Influence of the connection design and titanium grades of the implant complex on resistance under static loading

PURPOSE: The purpose of this study was to evaluate the resistance to deformation under static overloading by measuring yield and fracture strength, and to analyze the failure characteristics of implant assemblies made of different titanium grades and connections. MATERIALS AND METHODS: Six groups of implant assemblies were fabricated according to ISO 14801 (n=10). These consisted of the combinations of 3 platform connections (external, internal, and morse tapered) and 2 materials (titanium grade 2 and titanium grade 4). Yield strength and fracture strength were evaluated with a computer-controlled Universal Testing Machine, and failed implant assemblies were classified and analyzed by optical microscopy. The data were analyzed using the One-way analysis of variance (ANOVA) and Student's t-test with the level of significance at P=.05. RESULTS: The group IT4S had the significantly highest values and group IT2 the lowest, for both yield strength and fracture strength. Groups IT4N and ET4 had similar yield and fracture strengths despite having different connection designs. Group MT2 and group IT2 had significant differences in yield and fracture strength although they were made by the same material as titanium grade 2. The implant system of the similar fixture-abutment interfaces and the same materials showed the similar characteristics of deformation. CONCLUSION: A longer internal connection and titanium grade 4 of the implant system is advantageous for static overloading condition. However, it is not only the connection design that affects the stability. The strength of the titanium grade as material is also important since it affects the implant stability. When using the implant system made of titanium grade 2, a larger diameter fixture should be selected in order to provide enough strength to withstand overloading.

The effect of zirconia framework design on the failure of all-ceramic crown under static loading

PURPOSE: This in vitro study aimed to compare the failure load and failure characteristics of two different zirconia framework designs of premolar crowns when subjected to static loading. MATERIALS AND METHODS: Two types of zirconia frameworks, conventional 0.5 mm even thickness framework design (EV) and 0.8 mm cutback of full contour crown anatomy design (CB), were made for 10 samples each. The veneer porcelain was added on under polycarbonate shell crown made by vacuum of full contour crown to obtain the same total thickness of the experiment crowns. The crowns were cemented onto the Cobalt-Chromium die. The dies were tilted 45 degrees from the vertical plane to obtain the shear force to the cusp when loading. All crowns were loaded at the lingual incline of the buccal cusp until fracture using a universal testing machine with cross-head speed 0.5 mm/min. The load to fracture values (N) was recorded and statistically analyzed by independent sample t-test. RESULTS: The mean and standard deviations of the failure load were 1,170.1 +/- 90.9 N for EV design and 1,450.4 +/- 175.7 N for CB design. A significant difference in the compressive failure load was found (P<.05). For the failure characteristic, the EV design was found only cohesive failures within veneering porcelain, while the CB design found more failures through the zirconia framework (8 from 10 samples). CONCLUSION: There was a significant difference in the failure load between two designs, and the design of the framework influences failure characteristic of zirconia crown.

The effect of zirconia framework design on the failure of all-ceramic crown under static loading

PURPOSE: This in vitro study aimed to compare the failure load and failure characteristics of two different zirconia framework designs of premolar crowns when subjected to static loading. MATERIALS AND METHODS: Two types of zirconia frameworks, conventional 0.5 mm even thickness framework design (EV) and 0.8 mm cutback of full contour crown anatomy design (CB), were made for 10 samples each. The veneer porcelain was added on under polycarbonate shell crown made by vacuum of full contour crown to obtain the same total thickness of the experiment crowns. The crowns were cemented onto the Cobalt-Chromium die. The dies were tilted 45 degrees from the vertical plane to obtain the shear force to the cusp when loading. All crowns were loaded at the lingual incline of the buccal cusp until fracture using a universal testing machine with cross-head speed 0.5 mm/min. The load to fracture values (N) was recorded and statistically analyzed by independent sample t-test. RESULTS: The mean and standard deviations of the failure load were 1,170.1 +/- 90.9 N for EV design and 1,450.4 +/- 175.7 N for CB design. A significant difference in the compressive failure load was found (P<.05). For the failure characteristic, the EV design was found only cohesive failures within veneering porcelain, while the CB design found more failures through the zirconia framework (8 from 10 samples). CONCLUSION: There was a significant difference in the failure load between two designs, and the design of the framework influences failure characteristic of zirconia crown.

Analysis of Biomechanical Properties of Whole Cervical Spine under Static Loading with 3-D Finite Element Model / 대한정형외과학회잡지

The biomechanical responses, such as nucleus pulposus pressure, facet contact force, stress distribution among ligaments in the cervical spine under static loading like flexion and extension, were examined with 3-D nonlinear finite element model. Finite element model consisted of whole cervical spines with intact discs and ligaments was developed from 1mm thick CT-cross sections of a 25-year-old healthy young man. Geometrical nonlinearity was considered for the large deformation and ABAQUS package was used for calculation. Results were verified comparing with those of existing in vivo and in vitro experiments. Results indicated that, developed cervical spine FEM was well consistent with other experiments. Nucleus pulposus pressure increased in flexion and extension more in lower cervical region. Facet contact force increased more in lower cervical spine in extension. In addition, capsular ligament was the most important one among 7 cervical ligaments surrounding cervical spine both in flexion and extension. We could better understand the biomechanics of whole cervical spine with developed finite element model and it might be applied to dynamic or postoperative study.