The substitution of between 0 and 1.6 wt% silicon (Si-HA) in hydroxyapatite (HA) inhibited densification at low temperatures (1000degrees-1150degreesC), with these effects being more significant as the level of silicon substitution was increased. For higher sintering temperatures (1200degrees-1300degreesC), the sintered densities of HA and Si-HA compositions were comparable. Examination of the ceramic microstructures by scanning electron microscopy (SEM) showed that silicon substitution also inhibited grain growth at higher sintering temperatures (1200degrees-1300degreesC). The negative effect of silicon substitution on the sintering of HA at low temperatures (1000degrees-1150degreesC) was reflected in the hardness values of the ceramics. However, for higher sintering temperatures, e.g., 1300degreesC, where sintered densities were comparable, the hardness values of Si-HA compositions were equal to or greater than that of HA, reflecting the smaller grain sizes observed for the former.