Fracture toughness of three heat pressed ceramic systems - Fiorin, Livia; Theodoro, Guilherme Teixeira; Moris, Izabela Cristina Mauricio; Rodrigues, Renata Cristina Silveira; Ribeiro, Ricardo Faria; Faria, Adriana Cláudia Lapria (Brazilian Journal of Oral Sciences, 2018)