Effect of Different Materials of Primary Telescopic Crowns on The Frictional Fit of Pekkton Partial Denture Frameworks in Kennedy Class I

Abstract

An educational mandibular Kennedy class I partially edentoulus cast was scanned and a Standard Tessellation Language (STL) file was generated. The virtual cast was modified to create four abutments in the place of the first and second premolars bilaterally. Then, the STL file was sent to the 3D printing device to construct twelve identical 3D casts with a hollow base. Then, the printed casts were finished and scanned to generate an STL file. Primary crowns were designed for all groups using Exocad software. Then, the STL file was sent to the milling machine. For group (A) 24 primary crowns were milled from PEKK (Pekkton®) blanks while for group (B) 24 primary crowns were milled from zirconia. The 3D cast with primary crowns in place was scanned to generate an STL file which was used to design the RPD frameworks including secondary crowns, denture base and mandibular major connector. The STL file was sent to the milling machine to produce an initial telescopic framework from a poly methyl methacrylate (PMMA) blank. After verification of the fit of the trial framework on the cast, the STL file of the design was used again to mill the frameworks from the PEKK (Pekkton®) blank. Then, the Pekkton frameworks were finished, polished and seated on the primary crowns. The Pekkton primary crowns were sandblasted, and their inner surfaces were conditioned with light cured Visio.link adhesive primer.

The zirconia primary crowns were sandblasted, and their inner surfaces were conditioned with MKZ Primer. The casts were also sandblasted and the primary crowns of both groups were cemented using self-adhesive resin cement. Each group was tested under the same conditions, i.e., moistening of the abutments with artificial saliva and loading the framework with a compressive pre-weight of 50 N for 20 s. The machine was set at a constant crosshead speed of 50 mm/min. The Universal Testing machine was used to apply vertically dislodging forces until the separation of the framework. The pull off test was done to record the friction fit values at baseline. The Chewing simulator was used to apply dynamic cyclic loading to each group. The exact point of load application was marked at the centre of the horizontal metal plate that was attached to the occlusal surface of each framework. Then, the specimen chamber was adjusted antero-posteriorly and medio-laterally to ensure receiving the load into the marked point. Each framework was tested under the same conditions, i.e., filling the specimen chamber with artificial saliva and load settings of 49 N loads. Software parameters were set at 60 mm/sec speed, 3 mm vertical path, 0.7 mm horizontal path, 1.6 Hz frequency. Then, each cast was mounted again on the universal testing machine to measure the friction fit. It was repeated after 50,000 and after 100,00 cyc