Retention of metallic and non-metallic double-crown-retained mandibular overdentures on implants: An in-vitro study

Retention forces between primary and secondary CAD/CAM manufactured telescopic crowns: an in vitro comparison of common material combinations

“…The fact that the two groups in which retention forces increased were among the groups with the lowest relative weight loss supports the theory that material wear in these groups did not reach the critical limit to precipitate a decrease in retention force. At the beginning (10 cycles) and at the end of the cyclic connections and disconnections (10,000 cycles), significantly different retention forces between most of the material groups were observed, which was also demonstrated in a previous study applying similar material combinations [31]. Comparing the evolution of retention forces, no significant differences between the control group and group 2 (TI/ PEEK, 4 (NPA/PEEK) or 6 (NPA/NPA) were found, which means that all groups including at least one metal part demonstrated similar retention behavior.…”

“…This may explain why the retention forces in this study are significantly higher than the 5–10 N described as ideal in the literature, especially considering that the retention forces in the control group were in a similar high range. Such comparatively high retention forces have also been demonstrated in previous in vitro studies on retention forces under moist conditions [ 19 , 31 ]. Using the present telescopic-crown materials under in vivo conditions, the retention forces should be tested intraorally, and if exceeding the desired forces, manual polishing of the primary crowns’ outer and/ or secondary crowns’ inner surfaces may be applied.…”

“…The moist conditions are necessary to generate hydraulic adhesion between primary and secondary crowns [ 30 ]. Both distilled water [ 31 ] and artificial saliva [ 32 ] have been used in previous studies to create a moist environment. Our preliminary tests showed no difference between the two media; therefore, we decided to use distilled water for simplicity.…”

“…In general, it can be assumed that an increase in roughness leads to an increase in retention force. In addition, the mechanical adaptation of the primary and secondary crowns at their interfaces may play a role in the increase [ 31 ]. However, this increase in retention force only continues until a critical limit of plastic deformation of at least one of the two crowns is reached.…”

Parameters Affecting the Retention Force of CAD/CAM Telescopic Crowns: A Focused Review of In Vitro Studies

“…The construction procedure of the primary crowns is as follows: (A) a casting wax is modeled directly on the die and trimmed using wax burs mounted on parallelometer; (B) the wax pattern is invested and casted; (C) the cast pattern is checked for fitting on the die; (D) the required parallelism or degree of taper is verified using metal burs mounted on the parallelometer and finally; and (D) finishing and polishing. Regarding the construction of the secondary crowns, casting wax was modeled directly on the primary crowns then invested, casted, finished, and polished [ 15 , 16 , 17 , 18 ]. The casting technique needs multiple steps which is considered technique sensitive and requires a highly skilled dental technician to establish accurate fitting with proper retentive force [ 19 , 20 ].…”