الفهرس 
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Abstract
This study involved two parts; it was started with in vivo study then proceeded with in vitro one. It was performed on partially edentulous mandibular arch representing Kennedy Class I classification and the abutments were first and second premolars bilaterally.
Two types of materials were used in construction of CAD/CAM milled telescopic retained removable partial denture; thus, two groups were defined:
• group I: Primary copings and the telescopic retained removable partial denture framework were milled from metal (Co-Cr).
• group II: Primary copings and the telescopic retained removable partial denture framework were milled from polyether-ketone-ketone (PEKK).
Patients were selected from the outpatient clinic of Prosthodontics department, Faculty of Dentistry, Ain-shams University to participate in this study, according to the listed inclusion criteria.
Patient’s approval was taken, and case evaluation was done before starting in the prosthetic procedures.
A digital impression of the entire maxillary arch, mandibular arch and centric occlusion was obtained from the patient using a chair side intraoral 3D scanner.
The digital scan file was then processed into STL file and virtualized into a digital model.
The abutment teeth 4,5 bilaterally were prepared and sufficient clearance was checked.
A digital impression of the prepared abutment teeth bilaterally was then obtained using a chair side intraoral 3D scanner.
The digital scan file of the prepared teeth was processed into STL file and virtualized into a digital prepared model to print two copies of 3-D printed master cast model with gingival simulator.
A software was used to perform the design of the telescopic removable partial denture on the digital virtual model as follows:
• The virtual model was digitally surveyed according to the suitable path of insertion. Undercuts were blocked out along the selected path of insertion.
• Primary crowns were designed to fit on the prepared teeth with Marburg design.
• Secondary crowns were designed to fit to the primary crowns and then the rest of the removable partial denture framework were joined with lingual plate.
The STL files of telescopic copings and RPD framework were sent to the milling machine to get two copies of the design; one made from Co-Cr and the other made from PEKK.
Following that the acrylic teeth were set and waxed up on the 3D printed models with articulating pins for centric occlusion. Then, the RPDs were processed with self-cured acrylic resin.
Then, for both groups, the primary copings cemented to the abutment teeth on the model and the telescopic RPD frameworks were scanned using intra-oral scanner, then STL files were obtained. The inner surface of the telescopic RPD secondary copings were scanned also for further wear evaluation.
Accuracy assessment of the primary copings and the telescopic RPD frameworks between the designed STL files and the milled ones was performed using surface machining software. Deviations of the copings and telescopic RPD framework were recorded and then tabulated for statistical analysis.
Retention assessment was performed using universal Testing. The initial pull off test was done, and maximum tensile loads needed to dislodge the RPD from the model were calculated in Newtons and recorded.
A chewing simulator was used to apply dynamic cyclic loading to each RPD group. Each telescopic retained overdenture was manually inserted and removed 540 times, and then was mounted again on the universal testing machine to measure the final retentive force. The pull off test was done to record the final retention values after simulation of 6 months of RPD use.
Then, for both groups, the cemented primary copings and the inner surface of telescopic RPD frameworks were scanned again after functional simulation using intra-oral scanner, then STL files were obtained.
Primary copings and the inner surface of secondary copings deviations after functional simulation were assessed using 3D assessment. For each evaluation, the deviation map for 2D compare was analyzed and areas of material loss or wear were identified with negative deviations. The average deviation values were then recorded, and statistically analyzed.
The results showed a statistically higher accuracy in group II (PEKK) than group I (Co-Cr) in both primary copings and the telescopic RPD framework.
The results revealed a statistically significant higher final retentive values after 6 months of function simulation in group II (PEKK) than group I (Co-Cr). Moreover, the results showed that loss of retention after function simulation of 6 months was higher in group I (Co-Cr) compared to group II (PEKK).
Regarding wear of primary copings of the telescopic retained RPD, the results obtained revealed a statistically significantly higher deviation in group I (Co-Cr) than group II (PEKK). Moreover, this study indicated that there is a statistically significant correlation between loss of retention and wear regarding the primary copings of CAD/CAM telescopic retained RPD in the two groups.
Regarding wear of secondary copings of the telescopic retained RPD, the results obtained revealed no statistically significant difference in deviation between the two groups. Moreover, the results indicated that there is no statistically significant correlation between loss of retention and wear regarding the secondary copings of CAD/CAM telescopic retained RPD in the two groups.
Finally, after assessment of in vitro tests of the study, the most favorable telescopic retained RPD material (PEKK) was delivered to the patients.