STRUCTURE AND ORIGIN OF THE TOOTH PEDICEL (THE SO-CALLED BONE OF ATTACHMENT) AND DENTAL-RIDGE BONE IN THE MANDIBLES OF THE SEA BREAMS ACANTHOPAGRUS-AUSTRALIS, PAGRUS-AURATUS AND RHABDOSARGUS-SARBA (SPARIDAE, PERCIFORMES, TELEOSTEI)

Scanning electron and light microscopy were used to show that the pedi cels of fish teeth (the so-called ''bones of attachment'') consist of three types of dentine that lie concentrically around a pulp cavity li ned with typical odontoblasts with cytoplasmic processes in dentinal t ubules. Circumpulpal canalar dentine forms on a thin layer of orthoden tine that is encased in mantle dentine. Canalar dentine is a new name given to a dentine that is similar to vasodentine in canal arrangement , but not apparently in canal content. An inner series of wide, radial canals and an outer series of highly-branched thin canals of two diam eters are inhabited by a population of cells, the osteodentocytes, and collagen fibril bundles. The flat, oval osteodentocytes appear to be quiescent cells, lying on the sides of the tubules and covered by a sh eath. Plump, intensely metachromatic osteodentocytes appear to be more synthetically active. The canals and the osteodentocytes originate fr om blood capillaries enclosed in the predentine during dentinogenesis. New teeth begin within the small cavities present in spongy bone that were enlarged by multinucleated osteoclasts during tooth growth. Pedi cel formation is initiated by the extension of the crown mantle dentin e, forming the outer layer of the crimped ligament and outlining the f uture length and curvature of the pedicel. Central and inner ligament zones are subsequently formed as orthodentine is secreted in both crow n and pedicel, and canalar dentine in the pedicel. Spongy bone osteoge nesis begins during stage 1 of pedicel formation with the aggregation of osteoblasts and blood capillaries in the bone cavities and in the d ermis between the pedicels. Loose fibrillar osteoid condenses into inc omplete thin trabeculae bordered by intensely metachromatic osteoblast s. Osteoblasts become enclosed in the developing trabeculae that thick en to give mature spongy bone with osteocytes throughout. We conclude that the pedicels are the true bases of teeth, that the dental ridge i s formed from pedicels and spongy bone, and that sea bream spongy bone is cellular. The term ''bone of attachment'' is inappropriate for the pedicel. It can be used for the spongy bone between the compact bone of the jaw and between adjacent pedicel.