الفهرس 
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Abstract
Research is one of the most important tools to guide us, dentists, through our daily clinical decisions. One of the common and very controversial clinical cases is bruxism and its related consequences.
To study bruxism, a method of simulating one year of physiological chewing movements and parafunctional movements of sleep bruxism was developed. Physiological chewing was performed in a chewing simulator and parafunctional movements were performed in a special device attached to the universal testing machine designed to exert lateral loads.
Excessive tooth wear is the main sign of bruxism, usually treated conservatively by occlusal veneers. In this study, occlusal surfaces of sixty posterior teeth were cut flat to receive occlusal veneers of three CAD/CAM materials: IPS e.max CAD, Vita Enamic and Bruxzir. All occlusal veneers had non-anatomical occlusal surfaces with a minimum thickness of 1.5 mm at the position of the central fossa, two flat occlusal planes and a 150° angle between them.
The fabrication process started with scanning of teeth in the Identica hybrid 3D dental scanner followed by designing of the occlusal veneers in the DentalCAM software, milling them out of the three CAD/CAM materials in a 5-axis dry and wet CAD/CAM milling machine, vhf S1, and firing them for crystallization/sintering (with the exclusion of Vita Enamic). Surface treatment of teeth and of the fitting surface of occlusal veneers was done for each material according to its manufacturer’s instructions and an MDP-containing resin cement (Panavia F2.0) was used for cementation. Samples were finished, polished and mounted in the center of a customized sample holders with acrylic resin covering 1 mm above the CEJ.
Half the samples were statically loaded with a cross-head speed of 0.25 mm/min in the lateral loading device in the universal testing machine. The other half was first aged in a chewing simulator for 300,000 cycles at an average load of 50 N and a loading frequency of 4 Hz, before accelerated lateral fatigue loading was run. The load applied started from 50 N and increased linearly at a loading frequency of 4 Hz till 500 N, to complete 115,200 cycles over a duration of 8 hours. Both, fast fracture and fatigue tests, were run until failure occurred. Load and number of cycles at failure were recorded; mean and standard deviations were calculated and statistically analyzed. Weibull analysis was then performed to compare the reliability of the three materials.
Acoustic emission monitoring was done throughout the fast fracture and fatigue tests. A measurement, display and storage equipment were connected to a preamplifier and further connected to a broad band acoustic emission sensor. The sensor was placed as close as possible to the tooth, to capture any acoustic signals emitted from the sample. Acoustic emission parameters such as energy, amplitude, counts and average frequency were saved and plotted for a parameter-based acoustic emission analysis.
All specimens survived the chewing simulation without any cracking, ceramic chipping or fractures. Results of both, the fast fracture and the fatigue tests, revealed that the type of material had a statistically significant effect on the performance of occlusal veneers during lateral loading. Comparison between the groups shows no statistical significance between IPS e.max CAD and Vita Enamic. It is the difference between Bruxzir and the two other materials, that showed high statistical significance, with Bruxzir showing the highest values. Weibull analysis revealed a higher Weibull modulus of fatigue for Vita Enamic, which makes it more reliable than the two other materials. Through acoustic emission monitoring a faster progression to failure was seen in debonded Bruxzir samples as well as in fractured Vita Enamic samples. Fracture of Bruxzir and IPS e.max CAD proved to be a slower process with gradual increase of AE signals.
The null hypothesis, that there was no difference between the three restorative materials used as occlusal veneers for bruxism-simulated dynamic loading, was rejected as clear differences in their behavior were evident.