Effects of dental implant diameter and tapered body design on stress distribution in rigid polyurethane foam during insertion.

Anchorage, evaluated by the maximum insertion torque (IT), refers to mechanical engagement between dental implant and host bone at the time of insertion without external loads. Sufficient anchorage has been highly recommended in the clinic. In several studies, the effects of implant diameter and taper body design under external loading have been evaluated after insertion; however, there are few studies, in which their effects on stress distribution during insertion have been investigated to understand establishment of anchorage. Therefore, the objective of this study was to investigate the effects of dental implant diameter and tapered body design on anchorage combining experiments, analytical modeling, and finite element analysis (FEA). Two implant designs (parallel-walled and tapered) with two implant diameters were inserted into rigid polyurethane (PU) foam with corresponding straight drill protocols. The IT was fit to the analytical model (R2 = 0.88-1.0). The insertion process was modeled using explicit FEA. For parallel-walled implants, normalized IT and final FEA contact ratio were not related to the implant diameter while the implant diameter affected normalized IT (R2 = 0.90, p < 0.05, ß1 = 0.20 and ß2 = 0.93, standardized regression coefficients for implant diameter and taper body design) and final FEA contact ratio of tapered implants. The taper design distributed the PU foam stress further away from the thread compared to parallel-walled implants, which demonstrated compression in PU foam established by the tapered body during insertion.

Analytical model for dental implant insertion torque.

Maximum insertion torque (IT) for threaded dental implants is a primary clinical measurement to assess implant anchorage, and strongly influences the clinical outcome. Insertion torque is influenced by surgical technique, implant designs, and patient factors such as bone density and quality. In this study, an analytical model was proposed for IT to estimate contributions from the thread and taper separately. The purpose of this study was to test if the analytical model could 1. differentiate the parallel-walled and tapered implant; and, 2. represent four factors: bone surrogate density, drill protocol, implant surface finish and cutting flute. The IT was modeled as the sum of the torques from the thread's inclined plane and interface shear stress from the tapered body integrated over the surface area, respectively, with two main parameters: effective force, F', F' and effective pressure, p'. The effective force, relates to the clamping force from the thread, while the effective pressure, p', associates with the contact pressure at the bone-implant interface. The model performed well (R2 = 0.88-1.0) and differentiated between the parallel-walled (p'= 0) and tapered implants (p'= 0.12). The model's parameters could individually represent the effects of the four factors. High bone surrogate density, two-step drill protocol, and rough surface increased both F' and p'. The cutting flute had opposing effects on F' and p' (ß4 = 0.35 and -0.24, respectively); and therefore, had the lowest net effect on IT. The proposed analytical model therefore improves the understanding of the principal contributors to dental implant IT by considering thread and taper mechanics independently.

Evaluation of experimental, analytical, and computational methods to determine long-bone bending stiffness.

Methods used to evaluate bone mechanical properties vary widely depending on the motivation and environment of individual researchers, clinicians, and industries. Further, the innate complexity of bone makes validation of each method difficult. Thus, the purpose of the present research was to quantify methodological error of the most common methods used to predict long-bone bending stiffness, more specifically, flexural rigidity (EI). Functional testing of a bi-material porcine bone surrogate, developed in a previous study, was conducted under four-point bending test conditions. The bone surrogate was imaged using computed tomography (CT) with an isotropic voxel resolution of 0.625 mm. Digital image correlation (DIC) of the bone surrogate was used to quantify the methodological error between experimental, analytical, and computational methods used to calculate EI. These methods include the application of Euler Bernoulli beam theory to mechanical testing and DIC data; the product of the bone surrogate composite bending modulus and second area moment of inertia; and finite element analysis (FEA) using computer-aided design (CAD) and CT-based geometric models. The methodological errors of each method were then compared. The results of this study determined that CAD-based FEA was the most accurate determinant of bone EI, with less than five percent difference in EI to that of the DIC and consistent reproducibility of the measured displacements for each load increment. CT-based FEA was most accurate for axial strains. Analytical calculations overestimated EI and mechanical testing was the least accurate, grossly underestimating flexural rigidity of long-bones.

Effect of insertion factors on dental implant insertion torque/energy-experimental results.

Anchorage of dental implants is quantified with a mechanical engagement to insertion, for example maximum insertion torque (MIT) and insertion energy (IE). Good anchorage of dental implants highly correlates to positive clinical outcomes. However, it is still unclear how bone density, drill protocol, surface finish and cutting flute affect anchorage. In this study, effects of the insertion factors on both MIT and IE were investigated using a full-factorial experiment at two levels: bone surrogate density (0.32 g/cm3 versus 0.48 g/cm3), drill protocol (Ø2.4/2.8 versus Ø2.8/3.2 mm), implant surface finish (machined versus anodized surface) and cutting flute (with versus without). Osteotomies were prepared on rigid polyurethane foam blocks with dimensions of 40 × 40 × 8 mm. Screw shaped dental implants with variable tapered body were consecutively inserted into and removed from the polyurethane foam blocks three times under constant axial displacement and rotational speed. Axial force and torque were recorded synchronously. Insertion energy was calculated from the area under the torque-displacement curve. In this study, we found the main insertion mechanics were thread forming for the first insertion. For the second and third insertions, the main mechanics shifted to thread tightening. Maximum insertion torque (MIT) responded differently to the four insertion factors in comparison to IE. Bone surrogate density, drill protocol and surface finish had the largest main effects for first MIT. For the first IE, drill protocol, surface finish and cutting flute were significant contributors. These results suggest that MIT and IE are influenced by different mechanics: the first MIT and the first IE were sensitive to thread tighten and forming, respectively. Together MIT and IE provide a complete assessment of dental implant anchorage.

Monitoring of keyhole entrance and molten pool with quality analysis during adjustable ring mode laser welding.

The process monitoring of the top side and the evaluation of surface quality were applied in adjustable ring mode (ARM) laser welding of 316 stainless steel by using visual monitoring and confocal sensor technology. Experiments were conducted in different power arrangements of an ARM laser. In this study, the process status was evaluated based on the area of keyhole entrance and the width of the pool. The geometric characteristics of the topside weld were measured by a confocal sensor. The shape of the fusion zone was analyzed based on its cross section. The process mechanism of a different mode of ARM laser welding was investigated by analyzing the process status and geometric characteristics of the surface bead. Experimental results showed that dual-mode laser welding could stabilize the keyhole entrance with a uniform weld surface formation in comparison to the pure ring-mode laser weld. The dual-mode laser also generated a wider molten pool with a wider fusion zone than the pure center laser weld.