AbstractsEngineering

Objectives: The present thesis was conducted to characterize a novel dental CAD/CAM restorative material, based on two interpenetrating networks of ceramic and polymer. The novelty of the material is defined by its structure. Some natural biomaterials such as spongy bone and dentin exhibit interconnected dual phase structures enhancing the mechanical properties under loading. The goal during development of the novel material (PICN; polymer-infiltrated-ceramic-network) was to emulate the structure of natural materials and thereby resulting in superior characteristics compared with traditional dental restorative materials. The major objective of this study was the assessment of the suitability and characteristics of the novel PICN material intended for dental restorations by means of comparative in-vitro studies. The specific objectives were to determine and identify correlations between flexural strength, strain at failure, elastic modulus and hardness versus ceramic network densities of a range of PICN materials. Furthermore to determine the damage tolerance of these materials, by comparing the strength degradation, following various sharp and blunt contact indentation loading situations. The response of the PICN materials is compared with a range of dental CAD/CAM ceramic materials and the results are discussed in terms of the factors contributing to the toughness of these different materials. In addition the damage tolerance and strength degradation after typical clinician and technician adjustments of PICNs and comparative materials was simulated in-vitro by utilizing different bur grinding procedures. Methods: First, a literature review was undertaken to identify the structural and mechanical behavior of existing dental CAD/CAM materials as well as materials based on interpenetrating networks. Dental and non-dental interpenetrating phase composites as well as biomaterials were included. Secondly, experimental in-vitro studies were carried out for a range of PICNs and comparative dental materials: a) Four experimental porous feldspar ceramic network densities ranging from 59 % to 72 % of theoretical density, resin infiltrated PICN as well as pure polymer and dense feldspar ceramic cross-sections were subjected to Vickers indentations for hardness evaluation. The flexural strength and elastic modulus were measured using three-point-bending. The fracture response of PICNs was determined for cracks induced by Vickers indentation. Scanning electron microscopy (SEM) was employed to observe the indented areas and material structures. b) A comparative study with an number of existing CAD/CAM materials (Mark II, PICN test material 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ; all VITA Zahnfabrik, Bad Saeckingen, Germany) and (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein) was conducted. Bending bars were cut and lapped. The initial flexural strength was determined in three-point-bending. To evaluate the damage tolerance, Vickers indentations were placed on the bending bars with varying loads (1.96…