Biomedical subjects
Publications and source records attributed to J I Nicholls.
This study compared heat-cured acrylic resin denture baseplate distortions following a second heat cure used to add the denture teeth. The second heat cure was done with three different water-bath curing temperatures. The distortions were evaluated in three planes by use of a measuring microscope. Recorded distortions were not clinically significant.
The torsional properties of a new type of endodontic hand instrument, the Canal Master, were compared with conventional machined K-type endodontic files. Sizes 20 through 50 were tested in clockwise (CW) and counterclockwise (CCW) directions. Canal Master instruments exhibited significantly less torque at yield and at failure in both the CW and CCW directions. Rotation at failure was significantly greater for the Canal Master instruments in both CW and CCW directions. There was no significant difference in either torque or the amount of rotation for the Canal Master instruments when comparing CW versus CCW rotation. There was no clinically visible evidence of deformation of the Canal Master instruments prior to torsional failure.
A three-surface MOD preparation measuring one third of the isthmus cavity distance at the isthmus was prepared for five extracted, intact human maxillary premolar teeth. The teeth were restored with a posterior resin and a dentin bonding agent. Each tooth was tested under a cyclically varying load in a fatigue machine made at the University of Washington. The cyclic load rate was 75 cycles per minute. A strain gauge was applied to the buccal surface of each tooth. Under the load applied at an angle of 60 degrees to the long axis of the tooth, reinforcement of the tooth was established by the reduced deflection of the buccal surface of the restored tooth as compared with the unrestored tooth. The loss of this reinforcement due to the application of the cyclically varying load established the end point of the fatigue testing. Four different load values of 13, 16, 19, and 22 lb loads were applied separately to each tooth. The results of this testing were classic wherein the smallest load required the greatest number of load cycles before loss of adhesion was registered by the strain gauge. Failure always occurred within the adhesive joint.
Inlay-onlay composite resin restorations have been introduced to the profession as alternatives to amalgam and direct composite resins. Two-body wear testing was performed on three inlay-onlay resins and one direct composite resins using a machine designed to produce sliding wear. The composite resins were opposed by human enamel, type III gold alloy, and porcelain. Of the investigated materials, the homogeneously microfilled inlay-onlay material showed significantly less wear. The direct composite resin showed significantly the greatest wear. The hybrid inlay-onlay resins showed intermediate wear. The hybrid inlay-onlay resins and the direct composite (small particle, heavily filled) resin created wear tracks in the opposing surfaces while the homogeneous microfill inlay-onlay resin did not. The depth of the observed wear tracks in the opposing surface was sufficiently substantial to warrant further investigation into the wear of materials that oppose composite resin restorations.
New retentive mechanisms between veneering resins and casting alloys are claimed to have a chemical bond that results in a high bond strength combined with low microleakage between the veneering resin and cast restoration. This study compared the microleakage of four chemical bonding mechanisms when three veneering resins were bonded to two dental casting alloys. Resin-veneered alloy disks were immersed in red India ink and kept at 37 degrees C for 72 hours. The disks were then bench dried for 24 hours. The resin veneer was sectioned into eight sectors in an engineering milling machine and these resin sectors were removed to display the microleakage pattern. It was concluded that (1) no microleakage was found in two combinations, and (2) the highest microleakage was with Sr-Isosit-N/Panavia EX/Firmilay combinations.
Twenty-five extracted human maxillary central incisors were randomly divided into five equal groups. Crowns were removed 1 mm incisal to the cementoenamel junction. Endodontic treatment was carried out and each tooth was affixed with two strain gauges. The strain gauge wires were connected to a Wheatstone Bridge circuit. Each group of five teeth was restored with either a Para-Post Plus (the control post), Flexi-Post, Vlock post, Kurer Fin Lock Anchor, or a Radix Anchor. Strains generated during post placement were recorded and compared for the five groups using a one-way analysis of variance. The maximum strains accompanying placement of the Kurer Fin Lock Anchor and the Radix Anchor were significantly higher than those induced by placement of the other posts. Also, when the threaded posts were allowed to contact the bottom of the prepared channel, high strains resulted.
The S-N diagram (applied stress vs. cycles to failure) for the gold-palladium alloy/585 solder combination was generated. Au-Pd alloy specimens were cast, prepared for soldering, and joined with 585 solder. After milling and polishing of the joint, testing was carried out in a specially designed machine. This device loaded the cantilevered test specimen in a unidirectional mode at a rate of 70 strokes per minute. The applied tensile stress ranged between 294.2 and 686.5 MPa. Three specimens were cycled for each stress level until fracture occurred. The number of fatigue cycles to failure ranged from one cycle (stress level, 686.5 MPa) to 4.83 x 10(6) cycles (stress level, 294.2 MPa). On a logarithmic scale, the relationship between the applied stress and the number of cycles to failure was linear. Under the present (ideal) experimental conditions, the Au-Pd/585 solder combination behaved favorably on the high-cycle end of the diagram. However, no definite endurance limit could be detected within the stress range examined.
A passive fit between osseointegrated implants and the prosthesis they will support has been advocated. An experimental model was developed to test the accuracy of three impression techniques and the components used to make the transfer records. Statistically, no significant difference was found between the three methods tested. From this initial study, it appears that further work is needed to isolate techniques that will predictably provide accurate registration of the position of endosseous implants.
The torsional properties of conventionally twisted K-type endodontic files and recently developed machined K-type endodontic files were compared. File sizes 10 through 40 were subjected to torsional load in clockwise and counterclockwise directions independently. Results showed that a statistically significant reduction in clockwise rotation occurred at failure with all of the machined files except size 10. Counterclockwise rotation at failure was also significantly lower for the machined files in sizes 10 through 30. There was no difference in torsional strength between the file types regardless of rotation direction. Therefore, machined files exhibit less ductility than twisted files prior to fracture and may be more susceptible to torsional failure clinically.
The Triad light-cured resin system appears to have potential for making processed record bases for special patients. The close adaptation of this material to the dental cast often results in internal voids and defects. These defects are greatly reduced when a dry cast is used instead of one with a high moisture content. Vacuum-assisted adaptation using a sheet of rubber dam in connection with a vacuum adaptor also results in an improved internal surface. Finger pressure alone is not a dependable method of adaptation.
Fifty extracted maxillary central incisors with the crowns removed 1 mm coronal to the labial cementoenamel junction were endodontically treated. Post spaces were made 7 mm into the roots prior to cementing a 13-mm post with zinc phosphate cement. Twenty-five of the teeth were restored using a #6 (0.060-inch) Para-Post, and the remaining 25 teeth were restored with a #6 Para-Post Plus. Three core buildup materials, Ketac-Silver, Miracle Mix, and Tytin alloy were used in conjunction with the posts. Cast gold copings 10 mm in height with 1 mm collar on the root were cemented to the buildups. The teeth were loaded to failure at 130 degrees to the long axis of the root from the lingual with an Instron testing machine. The mean failure load of all of the teeth in this study was 21.6 kg. All of the teeth failed when the posts dislodged from the canals. The Para-Post Plus was not significantly more retentive than the Para-Post. No failures occurred within the buildup materials. No significant differences were demonstrated between the mean failure loads of the different buildup materials. Increased buccolingual root diameter, however, had a positive correlation (r = 0.46) with higher failure loads which was statistically significant (p less than 0.001).
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
An in vitro study of 45 teeth compared the failure loads of endodontically treated teeth restored with pin and amalgams, Para-Post dowel and composite, and glass ionomer/amalgam alloy coronal-radicular buildups. The following conclusions were made. The Para-Post and composite buildups exhibited the highest mean failure load, 35.3 kg. The mean failure load for pin and amalgam buildups was 27.9 kg. Glass ionomer/amalgam alloy coronal-radicular buildups exhibited the lowest mean failure load, 14.1 kg. Restoration of endodontically treated anterior teeth with glass ionomer/amalgam alloy coronal-radicular buildups is contraindicated.