM1 vs CADCAM MCT Yes *** CADCAM SEM1 vs CADCAM SEM Yes *** µm CADCAM MCT1 CADCAM MCT2 CADCAM SEM1 Data 1 CADCAM MCT3 CADCAM SEM2 CADCAM MCT4 CADCAM SEM3 CADCAM SEM4 66 Volume 7 Issue 1 January / March 2017

6 THE MARGINAL FIT OF MILLED-CERAMIC INLAYS A COMPARATIVE THREE DIMENSIONAL AND MICROSCOPIC RESEARCH CADCAM SEM1 vs CADCAM MCT Yes ** CADCAM SEM1 vs CADCAM SEM No ns CADCAM SEM1 vs CADCAM MCT No ns CADCAM SEM1 vs CADCAM SEM No ns CADCAM MCT2 vs CADCAM SEM No ns CADCAM MCT2 vs CADCAM MCT No ns CADCAM MCT2 vs CADCAM SEM Yes *** CADCAM MCT2 vs CADCAM MCT No ns CADCAM MCT2 vs CADCAM SEM Yes *** CADCAM SEM2 vs CADCAM MCT No ns CADCAM SEM2 vs CADCAM SEM Yes *** CADCAM SEM2 vs CADCAM MCT No ns CADCAM SEM2 vs CADCAM SEM Yes *** CADCAM MCT3 vs CADCAM SEM Yes *** CADCAM MCT3 vs CADCAM MCT No ns CADCAM MCT3 vs CADCAM SEM No ns CADCAM SEM3 vs CADCAM MCT No ns CADCAM SEM2 vs CADCAM MCT No ns CADCAM SEM2 vs CADCAM SEM Yes *** CADCAM MCT3 vs CADCAM SEM Yes *** to CADCAM MCT3 vs CADCAM MCT No ns to 6.66 CADCAM MCT3 vs CADCAM SEM No ns to CADCAM SEM3 vs CADCAM MCT No ns to 18.7 CADCAM SEM3 vs CADCAM SEM No ns to 12.3 CADCAM MCT4 vs CADCAM SEM No ns to DISCUSSION 5. CONCLUSIONS Acceptable clinical values were obtained for the marginal gap. The scores found out with both investigation methods are comparable with the ones quoted in the literature. As the results show, the values for the minimal and maximal gap are very close for all molars when using micro CT and SEM. There were no significant discrepancies in statistical meaning when measuring the marginal adaptation on two out of the four molars, namely on the second and fourth molar, but there appeared a statistical significance for the first and third molar. Generally, the scores registered using SEM were lower for the minimal gap compared to micro CT and higher for the maximal gap and average values, which means that our null hypothesis was rejected. The use of aesthetic inlays is increasing due to improvements registered in the mechanical properties of ceramic materials. Milled leucite ceramic materials also assure a good marginal adaptation, a natural color and even higher mechanical resistance than other ceramic materials. SEM analysis is a nondestructive investigation which allows measuring of the marginal gaps without sectioning. Also, it does not need to enhance the contrast of the samples. Micro CT, on the other hand, offers better information, yet at higher costs, so that it is not available to all scientific researches. Our comparative study scored acceptable values of the marginal gap for both investigation methods, ranging within the accepted clinical International Journal of Medical Dentistry 67

7 Sorana BACIU, Cristian BERCE, Alexandru Victor BURDE, Marius MANOLE, Adrian FLOREA limits quoted in the international literature. Both analyzing methods offer reliable results and can help clinicians to improve the quality of their restorative treatments. References 1. Fasbinder DJ. Multi-Center Trial: Margin Fit and Internal Adaptation of CEREC Crowns. In: Mörmann WH, editor. State of the Art of CAD/CAM Restorations, 20 Years of CEREC. Berlin: Quintessence;2006, Poster. 2. Posselt A, Kerschbaum T. Longevity of 2328 chairside CEREC inlays and onlays. Int J Comput Dent Jul;6(3): Reiss B. Eighteen-Year Clinical Study in a Dental Practice. In: Mörmann WH, editor. State of the Art of CAD/CAM Restorations, 20 Years of CEREC. Berlin: Quintessence;2006. pp Hopp CD, Land MF. Considerations for ceramic inlays in posterior teeth: a review. Clin Cosmet Investig Dent. 2013;5: Baciu S, Florea A, Manole M, Alb C, Pirte A, Rusu LC, Sinescu C. An electron microscope comparative study of the marginal fit of cast metal crowns using several waxing techniques and different cervical preparation techniques. Materiale Plastice. 2015;52(2): Baciu S, Florea A, Manole M, Roman A, Alb S, Alb C, Pirte A, Sinescu C. Importance of waxing techniques for the marginal fit of cast metal crowns. a scanning electron microscope technique study. Materiale Plastice. 2015;52(3): Varvara AM, Varvara EB, Culic B, Gasparik C, Burde A, Diana D. Ceramica feldspatică frezabilă CADCAM. Proceedings of Napoca Biodenta International Symposium; Cluj Napoca: Colorama Publishing House; pp Scientific Documentation IPS Empress CAD [Internet] [updated 2011 October; cited 2016 February 5]. Available from:ips Empress CAD Scientific Documentation - Ivoclar Vivadent 9. Preparing samples for the electron microscope [Internet] [updated 2012 February 29; cited 2017 January 15]. Available from: sciencelearn.org.nz/resources/500-preparingsamples-for-the-electron-microscope 68 Volume 7 Issue 1 January / March 2017