الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
 |  | from | 130 |  |  |
| | | from | 130 | | |
Abstract
The success of dental restorations is determined by four main factors: biocompatibility, aesthetic value, resistance to fracture and marginal adaptation. An inadequate marginal fit may compromise the longevity of the restoration since cement film exposure to the oral environment can lead to its dissolution. The consequent plaque accumulation increases the risk of secondary caries, micro leakage, endodontic inflammation and periodontal diseases causing the failure of the restoration. Marginal and internal fit can be influenced by several factors, starting from the impression phase to the final cementation process. In general dental practice impressions using elastomeric materials are a conventional procedure. These can be made with monophase or multiphase consistencies as well as one- or two-step technique. Although high quality impressions are achievable by these impression techniques and workflows, several mistakes associated with the intraoral phase or laboratory procedures may occur, leading to inaccuracies. The computer aided design/computer aided manufacturing (CAD/CAM) techniques for dental restorations have been developed to optimize the quality of the restorations as well as the efficiency of the workflow. Another target is the production of high resistance ceramic restorations which, up to date, can only be produced with these techniques.
This randomized clinical study was done to compare the marginal fit and internal adaptation of the ceramic zirconia fixed restorations obtained from two impression techniques: Conventional technique dual mix two step technique and Digital Intra-oral technique.
Thirty two monolithic zirconia single crowns were fabricated using in Coris TZI C zirconia blocks. The patients were selected according to eligibility criteria and divided into two groups according to the impression technique group 1 (control group) Conventional impression technique. group 2 (intervention group) intra-oral digital impression techniques.
All teeth preparations were performed by one single operator (researcher) for standardization. Uniform reduction was made using depth grooves, with 1.5mm axial reduction and 2mm occlusal or incisal reduction with 8-10° convergence angle and 0.8mm chamfer finish line using tapered stone with rounded end.
All sharp line angles that might serve as a point for stress concentration were rounded using finishing tapered rounded end diamond stone. Temporization and bite registration were made.
In the Conventional impression technique polyvinyl siloxane (PVS) material was used in a two-step impression technique in stainless-steel metal trays. The light viscosity was applied on the full arch putty impression which was taken before teeth preparation and then poured for the production of the master cast which was scanned using extraoral scanner (inEos X5 extraoralscanner, cerec, Sirona).while in the intra-oral digital impression technique the prepared teeth were directly scanned using a 3D powder-free intraoral camera (CEREC Omnicam, Sirona) using contralateral tooth as a reference and 40 μm cement space. For standardization in the present study the same milling machine (MC X5, Sirona, Germany) was used for milling all the specimens. after completion of the milling process, all crowns were placed inside the ultrasonic cleaner and then dried 10 minutes at 150°C (302°F) in the drying cabinet and then densely sintered using in Fire HTC speed furnace with pre-programmed settings according to the manufacturer’s instructions.
After milling and sintering the zirconia crowns checked extra-orally on master cast and intra-orally in patient mouth for any needed adjustment in seating, interproximal contacts, margin location, occlusion and contour which was done under constant water cooling. Crowns were then polished by using soft, diamond rubber polishers.
Marginal fit and internal adaptation were measured by an in vivo impression replica technique. The crowns were first filled with a light-body silicone material, then seated on the abutment teeth with maximum finger pressure and then fixed with a cotton roll while the patient closed his mouth to simulate clinical cementation of the restoration.
After two and a half minutes the crowns were dragged off the preparation and the light-body material adhering to the inner surface of the crown was stabilized using another more viscous polyvinylsiloxane material and after setting, both silicone materials were simultaneously removed from each crown. Two replicas were made for each crown. The silicone replicas were cut with a sharp scalpel blade in both mesio-distal and bucco-lingual directions, resulting in four sections to be measured per abutment. All sample measurements were carried out by one examiner who was blinded. Cross-sections were adjusted horizontally on modeling clay to obtain a parallel orientation to the microscope’s plate. Replica film thickness was examined at mesial, distal, buccal, and lingual locations using a stereomicroscope at magnification factor ×16, with a built-in charge-coupled device camera that captured the zone to be analyzed. Measurements were made at five points at each section for 16 samples in each group.
After measuring the marginal and internal fit of each crown obtained from both indirect digitalization using conventional impression (CIS) and digital impression techniques (IDI) the crown that showed better marginal adaptation and internal fit was sandblasted in the one-way blasting process with max.50 µm corundum (Al2O3). Pressure < 2.5 bar and finally cemented inside the patient mouth using dual cure adhesive resin cement.
Data were collected and statistically analyzed.