1 The median is the middle value of the data set. 2  The lower quartile (Q 1) is the median of the lower half of the data set. 3  The upper quartile (Q 3) is the median of the upper half of the data set. 4  The interquartile range (IQR) is the spread of the middle 50% of the data values.
Removable Essix retainers typically cost between $100-$250 for one or $200-$500 for two. They are made from a vacuum sealed clear plastic that is less noticeable but more likely to break or warp, meaning that you could be paying the price more than once for this style of retainer.
1 However, a retainer is usually included in the overall braces fee, so there is no additional charge for the first set of retainers -- and some orthodontists include one or two replacements in their standard braces package. 2  If not included, replacement retainers can cost $70-$250 for one or $140-$500 or more for a set. Most dental insurance does not cover replacement retainers. 2  Removable Essix retainers made of vacuum-formed clear plastic typically cost $100-$250 for one or $200-$500 for a set. 3  They are prone to warping or breaking, so they may need replacing to be replaced relatively frequently.