Assessment of a Proposed Composite Restorative Monoblock Approach for Intact Endodontically Treated Anterior Teeth to Optimize Their Esthetic and Functional Outcome with Bonded Ceramic Crowns. “In-Vitro Study”

Statement of the Problem: There is general acceptance among different authors about restoring the access cavity of intact endodontically treated anterior teeth with just a composite filling. However, in many instances, for esthetic reasons these teeth need to be crowned. Here, a question is raised about the restorative approach that gives optimum esthetic and functional performance.
Objectives: The aim of the present investigation was to test a proposed monoblock adhesive composite restoration bonded to a prepared channel in the coronal third of the root canal; in comparison to two other conventional approaches: composite filling of the access cavity and glass fiber post in the root canal as far as fracture resistance and failure mode are concerned after the teeth being bonded with CAD/CAM ceramic crowns.
Materials and Methods: Twenty-one intact maxillary central incisors were randomly divided into three groups of seven each. All the teeth were endodontically treated to be restored with three different treatment options: in the first group just composite restoration (CR) of the access cavity and the second group was assigned for the proposed monoblock adhesive composite restoration (MACR) and the third group for the glass fiber post bonded in the prepared root canal (GFP). All the teeth were prepared to standardized specifications for CAD/CAM all-ceramic crowns that were adhesively bonded to their preparations in the three groups. All the test specimens were subjected to thermocycling between 5°C and 55°C for 2000 cycles before being dynamically loaded in the Instron testing machine for 10,000 cycles. The specimens were then subjected to static loading until fracture, and the load at failure (N) of each specimen was recorded for the statistical analysis.
The fractured specimens were examined to detect the mode of failure.
Results: All the test samples survived the 10,000 dynamic loading cycles without any signs of cracks or flaws as detected by magnification. The statistical analysis of the data obtained after static loading of the samples revealed that the group with glass fiber posts (GFP) showed the highest significant fracture resistance mean value (579.6 ± 48.3 N) compared to the other two groups: the conventional (CR) and the proposed design (MACR) that revealed (415.1 ± 58.6) and (370.6 ± 64.2 N) respectively, that were not significantly different statistically from each other. The detected mode of failure was an oblique fracture extending from the lingual surface to the labial surface at or just below the insertion of the tooth in the epoxy resin block. The majority of samples (fifteen test sample) presented repairable fractures (71%) and six samples (29%) showed non-repairable fractures. The proposed monoblock design (MACR) presented the highest percentage of repairable fractures (86%) followed by the glass fiber post group (GFP) (71%) and the least was the conventional group (CR) (57%).
Conclusions: 1- The three treatment modalities offered successful options for restoring intact endodontically treated maxillary incisors in terms of mechanical and esthetic standpoints. 2- The fracture resistance values of the three tested restorative designs exceeded the normal masticatory forces in this anterior region considerably. 3- The teeth restored with glass fiber posts (GFP) presented the highest statistically significant fracture resistance mean value as compared to the other two groups. 4- The proposed monoblock adhesive composite restoration (MACR) together with the composite restoration (CR) groups provided comparable fracture resistance mean values. 5- The majority of the tested samples (71%) showed repairable fractures, with the proposed monoblock technique presenting the highest percentage (86%) of repairable fractures. 6- The mode of failure was mainly adhesive-cohesive in nature.