Etiology and the stage of teeth development govern the outcome of the defective tissue. In cases of genetically originated effects, the resultant defects have affected the entire tissue from the start to the end of its development because the genetic effect has been continuous. In comparison, defects caused by environmental factors are determined by the starting time and the length of exposure to the environmental factor.
Tooth formation involves a series of developmental processes, and any disturbance in these processes could lead to defects proportionate to the severity and timing of the disturbance.
4.1 Genetically Originated Defects
4.1.1 Disturbances in Teeth Count
Normal infants develop their primary dentition (milk teeth, deciduous teeth) of 20 primary teeth, while adults develop their permanent dentition by replacing the primary teeth in addition to adding other permanent teeth posteriorly, making 32 teeth in total. Any disturbances in these numbers can lead to abnormalities in occlusion, function, and aesthetic. In contrast, hyperdontia is when the number of teeth exceeds the normal number and hypodontia is lowered the normal number.
22.214.171.124 Reduced Numbers; Missing Teeth
Accurate assessment requires a clinical and radiographic examination.
A reduced number of teeth could manifest clinically as a single missing tooth or multiple missing teeth. Hypodontia is the general term used when the normal number of teeth is reduced. More accurately, one to four missing teeth is hypodontia (Figures 4.1, 4.2, and 4.6), more than four missing teeth should be termed oligodontia (Figures 4.3–4.13), and anodontia is the correct term when there is complete absence of teeth (Figure 4.14).
Hypodontia can affect both dentitions as it is genetically determined. If there is an abnormality of number in the primary dentition, then there is a 40% chance of a numerical abnormality in the permanent dentition.
These cases are more commonly associated with syndromes where other organs are also affected. An example is ectodermal dysplasia, where the affected patients usually only have a few conical deformed teeth. Existing teeth are abnormally positioned within the bone of the arches with significant spacing. In most instances, erupted teeth tend to be located anteriorly, with no teeth in the premolar and molar areas (Figures 4.3–4.5 and 4.10–4.13).
There are no teeth in either arches, and the clinical appearance is of a reduced vertical face height and protuberant lips. This appearance is due to the reduced vertical height resulting from missing teeth and the absent alveolar process. The prevalence of anodontia is very low. These patients are otherwise healthy and usually free from any systemic disease – an exception being the association with ectodermal dysplasia (Figure 4.14).
126.96.36.199 Increase in Numbers; Extra Teeth
Accurate assessment requires a clinical and radiographic examination. One classification refers to the location of the extra teeth; anterior or posterior (most commonly incisor or molar regions), and either in the maxilla or mandible.
188.8.131.52.1 Supernumerary: Conical, Tuberculate, and Supplemental Mesiodens
Located in the maxillary midline and empirically called mesiodens, they can be conically shaped, tuberculate shaped, or supplemental (identical to a normal tooth). These cases are more usually seen as a single tooth but not uncommonly as a pair of extra teeth on the palatal side of the crowns of the upper central incisors. They are usually found on routine radiographic examination with no clinical signs or symptoms (more commonly conical), or when permanent incisor eruption is delayed (more commonly tuberculate). They can also sometimes interfere with the position of primary centrals following their eruption, even causing early loss of the primary incisors (Figures 4.15–4.18).
A proper radiographic evaluation of the region will clarify the exact cause of delayed or interrupted eruption of permanent teeth. Surgical removal of the supernumerary teeth is normally the treatment of choice. The child’s age will dictate the appropriate time for surgical intervention, avoiding unwanted damage to the immature permanent teeth crown and root. If the timing of the surgical intervention is appropriate, the unerupted permanent teeth may erupt without orthodontic traction. If surgical intervention is delayed and the permanent incisor root is nearly mature, then traction will normally be required. If a supplemental supernumerary erupts, then a decision will need to be made whether to extract the supernumerary supplemental tooth or the normal tooth. This decision will be influenced by which extraction gives the best orthodontic result.
184.108.40.206.2 Supernumerary: Para‐molar
These teeth are positioned beside and between molar teeth in either the maxilla or mandible. The shape of these teeth is very similar to the normal dentition and most commonly similar to premolars. While the removal of paramolars is usually encouraged, their potential use has been suggested to replace severely destroyed molars. They are usually found on routine radiography (Figure 4.19).
220.127.116.11.3 Supernumerary: Natal and Neonatal Teeth
Those teeth that are present in the mouth at birth are known as “natal teeth,” while “neonatal” teeth appear in the oral cavity shortly after birth. They are usually seen in the lower incisor region. Signs of teeth in the mouth have been reported as early as 26 weeks in uterine life in premature babies. The incidence is from 1 in 700 to 1 in 6000 live births. It is believed that only 10% of such teeth are supernumerary. In 90% of cases, they are the normal primary mandibular central incisors (Figures 4.20–4.22). Occasionally, these teeth are seen in certain syndromes, such as Ellis–Van Creveld syndrome, pachyonychia congenita, steatocystoma multiplex, and Hallermann–Streiff syndrome. Riga–Fede syndrome or disease is when an ulcer under the tongue forms in the presence of teeth. Reasons for the removal of natal or neonatal teeth are: painful breast feeding, ulceration of the tongue, or mobility endangering the airway – otherwise, every attempt should be made to retain them.
White, smooth, firm swellings similar to the appearance of natal and neonatal teeth sometimes appear on the buccal aspect of the alveolar ridges or in the midline of the palate. These are fibroepithelial embryonic remnants, and their natural history is to resolve within months. These fibroepithelial remnants are called “gingival cysts of newborn,” “Bohn’s nodules,” or “Epstein pearls” (Figure 4.23).
4.1.2 Disturbances in Proportion and Size of the Teeth
There are minor variations in tooth sizes between races and sexes. However, there are instances where the tooth size is increased or decreased under direct genetic influence. These changes may also be associated with changes in jaw size, preventing any crowding. However, in many instances, no such jaw growth occurs, resulting in crowding. Changes in size may be seen with or without changes in the shape of the involved teeth. A larger tooth size is called macrodontia, and a reduced tooth size, microdontia.
18.104.22.168 Large Size – Macrodontia
In general, maxillary central incisors are 9 mm wide, while maxillary lateral incisors are 7.5 mm wide. Any size above these figures are considered enlarged or macrodont (Figure 4.24).
22.214.171.124 Small Size – Microdontia
126.96.36.199 Short Roots
The shortness of the root is judged in comparison with a normal root. Various environmental and genetic factors can cause the root to be underdeveloped, examples of which are the results of radiotherapy and dentine dysplasia (see Section 188.8.131.52).
4.1.3 Disturbances of Teeth Morphology
Each tooth is formed in a specific shape, with all angles and dimensions dictated by the genetic code.
184.108.40.206 Dens Invaginatus
The enamel and dentine fold into their own structure, producing a cleft. This is usually seen on the lingual aspect of the upper incisor teeth and more commonly on lateral incisors, and is reported in both dentitions. In more severe cases, the invagination may leave a path to the pulp, leading to early pulpal necrosis after eruption. In some circumstances, the folding is extreme and produces the radiographic image of an inverted tooth inside the involved tooth – a condition termed dens in dente (Figures 4.28 and 4.29). Oehlers (1957a, b) has suggested the following classification:
- Type I: Invagination limited to the crown
- Type II: Invagination below the Cemento Enamel Junction (CEJ)
- Type III: Invagination fully extended to the apex of the tooth
Accurate diagnosis is essential to inform correct treatment. Pulpal involvement is common. Negotiation of canals often requires an operating microscope. Most of the involved teeth develop pulpitis and pulp involvement, as the enamel and dentine that lines the in‐folded areas is very thin and easily breached by early caries.
Dens invagination in general and Dens in dente cases in particular are seen more frequently in the upper lateral incisors and less frequently in the molar regions (Figure 4.30).
220.127.116.11 Dens Evaginatus (Talon Cusp)
This condition manifests with a prominence covered with enamel (Figure 4.31), usually but not exclusively seen on the occlusal surface of the buccal cusp in premolar tooth, with a high incidence in Asian and Caucasian populations. It is more common in lower premolars, and the enamel prominence contains dentine and pulp in nearly 50% of cases. Evaginated odontome is another term used to describe this condition. Supernumerary teeth have also been reported with the condition. Both primary and permanent dentitions may be involved, and the evaginations may be bilateral. Merril has classified dens evaginatus into two groups: (i) originating from the lingual crest of the buccal cusp, and (ii) originating from the middle of the occlusal surface.
Extension of the evaginatus to the incisal edge of a tooth forms a “talon” cusp. Mitchell introduced the term in 1982, and Mellor and Ripa (1970) later named it “talon cusp” because of its likeness to the talon of an eagle (Figure 4.32). A classification based on size and shape was introduced by Hattab et al. (1996):
- Type I (talon): An extra cusp on the palatal or labial surface of a primary or permanent tooth at half its clinical height.
- Type II (semi‐talon): An extra cusp of more than 1 mm, but less than half of the clinical crown. This excess part is either isolated or conjoint with the palatal surface of the tooth.
- Type III (trace talon): A large cingulum with different shapes of conical, bifid, or tubercle‐like projections.
In radiographic images, talons appear as radio‐opaque structures overlying normal anatomy. The pulp portion of the talon may be visible and superimposed on normal pulp horns. In larger evaginated masses, the pulp is more easily visible. No clear etiology has been determined for talon cusps. The highest incidence is on primary maxillary lateral incisors and permanent maxillary central incisors. They are usually unilateral, but bilateral cases have been reported. Talon cusp may affect occlusion, function (speech and trauma to the lip), and aesthetics. Care must be taken to correctly diagnose talon cusp on unerupted teeth and thereby avoid unnecessary surgical interventions.
There is a higher potential for caries development in the deep grooves at the junction of talon cusps and the involved teeth. Fissure sealing or adhesive restorations in the grooves are required. Treatment involves occlusal adjustment without pulp exposure; otherwise, a pulpotomy (preferable) or pulpectomy may be necessary. Fluoride therapy can reduce sensitivity after occlusal adjustments.
18.104.22.168 Peg‐shaped Laterals
The shape and size of the tooth is reduced with a classic tapered appearance, giving it a conical shape (Figure 4.33). The basic structure and composition are unchanged. The aesthetics is dramatically affected, and restoration at an early age with ceramic or composite laminate veneers is the treatment of choice, with full porcelain crowns being an option in severe cases.
Two adjacent teeth have fused together coronally and are seen clinically as one tooth. This may occur between two teeth of the normal dentition, or between one tooth of the normal dentition and a supernumerary tooth. In true fusion between two teeth of the normal dentition, the number of teeth in the arch is reduced (Figures 4.34–4.37).