title: Flexural strength of small connector designs of zirconia-based partial fixed dental prostheses.
abstract: BACKGROUND
  Partial fixed dental prostheses with a small connector size are required for optimal esthetics and limited interarch space; however, final strength is endangered.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the effect of different connector designs on the flexural strength of simulated 3-unit partial fixed dental prostheses made of yttria-stabilized tetragonal zirconia polycrystalline using computer-aided design and computer-aided manufacturing technology.
  
  
  METHODS
  To simulate a 3-unit partial fixed dental prosthesis, 20 rectangular bar-shaped specimens were fabricated with dimensions of 4 ± 0.05 mm (H) × 4 ± 0.05 mm (W) × 30 0.5 mm (L). Each bar specimen had 2 constricted parts on both sides, representing the connector and defining a central pontic of 10 ± 0.10 mm in length. The specimens were divided into 4 groups according to the connector diameter and design, as follows: SR: 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; SS: 2 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature; CR: 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; and CS: 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature. An additional 5 specimens were fabricated with no constriction and served as the control group. The specimens were subjected to a 3-point flexural strength test in a universal testing machine with a crosshead speed of 0.5 mm/min until failure. Scanning electron microscopic and photomicrograph images were used to examine the fracture surfaces. Two-way ANOVA and the Tukey-Kramer post hoc test were used to analyze the data (α = .05).
  
  
  RESULTS
  The mean flexural strength for SR 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (583.6 ± 49.7 MPa) was significantly higher than that of SS, which was 2 mm (H)× 3 mm (W) sharp 0.1 mm radius of curvature (502.8 ± 23.3 MPa). Similarly, the mean flexural strength for CR was 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (682.9 ± 36.8), which was significantly higher than that of CC, 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature (486.7 ± 35.6 MPa).
  
  
  CONCLUSIONS
  The flexural strength of the yttria-stabilized tetragonal zirconia polycrystalline-based ceramics was affected by the connector dimension and design. The 2-round connector design was more able to withstand occlusal forces than the sharp design. The 3-connector design with a minimum cross section of 2 × 3 mm is recommended for anterior fixed dental prostheses, provided it has a round curvature.
authors.affiliation: Associate Professor, Crown and Fixed Prosthodontics Department, Faculty of Dental Medicine, Al-Azhar University, Cairo, Egypt. Electronic address: drtamerhamza@hotmail.com.
authors.forename: Tamer A
authors.initials: TA
authors.lastname: Hamza
authors.affiliation: Lecturer, Crown and Fixed Prosthodontics Department, Faculty of Oral and Dental Medicine, Beni Suef University, Cairo, Egypt.
authors.forename: Mazen A
authors.initials: MA
authors.lastname: Attia
authors.affiliation: Professor, Crown and Fixed Prosthodontics Department, Faculty of Dental Medicine, Al-Azhar University, Cairo, Egypt.
authors.forename: Mohamed Mahmoud Khalil
authors.initials: MM
authors.lastname: El-Hossary
authors.affiliation: Professor, Fixed Prosthodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia.
authors.forename: Ihab E
authors.initials: IE
authors.lastname: Mosleh
authors.affiliation: Associate Professor, Crown and Fixed Prosthodontics Department, Faculty of Dental Medicine, Al-Azhar University, Cairo, Egypt.
authors.forename: Tamer E
authors.initials: TE
authors.lastname: Shokry
authors.affiliation: Section Head, Maxillofacial Prosthodontics, Veterans Affairs Nebraska Western Iowa Health Care System, Omaha, Neb.; and Special Professor, Department of Prosthodontics, Creighton University School of Dentistry, Omaha, Neb.
authors.forename: Alvin G
authors.initials: AG
authors.lastname: Wee
mesh_terms: D003776:Dental Porcelain; D003799:Dental Stress Analysis; D003830:Denture, Partial, Fixed; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003776:Dental Porcelain; D015040:Zirconium