PubMed · 4502136
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K Schmidt-Diemel. 1972-03-25. [Working with individually adjustable articulators].. https://pubmed.ncbi.nlm.nih.gov/4502136/
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OBJECTIVE: To design, fabricate, and perform preliminary in vitro testing of a portable, hand-held, three-dimensional (3D) dental X-ray system using options unique to Tuned-Aperture Computed Tomography (TACT). The design allows for task-specific positioning over an unlimited range of user-selected angles and incorporates an integrated laser guidance system to constrain the focal-object distance. METHODS: A prototype system was fabricated consisting of an extremely lightweight X-ray source cantilevered from an aluminum gunstock-type handle to which a transparent radiation scatter shield was attached. Aiming was facilitated by task-specific visual cues used in conjunction with a spherically shaped radiolucent alignment jig coupled to the tissues of interest. Proper range was assured by a laser-assisted guidance system. The image transducer was an extrinsically modified commercially available CMOS device. The irradiated patient was simulated by a DXTTR phantom. RESULTS: The prototype demonstrated automated display of radiographed intra-oral tissues in three dimensions from arbitrary projection geometries and simulated task-specific sequences. Uncontrolled movements between exposures produced no obvious degeneration of 3D image quality. The aiming system minimized technical errors from misangulation. All dental regions in the phantom were imaged without difficulty. Projected risk was observed to be within clinically acceptable limits. CONCLUSIONS: Task-specific 3D images can be generated from as few as three uncontrolled projections. Total exposures can be prorated to levels not greatly exceeding those required for conventional two-dimensional radiographs of comparable image quality. Predicted radiation risks lie well below existing guidelines for occupational exposure.
AIM: This study was carried out to investigate the reasons for fracture of a new rubber-dam clamp used for the first time. SUMMARY: The fractured surfaces of the broken clamp were studied with optical microscopy. Characteristic surface patterns of tensile fracture were identified. Cracks originated from the groove of letter D mechanically engraved on the inner surface of the clamp bow, and developed with high velocity (unstable crack growth rate) leading to catastrophic fracture. This behaviour was attributed to the residual stresses introduced by the labelling technique due to local thermal alterations. KEY LEARNING POINTS: The labelling technique used to number clamps may be implicated with catastrophic failure. Dentists should be aware that even new clamps can fracture. It is important that clamps are secured to prevent inhalation of metal fragments, should catastrophic failure occur.