Zygomatic and mandibular augmentation with proplast and porous hydroxyapatite in rhesus monkeys

Using an extraoral approach, subperiosteal pockets were created bilaterally over the zygomatic and mandibular regions in six Rhesus monkeys. One side of each animal received a Proplast I (Vitek Inc, Houston) implant and the contralateral side received an equivalent sized block of porous hydroxyapatite (HA). The animals were followed clinically and radiographically. Two animals were killed postoperatively at 3, 6, and 12 months, respectively. The implants were retrieved en bloc and halved. Half of each specimen was decalcified, embedded in paraffin, and stained. The other half was embedded in plastic, and sections were stained or carbon-coated for histometry scanning under electron microscopy. Clinical evaluation revealed that porous HA implants were more stable than Proplast implants. The Proplast implants showed complete encapsulation by infiltration with fibrovascular connective tissue, and progressive fragmentation with giant cell reactions. The porous HA implants were united to the underlying cortex by bony ingrowth. The volume of implants sampled within 2.5 mm of the underlying cortex contained 42.5% HA matrix and 23.8% bony ingrowth, and the surface area of the HA matrix (9.7 mm2/mm3) was 47.8% covered by bony ingrowth. No giant cell response, fragmentation, or biodegradation was observed or measured in the porous HA implants. The data from this primate model further substantiate previous canine studies and permit more reliable estimation of clinical performance. These results provide comparative data that can contribute to the decision-making process in selecting clinical implants.