Your jaw is a set of bones that holds your teeth. It consists of two main parts. The upper part is the maxilla. It doesn't move. The moveable lower part is called the mandible. You move it when you talk or chew. The two halves of the mandible meet at your chin. The joint where the mandible meets your skull is the temporomandibular joint.

Jaw problems include

• Fractures
• Dislocations
• Temporomandibular joint dysfunction
• Osteonecrosis, which happens when your bones lose their blood supply
• Cancers

Treatment of jaw problems depends on the cause.

The mandible forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull. Each side of the mandible consists of a horizontal body and posteriorly, a vertically oriented ramus of the mandible (ramus = “branch”). The outside margin of the mandible, where the body and ramus come together is called the angle of the mandible (Figure 7.15).

The ramus on each side of the mandible has two upward-going bony projections. The more anterior projection is the flattened coronoid process of the mandible, which provides attachment for one of the biting muscles. The posterior projection is the condylar process of the mandible, which is topped by the oval-shaped condyle. The condyle of the mandible articulates (joins) with the mandibular fossa and articular tubercle of the temporal bone. Together these articulations form the temporomandibular joint, which allows for opening and closing of the mouth (see Figure 7.5). The broad U-shaped curve located between the coronoid and condylar processes is the mandibular notch.

Important landmarks for the mandible include the following:

• Alveolar process of the mandible—This is the upper border of the mandibular body and serves to anchor the lower teeth.
• Mental protuberance—The forward projection from the inferior margin of the anterior mandible that forms the chin (mental = “chin”).
• Mental foramen—The opening located on each side of the anterior-lateral mandible, which is the exit site for a sensory nerve that supplies the chin.
• Mylohyoid line—This bony ridge extends along the inner aspect of the mandibular body (see Figure 7.11). The muscle that forms the floor of the oral cavity attaches to the mylohyoid lines on both sides of the mandible.
• Mandibular foramen—This opening is located on the medial side of the ramus of the mandible. The opening leads into a tunnel that runs down the length of the mandibular body. The sensory nerve and blood vessels that supply the lower teeth enter the mandibular foramen and then follow this tunnel. Thus, to numb the lower teeth prior to dental work, the dentist must inject anesthesia into the lateral wall of the oral cavity at a point prior to where this sensory nerve enters the mandibular foramen.
• Lingula—This small flap of bone is named for its shape (lingula = “little tongue”). It is located immediately next to the mandibular foramen, on the medial side of the ramus. A ligament that anchors the mandible during opening and closing of the mouth extends down from the base of the skull and attaches to the lingula.

Figure 7.15 Isolated Mandible The mandible is the only moveable bone of the skull.

Lateral View of Skull

A view of the lateral skull is dominated by the large, rounded brain case above and the upper and lower jaws with their teeth below (Figure 7.5). Separating these areas is the bridge of bone called the zygomatic arch. The zygomatic arch is the bony arch on the side of skull that spans from the area of the cheek to just above the ear canal. It is formed by the junction of two bony processes: a short anterior component, the temporal process of the zygomatic bone (the cheekbone) and a longer posterior portion, the zygomatic process of the temporal bone, extending forward from the temporal bone. Thus the temporal process (anteriorly) and the zygomatic process (posteriorly) join together, like the two ends of a drawbridge, to form the zygomatic arch. One of the major muscles that pulls the mandible upward during biting and chewing arises from the zygomatic arch.

On the lateral side of the brain case, above the level of the zygomatic arch, is a shallow space called the temporal fossa. Below the level of the zygomatic arch and deep to the vertical portion of the mandible is another space called the infratemporal fossa. Both the temporal fossa and infratemporal fossa contain muscles that act on the mandible during chewing.

Figure 7.5 Lateral View of Skull The lateral skull shows the large rounded brain case, zygomatic arch, and the upper and lower jaws. The zygomatic arch is formed jointly by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The shallow space above the zygomatic arch is the temporal fossa. The space inferior to the zygomatic arch and deep to the posterior mandible is the infratemporal fossa.

Dislocation of the TMJ may occur when opening the mouth too wide (such as when taking a large bite) or following a blow to the jaw, resulting in the mandibular condyle moving beyond (anterior to) the articular tubercle. In this case, the individual would not be able to close his or her mouth. Temporomandibular joint disorder is a painful condition that may arise due to arthritis, wearing of the articular cartilage covering the bony surfaces of the joint, muscle fatigue from overuse or grinding of the teeth, damage to the articular disc within the joint, or jaw injury. Temporomandibular joint disorders can also cause headache, difficulty chewing, or even the inability to move the jaw (lock jaw). Pharmacologic agents for pain or other therapies, including bite guards, are used as treatments.

Figure 9.15 Temporomandibular Joint The temporomandibular joint is the articulation between the temporal bone of the skull and the condyle of the mandible, with an articular disc located between these bones. During depression of the mandible (opening of the mouth), the mandibular condyle moves both forward and hinges downward as it travels from the mandibular fossa onto the articular tubercle.

Temporomandibular disorders (TMDs) are a group of more than 30 conditions that cause pain and dysfunction in the jaw joint and muscles that control jaw movement. “TMDs” refers to the disorders, and “TMJ” refers only to the temporomandibular joint itself. People have two TMJs; one on each side of the jaw. You can feel them by placing your fingers in front of your ears and opening your mouth.

There are three main classes of TMDs:

1. Disorders of the joints, including disc disorders.
2. Disorders of the muscles used for chewing (masticatory muscles).
3. Headaches associated with a TMD.

There are several disorders within each class. See diagram below for some examples.

Classification of Temporomandibular Disorders (TMDs) with Examples

Many TMDs last only a short time and go away on their own. However, in some cases they can become chronic, or long lasting. In addition, TMDs can occur alone or at the same time as other medical conditions such as headaches, back pain, sleep problems, fibromyalgia, and irritable bowel syndrome.

A recent study found that about 11-12 million adults in the United States had pain in the region of the temporomandibular joint.

Temporomandibular disorders are twice as common in women than in men, especially in women between 35 and 44 years old.

The temporomandibular joint (TMJ) is the joint that allows for opening (mandibular depression) and closing (mandibular elevation) of the mouth, as well as side-to-side and protraction/retraction motions of the lower jaw. This joint involves the articulation between the mandibular fossa and articular tubercle of the temporal bone, with the condyle (head) of the mandible. Located between these bony structures, filling the gap between the skull and mandible, is a flexible articular disc (Figure). This disc serves to smooth the movements between the temporal bone and mandibular condyle.

Movement at the TMJ during opening and closing of the mouth involves both gliding and hinge motions of the mandible. With the mouth closed, the mandibular condyle and articular disc are located within the mandibular fossa of the temporal bone. During opening of the mouth, the mandible hinges downward and at the same time is pulled anteriorly, causing both the condyle and the articular disc to glide forward from the mandibular fossa onto the downward projecting articular tubercle. The net result is a forward and downward motion of the condyle and mandibular depression. The temporomandibular joint is supported by an extrinsic ligament that anchors the mandible to the skull. This ligament spans the distance between the base of the skull and the lingula on the medial side of the mandibular ramus.

Dislocation of the TMJ may occur when opening the mouth too wide (such as when taking a large bite) or following a blow to the jaw, resulting in the mandibular condyle moving beyond (anterior to) the articular tubercle. In this case, the individual would not be able to close his or her mouth. Temporomandibular joint disorder is a painful condition that may arise due to arthritis, wearing of the articular cartilage covering the bony surfaces of the joint, muscle fatigue from overuse or grinding of the teeth, damage to the articular disc within the joint, or jaw injury. Temporomandibular joint disorders can also cause headache, difficulty chewing, or even the inability to move the jaw (lock jaw). Pharmacologic agents for pain or other therapies, including bite guards, are used as treatments.

The temporomandibular joint (TMJ) connects your jaw to the side of your head. When it works well, it enables you to talk, chew, and yawn. For people with TMJ dysfunction, problems with the joint and muscles around it may cause

• Pain that travels through the face, jaw, or neck
• Stiff jaw muscles
• Limited movement or locking of the jaw
• Painful clicking or popping in the jaw
• A change in the way the upper and lower teeth fit together

Jaw pain may go away with little or no treatment. Treatment may include simple things you can do yourself, such as eating soft foods or applying ice packs. It may also include pain medicines or devices to insert in your mouth. In very rare cases, you might need surgery.

Your jaw works hard every day so you can laugh, talk, smile, and eat. When it’s working properly, you may not give it much thought. But if your jaw starts to hurt, it can take the joy out of simple, everyday things.

The jaw joint is one of the most complex joints in the human body. For most people, it moves effortlessly up and down, side to side, and in and out, transitioning from one movement to the next seamlessly. But, more than 10 million people in the U.S. live with jaw pain and dysfunction.

Doctors call these conditions temporo-mandibular disorders. They’re more commonly called temporomandibular joint (TMJ) disorders.

“Temporomandibular disorders—and how people respond to them—vary widely,” explains Dr. Dena Fischer, a dental health expert at NIH. “For example, some experience discomfort, others tension, and still others severe pain.”

Some people get symptoms in the muscles that move the jaw. For others, it’s in a disc within the jaw joint that’s damaged. You can also develop arthritis, or joint inflammation . You can even have more than one kind of disorder at the same time.

TMJ disorders sometimes start after an injury. But for most people, there’s no obvious cause. In addition to pain, other symptoms can include stiffness, limited jaw movement, painful clicking or popping in the joint, or changes in the way the teeth fit together.

If you have any of these symptoms, talk with your health care provider. To diagnose a TMJ disorder, they’ll ask you questions about your symptoms and examine your head, neck, face, and jaw. They’ll also check your dental and medical history. They may use imaging tests, like X-rays, too.

Experts recommend starting with simple, self-care practices for jaw pain (see the Wise Choices box for tips). “For a lot of people, the pain will resolve over time,” Fischer explains. “Your doctor may also recommend trying a bite guard. These are plastic splints that fit over the teeth.”

Sometimes, TMJ disorders can become chronic—causing pain or discomfort that lasts more than three months. Aggressive treatments include surgery, splints that change the bite, and even adjusting or removing teeth. But whether these treatments help hasn’t been scientifically studied, explains Fischer.

For some people, they may make things worse. “And once you have surgery, you can’t put things back the way they were before,” she says.

If you have symptoms that last more than three months, your dentist or health care provider may refer you to a specialist. Doctors who specialize in muscles and bones, arthritis, pain, and the nervous system may be able to help.

But better treatments are needed. NIH-funded researchers have been studying the role that genes play in who develops a TMJ disorder and how long it lasts. In a large study, researchers identified several genes that are more common in people who have severe jaw pain. They’re now testing whether early treatment can help people with certain genes lower their risk of developing a chronic disorder.

“We hope that having a better understanding of why temporomandibular disorders develop will ultimately help us prevent them and find new treatments,” Fischer says.

Note: The title of this article was changed after publication.

Tackling Jaw Pain

Simple, self-care practices to try:

• Avoid hard foods.
• Use ice packs on the joint.
• Try over-the-counter pain medications, like ibuprofen, for a short amount of time.
• Avoid extreme movements, like wide yawning and chewing gum.
• Learn relaxation and stress reduction techniques.

Face injuries and disorders can cause pain and affect how you look. In severe cases, they can affect sight, speech, breathing and your ability to swallow. Broken bones, especially the bones of your nose, cheekbone and jaw, are common facial injuries.

Certain diseases also lead to facial disorders. For example, nerve diseases like trigeminal neuralgia or Bell's palsy sometimes cause facial pain, spasms and trouble with eye or facial movement. Birth defects can also affect the face. They can cause underdeveloped or unusually prominent facial features or a lack of facial expression. Cleft lip and palate are a common facial birth defect.

Trigeminal neuralgia (TN) is a type of chronic pain that affects your face. It causes extreme, sudden burning or shock-like pain. It usually affects one side of the face. Any vibration on your face, even from talking, can set it off. The condition may come and go, disappearing for days or even months. But the longer you have it, the less often it goes away.

TN usually affects people over 50, especially women. The cause is probably a blood vessel pressing on the trigeminal nerve, one of the largest nerves in the head. Tumors and multiple sclerosis can also cause TN, but in some cases the cause is unknown.

There is no specific test for TN. It can be hard to diagnose, since many other conditions can cause facial pain. Treatment options include medicines, surgery, and complementary techniques.

Trigeminal neuralgia (TN), also called tic douloureux, is a chronic pain condition that affects the trigeminal or 5th cranial nerve, one of the most widely distributed nerves in the head. TN is a form of neuropathic pain (pain associated with nerve injury or nerve lesion.) The typical or "classic" form of the disorder (called "Type 1" or TN1) causes extreme, sporadic, sudden burning or shock-like facial pain that lasts anywhere from a few seconds to as long as two minutes per episode. These attacks can occur in quick succession, in volleys lasting as long as two hours. The “atypical” form of the disorder (called "Type 2" or TN2), is characterized by constant aching, burning, stabbing pain of somewhat lower intensity than Type 1. Both forms of pain may occur in the same person, sometimes at the same time. The intensity of pain can be physically and mentally incapacitating.

The trigeminal nerve is one of 12 pairs of nerves that are attached to the brain. The nerve has three branches that conduct sensations from the upper, middle, and lower portions of the face, as well as the oral cavity, to the brain. The ophthalmic, or upper, branch supplies sensation to most of the scalp, forehead, and front of the head. The maxillary, or middle, branch stimulates the cheek, upper jaw, top lip, teeth and gums, and to the side of the nose. The mandibular, or lower, branch supplies nerves to the lower jaw, teeth and gums, and bottom lip. More than one nerve branch can be affected by the disorder. Rarely, both sides of the face may be affected at different times in an individual, or even more rarely at the same time (called bilateral TN).

Prognathism and retrognathism

Cephalometric analysis allows for comparison of the positions of the mandible and maxilla in relation to the skull. Prognathism is when either of the jaws protrudes beyond an imaginary plane (usually that of the forehead) that is parallel to the coronal plane of the skull. The word prognathism derives from Greek (pro = forward and gnáthos = jaw). Prognathism may result in malocclusion.

Prognathism can involve a projecting maxilla, mandible or both and it is usually the result of extensive growth of these bones. Not all alveolar prognathism is anomalous, and significant differences can be observed among ethnic groups. Prognathism, if not extremely severe, can be treated in growing patients with orthodontic functional or orthopaedic appliances. In adult patients this condition can be corrected by means of a combined surgical/orthodontic treatment.

Alveolar prognathism is a special case in which the maxilla and the mandible have normal size and position but the incisors are tilted labially. This condition can be exaggerated or caused by thumb sucking or tongue thrusting. Functional appliances can be used by growing children to help modify behavioral habits and avoid this condition. Otherwise, alveolar prognathism can be corrected with fixed orthodontic therapy.

Retrognathism is a condition in which the maxilla or mandible, particularly the mandible, has an abnormally posterior position relative to the rest of the skull.

Abnormally small jaw.

Do you wake up with a tired or sore jaw in the morning? It could be a sign that you’re grinding or clenching your teeth at night. Over time, this can damage your teeth and lead to jaw problems. It can cause teeth to crack, loosen, and even fall out.

Teeth grinding and clenching—also called bruxism—can cause serious issues if left untreated. And people aren’t always aware that they’re doing it.

“Someone may not know they grind their teeth at night until they’re told by a bedtime partner,” explains Dr. Dena Fischer, a dental health expert at NIH.

You can grind your teeth during the daytime, too—although clenching your jaw is more common. Some experts think of daytime and nighttime bruxism as separate conditions. They may have different causes.

Your dentist may spot the tell-tale signs of teeth grinding and clenching. These can include wear and early cracks on the outer layer of the tooth. Teeth grinding and clenching can cause a dull headache or tired jaw muscles. Often, nighttime teeth grinding isn’t diagnosed until there are significant symptoms.

Teeth grinding and clenching while awake is easier to recognize. It’s thought to be caused by stress and anxiety. Some people may also grind or clench their teeth while deep in concentration. Once you realize that you’re doing it, it’s important to figure out when and why.

Situations that are stressful or frustrating can trigger the behavior. “People often mention that they grind or clench their teeth while driving in traffic,” Fischer says.

How do you treat bruxism? Fischer helps patients by having them set reminders to check their habits. People who grind or clench their teeth during traffic may find it helpful to put a sticky note on the wheel reminding them to relax their jaw. Setting an alarm to go off regularly at your desk can help if you tend to clench your teeth while deep in thought.

“An alarm or sticky note can be used as a reminder to make sure that your teeth are apart,” Fischer says. “Tell yourself ‘lips apart and teeth apart’ to help make sure clenching isn’t occurring.”

Activities that reduce stress, like yoga and meditation, may help lessen daytime teeth clenching. Counseling can help you learn to manage intense emotions, which may also ease the habit.

If these strategies don’t help, you may consider wearing a plastic mouthguard while awake. Fischer says that a “boil and bite” mouthguard from a store may be enough to stop the problem.

Teeth grinding and clenching at night are usually treated with a mouthguard as well. A dentist can make you a custom fitted guard to protect your teeth. You also may need to be tested for sleep disorders.

Researchers are examining if issues like sleep apnea, which cause people to stop breathing, contribute to nighttime teeth grinding. They’re looking at whether brain activity and sleep stages are linked to sleep bruxism.

If you think you may be grinding or clenching your teeth, talk to a dentist. They can evaluate your mouth and recommend treatments.

Sometimes dentists will recommend reshaping the surfaces of your teeth to change your bite. But Fischer advises against approaches that permanently alter your teeth. She says to seek a second opinion and try less invasive treatment options first.

Easing Teeth Grinding and Clenching

• Try to reduce your daily stress and use relaxation techniques.
• Practice good sleep habits. Seek treatment for sleep problems.
• Apply ice or wet heat to sore jaw muscles.
• Avoid eating hard or dense foods. Don’t chew gum.
• Find ways to relax your face and jaw muscles throughout the day. The goal is to make facial relaxation a habit.
• Schedule regular dental exams. Your dentist can spot early signs of teeth grinding.

Fractures of the upper or lower jaw.

A malocclusion is a misalignment or incorrect relation between the teeth of the two dental arches when they approach each other during mouth closure. Malocclusions are common, although usually not serious enough to require treatment. Severe malocclusions may involve craniofacial anomalies and require orthodontic or sometimes surgical treatment (orthognathic surgery) to correct the problem. Correction of malocclusion may reduce the risk of tooth decay and prevent damage to the temporomandibular joint. Orthodontic treatment is also used to correct minor misalignments for aesthetic reasons.

Malocclusions can involve teeth that are mispositioned, tilted, rotated, deformed extranumerary or missing, and with dozens of teeth in the mouth, diagnosis can be a complicate process. Angle (1899) produced one of the oldest and simplest way of classifying malocclusions. It focuses on the position of the teeth. Several other classification systems have been proposed later to account for the limitations of Angle's system. This includes classifications by Martin Dewey (1915), Benno Lischer (1912, 1933), Simon (1930, the first 3D system), Jacob A. Salzmann (1950, based on skeletal structures) and James L. Ackerman and William R. Proffit (1969).

The performance of an organism in biting and chewing is strongly influenced by the alignment of the teeth. It takes a precisely tuned developmental program not only to form each tooth and bring it into position, but also to account for the replacement of deciduous teeth without significant loss in functionality. The fine positioning of the teeth is based on remodeling of the alveolus in the supporting bone, and adjustment to the periodontal ligaments, the collagen fibers that attach the tooth to the bone. This mechanism remains active throughout life, constantly adjusting the position of the teeth in response to any changes in the forces experienced during mastication. Orthodontics is the study of tooth movement and alignment. It includes normal and abnormal tooth movement, bone growth, tooth eruption and shedding of baby teeth. Orthodontists study these mechanisms to make adjustments to the alignment of the teeth. This chapter explains the processes above, introduces the most common problems and treatment in humans and reviews dental alignment in other mammals.

Dental occlusion

Occlusion, in dentistry, means the contact between teeth. With the teeth ideally positioned, all mandibular teeth should touch maxillary teeth at the same time during mouth closure. The real condition tends to be very close to this ideal due to feedback-driven adjustment of tooth position. Tooth eruption progresses until it is inhibited by pressure received from the opposing tooth at the occlusal surface. Similarly, the position of the tooth along the mesio-distal axis is also adjusted such that the alveolar bone tends to grow in areas of high pressure between teeth and be resorbed in areas of low pressure between teeth. These processes tend to position teeth to spontaneously maintain tight occlusion along the entire dentition and to approximate even spacing among teeth along the arcades.

The occlusal plane is the imaginary surface formed by the occlusal surfaces of the teeth with the mouth closed. This surface is actually curved in humans. The Curve of Spee is the curvature of the mandibular occlusal plane beginning at the tip of the lower incisors and following the buccal cusps of the posterior teeth, continuing to the posterior molar. According to another definition the curve of Spee is an anatomic curvature of the occlusal alignment of the teeth, beginning at the tip of the lower incisor, following the buccal cusps of the natural premolars and molars and continuing to the anterior border of the ramus. It is named for the German embryologist Ferdinand Graf von Spee (1855–1937), who was first to describe the anatomic relations of human teeth in the sagittal plane.

The pull of the main muscle of mastication, the masseter, is at a perpendicular angle with the curve of Spee. This directs force to the teeth in alignment with their longitudinal axis, which is structurally favorable. The longitudinal axis of each lower tooth is also nearly parallel with its arch of closure. The curve of Spee is, essentially, a series of sloped contact points between upper and lower teeth. It is of importance to orthodontists as a flat or mild curve of Spee is essential to an ideal occlusion.

The curve of Spee is at a right angle with the curve of Wilson, which is the upward (U-shaped) curvature of the maxillary and mandibular occlusal planes in the coronal plane. The occlusal surfaces of the mandibular molars are slightly higher on the vestibular side than on the lingual side because the teeth are tilted inwards. Both curves (Spee and Wilson) are believed to be relevant for stability of the temporomandibular joint and for the appropriate distribution of the forces of mastication on the teeth and supporting bones.

Alignment of anterior teeth

In a normal dentition, the incisive edge of the inferior incisor occludes against the cingulum of the superior incisor. The incisive edges of the two teeth do not touch but move past each other, creating some overlap between the teeth. The horizontal overlap is called overjet, whereas the vertical overlap is called overbite.

Conditions of malocclusion can exaggerate the overlap, reduce it or even invert the positions of the teeth. The inferior incisors have most commonly 30-50% of their height overlapped by the superior incisors. Both increased and reduced overlaps may be considered malocclusions. An excessive overlap is also called deep bite whereas a lacking overlap is called open bite.

Maxillary or alveolar prognathism and mandibular retrognathism tend to increase the overjet. Mandibular prognathism, on the other hand, reduces the overjet and can result in negative overjet, with the mandibular incisors occluding anteriorly to the maxillary ones. The condition of negative overjet is also called underbite or anterior crossbite. Notice that overbite is a quantitative property of the alignment of incisors, whereas underbite refers to a condition of malocclusion characterized by negative overjet.

Teeth are dynamically positioned

Each of our teeth articulate at an alveolus of the maxillary bone or mandible. The shape and position of the alveolus is adjusted by our body through the process of bone remodeling. This process is most intense during development allowing, the growth of jaw bones and the replacement of the primary dentition.

Alveolar remodeling occurs constantly throughout our lives, however. Adjustments are made in response to external forces, particularly occlusal forces. Bone is removed from areas where it is no longer needed and added to areas where it is needed. Osteoblasts are found in large numbers in the areas of the alveolus where tension is high, whereas osteoclasts are found in large numbers where the tissues are being compressed. These forces also influence the density and alignment of trabeculae inside the bone. The bony trabeculae are aligned in the path of tensile and compressive stresses to provide maximum resistance to occlusal forces with a minimum of bone substance. When forces are increased the bony trabeculae also increase in number and thickness.

The fibers of the periodontal ligament hold the tooth in the alveolus, allowing for a minimal amount of movement of the tooth. They also rely on mechanical stimulation to preserve their structure. Within physiologic limits, the fibers become thicker in response to increased stresses. If occlusal forces are reduced, the fibers become thin. This phenomenon is called disuse atrophy.

Tooth mobility

Healthy teeth are not completely immobile inside the alveolus. It is normal for them to move about 0.25 mm in response to pressure in the bucco-lingual direction. This is because the tooth is not fused to the bones of the jaws but is connected to the alveolus by the periodontal ligament. This slight mobility accommodates forces exerted on the teeth during chewing without damaging them. Milk (deciduous) teeth also become looser naturally just before their exfoliation. This is occurs through gradual resorption of their roots and periodontal ligaments when stimulated by the developing permanent tooth underneath.

Tooth mobility is evaluated by applying pressure with the ends of 2 metal instruments and trying to rock a tooth gently in a bucco-lingual direction. Multiple classifications of tooth mobility have been proposed:

Grace & Smales Mobility Index

• Grade 0: No apparent mobility
• Grade 1: Perceptible mobility 1 mm in bucco-lingual direction
• Grade 2: 2 mm
• Grade 3: > 2 mm or can be depressed in the alveolus

Miller Classification

• Class 1: 1 mm (horizontal)
• Class 2: >1 mm (horizontal)
• Class 3: > 1 mm (horizontal+vertical)

Teeth become loose when they loose their attachments or when they are exposed to abnormal mechanical forces. Loss of attachment includes periodontal disease, and dental abscesses. Abnormal mechanical forces include those produced in bruxism (tooth grinding or clenching), dental trauma (blow), or when a new filling or crown is too prominent and concentrates the pressure of the bite on a single occlusal surface.