dental

The teething of a human is divided into primary (milkteeth) and permanent (Fig. 1). Teeth are also organized in two arches: superior which is called maxillary, and inferior which is called mandibular. Those arches are further divided into left and right halves. Each tooth is linked to the bone by suspensory periodontal ligament (Fig. 2). Teeth have classifications according to their shape, that is in turn reflects a specified function. Incisors do the cutting of a bite; canines or eyeteeth do the tearing and biting. The premolars (bicuspids) and molars crush and grind the food due to their shape with broad crowns and rounded cusps (tips) (Fig. 3). 

The primary teeth, which are temporary, begin to appear at the age of 6 months. As we mentioned earlier, they are composed of 20 teeth, divided into 10 in each jaw, and 5 in each quadrant. They are two incisors (central and lateral), a canine, and two molars, and named as letters A, B, C, D and E (Fig. 4).

The permanent teeth are a set of 32, 16 in each arch and 8 in each quadrant, Consisting of two incisors (central and lateral), a canine, two premolars, and three molars. They are numbered by 1 for central incisor to 8 3rd molar or ‘wisdom’ tooth. They begin to appear at the age of 6, and complete the set at the age of 13, except of the third molars, that may appear at the age of 21 or do not appear at all (Fig. 5).  

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Anatomically, the tooth is divided into two main structures: the crown and the root, which characterized by their components and type of hard tooth tissue on the surface. 

The anatomic crown is covered by enamel. Enamel is the outer hard layer, lacking blood vessels, composed of water, proteins, and high concentrations of minerals. It plays a vital role in protecting other inner fragile components, as well the first defense against caries (Fig. 6).

The anatomic root in turn is covered by cementum, which is a softer content, with bonelike material. It is stocked in gum socket and become visible only with dental injuries or periodontal diseases (Fig. 6).

Clinically, the tooth has two other classification parts: clinical crown, what we could see with the eye; and clinical root, the other hidden part of the tooth. 

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Underneath enamel and cementum, lies down a middle structure of the tooth called dentine (Fig. 6). Dentine is a living tissue, containing vessels and nerves; it consists of minerals making it the second hard tissue after enamel, in addition to water. The dental pulp is the center part of the tooth, it is vascularized and innervated tissue, with soft gelatinous structure. This dental pulp exists in a space called the pulp cavity. This cavity extends throughout the root until it reaches the apex, that open with the apical foramen making a route for blood vessels and nerves to enter the dental pulp; this also makes the root vulnerable to infections affecting the surrounded tissues (Fig. 7). The crossing area between the dentine and enamel is called the dentineo-enamel junction (DEJ) (Fig. 7). The edge where the anatomic crown meets the anatomic root (where the enamel meets the cementum) is called the cemento-enamel junction (CEJ).

The permanent dentition consists of four main types of teeth: incisors, canines, premolars, and molars. In order to name the teeth, we have the following formula: Dentition, arch, quadrant, tooth type. For example: permanent maxillary left lateral incisor (Please note that premolars do not present in the milk teeth) (Fig. 8). 

Each jaw has 4 incisors; thus, the primary and permanent dentition consists of 8 ones. They are positioned frontal to the mouth and have straight edges which help in cutting bites. The central incisors are the nearest to the median plane of the body, and lateral incisors lie between the central incisors and the canines. Maxillary incisors are the most susceptible teeth to traumas due to their position and shape, especially between children with incidence rates of 1 in 10. This kind of traumas has significant complications on the digestion process, in addition to other cosmetic and psychologic complications (Fig. 9). 

Canines or cuspid teeth exist in both primary and permanent dentition, being two in each jaw. They serve as a breaker and holder of the food, that is why their edges take incisal shape with sharp, triangular projections. This kind of dentition has different related morbidities; teenagers with crowded teeth may have canines failed to appear, requiring surgery to fix this deficit. Teeth crowding happens when there is inconsistency between the size of the teeth and dimension of the arch; this led to canines positioned radiographically in the palate, or high the buccal sulcus (Fig. 10). 

Premolars do not erupt with the primary teeth. Premolars are transitional teeth between molars and canines and have features ranging between these two types. In general, the permanent dentition consists of 8 of them with 2 cusps. In order to fix crowded teeth problem, surgeons used to extract premolars to free space for other teeth, especially, before starting orthodontic treatment (Fig. 11).

Molars are located backwards in the mouth, and they are responsible of breaking and chewing the food before swallowing it. The primary teeth consist of 8 molars, whereas permanent teeth consist of 12 molars, 6 in the upper jaw (maxillary) and 6 in the lower jaw (mandibular), with cusps ranging from 3 to 5. Because of their shape of the surface, molar teeth are more vulnerable to dental caries. In addition to the shape, the molars are to close in this area, making cleaning them more difficult (Fig. 12). 

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Impacted teeth are the case when they fail to erupt and remain fixed in the gum or bone. They could present symptoms such as pain, that is why they need to be handled by surgical removal. Wisdom teeth are the most commonly impacted teeth encountered (Fig. 13). 

Dental caries are tiny holes within the hard structure of the tooth. It called commonly tooth decays. The process of which carries developed is based on plaques formation by bacteria, which then converts carbohydrates into acid and damages the normal structure of the tooth. The best way to prevent dental caries is by caring of the oral hygiene properly (Fig. 14). 

We all have encountered cases where malocclusions of teeth existed and required special treatments. These cases make of around 30% of the population. The special deals with those are the orthodontics. Orthodontics is concerned with the diagnosis, prevention and treatment of mal positioning of teeth and jaws. Dentofacial orthopedics is branch of orthodontics deals with facial deficits. Dealing with the main structures of the body is not easy, that is way a treatment for such cases takes a time, and as early as we begin, as better outcomes we receive. The treatment could be surgical in some severe cases, and non-surgical, in which dental braces are used. Braces are tools help to correct the aligning of the teeth, and fix gaps between them (Fig. 15).

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  a. 30 teeth

  b. 24 teeth

  c. 32 teeth

  d. 20 teeth

  a. 6

  b. 8

  c. 9

  d. 7

  a. Enamel

  b. Cementum

  c. Dentine

  d. Periodontal ligament

  a. Molar

  b. Premolar

  c. Incisor

  d. Canine

  a. Incisor teeth

  b. Canine teeth

  c. Wisdom teeth

  d. Premolar teeth