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and consistent to ensure that the final restoration is capable of withstanding the masticatory forces over extended periods of time. At Elos Medtech, our resources are dedicated to the development and manufacturing of the best possible components for dental restorations. Throughout the years, our extensive testing activities have revealed that the critical cementation process is more of an art than an exact science, with cementation jobs be- ing performed at different labs, or at different time points at the same lab, showing significantly differ- ent behavior when it comes to adhesive retention of the crown, even when the same cement systems are used. While studies are present in the scientific liter- ature [3-7], it is difficult to translate the effects of various surface pre-treatments and, thus, allow for eluting the performance of varying cement systems across different components. Based on this, the current study is intended to circle in on some of the critical aspects associated with the cementation process for the Elos Accurate Hybrid bases and to yield insights into which measures to employ for ensuring a consistent quality of the ce- mented interface, every time. The study utilizes the popular Panavia V5 dental cement and examines the influence of cementation gap size, different cleaning agents, blasting media size, and effects resulting from ageing of the cemented components, with re- spect to the adhesive strength of the hybrid base/crown interface. Materials and Methods Sample preparation The influence of cementation gap size, cleaning method, blasting media size, and ageing on the ad- hesive strength of the hybrid base/crown interface was examined via four sets of experiments. Common to all these experiments was the use of purpose- made ceramic crowns, manufactured from Zirconia (Lava ™ Frame Zirconia, REF: X-69222, 3M ESPE). The external geometry of the crown was designed to al- low for mounting the cemented part in a tensile test- ing machine, see Figure 1 for an overview of the test setup. Figure 1: Overview of the component design used for the various experiments. From bottom to top, the components are as fol- lows. (Dark gray) Implant analog, (Purple) Prosthetic screw, (Gray) Hybrid base, (Red) Cement and (light gray) ceramic crown. All groups were comprised of 15 specimens. The first experiment was designed to test the influ- ence of the cementation gap size on the mechanical retention of the hybrid base/crown assembly. To achieve this, the internal geometry of the crown was varied to obtain a gap distance between the cement- ing surface of the crown and the cementing surface of the hybrid base of either 20, 40, or 80 µm. Follow- ing manufacturing and sintering, the manufactured parts were measured to assess the precision of the components. Based on these measurements, the nominal dimensions of the cement gaps were 17±1, 40±2, and 79±2 µm. To prepare for the cementation process, the cementing surface of the crown was blasted using 50 µm (Edelkoround, Elstrøm Dental A/S, Denmark) at a pressure of 2 bar at a distance of 1 cm from the surface of the crown. Subsequently, excess blasting media was removed using a jet of compressed air. The crown and hybrid base were then cleaned by submerging the component in iso- propanol, 99.9% (Borup Kemi, Denmark) inside an ul- trasonic cleaning bath (Bransonic CPX1800-E, Emer- son Automation Solutions, Denmark) for a period of 5 minutes. Subsequently, the hybrid base was mounted on a compatible print model analog (PMA) (Elos Medtech, Denmark) before both parts were rinsed in mem- brane filtered water (RO water) and dried under a stream of oil free compressed air. All handling was performed using nitril gloves. The cementing surfaces of the crown and the hybrid base were then primed using Cerafil Ceramic Primer Plus 2

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(LOT:7L0055, Kuraray Noritake Dental Inc., Japan), in accordance with the manufacturer’s specifications. When the primer was dry, freshly mixed Panavia V5 Paste (LOT:7P0137, Kuraray Noritake Dental Inc., Ja- pan) was applied as a uniform layer, completely cov- ering the cementing surface of the hybrid base. Im- mediately after, the crown was placed on the hybrid base and excess cement was removed from the mar- gin and the screw channel. The components were then mounted in a jig, to ensure correct positioning during the curing step. Curing was performed by irradiating the cement with UV light (Bluephase G4 LED Curing Lamp, Ivoclar Vi- vadent, Liechtenstein) from four different positions around the interface line of the crown/hybrid base assembly. At each position, irradiation was per- formed for 20 seconds. Following irradiation, the as- sembly was left in the jig for 3 minutes. To assess the impact of different cleaning agents, hy- brid bases and ceramic crowns were cleaned using either steam, isopropanol, or the commercially avail- able cleaning agent, Katana Cleaner (Kuraray Nor- itake Dental Inc., Japan). For these tests, the gap dis- tance was kept constant at a width of 40 µm. The ce- mentation protocol utilized for these tests was iden- tical to the one used for the evaluation of the cemen- tation gap size; however, isopropanol was ex- changed for either steam or Katana Cleaner. Steam cleaning was performed using a steam cleaner (SU- PER STEAMER, Feinwerktechnik GmbH, Germany) at 6 bar and at a distance of 5 cm from the surface for one minute, ensuring even contact between the steam jet and the cementing surface of the parts. Cleaning using Katana Cleaner was performed in ac- cordance with the manufacturer ’ s specifications. The test to evaluate the influence of blasting media particle sizes was performed using either 50 or 100 µm particles (Edelkoround, Elstrøm Dental A/S, Den- mark) for the pretreatment of the crown cementing surface. The cementing surface of the hybrid base was not subjected to the blasting step. For this round of testing the Katana Cleaner was used and the re- maining steps of the cementation protocol was iden- tical to the previous tests. The last test series was performed to evaluate the effect of ageing of the cemented components. In this context, ageing is considered to be subjecting the ce- mented components to clinically relevant external factors that could potentially affect the properties of the cemented hybrid base/crown interface. Again, preparation was performed by subjecting the ce- menting surface of the crown to blasting with 50 µm particles, followed by cleaning of the cementing sur- faces using Katana Cleaner. The remaining cementa- tion protocol was performed as described for the other test series. Subsequent to cementation, the test groups were ei- ther stored at ambient condition for three weeks (Dry Storage) or kept hydrated inside a plastic bag, prior to being subjected to alternating temperatures under wet conditions (Thermocycling). Thermocy- cling was performed for 10,000 cycles during which the items were alternatingly dipped into water at temperatures of 5°C and 55°C using the Thermocy- cler 1100/1200 (SD Mechatronik, Germany). At each temperature, the items were submerged for 20 sec- onds. Mechanical testing Prior to performing the retention test, all specimens were subjected to steam sterilization at 134°C (Lina Sterilizer, PRO13-003-17, W&H, Denmark). Subse- quently, Items were mounted in a tensile testing ma- chine (H5K-S, Tinius Olsen, Denmark) equipped with a 5 kN load cell. Tensile testing was performed at an extension speed of 0.5 mm/min, until failure. The re- tention force was logged throughout the experiment and the maximum retention force was determined as the highest recorded value, prior to failure. Statistical analysis and data representation Data from the mechanical testing is represented as boxplots with median values represented by a bold black line, the interquartile range (IQR) is repre- sented by a gray box, and the first (Q1) and fourth (Q4) quartiles are represented by dotted lines with bars at the end. Outliers are marked by circles and are defined as values that are separated from the mean by at least 1.5 x IQR. Analysis for statistical sig- nificance for differences between the median values has been performed using a two-sided Mann Whit- ney U Test, with a confidence level of 0.95. All statis- tical analysis and plots have been prepared using RStudio (RStudio, Version 1.4.1717, PBC, Boston, MA). 3

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