الفهرس 
Introduction and Review of LiteratureOnly 14 pages are availabe for public view
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Abstract
At a time when implant placement has become the most convenient and preferred option for replacement of teeth, maintaining bone and soft tissue around the implant are of critical importance specially if in the esthetic zone.
There have been many trials in the implant design and also crown abutment materials that favor stress distribution away from the crest of the implant, thus preserving the tissues around it and improving the esthetic outcome.
Our study was conducted in two lines along each other, an in-vitro and an in-vivo study. The primary aim of our study was clinical, radiographic and volumetric analysis of the peri-implant tissues with two different types of implant-abutment connections: internal hex and conical connection. To check whether the conical connection preserved the peri-implant tissues better than the internal hex connection in immediately placed and loaded implants in the esthetic zone.
The secondary aim was FEA and strain gauge measurements of these two types of connections (internal hex and conical tapered) with three different materials ( IPS Emax, Cubic Zirconia and Vita Enamic). To allow better understanding of the different combinations of crown materials with the proper implant-abutment connection to better choose the correct restoration for better preservation of peri-implant tissues.
A three-dimensional (3D) model simulation of the implants and its components was obtained from the manufacturer and modelled in the 3D FEA software. Six different models were created according to combinations of restoration materials (LD,CZ, VE) and abutment connections (IH and CT). The hybrid abutment crowns were loaded virtually 100N vertically in the central fossa and 30⸰ oblique direction. The stress distribution in the crown, implant, abutments and surrounding bone were evaluated through the Von Mises stress analysis.
3D FEA results were verified by a strain gauge measurement of six hybrid abutment crowns that were milled using a CAD/CAM software.
FEA showed that the stress transfer to surrounding bone was similar between all materials with same connection, but the stress transfer with CT was lower than IH. In vertical loading SG showed that VE had low strain reaching bone with both connections, CZ with CT, and LD with IH, while in 30⸰ direction VE and LD on IH and CZ on CT showed the least strain in the surrounding bone.
20 patients were involved in the study and allocated randomly into one of the two groups equally. Both groups received immediate implant placement with immediate loading in the upper esthetic zone, but one group with internal hex connection and the other with conical tapered one.
Clinical assessment was done using the PES score at (T0) which was the time of provisional restoration delivery and at (T6), 3 months after delivery of final crown. Both connections showed statistically significant higher values at T6 than T0. And overall, the conical tapered connection showed significantly higher mean values than the internal hex.
Radiographic assessment was done using CBCT, one was taken at provisional crown delivery (D0) and the other taken 6 months after (D2). where the difference in bone was measured at 0 and 2 mm, (B0) and (B2) respectively from the implant crest as a horizontal line towards the buccal plate. The internal hex showed statistically significant higher values of bone loss than the conical tapered connection group.
Volumetric changes were done by taking addition silicone rubber base impressions pre-operative (L0) and 3 months after final crown delivery (L1). A cast model made from dental stone was fabricated. Then these casts were scanned with a desktop 3D scanner and stereo lithographic files (STL) were obtained. The scanned models were superimposed and at the labial aspect of the placed implant, a defined area of interest was measured and then the difference in volume between (L0) and (L1) was calculated. It was shown that the internal hex connection has statistically significant higher mean value than the conical connection.
Conclusion
Within the limitations of the study, it was concluded that:
1. Immediate implant placement with immediate loading with conical implant abutment connection is an effective treatment option for the expected loss of peri-implant tissues and helps achieve good esthetic results and result in better clinical, radiographic, and volumetric outcomes.
2. Hybrid ceramic crowns have exhibited favorable but non-significant stress values in the peri-implant bone when compared to cubic zirconia or lithium disilicate.
3. Oblique non-axial load transferred higher than threshold stress values to the surrounding bone with all materials, thus it’s better to be avoided in implant retained restorations.
Recommendations
1. Elimination of oblique and lateral occlusal loads completely in implant retained restorations, due to their negative effect on the peri-implant tissues.
2. It is vital to choose the right crown material with the correct implant abutment connection to transfer favorable stresses to the surrounding tissues; Cubic Zirconia goes better with conical connection, while IPS Emax goes better with the internal hex, and the Vita Enamic can be used with both connections since they have low strain values in the surrounding bone.
3. Further studies with longer follow up time is needed.
4. Larger sample size with a greater number of patients to enhance the scientific evidence.