Fracture load and chewing simulation of zirconia and stainless-steel crowns for primary molars Kist S, Stawarczyk B, Kollmuss M, Hickel R, Huth KC. Fracture load and chewing simulation of zirconia and stainless-steel crowns for primary molars. Eur J Oral Sci 2019; 00: 1–7. © 2019 Eur J Oral Sci Aesthetic alternatives to stainless-steel crowns for restoring primary molars attain growing interest. We studied the mechanical properties of prefabricated zirconia crowns and conventional crowns. Three brands of prefabricated zirconia crowns were compared with computer-aided design/computer-aided manufacturing (CAD/ CAM) zirconia crowns, preveneered stainless-steel crowns, and conventional stain- less-steel crowns regarding: (i) fracture load under each of three conditions [no pre- treatment, artificial aging in saliva for 12 wk, and after chewing simulation/ thermocycling (1.68 9 10 6 cycles/5–55°C)]; and (ii) survival rate during chewing simulation, considering decementation, fracture, chipping, fatigue cracks, and occlu- sal holes. Without pretreatment, the prefabricated zirconia crowns showed mean fracture load values between 893 N and 1,582 N, while the corresponding values for CAD/CAM zirconia crowns and preveneered stainless-steel crowns were 2,444 N and 6,251 N. Preveneered stainless-steel crowns showed significantly lower fracture loads after artificial aging (5,348 N after saliva aging; 3,778 N after chew- ing simulation) than without artificial aging, whereas the fracture load of zirconia crowns was not influenced negatively. The survival rate of the different groups of zirconia crowns and preveneered stainless-steel crowns during chewing simulation was 100%, but only 41.7% for the stainless-steel crowns. These in-vitro data suggest that prefabricated zirconia crowns are aesthetically and durable alternatives to stain- less-steel crowns for primary molars. Stefan Kist 1 , Bogna Stawarczyk 2 , Maximilian Kollmuss 1 , Reinhard Hickel 1 , Karin C. Huth 1 1 Department of Conservative Dentistry and Periodontology, University Hospital,LMU Munich, Munich; 2 Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany Karin C. Huth, Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestrasse 70, 80336 Munich, Germany E-mail: khuth@dent.med.uni-muenchen.de Key words: aesthetic restoration; ceramic crowns; primary dentition; prosthetic restoration Accepted for publication May 2019 The preservation of primary teeth until physiological exfoliation is of high importance because of their space maintenance and chewing function. Dental restorations of primary teeth should be time and cost efficient, and also easy to carry out, as young patients usually have only a limited period of cooperation during treatment. Prefabricated stainless-steel crowns are often used in cases of extensive decay after pulpotomy treatments. However, parents and patients prefer tooth-coloured restorations because of the increasing importance of aesthetics (1). In previous studies, composite strip crowns, preve- neered stainless-steel crowns, and zirconia crowns proved to be highly satisfactory regarding colour, size, and shape (2–5). As far as durability is concerned, there are differences between these materials. In the case of strip crowns, 10% of the restorations showed small areas of material loss and 2% showed large areas of loss, after an average period of 18 months (2). The overall parental satisfaction was 78%. Reports on veneer fractures of preveneered stainless- steel crowns are associated with a considerable decrease in parental satisfaction (3). After 1 yr, 9% of the posterior crowns fractured on the buccal surface and 23% fractured on the occlusal surface. However, after 3 yr the occurrence of fractures on the buccal and occlusal surfaces increased to 24% and 42%, respec- tively. In clinical studies, prefabricated zirconia crowns seem to demonstrate the highest durability (5, 6). WALIA and coworkers reported that 100% of zirconia crowns, 95% of preveneered stainless-steel crowns, and 78% of resin composite strip crowns were intact after 6 months (6). Loss of material was observed in 5% of the restorations in the preveneered stainless-steel crown group as well as in the strip crown group. Additionally, 17% of the strip crowns showed total loss of the restoration. In another clinical study, two of 44 zirco- nia crowns debonded after 21 months on average; how- ever, no chipping or fracture was observed (5). So far, mean values have been reported for the frac- ture load of prefabricated zirconia crowns for posterior use; these range from 576 N (Kinder Krowns, St Louis Park, MN, USA) to 1,091 N [Sprig Oral Health Tech- nologies (formerly Ez-Pedo), Loomis, CA, USA] (7). Preveneered stainless-steel crowns showed much higher Eur J Oral Sci 2019; 1–7 DOI: 10.1111/eos.12645 Printed in Singapore. All rights reserved © 2019 Eur J Oral Sci European Journal of Oral Sciences