The influence of stiffness of implant-abutment connection on load-deflection ratios of a screw-retained stiff cantilever beam. 3-D measurements in vitro.

AIM: The purpose of this in vitro study was to investigate the influence of degree of stiffness of implant-abutment connection of a Brånemark implant system on load- deflection ratios in three dimensions of the beam-end of a screw-retained stiff cantilever beam when subjected to vertically directed loads. MATERIAL AND METHODS: Two different implant-abutment connections were tested; welded and screw-retained. One of the abutments (EsthetiCone 2.0; Nobel Biocare AB) was screwed with a torque force of 20 N cm and then laser welded around its entire periphery to one of two Brånemark implants (welded unit). This unit and the other implant were tightly screwed into each of two pre-threaded holes in a steel plate so that the implants became submerged in the plate. The remaining abutment was thereafter screwed to its implant with a torque force of 20 N cm (screw-retained unit). A cantilevered gold beam of 6 mm height and width comprising a gold cylinder (Nobel Biocare AB) was attached to each abutment with a slotted, flat headed, prosthetic gold screw (torque force 10 N cm). A force transducer, synchronized with a 3-D motion analysis system, was glued on the upper surface of each beam-end 19.4 mm from the implant, to register the loads transferred from a specially built loading device. The beam-ends were stepwise subjected to vertically directed loads from 14.9 to 40.3 N and the vertical and horizontal deflections of the beam-ends were registered with the 3-D motion analysis system. RESULTS: For load 14.9-40.3 N the vertical (z-axis) deflections of the beam-end were for the welded implant-abutment connection reduced with 18-46% compared with the screw-retained unit. After maximal loading (40.3 N) the horizontal counter-clockwise rotation of the beam around the screw joints (y-axis rotations) was reduced with 61% for the welded connection. The horizontal movements of the beam-end along the x-axis (x-axis deflections) were reduced with 49% at maximal loading. CONCLUSION: It was concluded that increased implant-abutment stiffness will substantially reduce both vertical and horizontal deflections of a screw-retained stiff cantilever beam subjected to vertically directed loads.

Deflections of an implant-supported cantilever beam subjected to vertically directed loads: in vitro measurements in three dimensions using an optoelectronic method. I. Experimental set-up.

AIM: The aim of this in vitro study was to develop and test an experimental set-up consisting of a video camera and computer-based optoelectronic motion analysis system, synchronized with a loading device, for studying load-dependent deflections in three dimensions of single implant-supported cantilever beams. MATERIAL AND METHODS: One Brånemark System implant was tightly screwed into a steel plate so that the entire implant became submerged. An abutment was attached to the implant and a cast 22-mm-long cantilever gold alloy beam incorporating a prefabricated gold cylinder was attached to the abutment with a prosthetic gold screw. A force transducer was glued on the upper surface of the beam end with its centre 19.4 mm from the centre of the implant abutment gold cylinder unit to register the applied load. A specially designed loading device was used to apply increasing vertical loads of the beam end via the transducer. The motion analysis system was synchronized with the transducer to enable measurements of three-dimensional positional changes of the beam end related to known loads. RESULTS: Vertical loads from 15.7 to 40.4 N were applied resulting in vertical positional changes of the beam end ranging from 40.8 to 225.2 µm (z-axis). The corresponding horizontal changes perpendicular to the long axis of the beam (y-axis) due to counterclockwise horizontal rotation of the beam around the abutment- and prosthetic cylinder threads varied from 7.4 to 77.4 µm. This rotation changed the position of the beam end from 11.9 to 49.3 µm along the x-axis of the coordinate system toward the supporting implant. CONCLUSION: It was possible to arrange an experimental set-up for optoelectronic 3-D measurements within such a limited measurement volume that would permit satisfactory registrations of small load-dependent deflections of the prosthetic beam and implant components.

The relative skin movement of the foot: a 2-D roentgen photogrammetry study.

OBJECTIVE: This paper describes a validation of the relative motions of skin-mounted markers on the foot. DESIGN: The movement of a skin-mounted marker on the foot was evaluated by the use of 2-D roentgen photogrammetry. BACKGROUND: Validations of skin-mounted markers are needed in order to assess whether clinical use of motion analysis systems is accurate. METHODS: Six healthy volunteers participated in the study. Measurements were made with 2-D roentgen photogrammetry from the medial aspect of the foot. Spherical lead markers, with a diameter of 2 mm, were glued on the skin over the following landmarks: the medial malleolus, the navicular bone, the medial part of calcaneus, the base and the head of the first metatarsal bone, and the base of the fifth metatarsal bone. The foot was placed on a platform that was adjustable in three directions: horizontal, 20 degrees upward (towards dorsal flexion), and 30 degrees downward (towards plantar flexion). RESULTS: In relation to the underlying bones, the markers were found to move up to 4.3 mm. The markers with the largest movements were the ones over the medial malleolus, the navicular bone and the calcaneus. For the distally placed markers i.e. at the base and the head of the first metatarsal bone, and the base of the fifth metatarsal bone, the displacements were a maximum 1.8 mm. CONCLUSIONS: Markers mounted on the foot moved between 1.8 and 4.3 mm corresponding to the underlying bones. The most proximal attached markers demonstrated the largest movements.

A method to determine joint moments and force distributions in the shoulders during ceiling work -- a study on house painters.

OBJECTIVE: The purpose of this study was to propose and apply a method to study the net load and the force distribution in the shoulder during sanding of a ceiling. DESIGN: Sanding of a ceiling was studied in an experimental set-up. BACKGROUND: Among painters there is a high frequency of neck and shoulder complaints and some particularly strenuous tasks are sanding and painting of ceilings with tools attached to extension handles. METHODS: A biomechanical model predicted the load pattern in the shoulder from measured external forces and body postures. Measurements were made on 40 subjects by means of a force plate, an extension handle supplied with two pairs of strain gauges and a load cell, and a 3D optoelectronic measurement system. RESULTS: Work techniques may seem to be similar at visual inspection, but nevertheless produce quite different loading patterns in the shoulder. The observed work techniques varied largely among the subjects but the intra-individual variability was rather small. CONCLUSIONS: The study showed that the proposed method can be used to evaluate loads and force distribution in the shoulder. Since the method involves the use of a biomechanical model that can scarcely be validated, results must be interpreted cautiously.