WELCOMETO MIXED DENTITION
DEFINITIONThe period during which both primary & permanent teeth are in the mouth together is known as the mixed dentition period.
Successional teeth : Those permanentteeth that follow into a place in the arch once held by primary tooth E.g.-Incisors, Canines, Premolars
Accessional teeth : Those permanentteeth that erupt posteriorly to the primary teeth E.g.-Molars
Phases of Mixed Dentition# First transitional period # Inter transitional period # Second transitional period
First Transitional PeriodIt is characterized by :
The emergence of first permanent molars The exchange of primary incisors with permanent incisors
Emergence of first permanent molarsThe location & relationship of first permanent molar depends much upon the distal surface relationship between the upper & lower second primary molars.
Changes in Occlusion Flush terminal plane may lead to:- Class I [ with late mesial shift ]
- Class II - End-to-end Mesial step may lead to:- Class I [ normally ]
- Class III Distal step leads to: - Class II
FLUSH TERMINAL PLANE (FTP)
Class II Class I (desirable) FTP End-to-end
Class I (desirable) MESIAL STEP
Early Mesial shiftIf the primary dentition is spaced dentition with flush terminal relationship of second primary molars, the eruptive forces of the permanent molar causes closing of any existing spaces between the primary molars (primate spaces) effectively causing a decrease in arch length.
Late Mesial shiftWhen no spaces exist, the erupting first permanent molar is not able to close spaces. In these cases when the primary molars exfoliate the permanent molars migrate mesially to use up the Leeway space.
Late Mesial shift
Class IMolar moves into this space
Exchange of incisorsThe permanent incisors are larger than the primary teeth they replace. This difference between the amount of space needed for the accommodation of the incisors & the amount of space available for this is called INCISAL LIABILITY.7 mm (maxillary arch) 6 mm (mandibular arch)
Overcoming Incisal Liability1) Interdental spacing of primary incisors 2) Intercanine arch width growth 3) Labial positioning of permanent incisors 4) Favorable size ratio between primary & permanent incisors
1) Interdental spacing of primary
incisorsGood interdental spacing of primary incisors allows for better alignment of the larger permanent incisors.
2) Intercanine arch width growth- Increased intercanine width creates more
room for the permanent incisors. - Mandibular intercanine width increases mostly during permanent incisor eruption. - Maxillary intercanine growth occurs during incisor eruption & continues unpredictable.
3) Labial positioning of the permanent incisorsPermanent incisors erupt to a more labial position & are angled more labially, thereby increasing the arch length.
4) Favorable size ratio between the primary & permanent incisorsSize ratio may be favorable or unfavorable. Favorable : large primary, small permanent
Unfavorable : small primary, large permanent
UGLY DUCKLING STAGE(Broadbent phenomenon) It is a transient/self-correcting malocclusion seen in the maxillary incisor region between 8-9 yrs of age. Erupting permanent canines displace the roots of lateral incisors mesially, resulting in transmission of force on to the roots of central incisors which also get displaced mesially.
A resultant distal divergence of crowns of two central incisors causes a midline spacing. This situation has been described by Broadbent as the UGLY DUCKLING STAGE as children tend to look ugly during this phase of development.
Inter-transitional PeriodIn this period the maxillary & mandibular arches consists of sets of primary & permanent teeth i.e. - permanent incisors - primary canines & molars - first permanent molars
Features of Inter-transitional period Under the influence of tongue, the mandibular lateral incisors assume their proper position in the arch & its initial lingual location is eliminated. Small discrepancies are corrected pressure exerted by tongue & lips. by
No fixed intercusp relation is present, this helps in mesial drift of mandibular teeth.
Second Transitional PeriodIt is characterized by the replacement of the primary molars & canines by the premolars & permanent canines respectively. The combined mesiodistal width of the permanent canines & premolars is usually less than that of the primary canines & molars. This surplus space is called LEEWAY SPACE . It is - 1.8 mm in Maxilla (0.9 mm each side) - 3.4 mm in Mandible (1.7 mm each side)
Features of Second Transitional Period Early Duckling stage is corrected.
Arch loses its roundness. Most common sequence of eruption is : 4-3-5 in maxilla 3-4-5 in mandible This sequence is essential to prevent crowding & utilization of Leeway space. The dental arch length & arch circumference decreases with mesial force.
MIXED DENTITION ( Late childhood )
REFERENCES:1. TEXTBOOK OF PEDODONTICS: SHOBHA TANDON 2. DENTISTRY FOR CHILDHOOD AND ADOLESCENT: McDONALD, AVERY 3. TEXTBOOK OF ORTHODONTICS: GURKEERAT SINGH