A significant lower mean deviation at the entry point ( 1.4 mm , range : 0.3-3 .7 ) , at the apex ( 1.6 mm , range : 0.2-3 .7 ) and angular deviation ( 3.0 , range : 0.2-16 ) was observed for the guiding systems when compared to mental navigation ( 2.7 mm , range : 0.3-8 .3 ; 2.9 mm , range : 0.5-7 .4 and 9.9 , range : 1.5-27 .8 ) and to the surgical template group ( 3.0 mm , range : 0.6-6 .6 ; 3.4 mm , range : 0.3-7 .5 and 8.4 , range : 0.6-21 .3 ) .