kinds of Teeth “permanent teeth”

The teeth have the most important role and the hardest structure in human's jaws and many other spinescent animals. The main function of the teeth is cutting and grinding the food pieces. Further more, they help us in speaking properly.

Two kinds of teeth grow during every human's life cycle:

1-primary teeth.

2-permanent teeth .

The number of primary teeth is 20 which are distributed equally in the two jaws.

After a while, the 32 permanent teeth are replaced the primary ones gradually.

As the primary teeth are the base of the permanent teeth, having good oral hygiene is necessary.

Around the 8th week after conception, oval-shaped tooth buds start to form and harden in the embryo's mouth. Although the baby teeth aren't visible when a child is born, both the primary and permanent teeth are partially formed below the gums. The tooth crown develops first and after it is fully grown, the root begins to develop.

Then between about six months and 1 year old, the deciduous teeth begin to push through the gums. This process is called baby teeth eruption . A child gets his first complete set of primary teeth by the age of 3. The baby teeth chart shows the average age that each primary tooth is expected to erupt. But not all baby teeth follow these rules. Some infants may have their first primary tooth (usually one of the bottom middle teeth) erupted as early as 3 months.Others may reach their first birthday or more without getting their first deciduous tooth. If there is no sign of teething by this age you should ask for a pediatrician's advise. That kind of late development of primary teeth is more common in premature babies. In some rare cases (1 every 2.000) infants are born with one or more teeth (called natal teeth) or may have teeth emerge within the first month (called neonatal teeth). A dentist should evaluate the teeth's condition, as they could be loose, interfere with feeding or irritate the baby's tongue.

2- permanent (adult) teeth:

Adult teeth or permanent teeth replace the primary teeth. They aid in digestion, speech and general appearance. There are 32 permanent teeth, with the main difference from primary teeth is that there are 4 premolars and 6 molars in each arch. Permanent teeth begin erupting at 6yrs of age and end at 21yrs of age. Some people may not have some if not all their 3rd molars due to evolutionary changes leading to the lack of development of these teeth. 3rd molars may not erupt due to becoming embedded in jaw. The tooth consists of a crown and root, and the tooth is composed of different materials that aid in strengthening, preserving and maintaining its function.

Adult teeth begin to replace the front milk teeth from the age of about six. For the next six to eight years there is a gradual replacement of milk teeth by adult teeth. This stage is called mixed dentition, as both milk and adult teeth will be from the mouth at the same time. By the age of about 12-14 all adult teeth should have appeared using the exception of wisdom teeth (third molars). At this stage the mouth will contain twenty-eight teeth. These teeth have to last for life as we only get one set.

The permanent tooth begins to grow under the baby tooth.

• The root of the baby tooth begins to dissolve (reabsorb), and the baby tooth becomes loose.


• It takes three and a half years for the baby tooth to lose its roots, and for it to be replaced by the permanent tooth.


• The crown of the permanent tooth is the first part of the tooth to develop.


• It grows into the space left by the root of the baby tooth.


• The root of the permanent tooth then continues to form.


• When the crown erupts, it is covered by a cuticle or covering that protects the enamel. The cuticle is slowly worn away by chewing and tooth brushing.

During 7 years, 20 baby teeth are lost and are replaced by 28 permanent teeth.

The mixed dentition stage is the period when some baby and permanent teeth are visible in the mouth at the same time.   

In addition, 4 wisdom teeth will erupt by the age of 21 years, taking the total number of permanent teeth to 32.

The eruption of the 32 permanent teeth starts at age 6, and is completed between the ages of 20 and 23, after the wisdom teeth (3^rd molars) have arrived.

The final four adult teeth should come through during late teens totaling 32 adult teeth. The descriptions below explain the functions of each of the teeth. To view a model showing all the milk and adult teeth erupting, take a look at the timeline showing the lifetime of teeth.

third molars often are not needed for chewing and are difficult to keep clean. Your dentist may recommend their removal to prevent potential complications when third molars are erupted partially or are impacted. The chart and photograph identify the names of the permanent teeth and provide the approximate ages at which you can expect the teeth to erupt. Heredity and other factors may influence the approximate ages at which children’s primary teeth shed and their permanent teeth emerge. Thorough brushing and flossing help remove food particles and plaque (a sticky film of bacteria) from the smooth surfaces of teeth. But toothbrush bristles cannot reach into the pits and fissures (depressions and grooves) of the chewing surfaces to remove food and plaque. Dental sealants protect these vulnerable areas by sealing out debris and plaque bacteria. A sealant is a plastic material that usually is applied to the

chewing surfaces of the back teeth—premolars and molars—where decay occurs most often. The plastic resin bonds into the pits and fissures of the chewing surfaces of back teeth. The sealant acts as a barrier, protecting enamel from plaque and acids.

Eruption Sequence of Permanent Dentition:

• Central incisors= 6-8 yrs


• Lateral incisors= 6.5-8.5yrs


• Canine = 9-13 yrs


• 1st Premolars= 9.5-11.5yrs


• 2nd Premolars= 10-13yrs


• 1st Molars =5.5-7yrs


• 2nd Molars= 11-13yrs


• 3rd Molars= 17-21yrs

 

 

The 32 fit into the jaw space for 20 baby teeth

The bones of the face grow during the period of tooth development.

• The jawbone normally grows in size to accommodate the extra teeth.


• The jaws grow at a faster rate than the rest of the face, and eventually measure up to 1/3 of the size of the face. This is a dramatic increase from the proportion at birth.


• If the jaws do not grow sufficiently, crowding or impacted teeth will result.

Permanent incisors: These are the front teeth, and there are 8 of them altogether (four at the top and four at the bottom). They are usually the first permanent teeth to come through, and are good for cutting into food (for example biting into an apple). You can tell which are the incisors by their flat edge at the top, and because they each have only one root.

Permanent canines: These front teeth are also known as 'eye teeth', and are more pointed in shape than the incisors, but like the incisors they each have a single root. There are 4 altogether, and in animals such as dogs and cats the canines are much longer, and are used for tearing off chunks of food. In humans they are smaller in size, and are good for cutting into food similar to incisors.

Premolars: These are the new, adult back teeth which replace the first and second deciduous molars. There are eight altogether, four first premolars and four second ones. Deciduous teeth don't have premolars as back teeth, just molars.

Permanent molars: These are the larger back teeth, which are good for crushing food into smaller pieces before being swallowed. This is known as chewing. Molars usually have more than one root each, and have irregular, or 'bumpy' surfaces with grooves called 'fissures'. There are first, second and third permanent molars, which come through in that order.

First permanent molars: The four first permanent molars are similar in size to the second molars and come through at around age 6 to 8 years.

Second permanent molars: The four second permanent molars are similar in size to the first permanent molars and come through at around age 12 years.

Third permanent molars: These are the very last of the adult teeth to appear between age 18 and 21 years, and are also called 'wisdom teeth'. There are four, and they come through at the very back and sometimes cause problems if there isn't enough room for them.

Kinds of teeth “primary teeth”

The teeth have the most important role and the hardest structure in human's jaws and many other spinescent animals. The main function of the teeth is cutting and grinding the food pieces. Further more, they help us in speaking properly.

Two kinds of teeth grow during every human's life cycle:

1-primary teeth.

2-permanent teeth .

The number of primary teeth is 20 which are distributed equally in the two jaws.

After a while, the 32 permanent teeth are replaced the primary ones gradually.

As the primary teeth are the base of the permanent teeth, having good oral hygiene is necessary.

   Around the 8th week after conception, oval-shaped tooth buds start to form and harden in the embryo's mouth. Although the baby teeth aren't visible when a child is born, both the primary and permanent teeth are partially formed below the gums. The tooth crown develops first and after it is fully grown, the root begins to develop.
Then between about six months and 1 year old, the deciduous teeth begin to push through the gums. This process is called baby teeth eruption . A child gets his first complete set of primary teeth by the age of 3. The baby teeth chart shows the average age that each primary tooth is expected to erupt. But not all baby teeth follow these rules. Some infants may have their first primary tooth (usually one of the bottom middle teeth) erupted as early as 3 months.Others may reach their first birthday or more without getting their first deciduous tooth. If there is no sign of teething by this age you should ask for a pediatrician's advise. That kind of late development of primary teeth is more common in premature babies. In some rare cases (1 every 2.000) infants are born with one or more teeth (called natal teeth) or may have teeth emerge within the first month (called neonatal teeth). A dentist should evaluate the teeth's condition, as they could be loose, interfere with feeding or irritate the baby's tongue.

1-primary teeth (baby or deciduous teeth):

The first teeth which are shed and replaced by permanent teeth.the first teeth begin to break through the gums at about 6 months of age. Usually, the first two teeth to erupt are the two bottom central incisors (the two bottom front teeth). Next, the top four front teeth emerge. After that, other teeth slowly begin to fill in, usually in pairs - one each side of the upper or lower jaw - until all 20 teeth (10 in the upper jaw and 10 in the lower jaw) have come in by the time the child is 2 ½ to 3 years old. The complete set of primary teeth is in the mouth from the age of 2 ½ to 3 years of age to 6 to 7 years of age.

Other primary tooth eruption facts:

•     A general rule of thumb is that for every 6 months of life, approximately 4 teeth will erupt.


•     Girls generally precede boys in tooth eruption


•    Lower teeth usually erupt before upper teeth.


•    Teeth in both jaws usually erupt in pairs ? one on the right and one on the left


•    Primary teeth are smaller in size and whiter in color than the permanent teeth that will follow


•    By the time a child is 2 to 3 years of age, all primary teeth should have erupted

Shortly after age 4, the jaw and facial bones of the child begin to grow, creating spaces between the primary teeth. This is a perfectly natural growth process that provides the necessary space for the larger permanent teeth to emerge. Between the ages of 6 and 12, a mixture of both primary teeth and permanent teeth reside in the mouth.

When tooth falls out	When tooth emerges	Upper Teeth
6 to 7 years	8 to 12 months	Central incisor
7 to 8 years	9 to 13 months	Lateral incisor
10 to 12 years	16 to 22 months	Canine (cuspid)
9 to 11 years	13 to 19 months	First molar
10 to 12 years	25 to 33 months	Second molar
		Lower Teeth
10 to 12 years	23 to 31 months	Second molar
9 to 11 years	14 to 18 months	First molar
9 to 12 years	17 to 23 months	Canine (cuspid)
7 to 8 years	10 to 16 months	Lateral incisor
6 to 7 years	6 to 10 months	Central incisor

The table shows when the primary teeth emerges.

Tooth Anatomy” part 3 ”structure supported tooth

Gingiva:

   is tough connective tissue which lines the base of the teeth, holding them in place and protecting the jaw and teeth roots from infections. Known informally as the gums, the gingiva are a very important part of the oral anatomy, and caring for them is critical to maintaining oral health. Problems with the gingiva can be identified during routine oral examinations, or noted by patients who experience changes in their mouths.

connective tissue has a strong fibrous underlayer, covered in a layer of mucous membranes. The gingiva are very tough, designed to resist trauma from chewing and hard foods which enter the mouth. The base of this tissue is firmly anchored to the bone, while the upper portion is free, allowing the gingiva to run between the teeth to help stabilize them and keep them in place. In addition to anchoring the teeth, the gingiva also create a seal which prevents bacteria, plaque, and other foreign material from entering the roots of the teeth, where it could cause trauma or infection.

When a patient's gingiva become chronically inflamed, the condition is known as  gingivitis. Classic symptoms of gingivitis can include changes in the color of the gingiva, along with swelling and bleeding. Patients may find that their gums are very tender after brushing their teeth, or that the gums bleed freely after oral care or eating. Gingivitis can lead to complications which include serious infections, and it is an issue which needs to be addressed.

Over time, the gingiva can recede. Sometimes gum recession is caused by gingivitis, but it can also be associated with other oral problems, or occur on its own. Receding gums are a cause for concern because they can expose a patient to the risk of infections and destabilize the teeth. Other gingival diseases can include gingival cancer, in which the cells in the gums become malignant, and gingival hyperplasia, in which the gums grow grossly enlarged.

The gingiva is that portion of the gums that surrounds the teeth and lies above the level of the bone.  The diagram to the right is a detail which shows the microscopic structure of this vital attachment of the gums to the tooth.  The soft tissue is covered by an epithelial layer (red) called the oral epithelium.  This attaches to the surface of the tooth on the dentin between one and three millimeters below the level of the crest of the gingiva.  The part of the gingiva below the crest but above the attachment is called the free gingival margin.  The potential space between the free gingival margin and the tooth (collapsed in life) is called the gingival sulcus.  Just below the epithelial attachment lies a large number of connective tissue fibers (blue) called the gingivo-dental fibers.  Some, which are not visible here actually circle the entire tooth and are called circular fibers.  These fibers are responsible for securely attaching the gingiva to the tooth.

In light-skinned individuals the gingiva can be readily distinguished from the adjacent dark red alveolar mucosa by its lighter pink color.

In dark-skinned people the gingiva may contain melanin pigment to a greater extent than the nearby alveolar mucosa. This melanin pigment is synthesized in specialized cells and is produced as granules that are stored within the cells that produce melanin. If pigmented gingiva is surgically inspected it will often heal with little or no pigmentation. Therefore surgical procedures should be designed so as to preserve the pigmented tissues. Clinicians sometime use the terms free and attached gingiva. Attached gingiva refers to the portion of the gingiva towards the top of the tooth. Free gingiva is firmly bound to the underlying tooth and alveolar bone.

The area of the gingiva near the crown of the tooth (Gingival margin) in young people is more likely to become exposed as a result of tooth eruption.

he gingiva occupies the spaces between teeth. It is composed of a pyramidal papilla in the incisor region. The gingiva is attached to the tooth by an epithelium and by connective tissue fibers at the top.

The attachment (between the gingiva and the teeth) is responsible for separating the dirty oral environment from the totally clean environment inside the body.  The gingival attachment is doubly important because it protects the underlying bone (alveolar crest) from becoming infected.  Nature is especially protective of the bone because it is not highly vascularized  and an infection in bone, especially in pre modern man's environment would have been a death-dealing event.  An infection in bone is called osteomyelitis, and even today, with modern antibiotics, it is still quite a dangerous condition.  Thus nature built in a simple mechanism to protect mammals from getting osteomyelitis as they aged and became more susceptible to oral infection.  She programmed the bone to reabsorb (to be absorbed); to "get out of the way" before the infection reached it.  This is the basis of periodontal disease---The loss of bone as a protective mechanism against a dangerous bone infection.  Better the loss of the teeth than the premature loss of life!

Problems with the gingiva include the following medical conditions:

Gingivitis Periodontitis Acute Necrotizing Ulcerative Gingivitis Primary Herpetic Gingivostomatitis Gingival Hyperplasia or Enlargement Epulis (Localized gingival enlargement) Gingival Erosions.

The periodontal Ligament (PDL):

It is the soft tissue that lies between the tooth and its bony socket.  As you can see, it is really just a continuation of the connective tissue associated with the gingivo-dental fibers.  In a healthy situation, there is never a direct attachment between the bone and the tooth itself.  Such a direct attachment, when it occurs in pathological situations, is called ankylosis.

The PDL is composed of fibrous connective tissue in which the fibers run approximately perpendicularly from the tooth surface to the bony socket.  In any given area, a cross section looks like a tangled mass of nearly parallel fibers that attach at one end into the cementum overlying the root of the tooth, and at the other end, into the aveolar bone inside the socket.

The bone that supports the teeth is called alveolar bone.  It's only purpose in life is to support the teeth, and if a tooth is extracted, the alveolar bone that originally supported it will eventually be reabsorbed by the body.  The part of the alveolar bone that lines the socket is a thin layer of dense cortical bone called the lamina dura.   The bone that underlies the lamina dura is cancellous bone (sometimes called medulary bone).  Cancellous bone looks spongy and contains blood producing "organ" called bone marrow.  In fact, all three of the features discussed in this section, the lamina dura, the periodontal ligament and the cancellous bone can be seen on any intraoral dental x-ray.  In the x-ray seen on the left, follow the edge of any of the three teeth present from the top of the crown down into the bone.  The dark line that separates the tooth from the bone represents the space where the periodontal ligament lives.  The thin bright strip of bone directly beside the periodontal ligament space is the lamina dura.  Under the lamina dura is the less bright cancellous bone.  If you look carefully you can see the trabeculii --the tiny spicules of bone crisscrossing the cancellous bone that make it look spongy.  These trabeculii separate the cancellous bone into tiny compartments which contain the blood producing marrow.  These marrow spaces are seen in the colored image of the PDL above as bright "blobs".

he PDL acts like a shock absorber and transmits chewing forces from the tooth to the  bone. It gives a little, like a water bed, so that the tooth can move in its socket. When alveolar bone is lost from gum disease, the total amount of PDL tissue holding the tooth is reduced and the tooth become increasingly loose. Loose teeth are a bad sign.

The periodontal ligament feels and sends pressure information to the brain when you bite. The PDL also feels pain. It tells the brain when you are biting down and the information is used to coordinate chewing. A tight ligament around the tooth also prevents bacterial invasion. A healthy PDL also protects the nerves and blood vessels contained in the area.