Evaluation of internal fit, marginal integrity and fatigue resistance of E-max CAD crowns on two different preparation designs for maxillary anterior teeth. An Invitro study

Statement of the problem: Preservation of the cingulum in anterior teeth have been recommended however with recent ceramic restorations its contribution to internal adaptation and fatigue resistance needs further study.
Objective: The purpose of this in-vitro study was to evaluate the internal fit, marginal integrity and the fatigue resistance of E-max CAD crowns on two preparation designs for maxillary anterior teeth.
Material and methods: Twenty defect free human maxillary central incisors were prepared to receive E-max CAD ceramic crowns. 10 samples were prepared with parallel labiolingual wall (anatomic) group A and 10 samples were prepared with elimination of the cingulum (non-anatomic) group B. Scanning was done using powder free Identica hybrid scanner (Medit 02855] 23, Inchon-ro 22-gil, Seongbuk-gu, Seoul, Korea), designing was made by Exocad software version 2016 (Exocad Gmbh Julius-Reiber-Strabe 37, 64293 Darmstadt, Germany) then the restoration was milled by Roland DWX-510 milling machine (15363 barranca Parkway Irvine, California 92618) from E-max CAD blocks (LT) (Ivoclar Vivadent AG, 9494 Schaan, Princiability of Liechtenstein). Internal fit, marginal adaptation was measured before cementation using replica technique on prepared tooth using stereomicroscope. Duplication of the preparation was made in order to get epoxy resin dies for crown cementation, then restorations were cemented on the corresponding epoxy resin die and marginal adaptation was reevaluated under stereomicroscope. Specimens were then subjected to thermomechanical aging using four stations multimodal ROBOTA chewing simulator (Model ACH-09075DC-T, AD-TECH TECHNOLOGY CO., LTD., GERMANY) followed by fatigue resistance measurement using universal testing machine (Model 3345; Instron Industrial Products, Norwood, MA, USA).
Results: It was found that group B recorded statistically significant (P<0.05) higher marginal gap mean value (29.7±3.97 µm) than group A (25.39±3.24 µm) as indicated by unpaired t-test before cementation while after cementation it was found that group B recorded statistically non-significant (P>0.05) higher marginal gap mean value (37.15±5.34 µm) than group A (34.2±4.84 µm). while for the internal adaptation it was found that group A recorded statistically significant higher internal gap mean value (91.93±17.41 µm) than group B (57.97±14.08 µm). It was found that Group B recorded statistically non-significant higher fatigue resistance mean value (1130.58±31.53N) than Group A (1114.84±45.04N).
Conclusion: Different preparation designs affect the marginal adaptation of the restoration which was statistically significant only before cementation. The non-anatomic group (B) showed statistically significant lower internal gap than anatomic group (A). While there was no significant difference in the fatigue resistance of both groups after thermocyclic loading.