[Alumina reinforced porcelain jacket crown].
Aluminum oxides provide one of the most useful sources of high-strength and high-modulus crystals. New types of high alumina content glasses may replace feldspathic porcelains. Esthetics compare favorably.
Which all-ceramic system is optimal for anterior esthetics?
BACKGROUND
As ceramic materials for dentistry evolve and patients' demand for esthetic restorations increases, practitioners must keep up with the science as well as the demand. The authors offer guidance to the practitioner in selecting the appropriate all-ceramic systems for crowns when faced with different esthetic demands.


CONCLUSIONS
Clinicians should reserve dental ceramics with high translucency for clinical applications in which high-level esthetics are required and the restoration can be bonded to tooth structure. Ceramics with high strength tend to be more opaque and pose a challenge when trying to match natural tooth color, but they can mask discoloration when present.


PRACTICE IMPLICATIONS
Knowledge of the optical properties of available ceramic systems enable the clinician to make appropriate choices when faced with various esthetic challenges.
Strength of Silica Glass
GRIFFITH1 extrapolated from his experiments the strength of glass to the order of 1,000 kp./mm.2, which is many times larger than the strength of the best steel. Orowan2 calculated from mechanical principles a value of the same order. More recent measurements, however, gave a much higher value for several silica-glass fibres, namely, 2,460 kp./mm.2 (ref. 3) ; therefore a calculation based on the atomic structure of glass seems to be important.