The purpose of this in vitro study was to investigate the splinting effect on distal magnitudes of mobile abutment tooth movement when force was applied to denture base, which Removable partial denture(RPD) used primarily splinting by surveyed crown with RPI, RPA, distal rest Akers clasp and secondary splinting by Conical crown retained denture(CCRD) with Konus crown as direct retainers.
The testing model was designed Kennedy classification Ⅱ case, so all of the lower artificial teeth with root form, except lower left first and second molar, was embedded to mandibular was mold. To stimulate the periodontal membrane, silicone rubber was coated to all of the artificial teeth and to express mobility, 0.5mm thickness oh silicone rubber was coated to root surface of lower left first and second premolars and 0.2 to 0.3mm to test of dentition. The abutments of first and second premolars were prepared and Konus inner crowns were set. Two kinds of outer crowns were made, one is for RPI, RPA, Akers clasp and the other is for CCRD. Four Kinds of RPDs were made and concavities were made onto the area of central fossa of first and second molar.
Unilateral vertical loads were applied at the weight of 4kg, 6kg and 8kg on the concavities respectively with universal testing machine and distal magnitudes of abutment tooth movement were recorded with digital gauge against four RPDs.
The results were as follows.
1. Regardless of types of direct retainers and position of loading, as weight of load increased, distal magnitudes of abutment tooth movement were slightly increased.
2. Regardless of types of direct retainers and weight of loading, distal magnitudes of abutment tooth movement were greater when load was applied on second molar area than when on first molar.
3. When load was applied on first molar area, RPD with Konus crown showed significantly less distal magnitudes of abutment tooth movement than RPDs with other three retainers. But RPDs with RPI, RPA and Akers clasp showed no significant differences among them.
4. When load was applied on second molar area, RPDs with 4 different retainers showed no significant differences among them.
As above mentioned results, the splinting effect of CCRD was better than that of RPDs with primarily splinted abutments when force was applied on first molar area, and distal magnitudes of abutment tooth movement with primarily splinted abutments showed no significant differences in accordance with type with direct retainers.
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