Biomechanical properties of trabecular bones in femoral head under loads with different angles / 医用生物力学

Objective To investigate the effects from loads with different angles on morphological and biomechanical properties of trabecular bones in femoral head, so as to provide theoretical basis for studying biomechanical mechanism of necrosis and collapse of femoral head. Methods Ninety-four specimens of 12-month-old ovine trabecular bones in femoral head and forty-three specimens of human cadaver trabecular bones in femoral head were prepared. According to different angles between loading direction and principle compression direction, all the trabecular bones were divided into five groups by 10° interval (i.e. varus 10° and 0°, valgus 10°, 20° and 30°) to simulate the reduction condition under different Garden index after internal fixation of femoral neck fractures. Micro-CT scanning and calculation, compression failure test on ovine trabecular bones in femoral head and cyclic compression test on human cadaver trabecular bones in femoral head were performed to investigate morphological and mechanical indices, including BV/TV (bone volume vs. total volume), BS/BV (bone surface vs. bone volume), Tb.Th (thickness of trabecular bone), Tb.N (number of trabecular bone), Tb.Sp (trabecular separation), elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles. Results When the angle between loading direction and principle compression direction of trabecular bones was 0°, BV/TV, Tb.Th, elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles for trabecular bones were the maximum while BS/BV and Tb.N were the minimum, and all the formers presented decreasing tendency while BS/BV and Tb.N showed increasing tendency along with the angle increasing. ConclusionsAlong with the angle changes, the tendency of BV/TV and ultimate strength for 12-month-old ovine trabecular bones in femoral head displayed as the same as human trabecular bones in femoral head. Both the morphological and biomechanical properties of trabecular bones in femoral head will decrease when the angle between loading direction and principle compression direction of trabecular bones increases. The more the Garden index deviating from 160°, the more likely trabecular bones in femoral head to be damaged.

Resistencia de dientes restaurados con postes prefabricados ante cargas de máxima intercuspidación, masticación y bruxismo / Resistance of teeth restored with prefabricated posts to maximum intercuspidation loads, mastication and bruxism

Objetivo: determinar por el método de los elementos finitos la resistencia de dientes restaurados con postes prefabricados ante cargas estáticas de máxima intercuspidación y cargas cíclicas de masticación y bruxismo y analizar el efecto de la pérdida periodontal en la resistencia de las restauraciones. Métodos: se realizó una investigación in vitro mediante el método de los elementos finitos de dientes con pérdida periodontal, rehabilitados con postes prefabricados en fibra de vidrio, carbono y titanio. Los dientes fueron reconstruidos a partir de imágenes tomográficas de un paciente periodontalmente sano. Resultados: se muestra que ante cargas estáticas las rehabilitaciones no presentan tendencia a la falla, independientemente del material del poste o del grado de pérdida periodontal. En el caso de bruxismo y pérdida periodontal de 4 mm, la dentina presenta una durabilidad de 60 000 ciclos independiente del material del poste. Para cargas de masticación y periodonto sano, la falla en la dentina ocurre a los 100 000 ciclos con poste en titanio, 200 000 ciclos con poste en fibra de carbono y 1 100 000 ciclos con poste en fibra de vidrio. Para una pérdida periodontal de 2 mm la durabilidad de la dentina se reduce a 4 000 ciclos con poste en titanio, 5 000 ciclos con poste en fibra de carbono y 7 000 ciclos con poste en fibra de vidrio. Para pérdida periodontal de 4 mm, la durabilidad de la dentina se estima en 1 000 ciclos, independientemente del material del poste utilizado. Conclusiones: ante carga estática de máxima intercuspidación las rehabilitaciones con postes prefabricados en fibra de vidrio, carbono y titanio no presentan tendencia a la falla, independientemente del grado de pérdida periodontal. Ante cargas cíclicas, los postes prefabricados presentan una vida útil infinita, y es la dentina la estructura más afectada ante dichos eventos(AU)

Objective: using the finite element method, determine the resistance of teeth restored with prefabricated posts to maximum static intercuspidation loads, cyclical mastication loads and bruxism, and analyze the effect of periodontal loss on resistance by restorations. Methods: using the finite element method, an in vitro study was conducted of teeth with periodontal loss rehabilitated with prefabricated glass fiber, carbon and titanium posts. Reconstruction of the teeth was based on tomographic images from a periodontically healthy patient. Results: it was shown that rehabilitations did not tend to yield to static loads, irrespective of post material or the degree of periodontal loss. For bruxism and 4 mm periodontal loss, dentin durability was 60 000 cycles, irrespective of post material. For mastication loads and a healthy periodont, dentin failure occurs at 100 000 cycles with titanium posts, 200 000 cycles with carbon fiber posts, and 1 100 000 cycles with glass fiber posts. For 2 mm periodontal loss, dentin durability decreased to 4 000 cycles with titanium posts, 5 000 cycles with carbon fiber posts, and 7 000 cycles with glass fiber posts. For 4 mm periodontal loss, dentin durability is estimated at 1 000 cycles, irrespective of post material. Conclusions: restorations with glass fiber, carbon and titanium prefabricated posts do not yield to maximum static intercuspidation loads, irrespective of the degree of periodontal loss. Prefabricated posts exhibit endless resistance to cyclic loads. Dentin is the structure most severely affected by such events(AU)

A comparative study on the correlation between Korean foods and the fractures of PFG and all ceramic crowns for posterior applications / 대한치과보철학회지

STATEMENT OF PROBLEM: Recently, there have been increased esthetic needs for posterior dental restorations. The failure of posterior dental ceramic restoration are possible not only by the characters of the component materials but also by the type of food. PURPOSE: The research aim was to compare the in vitro fracture resistance of simulated first molar crowns fabricated using 4 dental ceramic systems, full-porcelain-occlusal-surfaced PFG, half-porcelain-occlusal-surfaced PFG, Empress 2, Ice Zirkon and selected Korean foods. MATERIAL AND METHODS: Eighty axisymmetric crowns of each system were fabricated to fit a preparation with 1.5- to 2.0-mm occlusal reduction. The center of the occlusal surface on each of 15 specimens per ceramic system was axially loaded to fracture in a Instron 4465, and the maximum load (N) was recorded. Afterwards, selected Korean foods specimens (boiled crab, boiled chicken with bone, boiled beef rib, dried squid, dried anchovy, round candy, walnut shell) were prepared. 15 specimens per each food were placed under the Instron and the maximum fracture loads for them were recorded. The 95% confidence intervals of the characteristic failure load were compared between dental eramic systems and Korean foods. Afterwards, on the basis of previous results, 14Hz cyclic load was applied on the 4 systems of dental ceramic restorations in MTS. The reults were analyzed by analysis of variance and Post Hoc tests. RESULTS: 95% confidence intervals for mean of fracture load 1. full porcelain occlusal surfaced PFG Crown: 2599.3 to 2809.1 N 2. half porcelain occlusal surfaced PFG Crown: 3689.4 to 3819.8 N 3. Ice Zirkon Crown: 1501.2 to 1867.9 N 4. Empress 2 Crown: 803.2 to 1188.5 N 5. boiled crab: 294.1 to 367.9 N 6. boiled chicken with bone: 357.1 to 408.6 N 7. boiled beef rib: 4077.7 to 4356.0 N 8. dried squid: 147.5 to 190.5 N 9. dried anchovy: 35.6 to 46.5 N 10. round candy: 1900.5 to 2615.8 N 11. walnut shell: 85.7 to 373.1 N under cyclic load (14Hz) in MTS, fracture load and masticatory cycles are: 1. full porcelain occlusal surfaced PFG Crown fractured at 95% confidence intervals of 4796.8 - 9321.2 cycles under 2224.8 N (round candy)load, no fracture under smaller loads. 2. half porcelain occlusal surfaced PFG Crown fractured at 95% confidence intervals of 881705.1 - 1143565.7 cycles under 2224.8 N (round candy). no fracture under smaller loads. 3. Ice Zirkon Crown fractured at 95% confidence intervlas of 979993.0 - 1145773.4 cycles under 382.9 N (boiled chicken with bone). no fracture under smaller loads. 4. Empress 2 Crown fractured at 95% confidence intervals of 564.1 - 954.7 cycles under 382.9 N (boiled chicken with bone). no fracture under smaller loads. CONCLUSION: There was a significant difference in fracture resistance between experimental groups. Under single load, Korean foods than can cause fracture to the dental ceramic restorations are boiled beef rib and round candy. Even if there is no fracture under single load, cyclic dynamic load can fracture dental posterior ceramic crowns. Experimental data with 14 Hz dynamic cyclic load are obtained as follows. 1. PFG crown (full porcelain occlusion) was failed after mean 0.03 years under fracture load for round candy (2224.8 N). 2. PFG crown(half porcelain occlusion) was failed after mean 4.1 years under fracture load for round candy (2224.8 N). 3. Ice Zirkon crown was failed after mean 4.3 years under fracture load for boiled chicken with bone (382.9 N). 4. Empress 2 crown was failed after mean 0.003 years under fracture load for boiled chicken with bone (382.9 N).