Induced Strain of Different Extra-Coronal Attachment Materials in Mandibular Kennedy Class I Metallic Removable Partial Dentures After One Year of Clinical Simulation: An in-Vitro study

Abstract

Abstract Background: The strain developed by different extra-coronal attachment materials during loading in aqueous environment as well as the effect of denture insertion and removal cycles is of prime importance. Accordingly, the aim of the current study was to assess the induced strain of different extra-coronal attachment materials in mandibular Kennedy class I metallic removable partial dentures after one year of clinical simulation. Methods: Twelve identical 3D-printed models representing mandibular Kennedy class I with first premolars as principal abutments bilaterally were fabricated having 4 removable dies each; canine and first premolar on which two splinted crowns with three different extra-coronal attachment materials (group A: PEEK/BioHPP, group B: zirconia, group C: metal)were fabricated bilaterally. Each of the 3D-printed models (n=4 for each group) was designed with four strain gauge slots, two on each side: 1mm distal to the first premolar (SG1 &SG3) and 1 cm away from the first one at the edentulous ridge (SG2&SG4). Removable partial dentures were constructed, and strain gauges were used to measure the strain applied both unilaterally and bilaterally by a universal testing machine before and after one year of clinical simulation where, an average of 5 readings were recorded for each model. Clinical simulation was performed through chewing simulator and dentures insertion/removal cycles. Repeated measures ANOVA and Tukey’s post-hoc test were used for data analysis at p < 0.05. Results: PEEK (BioHPP) group revealed the lowest induced strain before and after one year of clinical simulation compared to zirconia and metal groups during both unilateral and bilateral loading with significantly higher induced strain at SG2 & SG4 compared to that induced at SG1 & SG3. Metal group showed the same pattern but with significantly higher values compared to PEEK (BioHPP). For zirconia group after one year of clinical simulation, bilateral loading revealed significant decrease in induced strain at SG1&SG3 with a significant increase at SG2 &SG4. Conclusions: PEEK (BioHPP) is more effective in stress dissipation as an extra-coronal attachment in removable partial dentures compared to zirconia and metal. After one year of clinical simulation.