The cheeks, tongue, and palate frame the mouth, which is also called the oral cavity (or buccal cavity). The structures of the mouth are illustrated in image.

At the entrance to the mouth are the lips, or labia (singular = labium). Their outer covering is skin, which transitions to a mucous membrane in the mouth proper. Lips are very vascular with a thin layer of keratin; hence, the reason they are "red." They have a huge representation on the cerebral cortex, which probably explains the human fascination with kissing! The lips cover the orbicularis oris muscle, which regulates what comes in and goes out of the mouth. The labial frenulum is a midline fold of mucous membrane that attaches the inner surface of each lip to the gum. The cheeks make up the oral cavity’s sidewalls. While their outer covering is skin, their inner covering is mucous membrane. This membrane is made up of non-keratinized, stratified squamous epithelium. Between the skin and mucous membranes are connective tissue and buccinator muscles. The next time you eat some food, notice how the buccinator muscles in your cheeks and the orbicularis oris muscle in your lips contract, helping you keep the food from falling out of your mouth. Additionally, notice how these muscles work when you are speaking.

The pocket-like part of the mouth that is framed on the inside by the gums and teeth, and on the outside by the cheeks and lips is called the oral vestibule. Moving farther into the mouth, the opening between the oral cavity and throat (oropharynx) is called the fauces (like the kitchen "faucet"). The main open area of the mouth, or oral cavity proper, runs from the gums and teeth to the fauces.

When you are chewing, you do not find it difficult to breathe simultaneously. The next time you have food in your mouth, notice how the arched shape of the roof of your mouth allows you to handle both digestion and respiration at the same time. This arch is called the palate. The anterior region of the palate serves as a wall (or septum) between the oral and nasal cavities as well as a rigid shelf against which the tongue can push food. It is created by the maxillary and palatine bones of the skull and, given its bony structure, is known as the hard palate. If you run your tongue along the roof of your mouth, you’ll notice that the hard palate ends in the posterior oral cavity, and the tissue becomes fleshier. This part of the palate, known as the soft palate, is composed mainly of skeletal muscle. You can therefore manipulate, subconsciously, the soft palate—for instance, to yawn, swallow, or sing (see image).

A fleshy bead of tissue called the uvula drops down from the center of the posterior edge of the soft palate. Although some have suggested that the uvula is a vestigial organ, it serves an important purpose. When you swallow, the soft palate and uvula move upward, helping to keep foods and liquid from entering the nasal cavity. Unfortunately, it can also contribute to the sound produced by snoring. Two muscular folds extend downward from the soft palate, on either side of the uvula. Toward the front, the palatoglossal arch lies next to the base of the tongue; behind it, the palatopharyngeal arch forms the superior and lateral margins of the fauces. Between these two arches are the palatine tonsils, clusters of lymphoid tissue that protect the pharynx. The lingual tonsils are located at the base of the tongue.

The mouth, or oral cavity, is the first part of the digestive tract. It is adapted to receive food by ingestion, break it into small particles by mastication, and mix it with saliva. The lips, cheeks, and palate form the boundaries. The oral cavity contains the teeth and tongue and receives the secretions from the salivary glands.

Lips and Cheeks

The lips and cheeks help hold food in the mouth and keep it in place for chewing. They are also used in the formation of words for speech. The lips contain numerous sensory receptors that are useful for judging the temperature and texture of foods.

Palate

The palate is the roof of the oral cavity. It separates the oral cavity from the nasal cavity. The anterior portion, the hard palate, is supported by bone. The posterior portion, the soft palate, is skeletal muscle and connective tissue. Posteriorly, the soft palate ends in a projection called the uvula. During swallowing, the soft palate and uvula move upward to direct food away from the nasal cavity and into the oropharynx.

Tongue

The tongue manipulates food in the mouth and is used in speech. The surface is covered with papillae that provide friction and contain the taste buds.

Teeth

A complete set of deciduous (primary) teeth contains 20 teeth. There are 32 teeth in a complete permanent (secondary) set. The shape of each tooth type corresponds to the way it handles food.

Both physical and chemical digestion begin in the mouth or oral cavity, which is the point of entry of food into the digestive system. The food is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.

The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands (Figure 16.5). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. It also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the esophagus and the trachea. The esophagus leads to the stomach and the trachea leads to the lungs. The epiglottis is a flap of tissue that covers the tracheal opening during swallowing to prevent food from entering the lungs.

Figure 16.5 (a) Digestion of food begins in the mouth. (b) Food is masticated by teeth and moistened by saliva secreted from the salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by Mariana Ruiz Villareal)

Perhaps you have heard it said that the tongue is the strongest muscle in the body. Those who stake this claim cite its strength proportionate to its size. Although it is difficult to quantify the relative strength of different muscles, it remains indisputable that the tongue is a workhorse, facilitating ingestion, mechanical digestion, chemical digestion (lingual lipase), sensation (of taste, texture, and temperature of food), swallowing, and vocalization.

The tongue is attached to the mandible, the styloid processes of the temporal bones, and the hyoid bone. The hyoid is unique in that it only distantly/indirectly articulates with other bones. The tongue is positioned over the floor of the oral cavity. A medial septum extends the entire length of the tongue, dividing it into symmetrical halves.

Beneath its mucous membrane covering, each half of the tongue is composed of the same number and type of intrinsic and extrinsic skeletal muscles. The intrinsic muscles (those within the tongue) are the longitudinalis inferior, longitudinalis superior, transversus linguae, and verticalis linguae muscles. These allow you to change the size and shape of your tongue, as well as to stick it out, if you wish. Having such a flexible tongue facilitates both swallowing and speech.

The extrinsic muscles of the tongue are the mylohyoid, hyoglossus, styloglossus, and genioglossus muscles. These muscles originate outside the tongue and insert into connective tissues within the tongue. The mylohyoid is responsible for raising the tongue, the hyoglossus pulls it down and back, the styloglossus pulls it up and back, and the genioglossus pulls it forward. Working in concert, these muscles perform three important digestive functions in the mouth: (1) position food for optimal chewing, (2) gather food into a bolus (rounded mass), and (3) position food so it can be swallowed.

The top and sides of the tongue are studded with papillae, extensions of lamina propria of the mucosa, which are covered in stratified squamous epithelium (image). Fungiform papillae, which are mushroom shaped, cover a large area of the tongue; they tend to be larger toward the rear of the tongue and smaller on the tip and sides. In contrast, filiform papillae are long and thin. Fungiform papillae contain taste buds, and filiform papillae have touch receptors that help the tongue move food around in the mouth. The filiform papillae create an abrasive surface that performs mechanically, much like a cat’s rough tongue that is used for grooming. Lingual glands in the lamina propria of the tongue secrete mucus and a watery serous fluid that contains the enzyme lingual lipase, which plays a minor role in breaking down triglycerides but does not begin working until it is activated in the stomach. A fold of mucous membrane on the underside of the tongue, the lingual frenulum, tethers the tongue to the floor of the mouth. People with the congenital anomaly ankyloglossia, also known by the non-medical term “tongue tie,” have a lingual frenulum that is too short or otherwise malformed. Severe ankyloglossia can impair speech and must be corrected with surgery.

The Salivary Glands

Many small salivary glands are housed within the mucous membranes of the mouth and tongue. These minor exocrine glands are constantly secreting saliva, either directly into the oral cavity or indirectly through ducts, even while you sleep. In fact, an average of 1 to 1.5 liters of saliva is secreted each day. Usually just enough saliva is present to moisten the mouth and teeth. Secretion increases when you eat, because saliva is essential to moisten food and initiate the chemical breakdown of carbohydrates. Small amounts of saliva are also secreted by the labial glands in the lips. In addition, the buccal glands in the cheeks, palatal glands in the palate, and lingual glands in the tongue help ensure that all areas of the mouth are supplied with adequate saliva.

The Major Salivary Glands

Outside the oral mucosa are three pairs of major salivary glands, which secrete the majority of saliva into ducts that open into the mouth:

• The submandibular glands, which are in the floor of the mouth, secrete saliva into the mouth through the submandibular ducts.
• The sublingual glands, which lie below the tongue, use the lesser sublingual ducts to secrete saliva into the oral cavity.
• The parotid glands lie between the skin and the masseter muscle, near the ears. They secrete saliva into the mouth through the parotid duct, which is located near the second upper molar tooth (Figure).

Saliva

Saliva is essentially (98 to 99.5 percent) water. The remaining 4.5 percent is a complex mixture of ions, glycoproteins, enzymes, growth factors, and waste products. Perhaps the most important ingredient in saliva from the perspective of digestion is the enzyme salivary amylase, which initiates the breakdown of carbohydrates. Food does not spend enough time in the mouth to allow all the carbohydrates to break down, but salivary amylase continues acting until it is inactivated by stomach acids. Bicarbonate and phosphate ions function as chemical buffers, maintaining saliva at a pH between 6.35 and 6.85. Salivary mucus helps lubricate food, facilitating movement in the mouth, bolus formation, and swallowing. Saliva contains immunoglobulin A, which prevents microbes from penetrating the epithelium, and lysozyme, which makes saliva antimicrobial. Saliva also contains epidermal growth factor, which might have given rise to the adage “a mother’s kiss can heal a wound.”

Each of the major salivary glands secretes a unique formulation of saliva according to its cellular makeup. For example, the parotid glands secrete a watery solution that contains salivary amylase. The submandibular glands have cells similar to those of the parotid glands, as well as mucus-secreting cells. Therefore, saliva secreted by the submandibular glands also contains amylase but in a liquid thickened with mucus. The sublingual glands contain mostly mucous cells, and they secrete the thickest saliva with the least amount of salivary amylase.

Salivary glands The major salivary glands are located outside the oral mucosa and deliver saliva into the mouth through ducts.

HOMEOSTATIC IMBALANCES

The Parotid Glands: MumpsInfections of the nasal passages and pharynx can attack any salivary gland. The parotid glands are the usual site of infection with the virus that causes mumps (paramyxovirus). Mumps manifests by enlargement and inflammation of the parotid glands, causing a characteristic swelling between the ears and the jaw. Symptoms include fever and throat pain, which can be severe when swallowing acidic substances such as orange juice.

In about one-third of men who are past puberty, mumps also causes testicular inflammation, typically affecting only one testis and rarely resulting in sterility. With the increasing use and effectiveness of mumps vaccines, the incidence of mumps has decreased dramatically. According to the U.S. Centers for Disease Control and Prevention (CDC), the number of mumps cases dropped from more than 150,000 in 1968 to fewer than 1700 in 1993 to only 11 reported cases in 2011.

Regulation of Salivation

The autonomic nervous system regulates salivation (the secretion of saliva). In the absence of food, parasympathetic stimulation keeps saliva flowing at just the right level for comfort as you speak, swallow, sleep, and generally go about life. Over-salivation can occur, for example, if you are stimulated by the smell of food, but that food is not available for you to eat. Drooling is an extreme instance of the overproduction of saliva. During times of stress, such as before speaking in public, sympathetic stimulation takes over, reducing salivation and producing the symptom of dry mouth often associated with anxiety. When you are dehydrated, salivation is reduced, causing the mouth to feel dry and prompting you to take action to quench your thirst.

Salivation can be stimulated by the sight, smell, and taste of food. It can even be stimulated by thinking about food. You might notice whether reading about food and salivation right now has had any effect on your production of saliva.

How does the salivation process work while you are eating? Food contains chemicals that stimulate taste receptors on the tongue, which send impulses to the superior and inferior salivatory nuclei in the brain stem. These two nuclei then send back parasympathetic impulses through fibers in the glossopharyngeal and facial nerves, which stimulate salivation. Even after you swallow food, salivation is increased to cleanse the mouth and to water down and neutralize any irritating chemical remnants, such as that hot sauce in your burrito. Most saliva is swallowed along with food and is reabsorbed, so that fluid is not lost.

The normal human has 2 types of salivary glands: the intrinsic salivary glands and the extrinsic salivary glands.

The intrinsic salivary glands are an indefinite number of small glands found within the other tissues of the mouth. They are the lingual glands found in the tongue, the labial glands found inside the lips and buccal glands found on the inside of the cheeks. These glands secrete small amounts of saliva at a relatively constant rate whether one is eating or not. This saliva serves to moisten the mouth and prevent bacterial growth.

The extrinsic salivary glands are larger and more distinct organs that secrete saliva into the oral cavity through ducts. They are the parotid glands, submandibular glands, and sublingual glands. The parotid glands are found just beneath the skin, anterior to the earlobes while the submandibular glands are found along the body of the mandible. The sublingual glands are found in the floor of the mouth.

Components of the Digestive System All digestive organs play integral roles in the life-sustaining process of digestion

Your teeth are made of a hard, bonelike material. There are four parts:

• Enamel, your tooth's hard surface
• Dentin, the hard yellow part under the enamel
• Cementum, the hard tissue that covers the root and keeps your teeth in place
• Pulp, the soft connective tissue in the center of your tooth. It contains nerves and blood vessels.

You need your teeth for many activities that you may take for granted. These include eating, speaking and even smiling.

• Teeth are important for eating, speaking, self-confidence and overall health.
• We have two sets of teeth over our lifetime – baby (deciduous or primary) teeth and adult (permanent or secondary) teeth.
• Baby teeth begin to appear from around six months of age. Permanent teeth begin to appear at around the age of six or seven years.

Image: Dental Health Services Victoria

A person has two sets of teeth over their lifetime – baby teeth (also known as deciduous, primary or milk teeth) and adult (secondary or permanent) teeth. Baby teeth usually start to appear at about six months of age and children usually have their full set of 20 baby teeth by age three.

From about six or seven years of age, some baby teeth start to fall out and are slowly replaced by the adult teeth. By around 21 years of age, the average person has 32 adult teeth (which includes 4 wisdom teeth); 16 on the top and 16 on the bottom. Some people have less or even more than this number of teeth, which you can discuss with your oral health professional.

The health of your mouth is an important part of your overall health. Diseases in teeth and gums can affect other parts of your body, including the heart.

Role of teeth

Teeth play an important role in eating, chewing and nutrition. They are different shapes and sizes to bite, tear, crush or grind food before it is swallowed. They also help us to form sounds and speak clearly, and they are an important part of a person’s smile. In this respect, teeth can be associated with a person’s confidence and social interaction.

Baby teeth also play an important role in holding space for the adult teeth. For these reasons it is important to keep them healthy and prevent the early loss of these teeth due to disease.

Your tooth

Your teeth are made up of the following parts:

• crown – the part of the tooth that sits above the gum line
• enamel – the hard, smooth, white outer layer that protects the crown. Enamel is harder than bone and doesn’t have any nerves or a blood supply. Chipped or decayed enamel cannot grow back and may lead to further decay or wear.
• dentine – the middle layer under the enamel. If the enamel is damaged or decayed and the underlying dentine is exposed, the tooth can be sensitive to temperature and sweet or acidic foods.
• pulp – the living centre of the tooth containing blood vessels and nerves. The nerve provides the sensation of temperature, pressure and pain.
• root – the section of tooth that is usually below the gum line within the bone of the jaw. Different teeth can have one or many roots where nerves and blood vessels pass in and out of the pulp.
• cementum – a material that covers the root surface.

Teeth and eating

Teeth help us to eat by breaking food into smaller pieces so that it can be swallowed and digested. Over time, teeth can get worn down from normal and abnormal use.

Teeth have different shapes to do different jobs. Types include:

• incisors are front teeth which bite together like a pair of scissors. There are 4 upper and 4 lower incisors each in the baby and adult sets of teeth.
• canines are pointy shaped teeth (sometimes called fangs or eye teeth) just back from the incisors, which are used to tear food. There are 2 upper and 2 lower canines in the baby and adult sets of teeth
• premolars are between the canines and molars and help crush food. There are 4 upper and 4 lower adult premolars. There are no premolars in the baby teeth.
• molars are the back teeth, larger than premolars with big flat surfaces to grind food. There are six upper and six lower adult molars, and four upper and four lower molars in the baby teeth.

Caring for teeth

Teeth are important for eating, speaking and socialising, so it’s important to take good care of them.

Some tips include:

• Brush twice a day, in the morning and at night before bed - use a toothbrush with a small head and soft bristles. Gently brush your teeth and along your gum line, making sure to brush each tooth on the front, back, and top.
• Start toothbrushing from the first tooth - use toothbrushes with a small head and soft bristles. You can also use a wet cloth to wipe over teeth and gums for babies. Only use water to clean your baby’s teeth and gums until they are 18 months of age. Use age appropriate tooth brushes as you get older.
• From 18 months of age, use fluoride toothpaste - use a low-fluoride children’s toothpaste for children aged 18 months to six years, and standard fluoride toothpaste for from age six years and older.
• Avoid sugary, acidic or carbonated (fizzy) foods and drinks - watch out for sweet and sticky foods, soft drinks, fruit juices, energy drinks and even diet ‘no sugar’ carbonated drinks which can cause tooth decay in excess. If you do have these, it is better to have them at mealtimes rather than between meals.
• Drink plenty of tap water - most of Victoria’s has fluoridated tap water, which helps repair the tooth surface. If your water is not fluoridated (eg tank water), talk to your oral health professional about how to you can get the right amount of fluoride to best protect your teeth.
• Have a regular check-up - regular check-ups are important for identifying and treating any issues before they become bigger and harder to treat. There are also a number of treatments which help to prevent disease. Ask your oral health professional how often you should have a dental check-up.
• Wear a mouthguard when you train for and play sports where your teeth could get damaged - for example football, rugby, soccer, basketball, netball, water polo or hockey.
• Wear an occlusal splint or night guard at night if you have habits such as clenching or grinding of teeth - such habits can cause teeth and fillings to wear down, fracture, and be sensitive or even split in half.
• Quit smoking to improve your oral health and general health.

Tooth conditions

Some examples of problems that can affect the teeth include:

• tooth decay
• gum disease
• loss of the tooth surface (enamel) through:
  • dental erosion (caused by acids from food and drinks, or acids coming up from the stomach)
  • dental abrasion (often due to incorrect or forceful tooth brushing)
  • dental attrition and abfraction (often due to grinding or chewing)
• tooth and jaw alignment problems such as crooked, crowded or overlapping teeth
• tooth grinding (bruxism)
• tooth trauma, such as a broken or knocked out tooth
• developmental defects of the teeth such as ‘chalky teeth’ (molar hypomineralisation)

During the course of your lifetime, you have two sets of teeth (one set of teeth is a dentition). Your 20 deciduous teeth, or baby teeth, first begin to appear at about 6 months of age. Between approximately age 6 and 12, these teeth are replaced by 32 permanent teeth. Moving from the center of the mouth toward the side, these are as follows (image):

• The eight incisors, four top and four bottom, are the sharp front teeth you use for biting into food.
• The four cuspids (or canines) flank the incisors and have a pointed edge (cusp) to tear up food. These fang-like teeth are superb for piercing tough or fleshy foods.
• Posterior to the cuspids are the eight premolars (or bicuspids), which have an overall flatter shape with two rounded cusps useful for mashing foods.
• The most posterior and largest are the 12 molars, which have several pointed cusps used to crush food so it is ready for swallowing. The third members of each set of three molars, top and bottom, are commonly referred to as the wisdom teeth, because their eruption is commonly delayed until early adulthood. It is not uncommon for wisdom teeth to fail to erupt; that is, they remain impacted. In these cases, the teeth are typically removed by orthodontic surgery.

Do you know what’s in your mouth? It’s home to about 700 species of microbes. These include germs like bacteria, fungus, and more.

“Everybody has these microbes in their mouth,” says Dr. Robert Palmer, an NIH expert on oral microbes.

Some microbes are helpful. Others can cause problems like tooth decay and gum disease. Troubles begin when microbes form a sticky, colorless film called plaque on your teeth.

Brushing and flossing help to keep your mouth clean. But after you brush and floss, germs grow again and more plaque forms. That’s why you need to clean your mouth regularly.

Community Growth

Different microbes grow in different places. Some stick to your teeth. Others prefer your tongue. Some lurk in the tiny pockets between tooth and gum. Once they’ve found their homes, they form diverse communities with the other germs.

Mouth microbes work together to protect themselves with a slimy, sticky material called a matrix. The matrix in plaque makes it harder to remove it.

The communities within the matrix include both helpful and disease-causing microbes. The good microbes help keep the growth of bad microbes in check. Good microbes also help you digest food and can protect against harmful microbes in food.

Certain things you may be doing can help bad microbes grow better than the good ones. Sugary foods and drinks feed some microbes and help them increase in number and spread out.

Some of these sugar-loving microbes can turn sugar into matrix and acid. The acid destroys the surface of your teeth. The more sugar in your diet, the more fuel is available for these microbes to build up plaque and damage teeth.

“It’s more productive to think about the community than it is to think about the single microbe that causes disease,” Palmer explains.

You can’t stop tooth decay by getting rid of just one type of acid-making microbe. There are several different types of microbes in the plaque that make acid.

The good news is that limiting sweets and brushing and flossing regularly can help prevent bad microbes from growing out of control.

Helpful Neighbors

“Many bacteria in our mouths depend on help from other members of their community to survive and prosper,” says Dr. Floyd Dewhirst, a dental expert who studies microbes at the Forsyth Institute.

Because microbes grow in communities, it’s important to understand how both helpful and harmful microbes work. Dewhirst’s team is trying to identify all the different germs living in the mouth and what they do.

Before the team can study a microbe, they have to figure out how to grow it. The challenge is that some microbes don’t like to grow anywhere but in your mouth. About 30% of the 700 species haven’t been grown in the lab yet.

Dewhirst’s team is working on growing those microbes in the lab that no one has grown before. They’re using genetic and other information to identify each one and learn more about them.

“The question is,” he says, “once you know who is there and have a quick way of identifying them, what are all of these bacteria doing?”

Dewhirst’s studies have shown that some microbes make certain substances that help their neighbors grow. His team is trying to identify what those substances are.

They also want to find out how these microbes may affect people’s health. Being able to grow microbes in the lab lets scientists run tests to figure out how they’re involved in health and disease. This information could one day help scientists come up with better ways of preventing and treating oral diseases.

Partners in Decay

An important health problem caused by mouth microbes is early childhood tooth decay. “In the U.S., about 23% of our children between the ages of 1 and 5 are affected by this disease,” says Dr. Hyun (Michel) Koo, a dental researcher and oral health expert at the University of Pennsylvania.

Tooth decay can get worse very fast. The microbe matrix and acid from bacteria are thought to be the main cause of tooth decay in young kids.

Koo’s team has found that there’s also fungus in the plaque of kids with rampant tooth decay. The fungus partners with the matrix- and acid-making bacteria to worsen tooth decay.

“Bacteria by itself can cause tooth decay,” Koo explains. “But when fungus is there, it boosts up the entire machinery.”

Koo’s team has shown that some fungus can get energy from sugar that bacteria release while making acid. The fungus then releases substances that feed the bacteria’s growth. This helps the bacteria form an even tougher matrix and make more acid.

Busting Plaque

Koo’s team is looking for new ways to fight plaque buildup and tooth decay. They’ve developed tiny substances, called nanoparticles, that are small enough to get inside and destroy the matrix that protects microbes. The nanoparticles can also kill the acid-making bacteria without harming good bacteria in the mouth.

Koo’s team has shown that these tiny substances can reduce acid damage to the tooth surface. The researchers hope to test the approach in people in the future.

Nanoparticles are just one approach now being studied to prevent or treat mouth diseases.

Future technologies may help keep our mouths healthier. But there are many things you can do to keep bad mouth microbes in check now. See the Wise Choices box for some tips. You can’t have a healthy body without a healthy mouth.

Keep Mouth Microbes in Check

These tips can help prevent tooth decay and mouth infections:

• Brush your teeth with a toothpaste that contains fluoride.
• Floss away the plaque between your teeth.
• Don’t forget to brush your tongue.
• Limit sugary foods and drinks.
• Drink fluoridated water. Learn about fluoride levels in your water (CDC).
• Get regular dental exams and professional cleanings.

As noted earlier, normal oral microbiota can cause dental and periodontal infections. However, there are number of other infections that can manifest in the oral cavity when other microbes are present.

Herpetic Gingivostomatitis

As described in Viral Infections of the Skin and Eyes, infections by herpes simplex virus type 1 (HSV-1) frequently manifest as oral herpes, also called acute herpes labialis and characterized by cold sores on the lips, mouth, or gums. HSV-1 can also cause acute herpetic gingivostomatitis, a condition that results in ulcers of the mucous membranes inside the mouth (Figure). Herpetic gingivostomatitis is normally self-limiting except in immunocompromised patients. Like oral herpes, the infection is generally diagnosed through clinical examination, but cultures or biopsies may be obtained if other signs or symptoms suggest the possibility of a different causative agent. If treatment is needed, mouthwashes or antiviral medications such as acyclovir, famciclovir, or valacyclovir may be used.

(a) This cold sore is caused by infection with herpes simplex virus type 1 (HSV-1). (b) HSV-1 can also cause acute herpetic gingivostomatitis. (credit b: modification of work by Klaus D. Peter)

Oral Thrush

The yeast Candida is part of the normal human microbiota, but overgrowths, especially of Candida albicans, can lead to infections in several parts of the body. When Candida infection develops in the oral cavity, it is called oral thrush. Oral thrush is most common in infants because they do not yet have well developed immune systems and have not acquired the robust normal microbiota that keeps Candida in check in adults. Oral thrush is also common in immunodeficient patients and is a common infection in patients with AIDS.

Oral thrush is characterized by the appearance of white patches and pseudomembranes in the mouth (Figure) and can be associated with bleeding. The infection may be treated topically with nystatin or clotrimazole oral suspensions, although systemic treatment is sometimes needed. In serious cases, systemic azoles such as fluconazole or itraconazole (for strains resistant to fluconazole), may be used. Amphotericin B can also be used if the infection is severe or if the Candida species is azole-resistant.

Overgrowth of Candida in the mouth is called thrush. It often appears as white patches. (credit: modification of work by Centers for Disease Control and Prevention)

Mumps

The viral disease mumps is an infection of the parotid glands, the largest of the three pairs of salivary glands (Figure). The causative agent is mumps virus (MuV), a paramyxovirus with an envelope that has hemagglutinin and neuraminidase spikes. A fusion protein located on the surface of the envelope helps to fuse the viral envelope to the host cell plasma membrane.

Mumps virus is transmitted through respiratory droplets or through contact with contaminated saliva, making it quite contagious so that it can lead easily to epidemics. It causes fever, muscle pain, headache, pain with chewing, loss of appetite, fatigue, and weakness. There is swelling of the salivary glands and associated pain (Figure). The virus can enter the bloodstream (viremia), allowing it to spread to the organs and the central nervous system. The infection ranges from subclinical cases to cases with serious complications, such as encephalitis, meningitis, and deafness. Inflammation of the pancreas, testes, ovaries, and breasts may also occur and cause permanent damage to those organs; despite these complications, a mumps infection rarely cause sterility.

Mumps can be recognized based on clinical signs and symptoms, and a diagnosis can be confirmed with laboratory testing. The virus can be identified using culture or molecular techniques such as RT-PCR. Serologic tests are also available, especially enzyme immunoassays that detect antibodies. There is no specific treatment for mumps, so supportive therapies are used. The most effective way to avoid infection is through vaccination. Although mumps used to be a common childhood disease, it is now rare in the United States due to vaccination with the measles, mumps, and rubella (MMR) vaccine.

This child shows the characteristic parotid swelling associated with mumps. (credit: modification of work by Centers for Disease Control and Prevention)