The tooth is formed of  crown (the visible portion in the mouth) and  root (the part anchored in the alveolar bone).
The crown is made of enamel and dentin, which shelter inside the pulp chamber, where the nerve is found.
The root is made up of dentin (extension from the crown), outside is the cement, and inside is the extension of the pulp chamber - the root canals.

Picture 1. Tooth anatomy

Causes of structural anomalies

These structural anomalies can affect both dentition, the milk teeth and permanent teeth.
Milk teeth are formed during the intrauterine period; so the causes of these defects are most often the result of disorders of the mother's body:

• Rubella;
• Toxoplasmosis;
• Deficient nutritional during pregnancy;
• Abuse of alcohol or tobacco by the pregnant woman;
• Traumatic birth;
• Irradiators, medicines;
• Prenatal Asphyxia;
• Hereditary transmission.

Permanent teeth begin to form during intrauterine life and after birth, so abnormalities can result from both the mother and child's affections:

• Rachitis;
• Acute infections;
• Gastrointestinal diseases;
• Hypovitaminosis, low intake of minerals and proteins;
• Infections of temporary teeth;
• Medicines (tetracycline);
• Poisoning with various substances (fluorine).

Some anomalies are evident when the teeth appear on the arch, others become apparent after a period of time from the eruption.

Classification of structural anomalies

Structural abnormalities (dysplasia) can affect both the milk teeth and the final teeth. They can be isolated (affecting one tooth), symmetrical (affecting the teeth in the same category) or generalized (all teeth of a dentition), depending when the disorders of mother or child appear.
Anomalies can be hereditary, acquired or congenital.

Anomalies are classified according to the tissue they disturb:

1. Structural anomalies that interest the enamel:

-  Amelogenesis imperfecta: 
a. Hypoplasia
b. Hypocalcified
c. Hypomaturation

2. Structural anomalies that interest the dentin:
- Dentinogenesis imperfecta;
- Dentin dysplasia;
- Vitamin D resistant rickets.

3. Structural anomalies that interest the cement:
- Hypophosphatasia;
- Cledo-cranial dysplasia;
- Dystrophic epidermolysis  bullosa.

4. Structure anomalies that interest all tissues:
- Regional odontodisplasia.

Amelogenesis imperfecta

The enamel is formed from ameloblasts (specialized cells) through a process called amelogenesis. When disturbances occur in this process (usually genetic), amelogenesis imperfect  occurs and it can be transmitted hereditary.

There are three types:

a.Hypoplasia type. Enamel develops poorly, is thin, tough, white or brown, teeth have an irregular contour and the contact points between the teeth  are missing.

Picture 2.

b. Hypocalcified type. There is a calcium deficiency, the enamel color is yellow or brown, it's thin, abrases quickly  exposing the dentin.

Picture 3. Exposed dentin                              Picture 4. Yellow enamel

c. Hypomaturation type. The enamel is normal in thickness, but maturation is faulty, may be white, brown, yellow,  teeth seem to be covered with snow.

Picture 5. Teeth appear  to be covered with snow

Because of these defects, affected teeth are prone to rapidly evolving caries, fractures and trauma.
The treatment is mainly done using dental crowns, to compensate the enamel that is weak quantitative and qualitative. At milk teeth, metal or composite crowns are usually used, and in adolescence, after the bone finishes to grow, they are replaced with ceramic ones. In the most serious situations, extractions are recommended, and then replaced with implants.

Dentinogenesis imperfecta

The dentin is secreted by the odontoblasts through the dentinogenesis process. Like imperfecta amelogenesis, imperfecta dentinogenesis is caused by genetic factors and can be transmitted hereditary.
The main feature of this disease is the gray-blue coloration of the teeth.

Picture 6. Blue-gray stains from dentinogenesis imperfecta

There are 3 types of  dentinogenesis imperfecta after Shields:

I. Type I- is associated with osteogenesis imperfecta  (bone anomaly)
Temporary teeth are more affected than permanent teeth, the teeth are gray-blue to yellow-brown, the dentin is opalescent, bulbous crowns, obliterated pulp chamber.

Picture 7. Type I                                   Picture 8. Osteogenesis imperfecta

II. Type II- isn`t associated with bone damage. Both dentures are affected in the same way.
III. Type III- is characteristic only to the temporary teeth. The crowns have the shape of a bell.

The treatment of this condition consists in making the crowns, at least in the lateral area of the milk teeth, to maintain the vertical dimension of the occlusion. Dental crowns are required at permanent teeth. Fillings are not a long-lasting solution, with dentin being soft.

Picture 9.  Treatment of temporary teeth with metal crowns.

Picture 10.  The treatment of dentinogenesis imperfecta in adults

Regional odontodisplasia

It is an anomaly of unknown etiology, it is associated with osteogenesis imperfecta; superior teeth are more often affected, which may have eruption delays or even don`t erupt at all.
Radiologically, a large pulp chamber is observed, to the detriment of dentin and enamel that are thin, "ghost" teeth, no root and low bone density.

Picture 11.  Regional odontodisplasia- clinical and radiological aspect

Acquired anomalies

Acquired anomalies occur as a result of inappropriate use of drugs by children during the development of permanent teeth. It's about fluorosis and dystrophy from tetracycline.
These conditions are presented because they are similar to amelogenesis and dentinogenesis imperfecta.
Dental fluorosis occurs due to the inappropriate use of dental hygiene products with a high fluoride content. Clinically there appear white-creamy lines in the enamel, which is not affected. In severe cases, the spots are yellow to brown, enamel is irregular and prone to caries. A differential diagnosis is made with amelogenesis imperfecta.
As a precaution, it is recommended that oral hygiene products in children aged 6-8 years to have a lower fluorine content.
The treatment is cosmetic, with fillings, and in more serious cases with facets or crowns.

Picture 12. Simple / severe fluorosis

Discoloration by tetracycline is caused by the an antibiotic (tetracycline)  given to children less than 7 years old to treat various infections. Both teeth are affected, the coloration is final and varies from yellow to gray and brown. Differential diagnosis is done with dentinogenesis imperfecta.
Prevention is the information of parents and the use of other antibiotics, and the treatment consists in facets or crowns.

Picture 13. Discoloration by tetracycline

Author: Dr. Adriana Lepadatu - Cucoli, dentist at ABC Eurodent
Sources: www.romedic.ro, Estetica in odontoterapia restauratoare, Mariana Brandusa Popa, www.umfiasi.ro, www.doctoruldedinti.info, www.slideshare.net
Picture sources: printer-friendly.adam.com, www.slideshare.net, www.doctoruldedinti.info, skinoutfit.info, ro.pinterest.com, bondistry.com, archieve.ijds.in, www.scielo.br, www.dentistul.info, www.doctoruldedinti.info, www.ralph-badaoui.fr