Regeneration of Periodontal Ligament for Apatite-coated Tooth-shaped Titanium Implants with and without Occlusion Using Rat Molar Model

Regeneration of periodontal ligament (PDL) is still a major issue in implant dentistry. In this study, we evaluated the effects of hydroxyapatite (HA) coating and occlusion on the regeneration of PDL around tooth-shaped titanium implants with root form. Three groups of tooth-shaped titanium implants, namely, non-HA-coated without occlusion (HA-/OCL-), HA-coated without occlusion (HA+/OCL-), and HA-coated with occlusion (HA+/OCL+), were immediately implanted into extracted tooth sockets with remaining PDL of rat molar model and the regeneration of PDL was examined histomorphometrically and histologically. Direct bony attachments were formed at the HA+/OCL- implant interface. In contrast, soft peri-implant tissue was distinctly seen between the HA+/OCL+ implant surface and surrounding alveolar bones. The shape of the load-time curve for the HA+/OCL+ group was similar to that for natural teeth. Peri-implant tissue of the HA+/OCL+ implants exhibited alkaline phosphatase with a distribution and activity similar to those of the PDL. Collagen fiber bundles were found functionally oriented in some regions of the peri-implant tissue. These findings indicate that the remaining PDL tissue around extracted sockets has the ability to regenerate bone and PDL-like tissues on HA-coated tooth-shaped implants. Occlusal loads to the HA-coated implants may induce regeneration of PDL-like tissue in the peri-implant tissue.