title: Effect of spherical silica additions on marginal gaps and compressive strength of experimental glass-ionomer cements.
abstract: OBJECTIVE
  To clarify the effects of the addition of silanized (S) and unsilanized (U) spherical silica filler to resin-modified glass-ionomer cement and of powder-liquid ratio on (1) the early marginal gap-width of restorations in both tooth cavities and Teflon molds, (2) the gap-formation of restorations in Class V cavities, and (3) the compressive strength of the cement.
  
  
  METHODS
  Resin-modified glass-ionomer powder (Fuji II LC EM, GC) was modified by adding 5 and 10 wt% of powder respectively, of S and U, and then the powder-liquid ratio was increased up to 4.8. Human premolars, extracted for orthodontic reasons, were used for this study. Cylindrical cavities (1.5 mm deep, 3.5 mm in diameter; one cavity was prepared in each tooth in the coronal region and medial surface) were prepared in extracted human premolar teeth and restored with resin-modified glass-ionomer cements. Each restoration margin was inspected immediately after curing and polishing (as the immediate condition was the most severe), the maximum gap-width and the opposing width (if any) were determined microscopically (n = 10). An additional test was conducted in model Class V cavities. After finishing of restorations in model Class V cavities, each tooth was sectioned in a bucco-lingual direction through the center of the restoration, and the presence or absence of gaps along the cavity interface was evaluated (n = 10). Additionally, the maximum marginal gap-width and the opposing-width along margins of restorations in cylindrical Teflon molds were measured (n= 10). The compressive strengths of the restorative materials were determined immediately after light-activation (n = 10).
  
  
  RESULTS
  Marginal gap (tooth cavity: 0.32 to 0.25-0.20%, P < 0.05; Teflon cavity: 0.94 to 0.6-0.8%, P < 0.05) and cavity adaptation (no gap in the Class V: 22 to 40-50%, P < 0.05) of the restorations improved with increasing powder-liquid ratio (3.0 to 4.4-4.8) and compressive strength increased (111 to 150-170 MPa, P < 0.05). Highly significant correlation coefficients were found for the relationships between powder-liquid ratio and (1) percentage of marginal gap width in the tooth cavity (r = -0.96, P = 0.002, n = 6), (2) gap-free tooth/cement interfaces (r = 0.90, P = 0.015, n = 6), (3) percentage of marginal gap widths in the Teflon mold (r = 0.98, P = 0.0004, n = 6) and (4) compressive strengths of the cements (r = 0.95, P = 0.004, n = 6).
authors.affiliation: Department of Biomaterials, Okayama University Graduate School of Medicine, Dentistry and Phamaceutical Sciences, 2-5-1, Shikata-cho, Kita-ku, Okayama 700-8525, Japan. mirie@md.okayama-u.ac.jp
authors.forename: Masao
authors.initials: M
authors.lastname: Irie
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nagaoka
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tamada
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Maruo
authors.forename: Goro
authors.initials: G
authors.lastname: Nishigawa
authors.forename: Shogo
authors.initials: S
authors.lastname: Minagi
authors.forename: Werner J
authors.initials: WJ
authors.lastname: Finger
mesh_terms: D000180:Acrylic Resins; D001641:Bicuspid; D019245:Compressive Strength; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000145:classification / Q000379:methods*; D003799:Dental Stress Analysis; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D011208:Powders; D012822:Silicon Dioxide / Q000737:chemistry*; D014867:Water
chemical_list: D000180:Acrylic Resins; C493638:Fuji II LC EM; D005899:Glass Ionomer Cements; D011208:Powders; D014867:Water; D012822:Silicon Dioxide