R. M. Frank: Ultrastructurc of Human Dentine 259 



Ultrastructure of Human Dentine 



R. M. Frank 

 Institut Dentciire, Facultc dc Medecine, Strasbourg, France 



1. Introduction 



An extensive literature has been published on the structure and ultrastructure of 

 adult dentine and, through the use of different but convergent techniques, fairly 

 good agreement has been reached concerning the structure and ultrastructure of 

 calcified dentine. One of the main results of recent research, obtained through 

 classical methods of investigation as well as through histochemistry, microradio- 

 graphy, electron microscopy and diffraction has been the recognition of the true 

 nature of the tubular wall. This peritubular zone is more calcified than the inter- 

 tubular dentine, but both regions possess the same inorganic constituent, namely 

 apatite crystals. 



However, a certain number of problems remain unresolved among which the 

 ultrastructure of the adult odontoblast and its process, and the precise contents of the 

 dentinal tubules at different levels within the dentine have yet to be defined. Another 

 important though controversial point is the innervation of dentine and predentine. 

 Whereas, there is a general agreement concerning the presence of myelinated and 

 unmyelinated nerve fibres in the dental pulp as observed with light and electron 

 microscopy, the presence of unmyelinated nerve fibres in the predentine and dentine 

 has alternatively been confirmed and denied by a number of authors using light, or 

 polarizing microscopy. With the electron microscope, no nerve fibres could be located 

 at either of these sites, so that serious doubts have been raised concerning the specifi- 

 city of the silver Impregnation In the Identification of nerve fibres in dentine (Ander- 

 son, 1963). 



The purpose of this report Is not only to review our present knowledge of the 

 ultrastructure of adult dentine but, through improvements of fixation and embedding 

 techniques, new observations will be presented concerning the ultrastructure of human 

 adult dentine and predentine with special emphasis on the odontoblast and its 

 process. For the first time, unmyelinated nerve fibres will be described under the 

 electron microscope In the predentine and dentine. 



2, Technical remarks 



Erupted normal premolars from young people 12 to 15 years old, extracted for 

 orthodontic reasons, were immediately cleaved into small pieces. After 5 to 10 

 minutes fixation In phosphate buffered glutaraldehyde solution (Sabatini et ai, 

 1963), the coronal dentine fragments were postfixed in P/o phosphate buffered osmic 

 acid solution (Millonig, 1961). The tissue blocks irrespective of their degree of 

 calcification were embedded in Epon 812 (Luft, 1961) and cut with a Servall-Porter 

 microtome, equipped with a diamond knife. The ultrathin sections were observed 

 under an electron microscope "Optique et Precision de Levallois", unstained or 

 Impregnated with lead citrate (Reynolds, 1963). In some cases uranyl acetate In 

 saturated fresh alcoholic solution was used alone or followed by lead citrate staining. 

 Adjacent thick sections of Epon-embedded blocks, stained with toluldine blue, were 

 examined under the light microscope for purposes of orientation and comparison. 



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