Effect of material on stress transmission to the supporting structures in Kennedy Class I restored by Telescopic-retained Removable Partial Denture. (Strain Gauge Study)

Objectives: The aim of this in-vitro study was to compare the stresses transmitted to the abutments in mandibular Kennedy class I restored with telescopic-retained removable partial denture (RPD) made from two different materials; PolyEther Ether Ketone (PEEK) and Co-Cr alloy.
Materials and Methods: One mandibular model representing Kennedy class I, with second premolars as the last standing abutments, was fabricated using epoxy resin. Poly Vinyl Siloxane (PVS) impression material was used to simulate the mucosa and the periodontal ligament. The acrylic first and second premolar teeth bilaterally were prepared to receive primary telescopic copings. The latter and two removable partial denture (RPD) frameworks were fabricated out of PEEK and Co-Cr alloy. The 2 frameworks were then processed into fully finished RPDs using heat cured acrylic resin and acrylic teeth following the conventional techniques. Four strain gauges were installed in the epoxy resin model 1 mm mesial to the socket of the 1st premolar and 1 mm distal to that of the 2nd premolar, on the right and left sides respectively; channel 1, 2, 3 and 4. A load of 100 N was applied to the area of the first molar unilaterally on the right side and then bilaterally. The same procedure was repeated six times. Data on stresses were then collected, tabulated and statistically analyzed using one-way ANOVA and Tukey HSD Test (P≤0.05).
Results: In the unilateral loading condition, the highest compressive micro-strains were recorded at channel 3 for the Co-Cr alloy-group (-40±3.16 µm/m). While the least compressive micro-strains were recorded at channel 3 for the PEEK-group (-10±3.16 µm/m). The highest tensile micro-strains were recorded at channel 2 for the PEEK-group (540±10 µm/m). While the least tensile micro-strains were recorded at channel 4 for the PEEK-group (15±4.47 µm/m). In the bilateral loading condition, the highest tensile micro-strains were recorded at channel 2 for the PEEK-group (355±11.83 µm/m). While the least tensile micro-strains were recorded at the same channel for the Co-Cr alloy-group (50±3.16 µm/m). The highest compressive micro-strains were recorded at channel 1 for the PEEK-group (-170±11.4 µm/m). While the least compressive micro-strains were recorded at channel 3 for the Co-Cr alloy-group (-95±8.94 µm/m). Conclusions: The distal abutments always receive the highest stresses, regardless of the loading conditions and the materials from which the prosthesis was fabricated. Telescopic-retained RPD with metallic frameworks generate less strain to the supporting structures in Kennedy Class I compared to those with PEEK frameworks. The bilaterally applied force resulted in more favorable stress distribution pattern when compared to the unilateral one.