Influence of diameter in the stress distribution of extra-short dental implants under axial and oblique load: a finite element analysis

Aim: This study evaluated the influence of a wide diameter on extra-short dental implant stress distribution as a retainer for single implant-supported crowns in the atrophic mandible posterior region under axial and oblique load. Methods: Four 3D digital casts of an atrophic mandible, with a single implant-retained crown with a 3:1 crown-to-implant ratio, were created for finite element analysis. The implant diameter used was either 4 mm (regular) or 6 mm (wide), both with 5 mm length. A 200 N axial or 30º oblique load was applied to the mandibular right first molar occlusal surface. The equivalent von Mises stress was recorded for the abutment and implant, minimum principal stress, and maximum shear stress for cortical and cancellous bone. Results: Oblique load increased the stress in all components when compared to axial load. Wide diameter implants showed a decrease of von Mises stress around 40% in both load directions at the implant, and an increase of at least 3.6% at the abutment. Wide diameter implants exhibited better results for cancellous bone in both angulations. However, in the cortical bone, the minimum principal stress was at least 66% greater for wide than regular diameter implants, and the maximum shear stress was more than 100% greater. Conclusion: Extra-short dental implants with wide diameter result in better biomechanical behavior for the implant, but the implications of a potential risk of overloading the cortical bone and bone loss over time, mainly under oblique load, should be investigated

Effectiveness of the Semi-Adjustable Articulator Compared to Clinical Examination

ABSTRACT: This work aims to verify the effectiveness of the semi-adjustable articulator (SAA) when compared to a clinical examination of samples in individuals comparing the number of occlusal interferences. The research was carried out at FAESA (Integrated University of São Pedro), in which two independent researchers compared occlusal interferences in protrusion and laterality movements in the clinical examination and in models mounted on a semi-adjustable articulator, with carbon from Baush, in 77 patients who attended to the graduation clinic. Data were tabulated and evaluated by the Mann- Whitney statistical test and data normality was verified by the Kolmogorov-Smirnov test. When analyzing the interference of protrusion on central incisors, it was found that the mean was higher for the SAA on clinical examination. As for the right laterality in the canine guides, it was observed that the clinical examination had a higher interference average in relation to the SAA. The same was true for left laterality, where the mean interference was also higher for the clinical examination. That is, by increasing the values of occlusions in the SAA, the values of occlusions in the clinical examination also increase. As central incisor protrusions between the SAA and clinical examination were moderately positive, there was a strong positive relationship for the right sides and a moderate positive relationship for the left sides. It is concluded that a semi-adjustable articulator is an effective tool for the diagnosis and planning of the dentist, due to its ability to simulate mandibular movements. However, such a tool requires prior knowledge for an ideal assembly for treatment success.

RESUMEN: Este trabajo tuvo como objetivo verificar la efectividad del articulador semi-ajustable (SAA) cuando se compara con un examen clínico de muestras en individuos de acuerdo al número de interferencias oclusales. La investigación se llevó a cabo en FAESA (Universidad Integrada de São Pedro), en la que dos investigadores independientes compararon las interferencias oclusales en los movimientos de protrusión y lateralidad en el examen clínico y en modelos montados en un articulador semiajustable, con carbón de Baush, en 77 pacientes que acudieron a la clínica de graduación. Los datos se tabularon y evaluaron mediante la prueba estadística de Mann-Whitney y la normalidad de los datos se verificó mediante la prueba de Kolmogorov-Smirnov. Al analizar la interferencia de la protrusión en los incisivos centrales, se encontró que la media era mayor para el SAA en el examen clínico. En cuanto a la lateralidad derecha en las guías caninas, se observó que el examen clínico tuvo un promedio de interferencia más alto en relación al SAA. Lo mismo ocurrió con la lateralidad izquierda, donde la interferencia media también fue mayor para el examen clínico. Es decir, al aumentar los valores de oclusiones en el SAA, también aumentan los valores de oclusiones en el examen clínico. Como las protuberancias de los incisivos centrales entre el SAA y el examen clínico fueron moderadamente positivas, hubo una fuerte relación positiva para los lados derechos y una relación positiva moderada para los lados izquierdos. Se concluye que un articulador semi-ajustable es una herramienta eficaz para el diagnóstico y planificación del odontólogo, debido a su capacidad para simular movimientos mandibulares. Sin embargo, tal herramienta requiere conocimientos previos para un montaje ideal para el éxito del tratamiento.

Resin-matrix ceramics for occlusal veneers: Effect of thickness on reliability and stress distribution.

OBJECTIVE: To evaluate the influence of resin-matrix ceramic material and thickness on reliability and stress distribution of occlusal veneers (OV). METHODS: One hundred and twenty-six OV of a mandibular first molar were milled using a CAD/CAM system and allocated according to materials (resin nanoceramic (RNC) or polymer-infiltrated ceramic network (PICN)) and thicknesses (0.5, 1.0 and 1.5 mm), totaling six groups (RNC0.5, RNC1, RNC1.5, PICN0.5, PICN1, and PICN1.5). Step-stress accelerated-life testing was performed (n = 21/group) with the load applied at the distobuccal cusp tip of the occlusal veneer until failure or suspension. The use level probability Weibull curves and reliability were calculated and plotted (90% CI). Finite element analysis evaluated the stress distribution according to maximum principal stress (σmax) on the restoration and maximum shear stress (τmax) on the cement layer. RESULTS: There was no difference in the probability of survival for the estimated missions among the groups, except at 600 N in which the results were significantly lower to PICN1.5 (6%) compared to RNC1 (55%) and RNC1.5 (60%). The σmax values were higher for PICN (31.85-48.63 MPa) than RNC (30.78-33.09 MPa) in the same thicknesses. In addition, 0.5 mm groups concentrated more stress in the restoration (33.09-48.63 MPa) than 1.0 mm (31.11-35.36 MPa) and 1.5 mm (30.78-31.85 MPa) groups in the same material. SIGNIFICANCE: Both resin-matrix ceramic materials seem up-and-coming restorative systems for occlusal veneers irrespective of the thicknesses as a consequence of the high reliability.