Relationship between compressive strength and cervical shaping of the all-ceramic Cerestore crown

The two types of cervical shaping recommended for the preparation of Cerestore crowns are shoulder or deep chamfer. 14 specimens shaped like stylized Cerestore crowns on a shoulder preparation and 14 on a deep chamfer preparation were produced. Thereafter each crown was placed on the epoxy resin die on which it had been produced. 7 epoxy dies from each of the two series were shortened 1 mm occlusally in order to elucidate the importance of the cervical shaping. Placed on its own epoxy die each of the 28 Cerestore crowns was then subjected to occlusal stress until fracture occurred. The force needed for fracture was three times greater for the crowns produced on a shoulder preparation than for those produced on a chamfer preparation. No significant differences was obtained when crowns with the same cervical shaping were tested on intact and shortened dies respectively.