Assessment of the effect of two different digital fabrication techniques on marginal and internal fit of interim fixed dental prosthesis / Submitted by Mohamed Amir Shalaby, (B.D.S. University of Sharjah (2012); Supervision by Prof. Ahmed Naguib Mohamed, Professor, Fixed prosthodontics Department, Faculty of Oral and Dental Medicine, Future University in Egypt, Prof. Hisham Ibrahim Al Ansari, Professor, Fixed Prosthodontic Department, Faculty of Dentistry, Cairo University, Dr. Mennatallah Mohie El Din Wahba, Lecturer, Fixed Prosthodontics Department, Faculty of Oral and Dental Medicine Future University in Egypt

Supervision of Prof. Ahmed Naguib Mohamed, Professor, Fixed prosthodontics Department – Faculty of Oral and Dental Medicine Future University in Egypt
Prof. Hisham Ibrahim Al Ansari, Professor, Fixed Prosthodontic Department – Faculty of Dentistry, Cairo University, Dr. Mennatallah Mohie El Din Wahba, Lecturer, Fixed Prosthodontics Department – Faculty of Oral and Dental Medicine Future University in Egypt

Thesis (M.Sc.)-Future University in Egypt, Faculty of Oral and Dental Medicine, Department of Fixed prosthodontics Department, 2022.

Includes bibliographical references.

Interim restoration provides esthetics and function for a specific time until the
permanent restoration is fabricated. It should maintain the biological,
mechanical, and esthetic principles to protect the pulp from any irritation, to
preserve the periodontal health, and to maintain occlusal compatibility. The
interim materials fabricated with CAD/CAM technologies exhibit high
mechanical properties, color stable, and allow better fit integrity by
eliminating polymerization shrinkage.
Nissin dental model with missing upper left first premolar and upper left first
molar, and upper right central incisor, upper right canine, and upper right first
molar was used. The model was scanned using laboratory scanner, and the
scanned file was saved as pre-operative STL format. Following that, the
abutments were prepared using the CNC milling machine to maintain ideal
standardization of the preparations. Then the prepared abutments were
scanned again using the laboratory scanner, and the scanned file was saved as
post-operative STL format. After scanning, the design of the restorations were
chosen from the software library and adapted to the pre-operative STL file in
order to be fabricated using the additive and subtractive technologies.
A total of 24 interim bridges fabricated by different CAD/CAM technologies were
used in this current in vitro study. The specimens were divided into two groups
according to the fabrication method and span length; Group1 (n=12), 6 short span
bridges were fabricated by additive technology, and 6 short span bridges
fabricated by subtractive technology. Group II (n=12) 6 long span bridges were
fabricated by additive technology, and 6 long span bridges fabricated by
subtractive technology.
Finally the fabricated bridges were scanned using the laboratory scanner and
superimposed on the post-operative STL file using the Geomagic software in
order measure the marginal and internal fit along the mesio-distal and buccolingual
directions.
The results showed that the fabrication process of the additive technology of
the internal fit of long span bridge had a statistically significant effect
compared to subtractive technology. The additive technique showed better fit
in the the bucco-lingual direction and mesio-distal direction, with values of
40.5 μm and 73.4 μm in the bucco-lingual direction compared to the
subtractive technique, and 62.3 μm and 91 μm in the mesio-distal direction.
Furthermore, the internal fit of the short span bridges fabricated with additive
technology showed statistically significant difference only in the buccolignual
direction, with values 39 μm compared to 54.4 μm in the subtractive
technique. By contrast, the span length influenced the internal fit in the
subtractive technique which has led to a statistical significant difference.
Regarding the effect on fabrication method on the marginal fit in the long
span bridges, there was no statistical difference between the two technologies.
On the other hand, regarding the span length, there was statistically
significant difference between the fabrication technologies, where the additive
technology exhibited lower mean values in the marginal area. In the short
span bridges, the mean marginal fit of the additive technology was 57.7 μm
whereas in the short span of the subtractive technology was 35.1 μm,
indicating a statistically significant difference.

Text in English, abstracts in English and Arabic.