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.