The effect of framework design and attachment type on stress in implant-supported removable partial denture: Finite element analysis

Implant supported removable partial dentures (ISRPD) is a treatment approach in which the retention of removable partial dentures is increased with the implant in free end cases. While implant placement contributes to retention and stability, it also has advantages such as protecting bone around the implant and improving patient comfort. However, in such prostheses, stress formation will be seen in the final abutment teeth and adjacent implant. It is thought that rigidity of framework and change of attachment type in ISRPDs will affect stress in supporting tissues. The aim of this study was to investigate distribution of stress on the implant, bone surrounding the implant, final abutment tooth, periodontal ligament of final abutment tooth and and bone surrounding the tooth with the change of the framework design and attachment type in ISRPD. Three-dimensional models of a bilateral distal extension partially edentulous maxilla containing anterior teeth were formed. The ISRPD was designed with implant placement on first molar area of both side. U plate and anterior posterior palatal band (APPB) were used as framework, Novaloc and ball attachment were used as attachment. 200 N vertical and 200 N oblique loads were applied in four different models with two different framework design and two different attachment types. Von Mises stress values and distributions in canine tooth, periodontal ligament of canine tooth and implant, minimum and maximum principle stress values and distribution in the cortical and cancellous bone surrounding tooth and implant were investigated. Three dimensional finite element stress analysis and static linear analysis were carried out with in scope of this study. Comparing the frameworks, when the von Mises stress values in the canine tooth under vertical and oblique loads were examined, more stress was observed in the tooth with the use of U plate. More von Mises stress values in implant were observed when APPB was used under vertical and oblique loads. When the minimum and maximum principle stress values in cortical and cancellous bone were examined, no significant difference was found between the frameworks. When attachment systems were compared, it was observed that stress values in implant and cortical bone surrounding implant were higher with the use of Novaloc attachment system while stresses in the tooth, periodontal ligament and surrounding bone were not significant between attachment systems. In addition, within the limitations of this study, it was concluded that oblique forces have a more destructive effect against vertical forces. In order to have a better understanding on biomechanics, long-term clinical studies to examine the effects of variables that are difficult to imitate in laboratory conditions, such as the mechanical properties of the bone around the implant, the properties of the mucosa supporting prosthesis and the forces occurring in the mouth should be supported.