Effect of the Controlled Delivery of Chelating Agents on the Pulp Tissue Dissolution Ability of Fresh Sodium Hypochlorite Solutions.

INTRODUCTION: The purpose of this study was to evaluate pulp tissue dissolution ability of sodium hypochlorite (NaOCl) when mixed with tetrasodic etidronate (Na4HEBP) and disodic ethylenediaminetetraacetate (Na2EDTA) under controlled flow. METHODS: Bovine pulp tissue was extracted from the lower incisors of 10 bovine jaws. Pulp specimens were standardized in size (1 × 3 × 10 mm), blotted dry, and weighed (initial weight [T0]: mean (SD) = 31.98 (1.18) mg). Specimens from the same jaw were randomly assigned to 2 control (n = 3 each) and 4 experimental groups (n = 10 each): NC (negative control/distilled water), PC (positive control/6%NaOCl), G1 (3%NaOCl), G2 (3%NaOCl-17% Na2EDTA), G3 (3%NaOCl-18% Na4HEBP), and G4 (3%NaOCl-9% Na4HEBP). Distilled water and NaOCl were provided using a delivery pump under a continuous controlled rate (1 mL/min). A second pump alternately delivered either Na2EDTA or Na4HEBP at the same rate with a 30-second programmed interval. Percentage of tissue weight loss was calculated at 2, 5, and 10 minutes (T2, T5, and T10) and compared among groups with analysis of variance. Free available chlorine and pH were controlled at T0 and T10. RESULTS: No tissue remained in PC at T5. No dissolution occurred in NC. There were no significant differences in the percentage of weight loss among experimental groups at any point of time. Some remnant tissue was found in G3 (1.4% ± 2.4) and G4 (1.6% ± 2.3) at T10, whereas nothing was left in G1 and G2. CONCLUSIONS: The controlled delivery of Na2EDTA and Na4HEBP did not alter tissue dissolution ability of NaOCl when fresh solutions were mixed in the root canal.

Full mapping tensile bond strength of luting in search for differences due to centripetal curing shrinkage.

OBJECTIVES: testing if hypothetical transverse centripetal strains due to polymerization contraction of luting materials produce differential alterations in its bonding to luted structures, depending on distances to the center of the luting mass, and if this effect is C-factor related. Two hypotheses were tested: (1) there is a statistically significant decreasing relationship between the bonding strength and the transverse distances to the center of the luting material, and (2) there is a statistically significant difference between bonding strengths among luting spaces with different configuration factors. METHODS: 10 PMMA (15 mm Ø) pairs of cylinders were cemented (Scotchbond Universal adhesive & Relyx Universal, both chemically cured) in a compliant setup under two (20 and 70 N) luting forces forming 2 groups (5 samples each), resulting in different C-factors. Whole samples were sectioned in x and y directions obtaining non-trimmed beams from all along the luting surfaces. Their relative positions in each sample were assessed before separating and categorized (10 categories) according to their distances to the center of the sample. All beams were tested in tension and, because of their uneven bonding areas and to balance its influence, UTS results were transformed into UTSres. First hypothesis was tested trough a linear relationship between UTSres and distances to vertical centers per samples. Second hypothesis was tested using Mann-Whitney U tests to compare UTSres between groups, along all categories. Further Weibull analysis was applied. RESULTS: ANOVA's p of the regression UTSres - categories were statistically significant for all samples in group 70 N and for all except one in group 20 N: first hypothesis is partially maintained. Although Mann-Whitney tests p comparing UTSres of both groups for all categories but the first were statistically significant this hypothesis was maintained relying in Weibull analysis. SIGNIFICANCE: bonded attachment of cemented materials decreases from centers to outbounds in plane, extensive surfaces, and this decrease is C-factor related.

Impact of a modified motion on the fatigue life of NiTi reciprocating instruments: a Weibull analysis.

OBJECTIVES: To evaluate the impact of a modified motion on the fatigue life of four brands of nickel-titanium (NiTi) reciprocating instruments. MATERIALS AND METHODS: Cyclic fatigue (CF) resistance of 160 instruments was evaluated in an artificial stainless-steel canal (90° angle, 5-mm radius of curvature). WaveOne and WaveOne Gold (Denstply Maillefer, Baillagues, Switzerland) and Reciproc and Reciproc Blue (VDW, Munich, Germany) were tested with two different motions: (1) X-Smart Plus (Denstply Maillefer) endodontic motor and (2) a 4:1 contra-angle with an experimental motion (EVO) with different rotation angles and based on a sinusoidal acceleration. Motions with X-Smart Plus and EVO were recorded and analyzed at a reduced speed with VLC Media Player software for a more accurate analysis. Mean half-life, beta, and eta Weibull parameters were determined and compared. RESULTS: Reciproc Blue resulted the most resistant instruments either with EVO or X-Smart. WaveOne Gold lasted significantly longer than WaveOne with EVO (probability of 91%) while no significant differences were found with X-Smart. Considering NCF, Reciproc, WaveOne Gold, and Reciproc Blue lasted significantly longer with EVO (probabilities of 66%, 80%, and 89% respectively). WaveOne Gold showed the highest beta parameter. CONCLUSIONS: The experimental motion was found to have a positive impact on fatigue lifetime of reciprocating instruments. CLINICAL RELEVANCE: Current findings provide insight for future improvements in the clinical use of reciprocating files. Experimental motions may be considered when searching for additional strategies in order to increase the safer use of NiTi files during endodontic procedures.

Variable impact by ambient temperature on fatigue resistance of heat-treated nickel titanium instruments.

OBJECTIVES: The purpose of this study was to evaluate the effect of different ambient temperatures on cyclic fatigue (CF) life of two NiTi rotary systems and correlate the results with martensitic transformation temperatures. MATERIALS AND METHODS: Heat-treated NiTi Vortex Blue (VB) and EdgeSequel Sapphire (SP) instruments (tip sizes no. 20, 25, 30, 35, 40) were tested for CF resistance at room and body temperature (n = 20 each group) in a simulated canal (angle of curvature 60°; radius 3 mm; center from instrument tip 4.5 mm) with a motor controlled by an electric circuit. Mean half-life, beta and eta Weibull parameters were determined and compared. Two further instruments of each brand were subjected to differential scanning calorimetry (DSC). RESULTS: Temperature had an effect on fatigue behavior: all instruments lasted significantly longer at room than at body temperature. All VB significantly outlasted those of SP at body temperature; while smaller diameters of VB (size no. 20) were also significantly more resistant than SP when tested at room temperature; SP with larger diameters (sizes no. 30, no. 35, and no. 40) lasted significantly longer than VB did. CONCLUSIONS: Immersion in water at body temperature was associated with a marked decrease in the fatigue life of all rotary instruments tested. VB instruments were significantly more CF resistant at body temperature and showed the highest predictability in terms of fracture resistance. CLINICAL RELEVANCE: Rotary instruments manufactured with different post-machining heat treatment responded differently to changed ambient temperatures. DSC assessment of martensitic conversion temperatures helps to predict the behavior of nickel titanium rotaries in different environments.

Prospective case controlled clinical study of post-endodontic pain after rotary root canal preparation performed by a single operator.

OBJECTIVES: The aim of this study was to assess the influence of the shaping technique on incidence, intensity, duration and type of postoperative pain (PP). METHODS: Root canal treatments were carried out with rotary instrumentation (n=80) during a single-visit, and data about pre-treatment conditions were collected. Patients were given a questionnaire to record the presence or absence of post-endodontic pain, its duration and level of discomfort. A matching patient (same pre-treatment conditions but manual instrumentation) was randomly selected from a pool (n = 374) and assigned to the control group. A total of 44 pairs of patients matched completely and were included in the study. Incidence (yes/no) of PP was assessed using Chi-square tests, intensity (mild, moderate, severe) with trend tests and duration (days) with Mann-Whitney U tests. RESULTS: A significantly greater proportion of the patients in the control group reported pain than did patients in the rotary shaping group (p < 0.05). However, pain duration was shorter (p = 0.008) in the control group. Differences in level of discomfort were not statistically significant. CONCLUSIONS: The results of this prospective in vivo study suggest that a higher incidence of PP should be expected after manual root canal preparation. However a second major finding of the study is that when present, PP after a rotary canal preparation is expected to last longer. CLINICAL SIGNIFICANCE: There has been an increase in the use of rotary techniques among dentists in recent years. The present study analyses the differences in the incidence and characteristics of postoperative pain that should be expected after rotary canal preparation compared to traditional manual methods that had not been reported yet.

Differences in cyclic fatigue resistance between ProTaper Next and ProTaper Universal instruments at different levels.

INTRODUCTION: New designs and alloys have been developed to increase cyclic fatigue (CF) resistance of rotary files. The aim of this study was to compare CF resistance of ProTaper Universal (PTU; Dentsply Tulsa Dental, Tulsa, OK) and ProTaper Next (PTN, Dentsply Tulsa Dental) instruments at different points of curvature. METHODS: A total of 420 files (240 PTU, S1, F1, F2, and F3 and 180 PTN, X1, X2, and X3) were divided in 14 groups of 30 instruments each. Instruments in groups S1-5, F1-5, X1-5, F2-5, X2-5, F3-5, and X3-5 were tested at 5 mm from the tip. Groups S1-12, X1-12, and F1-12 were tested at 12 mm from the tip because S1, X1, and F1 instruments have the same diameter at that level. Groups F2-8, X2-8, F3-8, and X3-8 were tested at 8 mm (F2/X2 and F3/X3, respectively, had the same diameter at 8 mm). All files were rotated at 300 rpm until fracture. CF resistance was tested in stainless steel curved canals (60°, r = 3 mm). Time to fracture was recorded. The mean half-life and beta and eta were calculated for each group and were compared with Weibull analysis. RESULTS: PTN instruments will last significantly longer than PTU files with a probability higher than 98% at all tested levels except for S1, which was the significantly the most resistant instrument to CF at 5 mm from the tip. CONCLUSIONS: PTU S1 was significantly the most resistant instrument at 5 mm from the tip. PTN files were significantly more resistant to CF than PTU instruments at all the other tested levels.

Microtensile bond strength test bias caused by variations in bonded areas.

PURPOSE: While it has been shown that no method produces specimens with exactly the same cross-sectional bonded area (BA), BA variations within and between studies are a well-known covariate in microtensile test results. However, no method has yet been described to accurately account for its influence. A procedure is presented that allows controlling for variations of BA effects on results. Further, a proposal for reporting is presented which enables results of different studies to be compared. MATERIALS AND METHODS: Partially using the results of the report in which the microtensile test was originally described, 144 both general (caused by differences in BA) and specific (due to a material's performance differences and intrinsic biological variability of specimens) variabilities were separated through linear regression of microtensile (MPa) to BA (mm2) pooled results. Comparing the specific variability of specimens - the residuals to the regression line - of groups allowed assessing differences between groups. RESULTS: A means comparison of residuals showed that specific differences were significant (t-test, p = 0.0004). The null hypothesis could be rejected: materials' performances were different. This could not be determined in the original report, since BA variability was very high. A proposal for reporting of results to facilitate their clinical interpretation and comparison between studies is presented. CONCLUSION: Controlling for general variability caused by differences in BA size allows precise comparison of microtensile tests results.

Cyclic fatigue resistance of K3, K3XF, and twisted file nickel-titanium files under continuous rotation or reciprocating motion.

INTRODUCTION: New designs and alloys and different motions have been introduced to increase the cyclic fatigue (CF) resistance of nickel-titanium (NiTi) files. The aim of this study was to compare the CF resistance of K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and TF (SybronEndo) files under continuous rotation and reciprocating motion. METHODS: A total of 210 files (30-tip diameter, 0.06 fixed taper), 60 K3, 60 K3XF, and 90 TF files, were divided into 7 groups (30 files each): K3-C, K3XF-C, and TF1-C were rotated at 300 rpm; TF2-C was rotated at 500 rpm; and K3-R, K3XF-R, and TF1-R were used in a reciprocating motion. CF resistance was tested in stainless steel, curved canals (60°, r = 3 mm) until fracture, and the time to fracture was recorded. The mean half-life, beta, and eta were calculated for each group and were compared with Weibull analysis. RESULTS: The probability of a longer mean life was greater under reciprocating motion for all of the files (100% for K3, 87% for K3XF, and 99% for TF). Under continuous rotation, K3XF was more resistant than K3 and TF. TF lasted significantly longer than K3. TF was more resistant to CF when rotated at 300 rpm instead of 500 rpm. Under reciprocating motion, there were no significant differences between K3XF and TF mean lives, but both were significantly longer than the K3 mean life (78% for TF and 86% for K3XF). CONCLUSIONS: Reciprocating motion and R-phase increase CF resistance.

Differences in cyclic fatigue resistance at apical and coronal levels of Reciproc and WaveOne new files.

INTRODUCTION: Recent improvements in alloys, kinematics, and concepts have been combined to increase the cyclic fatigue resistance of nickel-titanium (NiTi) instruments. The aim of this study was to compare the cyclic fatigue resistance of new M-Wire reciprocating WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) and Reciproc (VDW GmbH, Munich, Germany) files at 2 levels. METHODS: Sixty Reciproc and 60 WaveOne new files were fixed to a specifically designed device and tested in tempered steel canals with a 3-mm radius and a 60° angle of curvature. The motor used was programmed as defined by each manufacturer, and the specific reciprocating motion was followed. Thirty files of each brand were tested at 5 mm, and 30 were tested at 13 mm from their tips. The time to failure was registered. Weibull analysis was used to calculate the mean life, beta, and eta parameters. RESULTS: The probability of the mean life was higher for Reciproc than WaveOne files at both levels, with the probability of the Reciproc mean life being 62% higher than that of WaveOne at 5 mm from the tip and 100% higher at 13 mm (all statistically significant). The probability of the mean life was higher at 5 mm than at 13 mm in both systems. The results may have been partially conditioned by the different motions that manufacturers propose for each system. CONCLUSIONS: Reciproc files were more resistant to cyclic fatigue than WaveOne files at both distances from the tip. Both systems had greater cyclic fatigue resistance at 5 mm than at 13 mm from the tip.

Regional variations of µTBS of light- and chemically cured resin composite restorations in clinically relevant situations.

PURPOSE: To test whether the distance to the mass center of a buildup made of visible-light- or chemically curing composite resin bonded to dentin and cured in one increment has an influence on µTBS. MATERIALS AND METHODS: In the experimental groups, one-increment visible-light (Z250) or chemically-cured (TiCore) composite-resins buildups were bonded to flattened bovine dentin surfaces. In the control groups, the same materials were bonded as separate buildups on circumscribed areas to minimize the effect of shearing polymerization contraction. Compound composite/interface/dentin specimens were trimmed out of buildups and tested in tension until detachment; the distances to the mass centers of their respective buildups were recorded as the independent variable. The correlation between µTBS and distances was tested in each group. Slopes and intercepts of regression lines (µTBS to bonded area) were compared in the experimental groups. RESULTS: The correlation between µTBS and distances was negative and statistically significant for both experimental groups (p < 0.0001), but not for the two control groups (p > 0.34). CONCLUSION: In clinical situations such as direct resin veneering or resin core construction, where a first layer of a light- or chemically cured resin composite is bonded and cured on a broad surface, the µTBS of the interface decreases proportionally to the distance to the mass center of the restoration.

Frequently asked questions in composite restorative dentistry.

UNLABELLED: With an increasing number of dental practitioners using composite resins as the restorative material of choice, knowledge of terminology, handling properties and restorative techniques are important. CLINICAL RELEVANCE: This paper addresses many of the questions raised by participants at lectures and courses given by the authors across Europe.

Effects of polymerization contraction on interface's microTBS of luting material and dentin.

Polymerization contraction of composite resin luting materials is known to produce high stresses in the interfaces being cemented that are described as perpendicular to them. This study describes the effect of shearing strains of curing luting materials on microtensile bond strength (microTBS) of interfaces. A flat surface of labial dentin of bovine incisors was exposed and teeth randomly assigned to A (n = 12) or B (n = 6) groups. Adoro rectangular (2 x 3 x 11 mm) restorative composite resin blocks were cemented (Excite DSC + Variolink II) completely (group A) or partially (group B, only on extremes and center) occupying luting space. After visible light curing, stick compound bars were sectioned perpendicular to interface and submitted to tension until detachment. microTBS decreased from the center to the extremes in group A (Spearman tests p < 0.0008) and not in group B, where microTBS was higher in extremes than in correspondent locations in group A and equivalent to that in group A in the central location. Weibull's analysis showed that m modulus and characteristic stresses also decreased from the center to periphery of restorations in group A. Mechanical resistance of bonded interface of a luting material and dentin decreases peripherally, and this reduction is caused by polymerization contraction.

Relationship between postendodontic pain, tooth diagnostic factors, and apical patency.

This study compares the incidence, degree, and length of postoperative pain in 300 endodontically treated teeth, with and without apical patency, in relation to some diagnostic factors (vitality, presence of preoperative pain, group, and mandible of treated tooth). Of the questionnaires received back, apical patency was maintained during shaping procedures with a #10 K-file in one group (n = 115) and not in the other (n = 121). There was significantly less postendodontic pain when apical patency was maintained in nonvital teeth. If pain appeared, its duration was longer when apical patency was maintained in teeth with previous pain or located in the mandible. Maintenance of apical patency does not increase the incidence, degree, or duration of postoperative pain when considering all variables together.

Microtensile bond strength of self-adhesive luting cements to ceramic.

PURPOSE: To test the null hypothesis that three self-adhesive luting materials had the same microtensile bond strength when used to lute ceramic IPS Empress II disks to the dentin of perfused teeth. MATERIALS AND METHODS: Occlusal enamel and the roots of 9 human third molars were removed and crown segments connected to a perfusion system (30 cm H2O). Nine ceramic disks (IPS Empress II) were prepared, conditioned with 5% HF (20 s), rinsed with water, and air dried. A primer silane agent was applied (Monobond-S) for 60 s and air dried. Teeth were bonded to disks using one of three materials: Multilink System, RelyX Unicem, or Panavia F light. Specimens were vertically sectioned to obtain square bars. Each bar was fixed to a rigid custom-made tensile device and submitted to tensile force until debonding. Microtensile bond strength (microTBS) was given in MPa. Because the means of bonded areas (BA) were different between groups, it was impossible to compare microTBS results directly. Thus, the regression line TBS(MPa) = -2.15 + [19.92 / BA (mm(2))] was calculated to correlate microTBS results and BA. Residuals (difference between the value estimated by the regression line and the actual value) were stored as "distances". ANOVA was performed to examine the statistical significance of differences between means distances of the groups', and the Tamhane's post hoc test was used to locate eventual differences. RESULTS: The number of bars used in the analysis was n = 147. Residuals should not be statistically different if the null hypothesis (represented by the regression line) was credible. ANOVA showed statistically significant differences between the distances of the groups' means (p < 0.00001). Tamhane's post hoc test (p < 0.05) showed that different group means were RelyX < Multilink < Panavia F. CONCLUSION: The null hypothesis was rejected: materials showed different tensile bond strengths. Panavia F obtained highest bonding values, followed by Multilink System. RelyX Unicem, the only material that does not require pretreatment of dentin, achieved the lowest TBS values under these study conditions.

Effects of etching time of primary dentin on interface morphology and microtensile bond strength.

OBJECTIVES: To determine the influence of different etching times (5, 15 or 30 s) on the morphology and micro-tensile bond strength (muTBS) of primary dentin. METHODS: For muTBS study, nine primary molars were randomly distributed in three experimental groups. Three Class I cavities per tooth were drilled and etched (37% orthophosphoric acid gel for 5, 15 or 30 s). Excite adhesive was applied and cavities restored with a resin composite (Tetric Ceram). Composite/dentin bars (ca. 1 mm2 section) were obtained from teeth and tested in tension until debonding. Means of muTBS results were compared with ANOVA and Student-Neuman-Keuls post hoc tests. Morphology: Three occlusal cavities were prepared in five primary molars. Each cavity was etched and restored as described for previous groups and teeth were sectioned mesio-distally. One half of each tooth was prepared for using under optical microscopy using Masson's trichromic dye technique and the other half was examined by SEM. RESULTS: muTBS mean (S.D.) results (in MPa) were 5 s etch: 6.20 (2.81), 15 s: 13.43 (5.91), 30 s: 13.04 (5.67). muTBS groups were Excite 5 s < Excite 15 s = Excite 30 s. Masson's trichromic technique stained the demineralized dentin layer red in all specimens. The mean (S.D.) thickness of the demineralized layers (in mu) were 5 s: 3.28 (1.23), 15 s: 3.83 (1.26), 30 s: 4.44 (1.70). There is a statistically significant linear relationship between time of application of etching and mean depth of demineralized layer. This relationship was established as depth (in mu) = 3.08 + 0.05 time (in s). SIGNIFICANCE: The minimum adequate etching time for primary dentin is 15s.

Method to compare mu-tensile bond strength of a self-etching adhesive and mu-cohesive strength of adjacent dentin.

UNLABELLED: Laboratory results from tensile or micro-tensile testing of adhesive/restorative systems need a gold standard to make their interpretation possible. This can be done by comparing the mu-tensile bond strength (muTBS) of the tested adhesive(s) with the mu-tensile cohesive strength (muTCS) of the adjacent dentin, which is meant to be replaced by the restoration. OBJECTIVES: To test immediate muTBS of an adhesive/restorative system versus muTCS of the dentin adjacent to the bonded interface, in perfused specimens. METHODS: Enamel and roots of five-third sound molars were removed and teeth were perfused (30 cm distilled H2O) until after the bonding procedure was completed. Parallel grooves (1.5-mm widex 1.5-mm deep, separated by 1.5mm), were drilled in the exposed dentin, under water refrigeration. Teeth were restored (AdheSE/Filtek Z250). Specimens were sawn from grooves to test muTBS (n = 30) and from between grooves to test muTCS (n = 32) of dentin, adjacent to adhesive interfaces, both areas to be tested at the same relative depth. Areas to be studied were rounded (mean bonded surface area for both groups, BA = 0.68 mm2), and muTBS and muTCS were found. As not all BAs were identical, residuals of muTBS and muTCS values to the regression line relating BA and tensile test results (representing the null hypothesis, i.e. muTBS = muTCS) were compared using a non-parametric test. RESULTS: Difference in the means of residuals was not statistically significant (two tails p = 0.067). SIGNIFICANCE: mean muTBS of the tested adhesive was not different to mean muTCS of adjacent dentine. The null hypothesis was not rejected.

Inverse relationship between tensile bond strength and dimensions of bonded area.

It is a known fact that there is a relationship between magnitude of bonded area and laboratory tensile test results. This relationship has been described for a range of areas between 1 and 10 mm(2), in extracted, nonperfused teeth. The aim of this study is to test this relationship in perfused teeth, with bonded areas ranging from 0.7 to 110.9 mm(2). Dentin of 92 sound third human molars was exposed and perfused, and three groups of bonded areas (BA) were delimited: small (0.69-1.89 mm(2)), medium (8.66-19.54 mm(2)), and large (58.91-110.86 mm(2)). Tensile bond strength (TBS) of three adhesive restorative systems was found. The best nonlinear curve estimation was searched (SPSS 9.0) between TBS and BA, for each and all materials. The best estimation was, for all materials, TBS = 4.17 + 10.35/BA (p < 0.0001).

Conventional and adhesive luting cements.

Luting materials for fixed prosthesis must fulfill special requirements in order to retain indirect restorations and fully maintain the integrity of abutments. The main requirements (inhibition of plaque accumulation, sealing of interface, possible antibacterial effects, acceptable solubility, wear, mechanical properties, adhesion, radiopacity, film thickness, type of curing, esthetics, storage, and cost) are reviewed to update clinical criteria on the selection of suitable materials. It can be concluded that there is no ideal luting material on the market. Alleged improvements in the physical data of newer materials do not necessarily result in better clinical performance. Only clinical trials can confirm the assumed benefits of materials.

Comparison of two methods to measure permeability of dentin.

Dentin permeability was measured alternatively with two methods: a 10-microl capillary method with visual evaluation (PC) and a motorized automatic measuring device (Flodec, FD), both interposed in a simulated perfusion system. Eight human third molar coronal fragments were connected to systems, and their permeability to distilled water measured at 0, 5, 10, 15, 20, 25, and 29 cm H(2)O pressure. Resultant permeabilities (in microl/s) for both techniques were interrelated with the use of the Passing and Bablok nonparametric method, which gives information about the range of constant and proportional errors and their 95% confidence intervals (95CI). The relationship between the methods is described by the regression formula: FD = -0.0003 + 0.945.PC, with 95CI for constant (-0.0015-0.0009) and for slope (0.738-1.168), indicating that both methods are interchangeable, although not identical.