Development and evaluation of porous dental implants in miniature swine

Organized bone ingrowth in endosteal porous implants fabricated from VMC titanium alloy and surgically implanted with a tight interference fit, securely anchored the implants in fresh and healed mandibular premolar sites of miniature swine. This bone-implant union retained its integrity under high as well as slight masticatory stresses up to one-year after implantation. Bone invasion of the alumina porcelain implants was impeded by the lack of adequate interconnecting porosity; when the porosity was increased, insufficient ceramic strength prohibited a tight initial bone-implant fit. As a consequence, inadequate initial implant stability resulted in a soft tissue encapsulation of the majority of the ceramic implants. Histological examination and mechanical testing results were similar for bone-ingrown implants exposed to different experimental stresses for 4, 5, 8, and 12 months. Bone ingrowth and interface shear strengths were also similar in the different VMC pore sizes and shapes investigated. The design of intraoral attachments appeared critical, at least in swine where no postoperative treatment was administered. Gingival inflammation and alveolar bone resorption caused by calculus were severe around truncated cone-shaped devices. Slender transgingival posts, occlusal caps, and crown restorations were less susceptible to calculus accumulation, resulting in a more satisfactory gingival and subgingival response. Excessive epithelial invagination was a problem only in implants with transgingival truncated cones. Good adherence of soft tissue to metal under the gingival mucosa prevented epithelial migration around implants with other transgingival devices. Alveolar bone resportion around the tops of bone-ingrown implants was minimal at the time intervals examined (up to one year); however, a definite conclusion should be delayed until longer-term implants under full occlusion are evaluated.