|SECTION V||VESSELS ASSOCIATED WITH THE ORAL CAVITY (ARTERIES, VEINS, AND LYMPH VESSELS)|
The objectives for this section are to prepare the reader to perform the following:
- Trace blood through the major blood vessels (arteries) from the heart to the teeth and back (through major veins) to the heart.
- Describe the pathway (fossa, spaces, etc.) of the key arteries that supply the teeth and, where possible, feel the pulse.
- Trace the route of infection from teeth and associated oral structures as it passes through the lymph system.
- Palpate the location of lymph nodes associated with the spread of infection of the oral cavity.
Arteries that move blood from the heart to the face and oral cavity meet up with nerves from the brain that innervate the face and oral cavity. Arteries and nerves of the same name begin to parallel one another somewhere in the neck or on the face. They may pass through the same foramen and canals within bones after they meet. Generally, arteries of the face and jaw run a more wiggly or corkscrew course than do veins.
Refer to the pathway of blood from the heart to the teeth in Figure 14-47. Blood courses from the left ventricle of the heart through the aorta to the common carotid artery, which ascends in the neck and divides into the external carotid [kah ROT id] artery (Fig. 14-48) and internal carotid artery. The external carotid artery gives off the maxillary branches supplying structures in the mouth (maxillary and mandibular), and the internal carotid artery enters the skull through the carotid canal and does not supply the mouth. You can feel the pulse of the external carotid just in front of the sternocleidomastoid muscle as required during cardiopulmonary resuscitation training.
As the external carotid passes superiorly, it gives off three important branches to the mouth: the lingual, facial, and maxillary arteries. First, the lingual artery (not seen on Fig. 14-48) comes off near the hyoid bone and then enters the tongue. Like the lingual nerve, this artery supplies the floor of the mouth, adjacent gingiva, and the sublingual gland.
Second, the facial artery (Fig. 14-48) comes off near the lingual artery. It then passes forward obliquely inferior to the submandibular gland and then laterally around the lower border of the mandible. The facial artery and facial nerve pass together through a shallow notch on the inferior border of the mandible just anterior to the insertion of the masseter muscle. This notch is called the antegonial notch (recall Fig. 14-14). This is an important landmark to be aware of so that you will be able to stop the flow of blood to the lower part of the face in an emergency. Try to find the facial artery in the antegonial notch with your finger or thumb. You should feel the pulse of the facial artery if you are in the correct spot. From here, the facial artery goes upward over the outer surface of the mandible to the face.
There are four branches of the facial artery. Two branches come off before it passes onto the face. First, the ascending palatine artery ascends to supply structures adjacent to the pharynx (including the soft palate, the pharyngeal muscles, the mucosa of the pharynx, and the palatine tonsil), and second, the submental artery converges with the mylohyoid nerve to supply structures in the floor of the mouth (such as the mylohyoid muscle, anterior belly of the digastric muscle, and lymph nodes inferior to the mylohyoid muscle). After passing onto the face, the inferior and superior labial arteries (branches) (Fig. 14-48) surround and supply the lips and the orbicularis oris muscle, and finally, lateral nasal and angular arteries are the terminal branches of the facial arteries.
There is considerable merging at the midline of the arteries from both sides of the face, rather than the more conventional system whereby an artery terminates with many small capillaries. This merging of small arteries from opposite sides is called an end-to-end anastomosis [a NAS te MO sis]. One example is where the right and left superior and inferior labial arteries join at the midline. As one might guess, such an anastomosis can cause problems in arresting hemorrhage on the face.
MAXILLARY ARTERY: The third branch of the external carotid artery is the maxillary artery, which is probably the most important artery to the dentist and dental hygienist. It arises from the external carotid within the parotid gland (Fig. 14-48). The branches of this artery can be considered in three parts as shown in Figure 14-49. The branches of the mandibular and pterygopalatine part (or first and third parts) are directly involved with the blood supply to the mandibular and maxillary teeth, respectively. The branches of the pterygoid part (or middle part) provide blood to the four pairs of muscles of mastication. Study Figure 14-49 as you read about the following branches of each part of the maxillary artery. Also, notice the similarity between the names of the vessels and the names of the nerves that supply the same structures.
- Mandibular Part of the Maxillary Artery: Arteries labeled in red in Figure 14-49
Branches coming off of the mandibular (or first) part of the maxillary artery supply the mandibular teeth and their periodontal ligaments. You read correctly: branches of the maxillary artery supply the mandible. The inferior alveolar artery, which, like the inferior alveolar nerve, enters the mandible through the mandibular foramen, supplies branches to the mandibular molars and premolars. It then divides into two branches: the mental artery, which exits from the mental foramen to the lower lip and chin, and the incisive artery, which continues forward within the mandible to supply the anterior teeth (similar to the path of nerves of the same name seen in the mandible in Fig. 14-43).
- Pterygoid Part of the Maxillary Artery: Arteries to the muscles labeled in blue in Figure 14-49
Branches coming off of the pterygoid (or second) part of each maxillary artery are not involved directly with the teeth but supply blood to the muscles of mastication (posterior and anterior deep temporalis, masseteric, and pterygoid branches labeled with (#) in Fig. 14-49) and a buccinator branch.
- Pterygopalatine Part of the Maxillary Artery: Arteries to the maxillae labeled green in Figure 14-49
Branches that come off of the pterygopalatine (or third) part of the maxillary artery supply the maxillary teeth and their periodontal ligaments. The PSA artery traverses the maxillary sinus and, like the PSA nerve, supplies the maxillary molars. While within the infraorbital canal, the infraorbital artery, like the infraorbital nerve, gives off the MSA artery that supplies the premolars and the ASA artery, which supplies the anterior teeth. Each descending palatine branch of the maxillary artery supplies part of the nasal cavity before it emerges onto the palate through the greater palatine foramen (Fig. 14-39) like the nerves to supply the mucosa of the hard and soft palate and the lingual gingiva. Its terminal part ascends through the incisive canal into the nasal cavity.
The TMJ is supplied with oxygenated blood from five branches labeled with (*) in Figure 14-49: the ascending pharyngeal (not visible in figure) and superficial temporal branches of the external carotid artery and by the anterior tympanic, masseteric, and middle meningeal branches of the maxillary artery (Fig. 14-49).
Veins tend to be straighter than arteries.11,34 In many instances, they travel almost the same course as arteries. Veins that drain blood from the face on its way back to the heart are shown in Figure 14-50.
Numerous deep veins drain blood from the upper part of the face, the tissue of the lips and muscles around the mouth, the posterior part of the nasal cavity, the palate, the maxillary alveolar process, and maxillary teeth into a pterygoid [TER i goid] plexus of veins. Also, inferior alveolar veins carry blood to the pterygoid plexus from the mandible and its teeth, that is, from the area of the oral cavity supplied by the inferior alveolar artery (and the area innervated by the inferior alveolar nerve). The pterygoid plexus is a network of thin-walled veins medial to the upper part of the ramus of the mandible, located between the temporal and lateral pterygoid muscles or between the lateral and medial pterygoids.34 The dense venous plexus that surrounds the maxillary artery helps protect the artery from becoming flattened when the masticatory muscles contract. During muscle contractions, however, blood is driven from the veins.34
It was previously thought that an infection in the face could travel through veins in either direction because of the lack of valves in these veins. Now, we know that facial veins do have valves, but infection of the teeth and associated oral structures can spread due to the interconnection of superficial and deep veins of the face into the pterygoid plexus of veins and then to other tissues and organs. Also, the pterygoid plexus of veins connects with another collection of thin-walled veins called the cavernous sinus located on the base of the brain. If infection reaches the cavernous sinus, it can spread to the brain with life-threatening effects.
The veins of the pterygoid plexus empty into the short maxillary vein. While within the parotid gland, blood from the maxillary vein (and from the superficial temporal vein) passes into the retromandibular vein to drain those areas that had received blood through the maxillary and superficial temporal arteries. The retromandibular vein drains into the facial vein where it becomes the short common facial vein that then empties into the internal jugular vein.
An important superficial vein that also drains blood from the face is the facial vein, which roughly follows the course of the facial artery but, of course, carries blood in the opposite direction. The facial vein receives blood from the area around the eyes and nose (via the angular and lateral nasal veins) and receives blood from the lips (via the superior and inferior labial veins). It can also receive blood from the muscles of mastication. Just like the retromandibular vein, the facial vein empties through the common facial vein into the internal jugular vein. Blood from the tongue drains through lingual veins (not visible on Fig. 14-50) that also empty into the internal jugular vein (possibly via the common facial vein).
Venous drainage of the face becomes even more complex when you consider that there is a deep facial vein, which connects the deeper pterygoid plexus with the more superficial facial vein. Therefore, blood from the head can make its way down to the internal jugular vein either through the pterygoid plexus and retromandibular vein or through the facial vein and its branches.
Once blood reaches the internal jugular vein, it passes into the brachiocephalic vein to the superior vena cava and then through the heart and lungs to become oxygenated before being pumped back to the mouth (Fig. 14-47).
Draw the route of a drop of blood from the heart to both maxillary and mandibular teeth and then back to the heart as shown in Figure 14-47. Name each vessel along the way. Try to visualize this interesting round trip, which takes place about every 10 to 15 seconds. Remember, the maxillary artery and its branches are probably the most important to the dentist or dental hygienist.