Ceramics are commonly used in dental applications as restorative materials like crowns, cements, and dentures due to their hardness and wear resistance. Ceramics are also used in some orthopedic applications like bone repair and augmentation, but their use is more limited compared to metals and polymers because ceramics have poor fracture toughness. Alumina and zirconia ceramics are suitable for joint replacements and dentistry due to their high hardness, while hydroxyapatite is used for bone bonding surfaces in implants. Pyrolytic carbon is used in heart valves due to its biocompatibility, but it is brittle so cracks can propagate, potentially causing device failure.