CEMENTOGENESIS REVIEWED - A COMPARISON BETWEEN HUMAN PREMOLARS AND RODENT MOLARS

Background: Cementum continues to be the least-known mineralized tissu e. Although recent advances in the field of molecular biology have con tributed to an understanding of the involvement of molecular factors i n cementum formation during development and regeneration, cementogenes is on a cell biological basis is still poorly understood, Virtually no thing is known about cementoblast origin, differentiation, and the cel l dynamics during normal development, repair, and regeneration. This r eview describes the recent findings of cementogenesis on roots of huma n premolars and opposes them to those of teeth from other mammals, par ticularly the rodent molar. Methods: Using light and electron microsco py, light microscopic radioautography, and various measurements, a com prehensive insight into the development and repair of cementum during and after root formation and tooth eruption has been achieved for huma n premolars. Results: Cementum is a highly responsive mineralized tiss ue. This biological activity is necessary for root integrity and for b ringing and maintaining the tooth in its proper position. With regard to cementum formation and periodontal fiber attachment, considerable s pecies-particularities exist that are mainly based on differences in g rowth rates and tooth sizes. Since root development and initial cement ogenesis last on the average 5-7 years in human premolars, cementum fo rmation in these teeth is characterized by a long-lasting phase of pre functional development, which occurs independent of principal periodon tal fiber attachment to the root and which may take 5 years or more. T he first molar of the rat, however, is in functional occlusion 3 1/2 w eeks after the onset of root formation. Since initial cementum formati on and periodontal fiber attachment to the root occur almost at the sa me time in this tooth, the distinction between cells associated with o ne or the other process is very difficult to achieve, and cementogenes is cannot be described independent of periodontal fiber attachment to the root. Therefore, the determination of cementoblast origin in the r odent molar may be intricate. Conclusions: Taking into account these s pecies differences, the current description on the origin and differen tiation of cementoblasts is inconsistent and the description of cement ogenesis is still incomplete. This review calls into question the curr ently held concept of cementogenesis and offers a possible alternative . (C) 1996 Wiley-Liss, Inc.