Retrognathic MandibleWhen neonatal jaws are closed, there iscontact only in the posterior region ofthe gum pads & the mandible is severelyretruded in relation to the maxilla.
This retrognathia is for the mostpart corrected by the increased paceof forward growth of the mandible ascompared to that of the maxilla seenin most people.Although the mandibular deficit(ANB) may approach 14° at birth, byadulthood it is reduced to only 2°.
Infantile Swallowing The ability to feed from the breast is present in the new born child. During the process of suckling the nipple is drawn into the mouth by negative pressure. The tongue lies over the lower gum pads & protrudes between the nipple & lower lip.
The milk is directed continuously to the pharynx by an automatic peristaltic movement of the tongue & mylohyoid muscle. During the process, regular breathing continues. The milk passes between the faucial pillar & the lateral channel of the pharynx. The infantile swallowing pattern changes to the mature or adult type during the first year of life with the introduction of solid foods in the diet.
Anterior open bite of the gum pads Clinch & Sillman have shown that there is rarely any contact between the gum pads anteriorly when they are approximated, contact being found only in the first molar region. The open bite is corrected when the primary incisor teeth erupt.
TRANSIENT MALOCCLUSIONS IN THEPRIMARY DENTITION
Anterior Deep BitePrimary teeth are upright i.e. they have analmost vertical inclination with an interincisalangle of about 150° between the maxillary andmandibular primary central incisors. Theprimary incisors generally erupt into a ratherdeep overbite.This deep bite is reduced by the eruption ofthe primary molars & attrition of the incisaledges of the primary anterior teeth.
SpacingThe primary dentition may classified as Type I (spaced) Type II (closed) - Baume (1950)Spaces in the primary dentition may be generalized (developmental/physiological spaces) or localized (primate spaces)
Primate spaces: Spaces found mesial to the primary canine in the maxilla & distal to the primary canine in the mandible So called because most subhuman primates have these spaces throughout life Also known as anthropoid or simian spaces
Significance of spacingSpacing in the primary dentition is essentialto the normal eruption & alignment of thelarger permanent successors.Failure of incisor spacing to appear before 5years of age usually indicates crowding in thepermanent dentition.Spaces that exist between the primarymolars usually close by the time of eruptionof the first permanent molars, whereas thosebetween the primary incisors persist untilthese teeth are replaced.
Edge-to-edge bite At 2 years, the overjet is on average 4 mm,with a range of 2-6mm. With attrition of theteeth, lengthening of the ramus & downward &forward growth of the mandible, the overjetexhibits a steady decrease up to the age of 5years, where an edge-to-edge incisorrelationship is common.This edge-to-edge incisal relationship iscorrected when the permanent incisors erupt.
Flush terminal planeWhen the distal surface of maxillary andmandibular deciduous second molar are in the samevertical plane. this is the normal molar relationshipin the primary dentition because the mesiodistalwidth of mandibular molar is greater thanmaxillary molar.
TRASIENT MALOCCLUSION INMIXED DENTITION PERIOD
Anterior deepbite Deepbite because of larger permanentincisors and shedding of primary molars whichis usually alleviated following exfoliation ofsecond primary molars.
Crowding in upper and lower anterior regionAfter exchange of the canines which isusually alleviated following exfoliation ofthe second primary molars.
Ugly-Duckling StageIt is an ugly arrangement of the anteriorteeth which is a merely a temporary phaseduring the process of normal development.Here the developing permanent caninesespecially the upper canines cause mesialdisplacement of the roots of permanentincisors around the age of 8 to 9 years.This cause a distal divergence of crown ofthe incisors.
Initial end-on relationshipIt is of the upper and lower firstpermanent molars which is later correctedwhen the lower first molar moves mesiallyby utilizing the physiological spaces.
Increased OverjetIt is the horizontal distance between thelingual aspect of the maxillary incisors andlabial aspect of mandibular incisors. During the transition of deciduousanteriors with the permanent incisorscauses increased overjet beyond2mm-3mm.
Increased OverbiteIt is the distance which the incisal edge ofthe maxillary incisors overlap verticallypast the incisal edge of the mandibularincisors.During the transition of deciduous incisorswith the permanent incisors causesincreases overbite 2-3mm
References:-• Textbook of Pedodontics - Shobha Tandon- 1st edi. – pg. 113-15• Orthodontics The Art & Science – S.I. Bhalajhi – 3rd edi. – pg.129-40