Purpose: To quantify the effect of support stiffness on the retention forces of telescopic crowns and to evaluate a prototype attachment system incorporating a nickel-titanium element.
Materials and methods: In the first part of the study, telescopic crowns were fabricated employing standard laboratory procedures. For six combinations of telescopic crowns, the separation force was determined while varying the stiffness of their supporting implants. In the second study part, an in vitro mandibular model with three interforaminal implants was equipped with strain gauges and extensometers. Two prostheses either employing cylindrical telescopic crowns or prototype attachments were fabricated and statically loaded on the model using either the midline or the left canine or both canine implants for support while strain in the peri-implant area and prosthesis displacement were recorded. Statistical analysis of both study parts was based on pairwise comparisons with the level of significance set at α = .05.
Results: With one exception (P = .161), for each assembly of two telescopic crowns, the separating force was always dependent on the stiffness of the supporting implants. With 3 exceptions out of a total of 14 comparisons for peri-implant strain and prosthesis displacement, the use of the prototype attachments always led to significantly lower mean values compared to the use of cylindrical telescopes (P < .00).
Conclusion: The individual retention force of telescopic crowns on implants should be set at a lower level compared to telescopic crowns on natural abutments. Incorporating a nickel-titanium element into attachment systems for implant-supported removable prostheses reduces peri-implant strain and may facilitate the use of telescopic crowns.