VERTICAL MARGINAL GAP DISTANCE AND RETENTION OF DIFFERENT CAD/CAM CERAMIC ENDOCROWNS WITH TWO PREPARATION DESIGNS

Statement of the problem: The rehabilitation of severely damaged coronal hard tissue and endodontically treated teeth has always been a challenge in reconstructive dentistry. These teeth have been shown to exhibit a significantly shorter service life and an increased failure rate when compared with vital teeth.
Objective: This study evaluated the vertical marginal gap distance and retention of bonded CAD/CAM Ceramic Endocrowns as a conservative alternative in endodontically treated molar teeth following thermal cycling and fatigue loading compared to post and core supported Ceramic crowns.
Methods: Ninty caries free human molar teeth were selected and mounted in epoxy resin blocks. For vertical marginal gap distance test, sixty teeth were assigned into six groups (n=10) according to type of restoration as follows; GroupI: Endodontically treated teeth incorporating 1mm ferrule restored with IPS Empress CAD endocrowns. Group II: Endodontically treated teeth incorporating 1mm ferrule restored with IPS e.max CAD endocrowns. Group III: Endodontically treated teeth without incorporating ferrule restored with IPS Empress CAD endocrowns. Group IV: Endodontically treated teeth without incorporating ferrule restored with IPS e.max CAD endocrowns. Group V: Endodontically treated teeth incorporating 1mm ferrule restored with glass-fiber posts, composite cores and IPS Empress CAD crowns serving as a control group. Group IV:Endodontically treated teeth incorporating 1mm ferrule restored with glass-fiber posts, composite cores and IPS e.max crowns serving as another control group. For retention test, thirty teeth were divided into six groups (n=5). Same designs and types of restorations for the previous test were used for the retention test. All teeth were sectioned perpendicular to the long axis 2mm coronal to the proximal CEJ and then subjected to a standard endodontic treatment. A special milling machine was used for teeth preparation. All-Ceramic endocrowns and crowns were constructed using the Cerec InLab system and cemented with Rely x ARC dual cure adhesive resin cement. The vertical marginal gap distance was measured after cementation using a stereomicroscope. Measurements were made at twenty points for each specimen. 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. The vertical marginal gap distance was re measured at the same points to determine the effect of thermal cycling and fatigue loading. Retention was measured by dislodging the crowns along the long axis of the tooth using a computer controlled universal testing machine. The recorded data were tabulated and statistically analyzed.
Results: Regarding the vertical marginal gap distance; endocrowns with 1 mm ferrule showed the statistically significant highest mean gap distance. There was no statistically significant difference between endocrowns without ferrule and post & core supported crowns. For endocrowns with 1 mm ferrule; Empress CAD scored statistically significant higher mean marginal gap values than e.max CAD. There was a statistically significant increase in mean gap distance after thermal cycling and fatigue loading for all test groups. Regarding the retention; endocrowns with 1 mm ferrule showed the statistically significant highest mean retention value. Post & core supported crowns showed statistically significant lower mean value. While, endocrowns without ferrule recorded the lowest mean retention value. In both endocrowns with 1 mm ferrule and post and core supported crowns e.max CAD scored statistically significantly higher mean retention values than Empress CAD, while for the endocrowns without ferrule there was no statistically significant difference between e.max CAD and Empress CAD.
Conclusions: Endocrowns represent a successful conservative alternative to post and core supported crowns for restoring mutilated endodontically treated posterior teeth. All tested endocrown designs with both materials proved to have a clinically acceptable marginal gap distances. Preparation geometry for endocrown designs is a crucial factor for the retention of this kind of restorations