Can the Remaining Coronal Tooth Structure Influence the Mechanical Behavior of Nonpost Full Crowns?

OBJECTIVES: This study investigated the impact of the remaining coronal tooth structure on the mechanical behavior of nonpost (NP) full crowns on endodontically treated maxillary central incisors. MATERIALS AND METHODS: Forty bovine incisors with NP and 2-mm of ferrule were divided into four groups based on the remaining structure: complete 2-mm ferrule (NP-2), absence of mesial and distal ferrule effect (NP-BL), absence of buccal and lingual ferrule effect (NP-MD), and no ferrule (NP-0). The specimens underwent a stepwise stress fatigue test until fracture occurred, and stress distribution was analyzed using in silico finite element analysis (FEA). Additionally, groups with endodontic posts (P) were simulated in the FEA. RESULTS: The results showed that the survival rates varied among the different groups under oblique loading. The NP-2 group exhibited the highest survival rate, with all samples enduring loads up to 200 N and some surviving up to 520 N. The NP-MD and NP-BL groups had lower survival rates, while the NP-0 group had the poorest survival rate. The predominant failure mode was a nonrepairable root fracture. FEA results indicated no significant difference between groups with and without posts. NP intraradicular restorations on nonweakened roots with a minimum height of 2mm and partial or total ferrule thickness of 1mm offer a promising treatment option. CONCLUSION: A complete 2-mm ferrule was found to be the most favorable configuration for NP full crowns. However, maintaining the remaining tissue is crucial, as both combinations with preserved ferrule effect exhibited superior behavior in terms of fatigue and fracture load compared to the group with no ferrule. These findings contribute to understanding the mechanical considerations for NP full crowns and provide insights into treatment planning and design choices in restorative dentistry.

Fracture resistance and biomechanical behavior of different access cavities of maxillary central incisors restored with different composite resins.

OBJECTIVES: The aim of this study was to compare the effect of three different access cavities on the tissue removal, deflection, fracture resistance, and stress distribution of extracted maxillary central incisors. MATERIALS AND METHODS: Forty human maxillary central incisors were randomly assigned in four experimental group (n = 10) including conservative access cavity "CAC," traditional access cavity "TAC," invasive access cavity "IAC," and without access cavity (control group). Cone-beam computed tomography "CBCT" scans were used to evaluate the tissue removal during the different access cavities. All specimens were restored with composite resin (Admira Fusion, Voco, Cuxhaven, Germany) and embedded in acrylic resin blocks after simulating the periodontal ligament using red wax, then the specimens were submitted to the deflection test applying a load of 250 N and to the load-to-fracture test after artificial aging in a mechanical cycling machine (150 N, 5 × 106 cycles, 10 Hz). Lastly, stress distribution was assessed by three-dimensional finite element analysis (3D-FEA), simulating the specimens restoration by two types of composite resins of low and high elastic modulus (8 and 18 GPa respectively) after the access cavities. The data were submitted to Shapiro-Wilk and KS normality tests. Then, they were analyzed by one-way ANOVA and Tukey tests with a significance level (α ≤ 0.05). RESULTS: CBCT scans showed a significant difference of worn tissues in CAC and TAC when compared to the IAC (P < 0.0001). In deflection test, CAC showed lower deformation values than the TAC and IAC. Load-to-fracture test presented no significant difference among the three experimental groups (P = 0.6901). 3D-FEA showed that the more conservative the access cavity, the higher the stress magnitude. CONCLUSIONS: CAC promote less worn tissue; however, this does not improve the stress distribution or fracture resistance of endodontically treated maxillary incisors. CLINICAL RELEVANCE: Clinicians should reconsider the pros and cons of the conservative access cavity.

Effect of three different veneering techniques on the stress distribution and in vitro fatigue behavior of core-veneer all-ceramic fixed partial dentures.

Background. The present study aimed to evaluate the influence of the veneering technique on the tensile stress distribution and survival of full-ceramic fixed dental prostheses (FDPs). Methods. A three-dimensional model of an FDP was modeled on a second premolar and a second molar with a pontic between them for finite element analysis (FEA). The groups were divided according to the veneering technique: conventional stratification, rapid layer, and CAD-on techniques. A mesh control test determined the number of elements and nodes. The materials' properties were attributed to each solid component with isotropic, homogeneous, and linear elastic behavior. For the in vitro fatigue test (n=30), the FDPs were cemented on dentin analog abutments and submitted to 2×106 mechanical cycles (100 N at 3 Hz). Results. Maximum principal stress showed that the connector between the pontic and the second molar concentrated higher stresses, regardless of the techniques: Rapid layer (6 MPa) > CAD-on (5.5 MPa) > conventional stratification (4 MPa). The conventional stratification technique concentrated high stresses at the interface between the framework and veneering ceramic (2 MPa), followed by the rapid layer (1.8 MPa) and CAD-on (1.5 MPa) techniques. The crowns fabricated using the rapid layer and CAD-on techniques exhibited a 100% survival rate, while the conventional stratification group had 0% survival. Conclusion. Even with similar stress distribution between the veneering techniques, the conventional stratification technique was more prone to failure under fatigue due to higher defects incorporated than CAD-on and rapid layer techniques.

Does overlay preparation design affect polymerization shrinkage stress distribution? A 3D FEA study.

This study evaluated the polymerization shrinkage stress of three tooth preparation designs for indirect ceramic overlay by finite element analysis: isthmus preparation (IST); without isthmus preparation (wIST); and non-retentive preparation (nRET). The models were created based in prepared dental typodonts and were digitally impressed with an intraoral scanner. The interfaces in all models were considered perfectly bonded and all materials were considered homogeneous, linear, and isotropic. The polymerization shrinkage of the cement layer (100 µm) was simulated and evaluated by maximum principal stress criteria. The stress peaks followed this sequence: restoration = IST (13.4 MPa) > wIST (9.3 MPa) > nRET (9 MPa); cement layer = IST (16.9 MPa) > wIST (12.6 MPa) > nRET (10-7.5 MPa); and teeth = IST (10.7 MPa) > wIST (10.5 MPa) > (9 MPa). For the cement layer, the non-retentive preparation (nRET) had the lowest shrinkage stress from all the groups, obtaining a more homogeneous stress distribution on the cement surface. Regarding the abutment teeth, the IST generated a higher shrinkage stress area on the dental structure, concentrating higher stress magnitude at the axiopulpar and axiogingival angles. Non-retentive preparation seems to reduce polymerization shrinkage stress.

Apicoectomy of Perforated Root Canal Using Bioceramic Cement and Photodynamic Therapy.

Root perforation is a common endodontic accident. Its management depends mainly on root canal disinfection and sealing the perforation area by preventing any communication with the periodontium to prevent recontamination. A patient was referred to treat root perforation due to a previous treatment of tooth #22. The diagnosis was symptomatic periapical periodontitis, and the treatment plan was to retreat the root canal of #22 and make a surgical intervention (apicoectomy) associated with antimicrobial photodynamic therapy as a complementary technique. Five mineral oxides (5MO) cement was used as a root-end filling material. The procedures were performed in two sessions and controlled in two visits (after 30 days and 12 months). A bone neoformation was observed at the periapical area of tooth #22. 5MO bioceramic cement was effective in inducing the repair of the periapical lesion and had the ability to seal the exposed periapical area of the tooth. Its success depended mainly on root canal and surgical site disinfection.

Pictograph system for diagnosis making and data management in endodontics / Sistema de pictograma para elaboração de diagnóstico e gerenciamento de dados em endodontia

Objective: this questionnaire aimed to evaluate the approval of a new pictograph system for endodontic diagnosis by undergraduate and graduate students/endodontist instead of a conventional method. Methods: after a presentation to a total of 224 participants explaining the pictograph system, the participants (166 undergraduate students and 58 graduate students/endodontist) received a standardized questionnaire with three questions. The data were analyzed using the mult prop macro basing on Tukey's test for multiple comparison with (P ≤ 0.05). The first question was to define the education level of the participants; the second question about which diagnosis method is preferred; and the third question about the intention of using one of the methods in the future. The questionnaire was realized in May 2019. The response rate was 97.7%. Results: the first question showed that 74.10% and 25.90% were under graduate and graduate students/endodontist respectively. After statistical analysis there was no significant difference between the groups in the second and the third questions. In the second question (71.08% and 62.06%) of undergraduate and graduate student/endodontists respectively preferred the pictograph method over the conventional method. In the third question (60.24% and 51.72%) of undergraduate and graduate student/endodontists respectively showed interest in using the pictograph method in their professional career. Conclusion: the pictograph method in endodontic diagnosis is accepted by the majority of undergraduate and graduate students/endodontists. Training and experience affect the diagnosis making. (AU)

Objetivo: este questionário teve como objetivo avaliara aprovação de um novo sistema de imagem para diagnóstico endodôntico por estudantes de graduação e pós-graduação/endodontista, em vez de um método convencional. Métodos: após uma apresentação a um total de 224 participantes explicando o sistema de pictograma, os participantes (166 estudantes de graduação e 58 de pós graduação/endodontista) receberam um questionário padronizado com três perguntas. Os dados foram analisados usando a macro multi propósito baseada no teste de Tukey para comparação múltipla com (P ≤ 0,05). A primeira pergunta foi definir o nível de escolaridade dos participantes; a segunda pergunta sobre qual método de diagnóstico é preferido; e a terceira pergunta sobre a intenção de usar um dos métodos no futuro. O questionário foi realizado em maio de 2019. A taxa de resposta foi de 97,7%. Resultados: a primeira pergunta mostrou que 74,10% e 25,90% eram estudantes de graduação e pós-graduação / endodontista, respectivamente. Após análise estatística, não houve diferença significativa entre os grupos na segunda e na terceira questões. Na segunda questão (71,08% e 62,06%) dos estudantes de graduação e pós-graduação / endodontistas, respectivamente, preferiram o método de pictograma ao método convencional. Na terceira questão (60,24% e 51,72%) dos estudantes de graduação e pós-graduação /endodontistas, respectivamente, demonstraram interesse em utilizar o método de pictograma em sua carreira profissional. Conclusão: o método do pictograma no diagnóstico endodôntico é aceito pela maioria dos estudantes de graduação e pós-graduação / endodontistas. Treinamento e experiência afetam a elaboração do diagnóstico (AU)