MODEL ANALYSIS

 Why – to determine the arch length and tooth material discrepancy
o If the discrepancy less than 2.5 mm - proximal stripping prior to ortho
o If the discrepancy more than 2.5mm – 5 mm - extraction of 2nd PM, usually after starting ortho
o If the discrepancy more than 5 mm – 10 mm - extraction of 1st PM
 Proximal stripping remove only 50% enamel, otherwise there will be severe sensitivity.
 Normal occlusion — Andrew’s six keys
 7th key added — Bolton ratio = 91.3%