A recent in vitro study evaluated stress patterns and retention of ball and socket and telescopic attachments of different convergence angles retaining a mandibular implant-supported overdenture. Using an edentulous mandibular acrylic resin educational model, the authors installed 4 dummy implants, 3.5 mm in diameter and 11 mm in length, in the interforaminal area. The framework of the overdenture was cast. They attached 8 strain gauges to the buccal and distal surfaces of all implants. The experiment was divided into 3 phases with: (1) the ball and socket attachment, (2) the 4° angle telescopic retainers, and (3) the 6° angle. The retention and stress analysis studies were completed for the ball attachments, followed by the telescopic retainers. The universal testing machine measured the retentive forces of the studied attachments. A 4-channel strain-meter recorded the microstrains transmitted to each strain gauge while the machine was adjusted to move in a tensile mode. Statistical analysis showed the highest significant retention values for the ball and socket followed by telescope angle 4° and angle 6°; the same was found on comparing the mean strains developed at the implants. This showed that implant overdenture attachment design and dislodging forces may significantly influence stress magnitude around implants; the higher the retention (resistance to dislodging forces) of the attachments the more the transferred stresses.
(Source: Implant Dentistry. June 2011, Volume 20, Issue 3)