Andrzej S. Juszczyk

In vitro assessment of image-guided otologic surgery: Submillimeter accuracy within the region of the temporal bone

OBJECTIVES: Application of image-guided surgery to otology has been limited by the need for sub-millimeter accuracy via a fiducial system that is easily usable (noninvasive and nonobstructive). METHODS: A dental bite-block was fitted with a rigid frame with 7 fiducial markers surrounding each external ear. The temporal bones of 3 cadaveric skulls were removed and replaced with surgical targets arranged in a bulls-eye pattern about the centroid of each temporal bone. The surgical targets were identified both within CT scans and in physical space using an infrared optical tracking system. The difference between positions in CT space versus physical space was calculated as target registration error. RESULTS: A total of 234 independent target registration errors were calculated. Mean ± standard deviation = 0.73 mm ± 0.25 mm. CONCLUSIONS: These findings show that image-guided otologic surgery with submillimeter accuracy is achievable with a minimally invasive fiducial frame. SIGNIFICANCE: In vivo validation of the system is ongoing. With such validation, this system may facilitate clinically applicable image-guided otologic surgery. EBM rating: A.

Long-term dimensional stability and reproduction of surface detail of four polyvinyl siloxane duplicating materials

OBJECTIVES Duplicating materials must routinely accurately reproduce the details of dental casts and thus contribute significantly to the close adaptation and success of a removable prosthesis or fixed indirect restoration. It is important to establish the long-term dimensional stability of polyvinyl siloxane materials (PVS) as they are widely used in dental technology and over the duration of a course of treatment, are stored under dental laboratory conditions. The dimensional stability of four PVS duplicating materials was investigated over a 13-week period. MATERIALS AND METHODS Forty PVS duplicate moulds of a partially dentate maxillary arch were produced from four materials (Elite double 8, Gemini transparent, C & J pourable silicone and Z Dupe). Three dimensions were measured in triplicate at baseline 1, 5, 9 and 13 weeks using computerised image analysis. Half of the specimens were measured following storage at room temperature (21+/-2 degrees C) and half at 37 degrees C to represent storage in hot climates. Specimens for scanning electron microscopy were prepared by duplicating a rugosity standard. RESULTS At room temperature two materials Elite Double 8 and Z Dupe showed no statistically significant dimensional change, the other two materials showed a slight increase of dimensions. Specimens stored at 37 degrees C showed greater differences in dimensions with Z Dupe showing statistically significant shrinkage. SEM investigation showed no surface deterioration of two materials. CONCLUSIONS None of the materials showed a change in dimension greater than 2% and the four PVS materials showed good dimensional stability over the time period of the study.

Investigation of retentive force reduction and wear of the locator attachment system with different implant angulations.

PURPOSE To evaluate the effect of cyclic disengagement on the retentive force and wear patterns of pairs of three Locator inserts (blue, pink, and clear) in vitro. MATERIALS AND METHODS Implant analogs (Astra Tech) were positioned into aluminum blocks parallel to each other and perpendicular to the horizontal plane, with one analog angulated mesially by 10 degrees (0/10), or with two implant analogs each angulated mesially by 5 degrees (5/5). Ninety Locator attachments, in 15 pairs of each standard retention strength (blue, pink, and clear), underwent 2,500 cycles of testing, lubricated with artificial saliva. Data were analyzed after 6, 12, and 18 months of simulated clinical use (720, 1,440, or 2,160 cycles). The wear patterns of the Locator inserts were examined before and after the cyclic dislodgments using scanning electron microscopy. RESULTS There were significant differences in retentive force between clear, blue, and pink inserts at baseline, with the clear insert being the most retentive in the 0/10 model. The lowest percentage reduction in retentive force from baseline to 2,160 cycles was the pink insert in the 0/10 model, and the highest was the blue insert in the 5/5 angled model. CONCLUSION A rapid decrease in retentive force was observed in all three models after 720 cycles for all three inserts. The most retentive combination was the clear insert in the 0/10 model, and the least retentive was the blue insert in the 0/10 model. After 2,160 cycles, there was a significant reduction in retentive force of 59% to 70%. However, the values of retention were still higher than those claimed by the manufacturer.

Sensitivity of a disc rupture strength test to air bubble pores in phosphate-bonded investment materials at elevated temperatures

OBJECTIVES To investigate the sensitivity of a modified disc rupture test to variables affecting the strength of four phosphate-bonded investment materials under conditions closely resembling the in-service environment. This study examined the influence of air bubble pores on the strength of phosphate bonded investment materials at a temperature of 900 degrees C. METHODS A modified disc rupture configuration was used to test a circular investment diaphragm with clamped edges, in tension, initiated by bending. A sequentially-varying molten metal mass was used to apply the load using an electronic centrifugal casting machine. The staircase method was used to determine the increase or decrease of the applied load with the standardized increment of load being no greater than 1 or 2g. The mean load applied to 30 samples defined the transition of survival to failure of the investment disc and was taken as a measurement of investment strength. Two material handling techniques, one giving virtually no pores and one showing a wide pore size distribution were used. RESULTS The diaphragm clearly either failed or survived the test with the pattern of fracture indicating brittle failure. A statistically significant difference in strength (P<0.050) of diaphragms with and without air bubble pores was demonstrated for three materials. Fewer pores resulted in increased strength of those materials and produced a much reduced scatter of strength in the fourth. SIGNIFICANCE The modified disc rupture test is sufficiently sensitive to identify variations in strength of phosphate bonded investment materials caused by differing pore size distributions.