Margin Fracture Strength of Two Different Ceramic Inlays

Method: A master die with a MOD preparation was fabricated in stainless steel with a corresponding stainless steel form with a 45^o and 60^o angled surface. The master die was duplicated in resin with a modulus of elasticity similar to dentin. Wax patterns were made on resin dies and the stainless steel angled form was heated and passed over the wax patterns to produce the desired occlusal angles of 45^o and 60^o. The patterns were sent to a dental laboratory to fabricate inlays from IPS Empress and e.max ceramic. The inlays were seated in the dies, fit was checked and they were cemented with adhesive resin cement (Nexus 3). The specimens were stored in a dark humidor for 48 hours before testing. Four groups of 10 samples each: A: 45^o/IPS e.max, B: 45^o/IPS Empress, C: 60^o/IPS e.max and D: 60^o/IPS Empress were tested. A rod with a 1mm diameter radius, mounted in an Instron testing machine was used to apply compressive loads on buccal and lingual margins of the restoration within 1mm of the interface at 0.5mm/min crosshead speed until fracture. 

Result: Data was statistically described and analyzed (2-way ANOVA, independent t-test, p<0.05). A statistically significant difference was found between the 2 materials and the 2 occlusal angled surfaces. Mean load values were: 465N (e.max/45^o), 357.6N (Empress/45^o), 388.35N (e.max/60^o) and 215.8N (Empress/60^o). e.max/45^o inlays and Empress/45^o were significantly stronger than e.max/60^o and Empress/60^o respectively.  In addition, e.max/60^o was significantly stronger than Empress/60^o and e.max/45^o stronger than Empress/45^o. 

Conclusion: e.max ceramic inlays had higher margin fracture strength than Empress at both 45^o and 60^o. The 45^o inlays were stronger than the 60^o inlays for both e.max and IPS Empress.