pressing the vessel against the bone until clot formation begins is not sufficient, the area should be exposed for ligation of the artery.

Veins

A knowledge of venous anatomy is important in implantology to minimize undesirable surgical consequences, including infection. Major vessels should be avoided during implant surgery. Efficient drainage of a surgical site, facilitated by intact vessels, minimizes swelling and promotes healing.

The blood can flow in any direction in facial and cranial veins because these vessels lack valves and many, particularly the intracranial, are modified into sinuses with rigid walls. Thus an infection originating in the oral cavity can spread rapidly along open pathways toward the brain with serious consequences. Infection is always a concern in dental procedures that interupt oral epithelium, as implant surgery surely does. However, practicing sanitary procedures familiar to all dentists minimizes the danger. Furthermore, efficient antibiotic therapy can retard or prevent undesirable consequences. As for the presence of the implant it-self, a stable implant — endosteal or subperiosteal — has been shown repeatedly to have a tight elastic cuff similar to a false periodontal membrane around the posts protruding into the oral cavity. This cuff seals the site against microbial invasion and infection.

The venous pathways are highly irregular in the oral cavity and face. Generally each artery is accompanied by one or more veins which are closely associated with the artery. However, their pathways may diverge, and numerous anastamoses between veins may form a network of small veins that replaces more prominent single venous companions to an artery.

Eventually venous blood is drained from the head and neck almost entirely by the internal jugular vein (1). The internal jugular vein, the largest vein by far in the head and neck, merges with the subclavian vein in the upper part of the chest. These two form the innominate, or brachiocephalic, vein. The right and left innominate veins unite into the superior vena cava, which returns blood to the heart for recirculation.

Those veins forming the most direct pathways away from mandibular implant sites are the common facial (2) and the retromolar veins (3). The anterior facial vein (4), so called to distinguish it from its continuation below the mandibular angle —

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