PubMed · 14245331
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
M C LASKY. 1965. SEMIFIXED BRIDGEWORK.. https://doi.org/10.14219/jada.archive.1965.0257
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
STATEMENT OF PROBLEM: No study has evaluated the efficacy of auxiliary tooth preparation elements for crowns with originally reduced resistance form. PURPOSE: This study evaluated the effects of different auxiliary preparation features on the resistance form of crowns with reduced axial wall and total occlusal convergence. MATERIAL AND METHODS: An Ivorine tooth was prepared on a milling machine with 20-degree total occlusal convergence (TOC), 2.5 mm of occlusocervical dimension, and a shoulder finish line. This design lacked geometric resistance form. The crown preparation was subsequently modified to include mesiodistal grooves, mesiodistal boxes, buccolingual grooves, occlusal inclined planes, an occlusal isthmus, and reduced TOC in the axial wall from 20 to 8 degrees TOC in the cervical 1.5 mm of the axial wall. The grooves and boxes were placed into the tooth with the same 20-degree TOC as the initial axial walls. Ten standardized metal dies were used for each preparation design. Standardized complete metal crowns were fabricated for all specimens. The metal crowns were cemented on metal dies with resin-modified glass ionomer cement. A strain gauge was placed at the mid-lingual cervical area of each crown preparation margin. The resistance of each specimen was evaluated when force was applied at a 45-degree angulation to the long axis of the die in a lingual to buccal direction. The peak loads during crown dislodgment, as well as the tensile stress at the mid-lingual cervical area, were measured using a universal testing machine (Kgs) for each specimen. The control group consisted of 10 dies, with the original crown preparation having no geometric resistance form and no auxiliary preparation features. Strain gauges provided the force (Kgs) that resulted in electric currency disrupt at the crown/die interface, thus providing data regarding the force required for slight crown micromovement (2 microm). Data between control and experimental groups were compared using the Mann-Whitney U test (alpha=.05). RESULTS: Proximal grooves, proximal boxes, buccolingual grooves, occlusal inclined planes, and occlusal isthmuses were not effective at increasing a crown's resistance to dislodgement when the tooth preparation lacked resistance. The only crown modification that offered enhanced resistance form when compared with the control group was the reduced TOC in the cervical half of the axial wall. CONCLUSION: Within the limitations of this in vitro study the crown preparation modification that significantly enhanced the resistance form of a compromised tooth preparation was reducing the TOC at the cervical aspect of the axial wall. Placing auxiliary retentive features such as grooves and boxes into a compromised tooth preparation (2.5 mm occlusocervical dimension and 20-degree TOC) was not effective when these retentive features possessed the same 20-degree TOC as the prepared axial walls.
Explore the source record for details and available documents.
The rehabilitation program adopted immediately after a cementless total hip replacement is a very important factor, because of the known relationship between osseointegration and implant micromotion. The present study was aimed to evaluate which type of task is the most critical in terms of bone-implant relative micromotion. Both inter-task and inter-subject variability were taken into account to verify if the movement strategy could be determinant on this assessment. A previously validated finite element model was used to predict the peak total micromovements over the entire bone-implant contact surface in four different patients, performing nine different tasks, using published data on joint forces recorded by instrumented hip prostheses. The results predicted by the various simulations suggest that while stair climbing is surely a critical task for primary stability, for some subjects other tasks may be as critical as stair climbing. From a variance analysis for simple crossover design on the predicted peak micromotion, the inter-subject variability had much more influence on the primary stability of cementless implant than the inter-task variability. Even if the results of Patient IBL, who was reported to have difficulties to perform any activities in a normal way, were excluded from the statistical analysis, the inter-subject variability remained still higher than the inter-task variability. The results obtained from simulations suggest that the strategy the hip replacement patient adopts to perform a given motor task, may be, for the implant stability, equally or even more critical than the type of motor task performed.