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ORTHODONTICS BONDING ORTHODONTIC RESIN CEMENT TO ZIRCONIUM OXIDE UNDER ORTHODONTICS LOAD AND THERMOCYCLING EFFECT Hind S. Hussein 1a , Nader Abdulhameed 1b , Chiayi Shen 1c , Calogero Dolce 2d , Jean-François Roulet 1e* Department of Restorative Dental Sciences, College of Dentistry, University of Florida Department of Orthodontics, College of Dentistry, University of Florida 1 2 BDS, Courtesy Clinical Assistant Professor BDS, MS, PhD Student, Clinical Assistant Professor c PhD, Associate Professor d DDS, PhD, Professor e Dr med dent, Dr hc, Professor, Director of Center for Dental Biomaterials a, b ABSTRACT DOI: 10.25241/stomaeduj.2018.5(2).art.4 Purpose: Evaluate the microshear bond strength (µSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) under orthodontic load (OL) and thermocycling (TC) effect. Materials and Methods: Glazed MZ blocks (Zenostar, Ivoclar Vivadent) were tested after air abrasion with 30-µm silica coated aluminum oxide (Al 2 O 3 ) particles (CoJet, 3M ESPE). The specimens were randomly divided into 4 groups (n = 15): G1, OL with TC; G2, OL without TC; G3 no OL with TC; and G4, no OL, no TC (control). Orthodontic cement cylinders (Heliosit Orthodontic, Ivoclar Vivadent) were bonded to the primed samples (Monobond Plus, Ivoclar Vivadent) using the Ultradent SBS system and light cured (SmartLite Max, Dentsply Sirona, 1400 mW/cm 2 , 40 s). G1 and G2 were subjected to 70 ± 15 N load perpendicular to the cylinder axis, G1 and G3 were thermo-cycled (5000 cycles 5-55°C, 90 s/cycle). G2 and G4 were stored in distilled water at 37 ± 1°C. The specimens were subjected to µSBS test (crosshead speed 0.5 mm/min). Data were analyzed using two-way ANOVA, and one-way ANOVA and Tukey test (HSD). Results: Two-way ANOVA for µSBS values (MPa) showed significant (p = 0.0004) load effects, but not thermal effect (p = 0.2455) with significant load/thermocycling interactions (p < 0.0001). The ranking of the single groups by Tukey test (α = 0.05) showed that G1 exhibited the highest µSBS (8.4 ± 2.8 MPa), G4 (6.3 ± 1.1 MPa) and G2 (5.8 ± 1.1 MPa) as a group was second, and G2 and G3 (4.7 ± 1.1 MPa) as a group was the lowest. Conclusion: G1, which is the closest to clinical reality, yielded the best results. Keywords: orthodontics, dental materials, orthodontic resin cement, monolithic zirconium oxide ceramic, microshear bond strength test. 1. Introduction Due to the patients’ increased esthetic demands and the development of technology in dental materials, porcelain fused to metal (PFM) crowns and bridges are being replaced by glass based ceramic materials and monolithic Zirconium oxide (MZ) [1]; they are more esthetic, biocompatible, resistant to wear, show low thermal conductivity, and are color stable [2]. However, despite these advantages, the brittle nature of these materials restricts their use [3]. Therefore, there is a need for new materials which have the same esthetic properties as glass based all ceramic materials and a strong framework like PFM for fixed dental prosthesis (FDPs). The introduction of zirconium oxide fulfilled these requirements [4]. The advantages of zirconium oxide include high fracture resistance and high flexural strength (> 1000 MPa), which allowed for thinner restorations. Furthermore the material can be stained which allows better esthetic results [5]. These properties make it a very good candidate for aesthetic FDPs. The tetragonal zirconia polycrystals (TZP), especially 3 mol % Y 2 O 3 stabilized zirconia (3Y-TZP) has been used as a material for dental and medical 102 OPEN ACCESS This is an Open Access article under the CC BY-NC 4.0 license. Peer-Reviewed Article Citation: Hussein HS, Abdulhameed N, Shen C, Dolce C, Roulet J-F. Bonding of orthodontic resin cement to zirconium oxide under load and thermocycling. Stoma Edu J. 2018;5(2):102-108. Academic Editor: Diana Dudea, DDS, PhD, Professor, “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj-Napoca, Cluj-Napoca, Romania Received: May 28, 2018 Revised: June 06, 2018 Acccepted: June 11, 2018 Published: June 12, 2018 *Corresponding author: Professor Jean-François Roulet, DMD, PhD, Dr hc Center for Dental Biomaterials, College of Dentistry, University of Florida 1395 Center Drive, Room D9-26, Gainesville, FL 32608 Gainesville, FL 32608, USA Tel: [phone]; Fax: [phone], e-mail: [email protected] Copyright: © 2018 the Editorial Coun- cil for the Stomatology Edu Journal. restorations [6]. Previous studies have reported that the life expectancy of (3Y-TZP) zirconium oxide when compared to PFM FDPs for posterior indication, is shorter because of the delamination and chipping of veneering ceramic; to overcome this problem, the monolithic zirconium oxide (MZ) was introduced to the dental market [1,2,4,7]. Full contour MZ FDPs are produced using CAD/CAM technologies. The restorations are milled from blocks which can be used either glazed or polished for better esthetic results [8]. Although polishing may provide sufficient esthetic appearance by decreasing the surface roughness, technicians like to glaze the ZrO 2 surface to improve the esthetic properties. With this process, the glass will infiltrate the zirconium oxide [9]. Since the number of adult patients who have been seeking orthodontic treatment is increasing [9], it means that the orthodontist will sometimes apply orthodontic brackets on dental restora