Noura. Mokhtar ; Samir. Zidan And Ashraf. Taher,
ABSTRACT
Statement Of The Problem: When Dental Ceramic Materials Are Exposed To The Oral Environment, They May Undergo Physicochemical Alterations. The Incidence Of Repeated Forces During Chewing Results In Stress Concentration, And Thermal Variations Induce Fatigue Of The Materials. Thus, Restorations Are Prone To Catastrophic Failure When Subjected To Stress. Efforts To Enhance The Service Life Of All-ceramic Materials Have Been Undertaken To Improve Their Strength (s) And Fracture Toughness (KIC).
Purpose: The Aim Of This Study Was To Evaluate The Fracture Toughness And Hardness Of Vita Suprinity CAD/ CAM With And Without Cyclic Loading And Thermocycling.
Materials and Methods: A Total Of 24 Vita Suprinity Plates Of 3mm Thickness Were Cut By An Isomet Cutting Machine. All The Specimens Were Sintered And Then Auto-glazed According To Manufacturer?s Instructions. All Specimens Were Stored In Distilled Water At 37oC For 24 Hours In Sealed Containers In Incubator. Half Of The Specimens Were Exposed To Thermal Cycling With Number Of Cycles Was 500 Cycle , Dwell Times Were 25 S. In Each Water Bath With A Lag Time 10 S. And The Low-temperature Point Was 5 0C). The High Temperature Point Was 55 0C,and Also Were Exposed To Cyclic Loading In Chewing Simulator Machine In Which Twelve Specimens Of Experimental Ceramic Group Were Exposed To The Mouth-motion Fatigue At Load Of 50 N For 20,000 Cycles With A Frequency Of 1.6 Hz. The Other Half Was Left Without Any Aging Procedures. Surface Hardness And Fracture Toughness Were Measured Before And After Storage Where The Surface Hardness Was Measured Through Vicker?s Indentation By Using This Equation. HV=1.854 P/d2. Fracture Toughness Was Calculated By The Indentation Method Through This Equation. KIC = 0.016(E/H) 0.5 (P/c1.5).
Results: It Was Found That: Aging Procedure Affected On Vickers Hardness Mean Value Significantly. It Was Found That The Highest Mean Value Of Hardness Recorded At Baseline Then After Water Storage While The Lowest Mean � SD Value Of Hardness Recorded After Thermo-mechanical Aging. The Difference Was Statistically Significant. It Was Found That Aging Procedure Affected On Fracture Toughness Mean Value Non-significantly. It Is Found That The Highest Mean Value Of Fracture Toughness Recorded At Baseline Then After Thermo-mechanical Aging While The Lowest Mean � SD Value Of Fracture Toughness Recorded After Water Storage. The Difference Was Statistically Significant.
Conclusions: From The Findings Of Our Study, Ageing Procedure With Thermocycling And Cyclic Loading Negatively Affected The Surface Hardness And Cause Non-significant Increase In The Fracture Toughness Of Vita Suprinity.
