Purpose: This study is designed to investigate the strains of mini dental implants in mandibular overdenture. Load distribution was analyzed in the same model by utilizing mechanics of materials including allowable stress design and load and resistance factor design. The prognosis of four mini dental implant retained overdenture in totally edentulous mandible in possible clinical situations including failures of mini dental implants is to be discussed.

Materials and methods: Mandibular complete denture was fabricated and converted to mini dental implant retained overdenture with O-ring attachments after placing four mini dental implants (3M ESPE, St. Paul, MN, USA) on the cast. Four strain gauges (KFG-1-120-C1-11L1M2R, Kyowa, Japan) were then attached to buccal surfaces of mini dental implants. Strain gauges were connected to strain amplifier (PCD-300, Kyowa Electronic Instrument, Kyowa, Japan) and strains were measured with electric resistance strain gauges when the load from 0-100N (EZ-Test, Shimadzu, Kyoto, Japan) was applied to posterior part of overdenture. Combinations of possible clinical failures of mini dental implants were presented under same loading protocol. Then, load distribution was calculated by elastic stress analysis to confirm the strain gauge measures.

Results: Strain gauge analysis and elastic stress analysis concurred and showed similar results. When all four mini dental implants were presentin overdenture, more load distribution was observed on posterior implants than anterior implants. With loss of anterior implant, there was no significant change in strains of other implants. With loss of posterior implant, however, there was significant increase in strains of other implants.

Conclusion: Posterior mini dental implants were being loaded significantly more than anterior mini dental implants. An additional placement of mini dental implant is required when posterior implant failed in mini dental implant retained overdenture in clinical situations.

Keywords : Mini dental implant, implant overdenture, strain gauge