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Biomedical subjects

B I Cohen

Publications and source records attributed to B I Cohen.

At least 19 recordsLinked to original sources
PubMed2000

Pilot study of the cyclic fatigue characteristics of five endodontic posts with four core materials.

This pilot study concerned the cyclic fatigue of five different endodontic post systems (AccessPost(R), Flexi-Flange(R), Flexi-Post(R), ParaPost(R), and Vlock(R)) with four different core materials (Tytin(R) Silver amalgam, Ti-Core(R), Ketac-Silver(R) and G-C Miracle Mix(R)). In vitro cyclic fatigue was performed using a fatigue machine that simulates masticatory fatigue forces. An instantaneous force of 5 lb was applied to each post and core combination for a test configuration of 4 000 000 repetitions or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way ANOVA was used to compare groups. All posts/core samples with Ti-Core and Tytin Silver amalgam completed the test configuration of 4 000 000 cycles without failures. All posts/core samples with Ketac-Silver failed before the 4 000 000 test cycle configuration, all as a result of core failures. All posts/core samples with G-C Miracle Mix failed in a similar way. The Newman-Keuls multiple comparison test illustrated that Ti-Core and Tytin Silver amalgam were similar to each other and were superior to both G-C Miracle Mix and Ketac-Silver. Similar fatigue test results are found in the literature.

Bicuspid↗
PubMed2000

Torsional resistance of crowns cemented to composite cores involving three stainless steel endodontic post designs.

STATEMENT OF PROBLEM: There are no studies analyzing the effects of a crown in relationship to torsional resistance for a titanium-reinforced core material supported by a post. PURPOSE: This study investigated the effects of post design on the torsional resistance of a crown supported by a titanium-reinforced composite core material (Ti-Core) and 3 endodontic posts (AccessPost, Flexi-Post, and ParaPost). MATERIAL AND METHOD: Three groups of 10 specimens per group were studied. A total of 30 recently extracted human single-rooted (incisors) teeth with their crowns removed were used. Post holes preparations were created according to manufacturer's instructions. All posts were cemented using Flexi-Flow with titanium cement. Scotchbond Multi-Purpose bonding system was used as the bonding system for all groups. All cores were fabricated with Ti-Core with titanium core material with hard copper bands as the matrix. The Ti-Core core material was allowed to set for 1 hour. Metal crowns were fabricated and cemented with zinc phosphate cement. Specimens were placed in a special jig and a clockwise torsional force was applied. Torsional force was measured on a Lebow 1102-200 torque transducer and recorded on a Hewlett Packard 7015B X-Y recorder in inch x ounce. A 1-way analysis of variance (ANOVA) was used to test for statistical significance (P < .001). RESULTS: The torsional values (inch x ounce) were AccessPost 77.2 +/- 30.3, Flexi-Post 162.2 +/- 51.2, and ParaPost 60.9 +/- 28.4. SNK and Scheffé comparison tests revealed that the Flexi-Post group had significantly greater resistance to torque loading than the AccessPost and ParaPost groups, which were statistically similar to each other. CONCLUSION: Post design has an effect on torsional resistance of a crown supported by titanium-reinforced core build-up and post. The threaded split-shank design of the Flexi-Post dowel offers significantly greater resistance to torsional loading than the passive posts studied.

Analysis of Variance↗
PubMed2000

Retention of a core material supported by three post head designs.

STATEMENT OF PROBLEM: There are few studies on the retention of core build-up materials to prefabricated post head designs, especially for a new ceramic post design. PURPOSE: This in vitro study compared the retention of 2 types of core build-up materials (Ti-Core titanium-reinforced composite and a GC Miracle Mix silver-reinforced glass ionomer) supported by 3 post head designs (Flexi-Post, AccessPost, and Cerapost dowel). For all test groups, heads of the posts were placed into the core material at a 90-degree angle to the surface. Test specimens (unloaded) were then placed into a special jig and retention test was performed using an 810 MTS testing machine. MATERIAL AND METHODS: This study consisted of 6 groups with 10 specimens per group. A 3 x 2 factorial design was used to test for statistical significance and results were considered significant when P <.05. RESULTS: Results of the retention test were as follows: group 1, Flexi-Post/Ti-Core 220.0 lb (982.1 N), group 2, AccessPost/Ti-Core 212.7 lb (949.6 N), group 3, Cerapost/Ti-Core 41. 8 lb (186.6 N), group 4, Flexi-Post/Miracle Mix 43.4 lb (193.8 N), group 5, AccessPost/Miracle Mix 61.6 lb (275 N), and group 6, Cerapost/Miracle Mix 7.5 lb (33.5 N). Results of the ANOVA revealed a highly significant difference between posts and cores (P <.0001). CONCLUSION: Post head designs of the stainless steel AccessPost and Flexi-Post dowels offers greater retention then the smooth ceramic head design of the Cerapost dowel. In addition, the composite core material (Ti-Core) offers greater retentive strength values than the glass ionomer material (Miracle Mix).

Analysis of Variance↗
PubMed1999

Comparison of the retentive properties of six prefabricated post overdenture attachment systems.

STATEMENT OF PROBLEM: There are few research studies concerning prefabricated posts overdenture attachment systems using multiple pull cycles. PURPOSE: This study tested 6 prefabricated post overdenture attachment systems (AccessPost Overdenture, ERA white and ERA grey, Flexi-Overdenture, O-SO and ZAAG) measured to simulate wear over a 2000 pull cycle and compared the in vitro retention, measured (pounds). MATERIAL AND METHODS: Records of the pounds of force necessary to separate each system were made at the beginning of testing, at pull 10 and then at every 50th pull until the 2000th pull was attained. All pulls were performed manually with a Shimpo force gauge. Absolute force (AF) and relative force (RF) were compared, AF being the force required at any pull to separate the overdenture device, whereas RF is the force required at the first pull. RESULTS: There was considerable difference of the force required at pull 1 for the ERA white, O-SO and ZAAG anchor systems, then the AccessPost overdenture, and finally the Flexi-Overdenture and ERA grey attachment systems. CONCLUSION: At pull 2000, there was no statistical difference between any of the attachments studied. The amount of force necessary to offer functional retention to a specific patient wearing an overdenture may vary considerably, depending on the many factors in fabricating the overdenture, and the age, strength, musculature, and the expectations of the patient.

Dental Prosthesis Retention↗
PubMed1999

Pilot study of the effects of three bonding systems on the torsional resistance of a titanium-reinforced composite core.

STATEMENT OF PROBLEM: There are no studies analyzing the effects of a bonding agent on torsional resistance for a titanium-reinforced core material bonded with a multistep bonding system. PURPOSE: This pilot study investigated the effects of multistep bonding agents on torsional resistance of a titanium-reinforced composite core material (Ti-Core core material). MATERIAL AND METHODS: A total of 40 recently extracted human molars with their crowns removed were placed into acrylic resin blocks and divided into 4 groups of 10 specimens. Only multistep bonding systems were used (AllBond-2, ScotchBond Multi- PURPOSE: Tenure A&B, and the control without bonding agent). Specimens were prepared according to manufacturer's instructions. The control group was etched with a 37.5% phosphate acid. All cores were fabricated with Ti-Core titanium core material with No. 1 hard copper bands as the matrix. Ti-Core core material was applied and allowed to cure for 1 hour, then the cores were placed in 100% humidity (water) for 1 week. Test specimens were placed in a special jig and a clockwise torsional force applied. Torsional force was measured on a Lebow 1102-200 torque transducer and recorded on a Hewlett Packard 7015B X-Y recorder in inch x ounce then converted into Newton-meter. One-way analysis of variance (ANOVA) was used to test for statistical significance (P <.05). RESULTS: Torsional values (Newton-meter) were AllBond-2, 0.1980, ScotchBond Multi- PURPOSE: 0.1890, Tenure A&B, 0.2142; the control group recorded a value of zero. Statistical analysis revealed that bonding systems did not differ from one another. CONCLUSION: Use of a bonding agent increased the core's resistance to torsional forces. Lack of a bonding agent dramatically reduced the resistance to torque.

Analysis of Variance↗
PubMed1999

Effects of three bonding systems on the torsional resistance of titanium-reinforced composite cores supported by two post designs.

STATEMENT OF PROBLEM: There are no studies that have investigated the effects of bonding agents on the resistance to torque of a composite core supported by a prefabricated post. PURPOSE: This study investigated the ability of bonding agents to resist rational forces applied to titanium-reinforced composite cores supported by 2 post designs. MATERIAL AND METHODS: Two post designs (AccessPost and ParaPost dowels) with titanium-reinforced core material and 4 bonding conditions (AllBond-2, ScotchBond Multi-Purpose, Tenure A&B, and without a bonding agent) were studied. A total of 80 specimens in 8 experimental groups were prepared and subjected to clockwise torsional forces until failure. RESULTS: Torsional values ranged from 53.31 in. x oz (ParaPost/ScotchBond Multi-Purpose) to 72.31 in. x oz (AccessPost/ScotchBond Multi-Purpose). Two-way of analysis of variance failed to demonstrate a significant difference among posts or type of bonding system. CONCLUSION: The use of a multistep bonding agent had no significant effect on the torsional resistance of a core supported by a passive endodontic post.

Acid Etching, Dental↗
PubMed1999

Comparison of the retentive and photoelastic properties of two prefabricated endodontic post systems.

This in vitro study compared the retention and photoelastic stress patterns from two loading conditions, vertical (133.2 N, 30 pounds) and oblique at a 26 degrees angle (133.2 N, 30 pounds) for two prefabricated post systems. The post studied were: (1) Flexi-Post (a split-shank threaded post) and (2) C-Post (a carbon fibre bound in an epoxy resin, passive double taper tier post). Two groups with 10 specimens per group were subjected to retentive forces with a universal testing machine (MTS 810 Material Testing Machine). In addition, two photoelastic test blocks were prepared with simulated root canals for each post studied. After cementation the photoelastic blocks were photographed before vertical and oblique loading and after loading. One-way analysis of variance (ANOVA) for retention data revealed a highly significant difference (P<0.0001) between groups. The Flexi-Post had a statistically higher mean retention force of 1180.6 N (265.9 pounds), while the C-Post had a mean of 171.8 N (38.7 pounds). Photoelastic analysis indicated minimal stresses for both the Flexi-Post and C-Post in the unloaded state. The C-Post showed asymmetrical apically stress patterns, while loaded in both states. The multi-tiered system of the Flexi-Post clearly distributes stress symmetrically, while the C-Post distributes stresses asymmetrically. The symmetric, even stresses and statistically higher retentive strength for Flexi-Post are more favourable than the asymmetric, uneven stresses and relatively low retentive strength for the C-Post.

Analysis of Variance↗
PubMed1999

Report of a simplified endodontic technique.

Using a simplified step-back sequence, which consists of traditional .02 tapered stainless-steel hand reamers, the No. 2 peeso reamer, and four manual nickel-titanium instruments, a dentist can easily, safely, and economically create a continuously tapered canal shape. This article discusses the complete coating of canal walls with EZ-Fill epoxy-resin sealer, which is delivered with a bidirectional spiral; and total obturation with a single gutta percha point, which is matched closely to the tapered shape. The results of this system are compared with other techniques.

Epoxy Resins↗
PubMed1998

Shear bond strength of a titanium reinforced core material after using multistep and single-step bonding agents.

STATEMENT OF PROBLEM: Recently introduced single-step bonding agents reduce the number of steps involved in the bonding process. Nevertheless, there are few studies on the bond strengths obtained with these new systems. PURPOSE: This in vitro study evaluated the shear bond strength of a titanium-reinforced cores bonded with 5 multistep bonding systems (ScotchBond Multi-Purpose, OptiBond, All Bond-2, Tenure, and ProBond) and 5 single-step bonding systems (Single-Bond, OptiBond Solo, One-Step, Tenure Quik, and Prime & Bond 2.1). MATERIAL AND METHODS: The experiment was divided into 10 groups with 10 specimens per group. The shear bond strengths were evaluated after 24 hours on an MTS universal testing machine with a crosshead speed of 6.35 mm/minute. RESULTS: A 2-way ANOVA showed that All Bond-2 and One-Step recorded the highest means and differed significantly from the Den-Mat systems (Tenure A&B and Tenure Quik), the Kerr systems (OptiBond and Opti-Solo), and the Caulk systems (ProBond and Prime & Bond 2.1). ProBond and Prime & Bond 2.1 bonding systems had the lowest mean and differed from the 3 other brands. Tenure A&B and Tenure Quik bonding systems and OptiBond and Opti-Solo bonding systems did not differ from one another. CONCLUSION: The single-step bonding agents did not produce an improvement in shear bond strengths. The wide range of shear bond strength reported for the single-step systems appeared to indicate that these bonding systems are technique sensitive.

Analysis of Variance↗
PubMed1998

Retention of three endodontic posts cemented with five dental cements.

STATEMENT OF PROBLEM: The retention of a post is believed to be a major factor in restoration survival. Therefore the cement with the greatest in vitro retention property should give the best performance for a restoration. PURPOSE: This study compared retentive values of three posts (Flexi-Post, AccessPost, and ParaPost) cemented with five cements (Flexi-Flow, zinc phosphate, Advance, Duet, and Ketac-Cem) plus a control group that consisted of a Flexi-Post No. 2 dowel without cement. MATERIAL AND METHODS: A total of 160 recently extracted human single-rooted teeth with crowns removed at the cementoenamel junction were divided into 16 groups of 10 samples. Post holes were prepared according to manufacturers' instructions. Posts were then cemented with one of the five cements. Each sample was placed into a specialized jig and on a tensile testing machine with crosshead speed of 0.638 cm/minute, applied until failure. A two-way analysis of variance and Newman-Keuls multiple range comparison tests were performed for all cemented groups. A one-way analysis of variance and a Student-Newman-Keuls multiple range comparison test were performed only for the groups with the Flexi-Post dowel, this included the no cement condition, with significant results if p < 0.05. RESULTS: Flexi-Post dowel with Flexi-Flow Natural cement obtained the highest retentive value (303.91 pounds). ParaPost dowel with Duet cement exhibited the lowest retention value (21.23 pounds). The Flexi-Post dowel demonstrated higher mean retention than AccessPost or ParaPost dowels, AccessPost dowel was higher than ParaPost dowel. Flexi-Flow cement had the highest overall mean retention followed, in decreasing order, by zinc phosphate, Advance, Ketac-Cem, and Duet cements. CONCLUSIONS: Flexi-Post dowel was the most retentive post studied with values ranging from 303.91 pounds with Flexi-Flow Natural cements to 150.93 pounds without cement. Flexi-Flow cements had a higher overall mean retention than other cements studied.

Analysis of Variance↗
PubMed1998

Effect of power settings versus temperature change at the root surface when using multiple fiber sizes with a Holmium YAG laser while enlarging a root canal.

The aim of this study was to determine if there is an increase in temperature at the root surface as the canal is enlarged when using a Holmium:YAG laser. An increase might be expected because, as the canal is enlarged, there is less dentin between the canal walls and the outer cementum surface of the root to absorb the heat. Sixty single-rooted human teeth were randomly assigned to 1 of 3 groups according to laser power settings: 0.50, 0.75, and 1.00 W. Each tooth in each power group was subjected to lasing using fiber sizes of 140, 245, 355, and 410 microns. The dependent variables in these analyses included: (a) change in temperature, measured with T-type thermocouples placed 2 mm from the coronal and apical ends of the root; (b) depth of laser in the tooth; (c) depth that a conventional fiber could be inserted after lasing; and (d) tooth physical dimensions. ANOVA for coronal temperature showed no interaction between fibers and power settings. Repeated-measures ANOVA for apical temperature showed a significant difference between fibers, but not between power settings. No interaction between fibers and power settings was observed. For the depth of tooth during lasing (how far the fiberoptic guide penetrated into the tooth), no interaction between fibers and power settings was observed. Pairwise contrasts revealed that all fibers were different from one another, with depth decreasing as fiber size increased. Depth files could be inserted that showed the depth significantly decreased as file size increased from 50 through 70. ANOVAs illustrated that there were no significant differences between power settings for any of the five tooth physical dimensions. All temperature differences observed apically and coronally were between 0 degree to 10 degrees C, with the majority (> 98%) being between 0 degree to 5 degrees C. After lasing with the 410-micron fiber, the root canals were widened to at least 45 or 50 K-files (450 or 500 microns). However, by using a 410-micron fiber, the laser did not seem to widen the canal beyond a 500-micron diameter.

Analysis of Variance↗
PubMed1998

Tear strength of four irreversible hydrocolloid impression materials.

PURPOSE: The purpose of this investigation was to examine the tear strength of four irreversible hydrocolloid (alginate) impression materials (Tare-Free Alg, Jeltrate, Identic, and Kromopan). MATERIALS AND METHODS: Eighty specimens, 20 for each alginate tested, were according to the manufacturers' instructions. A cutting die described in American Standard Test and Material document D-1004-94a was used to prepare test specimens. Immediately after removal from the cutting die, test specimens were measured at five points with an electronic caliper. Test specimens were placed into a specialized jig, and a Shimpo force gauge was used to measure tear strength. The tear test was performed no more than 10 minutes after mixing the alginate material with water. The tear strength was then calculated. One-way ANOVA was used to compare the mean force required to induce tearing for each of the four groups, followed by the Newman-Keuls pairwise multiple comparisons test. RESULTS: Results were considered statistically significant at p < .05. There was a statistically significant difference between alginate materials (p < .0001). The Newman-Keuls multiple comparisons procedure showed that Tare-Free Alg (514.5 g/cm) had a significantly higher tear strength value (p < .0001) than Jeltrate (259.0 g/cm), Identic (289.9 g/cm), and Kromopan (323.9 g/cm). CONCLUSIONS: Tare-Free Alg had the highest tear strength value, followed by Jeltrate, Identic, and Kromopan.

Alginates↗
PubMed1998

Simplified obturation of tapered canal preparations.

Canals shaped to wider tapers, specifically .06 mm and .08 mm, have traditionally been associated with thermoplastic fills. However, the canals shaped to .06 mm and .08 mm tapers correlate very closely to the shape of fine-medium and medium gutta-percha points, respectively. Combining the placement of these single-point fills with the patented EZ-Fill bi-directional spiral for well-controlled placement of the EZ-Fill epoxy resin sealer gives the dentist the ability to simplify the obturation procedure with results that are at least equal to those achieved with lateral condensation and thermoplastic techniques.

Epoxy Resins↗
PubMed1998

Formaldehyde evaluation from endodontic materials.

The purpose of this study was to measure the amount of formaldehyde released from three types of endodontic sealing cement (AH-Plus, EZ-Fill, and AH-26). Formaldehyde release was analyzed using High Performance Liquid Chromatography, which could detect as low as 0.25 ppm. The data was tabulated after two runs. The two paste system of AH-Plus endodontic sealing cement had the least amount of formaldehyde release (0.00039%, 3.9 ppm). This was followed by EZ-Fill (0.054%, 540 ppm) endodontic cement and AH-26 (0.1347%, 1347 ppm) endodontic cement which yielded the greatest formaldehyde release. Both of these cements (EZ-Fill and AH-26 endodontic filling cements) are based on a powder-liquid mix. The relative minute amounts of formaldehyde released by the endodontic cements studied (AH-Plus and EZ-Fill) warrant their use as endodontic sealing cements.

Bismuth↗
PubMed1998

A five year study. Fluoride release of four reinforced composite resins.

PURPOSE: The purpose of this study was to record the fluoride released measured in parts per million of four fluoride composite resins for five years. MATERIALS AND METHODS: Four fluoridated composites were separated into four groups. Two composite resins with high viscosity were core materials, Ti-Core with titanium (group 1) and Ti-Core Natural (group 2) and the other two resins studied were low viscosity post cements Flexi-Flow cement with titanium (group 3) and Flexi-Flow Natural (group 4). The fluoride release was studied under four experimental conditions. Three replications were studied in each condition. Fluoride release was measured for 260 weeks (5 years). STATISTICAL METHODS: A one-way analysis of variance (ANOVA) was used to compare the average weekly release followed by a Student-Newman-Keuls (SNK) pairwise multiple comparison test. All results were considered statistically significant if p < 0.05. RESULTS: The ANOVA analysis released a significant statistical interaction between group and week (p < 0.0001). Further analysis showed that the average weekly release for Ti-Core with titanium did not differ from Ti-Core Natural, and that Ti-Core with titanium and Ti-Core Natural differed from both Flexi-Flow Natural and Flexi-Flow with titanium, which were not different from one another. CONCLUSIONS: Ti-Core with titanium (Group 1) and Ti-Core Natural (Group 2) released a greater amount of fluoride than Flexi-Flow with titanium (Group 3) and Flexi-Flow Natural (Group 4). The fluoride released from these fluoridated resin composites are similar to reported ranges of other fluoride releasing dental restoration materials.

Analysis of Variance↗
PubMed1997

Fracture strengths of three core restorative materials supported with or without a prefabricated split-shank post.

PURPOSE: The aim of this study was to compare the fracture strengths of three restorative materials, a lanthanide reinforced composite (Ti-Core Natural), a silver amalgam (Tytin), and a hybrid glass ionomer (Advance), supported by either a multitiered, threaded split-shank post (Flexi-Flange) or with a dentin spur without a post. MATERIAL AND METHODS: A total of 60 recently extracted single-rooted human teeth were divided into six groups of 10. All groups were stored at 100% humidity at room temperature for 1 week before testing. Each specimen was placed in a special jig at a 45-degree angle to the buccolingual axis and subjected to a load that was recorded in pounds and converted to Newtons on a universal testing machine, with a crosshead speed of 0.63 cm/minute until failure. Two-way analysis of variance followed by the Newman-Keuls pairwise multiple comparisons test were used to compare the results. RESULTS: There was a statistically significant difference between core materials (p < 0.001), but not regarding post conditions. Ti-Core Natural material had a significantly larger mean failure threshold for fracture than either Tytin silver amalgam or Advance material and the letter two core materials (Tytin and Advance) do not differ from each other. There was no statistical difference between Ti-Core material supported by a post and Ti-Core material supported without a post.

Analysis of Variance↗
PubMed1997

Cyclic fatigue testing of five endodontic post designs supported by four core materials.

PURPOSE: This pilot study examined the cyclic fatigue of five endodontic post systems (AccessPost, Flexi-Flange, Flexi-Post, ParaPost, and Vlock) with four core materials (Tytin silver amalgam, Ti-Core, Ketac-Silver and G-C Miracle Mix). MATERIAL AND METHODS: In vitro cyclic fatigue was performed with a machine designed to simulate masticatory fatigue forces. An instantaneous force of 22.2 N (5 pounds) was applied to each post and core combination for a test configuration of 4,000,000 repetitions, or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way analysis of variance (ANOVA) was used to compare groups. RESULTS: All posts/core samples with Ti-Core composite and Tytin silver amalgam completed the test with no failures. All posts/core samples with Ketac-Silver material failed before the 4,000,000 test cycle configuration and all failures were core failures. All posts/core samples with G-C Miracle Mix material failed in a similar manner. Newman-Keuls multiple comparison test illustrated that, with this simulated fatigue test, Ti-Core material and Tytin silver amalgam were superior to both G-C Miracle Mix and Ketac-Silver materials.

Analysis of Variance↗