Susceptibility of a Polycaprolactone-Based Root Canal Filling Material to Degradation. I. Alkaline Hydrolysis
Franklin R. Tay, BDSc (Hons), PhD, David H. Pashley, DMD, PhD, M. Chad Williams, DMD, Rakesh Raina, DDS, Robert J. Loushine, DDS, R. Norman Weller, DMD, MS, W. Frank Kimbrough, DDS, MS, and Nigel M. King, BDS, MSc, PhD
Polycaprolactone, a thermoplastic aliphatic polyester, is reportedly susceptible to both alkaline and enzymatic hydrolyzes. This screening study examined the susceptibility of Resilon, a polycaprolactone-based root filling composite, to alkaline hydrolysis. There were 15-mm diameter disks of Resilon and Obtura gutta-percha prepared by compressive molding and immersed in 20% sodium ethoxide for 20 or 60 min. Control disks were immersed in ethanol for 60 min. These disks were examined using field-emission scanning electron microscopy and energy dispersive X-ray analysis. For Resilon, the surface resinous component was hydrolyzed after 20 min of sodium ethoxide immersion, exposing the spherulitic polymer structure and subsurface glass and bismuth oxychloride fillers. More severe erosion occurred after 60 min of sodium ethoxide treatment. Gutta-percha was unaffected after immersion in sodium ethoxide. As Resilon is susceptible to alkaline hydrolysis, it is possible that enzymatic hydrolysis may occur. Biodegradation of Resilon by bacterial/salivary enzymes and endodontically relevant bacteria warrants further investigation.
Effect of Root Canal Filling/Sealer Systems on Apical Endotoxin Penetration: A Coronal Leakage Evaluation
Anne E. Williamson, DDS, MS, Deborah V. Dawson, BA, ScM, PhD, David R. Drake, MS, PhD, Richard E. Walton, DMD, MS, and Eric M. Rivera, DDS, MS
Endotoxin, elaborated by gram-negative organisms, is an important factor in apical periodontitis. The objective of this study was to evaluate the magnitude of endotoxin penetration through root canal treated teeth using a dual chamber model system. Forty-four maxillary anterior teeth were prepared endodontically and canals filled either by lateral condensation or a warm thermoplasticized technique in combination with either Roth’s 801 or AH 26 sealer. Teeth were suspended in the model system with a mixed anaerobic bacterial suspension in the upper chamber and HBSS in the lower chamber. The QCL-1000 LAL assay was used to measure endotoxin at 0, 1, 7, 14, and 21 days. Response feature analysis using trapezoidal area under the curve was performed; the four treatment groups were compared using nonparametric methods. Groups differed (p = 0.028), with thermoplasticized root canal filling/ Roth’s 801 sealer permitting the least apical endotoxin penetration. Results suggest that Roth’s 801 sealer may have a role in inhibiting endotoxin penetration.
Immunolocalization of Receptor Activator of NF Kappa B Ligand in Rat Periapical Lesions
Xiaolei Zhang, DDS, and Bin Peng, DDS, PhD
The purpose of this study is to observe the immuno-histochemical localization of Receptor Activator of NF Kappa B Ligand (RANKL) in the rat periapical lesions. Periapical lesions were induced in Sprague-Dawley (SD) rats by occlusal exposure of the pulp of their mandibular first molars. Animals were sacrificed randomly at 0, 7, 14, 21, and 28 days after the exposure and their mandibles were removed, demineralized, and embedded in paraffin. Frontal sections in the region of the first molar were prepared for enzymehistochemistry and immunohistochemistry. Tartrate-resistant acid phosphatase (TRAP)-positive cells and RANKL-positive cells could be observed on day 7. From day 7 to day 14, increasing amounts of inflammatory infiltration and alveolar bone resorption were observed in the periapical region. The expression and number of TRAP-positive cells and RANKL-positive cells were climaxed on day 14. In the 21- and 28-day samples, the expression of RANKL decreased and fewer TRAP-positive cells could be observed. These findings demonstrated that RANKL could be observed, which may be associated with the pathogenesis of periapical lesions.
Reducing Surface Tension in Endodontic Chelator Solutions Has No Effect on Their Ability to Remove Calcium from Instrumented Root Canals
Matthias Zehnder, DMD, Olivier Schicht, DMD, Beatrice Sener, and Patrick Schmidlin, DMD
The aim of this study was to evaluate the effect of reducing surface tension in endodontic chelator solutions on their ability to remove calcium from instrumented root canals. Aqueous solutions containing 15.5% EDTA, 10% citric acid, or 18% 1- hydroxyethylidene-1, 1-bisphosphonate (HEBP) were prepared with and without 1% (wt/wt) polysorbate (Tween) 80 and 9% propylene glycol. Surface tension in these solutions was measured using the Wilhelmy method. Sixty-four extracted, single-rooted human teeth of similar length were instrumented and irrigated with a 1% sodium hypochlorite solution and then randomly assigned ( n = 8 per group) to receive a final one-minute rinse with 5 ml of test solutions, water, or the pure aqueous Tween/propylene glycol solution. Calcium concentration in eluates was measured using atomic absorption spectrometry. Incorporation of wetting agents resulted in a reduction of surface tension values by approximately 50% in all tested solutions. However, none of the solutions with reduced surface tension chelated more calcium from canals than their pure counterparts (p > 0.05).
Effects of Pre-Emptive Morphine, Ibuprofen or Local Anesthetic on Fos Expression in the Spinal Trigeminal Nucleus Following Tooth Pulp Exposure in the Rat
Maria T. Locher-Claus, DDS, MS, Ty E. Erickson, DDS, M.S., Alan S. Law, DDS, PhD, William T. Johnson, DDS, MS, and G.F. Gebhart, PhD
In the present study, we used Fos expression as an index of nociceptive input to the spinal trigeminal nucleus after exposure of the coronal pulp tissue of maxillary right first molars and examined the effects of pretreatment with an opioid, a nonsteroidal anti-inflammatory drug or a local anesthetic before pulp exposure. Exposure of the tooth pulp produced a significant increase in Fos-like immunoreactivity in the superficial laminae of subnucleus caudalis; pretreatment with a control infiltration injection of saline directly above the maxillary molar 30 min before pulp exposure had no effect on Fos expression. Pretreatment with morphine 30 min before pulp exposure dosedependently (2.5, 5, and 10 mg/kg subcutaneously) reduced Fos expression in subnucleus caudalis whereas pretreatment with ibuprofen (10–100 mg/kg subcutaneously) did not significantly affect Fos expression. Local anesthetic pretreatment was effective in reducing Fos expression only for the long acting bupivacaine; lidocaine without and with epinephrine (1:100,000) failed to significantly affect Fos expression. These results suggest that pre-emptive opioid treatment can decrease postoperative central nervous system changes associated with tooth pulp injury, and therefore, may decrease postoperative pain. Given the effects of local anesthetic on Fos expression, a combination of long acting local anesthetic with pre-emptive opioid would likely be most efficacious in decreasing postoperative dental pain.
Morphological Measurements of Anatomic Landmarks in Pulp Chambers of Human Maxillary Furcated Bicuspids
Allan S. Deutsch, DMD, Barry Lee Musikant, DMD, Steven Gu, PhD, and Mario Isidro, BS
The aim of this in vitro study was to measure key morphological features of pulp chambers from furcated maxillary bicuspid teeth. There were 107 random human maxillary bicuspid teeth used. Each bicuspid was radiographed using the Trophy RVG digital imaging system and a Belmont Acuray X-ray at 70 kVp. Measurements were made using the Digipan measuring mode of the Trophy system. Results were mean (mm): pulp chamber floor to furcation: 1.85 ± 0.85; pulp chamber ceiling to furcation: 4.61 ± 1.04; cusp to furcation: 11.55 ± 1.12; cusp to pulp chamber ceiling: 6.94 ± 0.70; pulp chamber height: 2.76 ± 0.97. The measurements showing the lowest percentage variance were: cusp to furcation (9.70%) and cusp to pulp chamber ceiling (10.09%). The only measurement that was statistically the same across maxillary molars, mandibular molars and bicuspids was measurement “B,” pulp chamber ceiling to furcation. The critical distance from cusp tip to pulp chamber ceiling in bicuspids was approximately 7.00 mm.
Geometric Factors Affecting Dentin Bonding in Root Canals: A Theoretical Modeling Approach
Franklin R. Tay, BDSc (Hons), PhD, Robert J. Loushine, DDS, Paul Lambrechts, DDS, PhD,R. Norman Weller, DMD, MS, David H. Pashley, DMD, PhD
Cavity configuration factor (C-factor) is the ratio of the bonded surface area in a cavity to the unbonded surface area. In a box-like class I cavity, there may be five times more bonded surface area than the unbonded surface area. During polymerization, the volume of monomers is reduced, which creates sufficient shrinkage stresses to debond the material from dentin, thereby decreasing retention and increasing leakage. The important variables influencing bonding adhesive root-filling materials to canals was examined using a truncated inverted cone model. C-factors in bonded root canals exhibit a negative correlation with sealer thickness. For a 20 mm-long canal prepared with a size 25 file, calculated C-factors ranged from 46 to 23,461 with decreasing sealer thickness (500–1 µm), compared to a C-factor of 32 when the canal was filled only with sealer. As the thickness of the adhesive is reduced, the volummetric shrinkage is reduced, which results in a reduction in shrinkage stress (S-factor). C-factors above 954 calculated with sealer thickness smaller than 25 µm are partially compensated by increases in bonding area and decreases in shrinkage volume. However, the interaction of these two geometrically related factors (C- and S-factors) predicts that bonding of adhesive root-filling materials to root canals is highly unfavorable when compared with indirect intracoronal restorations with a similar resin film thickness.
Preparations Through All-Ceramic Restorations: Air Abrasion and Its Effect Relative to Diamond and Carbide Bur Use
Christopher R. Sabourin, DDS, MS, MSD, Brian D. Flinn, PhD, PE, David L. Pitts, DDS, MSD, Timothy L. Gatten, DDS, and James D. Johnson DDS, MS
Access through porcelain restorations is a technically delicate and stressful procedure. Although this is a common dilemma in endodontics, little research has explored alternatives in cutting through porcelain. The purpose of this study was to compare the use of a carbide bur plus water, diamond bur plus water, and air abrasion to access through porcelain. All-ceramic samples were accessed using the different techniques. Samples were evaluated using two transillumination methods, white light, and fluorescent liquid penetrant described by the American Society for Testing and Materials. Edge chipping, microcracking, and catastrophic fracture of porcelain caused by the techniques were statistically compared. Fluorescent liquid penetrant was a more sensitive method for microcrack detection. There were significant differences between the preparation techniques. Air abrasion was significantly less destructive, and caused no catastrophic fractures, edge chipping or microcracks. Preparation by air abrasion took longer to complete.
An In Vitro Evaluation of the Cytotoxicity of Various Endodontic Irrigants On Human Gingival Fibroblasts
Brian D. Barnhart, DMD, Augustine Chuang, PhD, Jurandir J. Dalle Lucca, MD, PhD, Steven Roberts, DDS, Frederick Liewehr DDS, MS, and Anthony P. Joyce, DDS
The purpose of this study was to measure the cytotoxicity of six endodontic irrigants on cultured gingival fibroblasts using the CyQuant assay. Human gingival fibroblasts were grown in Dulbecco’s Modified Eagle Medium (DMEM) containing 10% fetal bovine serum at 37°C and 5% CO2. At confluence, cells were split, plated in 96-well plates and incubated for 24-h to allow attachment. The following irrigants were tested at various concentrations: Sodium hypochlorite (NaOCl); iodine potassium-iodide (IKI); Betadine scrub (BS); calcium hydroxide [Ca(OH)₂]; chlorine dioxide (SCD) and DMEM (positive control). Experimental groups were compared by the logarithmic difference between the clinical and LD₅₀ concentrations of a particular irrigant. The results showed that IKI and Ca(OH) ₂ were significantly less cytotoxic than SCD, NaOCl, and BS. In conclusion, IKI and Ca(OH) ₂ are well tolerated by human gingival fibroblasts.
The Contribution of Friction to the Dislocation Resistance of Bonded Fiber Posts
Cecilia Goracci, Andrea Fabianelli, Fernanda T. Sadek, Federica Papacchini, Franklin R. Tay, and Marco Ferrari
This study tested the null hypothesis that the use of dentin adhesives produces no improvement on the fixation of fiber posts with resin cements in endodontically treated teeth. Post spaces were prepared in 36 single-rooted root-filled teeth. Silanized glass fiber posts were cemented to the post spaces using a selfetch (ED primer/Panavia 21) and a total etch resin cement (Excite DSC/Variolink II), with or without the accompanying dentin adhesives. Fixation strengths and interfacial ultrastructure were evaluated using a “thin slice” push-out test and transmission electron microscopy. For both resin cements, the fixation strengths obtained from specimens luted with resin cement only did not differ significantly from those in which the intraradicular dentin was first bonded with a dentin adhesive. In the presence of incomplete smear layer removal and interfacial gaps, the dislocation resistance of bonded fiber posts was contributed largely by sliding friction.
Biocompatibility In Vitro Tests of Mineral Trioxide Aggregate and Regular and White Portland Cements
Daniel Araki Ribeiro, PhD, Marco Antonio Hungaro Duarte, PhD, Mariza Akemi Matsumoto, PhD, Mariangela Esther Alencar Marques, PhD, and Daisy Maria Favero Salvadori, PhD
Mineral trioxide aggregate (MTA) and Portland cement are being used in dentistry as root end-filling materials. However, biocompatibility data concerning genotoxicity and cytotoxicity are needed for complete risk assessment of these compounds. In the present study, genotoxic and cytotoxic effects of MTA and Portland cements were evaluated in vitro using the alkaline single cell gel (comet) assay and trypan blue exclusion test, respectively, on mouse lymphoma cells. The results demonstrated that the single cell gel (comet) assay failed to detect DNA damage after a treatment of cells by MTA and Portland cements for concentrations up to 1000 µg/ml. Similarly, results showed that none of the compounds tested were cytotoxic. Taken together, these results seem to indicate that MTA and Portland cements are not genotoxins and do not induce cellular death.
Sealer Penetration and Apical Microleakage in Smear-free Dentin After a Final Rinse with Either 70% Isopropyl Alcohol or Peridex
Gregory T. Engel, DMD, MS, Gary G. Goodell DDS, MS, MA, and Scott B. McClanahan, DDS, MS
Tensioactive agents may alter dentinal wettability allowing increased sealer penetration into dentinal tubules. This may improve the apical seal and better entomb remaining bacteria. The purpose of this study was to determine if a final rinse with either 70% isopropyl alcohol or Peridex in instrumented, smearfree canals would affect apical microleakage or Roth’s 801 sealer penetration into dentinal tubules. Sixty root segments were instrumented followed by smear layer removal. The segments were randomly divided into three groups receiving a final rinse with 6% sodium hypochlorite (NaOCl), 70% isopropyl alcohol or Peridex. Obturation was completed using lateral compaction and Roth’s 801 sealer pigmented with carbon black. Microleakage was measured by fluid filtration. Sealer penetration was measured using light microscopy. No significant differences were found between groups for microleakage or sealer penetration. Although a final rinse with either 70% isopropyl alcohol or Peridex did not increase sealer penetration, neither significantly affected apical microleakage compared to NaOCl.
Essential Elements of Evidenced-Based Endodontics: Steps Involved in Conducting Clinical Research
Mahmoud Torabinejad, DMD, MSD, PhD, and Khaled Bahjri, MD, MPH††
Endodontists have the opportunity to apply relevant research findings to the care of their patients using the principles and methods of evidence-based treatment. Finding evidence begins with a specific, well-built clinical question. Once a specific question is framed, the validity and relevance of the evidence need to be appraised. The best levels of evidence can then be used to inform decisions regarding care. The purpose of this paper is to discuss the history of evidence-based treatment and to clarify the process of conducting a systematic review. The various types of research designs appropriate for answering clinical questions most commonly encountered in dental practice, including a description of the strengths and weaknesses of each, are also presented. Finally, the implications of evidence-based research on endodontics and future research are outlined.