Dental ceramics can fail through growth of microscopic surface flaws t
hat form during processing or from surface impact during service. New
restorative dental ceramic materials have been developed to improve re
sistance to crack propagation. Eleven of these improved materials with
the common feature of a considerable amount of crystalline phase in t
he glassy matrix were evaluated. The ceramic materials studied include
d fluormica-, leucite-, alumina-, and zirconia-reinforced glasses. The
relative hardness and fracture toughness were determined by indentati
on technique. Alumina-reinforced materials resulted in the highest fra
cture toughness values, whereas the fluormica and leucite-reinfoced ma
terials showed more moderate but statistically significant greater val
ues compared with those of control materials. The hardness values of c
eramic materials with improved fracture toughness were both substantia
lly higher or lower than those of the control groups and suggested a l
ack of direct correlation between these two properties. Selection of a
ppropriate restorative materials depends on clinical application and r
equires consideration of several physical properties including fractur
e toughness.