Fatigue strength of a Au-Pd alloy/585 solder combination.

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.

Effect of ultrasonic ZnPO-4 cement removal on band adhesion and cement solubility under orthodontic bands.

The use of ultrasonic energy to remove excess ZnPO-4 cement from orthodontic bands reduces the solubility of the cement but does not affect band adhesion unless excessive band contact is made. Excessive band contact weakens band-to-tooth adhesion. The solubility of the cement is increased by decreasing the pH and is increased when organic anions capable of binding metal ions are present.

Torsional properties of stainless steel and nickel-titanium endodontic files.

The torsional properties of stainless steel (SS) endodontic files (Flex-O-File; Maillefer/L. D. Caulk Co., Milford, DE) and recently developed nickel-titanium (NiTi) endodontic files (Quality Dental Products, Inc., Johnson City, TN) were compared. File sizes 15, 25, 35, 45, and 55 were subjected to torsional load in clockwise (CW) and counterclockwise (CCW) directions independently. Results showed that SS files had a significantly greater rotation to failure in the CW direction, whereas the NiTi files had a significantly greater rotation to failure in the CCW direction. Despite these differences in rotation to fracture, there was essentially no difference between the SS and NiTi instruments in the torque that it took to cause failure in both the CW and the CCW directions. Therefore, whereas the number of CW and CCW rotations to failure differed for the two instruments, the actual force that it took to cause that failure was the same.

Intracanal isolating barriers as they relate to bleaching.

Four restorative materials were evaluated for effectiveness as intracanal isolating barriers to prevent leakage of bleaching agents into the coronal part of the root canal. Fifty-five teeth were stained in vitro, instrumented, and filled with gutta-percha. In the experimental groups, gutta-percha was removed 2 mm apical to the labial cementoenamel junction, and an intracanal isolating barrier (zinc oxide-eugenol, IRM, Ketac-Cem, or Scotchbond Multipurpose) was placed even with the facial and proximal cementoenamel junction areas in a sloped manner. All were bleached with a thermocatalytic and walking bleach technique until the crown was one shade lighter than the original shade. The roots were then examined for the occurrence of bleaching. The results indicate that none of the materials used was a totally effective intracanal isolating barrier. Although a significant difference was found when IRM was compared with Ketac-Cem or Scotchbond Multipurpose (p < 0.05), all restorative materials evaluated showed a high incidence of leakage as demonstrated by bleached roots. There was no significant difference between zinc oxide-eugenol and IRM.

A comparison of strains generated during placement of five endodontic posts.

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.

Torsional properties of the Canal Master instrument.

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.

Comparison of three core buildup materials used in conjunction with two post systems in endodontically treated anterior teeth.

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).

A comparison of curved canal instrumentation using nickel-titanium or stainless steel files with the balanced-force technique.

The Flex-R file was compared with the Onyx nickel-titanium file in respect to canal center movement and final canal area after balanced-force instrumentation. Forty-two root canals in extracted human molars were divided into two equal groups of 21, in all of which the angle of curvature ranged from 20 to 40 degrees. After mounting in a mold, each root was sectioned at two locations, providing an apical and a coronal section. Pre- and postinstrumentational 35-mm photographic slides of each section were superimposed, projected, traced, and then scanned into a computer. From these computerized pre- and postinstrumentation images, the movement of the canal center and the area of each canal were computed at both the apical and coronal sections. Results showed no significant difference in canal center movement or postinstrumentation area when Flex-R or Onyx files were used at the apical section. Coronally, the Flex-R files demonstrated more movement of the canal center. No significant correlation was found between the angle of root curvature and canal movement or the angle of root curvature and postinstrumentation canal area.

Comparison of stainless steel and nickel-titanium instruments in molar root canal preparation.

Forty mesial canals in extracted human molar teeth were embedded and sectioned at two root levels. Reassembled teeth were instrumented using a step-back technique with stainless steel (SS) or nickel-titanium (NT) K-type files. Superimposed pre- and postinstrumented cross-sectional root images were projected, traced, and scanned into a computer for analysis. The amount and direction of canal center movement, canal area change, and final canal shape were recorded. The results showed no significant difference in canal center movement or canal area change between the SS and NT groups. All canal centers deviated toward the furcation region at the height of curvature and in the opposite direction in apical sections. The degree of canal curvature had no correlation to canal center movement or canal area change. Fifty-three percent of SS and 68% of NT instrument preparations were classified as oval.

A comparison of curved canal transportation with balanced force versus lightspeed.

The Flex-R file was compared with the Lightspeed nickel-titanium file in respect to canal center movement and final canal area after instrumentation. Thirty-eight root canals in extracted human molars were divided into two equal groups of 19, in all of which the angle of curvature ranged from 20 to 35 degrees. After mounting in a mold, each root was sectioned at two locations, providing an apical and coronal section. Pre- and postinstrumentation 35 mm photographic slides of each section were projected, traced, and then scanned into a computer. From these computerized pre- and postinstrumentation images, the movement of the canal center and the area of each canal were computed at both the apical and coronal sections. Results showed significant difference in the apical canal center movement and postinstrumentation area with the Lightspeed yielding smaller values in both cases. Coronally, the Flex-R Lightspeed instruments demonstrated no significant difference in canal movement or postinstrumentation area. No significant correlation was found between the angle of root curvature and canal movement or the angle of root curvature and postinstrumentation canal area.

A comparison of instrumentation using Naviflex and Profile nickel-titanium engine-driven rotary instruments.

This study was designed to compare the changes in canal configuration resulting from instrumentation by either Profile or Naviflex instruments. Forty mesial canals in extracted human molar teeth were embedded and sectioned at two root levels. Reassembled teeth were instrumented with a modified crown-down technique as described in the Profile training video for Profile files and in a similar manner for Naviflex instruments. Superimposed pre- and postinstrumented cross-sectional root images were projected, traced, and scanned into a computer for analysis. Canal movement, in relation to the furca, and canal area change were recorded. The results showed no significant difference in canal center movement or canal area change between the Profile or Naviflex groups. The degree of canal curvature had no effect on canal center movement or canal area change.

Evaluation of fiber-composite laminate in the restoration of immature, nonvital maxillary central incisors.

The purpose of this study was to evaluate the use of fiber-composite laminate, a reinforcement ribbon embedded throughout a composite restoration, to reinforce immature maxillary central incisors. Twenty-six mature maxillary central incisors were prepared a minimum of 3 mm below the facial cementoenamel junction to simulate immature nonvital teeth. They were separated into 3 groups: group 1 was unfilled and served as a control; group 2 was filled to the depth of the preparation with composite; and group 3 was filled with composite and Connect Reinforcement Ribbon. The specimens were subjected to class I loading in an Instron Testing Machine until catastrophic failure occurred. The results indicate a highly significant difference between the groups (p < or = 0.003). Group 1 fractured at an average load of 31.08 kg, group 2 at 51.00 kg, and group 3 at 37.93 kg. These findings suggest that composite alone increases fracture resistance of the immature tooth model more than composite with Reinforcement Ribbon.

Torsional properties of twisted and machined endodontic files.

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.

Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems.

Thirty-six maxillary central incisors were endodontically treated and restored with a post and core and cast crown. Three different post and core systems were evaluated. Restored teeth were fatigue-loaded until preliminary failure of the casting occurred as detected by a strain gauge bonded across the lingual margin of the cast crown. After preliminary failure, fatigue loading was continued for 100,000 load cycles with the crown margin exposed to basic fuschin dye. Teeth were then immersed in dye for 24 h, sectioned, and evaluated for leakage. There was no significant difference in the number of load cycles required to cause preliminary failure among the three post and core systems. Leakage occurred in all three groups, with no significant difference between groups. The occurrence of preliminary failure is clinically undetectable, yet it allows leakage between the restoration and tooth that may extend down the prepared post space.

Implant-abutment screw joint preload of 7 hex-top abutment systems.

This study measured the screw joint preload of the implant-abutment interface for 7 common hex-top abutment systems. Increasingly, prosthetic designs are utilizing a direct prosthetic connection to the implant, placing the implant-abutment screw joint under direct functional loads and moments. Sufficiently high screw joint preloads are required to maintain screw joint integrity and confer clinical longevity to implant prosthetic components to prevent such complications as abutment screw loosening and screw fracture. Strain-gauged abutment load cells were calibrated to measure screw joint pre-load at the implant-abutment interface. Torque delivery by electronic torque controller was varied at low- and high-speed settings. At manufacturer's recommended torques, the overall mean preload measured was 181.6 +/- 60.0 N for the Nobel Biocare Standard abutment, 291.3 +/- 41.2 N for the Nobel Biocare EsthetiCone abutment, 456.5 +/- 44.0 N for the Nobel Biocare MirusCone abutment, 369.7 +/- 32.9 N for the 3i Titanium Abutment post, 643.4 +/- 143.1 N for the Nobel Biocare CeraOne abutment, 536.3 +/- 68.6 N for the Nobel Biocare "Gold Cylinder to Fixture" abutment, and 556.9 +/- 145.6 N for the Nobel Biocare TiAdapt abutment. Analysis of variance revealed significant differences between abutment systems (P < .001) and between torque driver speed settings (P < .001). Implant-abutment screw joint preload of external-hex implants is dependent on abutment design, screw diameter, material, tightening torque, and torque controller speed.

Tolerance measurements of various implant components.

Machining tolerance, an intrinsic characteristic that exists between machined implant components, identifies the amount of horizontal shift possible between paired components. Machining tolerances between implant components (abutment, gold, cylinder, impression coping, and brass abutment replicas) were measured with a coordinate measuring machine. The measured tolerances ranged from 22 to 100 microns. Machining tolerances between implant components should be included in future studies of accuracy, because it is an inherent characteristic of the component itself.

Load fatigue performance of two implant-abutment combinations.

The load fatigue performance of the CeraOne and EsthetiCone implant systems was investigated. Three torques (standard torque, standard torque + 20%, and standard torque -20%) were used to tighten the screws. A rotating-beam fatigue model was used. A 70-N load was applied to the specimens at a 30-degree angle to the long axis. Two-way analysis of variance revealed (1) no statistically significant difference between the three torques for each system, and (2) a statistically significant difference between the implant systems. Implant failure occurred in 10 of 15 CeraOne specimens. In the EsthetiCone system, only abutment screw failure occurred.

Accuracy of electronic implant torque controllers following time in clinical service.

Tightening of the screws in implant-supported restorations has been reported to be problematic, in that if the applied torque is too low, screw loosening occurs. If the torque is too high, then screw fracture can take place. Thus, accuracy of the torque driver is of the utmost importance. This study evaluated 4 new electronic torque drivers (controls) and 10 test electronic torque drivers, which had been in clinical service for a minimum of 5 years. Torque values of the test drivers were measured and were compared with the control values using a 1-way analysis of variance. Torque delivery accuracy was measured using a technique that simulated the clinical situation. In vivo, the torque driver turns the screw until the selected tightening torque is reached. In this laboratory experiment, an implant, along with an attached abutment and abutment gold screw, was held firmly in a Tohnichi torque gauge. Calibration accuracy for the Tohnichi is +/- 3% of the scale value. During torque measurement, the gold screw turned a minimum of 180 degrees before contact was made between the screw and abutment. Three torque values (10, 20, and 32 N-cm) were evaluated, at both high- and low-speed settings. The recorded torque measurements indicated that the 10 test electronic torque drivers maintained a torque delivery accuracy equivalent to the 4 new (unused) units. Judging from the torque output values obtained from the 10 test units, the clinical use of the electronic torque driver suggests that accuracy did not change significantly over the 5-year period of clinical service.

Fatigue resistance of soldered joints: a methodological study.

OBJECTIVES: In this investigation, the fatigue resistance of solder joints under cyclic loading was evaluated. METHODS: Au-Pd alloy rods were machined, prepared for soldering and joined using 735 solder. After trueing and polishing the joints, the S-N diagram (cycles to failure vs. applied stress) was generated. A conventional endurance limit (SN) was determined for 10(6) load cycles. Testing was carried out in a machine specifically designed to apply flexural fatigue loading to cantilevered test specimens. These were rotated around their main axes, and the device applied a sinusoidal, reverse-bending stress to the solder joints. The applied stress ranged from 300 MPa to 75 MPa in decrements of 25 MPa. Twelve specimens were cycled for each stress level until fracture occurred or 10(6) cycles were sustained (run-outs). In this first series of tests, the cycling speed corresponded to an average chewing rate, i.e., 1 Hz (60 rpm). In order to reduce the time required for testing, the cycling speed was then increased to 5, 10 and 15 Hz (300, 600 and 900 rpm). RESULTS: At 1 Hz, SN was 133.0 MPa, while at the higher cycling speeds, SN increased to 139.3, 160.8 and 175.8 MPa. SIGNIFICANCE: It was concluded that rotational fatigue tests as applied in this study were a feasible fatigue testing procedure. However, SN's gathered at faster rates might need correction factors if relationships with data pertaining to clinically relevant chewing rates are to be established.

Polymerization shrinkage of densely-filled resin composites.

A new group of restorative materials called "packable" composites has recently been introduced. These products are essentially highly-filled or densely-filled hybrid resin composites. One of the many claims made about these materials is that they undergo less polymerization shrinkage than their conventional counterparts. This in vitro investigation compared the amount of linear shrinkage that occurs within a variety of densely filled resin composites (DFC) and conventional hybrid resin composites when cured with a visible halogen light. Six DFC resins (Alert, Ariston, P60, Prodigy, Solitaire and Surefil) and two hybrids (TPH-Spectrum, Z100) were used in this study. Dimensional change was measured in a linear direction using a calibrated light microscope. Eighty samples of resin composite were tested, resulting in eight groups of 10 samples (N=10) each. The one-way ANOVA with Student-Newman-Keuls post-hoc test was used to compare the shrinkage between groups, and Pearson's Correlation was used to test the relationship between filler characteristics and shrinkage. Alert and P-60 had significantly less shrinkage than Solitaire, Ariston, Prodigy, Z-100 and TPH-S. Thus, the shrinkage values of some DFC resins were significantly less and others were no different from conventional hybrid resins. There is a moderate association between filler volume and shrinkage. Filler size and resin chemistry are other factors that may also effect shrinkage.