Purpose: The purpose of this study is to compare the factors of taper, length, angle and number of vertical axial walls that affect the retentive strength of a cemented crown on a partially customizedhybrid abutment in the esthetic zone.
Materials and method: A total of 35 metal copings were used in this study divided into one group with 30 copings cemented to their corresponding 8° tapered abutment with lengths from 3 to 8 mm with 1 mm increments. The remaining five consisted of a standardized metal coping matching a hexagonal abutment with 3 mm vertical axial walls and the sequential removal of 1, 2, and 3 contiguous vertical axial walls. Dislodgment tests were performed for all copings in both groups. Maximum retentive forces were measured in kgF with a conversion factor of 9.807 N to 1 kgF.
Results: At each tapered abutment length, the retentive strength increased proportionally and was significantly different from 31.67 ± SD 4.10 kgF to 67.68 ± SD 11.22 kgF, respectively [F (5,24) =20.46, p < 0.001]. An unmodified hexagonal abutment demonstrated the highest retentive strength of 70.15 ± SD 12.97 kgF. Sequential removal of 1, 2, and 3 contiguous vertical axial walls of the hexagonal abutment was 59.89 ± SD 10.06 kgF, 57.01 ± SD 9.62 kgF, and 55.99 ± SD 9.35 kgF, respectively with no significant difference (p > 0.05) in retentive strength.
Conclusion: A partially customized abutment with vertical axial walls on one side and a profile reduction on the opposite side can provide comparable retention of cemented copings at 1/3 the length and 1/6 the surface area of an 8 mm high abutment with an 8° taper.