66 



A MANUAL OF DENTAL ANATOMY. 



In fresh dentine every formative cell sends a process into 

 the dentinal tubes (Tomes, Kolliker, Lent, Waldeyer, Neu- 

 mann), and it has been found possible to demonstrate both 

 the sheaths and the fibres in the same sections (Neumann, 

 Boll). 



In transverse and even in longitudinal sections of decalci- 

 fied dentine the fibrils may be recognised in situ (Kolliker). 



The contrast between the dentinal sheaths and the fibrils 

 is this : the sheaths are very indestructible, and can be 

 demonstrated in teeth which have undergone all sorts of 



FIG. 29 0). 



change ; the soft fibril is no longer demonstrable when the 

 tooth has been placed in circumstances which would lead 

 to its soft parts perishing. In dentine, then, we have (i.) a 

 matrix permeated by tubes ; (ii.) special walls to these tubes 

 or "dentinal sheaths ;" and (iii.) soft fibrils contained in 

 these tubes, or " dentinal fibres ; " and it now remains to 

 consider these in farther detail. 



In fortunate sections of small fragments of dentine taken 

 from the edges of the pulp cavity and including the surface 

 of the pulp, the dentinal fibrils may be seen stretching from 

 the cells of the superficial layer of the pulp (odontoblasts) 

 into the dentinal tubes, as owing to these being extensile 

 they may be stretched or drawn out from the tubes for some 

 little distance without being broken across. In the same 



(*) Section of dentine from the edge of which hang out the dentinal 

 sheaths, and beyond these again the fibrils (after Boll). 



