After mixed dentition stage, the arch length from first molar to first molar usually:
Decrease in arch length : The arch decreases in the mixed and permanent dentition stages as a result of the uprighting of the incisors and the loss of the leeway space by the mesial movement of the first permanent molars.
Text book of orthodontics Gowrishankar 1st Ed P:92
Remains same
Increases
Decreases
Double