치아-임플란트 지지 가철성 국소의치에서 하악골의 광탄성학적 응력분석

Abstract

The purpose of this study was to suggest the proper guideline for selection of retainer for posterior implant in tooth-implant supported removable partial denture by comparing and evaluating the stress distribution of mandible according to five different designs of tooth-implant supported removable partial denture. For this study, a three-dimensional photoelastic stress analysis method was used. In the model which only six anterior teeth are remained, two implants were installed at both 2nd molar area. In all five cases, lingual bars were designed as a major connector and Akers clasps were designed for direct retainer of canine which were composed of cingulum rest and casting circumferential clasp using mesio-buccal undercut of canine. At the posterior implant, Akers clasp(Akers type), konus crown(Konus type), rotational path with long rest(Long rest type), Dalbo abutment(Dalbo type) and O-ring abutment(O-ring type) were designed. These five bilateral removable partial dentures were positioned on the photoelastic epoxy resin models, and then in the stress freezing furnace, the vertical and oblique load(15°) of 60 Ncm was applied on the central fossa and mesio-buccal cusp of mandibular left 1st molar of the every removable partial dentures. After the stress freezing cycle of 15 hours was done, these models were sliced mesio-distally with a thickness of 6㎜. The sliced specimens were examined with the polariscope and transmission photoelastic device to observe the distribution of stress, and the results were as follows.

1. In the vertical loading, stress of alveolar bone around implant was in the decreasing order as follows : Konus type > Long rest type > Akers type, Dalbo type > O-ring type In the oblique loading, stress of the alveolar bone around implant was in the decreasing order as follows : Konus type > Akers type, Long rest type, > Dalbo type > O-ring type Mesio-distal distribution of stress is more uniform in Long rest type, Dalbo type and O-ring type than in Akers type and Konus type.

2. In the vertical loading, stress of alveolar bone around the canine in Konus type, Long rest type and Akers type was slightly higher than in Dalbo type and O-ring type. In the oblique loading, there were no considerable differences among these models.

3. when the distance from loading point was increased, the stress of alveolar residual ridge was decreased in the vertical loading, but In the oblique loading, there were no considerable differences in these models.

Therefore, when the length of implant is short, supporting bone around implant is weak, periodontal support of anterior tooth is poor or occlusal force is heavy because of opposing natural dentition, the design of Dalbo or O-ring attatchment is more recommendable on implant than that of Konus. If the occlusal force is light when opposing dentition is removable partial denture and periodontal support is sufficient around implant and canine, the design of Akers clasp or long rest can be used on implant. Long rest design is much better for more uniform stress distribution.