• Kornthep Sukyukon D.D.S.
• Parnupong Wongthai D.D.S., M.S., Diplomate, Thai Board of Prosthodontics

Objective To investigate the accuracy of the master casts from three different implant impression
techniques. The master casts were compared with the master model.

Materials and methods Thirty master casts were divided into three groups according to three
impression techniques. Group 1 conventional impression technique at abutment level, group 2 direct
implant impression technique and group 3 splinted direct implant impression technique. The master
model was composed of two implants embeded in rectangular metal base with three reference points on
the shoulder of each abutment. The master model was duplicated by additional silicone with three
impression techniques then the impressions were poured with type IV stone. The dimensional changes
of master casts were measured by measurement microscope at resolution 1/1000 mm. The results
shown in coordinate point (x,y,z) for studying the direction of errors then changed the coordinate points
to true dimensional changes by Pythagoras' theory. Each reference point was analyzed by One-way
ANOVA and Tamhane Test.

Results The master casts made by the conventional impression technique at abutment level had
significantly less dimensional changes than the direct impression one in all reference points (p = 0.001,
< 0.001, < 0.001, 0.002, 0.003, < 0.001, respectively) and the splinted direct impression technique
(p < 0.001). The master casts from the direct impression technique was not significantly different from
the splinted direct impression technique (p = 0.446, 0.980, 0.212, 0.073, 0.108, 0.566, respectively).

Conclusion The conventional impression technique at abutment level had the most accuracy and
splinted transfer coping did not affect the accuracy of the master casts.

(CU Dent J. 2008;31:223-34)