Eruption consists of a series of events from initiation of coronal formation and the beginning of root formation until each tooth emerges into the mouth in a specific position. Eruption may be early or delayed, or may fail completely. Genetic factors play an important part in eruption, while hormonal influences and poor nutrition are also important. Certain diseases and syndromes can affect tooth eruption, predominantly delayed eruption. Local factors can also affect positioning in the arch, such as crowding and supernumerary teeth.
Eruption through bone takes longer than eruption through soft tissue. Once it has emerged through soft tissue (Figure 5.1), then occlusion is reached within a few months. It is expected that single‐rooted tooth will erupt faster than multi‐rooted ones.
5.2 Delayed Eruption
Eruption of each primary and permanent tooth is based on an exact and predetermined genetic plan. Delayed or disrupted occlusion can lead to future malocclusion. Long delays in eruption can lead to failure of eruption into the mouth, the so‐called impaction (Figure 5.2).
5.3 Early Eruption
Teeth appear in the oral cavity much earlier than normally expected. In the primary dentition, natal or neonatal teeth are not uncommon. In the permanent dentition, local causes such as premature loss of the primary predecessor tooth or localized hemangiomata may lead to early eruption. Systemic causes include hormonal disturbances with excess growth hormone or thyroid hormones. In early eruption, the root structure may be immature, thus endangering tooth survival (Figure 5.3).
5.4 Failed Exfoliation (Primary Dentition)
There are several reasons why the normal exfoliation of a primary tooth is disrupted. Ankylosis (replacement resorption) is one of the most common causes. Normal root resorption does not occur, and there is fusion of surrounding bone to the tooth root, with no discernible periodontal ligament. Ankylosed teeth are progressively infraoccluded and interfere with the normal eruption of the permanent successor (Figure 5.4).
5.5 Early Exfoliation/Loss of Primary Teeth
5.5.1 Localized Factors
- Trauma: Accidental trauma to the tooth can cause it to be completely avulsed or resorbed due to the consequences of the trauma, and subsequently lost.
- Infection: Severely carious teeth would end up with pulpal and periapical infections, and will eventually be lost if left unattended.
- Neoplasia: There are instances where teeth are removed along with the malignant tissues surrounding them as a preventive or therapeutic measure.
5.5.2 Systemic Factors
- Familial fibrous dysplasia (Cherubism): This is a rare disturbance in which teeth are lost sooner than expected, with no known and clear etiology. There have been reports of unilateral/bilateral enlargements of commonly posterior segments of the jaws, with multilocular cysts visible on radiographs.
- Acrodynia: Long‐term exposure to mercury leading to pink disease in children, presenting with fever, anorexia, and exfoliating skin of palms and feet. Oral inflammation and mucosal lesions are the two main intraoral findings, along with increased salivary rate, abnormal cementum thickness, alveolar bone resorption, and inevitable consequent tooth loss.
- Hypophosphatasia: Early loss of primary anterior teeth and alveolar bone are reported in such cases, owing to defective cementum, without any changes in gingival appearance. This condition is associated with lowered alkaline phosphatase, a condition widely known as hypophosphatasia (Figure 5.5).
- Pseudohypophosphatasia: This is a hereditary disease with signs of hypophosphatasia and cementum defects without any change in the serum alkaline phosphatase level.
- Anomalous dental structures: There are cases in which the crown or root structure are defective, causing delayed eruption to early loss of teeth. These include Dilaceration, Amelogenesis Imperfecta, dentine dysplasia, odontodysplasia and Ehlers Danlos Syndrome (Figures 5.6–5.9).
- Systemic diseases: There are certain systemic conditions where the teeth are easily exfoliated early: cyclic neutropenia associated with bone loss; acatalasia; increased growth hormone; juvenile diabetes; progeria; histiocytosis X; and leukemia (Figure 5.10).
5.6 Failed Eruption and Impaction
Wrong positioning of the tooth bud may result in failure of eruption into the oral cavity. This failure of eruption is called impaction, which could be due to several factors, including: the presence of a supernumerary tooth (Figure 5.11b); an ankylosed primary tooth (Figure 5.4a); sequel of trauma to primary teeth (Figure 5.4a and b); amelogenesis imperfecta (Figure 5.12b); fibrous tissue formation (Figure 5.12a); odontomas (Figure 5.13b); or cysts (Figure 5.14