Defined as correctly timed, planned removal of certain deciduous and permanent teeth in mixed dentition cases with dentoalveolar disproportion

1. Introduced by KJELLGREN 
2. Father of SE = nance 1940
3. RATIONALE
   1. Arch length deficiency as compared to the tooth material using Model analysis method
   2. Physiological tooth material = eg wilkinson extraction of 1st permanent molar
4. FACTORS THAT PLAY ROLE IN CORRECTION OF CROWDING IN ANTERIOR SEGMENT
   1. Leeway space of nace 
      1. Max = 1.8 mm
      2. Mand = 3.4 mm
   2. Tongue pressure 
   3. Interdental spacing 
   4. Incisal liability = amount of space available and required by permanent tooth
      1. Max = 7 mm
      2. Mand = 5mm 
5. INDICATIONS 2m
   1. Tooth material and arch length discrepancy of 10mm
   2. Class I malocclusion 
   3. Absence of Spacing 
   4. Midline shift 
   5. Premature loss of primary canine
6. CONTRAINDICATIONS 2m
   1. Class II and Class III malocclusion 
   2. Anodontia
   3. Oligodontia
   4. Deep bite 
7. ADVANTAGES =  Prevents fixed appliances and malocclusions in the pt
8. DISADV = 
   1. Long follow up = pt compliance
   2. Operator = highly trained 
   3. Delay of permanent tooth 
9. DWELLS PROCEDURE
   1. Extraction of three teeth 
      1. Primary canine = at age of 8-9 years
      2. Primary 1st molar = at age of 9-10 years
      3. 1st premolar 
   2. Always bilateral extraction in the same arch 
   3. If done unilateral = midline shift happens 
   4. In the 1 st Step, the deciduous canines are extracted to create a space for alignment of the incisors. This step is carried out at 8-9 years of age. 
   5. After 1 years, the deciduous 1st molars are extracted so that the eruption of 1st premolars is accelerated. 
   6. This is followed by the extraction of the erupting 1 st premolar to permit the permanent canines to erupt in their place. 

1. TWEED METHOD = D4C

1. NANCE METHOD = D4C 

• BOTH methods involve the extraction of the deciduous 1 st molars around 8 years of age. This is followed by the extraction of the 1 st premolar & the deciduous canines. 
• MOYERS METHOD = based on intercanine width = BCD4
  1. Maxillary arch 
     1. Boys = 10 years
     2. Girls = 9 years
  2. Mandibular arch 
     1. Boys = 18 years
     2. Girls = 12 years