1. Department of Dental Sciences and Surgery, Faculty of Medicine and Surgery, University of Bari ”Aldo Moro”, Bari, Italy
2. Department of Mechanical and Management Engineering, Polytechnic of Bari, Bari, Italy
3. Department of Human Anatomy and Histology, Faculty of Medicine and Surgery, University of Bari ”Aldo Moro”, Bari, Italy
4. Department of Biomedical Sciences, University of Foggia, Foggia, Italy
5. President of EuraSEM, European Society for Experimental Mechanics
6. Società Cooperativa Sociale e Sanitaria: ONLUS “Insieme con Padre Pio”
Aims. To investigate how the interfacial shear strength of the dentin - post interface with and without defects changes for different combinations irrigant/sealer.
Methods. In forty human decoronated and instrumented teeth, fibreglass posts were inserted. The obtained root segments were randomly assigned to four different groups according to the irrigant adopted and the cement used to seal the root canal. The root segments were processed for metyl-methacrylate embedding. Serial sections were obtained and submitted to histomorphometric analyses in order to observe any defect of adhesion at the dentin - post interface and to measure the defects' dimension. The serial sections were also submitted to micro-push-out test. The measured shear strength values were subjected to statistical analysis by one-way ANOVA. The values of bond strength determined for the defective samples were correlated with the dimension of the defects. Finite element models were built to interpret and corroborate the experimental findings.
Results. ANOVA showed that the generic combination irrigant/sealer does not affect the interfacial shear strength values. The bond strength of the samples without defects was averagely twice as large as that of the defective samples. The defects occupying more than 12 % of the total transverse section area of the endodontic cement layer led to a reduction of the bond strength of about 70 %. The predictions of the finite element models were in agreement with the experimental results.
Conclusion. Defects occupying less than 2 % of the total transverse section area of the cement layer were shown to be acceptable as they have rather negligible effects on the shear strength values. Technologies/protocols should be developed to minimize the number and the size of the defects.
Keywords: Defect of Adhesion, Finite Element Method, Histomorphometric Analyses, Interfacial Shear Strength, Micro-Push-Out Test, Microradiography.