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J I Nicholls
Quintessence international 05/2001; 32(4):338-9. · 0.76 Impact Factor
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J I Nicholls
Quintessence international 03/2001; 32(2):171-3. · 0.76 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 02/2001; 27(1):18-22. · 2.88 Impact Factor
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J I Nicholls
Quintessence international 11/2000; 31(9):688-9. · 0.76 Impact Factor
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ABSTRACT: Fracture is a clinical failure modality for ceramic veneers. Whether design of tooth preparation can affect the strength of ceramic veneers remains controversial.
This in vitro study evaluated fracture load and mode of failure of ceramic veneers, with 4 tooth preparation designs, that were bonded on extracted human maxillary central incisors. Identical parameters were also measured on unrestored intact teeth for comparison.
Fifty maxillary central incisors were randomly divided into 5 equal groups. Each group was assigned a different tooth preparation design: (1) no incisal reduction, (2) 2 mm incisal reduction without palatal chamfer (butt joint), (3) 1 mm incisal reduction and 1 mm height palatal chamfer, (4) 4 mm incisal reduction and 1 mm height palatal chamfer, and (5) unrestored (control). Forty teeth were prepared to accommodate ceramic veneers of equal thickness and incisocervical length. Stone dies were fabricated and veneers made from IPS Empress ceramic. Ceramic veneers were bonded and all teeth mounted in phenolic rings with epoxy resin. Fracture loads were recorded with a mechanical testing machine.
Mean fracture loads (SD) in kgf were as follows: group 1, 23.7 (6.11); group 2, 27.4 (9.63); group 3, 16.4 (3.44); group 4, 19.2 (6.18); and group 5, 31.0 (10.38). Modes of failure were also analyzed for both ceramic veneers and teeth. One-way ANOVA with multiple comparisons revealed 3 significant subsets: groups 1-2-5, groups 4-1, and groups 3-4 (P <.05). Groups 1 and 2 had no ceramic veneer fractures; group 3 had 3 ceramic veneer fractures, and group 4 had 6 ceramic veneer fractures.
Groups 1 and 2 recorded the greatest fracture loads that were comparable to an unrestored control.
Journal of Prosthetic Dentistry 02/2000; 83(2):171-80. · 1.32 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 07/1999; 25(6):457-60. · 2.88 Impact Factor
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J I Nicholls
Quintessence international 12/1998; 29(11):748-9. · 0.76 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 11/1998; 24(10):651-4. · 2.88 Impact Factor
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J I Nicholls
Quintessence international 06/1998; 29(5):336-7. · 0.76 Impact Factor
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ABSTRACT: The electric alloy brazed joints of removable partial denture alloys have failed frequently after routine usage.
A technique providing higher joint strengths was investigated. This investigation compared the tensile strengths of electric-brazed and laser-welded joints for a cobalt-chromium removable partial denture alloy.
Twenty-four cobalt-chromium standard tensile testing rods were prepared and divided into three groups of eight. All specimens in the control group (group 1) were left in the as-cast condition. Groups 2 and 3 were the test specimens, which were sectioned at the center of the rod. Eight specimens were joined by using electric brazing, and the remaining specimens were joined by using laser welding. After joining, each joint was ground to a uniform diameter, then tested to tensile failure on an Instron universal testing machine. Failure loads were recorded and fracture stress calculated. Statistical analysis was applied.
The student-Newman-Keuls test showed a highly significant difference between the joint strengths of the as-cast control specimens, the electric-brazed and laser-welded joints.
The tensile strengths of the as-cast joints were higher than those for the laser-welded joints, and both were higher than the electric-brazed joint strengths.
Journal of Prosthetic Dentistry 03/1998; 79(3):285-90. · 1.32 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 02/1998; 24(1):26-32. · 2.88 Impact Factor
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ABSTRACT: This in vitro investigation compared the amount of linear shrinkage that occurs when a light-cured composite resin is cured with a visible light source, and also with an argon laser.
When composite resins are light-cured, they undergo a certain degree of polymerization shrinkage, which can be clinically significant and affect the efficacy of the restoration. A new protocol utilizes laser curing instead of conventional visible light.
Two hybrid composite resins were used, Z100 and TPH-Spectrum. Dimensional change was measured in a linear direction, using a calibrated light-microscope. A total of 40 samples of composite resin was tested using two curing lights, and two hybrid composite resins, resulting in four groups of 10 samples (n = 10) each. According to manufacturer instructions, curing time for the laser was 10 sec, and for visible light was 40 sec.
With TPH-Spectrum, the mean shrinkage with visible light was 0.583% compared to that with laser light which was 0.591%. With Z100, the mean shrinkage with visible light was 0.565%, compared to that with laser light which was 0.551%.
There was no significant difference in amount of shrinkage of hybrid composite resins between using visible light or laser light. There was also no significant difference in shrinkage between the two hybrid composites for either light source.
Journal of Clinical Laser Medicine & Surgery 02/1997; 15(3):137-41.
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ABSTRACT: 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.
Journal of Endodontics 09/1996; 22(8):410-3. · 2.88 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 08/1996; 22(7):341-5. · 2.88 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 05/1996; 22(4):177-81. · 2.88 Impact Factor
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ABSTRACT: Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.
Journal of Prosthetic Dentistry 02/1996; 75(1):9-13. · 1.32 Impact Factor
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ABSTRACT: In this investigation, the fatigue resistance of solder joints under cyclic loading was evaluated.
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).
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.
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.
Dental Materials 06/1994; 10(3):215-20. · 3.13 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 05/1994; 20(5):228-32. · 2.88 Impact Factor
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ABSTRACT: 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.
Journal of Endodontics 06/1992; 18(5):222-7. · 2.88 Impact Factor
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ABSTRACT: 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.
Journal of Prosthetic Dentistry 05/1992; 67(4):556-62. · 1.32 Impact Factor
