Effect of nano-ceramic fibers on fracture toughness of In-Ceram Alumnina ceramics

Abstract

Dental ceramics are attractive materials because of their natural appearance, durable chemical properties, optical properties and biocompatibility. However, brittleness and low tensile strength represent a major weakness of some dental ceramic materials. Interpenetrating phase ceramics were developed to provide sufficient strength and toughness for use as all-ceramic fixed partial dental prostheses (FPDPs) and posterior crowns. In-Ceram Alumina ceramics (Vita Zahnfabrik, Bad Sackingen, Germany) was the first member of this class of dental ceramics. The material has favorable esthetics and strength, combined with a successful clinical history. However, this material possesses insufficient mechanical properties for use as a substructure for posterior 3-unit FPDPs. Objectives 1 -To reinforce In-Ceram Alumina ceramic material by adding alumina nano-fibers in an attempt to inhibit crack propagation. 2-To measure the fracture toughness of the reinforced material by using the single-edge-notched-beam technique. Materials and Methods: In-Ceram Alumina blocks (VITA In-Ceram Alumina BA-28) were cut to form bars with the following dimensions: 2 mm x 4mm x 28 mm. A mixture of alumin nano-ceramic fibers (Angonide, Sanford, USA) and In-Ceram Alumiina powder (Vita Zahnfabrik) was applied between 2 alumina In-Ceram bars joining the 2 bars to form a thick bar having, between the 2 bars, a layer of alumina powder with nano-fibers. A total of 120 bar specimens were subdivided into 2 groups according to sintering temperatures, 1120 degrees C and 1350 degrees C. Then, each group was subdivided into 6 sub-groups, a control group (n=10) and 5 test groups (according to the group’s fiber content of 5 %, 10 %, 20%, 30 % and 40 % weight %).A notch, 0.4 mm wide and 0.3 to 0.4 mm in depth, was created on 1 side ; then glass infiltration was performed according to the manufacturer's recommendation. The specimens were loaded in a 3-point bending fixture by using a universal testing machine (Model # 4202; Instron Corp, Canton, Mass.) with a 10-kN load cell at 0.5-mm/min cross-head speed. Bars were placed so that the notch was in maximal tension. Fracture toughness was then calculated according to the following equation: KIc = [3 LPa^5 /2 bw^2] x/(a/w) Where (P) is the fracture load in a 3-point bending test, (L) is the span tested, (a) is the depth of the notch, (b) is the width of the specimen, (w) is the height of the specimen, and / (a/w) is an extended series which provides the geometric correction of the single-edge-notched-beam technique, 3 –point bend specimens. Results: The fracture toughness of the In-Ceram Alumina ceramics sintered at 1120 degree C increased significantly when 5 %, 10 %, and 20 % nano-fiber content was added. The fracture toughness values were 4.69 MPa[nu]m, 5.21 MPa[nu]m, 4.635 MPa[nu]m respectively compared with the control group, which was 3.73 MPa[nu]m. Increasing the fiber content to 30 % or 40 % did not significantly increase the fracture toughness compared to the control group. When a sintering temperature of 1350 degrees C was used, the addition of nanofibers, in any concentration, did not significantly improve the fracture toughness of In-Ceram Alumina ceramics. Conclusion: Adding 5, 10 or 20 weight % of nano-fibers to In-Ceram Alumina powder, sintered at 1120 degree C , significantly increased fracture toughness values (P = 0.004), (P[less than] 0.001), (P = 0.008) respectively.