Microvascular corrosion casting of the rat mandibular joint: a technical approach

The rat mandibular joint is a ginglymoarthrodial joint deeply hidden under the zygomatic process of the squamosal bone. This joint was studied by scanning electron microscopy (SEM) of microvascular corrosion casts in 47 adult rats. Six additional rats were injected with India ink and thick sections of the joint area were examined by light microscopy. The small size of the joint (2.5 mm x 1.5 mm in occlusion), the existence of two slit-like joint compartments, the close proximity of bones and soft tissues in a mobile structure, and the intimate relationships of the joint with adjacent skeletal muscles made the vascular mapping difficult. Five different technical procedures (protocols) were tested. The most satisfactory approach is, briefly, as follows: each rat was injected simultaneously via both common carotid arteries with 9.5 ml of casting medium (Mercox-CL-2B diluted 4:1 with monomeric methyl methacrylate), and with an additional volume of 0.5 ml of the same medium after ligation of the external jugular veins used for outflow. After polymerization of the injected resin, the rats were frozen, and the heads were severed and spliced sagittally into two halves. These specimens were cut in the transversal (coronal) and sagittal planes into small blocks. Each block was then cut systematically either in the transversal or parasagittal plane running through the joint. Afterwards thick slices were macerated in warm (45 degrees C) 15% KOH, rinsed, (some were decalcified in 2% HCl), rinsed again in tap water, frozen in distilled water, freeze-dried, mounted, dissected, coated and examined under the SEM at 5 kV.