Sample size calculation
incisors
Sample size was calculated using the G*power 3.1.7 software presuming that a reduction of 30 per cent in total treatment duration could be evidenced with a power of 80 per cent at the 5 per cent significance level. The least clinically significant difference in the time needed for leveling and alignment of severely crowded incisors was assumed to be 52.8 days depending on a previous trial showing that anterior teeth alignment took a mean of 132 days with a standard deviation 39 days [