Methods: Forty implant fixtures of different lengths were allocated to two treatment groups. Group 1 included implants with tight abutment screws and group 2 included loosened abutment screws. All specimens were sectioned using a standardised cutting procedure. The internal geometry of all fixtures was replicated with an impression material. All specimens were uniquely marked then prepared ready for examination under scanning electron microscopy. The same procedure was repeated after crown retrieval. Retrieval was undertaken using a conventional and novel technique.
Results: For each treatment group there were obvious signs of damage to the internal threads after crown retrieval. No correlation was found between the extent of damage and the number of attempts to remove each crown. Non-parametric statistical tests revealed no significant difference in damage to internal threads between the conventional and novel retrieval methods. The same insignificant outcome was found when comparing damage when retrieving crowns of loosened abutment screw versus tight abutment screws. Comparison of all treatment groups showed no correlation.
Conclusion: Retrieval of cement-retained restorations using a conventional or a novel technique resulted in minimal damage to the internal threads of the implants tested. The effect of the looseness of the screw did not seem to have an effect on damage to the internal threads.