|SECTION II||INTRAORAL EXAMINATION: NORMAL STRUCTURES AS WELL AS LANDMARKS USED FOR PLACING LOCAL ANESTHETIC|
The oral cavity is bounded anteriorly by the lips, laterally by the cheeks, superiorly by the palate, and inferiorly by the floor of the mouth. The oral cavity can be divided into two parts: the oral vestibule and the oral cavity proper. The outer oral vestibule is the space between the teeth with the supporting alveolar processes and the lips or cheeks. The inner oral cavity proper is the space bounded anteriorly and laterally by the teeth and alveolar processes.
Mucous membrane (mucosa) lines any body cavity opening out to where it joins the skin on the outside of the body. Oral mucous membrane lines the oral cavity. It resembles the skin covering the outside of the body, except that it is moist. Some areas subjected to the most wear, such as the roof the mouth (over the hard palate) and the gingiva, are covered by a toughened outer tissue called a keratin [KER ah tin] layer. As wear occurs, this keratinized tissue may take on a grayish appearance. Other areas of the oral mucous membrane have no keratin layer so are more delicate in structure, such as the cheeks and floor of the mouth. This mucosa lining may be so thin that the blood vessels located in the underlying connective tissue may easily be seen, giving it a reddish or bluish color.
Many of the nerves that innervate the teeth and adjacent oral structures can be reached with the anesthetic syringe needle by penetrating the labial and buccal mucosa. The landmarks that are helpful for locating these injection sites will be described throughout this section.
The vestibule space between the teeth and the lips or cheeks can be divided into the labial vestibule next to the anterior teeth and the buccal vestibule next to the posterior teeth (premolars and molars). It extends superiorly into a mucosa-lined space next to maxillary teeth and inferiorly next to mandibular teeth. It is covered with dark pink–colored alveolar mucosa and is rich in blood vessels and minor salivary glands. The tip of your tongue can reach into each vestibule to assist in cleaning the facial surfaces of the teeth and, while chewing, to lift food back for additional chewing. The vestibular fornix (Fig. 15-7) is the lowest part of the vestibule next to the mandible or the highest part next to the maxillae. The vestibular fornix next to the cheeks is where food may collect in patients especially after nerve damage to the cheek (as with unilateral loss of function of the facial nerve from Bell palsy or from a stroke).
Refer to Figure 15-7 as a guide while studying the following structures. The labial frenum [FREE num] (plural: frena [FREE nah]) is the thin sheet of tissue at the midline that attaches each lip (upper and lower) to the mucosa covering the maxillae or mandible between the central incisors. The buccal frenum loosely attaches the cheek to the mucosa of the jaw in the area of the premolars (maxillary and mandibular). These buccal frena can be seen by pulling the lip and cheek out and upward and the lip and cheek out and downward. Facial muscles move the buccal frena forward and backward and upward and downward during eating to help, along with the tongue, place our food back over the chewing surfaces of our teeth while eating. Movement of these frena can dislodge complete dentures if the denture border is designed improperly.
Usually 4 to 6 mm posterior to the commissure of the lips, a slight bulge of mucous membrane called the commissural papule is commonly seen and may be palpated (Fig. 15-7). The parotid papilla [pa ROT id pah PILL e] is a rounded flap of tissue on the mucosa of the cheek next to the maxillary first and second molars at or just superior to the occlusal plane (Fig. 15-7). This papilla covers the opening to the parotid duct (Stensen duct).A
The lining of the buccal mucosa on the inside of the cheeks is shiny, but in spots may be rough. Often, there is a horizontal white line extending anteroposteriorly on each side at the level where the upper and lower teeth come together, called the linea alba [LIN e ah AL ba] buccalis (Fig. 15-8). (Hint: “Linea” means line; “alba” means white.) It may extend from the commissural area to the third molar region at a level of the occlusal surfaces of the posterior teeth. This area may become irritated by trauma from biting the cheek. Fordyce granules or spots are small, yellowish irregular areas and may be conspicuous in some persons. They are most commonly located on the buccal mucosa inside the cheeks posterior to the corner of the mouth (Fig. 15-8). They are really the manifestation of intraoral sebaceous glands—glands normally associated with hair follicles on the skin outside of the mouth. Their presence here may be the result of fusion of the upper and lower parts of the cheek during embryonic development. Such glands have also been found, however, on other parts of the oral mucosa.
Palpation of the cheeks (or lips) for lumps or bumps can be accomplished by pressing with the thumb on one side against the forefinger on the other side (called bidigital palpation), as seen in Figure 15-9.
TECHNIQUE FOR INJECTING LOCAL ANESTHETIC TO NUMB ORAL STRUCTURES: BACKGROUND
In order for you to “feel” pain in a tooth, the tooth or surrounding tissue that is being “hurt” must pass the signal to the brain by way of the branches of the trigeminal nerve. In order for the anesthetic to block the signal of oral pain being sent along these nerve branches that pass from each tooth to the brain, a sufficient concentration of anesthetic must enter the nerve cells along their passageway from the tooth to the brain to block the nerve. In order to accomplish this, anesthetic is applied as close as possible to a nerve before it enters the bone, or, if the bone is porous enough or thin enough, it may be applied outside of the bone where it can pass (infiltrate) through the bone directly to the dental nerve branches in the bone before they enter the tooth root. The maxillae bones are less dense than the mandible, permitting anesthetic to infiltrate more readily from adjacent soft tissue into bone and reach nerve branches that enter the tooth pulps. In the mandible, nerves supplying the pulps can be blocked more effectively by applying the anesthetic near the mandibular nerve before it enters the mandible (the inferior alveolar nerve) or into the mental foramen (which permits the solution to enter the mandible and block only the inferior alveolar nerve branches to the premolars and possibly the anterior teeth but not the molars).
Recall that most nerves parallel arteries and veins. In order to avoid injecting local anesthetic into these vessels where it can produce an exaggerated undesirable effect on the heart (systemic effect), an aspirating syringe is used. This type of syringe permits the operator to pull back on the stopper of the anesthetic cartridge and apply a negative pressure through the solution and needle. Therefore, if the needle tip is in a blood vessel, the negative pressure can aspirate (suck in) blood into the glass anesthetic cartridge where it can be seen. When blood is observed, the operator can reposition the needle prior to injecting the anesthetic and aspirate again to ensure that the anesthetic will not enter the vessel where it would quickly reach the heart, resulting in an increased chance of undesirable side effects.
INJECTIONS FOR THE PSA, MSA, AND ASA NERVES
Consider the nerves that must be blocked in order to anesthetize the teeth and surrounding tissues of the upper jaw. These are all branches of the maxillary division of the fifth cranial (trigeminal) nerve. In order to anesthetize the pulp of one or two teeth, or the soft tissue in a specified area, it is necessary to block the appropriate individual branches of the posterior superior alveolar (PSA), middle superior alveolar (MSA), or ASA nerve branches that innervate these tissues.
If you want to anesthetize only the maxillary second or third molar and adjacent tissue, you can reach the PSA (Fig. 15-10) before it enters the alveolar canals (Fig. 15-11) by directing the anesthetic toward the posterior surface of the maxilla, just superior, distal, and slightly medial to the apex of the third molar. Entry to this site is through the mucosa at the height of the buccal vestibule (vestibular fornix) superior to the maxillary tuberosity (Fig. 15-12). The cheek can be stretched slightly outward to permit an angle that is directed superiorly and medially. Specific dental branches of the PSA can also be blocked by depositing the anesthetic next to the maxilla as close as possible to the apex of the tooth being anesthetized, and the solution will infiltrate through the maxillary bone to block the dental branches to these molars. When using this technique to anesthetize a maxillary first molar, the anesthetic will reach not only the dental branches of the PSA that enter two of its roots but also the MSA branches that enter the third root.
For all other maxillary teeth and adjacent facial gingiva, you need to block branches of the MSA or ASA. Since you cannot easily reach the MSA and ASA nerves as they pass from the brain through the base of the orbit and maxillary sinus, you can deposit the solution in the soft tissue of the vestibular fornix adjacent to the maxillae, at a level of the tooth root tips of the teeth you want to get numb (Figs. 15-13 for the MSA and Fig. 15-14 for the ASA). The anesthetic can infiltrate through the soft tissue and bone to reach dental nerve branches of the ASA (supplying the pulps of anterior teeth, Fig. 15-15) or MSA (supplying the pulps of premolars and one root [mesiobuccal] of the maxillary first molar, Fig. 15-16) in order to block pain. As stated previously, the anesthetic placed to block the MSA nerve branches may also infiltrate through the bone to block some of the PSA nerve branches, thereby numbing the entire first molar.
End branches of the infraorbital nerve branches that supply the soft tissue facial to premolars and anterior teeth can be anesthetized using the infiltration technique described above. However, blocking all of the terminal branches of the infraorbital nerve may also be helpful. This nerve can be reached by applying the anesthetic near the opening of the infraorbital foramen (Fig. 15-17). This foramen may be palpated with the forefinger through the skin just below the inferior border of the eye socket. Then, using the thumb in the facial vestibule to raise the upper lip, you can pass the needle into tissue at the height (fornix) of the vestibule near the premolars (similar to the MSA injection) and continue to move the tip parallel to the facial surface of the maxilla until reaching the level of the infraorbital foramen (Fig. 15-18).
LONG BUCCAL INJECTION
The buccinator (long buccal) nerve is a branch of the mandibular nerve that does not pass through the mandibular foramen but is located in the soft tissue of the cheek. The anesthetic can be applied just beneath the buccal mucosa and just superior to the buccal shelf next to the mandibular molars that require facial tissue numbness (Figs. 15-19 and 15-20).
The hard palate is the firm anterior part of the roof of the mouth with mucosa over the underlying bone (namely, the horizontal plates of the palatine bones and palatine processes of the maxillae). The soft palate is the posterior movable part of the roof of the mouth without underlying bony support. The vibrating line is the junction between the hard and soft palate (Fig. 15-21).
1. Hard Palate Structures
Refer to Figures 15-21 and 15-22 while studying the structures of the hard palate. The hard palate is covered by keratinized, grayish-red to coral pink tissue. The incisive papilla is the small rounded elevation of tissue on the midline of the palate just lingual to the central incisors. This papilla is located over the incisive foramen, where the nasopalatine nerve passes from the nasal cavity onto the palate to innervate the anterior portion of the hard palate. It is the location for injecting anesthetic to numb palatal tissue in this area.B
The palatine raphe [RAY fee] is the slightly elevated ridge of firm tissue running anteroposteriorly along the midline of the hard palate (over the intermaxillary suture attachment between the palatine processes of the right and left maxillae) (Fig. 15-22). The mucosa over the raphe is firmly attached to the underlying bone without intervening fat or gland cells. The rest of the tissue on both sides of the raphe has fat or salivary gland tissue beneath the surface, so it is softer. This spongy tissue at the junction of the hard palate and alveolar process next to premolars and molars is the location of the greater palatine nerve. There are more than 350 very small palatine glands in the posterior third of the hard palate.2 They secrete thick but slippery saliva.
Palatine rugae [ROO guy] or [ROO jee] are a series of palatal tissue elevations, or wrinkles, located on the palate just posterior to the maxillary anterior teeth (Fig. 15-22). They form a pattern like branches on a tree, coming off of the common midline “trunk,” the palatine raphe.C Rugae function in two important ways: in tactilely sensing objects or food position and in aiding the tongue’s proper placement for the production of certain speech sounds.3 This part of the palate is often burned by eating pizza when it is too hot or becomes abraded from chewing too much popcorn.
NASOPALATINE NERVE INJECTION
In order to anesthetize the tissues of the palate, you need to block one or two nerves. The greater (anterior) palatine nerve innervates most of the palate (all tissue covering the hard palate lingual to molars and premolars) and the nasopalatine nerve for tissue lingual to the anterior teeth. Recall that both of these nerve branches split off of the maxillary nerve while in the pterygopalatine space and then pass through the nasal passageways before entering the palatal tissue. The nasopalatine nerve passes from the pterygopalatine space along the nasal septum in the nasal cavity and into palatal mucosa through the incisive foramen (Fig. 15-23), which is located immediately under the bump of very firm tissue called the incisive papilla (Fig. 15-24). This papilla is located on the palate just lingual to the midline between the maxillary central incisors. Since this tissue is very firm, only a small amount of anesthetic can be applied into this tissue, and this injection can be most painful. Applying pressure over the injection site with the handle of a mirror or with the end of a cotton-tipped applicator for 15 to 20 seconds prior to injecting can minimize this discomfort.
GREATER PALATINE NERVE INJECTION
The greater palatine nerve passes from the nasal cavity to palatal tissue through the greater palatine foramen located just lingual to the third molars at the junction of the most posterior part of the horizontal bone of the hard palate and the more vertical alveolar process surrounding the maxillary posterior teeth (Fig. 15-25). The greater palatine nerve spreads anteriorly toward the tissue lingual to the first premolar along the junction of the alveolar process and palate covered by tissue that is softer and more spongy than the tissue covering the midline of the hard palate. When locating or palpating this location, care must be taken to avoid touching the soft plate (posterior to the underlying bones of the palate) since this may elicit a gag reflex causing the patient to vomit. A small amount of anesthetic may be placed into this spongy tissue, resulting in numbness of tissues adjacent to and anterior to the injection site (Fig. 15-26).
Note: It is also possible to reach the entire maxillary branch of the trigeminal nerve just after it exits the cranium through the foramen rotundum while it is still within the pterygopalatine space and anesthetize all of the maxillary branches (called a second division block). This location is superior to the location of the PSA block already discussed. Anesthetic deposited in this location reduces pain to the structures supplied by the PSA, MSA, ASA, greater palatine, and nasopalatine nerves. Caution must be taken in this area because the pterygoid plexus of vessels is located here, and cutting a vessel wall could result in bleeding under the skin called a hematoma.