the cup wall 214 b and the upper surface 234 of the vacuum plate v so that when a vacuum is drawn through vacuum port 94 the polymer sheet 12 that is above each cup 214 is pulled downwardly into the cup to form onto each dental model 15 after heat has been applied to the polymer sheet 12 and a vacuum has been drawn in the cups 214 the polymer sheet 12 molds about the surface of each dental model 15 as seen in fig1 and 12 after the polymer sheet 12 has been molded about the surface of each dental model 15 the heater cap h is moved rearward to expose the molded aligners 16 see fig1 and 12 pneumatic pressure is applied to opening line 352 b to extend cylinder 328 to force heater block 329 and the attached heater cap h to move rearward away from the vacuum plate v a spring 333 is provided on shaft 324 to dampen the motion of the heater cap h as it opens by resisting the rearward motion of the housing block 329 often the dental models come out of the cups 214 together with the aligners 16 and they are then removed therefrom each aligner includes formed indentations 272 a that are formed from the indentations 272 in the adapter plates 270 the formed indentations may be used for subsequent handling of the aligner 16 before it has been trimmed.