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

Abstract

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 1 st premolar and 1 mm distal to that of the 2 nd 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 microstrains were recorded at channel 3 for the Co-Cr alloy-group (-95±8.94 µm/m).

Effect of Glass Abutment on Stress Distribution in Kennedy Class Ii Maxillary Telescopic Partial Dentures (In Vitro Study)

“…In a previous study by Emera, et al that was concerned with evaluation and comparison of stresses applied to the implants retaining mandibular complete overdenture with telescopic attachments made of Zirconia and PEEK they explained the higher stress values recorded by all PEEK group by the less flexure strength of PEEK (150-330 MPa) in comparison to ZrO2 (630-970 MPa) (27). Also, the tensile stresses to the ridge were coincident with a previous study by Bahgat, et al, (14) that was concerned with one treatment modality used for rehabilitation of mandibular Kennedy Class I cases, using two different materials, Co-Cr alloy and PEEK, and their effect on the strain induced in the supporting structures for these telescopic-retained (RPDs). The findings proved that PEEK telescopic retained RPDs resulted in statistically significant higher tensile strains in most of the channels when compared to Co-Cr RPD.…”

“…They explained this result by the much higher Young's modulus of Co-Cr alloy (220-230 GPa) (28). Compared to that of the PEEK (3-4 GPa) (26) and concluded that Co-Cr alloy telescopic-retained RPD could still be considered a better choice for rehabilitation of the Kennedy Class I partial edentulous situations compared to PEEK one, where Co-Cr generated less and better pattern of stresses to the denture-supporting structures (the residual alveolar ridges and abutments) (14). Rigid major connectors resist deflection, deformation, and torquing forces that could be conducted to the supporting structures as destructive forces (29).…”

“…Inspection of the microstrains recorded showed that the highest mean microstrains were always recorded at the distal aspect of the second premolar abutment during both vertical and oblique loading in the three groups, which makes sense if we took into consideration the movement of the distal extension saddles caused by the RPD vertical displacement. An RPD held in place with a rigid telescopic connector acts as a class I stiff lever, that is to say, rigid pole with a fulcrum on one side (14,21,22).…”

“…The fitting surface of the stone was packed with light body PVS and then repositioned over the reduced area with firm hold until complete polymerization. The epoxy resin model was removed from the stone index after setting of the PVS (14,15). For the casts that were used for the unilateral design oral mucosa simulation was only carried out for the residual ridge, there was no need to cover the palate.…”

Strains Induced by Zirconia and Metal Resin Bonded Attachments Versus Extracoronal Attachment With Full Veneer Retainer in Maxillary Distal Extension Removable Partial Dentures

“…Because of the tiny size and linearity of the resistance rate change, this method of stress analysis has provided a better understanding of stress transmission and distribution in different prosthetic appliances and different types of attachments in RPDs. 2,26,27 To the authors' knowledge, there is no available literature to evaluate the strains developed by zirconia and metal RBAs. Hence, the aim of this study was to assess the strains transferred by zirconia and metal RBAs to the maxillary distal extension RPD supporting structures and compare them with the strains generated by the extracoronal attachment with full veneer retainers.…”