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Know your mouth

The oral cavity or the mouth is an important part of the human body. Given below are the three basic structures that overall comprise the oral cavity.

They are:

1. Oral Mucosa –Is the mucous membrane that covers the entire oral cavity. It may be coloured from pink to brownish purple.

Muscles -Lips, cheeks and the tongue, all contain muscles in some form or the other. They facilitate the movements in the oral cavity.

Bones - The upper jaw (maxilla) and the lower jaw (mandible) are the bony components of oral cavity.

Lips, Cheeks & Floor of the Oral cavity

Lips - Are the only visible external part of the oral cavity. It is covered with skin on the outside and mucosa on the inner side. Their functions involve food and water intake as well as articulation of speech.

Cheeks – It forms the part of the face between the eyes, nose, ear and chin. The region is innervated with buccal nerve. They are covered with skin on the outside and by mucosa on the inside.

Floor of the Oral cavity - Holds the tongue at its interior end. It is formed of muscles and is covered with mucosa. It also serves as a diaphragm that separates the oral cavity.

Palate - Is the ceiling or the roof of the oral cavity. The front portion of the palate is constructed of bone (specifically two bones called the maxilla and the palatine) covered with a mucous membrane. Further back in the mouth, behind the hard palate, lies the soft palate. The hard and soft palate separates the oral cavity from the nasal cavity. The presence of the palate makes it possible to breathe and chew at the same time. The palate also aids speaking and singing.

Faucial Pillars -- It is located between the oral cavity and the throat. There are two pillars one in front of the tonsils and the other behind the tonsils.

Tonsils -- The tonsils are two clumps of tissue, on either side of the throat .They defend the body. Tonsils are active upto 12 years of age. If infected at a later stage, doctors recommend surgically removal.

Tongue -- Tongue is a highly mobile, flexible, muscular structure attached to the floor of oral cavity at one end and free at the other. The tongue is made of mainly skeletal muscle. The upper surface of the tongue is covered with tiny projections called papillae. Four main types of taste buds found here, are — sweet, salty, sour, and bitter.

It plays an important role in speech the formation of food bolus and swallowing.

Teeth

Humans are diphyodont, meaning that they develop two sets of teeth in a lifetime. The first set of teeth, the deciduous teeth are also called the milk, primary, temporary, or baby teeth. These teeth begin to develop before birth, start to appear in the mouth between the ages of 6 months and 1 year and usually start to fall out when a kid is around 6 years old. They are replaced by a set of permanent teeth, which are also called secondary or adult teeth.

Development of Teeth

Although teeth aren't visible at birth, both the deciduous and permanent teeth are forming beneath the gums.

Milk Teeth or Deciduous Dentition

The milk / primary teeth are the first set of teeth in humans and many mammals. They start to form in the embryo phase during pregnancy. The development initiates in the sixth week as dental lamina. The process starts at the midline and then spreads back into the posterior region. By the time of eight weeks, there are ten areas on the upper and lower arches that will eventually become deciduous dentition. These teeth continue to form until they erupt in the mouth.

The milk teeth usually start erupting from the 6th month of age. By the time a child is 3 years old, he or she has a set of 20 deciduous teeth, 10 in the lower and 10 in the upper jaw. Each jaw has four incisors, two canines and four molars.

Variations in tooth eruption from normal are not unusual and may be familial. Delayed eruption can also occur because of syndromes (ie: Down’s Syndrome, Ectodermal Dysplasia), developmental defects of teeth, cysts or tumors. Teeth usually erupt earlier for girls than boys and there are also reports of racial differences. Eruption is usually symmetrical and delays of more than 6- 12 months from normal should be evaluated.

Variations in infant and toddler behavior, sometimes associated with systemic manifestations are common during teething. Continuation of symptoms beyond 24-48 hours should be evaluated by the physician.

Symptoms Attributed to Teething

• Irritability
• Fever
• Drooling
• Diarrhea
• Mouthing
• Pain
• Sleep Disturbance
• Rash
• Biting
• Gum Rubbing
• Ear Rubbing
• Decreased Appetite

Around five to six years of age preschoolers will begin to notice teeth becoming loose occasionally causing discomfort. This may go on for some time before a tooth is lost – the lower front primary teeth usually are the first lost. This process will continue periodically for the next six to eight years. Again, variability is common with initiation of exfoliation, the rapidity of loss, the associated discomfort, the retention of very loose teeth, and the loss of the final primary tooth around twelve to fourteen years of age. It should be noted, that about the same time the primary teeth begin to exfoliate, the first permanent molars (six year old molars) may begin erupting. This occurs without the loss of any primary teeth, distal to the last primary molar. Here too, there can be some discomfort and irregularities that may require intervention.

One of the more common times for a parent to have dental concerns is with the eruption of the permanent lower incisors (front teeth). One or more incisors can erupt lingual or in back of the primary incisors. Often, the lower primary incisors have just become mobile and the parent and/or child is not aware that it is time for these teeth to exfoliate.

Early or delayed loss of primary teeth can be a concern and needs to be evaluated. Premature loss of primary teeth before 5 – 6 years of age can be associated with local factors or systemic problems and requires evaluation and intervention.

Around five to six years of age preschoolers will begin to notice teeth becoming loose occasionally causing discomfort. This may go on for some time before a tooth is lost – the lower front primary teeth usually are the first lost. This process will continue periodically for the next six to eight years. Again, variability is common with initiation of exfoliation, the rapidity of loss, the associated discomfort, the retention of very loose teeth, and the loss of the final primary tooth around twelve to fourteen years of age. It should be noted, that about the same time the primary teeth begin to exfoliate, the first permanent molars (six year old molars) may begin erupting. This occurs without the loss of any primary teeth, distal to the last primary molar. Here too, there can be some discomfort and irregularities that may require intervention.

One of the more common times for a parent to have dental concerns is with the eruption of the permanent lower incisors (front teeth). One or more incisors can erupt lingual or in back of the primary incisors. Often, the lower primary incisors have just become mobile and the parent and/or child is not aware that it is time for these teeth to exfoliate. Parents should be made aware that this is not a dental emergency. They should encourage the child to help exfoliation by wiggling the primary incisors.

Early or delayed loss of primary teeth can be a concern and needs to be evaluated. Premature loss of primary teeth before 5 – 6 years of age can be associated with local factors or systemic problems and requires evaluation and intervention.

Chronology of the Human Dentition

Primary Dentition (Milk teeth)Tooth Hard Tissue Formation BeginsEruptionRoot CompletedExfoliationMaxillary (Upper Jaw)Central incisor4 mo in utero8-12 mo1 1/2 yr 6-7 yrLateral incisor 4 1/2 mo in utero 9-13 mo 2 yr7-8 yrCuspid5 mo in utero16-22 mo 3 1/4 yr 10-12 yrFirst molar5 mo in utero13-19 mo2 1/2 yr9-11 yrSecond molar6 mo in utero25-33 mo3 yr10-12 yr Mandibular (Lower Jaw) Central incisor 4 1/2 mo in utero 6-10 mo 1 1/2 yr 6-7 yr Lateral incisor 4 1/2 mo in utero 10-16 mo 1 1/2 yr 7-8 yrCuspid 5 mo in utero 17-23 mo 3 1/4 yr 9-12 yrFirst molar 5 mo in utero 14-18 mo2 1/4 yr 9-11 yrSecond molar 6 mo in utero 23-31 mo3 yr 10-12 yrPermanent DentitionMaxillary (upper Jaw)Central incisor3-4 mo 7-8 yr 10 yr Lateral incisor 10-12 mo 8-9 yr 11 yr Cuspid 4-5 mo 11-12 yr 13-15 yr First bicuspid 1 1/2 - 1 3/4 yr 10-11 yr 12-13 yr Second bicuspid 2-2 1/4 yr 10-12 yr 12-14 yr First molar at birth 6-7 yr 9-10 yr Second molar 2 1/2 - 3 yr12-13 yr 14-16 yr Third molar 17-21 yr Mandibular (Lower Jaw) Central incisor 3-4 mo 6-7 yr 9 yr Lateral incisor3- 4 mo7-8 yr 10 yr Cuspid 4-5 mo 9-10 yr 12-14 yr First bicuspid1 3/4 - 2 yr 10-12 yr 12-13 yr Second bicuspid 2 1/4 - 2 1/2 yr 11-12 yr 13-14 yr First molar at birth 6-7 yr 9-10 yr Second molar 2 1/2 - 3 yr 11-13 yr 14-15 yr

Delayed exfoliation can also be a concern and may be due to local factors or syndromes. Again, with periodic professional oral care and monitoring of development, intervention can be recommended at appropriate times.

As primary teeth erupt the occlusion develops. Here too, alterations from normal are common. They too can be due to environmental factors (habits) and/or congenital/hereditary disorders. The occlusion is assessed by having the child bring their jaws together. This is not always a simple task for some children. When requested they may jut their lower jaw forward or bite to one side or the other. With the primary dentition we are most interested in the anterior posterior relationship of the jaws, the horizontal relationships (from cheek to cheek) and finally the position of the upper and lower teeth. Variations from normal should be evaluated depending upon the child, and if function is compromised, treatment may be indicated.

The deciduous teeth help the permanent teeth erupt in their normal positions; most of the permanent teeth form just beneath the roots of the deciduous teeth. When a deciduous tooth is preparing to fall out, its root begins to dissolve. This root has completely dissolved by the time the permanent tooth below it is ready to erupt.  The phase during which permanent teeth develop usually lasts for about 15 years as the jaw steadily grows into its adult form. The wisdom teeth (third molars) erupt between the ages of 17 and 21. Sometimes there is no room in a person's mouth for all the permanent teeth.

If this happens, the wisdom teeth may get stuck (or impacted) beneath the gum and may need to be removed. Overcrowding of the teeth is one of the reasons people get braces during their teenage years.

Structure of the Teeth

Enamel: It is the hardest tissue in the human body, covering the crown of the tooth. It is highly mineralised tissue as 96% of it’s content is mineral organic content and water comprising the rest.

Dentin: Dentin gives the tooth its slightly yellowish tint. Any injury to the dentin causes pain.

Cementum: Cementum covers the root and holds the tooth in place within the jawbone. It s as hard as bone but not as hard as enamel, which enables the tooth to withstand the pressure of chewing and protects it from harmful bacteria and changes in temperature from hot and cold foods.

Pulp: The pulp is the innermost portion of the tooth. Unlike the other parts of the tooth, the pulp is soft. It is made of connective tissue, nerves, and blood vessels, which nourish the tooth. Blood vessels and nerves enter the root through a small hole at the very bottom of the tooth called the apical foramen.

Gums and Supporting Bone

Gum tissue (gingiva), a specialised portion of the oral mucosa, connects to each tooth at the neck and extends over the root and supporting bone. In a healthy mouth, the root remains entirely out of sight below the gum line. The gum tissue attaches securely to the underlying structures except at the upper edge, where it forms a tiny flap about 1.5 millimeters wide, at the margin of the tooth and gum. The V-shaped hollow under this flap is called the sulcus.

It's easy for food and bacteria to get trapped in this sulcus. This can lead to inflammation and eventually to periodontal disease, also called gum disease. If a gum disease spreads further down it affects the supporting bone and causes the loosening of the tooth .

Salivary Glands

These glands are found in and around your mouth and throat. The glands secrete saliva into your mouth through salivary gland ducts. Salivary glands produce the saliva used to moisten your mouth, initiate digestion and help protect your teeth from decay.

Saliva

Secretion of saliva is under control of the autonomic nervous system, which controls both the volume and type of saliva secreted.

Functions of Saliva include:

Lubrication and binding: The mucus in saliva is effective in binding masticated food into a slippery bolus that (usually) slides easily through the oesophagus without inflicting damage to the mucosa.

Solubilises dry food: In order to be tasted, the molecules in food must be solubilised.

Oral hygiene: The oral cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean. Flow of saliva diminishes considerably during sleep, allow populations of bacteria to build up in the mouth -- the result is dragon breath in the morning. Saliva also contains lysozyme, an enzyme that lyses many bacteria and prevents overgrowth of oral microbial populations.

Initiates starch digestion: The serous acinar cells secrete an alpha- amylase which can begin to digest dietary starch into maltose. Amylase is not present, or present only in very small quantities, in the saliva of carnivores or cattle.

Provides alkaline buffering

Jaw Joint

The temporomandibular joint (TMJ) connects the lower jaw, called the mandible, to the temporal bone at the side of the head. These joints are flexible causing the jaw to move smoothly up and down and side to side, enabling us to talk, chew and yawn. Muscles attached to and surrounding the jaw joint controls its position and movement.