A range scanner is developed that can scan a gypsum dental cast and reconstruct the cast digitally for display and storage purposes. The scanner is based on subtractive light and computes the range values using optical triangulation. A fiducial marker is introduced that, when attached to a dental cast at the time of image acquisition, makes it possible to integrate multiview range images of the cast without image registration. A method for calibrating the scanner is described and experimental results showing the accuracy of the scanner are presented.

ASTM standard F1798-97 provides guidelines for evaluating the strength of interconnection mechanisms used in pedicle screws and hooks. A literature search indicates the following as common significant clinical complications: fractured pedicle screws; fractured rods; disconnection between the rods, bolts, nuts and screws; screw loosening; loss of correction; inaccurate screw placement; broken pedicles; dural leaks; infection; transient and permanent neural injury. The tests outlined in ASTM standard F1798-97 may correspond to disconnection between the rods and screws or loss of correction. The standard does not correspond to any other known causes of the common complications. Therefore, interconnection strength tests may not have any bearing on the clinical outcomes of patients since there is no direct evidence that they sufficiently test for relevant device failures.

Interbody cages are successfully used clinically to support the spine's anterior column to facilitate fusion of the motion segment. A standard, “Static Push-Out Test Method for Intervertebral Body Fusion Devices,” is under consideration by ASTM. The objective of this testing was to determine the loads required to extract interbody fusion cages from a simulated spinal motion segment (Grade 20 polyurethane foam model). The results obtained using the foam model were compared to results done using intact cadaver spinal motion segments (thoracic and lumbar). These data are contrasted with incidences of cage expulsion mentioned in the literature. Testing revealed a difference in the expulsion strength between the foam and cadaveric models. Differences between the 13 × 20 mm and the 9 × 20 mm cages were also found. The literature search revealed that posteriorly implanted cages may retropulse into the spinal canal due inadequate annular tension, undersized cages, and destabilization from laminectomy and partial facetectomy. The danger of retropulsion may be alleviated by the addition of posterior instrumentation (rods and screws). Standardized testing is a valuable tool in differentiating among designs but does not represent clinical failures.