La mortalidad de alevines

Areas of contact between Apoceram and bone show a variety of ultrastructural features. Figure 4.30 shows the direct attachment of an osteocyte on the surface o f the glass ceramic material. The cell is well spread on the implant surface and surrounded the other side by a matrix of mineralised collagen. There is no distinct direction of orientation of collagen fibres in this region in which osteocytes vdth cell processes are embedded in the matrix. Also present on the implant surface are polygonal osteoblasts with matrix vesicles and secreting collagen. A zone of osteoid, in which collagen fibres are clearly distinguishable, surrounds the secretory osteoblast and more electron dense mineralised matrix appears adjacent to this, extending along the surface of the implant material (Figure 4.31). In areas where osteoid was in contact with the implant surface, collagen fibres with characteristic banding can be seen immediately adjacent to the glass ceramic remnants without an intervening afibrillar zone. (Figure 4.32)

There are also areas where the implant surface is covered by one or multiple layers of loosely packed flattened cells. These cells frequently show signs of degeneration. (Figure 4.33)

A small number of the ultrathin sections contained parts of the multinucleated giant cells attached to the surface of the Apoceram particles. Numerous lysosomal granules are present in their cytoplasm. (Figures 4.34, 4.35)

In areas where more heavily mineralised matrix was adjacent to the Apoceram implant surface, the calcified material either appears to be continuous with the glass ceramic particles (Figure 4.36) or shows several other distinctive features at the interface zone. At x40,000 magnification, there were globular calcified deposits, often fused together, which were continuous with the Apoceram particles. Needle-like mineral aggregates as well as amorphous electron dense globules were interspersed between collagen fibrils at the interface zone (Figures 4.37, 4.38). Another type of interface arrangement showed this spherical calcified material adjacent to mineralised collagen matrix which was separated from the Apoceram particles by a layer o f loosely arranged fibrils (Figure 4.39).

43.4.2 Titanium

The tissue-titanium interface was represented by an electron dense line in the TEM sections presented. Some osteoblasts lie directly on this line, with osteoid laid down on the other sides of the cell (Figures 4.40 to 4.42). Mineralised bone matrix was separated from the electron dense line by a zone o f collagen fibres and a band o f fibrillar material around SOOnm thick, with a reticular appearance (Figures 4.43 and 4.44).

Figure 4.30 An osteoblast (o) on the surface o f Apoceram (gc) is being surrounded by

mineralised matrix (mm). Two osteocytes with cell processes (cp) can be seen within the bone matrix. Collagen fibres in cross- section can be seen at the top o f the field. Field width: 25 pm

Figure 4.31 The osteoid and mineralised matrix surrounding this osteoblast on Apoceram (gc) can be differentiated by the different levels o f electron density. Collagen fibres are visible within the osteoid (os) but not discernable where they are more heavily mineralised (mm). Matrix vesicles are present in the cytoplasm o f this bone form ing cell (arrow). Field width: 25pm

Figure 4.32 Apoceram. Collagen fibres at different orientation surrounding a lacuna containing the cell process o f an osteoblast.

Osteoid in direct apposition against the glass ceramic (gc) particles. # collagen fibres in longitudinal section. * collagen fibres in cross-section. Field

Figure 4.33 Apoceram. The presence o f ceramic particles (gc)

at the top o f the field reflects the preservation o f the interface.

The implant surface is covered by several elongated cells showing signs o f degeneration. Field width: 14pm

%

4

Figure 4.34 Part o f a

multinucleated giant cell on the surface o f Apoceram (gc). Two nuclei (n) are visible with many electron dense lysomal granules in the cytoplasm (*). m -

mineralised matrix. Field width: 17.5pm

Figure 4.35 Part o f a multinucleated giant cell attached to the surface o f an Apoceram implant (gc). Arrows:

lysosomal granules. Field width: 8.75 pm

Figure 4.36 Dense mineralised matrix (mm) making direct contact with Apoceram. The arrows indicate a continuous layer o f the glass ceramic remaining attached to the mineralised matrix following sectioning. Field width: 35pm

Figure 4.37 Apoceram (gc). Needle-like mineral aggregates (s) amongst the collagen fibres. The glass ceramic is continuous with amorphous globular deposits (g), collagen fibres (c) with characteristic banding intermingle with the mineral deposits. Field width: 1.75pm

Figure 4.38 Apoceram (gc). Fused globular mineral deposits continuous with the glass ceramic particles. Isolated spheres o f mineral (arrow) interspersed among banded collagen fibres (f) on a background o f thin fibrillar material. Field width: 1.75pm

Figure 4.39 Apoceram. A less dense fibrillar zone (f) is present between the mineralised matrix and the glass ceramic particles (gc). Spherical mineral deposits are present along the edge o f the calcified collagen matrix (me). Field width: 3.5pm

I'

Figure 4.40 Titanium. A continuous electron dense line at the metal interface with the tissue (arrows). Collagen fibres within a band o f osteoid

surround the cytoplasm and part o f the nucleus (n) o f this

osteoblast on the implant surface. A small area o f mineralised matrix (m) can be seen at the bottom right o f the field. Field width: 7pm

It»''

Figure 4.41 Titanium. Mitochondria (m) and rough endoplasmic reticulum (r) in the cytoplasm surrounding the nucleus (n) o f this osteoblast surrounded by osteoid (os) at the interface, i - implant space. Field width: 8.75pm

*

Figure 4.42 Titanium. Electron dense secretory granules (sg) within the cytoplasm o f a secretory cell depositing collagen (c). mm- mineralised matrix. Arrows - interface. Field width: 7f^m

Figure 4.43 Titanium. A layer o f loose fibrils with a reticular appearance (f) lies between the titanium surface and collagen fibres (c) on the surface o f the

mineralised matrix (mm). Arrows - electron dense line at the interface. Field width: 2.6pm

Figure 4.44 Titanium. Unmineralised layer with thin fibrils (f) between the titanium

surface (arrow) and collagen fibres (c)overlying the

mineralised matrix (m). Field width: 2.6pm

4.4 Discussion