Signs of a physiological permanent bite
During the formation of the maxillofacial region, the establishment of the permanent bite is a crucial stage. The norm is characterized by strict interlocking criteria. In the buccal segment, the distal surfaces of the second molars align to form a mesial step.
The main landmark of correct interlocking is the relationship of the first molars (key of occlusion): the mesiobuccal cusp of the upper first molar must clearly fit into the intercuspal groove of the lower first molar.
Each tooth contacts two antagonists. The only exceptions are the lower central incisors and the most posterior teeth of the upper arch — they each have only one antagonist.
The nature of the overlap is also strictly defined:
- In the buccal segments, the upper premolars and molars overlap the lower ones to the depth of the longitudinal groove.
- In the anterior segment, the upper incisors cover the lower ones by one-third of the crown.
With correct development, the midline passes strictly between the central incisors, and pathological interdental spaces (trema and diastema) are absent.
Anomalies of individual teeth: size and number
Developmental deviations of the dentofacial system often manifest at the level of individual teeth. Based on size, two main pathologies are distinguished:
- Macrodontia (macrodentia): the formation of excessively large teeth. In clinical practice, macrodontia of the upper permanent central incisors is frequently observed.
- Microdontia (microdentia): the development of unnaturally small teeth (often affecting the upper lateral incisors). Due to the mismatch between the size of the teeth and the dimensions of the dental arch, pathological spaces — tremas and diastemas — form between them.
Disorders in the number of teeth include hyperdontia (the appearance of supernumerary teeth, leading to crowding and aesthetic impairments) and hypodontia (partial or complete adentia). Eruption problems also occur: it can be premature or delayed (retention).
Tooth position disorders (dystopia)
Positional anomalies occur when a tooth erupts outside its correct position. The main vectors of displacement:
- Vestibular: the crown is located outside the normal arch, toward the oral vestibule (lips or cheeks). Characteristic of space deficiency, for example, for upper canines or lateral incisors.
- Oral: the tooth is positioned lingually/palatally to the dental arch. In the upper jaw, this displacement is called palatal (common in second premolars), and in the lower jaw, lingual. In such cases, fixed orthodontic appliances (arches) attached to the vestibular surface of the anterior teeth may be used for treatment.
Additionally, a tooth may be displaced anteriorly (mesially) or posteriorly (distally), located higher (supraposition) or lower (infraposition) than the occlusal plane. Rotation of a tooth around its axis — tortoanomaly — as well as transposition (teeth switching places), are also common.
Pathologies of the dental arches and jaw bones
Anomalies can affect entire dental arches. Dental arches may have an incorrect shape, disrupted contacts between adjacent teeth (crowding or spacing), as well as irregularities in sequence or symmetry. Transversely, dental arches may be narrowed or widened, and sagittally, lengthened or shortened.
Anomalies of the jaws themselves and their anatomical parts include deformation of shape and size (e.g., shortening or lengthening in the sagittal direction, or combined disorders in two to three directions). The classification also highlights disorders in the mutual arrangement of jaw parts and the incorrect position of the jaw bones as a whole.
Briefly: answers to topical questions
What is a mesial step and how does it form?
A mesial step is a characteristic dental relationship in the mixed dentition, formed by the distal surfaces of the second molars. In the primary dentition, the distal surfaces of the second molars lie strictly in one vertical plane, and upon transition to the mixed dentition, they form a mesial step. The exact mechanism of formation of this step is not described in the provided materials.
What are the periods of bite formation in childhood?
Throughout life, three periods of bite development are distinguished:
- Primary dentition — forms by the age of 2 and normally includes 20 teeth (incisors, canines, molars).
- Mixed dentition — begins around the age of 6 with the eruption of the first permanent teeth and continues until the complete replacement of deciduous teeth with permanent ones. The number of teeth during this period varies.
- Permanent dentition — usually forms by the age of 14, when deciduous teeth are absent in the oral cavity and only permanent ones are present; normally numbering 28–32 teeth (incisors, canines, premolars, molars).
Which types of bite are considered physiological?
Physiological types of bite include orthognathic, edge-to-edge (direct), progenic, and biprognathic bites. A physiological bite is congenital and characterized by contacts between all teeth, ensuring full chewing function. General signs of physiological bites:
- The midlines between the upper and lower central incisors lie in the same plane.
- Each tooth has two antagonists. Exceptions are the upper posterior teeth and lower central incisors (teeth 18, 28, 31, and 41), which have one antagonist each.
To remember the exceptions in the antagonist rule: "The extremes on top and in the center on the bottom" are the teeth that get only one antagonist each in the occlusion.
Class and exam questions
What is called the "key of occlusion" in permanent dentition?
This is the correct relationship of the first molars, in which the mesiobuccal cusp of the maxillary first molar rests in the buccal groove of the mandibular first molar.
What does microdontia in the anterior segment lead to?
Due to the mismatch between small tooth sizes (e.g., upper lateral incisors) and the dental arch size, interdental spaces — tremas and diastemas — appear.
How does the vestibular position of a tooth differ from the oral position?
In vestibular displacement, a tooth erupts outside the normal arch (toward the cheeks or lips), and in oral displacement, inside (toward the palate in the upper jaw or tongue in the lower jaw).
What else to study on this topic
- Hard tissue structure anomalies and tooth discoloration
- Causes and consequences of delayed eruption (retention)
- Disorder of the shape and size of dental arches in the transverse direction
- Combined anomalies of the jaw bones in two and three directions
- International two-digit tooth numbering system (FDI / ISO 3950)
Master the entire topic in the «Propaedeutics of Dentistry» course
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Other topics in "Chapter 11. Introduction to Orthodontics"
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