Dento-maxillary disharmony
Introduction :
Dento-maxillary disharmony (DMD) is manifested by an easily identifiable dental irregularity that alerts the general dentist and parents.
It presents numerous clinical and radiological signs allowing the practitioner to make an early diagnosis.
The diagnosis of DDM is made when the permanent dentition comes in, but certain signs may appear as early as the deciduous dentition, such as the absence of diastemas or crowding in the anterior sector.
- Definition :
This is a disproportion between the mesio-distal diameters of the permanent teeth and the perimeter of the corresponding alveolar arches. It results from a difference between the space available on the arch and the space necessary to ensure the eruption of the permanent teeth in an optimal position.
This anomaly affects approximately 30% of an orthodontic population
- Location :
DDM with anterior location (incisors and canines)
Lateral localization DDM (Premolars)
Anterior location DDM (Molars)
- Etiopathogenesis:
- The phylogenetic and embryological independence between the dentition and the maxillae explains the incoordination between the dimensions of the jaws and the dimensions of the teeth.
- Genetic transmission occurs through a mechanism of cross-heredity (small jaw of the mother, large teeth of the father).
– Many DDMs would be linked to an ethnic family type.
– Growth and development of the arches with widening around the age of 7-8 years and increase in intercanine width of 3 mm after eruption of the permanent incisors
- Classification of DDM:
A DDM may result from a deficiency or excess of paraportal arch length to dental size
4-1 Arch length deficiency: DDM due to relative macrodontia
This is a negative difference between the space available on the dental arch and the space needed to align the teeth.
It results in dental crowding or overlapping.
- Classification according to severity of congestion:
- Low or transient DDM (-4mm)
- Moderate DDM (-7 to -8mm)
- Severe DDM (greater than -8mm)
- Classification according to the etiology of congestion:
Depending on the etiology, three types of congestion are chronologically distinguished:
- Primary crowding: (of genetic origin) detectable from the temporary dentition, absence of BOGUE diastema.
- Secondary crowding: (of pathological origin) or iatrogenic coincides with the development of the canines and later of the 2 permanent molar cVmc (mesial thrust or caused by the premature loss of temporary teeth).
- Tertiary crowding: frequently observed in males. It corresponds to the active phase of eruption of wisdom teeth and terminal growth of the mandible.
These encumbrances can accumulate on top of each other during the establishment of occlusion.
4-2 Excess arch length: DDM by relative microdontia
This is a positive difference between the space available on the dental arch and the space needed to align the teeth.
It results in generalized interdental diastemas
- Diagnosis:
DDM can be detected and assessed during clinical examination, on casts when reading panoramic radiographs and on lateral teleradiographs.
Signs of DDM due to relative macrodontia:
5.1. Clinical signs:
- In temporary dentition: we note the absence of BOGUE diastema or interincisor diastemas
(Presumption of future lack of space).
- In constitutional mixed dentition:
- In the mandible:
Rhyzalysis of temporary lateral incisors by permanent central incisors and evolution of permanent central or lateral incisors in lingual position.
At the level of temporary canines, 3 possibilities are possible:
Type I: temporary canines persist
Significant incisal crowding and frequent denudation of the most vestibular lower central incisor.
Type II: unilateral expulsion of a temporary canine and deviation of the inter-incisal point.
The clutter is less important
Type III: spontaneous expulsion of the two temporary canines, reduced or even non-existent diastema for the permanent canine.
- In the maxilla:
There are incisor malpositions, lingual exclusion of one or both lateral incisors and elimination of one or both canines.
- In stable mixed dentition and in the phase of formation of permanent dentition:
Previous event:
Incisal crowding with abrasion facet on the teeth, and vestibular evolution in infra position or infra-mesio-vestibuloposition of the canines, inclusion of the canines.
Lateral manifestation:
Retention of the 1st premolar between the permanent canine and the 2nd temporary molar; or its evolution into lingoclusion.
Linguo or vestibuloclusion of the premolars with rotations.
Later events:
Impaction of the 1st upper molar and vestibulo-position of the 2nd lower molars impacted under the 1st molar .
Later, inclusion of wisdom teeth.
Dento-maxillary disharmony
- Radiological signs:
- Panoramic X-ray:
- Resorption of multiple milk roots during the development of a single permanent tooth
- Resorption of the distal root of second temporary molars by first permanent molars
- Quintero’s sign: Permanent mesioversion of the canine germs and distoversion of the upper lateral incisors
- Superposition of proximal faces
- Impacted premolars or canines
- Posterior staircase sign: concerns the staircase arrangement of the germs of the three molars
- Flower bouquet sign: This is the grouping of the germs of the canines and premolars
- Lower fan sign: This is the downward convergence of the roots of the lower incisors (non-parallelism)
- Teleradiography:
- Germ of the lower permanent canine in front and inside the symphyseal cortex
- Cusp tip of the upper canine projecting onto the apex of the lateral incisor
- Vestibular version of the incisors
- Decreased maxillary length
- Casting Review: Calculation of DDM
NANCE Index:
Calculated by the difference between the space available on the arch and the space required for the alignment of the permanent teeth
- the required space (P10): this is the sum of the mesio-distal diameters of all the teeth (premolars, canines and incisors)
Measure the PI0 using a caliper.
In case of missing teeth use the formulas:
P10 = (l+4) x4.7
P10 = (1+4+6) x2.84
P10 = (l+6) x3.83
- the available space (PHAA): is obtained by the extension of a brass wire which follows the contact points and the incisal edges of the mesial face of the right molar to that of the left molar without taking into account the malpositions
- The DDM is equal to PHAA-P10:
If the PHAa – P10 = 0 ± 2mm anterior dento -maxillary harmony .
If the PHAa – PIO > +2mm DDM by relative microdontic.
If the PHAa – IOP < – 2mm DDM by relative macrodonlia
In case of mixed dentition, the Lee Way must be taken into account: in the maxilla it is 0.9mm, in the mandible it is 1.7mm.
Dento-maxillary disharmony
- Differential diagnosis :
- A distinction must be made between a DDM itself and transient disharmony.
- Early eruption of permanent teeth may show signs of crowding which may disappear if growth is sufficiently compensatory
- Molar mesiopositions
- Endoalveoli or endognathia
- Vestibuloversions of the incisors
- Long-term consequences of DDM:
Ectopia, rotation, inclusion, impacted teeth, premolars, linguo-clusion or vestibulo-version incisors, premature abrasions and possible caries.
Conclusion :
The main objectives of early diagnosis of DDM are to prevent the worsening of this anomaly and its consequences and to establish early orthodontic treatment planned according to the severity, the stage of dentition and the etiology of the disharmony.
Dento-maxillary disharmony
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