Establishing occlusion
Establishing occlusion in temporary and mixed dentition, in normality and pathology
Introduction :
- Faced with the current large number of malocclusions occurring in young children, the orthodontist is led to explore their development and to seek therapeutic means capable of modifying dental alignment but also the morphogenesis and balance of bone structures.
- The morphogenesis of the dental arches presents a discontinuous character with an alternation of active phases and periods of stability; it extends over around twenty years.
1. Functions of the temporary dentition:
- Ensure the masticatory function.
- The lacteal occlusion is rudimentary, with a crude dental morphology, not comparable to the more complex one of the permanent teeth which must allow for more advanced grinding mechanics.
- Participate in the vertical dimension of the face.
- Preparing the permanent dentition: The temporary dentition prepares the establishment of the permanent dentition in two areas: guiding the permanent teeth and preparing the space necessary for their eruption.
2. Skeletal and neuromuscular characteristics in primary teeth:
- In the newborn, the glenoid cavities of the TMJs are flat; in the absence of teeth, the mandible performs only horizontal back-and-forth movements.
- At the time of eruption of temporary teeth, the organization of the articular disc and the deepening of the glenoid cavities are created with a progressive increase in the condylar slope.
- As occlusion develops, the muscles learn to perform the necessary functional movements.
3. The terminal plan:
Corresponds to the ratios of the distal faces of the 2 maxillary and mandibular temporary molars in the anteroposterior direction.
- Distal step CL II
CL I
- Right terminal plan CL II
CL III
CL I
- Mesial step
CL III
4. Characteristics of a normal lacteal occlusion:
Intra-arcade layout:
- The shape of the arches is practically comparable to a semicircle.
- Simien diastemas and inter-incisor diastemas are frequently observed.
- Temporary teeth do not have a specific axis, they are implanted vertically
- Occlusal plane is flat (no curve of Spee)
Inter-arcade layout
- The occlusion is of the interlocking type: one tooth is in occlusal relationship with two antagonist teeth, except the mandibular central incisors and the maxillary second molars.
- Vertical terminal plane, or terminal plane with mesial or distal step.
- The upper canine articulates between the lower canine and first baby molar (Mrs. Muller’s Class I).
- Brake alignment.
Noticed :
A normal deciduous occlusion does not necessarily guarantee a normal occlusion in the permanent dentition
. Generally, dentomaxillary disharmonies appear during the eruption of the permanent teeth. On the other hand, etiological factors and, in particular, disturbances of the functional matrices, appear during growth.
5. At-risk and pathological deciduous teeth:
A baby tooth may be considered at risk under one of the following conditions:
- absence of diastemas
- clutter
- Association of:
- mesially stepped terminal plane associated with a large lower postcanine diastema and an end-to-end incisal relationship predispose to Class III malocclusions
- vertical or distally stepped terminal plane and excessive upper canine diastema increase the probability of Class II
- mesially stepped terminal plane and palatal inclination of the upper and lower incisors and/or excessive incisal overbite are signs of risk of a Class II, Division 2
- Loss of space for the permanent tooth following extraction or untreated interproximal caries of the corresponding baby tooth
- Functional disorders due to:
- one-sided chewing to avoid painful contact with a tooth
- distorting habits (finger or pacifier sucking)
- dysfunctions: oral ventilation, atypical swallowing
• consequences of trauma:
– loss of space due to accidental expulsion of a baby tooth;
– indirect trauma to the germ of the permanent tooth;
– pulp necrosis accompanied by changes in delayed physiological rhizalysis
– TMJ problems (e.g. disc luxation) can cause deviations of the frenulum due to changes in the position of the condyle and different dental classes on both sides.
6. Composition of mixed dentition:
A) APPEARANCE OF THE 1ST PERMANENT MOLAR, REPLACEMENT OF THE TEMPORARY CENTRAL INCISORS BY THE PERMANENT ONES.
This phase takes place on average between 6 and 8 years of age, the lack of space for the placement of permanent incisors on a dental arch that is too small will be compensated by 3 mechanisms:
- A DENTAL MECHANISM: Use of inter-incisor diastemas and simian diastemas.
- AN INCREASE IN ARCH WIDTH by accentuating the version of the permanent incisors compared to the temporary incisors.
- GROWTH WIDENING: Increase in intercanine width 3mm during incisor replacement.
B) ERUPTION OF THE 6-YEAR-OLD TOOTH:
Closure of the diastemas or simian spaces.
Type 1 arch: the lower 6-year-old tooth is in malocclusion
(Inferior simian diastema larger than the upper one)
Arch Type 2: Cusp-to-cusp relationships of 6-year-old teeth.
This phase is particularly important in the formation of the dental arches. If a single compensation mechanism does not provide the necessary additional space, the permanent incisors will present various malpositions and malocclusions.
7. Changes in shape and size of the arches:
- The semicircular arches of the temporary dentition will become elliptical or “U” shaped and the curves of Spee and Wilson will form.
7.1 ARCADE LENGTH:
- The arch length is measured between a line tangent to the vestibular surfaces of the central incisors and a line tangent to the mesial surfaces of the permanent molars.
- This measurement is stable in temporary dentition.
- Growth at the time of incisor development (2.2 in the maxilla and 1.3 in the mandible).
- Greater decrease when replacing temporary molars (Mesial derivation).
- Late decrease due to lingual uprighting of the lower incisors.
- ARCADE WIDTH
- It varies by phenomena of growth of the bone bases: apposition at the level of the external cortices.
- In the maxilla:
- Increase from 5 to 8 and a half years.
- Decrease before canine eruption around 10 years of age.
- In the mandible:
- The distance between the canines is stable.
- At the premolar and molar level: Increase after 6 years on average: 1.9 mm up to the age of 13.
7.3 ARCADE PERIMETER:
Measured from the distal surface of the left 2nd temporary molar or the left 2nd permanent premolar to the distal surface of the right one, passing through the vestibular cusps and the incisal edge, without taking into account dental malpositions.
Its reduction is due to the mesial derivative and the lingual uprighting of the lower incisors
- In the Maxilla
Slight increase between 5-18 years: 1.3mm for boys and 0.5mm for girls.
- At the Mandible:
Decrease between 6 and 18 years: 3.4 mm for boys, 4.5 mm for girls.
Individual variations are very important depending on the ratios of temporary and permanent dentition, the sequence of eruption and the relative proportions between the two dentitions.
Conclusion :
- The shape and size of dental arches have important consequences in orthodontics on semiology, diagnosis and therapeutic decisions.
- They undergo continuous changes in their morphology, under the influence of teething phenomena, alveolar growth, maxillofacial growth and the action of neuromuscular factors throughout development and life.
Establishing occlusion
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