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Abstract
This study was designed to study effect of different preparation designs on
the vertical marginal gap distance, fracture resistance and retention of
different CAD/CAM ceramic endocrowns compared to fiber post and core supported crowns.For vertical marginal gap distance and fracture resistance tests, sixty teeth were divided into six groups of ten samples each, according to the type of restoration.For retention test, thirty teeth were divided into six groups of five samples each. Same designs and types of restorations for the previous tests were used for the retention test. All ceramic endocrowns and crowns were constructed from IPS Empress CAD and IPS e.max CAD ceramic materials. The crowns were cemented over their respective teeth with adhesive resin cement.The vertical marginal gap distance was measured after cementation using a Stereomicroscope connected to a computer and a digital camera. Measurements were made at twenty points for each crown. In order to mimic the intraoral conditions, all the specimens were subjected to thermal cycling and fatigue loading in a pneumatic fatigue device. Mechanical fatigue was performed for 1,200,000 cycles in a water bath subjected to temperature changes between 5oC and 60oC for 2 minutes immersion time in each dwelling temperature and 2 minutes drying time. The vertical marginal gap distance was re-measured at the same points using stereomicroscope to determine the effect of thermal cycling and fatigue loading. Fracture resistance was determined by applying a single static compressive load using a universal testing machine. Retention was measured by dislodging the crowns along the long axis of the tooth using the same universal testing machine. Within the limitations of this study, the following conclusions can be drawn:1- Endocrowns were found to be a successful mean of restoring mutilated endodontically treated posterior teeth.2- Endocrown preparation with 1mm ferrule can be the design of choice to achieve a higher fracture resistance in high stress bearing areas. 3- All tested endocrown designs with both materials proved to have a clinically acceptable marginal gap distances. 4- Preparation geometry for endocrown designs is a crucial factor for the retention of this kind of restorations.