Tooth eruption and normal eruption sequence

• Eruption is the process of the movement of the tooth from a developmental to functional position
• During eruption, the tooth moves from the alveolar bridge to the oral cavity until the occlusal plane is reached
• Eruption contains three phases: pre-eruptive, eruptive (pre-functional), post-eruptive (functional)
• Pre-eruptive phase: roots begin to form from the tooth germ and the tooth moves to the oral cavity
• Eruptive phase: the time between gingival emergence and full eruption to meet its antagonist
• Post-eruptive: tooth is in the oral cavity, meets its antagonist and is in function
• The most common theory of eruption is the root formation, which is that when the root forms, the space for the growing root is accomodated by occlusal movement of the crown
• Hydrostatic pressure theory states that pressure generated by fluid in the periapical tissues pushes the tooth occlusally
• Bone remodelling theory states hormones initiate bone resorption and formation, creating a gradient of pressure that drives the tooth towards the oral cavity
• Another theory on tooth eruption proposes that the tooth is pulled in an occlusal direction by cells and fibers of the periodontal ligament
• Pre-eruptive phase begins from when the root starts to form and the tooth begins to move towards the surface of the oral caivty
• Developing tooth germs move within the jaws to the buccal and occlusal sides, anterior tooth germs move mesially and posterior tooth germs move distally
• For anterior teeth, the permanent tooth germs are located lingually and apically
• For premolars, permanent tooth germs are usually located apically
• Pre-emergent eruption involves bodily movement (movement of the entire tooth germ), and eccentric growth (growth in one part of the tooth while others remain constant, shifting the center of the tooth)
• The eruptive phase is also known as the pre-functional eruptive phase, encompasses the time between gingival emergence and full eruption of the tooth to meet its antagonist at the occlusal level
• During eruption, the tooth germs mainly move in an occlusal direction and will enter the connective tissue and become in contact with the oral epithelium; the reduced enamel epithelium fuses with the oral epithelium and the crown penetrates the cavity
• The post-eruptive phase is also known as the functional eruptive phase, where the tooth will meet its antagonist and be in function, occurs as long as the tooth is in the oral cavity
• Pre-functional spurt: the tooth moves from the initial emergence into the mouth, up to occlusal plane
• Juvenile equilibrium: jaw continues to grow and eruption is relatively slower
• Adolescent eruptive spurt: growth accelerates and teeth have to erupt/move more to remain in occlusion
• Adult equilibrium: stops growing but tooth may experience some pressures/forces, so it may still be moving to maintain equilibrium and contact with opposing teeth
• For primary teeth, the mandibular central incisors usually erupt first (before 1 years old), then the maxillary central incisors, lateral incisors, molars, canines, and then second molars (at around 2 years old)
• Primary teeth: Mandibular central incisor → maxillary central incisor → maxillary lateral incisor → mandibular lateral incisor → maxillary first molar → mandibular first molar → maxillary canine → mandibular canine → mandibular second molar → maxillary second molar
• For permanent teeth, the lower central incisors erupt first, then upper central incisors, lateral incisors, premolars, canines, and then the second and third molars
• Permanent teeth: Maxillary and mandibular first molars → mandibular central incisor → maxillary central incisor → mandibular lateral incisor → maxillary lateral incisor → mandibular canine → maxillary first premolar → mandibular first premolar, both second premolars → maxillary canines → both second molars → third molars
• Most favorable eruption sequence for maxilla: first molar, central incisor, lateral incisors, premolars, canine, second molar
• Most favorable eruption sequence for mandible: first molar, central incisor, lateral incisors, canine, premolars, second molar
• The maxillary premolars can erupt before canines to maintain space around the canine region
• An unfavorable eruption sequence is when the second molar erupts earlier than the premolars in the maxilla and when canines erupt earlier than premolars in the mandible; molars and premolars tend to move mesially so may block the space
• Premature/accelerated eruption includes natal teeth (already present at birth) or neonatal teeth (erupts within first 30 days), may be part of primary dentition or a supernumerary tooth
• Premature eruption is problematic for breastfeeding, so the incisor may be rounded off to reduce pain for the mother
• Delayed eruption could be caused by supernumerary teeth, abnormal morphology (e.g. dilaceration), pathological obstruction (e.g. cyst, tumor), retained primary predecessor, ankylosis of primary predecessor (root fuses to alveolar bone), dense mucoperiosteum (too fibrous, tooth cannot emerge), crowding, etc.
• Ectopic eruption refers to the abnormal eruption of a tooth outside of position, most commonly seen in canines and permanent first molars
• Transposition refers to when adjacent teeth swap positions
• Eruption failure may arise from mechanical obstruction of eruption, or primary failure of eruption (PFE), where despite being unobstructed, the tooth may not have enough eruptive potential
• Submerged tooth refers to when a tooth does not come to the level of adjacent normal occluding teeth
• Teething refers to the process by which an infant’s primary teeth emerge; gums or the mucous membrane overlying the tooth may become inflamed, leading to pain and discomfort
• Discomfort can be relieved starting from a non-pharmacological approach, such as biting on chilled teeth toys, hard sugar-free teething rusks and rubbing gums with a cool spoon/wet gauze
• Teething symptoms can also be managed pharmacologically, but this is rare; an analgesic like paracetamol can be used