The Effect of Removable Partial Denture Material and Design on Load Distribution over the Supporting Structures

Problem: The number of partially edentulous patients is increasing, so the need for RPDs will increase in the clinical practice (Walmsley 2003). One of the most significant disadvantages of current RPDs affecting the health of the remaining oral structures is the unresolved issue of the load distribution between the supporting structures. This is dependent upon materials properties, design and fit of the RPD. A significant need exists to advance the knowledge surrounding this issue and the exploration of novel materials now available for this type of prosthetic treatment.Purpose of study: The aim of this project was to evaluate the RPD frameworks produced from Polyetheretherketone (PEEK) and their load distribution to the supporting structures in comparison to the conventional RPD materials. Further, to enhance the design in order to take advantage of the polymer’s mechanical properties. Therefore, the design will then be adjusted to optimise the load distribution.
The objectives for this study were firstly, to use 3D stress freezing digital photoelasticity in dental applications and produce a photoelastic model composed of two materials that have properties representing that of dentin and bone.
Secondly, to compare the load distribution of PEEK with that of the conventional materials, and thirdly, to design a PEEK RPD framework for the optimised load distribution.Method and Materials: A 3D digital photoelasticity technique was adapted for use in dentistry to analyse the load distribution of RPD frameworks. A novel photoelastic model was made with individual simulative materials for tooth structure, alveolar bone, PDL, and oral mucosa. For each experiment the RPDs were placed on the photoelastic model and loaded by a modified dental surveyor in the stress freezing oven. The models then sectioned to produce sample slices 2mm in thickness at selected points. The data was collected using Catchsix and CoPA photoelastic softwares packages.Results: Results of the resin model fabrication revealed that the ratio of the modulus of elasticity between Photoelastic materials PL1 and Araldite 2020 epoxy resins at Tg mimic that between dentin and bone.
3D digital photoelasticity was demonstrated to be a valuable technique which allows for viewing of the stresses in the model and the inclusion of digital technology in data processing advances photoelasticity to a modern technique of stress analysis.
Results of stress analysis revealed that:
• PEEK dimensions and designs should be tailored to the material properties to fulfil the objective of the supporting components
• Covering the palatal surfaces of the teeth above the height of the contour in acrylic denture designs assists in transferring some of the applied load to the teeth.
• PEEK dentures with a novel clasp design shows potential in comparison to the conventional tissue supported RPD materials.
• RPI assemblies are better in load distribution than circumferential and embrasure CoCr designs. This was found to be consistent with other studies.
• PEEK dentures with the novel clasp design are comparable in load distribution with that of the RPI assembly design.

Conclusion: PEEK is a promising RPD material. The flexibility of this material in combination with novel clasp design transfers the distribution of load in a favourable manner over the abutment teeth. However, further research is needed before it can be accepted as an option in RPD prosthodontics.