Incisal occlusion variants
Analysis of anterior tooth relationships allows for identifying several clinical situations, each with its own characteristics:
- Reverse incisal disocclusion: lower incisors overlap the upper ones (are positioned vestibularly). At the same time, the physiological contact between the cutting edges and palatal surfaces is completely lost.
- Vertical incisal disocclusion: in habitual occlusion, a pronounced vertical gap remains between the upper and lower anterior teeth. Contact is preserved only in the lateral (masticatory) segments.
- Straight incisal occlusion: the cutting edges of the upper and lower incisors meet edge-to-edge. There is no traditional crown overlap, but occlusal contact in the anterior region is present.
- Deep incisal occlusion: the crowns of the upper incisors excessively overlap the lower ones.
- Anterior crossbite: the upper incisors occupy a palatal position relative to the lower ones (reverse overlap).
Biological basis of orthodontic movement
Orthodontic treatment is possible due to the ability of bone tissue to remodel — a balance between apposition (formation of new bone) and resorption (bone loss).
Directed tooth movement is explained by modern theories that view this process as a complex reconstruction of the periodontium:
- Electric potential theory: bone deformation (as an inorganic crystal) causes electron redistribution. The resulting currents change ion concentration, which activates cellular reactions and collagen remodeling.
- Vascular theory: changes in the lumen of periodontal capillaries under the action of force. In the tension zone, hyperoxia occurs (stimulation of bone growth), while in the compression zone, hypoxia occurs (activation of resorption).
These genetically predetermined reactions normally ensure the eruption and mesial migration of teeth.
Changes in the gnathic system
Bite correction affects not only the teeth, but also the surrounding structures:
- Muscles: the myodynamic equilibrium of the maxillofacial region changes.
- Skull sutures: in the area of sutures (sutura serrata, sutura plana), osteogenic cells actively divide, forming new bone. This ensures jaw growth.
- TMJ: during treatment of distal occlusion, resorption of the anterior part of the condylar head and the mesial wall of the fossa occurs. The disc thickens in pressure-free zones. During treatment of mesial occlusion, resorption occurs in the distal parts of the fossa, and new bone is formed on the slope of the articular eminence.
Diagnostic methods
For accurate diagnosis and treatment planning, a set of examinations is used:
- Photogrammetry: standardized profile facial photographs (assessment of sagittal parameters, lip position) and en-face photographs (assessment of symmetry, transversal parameters).
- Lateral cephalometry: a lateral skull radiograph with cephalometric analysis to assess the growth type and position of the jaws relative to the cranial base.
- Hand wrist radiography: the "gold standard" for assessing bone age by ossification zones (epiphyses of phalanges, metacarpal, and radial bones), which is important for choosing the timing to start jaw growth stimulation.
- Axiography: study of the temporomandibular joint function.
- Analysis of diagnostic dental casts and intraoral radiographs.
Briefly: answers to topical questions
What X-ray diagnostic methods are used for orthodontic treatment planning?
The following methods are used to diagnose dentofacial anomalies and plan orthodontic treatment:
- Cephalometry — for assessing the growth type of the facial skeleton, the position of the upper and lower jaws, incisor inclination, and planning orthodontic treatment.
- Hand wrist radiography — for determining bone age and identifying the peak of pubertal growth.
- Dental cone-beam computed tomography (CBCT) — for accurate 3D visualization of the maxillofacial bone structures.
- Orthopantomography.
- Dental radiography.
- Axiography — for studying the function of the temporomandibular joint.
What anomalies of individual tooth positions are distinguished according to Kalvelis' classification?
According to the classification of individual tooth anomalies, the following are distinguished:
- Vestibular position;
- Oral position;
- Mesial position;
- Distal position;
- Supraposition;
- Infraposition;
- Rotation along the axis (tortoanomaly);
- Transposition.
Class and exam questions
What happens in the periodontal compression zone during tooth movement?
Ischemia and hypoxia occur in the compression zone. This leads to acidification of the environment, increased lysosome permeability, and the release of enzymes that break down bone tissue (resorption).
How does the Herbst appliance affect the mandible?
The Herbst appliance forcibly holds the mandible in an advanced (mesial) position, promoting TMJ remodeling and correction of distal bite.
Why is a hand X-ray performed in orthodontics?
This radiograph allows determining the patient's bone age and identifying the peak of pubertal growth, which is critical for the effective use of functional appliances.
What else to study on this topic
- Stages of periodontal complex reconstruction by hours and minutes
- Biomechanics of chin cup action
- Features of the cellular composition of cranial suture joints
- Theories of Kingsley and Flourens in historical perspective
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Other topics in "Chapter 11. Introduction to Orthodontics"
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