New telescopic crown design for removable partial dentures.

STATEMENT OF PROBLEM: Special technical skills and experiences are required to fabricate a telescopic crown to provide adequate retention with precise frictional retention ("conus friction force") between coping and telescope. It is also difficult to control clinically alterations of retentive forces after prolonged usage. PURPOSE: This study examined an innovative telescopic crown system for removable partial dentures that can be fabricated without special technical skill or experience and readily adjusted retentive forces. The retention of telescopic crowns was investigated after repeated insertion/separation tests. MATERIAL AND METHODS: Ten telescopic crowns were constructed to evaluate retentive forces. Each telescopic crown was adjusted to provide a retentive force of approximately 9.8 N. Each telescopic crown was then subjected to 10,000 insertion/separation cycles, and retentive force of each telescopic crown was recorded initially and after every 1,000 cycles. The retentive force of each telescopic crown was re-adjusted after these measurements to provide a retentive force of approximately 9.8 N. The retentive force was recorded a second time after each 1,000 insertion/separation cycles up to 10,000 cycles. RESULTS: Retention of the telescopic crowns gradually diminished, depending on the number of insertion/separation cycles. The mean retentive force after 10,000 insertion/separation cycles was over 2 N. All 10 telescopic crowns were re-adjusted to exert a retentive force of 9.8 N after the initial 10,000 cycles, and the retentive force also diminished on the second 10,000 cycles. CONCLUSIONS: Reduction of retention was dependent on insertion/separation cycles. This new telescopic crown with reduced retention could be easily readjusted. Readjusted retentive forces were at least equivalent to the initial retention.