Factors affect Molar adjustment in Mixed dentition

1. 1 Factors affect molar adjustment Factors affect molar adjustment in mixed dentition stage in mixed dentition stage Prepared by: Prepared by: Dr Mohammed Alruby Dr Mohammed Alruby لشاف كنا ملعاف ادقاح كل دجت مل اذا F Factors affect Molar adjustment in Mixed dentition stage actors affect Molar adjustment in Mixed dentition stage D Dr. Mohammed Alruby r. Mohammed Alruby

2. 2 Mixed dentition: Period where both deciduous and permanent teeth are present in the oral cavity, this stage spans from 6y to 12y of age begin from eruption of 1st permanent molars tooth or mandibular central incisors. Early mixed: ------ 6 -9 years of age Late mixed ------ 9 -12 years of age A-Relation of deciduous second molars to each other: Baume’s classification of primary molars relation: 1-Distal step: in which LE is distal to UE which lead to class II angle in permanent but few cases may undergo class I relationship in permanent dentition 2-Flush terminal plane: in which distal surface of LE in the same vertical relation with UE which lead to: -Developed into class II molar relation if forward mandibular growth is not sufficient -May initially assume cusp to cusp relation in molar and then transform into class I molar by early mesial shift and late mesial shift Early mesial shift: to close space in primary anterior segment and primate space due to eruptive force of 1st permanent molars Late mesial shift: mesial movement of 1st permanent molar to accommodate leeway space which occurs more in lower than upper 3-Mesial step: which the distal surface of LE is mesial to UE and lead to molar relationship and in few cases may progress to class III molar if growth of mandible presents B-Symmetry of dentition in arch and persistence of all deciduous dentition as early loss of LE may lead to change the position of 1st molar permanent as there is mesial migration will occur OR retained LE for long time due to missing L5 may lead to change the position and relation of 1st permanent molars C-Skeletal relationship of the case as the end relation of the molar change from relation to another as case is skeletal class I or 2 or 3 relationship (differential growth of mandible) D-Amount of leeway space if there is normal range or less than that E-Presence of hypodontia as missing L5 that lead to mesial migration of L6 F-Extraction of L6 or U6 due to any cause that lead to change the molar relationship after 7 migration and distal movement of 5 G-Abnormal relation of the teeth to dental arch that may lead to spacing of teeth or crowding of it Mechanism of proper occlusion: safety valve mechanism = It is a natural mechanism by which the maxilla and mandible maintain proper occlusion, the intercanine width of maxilla acts as safety valve N: B: Prenatal: maxilla close to cranium so completed 1st compared to mandible Postnatal: mandible more extended than maxilla and faster rate = intercanine width in mandible completed earlier 9 -10y than maxilla which extended up to 10- 12 years of age = maxilla in all direction acts as cheek to prevent abnormal growth of mandible that occurs up to 18 years of age = that is called safety valve mechanism: that keep maxilla and mandibular dentition in proper occlusion F Factors affect Molar adjustment in Mixed dentition stage actors affect Molar adjustment in Mixed dentition stage D Dr. Mohammed Alruby r. Mohammed Alruby

3. 3 Dimensional changes in dental arches 1-Intercanine width change: ---- discussed in safety valve 2-Decrease in arch parameter: Arch parameter measured from mesial side of permanent molars lower decreased by average 4mm and 2mm in maxilla due to greater extent of mesial movement of lower than upper due to high leeway apace in lower 3-Decrease arch length: Decreased when change from mixed dentition to permanent dentition due to uprighting of lower incisors lower and loss of leeway space by mesial movement 4-Increase in inter-molar width: Measure from one 1st molar to the other Increase on average 2.2mm in upper from 8 -13 years Increase on average 1mm in lower from 8 -13 years Intercanine: ------- more 5mm U and ------ more 3mm L Intermolar: -------- more 2.2mm U and ----- more 1mm L Arch length ----- less 1mm U and ---------- 1mm L Arch parameter: ------ less 2mm U and ---- 4mm L Factors considered to prevent crowding in incisors in mixed dentition OR: factors affect incisors alignment after exfoliation of deciduous dentition (Warren Mayne) Size of incisors between deciduous and permanent dentition called incisor liability and measured 7.0mm in U and 6mm in L, and is corrected by: 1-Interdental spacing: 4mm U and 3mm L 2-More labial inclination 3-Increase intercanine width about 3mm 4-Primate space N: B: Interdental spaces: 4mm U, and 3mm L Intercanine width: 4--6mm U and 3--4mm L Change in incisors inclination: 1—2mm U and 1-2 mm L F Factors affect Molar adjustment in Mixed dentition stage actors affect Molar adjustment in Mixed dentition stage D Dr. Mohammed Alruby r. Mohammed Alruby