Investigating failure behavior and origins under supposed "shear bond" loading.

PURPOSE: This study evaluated failure behavior when resin-composite cylinders bonded to dentin fractured under traditional "shear" testing. Failure was assessed by scaling of failure loads to changes in cylinder radii and fracture surface analysis. Three stress models were examined including failure by: bonded area; flat-on-cylinder contact; and, uniformly-loaded, cantilevered-beam. METHODS: Nine 2-mm dentin occlusal dentin discs for each radii tested were embedded in resin and bonded to resin-composite cylinders; radii (mm)=0.79375; 1.5875; 2.38125; 3.175. Samples were "shear" tested at 1.0mm/min. Following testing, disks were finished with silicone carbide paper (240-600grit) to remove residual composite debris and tested again using different radii. Failure stresses were calculated for: "shear"; flat-on-cylinder contact; and, bending of a uniformly-loaded cantilevered beam. Stress equations and constants were evaluated for each model. Fracture-surface analysis was performed. RESULTS: Failure stresses calculated as flat-on-cylinder contact scaled best with its radii relationship. Stress equation constants were constant for failure from the outside surface of the loaded cylinders and not with the bonded surface area or cantilevered beam. Contact failure stresses were constant over all specimen sizes. Fractography reinforced that failures originated from loaded cylinder surface and were unrelated to the bonded surface area. CONCLUSIONS: "Shear bond" testing does not appear to test the bonded interface. Load/area "stress" calculations have no physical meaning. While failure is related to contact stresses, the mechanism(s) likely involve non-linear damage accumulation, which may only indirectly be influenced by the interface.

Smear layer production of K3 and ProFile Ni-Ti rotary instruments in curved root canals: a comparative SEM study.

OBJECTIVE: The aim of this scanning electron microscopic study was to compare the quality and amounts of smear layer generated by 2 brands of nickel-titanium rotary instruments during canal preparation in the apical thirds of curved root canals. STUDY DESIGN: Forty mandibular mesial root canals with intact apex and mean curvature between 30 and 35 degrees were selected for this study. The root canals were randomly divided into 2 instrumentation groups of 15 each. Automated preparation was performed with ProFile (Dentsply Maillefer, Ballaigues, Switzerland; n = 15) and K3 (SybronEndo, Orange, Calif; n = 15) instrumentss using a crown-down technique. As a control group, barbed broaches (Mani; Matsutani Seisakusho, Takanezawa-Machi Tochibi-Ken, Japan; n = 10) were used to extirpate the necrotic pulp tissue from the root canals. All root canals were prepared to size #35. Glyde (File Prep, Dentsply Maillefer) was used as lubricant and 1% sodium hypochlorite solution as irrigant. At the conclusion of the experiments, all roots were split longitudinally and the root canal walls were examined at the apical third from 2 different perspectives using a scanning electron microscope. A 4-category scoring system for assessing the smear layer accumulation was used, and the resulting scores were statistically analyzed. RESULTS: Less smear layer was obtained in the K3 group at the selected apical third of curved root canals (P < .05). However, all instruments left a smear layer. The surface texture of the smear layer, in addition to the depth and the frequency of packed materials into the dentinal tubules, varied with instrument type. CONCLUSIONS: This finding may imply that, compared to ProFile, compression of the remaining smear layer is minimized when using the K3 rotary nickel-titanium system.

A comparison of the machining efficiency of two brands of stainless steel endodontic hand files.

The purpose of this study was to compare the machining efficiency of a flexible stainless steel K-type hand file recently introduced by Brasseler USA ("F-Style files"), with that of a well-studied Endodontic instrument ("Flex-o-files," Maillefer Dentsply), that has been on the market for more than 20 years. The comparison of machining efficiencies of these two brands of files was conducted on both dentin and plexiglas substrates, using an apparatus that allowed a constant force to be applied from each file being tested. The results indicated that the Brasseler instruments had poorer machining efficiency than those of the Maillefer files.

An objective evaluation comparing the physical properties of two brands of stainless steel endodontic hand files.

The purpose of this study was to evaluate the physical properties of a flexible stainless steel K-type hand file recently introduced by Brasseler USA (F-Style files; Brasseler USA, Savannah, GA), in comparison to those of a well-studied instrument (Flex-o-files; Maillefer-Dentsply, Ballaigues, Switzerland), that has been on the market for more than 20 yr. The physical properties measured included torque at failure, angular deflection at failure, flexibility, and consistency of diameter at 3 mm from the cutting tip; and the evaluations were carried out on size #10 through #50 files of each of the two brands being tested. The results indicated that the Brasseler instruments were inherently more flexible, but had smaller diameters, lower torque, and angular deflection values at failure, than those of the Maillefer files.

Chairside replacement of posterior teeth using a prefabricated fiber-reinforced resin composite framework technique: a case report.

UNLABELLED: The fixed replacement of a single posterior missing tooth for those patients who cannot have either implants or conventional laboratory-generated fixed prostheses has always been a challenge to clinicians. The development of fiber-reinforced composites (FRCs) has opened up new possibilities of chairside treatment options to manage these types of clinical situations. Techniques using FRCs as frameworks with traditional restorative resin composites as veneering materials can provide chairside fixed prostheses that are esthetic and potentially durable, with minimal abutment tooth loss. A clinical case is presented that will illustrate a novel concept for tooth replacement--the use of an FRC prefabricated framework--to allow for a single visit, chairside replacement of a missing molar. The assembly of the framework and the clinical steps used in the framework placement and pontic fabrication are shown in detail. CLINICAL SIGNIFICANCE: The combination of FRC technology and adhesive techniques can provide minimally invasive and cost-effective treatment options for the chairside replacement of missing posterior teeth.

Smear layer production by 3 rotary reamers with different cutting blade designs in straight root canals: a scanning electron microscopic study.

OBJECTIVES: The design of the cutting blade of rotary instruments may affect the outcome of root canal instrumentation in terms of cleanliness. The aim of this scanning electron microscopic study was to compare the quality and amount of smear layer generated in the apical third of straight root canals by 2 rotary nickel-titanium reamers and 1 rotary steel reamer with different cutting blade designs. STUDY DESIGN: Seventy intact, single-rooted human mandibular premolars with straight, fully developed roots were selected for this study. Before instrumentation, the cervical portion of all teeth was removed by using a microtome (Isomet), leaving 13-mm-long roots. Automated preparation was performed with ProFile (n = 20) and Hero 642 (n = 20) reamers by using the crown-down technique and with a stainless steel engine reamer (Mani; n = 20) by using a reaming motion. All root canals were instrumented to No. 40. A control group (pulp extirpation with barbed broaches; n = 10) was also included. Irrigation with 3 mL of a 1% sodium hypochlorite (NaOCl) solution was performed after each instrumentation. After the instrumentation, each root was split longitudinally, and a scanning electron microscope was used to examine the selected areas of the canal walls at the apical third from 2 different perspectives. A 4-category scoring system for smear layer was used, and the resulting scores were statistically analyzed. RESULTS: The least smear layer remained in the Hero 642 group at the selected apical third of straight root canals (P < .05). However, all instruments left a smear layer. The surface texture of the smear layer, in addition to the depth and the frequency of packed materials into the dentinal tubules, varied with instrument type. CONCLUSION: These data revealed that the design of the cutting blade of rotary instruments can affect root canal cleanliness in straight root canals. This information may be useful in the selection of nickel-titanium rotary reamers.

The influence of fiber reinforcement of composites on shear bond strengths to enamel.

STATEMENT OF PROBLEM: Fiber-reinforced composites (FRC) are used in direct intra-oral applications as periodontal splints and chairside tooth replacement by bonding them to etched enamel with resin adhesives and composites. There is little information regarding the effect of FRC on the shear bond strength of composite to etched enamel. PURPOSE: The purpose of this study was to examine the effect of resin preimpregnated and non-preimpregnated fiber-reinforced composites on enamel to composite shear bond strength (SBS). MATERIAL AND METHODS: Specimen groups (n = 12) consisted of a control (composite with no fiber reinforcement), Ribbond, Splint-It Unidirectional, Splint-It Woven, and Connect, which were bonded to 37% phosphoric acid etched Prime and Bond NT adhesive-treated bovine enamel surfaces on a bed of Tetric Flow composite. Specimens were thermocycled 1000 times between 5 degrees and 55 degrees C and loaded on a universal testing machine in shear at a linear increasing load until fracture (MPa). The fractured surfaces of the debonded specimens were evaluated to determine the nature of the fracture with a light binocular microscope (x10). Shear bond strength data were subjected to analysis of variance (ANOVA) and Student-Newman-Kuels tests (P <.05). RESULTS: Mean MPa +/- SD for the test groups were as follows: Control, 15.6 +/- 2.4; Splint-It Unidirectional, 15.3 +/- 2.4; Splint-It Woven, 16.5 +/- 1.8; Connect, 18.8 +/- 1.5; and Ribbond, 15.8 +/- 2.2. The Connect FRC group had significantly higher (P <0.05) enamel SBS than all other groups. Fracture analysis showed varying types of failures among the groups, with cohesive fractures within the fiber reinforcement of Splint-It Unidirectional and Connect, cohesive fractures within the bonding resin/flowable composite for Ribbond and the control, and adhesive fracture at the fiber reinforcement interface with Splint-It Woven. CONCLUSION: Within the limitations of this study, no differences in SBS were observed with the addition of 3 of the 4 FRCs compared to composite without FRC, with the exception of the Connect product which provided significantly higher SBS values.

Effect of fatigue testing on core integrity and post microleakage of teeth restored with different post systems.

The purpose of this study was to evaluate a new nondestructive test system, which could test concurrently fatigue and microleakage. Fifty, single-rooted teeth were restored with one of the following posts systems and a composite core: titanium ParaPost cemented with zinc phosphate cement; CosmoPost; C-Post; Esthetic C-Post; and FibreKor post, all cemented with resin cement. Samples were embedded and placed in a positioning jig. They were impacted at 45 degrees to the long axis of the tooth with a force of 55 N at a frequency of 3 Hz for a total of 100,000 impacts. After 60,000 impacts, samples were thermocycled. Core integrity and post microleakage were evaluated periodically throughout the 100,000 impacts. Samples showed no detectable displacement of any of the cores, but the metallic group showed a statistically significant increase in microleakage (p < 0.05) at the conclusion of the study compared with the nonmetallic groups.

Effect of caries disclosing agents on bond strengths of total-etch and self-etching primer dentin bonding systems to resin composite.

This study examined the effect of caries disclosing dyes on composite to dentin shear bond strengths of a total etch, one-bottle and two self-etching, non-rinsing primer dental adhesives. Two caries disclosing dyes were evaluated, Seek and Snoop, with three dentin adhesives, Prime & Bond NT, Prompt L-Pop and Clearfil SE Bond. Extracted human molars stored in 0.2% sodium azide were sectioned longitudinally to expose dentin and embedded in acrylic, leaving the dentin exposed. Each dentin adhesive had three test groups (n=12); a control and one with each of the caries disclosing dyes. The control group had the dentin conditioned and the adhesive applied following the manufacturer's instructions. The caries disclosing dye groups had the dentin first treated for 10 seconds with the disclosing dye, rinsed, then the dentin adhesives were applied as in the controls. A column of Tetric Ceram was bonded after dentin adhesive placement to each specimen and light cured. Specimens were stored in room temperature water for 24 hours, thermocycled for 1,000 cycles between 5 degrees C and 55 degrees C and tested in shear until failure. Mean +/- SD shear bond values (SBV) were determined in MPa. A one-way ANOVA and Student Neuman Keuls multiple comparison test within each DBS were performed at a significance level ofp<0.05 to analyze the caries disclosing dyes input on SBV versus the controls. Surface analysis to determine the nature of the type of dentin/composite fracture/ separation was also performed. For the fracture analysis data, a Chi-Square test was performed at a significance level of p<0.05. The results of this study indicate that using the two tested caries disclosing dyes, with a total etch, one bottle and two self-etching, non-rinsing primer dental adhesives did not negatively affect the dentin-to-composite shear bond strengths of the three tested dentin bonding systems (p>0.05).