Temporal and local appearance of alkaline phosphatase activity in early stages of guided bone regeneration - A descriptive histochemical study in humans

Alkaline phosphatase (ALP) catalyzes the hydrolysis of phosphate esters and it seems to be a prerequisite for normal skeletal mineralization. Also, AL P is the most widely recognized marker of osteoblast phenotypes. By a tissu e regenerative technique called Guided Bone Regeneration (CBR), it is possi ble nowadays to regenerate small bony defects. The aim of the present study was to investigate early events in bone healing and neogenesis by studying histochemically the temporal and local appearance of the marker Alkaline P hosphatase (ALP) in a GBR model system. Nine healthy volunteers (5 males, 4 females, mean age 31.7 years) participated in the experiment. After raisin g a mucoperiosteal flap from the mandibular second molar to the retromolar area in each volunteer, a hollow titanium test cylinder was placed into a c ongruent bony bed and the coronal end of the cylinder was closed with an eP TFE-membrane. Then the flap was adapted and sutured to obtain primary wound closure. After 2, 7 and 12 weeks, the regenerated tissue within the cylind ers was harvested. Histologically, ALP activity was observed associated wit h the osteoid seams in the very basal part of the regenerate where new bone trabeculae were in the process of being formed. More coronally, large roun d cells seemed to secrete an ALP-positive substance since in the center of such cell clusters strong ALP activity located extracellularly was detected . In the present experiment, ALP seemed to have been an early sign of osteo blast secretion of a matrix which subsequently was determined to become ost eoid. ALP activity was never seen isolated within connective tissue and awa y from bone. This is an indication that its source is linked to existing bo ne. The present study has documented for the first time the appearance of A LP activity in guided bone regenerations in humans. It has revealed that: 1 ) Osteogenesis in guided bone regeneration is preceded by localized, marked expression of ALP in an organized connective tissue environment. 2) Bone n eogenesis is an early event in this experimental setup and may be detected already 2 weeks after wounding. 3) Expression of ALP and subsequent bone ne ogenesis is originating from and topographically linked to pre-existing bon e structures.