FT-Raman spectroscopy of calcium hydroxide medicament in root canals

AIM

To investigate chemical changes in calcium hydroxide introduced into human root canals as a medicament using Fourier transform-(FT) Raman spectroscopy.

METHODOLOGY

Ten necrotic maxillary anterior teeth were selected in 10 patients. The teeth were divided into five treatment groups, according to the survey time. Root canal instrumentation was performed with hand instruments until the master apical file was size 40. Calcium hydroxide paste, in a 1 : 1.25 mixture by weight of powder and distilled water, was introduced directly into the root canal with a lentulo-spiral filler and then condensed with a finger plugger. The access cavity was sealed with a temporary dressing. After 2 and 4 days, then 2, 4 and 6 weeks, the calcium hydroxide paste was sampled with a K-file and then analysed using FT-Raman spectroscopy. The excitation source was an Nd : YAG laser with an excitation wavelength of 1064 nm. All spectra were taken with a laser power of 200 mW, 275-1185 scans, and 4 cm(-1) resolution. The conversion of calcium hydroxide to calcium carbonate was calculated on the basis of the spectral data obtained from the mixtures of both compounds.

RESULTS

The calcium hydroxide paste in the apical region showed weak bands at 1088 and 284 cm(-1), in addition to bands associated with calcium hydroxide. The weak bands, assigned to calcium carbonate, became stronger with time. Calcium carbonate content increased rapidly in the first 2 days and then tended to increase slowly. Approximately 11% of the calcium hydroxide at the apical portion of the canal was converted to calcium carbonate after 6 weeks. However, little alteration of the paste was noticed in the samples from the middle portion of the canal.

CONCLUSIONS

Calcium hydroxide medicament in root canals became transformed into calcium carbonate in the apical region within 2 days. Although the transformation continued with time, approximately 90% of the calcium hydroxide remained unchanged after 6 weeks.

Microorganisms growth in endodontic citric-acid solutions with and without microbiological stabilizer

The purpose of this study was to determine if citric-acid solutions for endodontic use can become contaminated and if the addition of a microbiological stabilizer to the acid would modify this situation. Five types of microorganisms were inoculated in tubes containing 10% citric-acid solutions, pH 1.8 (group A1), and 10% solution, pH 1.8, combined with 0.1% sodium benzoate (group A2). The results demonstrated that solutions of group A1 were contaminated with Candida albicans in 100% of the tubes, Escherichia coli in 80%, and Enterococcus faecalis in 50%. When stabilizer was added (group A2), C. albicans grew in only 30% of tubes and all bacterial species were neutralized.

Diffusion of calcitonin through the wall of the root canal

The aim of this study was to evaluate the in vitro diffusion of synthetic salmon calcitonin (CT), used as an intracanal medication, to the external root surface, with or without the presence of intact root cementum. Fifty-four human central incisors were used in the experiment, and were divided into two groups of 21 (test groups) and two groups of 6 teeth (control groups). After root canal preparation, 10 ml of calcitonin was inserted within the root canal chamber. The root was sealed and made externally impermeable. Specimens were then placed in tubes with saline solution buffered with phosphates and stored at 37°C. The diffusion of calcitonin was measured after 1, 4 and 7 days. To count calcitonin present at the external media (PBS), ELISA test (an antigen-antibody reaction) was used. Results showed that there was calcitonin diffusion through dentin in all of the test samples. The absence of cementum increased the diffusion of calcitonin (p=0.05). The highest counts of CT were obtained on day 7 for groups with or without cementum - showing a direct relation between time and diffusion of the medication.

Evaluation of pH levels and calcium ion release in various calcium hydroxide endodontic dressings

OBJECTIVE

The purpose of this study was to evaluate Ca(2+) release and pH of 3 calcium hydroxide-based products used routinely as intracanal dressings, as well as the new gutta-percha points with calcium hydroxide.

STUDY DESIGN

The pH and Ca(2+) release were assessed using Calen with camphorated paramonochlorophenol, saline calcium hydroxide paste, LC paste (Lopes and Costa paste-calcium hydroxide with olive oil), and calcium hydroxide containing gutta-percha points. The materials were inserted in polyethylene tubes and immersed in deionized water. The pH variation and Ca(2+) release were monitored periodically for 4 weeks.

RESULTS

After 72 hours, materials 1 and 2 raise the pH from 9.6 and 8.2 to 11.4 and 11.3, respectively, while a small change was observed for materials 3 and 4. The calcium concentration released from materials 1, 2, 3, and 4 after 72 hours was 6.54, 4.98, 1.31, and 1.74 mg/dL, respectively.

CONCLUSION

Calen plus camphorated paramonochlorophenol and saline calcium hydroxide paste exhibited the highest calcium release and pH levels.

Effect of medications for root canal treatment on bonding to root canal dentin

Use of resin-based restorative materials recently has become widely accepted for treatment of endodontically treated teeth. However, some solutions routinely used during endodontic treatment procedures may have an effect on bond strengths of adhesive materials to root canal dentin. The purpose of this in vitro study was to evaluate the effect of various medications on microtensile bond strength to root canal dentin. Fourteen extracted human single-rooted teeth were used. The crowns and the pulp tissues were removed. The root canals were then instrumented and widened to the same size. The teeth were randomly divided into seven groups of two teeth each. The root canal dentin walls of the roots were treated with 5% sodium hypochloride (NaOCI), 3% hydrogen peroxide (H2O2), the combination of H2O2 and NaOCl, or 0.2% chlorhexidine gluconate for 60 s; or calcium hydroxide or formocresol for 24 h. The teeth in control group were irrigated with water. The root canals were obturated using C&B Metabond. After 24 h of storage in distilled water, serial 1-mm-thick cross-sections were cut, and approximately 12 samples were obtained from each group. Microtensile bond strengths to root canal dentin were then measured by using an Instron machine. The data were recorded and expressed as MPa. The results indicated that NaOCI, H2O2, or a combination of NaOCl and H2O2 treatment decreased bond strength to root canal dentin significantly (p < 0.05). The teeth treated with chlorhexidine solution showed the highest bond strength values (p < 0.05). In conclusion, chlorhexidine is an appropriate irrigant solution for root canal treatment before adhesive post core applications.

Evaluation of the combined solar TiO2/photo-Fenton process using multivariate analysis

The effect of combining the photocatalytic processes using TiO2 and the photo-Fenton reaction with Fe3+ or ferrioxalate as a source of Fe2+ was investigated in the degradation of 4-chlorophenol (4CP) and dichloroacetic acid (DCA) using solar irradiation. Multivariate analysis was used to evaluate the role of three variables: iron, H2O2 and TiO2 concentrations. The results show that TiO2 plays a minor role when compared to iron and H2O2 in the solar degradation of 4CP and DCA in the studied conditions. However, its presence can improve TOC removal when H2O2 is totally consumed. Iron and peroxide play major roles, especially when Fe(NO3)3 is used in the degradation of 4CP. No significant synergistic effect was observed by the addition of TiO2 in this process. On the other hand, synergistic effects were observed between FeOx and TiO2 and between H2O2 and TiO2 in the degradation of DCA.

Degradation of 4-chlorophenol mediated by Fe(III)-NTA in homogeneous and heterogeneous systems

In this work, the comparison of 4-chlorophenol (4-CP) degradation by two different AOT processes has been performed: a) a homogeneous system with Fe(III)-NTA (1:1 complex), b) a TiO2/Fe(III)-NTA heterogeneous system. In both cases, NTA appears to play a positive role in the photochemical reaction. In the homogeneous system, the iron salt is the only absorbing species and is proved to be able to photoinduce 4-CP degradation ([4-CP] = 0.1-0.2 mM, [FeNTA] = 0.3-0.9 mM, pH 4, lambda = 365 nm). The progress of the reaction was positively affected by the FeNTA concentration, and the reaction kept going even after the total disappearance of FeNTA. However, 4-CP complete degradation requires the presence of oxygen, otherwise the reaction stops. In the heterogeneous system ([4-CP] = 2.0 mM, [FeNTA] = 1.0-2.0 mM, [TiO2] = 0.1 and 1.0 g L(-1), pH 3, lambda = 300-400 nm), an important effect of the complex on the degradation extent and on the initial reaction rate can be seen, which overcomes the effect of non-complexed Fe(III). This behaviour is more important at the highest TiO2 concentration.

Mechanistic implications of the effect of TiO2 accessibility in TiO2-SiO2 coatings upon chlorinated organics photocatalytic removal in water

The photocatalytic removal rates r of dichloroacetic acid (DCAA), 4-chlorobenzoic acid (4-CBA) and 4-chlorophenol (4-CP) in water were compared for TiO2 samples used either as a powder or as a coating on a fiber glass tissue, SiO2 being the binder. From SEM-EDX measurements it was deduced that SiO2 prevails over TiO2 in the coating top layers and 18O2-Ti16O2 isotopic exchange showed that the accessibility of O2 to TiO2 was markedly reduced when TiO2 was thus coated. The unfavorable effect of the restricted TiO2 accessibility on r was drastic for DCAA, much less pronounced for 4-CBA, and still smaller for 4-CP. It is inferred that DCAA can be attacked only when it directly interacts with TiO2, whereas 4-CP can also react within the near-TiO2 surface water layers. The 4-CBA intermediate behavior is in line with the structural similarities of 4-CBA with DCAA and 4-CP.

Influence of different vehicles on the pH of calcium hydroxide pastes

The main known benefit of calcium hydroxide as an intracanal medicament lies in the bactericidal effect conferred by its pH. The objective of this work was to determine the influence of the vehicle on the pH of calcium hydroxide pastes after usage in patients and in vitro. The incisor root canals of 180 patients were instrumented and filled with calcium hydroxide pastes containing distilled water, chlorhexidine, propylene glycol, anesthetic solution, camphorated p-monochlorophenol and camphorated p-monochlorophenol-propylene glycol. The pH of the paste in the patients' root canals was measured at 7, 14 and 21 days. Similarly, pH was measured in vitro up to 21 days. The pH of all the pastes remained constant throughout the time periods assessed. The calcium hydroxide-water combination showed significantly higher pH values than the other pastes in clinical use. Comparative analysis showed that the pH values of the anesthetic solution, camphorated p-monochlorophenol and camphorated p-monochlorophenol-propylene glycol were significantly higher in vitro. The type of vehicle was shown to influence the final pH of the pastes. However, the alkalinity of all pastes was maintained over time under the experimental conditions.

Chelating agents in root canal treatment: mode of action and indications for their use

Chelating agents were introduced into endodontics as an aid for the preparation of narrow and calcified root canals in 1957 by Nygaard-Østby. A liquid solution of ethylenediaminetetraacetic acid (EDTA) was thought to chemically soften the root canal dentine and dissolve the smear layer, as well as to increase dentine permeability. Although the efficacy of EDTA preparations in softening root dentine has been debated, chelator preparations have regained popularity recently. Almost all manufacturers of nickel-titanium instruments recommend their use as a lubricant during rotary root canal preparation. Additionally, a final irrigation of the root canal with 15-17% EDTA solutions to dissolve the smear layer is recommended in many textbooks. This paper reviews the relevant literature on chelating agents, presents an overview of the chemical and pharmacological properties of EDTA preparations and makes recommendations for their clinical use.

Photochemistry of 4-chlorophenol on cellulose and silica

The photochemistry of 4-chlorophenol (4-CP) was studied on silica and cellulose, using time-resolved diffuse reflectance techniques and product degradation analysis. The results have shown that the photochemistry of 4-CP depends on the support, on the concentration, and also on the sample preparation method. Transient absorption and photoproduct results can be understood by assuming the formation of the carbene 4-oxocyclohexa-2,5-dienylidene in both supports. On cellulose, at concentrations lower than 10 micromol g(-1), the carbene leads to the unsubstituted phenoxyl radical, and phenol is the main degradation product. At higher concentrations a new transient resulting from phenoxyl radicals coupling was also observed, and dihydroxybiphenyls are also formed. The reaction of the carbene with ground-state 4-CP was also detected through the formation of 5-chloro-2,4'-dihydroxybiphenyl. 4-Chlorophenoxyl radical and degradations products resulting from its coupling were also detected. Oxygen has little effect on the photochemistry of 4-CP on cellulose. On silica the transient benzoquinone O-oxide was formed in the presence of oxygen. Benzoquinone and hydroquinone are the main degradation products. In well-dried samples the formation of hydroquinone is reduced. At higher concentrations the same products as detected on cellulose were observed. 4-CP undergoes slow photochemical decomposition under solar radiation in both supports. The same main degradation products were observed in these conditions.

Evaluation of penetration and adaptation of three different sealers: a SEM study

In this study, dentinal penetration and adaptation of three endodontic sealers were evaluated by using scanning electron microscope (SEM). Seventeen recently extracted, human maxillary anterior teeth were used. After the crowns were removed from the cementoenamel junction, the root canals were instrumented. The teeth were then randomly divided into three groups of five roots each and two teeth were used as controls. The smear layer was removed with EDTA and NaOCl. The canals were obturated with AH 26, CRCS, RSA sealers and gutta-percha using lateral condensation technique. Each root was sectioned longitudinally and then prepared for SEM evaluation. The SEM results showed that AH 26 was the best sealer penetrating into dentinal tubules and adapted to dentinal walls when compared with the CRCS and RSA. The CRCS and RSA occluded the orificies of dentinal tubules. The RSA showed that the penetration was less than AH 26 and more than CRCS.

Influence of torque control motors and the operator's proficiency on ProTaper failures

OBJECTIVE

The purpose of this study was to evaluate the influence of 2 electric torque control motors and operator experience with a specific nickel-titanium rotary instrumentation technique on the incidence of deformation and separation of instruments.

STUDY DESIGN

ProTaper (PT) nickel-titanium rotary instruments were used at 300 rpm. In the first part of the study, electric high torque control (group 1) and low torque control (group 2) motors were compared. In the second part of the study, 3 operators with varying experience (groups 3, 4, and 5) were also compared. Twenty sets of PT instruments and 100 canals of extracted human molars were used in each group. Each set of PT instruments was used in up to 5 canals and sterilized before each case. For irrigation, 2.5% NaOCl was used. The number of deformed and separated instruments among the groups (within each part of the study) was statistically analyzed for significance with pair-wise comparisons by using the Fisher exact test (alpha =.05).

RESULTS

In part 1, instrument deformation and separation did not occur in groups 1 and 2. In part 2, 25 and 12 instruments were deformed and separated, respectively, with the least experienced operator. Instrument deformation and separation did not occur with the most experienced operator. The Fisher exact test revealed a significant difference between groups 3 and 4 with respect to instrument deformation (P =.0296). In addition, the Fisher exact test revealed that the incidence of instrument deformation was statistically different between groups 3 and 5 (P <.0001) and groups 4 and 5 (P =.0018). The incidence of instrument separation was significantly higher in group 5 than in groups 3 and 4 (P =.001).

CONCLUSIONS

Preclinical training in the use of the PT technique at 300 rpm is crucial to prevent instrument separation and reduce the incidence of instrument deformation. The use of an electric high torque control motor is safe with the experienced operator.

Calcium hydroxide's association with different vehicles: In vitro action on some dentinal components

OBJECTIVE

Calcium hydroxide, Ca(OH)(2), is a common intracanal medicament. Ca(OH)(2) powder can be mixed with different vehicles and used as a paste for temporary intracanal treatment. The vehicle may influence the dissociation of calcium hydroxide into ions. We sought to evaluate the level of pH and to quantitatively estimate the release of proteins, hydroxyproline, and phosphorus from pieces of radicular dentin kept in different Ca(OH)(2) solutions.

STUDY DESIGN

Twenty-eight extracted incisors were maintained for 35 days in Ca(OH)(2) aqueous solutions prepared in chlorhexidine digluconate, propylene glycol (PG), anesthetic solution, camphorated monochlorophenol (CMCP), and CMCP-PG. The control solution contained Ca(OH)(2) without vehicle.

RESULTS

The pH values changed little during the experiment. The concentrations of proteins, hydroxyproline, and phosphorus rose for all the solutions under study. Statistical analysis of the data from the control and the experimental groups revealed an increase in the concentration of proteins when chlorhexidine, anesthetic solution, and PG were used; a rise in hydroxyproline levels when CMCP-PG, CMCP, and PG solutions were used; and an increase in phosphorus when PG and chlorhexidine vehicles were used.

CONCLUSION

The test solutions with the root dentin remained alkaline. A release of proteins, hydroxyproline, and phosphorus was observed.

The effect of various intracanal oxidizing agents on the push-out strength of various perforation repair materials

OBJECTIVE

The purpose of this study was to determine the effect of intracanal oxidizing agents on the strength of materials used to repair root perforations.

STUDY DESIGN

Standardized perforations in bovine root samples were repaired with mineral trioxide aggregate (MTA), Super-EBA cement (S-EBA), or intermediate restorative material (IRM). After 7 days, 10 samples from each group were tested for push-out strength with an Instron machine (controls). The remaining samples were immersed in NaOCl, sodium perborate mixed with saline (SPB+S), Superoxol (SO), sodium perborate mixed with Superoxol (SPB+SO), or saline for 7 days to investigate the effect of irrigating and walking bleach compounds on the perforation repair materials. Push-out strength values were compared with those of the dry materials to determine whether any loss of integrity had occurred.

RESULTS

MTA was statistically significantly less resistant across conditions to displacement than S-EBA or IRM. IRM was consistent across treatment conditions, whereas S-EBA lost strength when exposed to NaOCl, SPB+S, or SPB+SO. Exposure to SPB+S had the greatest effect on all 3 materials.

CONCLUSIONS

IRM performed consistently as a perforation repair material despite exposure to oxidizing agents, whereas MTA was less resistant to dislodgement than either IRM or S-EBA and was more affected than IRM by sodium perborate-containing bleaching solutions.

A new solution for the removal of the smear layer

Various organic acids, ultrasonic instruments, and lasers have been used to remove the smear layer from the surface of instrumented root canals. The purpose of this study was to investigate the effect of a mixture of a tetracycline isomer, an acid, and a detergent (MTAD) as a final rinse on the surface of instrumented root canals. Forty-eight extracted maxillary and mandibular single-rooted human teeth were prepared by using a combination of passive step-back and rotary 0.04 taper nickel-titanium files. Sterile distilled water or 5.25% sodium hypochlorite was used as intracanal irrigant. The canals were then treated with 5 ml of one of the following solutions as a final rinse: sterile distilled water, 5.25% sodium hypochlorite, 17% EDTA, or a new solution, MTAD. The presence or absence of smear layer and the amount of erosion on the surface of the root canal walls at the coronal, middle, and apical portion of each canal were examined under a scanning electron microscope. The results show that MTAD is an effective solution for the removal of the smear layer and does not significantly change the structure of the dentinal tubules when canals are irrigated with sodium hypochlorite and followed with a final rinse of MTAD.

Mechanism of action of sodium hypochlorite

The choice of an irrigating solution for use in infected root canals requires previous knowledge of the microorganisms responsible for the infectious process as well as the properties of different irrigating solutions. Complex internal anatomy, host defenses and microorganism virulence are important factors in the treatment of teeth with asymptomatic apical periodontitis. Irrigating solutions must have expressive antimicrobial action and tissue dissolution capacity. Sodium hypochlorite is the most used irrigating solution in endodontics, because its mechanism of action causes biosynthetic alterations in cellular metabolism and phospholipid destruction, formation of chloramines that interfere in cellular metabolism, oxidative action with irreversible enzymatic inactivation in bacteria, and lipid and fatty acid degradation. The aim of this work is to discuss the mechanism of action of sodium hypochlorite based on its antimicrobial and physico-chemical properties.

Ferrioxalate-mediated photodegradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND

Advanced oxidation processes are powerful methods which are capable of transforming refractory, nonbiodegradable and/or toxic organic compounds into harmless end products such as carbon dioxide and water. However, one commen problem of all advanced oxidation processes is the high demand of electrical energy for ultraviolet lamps, which causes high operational costs. Minimization of the required irradiation time, and therefore the energy consumption, by optimization of other reaction conditions such as catalyst-oxidant type and concentration, pH, temperature, pollutant/oxidant ratio etc., therefore continues to gain importance.

OBJECTIVE

The main objective of this study was the minimization of the required irradiation time through optimization of the use of a newly patented catalyst, ferrioxalate, and also to compare the performance of this catalyst with the performance of other AOPs.

METHODS

Oxidation of 4-chlorophenol by photo-Fenton process using potassium ferrioxalate as a mediator was studied in a lab scale photoreactor. The influence of parameters such as hydrogen peroxide and ferrioxalate concentrations, initial pH, power-output, oxalate/iron ratio and different iron sources was evaluated. An upflow photoreactor equipped with a 1000 Watt high-pressure mercury vapour lamp and operating in a recirculation mode was used during photodegradation experiments. The extent of the reduction of 4-chlorophenol, Total Organic Carbon and Chemical Oxygen Demand was used to evaluate the photodegradation reaction.

RESULTS AND DISCUSSION

The optimum pH range observed was found to be 2.7-3. The efficiency of 4-chlorophenol oxidation increased with increasing concentrations of hydrogen peroxide and ferrioxalate, reaching a plateau after the addition of 10 and 0.072 mM of those reagents, respectively. Using an Oxalate/iron ratio of 12 was 18% less efficient than using a ratio of 3:1. The efficiency increased with increasing radiation power. However, this increase was not linear. The UV/ferrioxalate/H2O2 process, by which complete mineralization of 100 mg l(-1) 4-chlorophenol was achieved in 20 min of total reaction time, was the most efficient process among the alternatives applied.

CONCLUSIONS

The use of ferrioxalate as the catalyst was found to be more efficient than the use of Fe(II) and Fe(III) iron species. It was possible to completely mineralize 4-chlorophenol.

RECOMMENDATION AND OUTLOOK

The results of this study demonstrate that the ferrioxalate-mediated degradation of 4-chlorophenol requires less irradiation times than other advanced oxidation processes. There are mainly 19 phenol isomers and other toxic and nonbiodegradable organic compounds. We recommend that similar studies should be performed on many such compounds in order to attain a clear understanding of the performance of this catalyst. Because of its light sensitivity, this catalyst should be used immediately after its preparation. The use of low pressure mercury vapour lamps in this process should also be considered, since low power outputs may be enough for the process.

The effect of endodontic solutions on resorcinol-formalin paste

This study determined if any of four endodontic solutions would have a softening effect on resorcinol-formalin paste and if there were any differences in the solvent action between these solutions. Resorcinol, formalin, and zinc oxide were mixed and allowed to set for 30 days. The solutions tested were 0.9% sodium chloride, 5.25% sodium hypochlorite, chloroform, and Endosolv R. Seven samples per solution were tested and an additional seven samples served as controls. Each sample was saturated with one of the solutions and the depth of penetration was tested at 1, 2, 5, 10, and 20 min using a dial strain gauge. At 2 min, sodium hypochlorite and sodium chloride had significantly greater penetration than the other groups (p < 0.0010). Sodium hypochlorite was superior to all other groups after 5 min. This study showed that both sodium chloride and sodium hypochlorite exhibited a significant softening effect within 2 min.

Effect of NaOCl treatment on bond strength between indirect resin core-buildup and dentin

The aim of this study was to investigate the bond strength between indirect resin core-buildup and dentin treated with or without hypochlorite (NaOCl) gel. The post-space was made in five extracted human molars with obturated root canals, and the indirect resin core was produced on a gypsum model. Then, the dentin surface was treated with/without NaOCl, followed by luting of the resin core into the cavity. After storage for 24 h in 37 degrees C water, the specimens were sectioned for measuring bond strength to the root and coronal dentin, and were subjected to micro-tensile bond strength (MTBS) testing. Two-way ANOVA showed that significant differences in MTBS were revealed for both factors of NaOCl treatment and dentin region. It is concluded that, for indirect resin core-buildup, the proper use of the NaOCl gel to dentin could increase the bond strength.

Tissue-dissolving capacity and antibacterial effect of buffered and unbuffered hypochlorite solutions

OBJECTIVE

The goal of this study was to compare the dissolving potential of Dakin's solution with that of equivalent buffered and unbuffered sodium hypochlorite solutions on fresh and decayed tissues. In addition, the antimicrobial effect of Dakin's solution and equivalent unbuffered hypochlorite was tested.

STUDY DESIGN

Tissue specimens were obtained from freshly dissected pig palates. Unbuffered 2.5% and 0.5% sodium hypochlorite solutions and 0.5% solutions buffered at a pH of 12 and a pH of 9 (Dakin's solution) were tested on fresh and decayed tissue. Tissue decay was assessed histologically. Antimicrobial testing was performed with Enterococcus faecalis in dentin blocks and on filter papers.

RESULTS

The 2.5% NaOCl solution was substantially more effective than the three 0.5% solutions in dissolving the test tissues. Buffering had little effect on tissue dissolution, and Dakin's solution was equally effective on decayed and fresh tissues. No differences were recorded for the antibacterial properties of Dakin's solution and an equivalent unbuffered hypochlorite solution.

CONCLUSIONS

In contrast to earlier statements, the results of this study do not demonstrate any benefit from buffering sodium hypochlorite with sodium bicarbonate according to Dakin's method. An irrigation solution with less dissolving potential may be obtained by simply diluting stock solutions of NaOCl with water.

Influence of irrigants on the coronal microleakage of laterally condensed gutta-percha root fillings

AIM

To assess in vitro coronal microleakage in extracted human teeth after root-canal treatment, using different endodontic irrigants.

METHODOLOGY

Fifty teeth with single root canals were prepared and filled using the lateral condensation of gutta-percha and Endométhasone sealer. Canal preparation consisted of initial shaping of the coronal two-thirds with Gates-Glidden burs size 2 and 3, followed by preparation of the apical stop and step-back flaring with manual files. Each group (n = 10) was irrigated with the following solutions: I--1% NaOCl, II--1% NaOCl + 17% EDTA, III--2% chlorhexidine gel, IV--2% chlorhexidine gel + 1% NaOCl, and V--distilled water. After root-canal filling, the teeth were incubated at 37 degrees C for 10 days followed by 10 days immersion in human saliva and an additional 10 days in India ink. The teeth were cleared and maximum dye penetration was determined digitally in millimetres. Statistical analysis was carried out using the Kruskal-Wallis test.

RESULTS

Least leakage occurred with 1% NaOCl + 17% EDTA (2.62 mm) and 2% chlorhexidine gel (2.78 mm) (P > 0.05). NaOCl (3.51 mm), distilled water (6.10 mm) and 2% chlorhexidine gel + 1% NaOCl (9.36 mm) gave increased leakage with a significant difference compared to NaOCl + 17% EDTA and 2% chlorhexidine gel, and compared to one another (P < 0.05).

CONCLUSIONS

Under the condition of this study, irrigation method during root-canal treatment influenced coronal microleakage. NaOCl + EDTA and chlorhexidine gel allowed better sealing following root filling.

Inactivation of the antibacterial activity of iodine potassium iodide and chlorhexidine digluconate against Enterococcus faecalis by dentin, dentin matrix, type-I collagen, and heat-killed microbial whole cells

The antibacterial activity of chlorhexidine digluconate and iodine potassium iodide on Enterococcus faecalis A197A was tested in the presence of dentin, dentin matrix, dentin pretreated by EDTA and citric acid, collagen, and heat-killed cells of Enterococcus faecalis and Candida albicans. Medications were preincubated for 1 h with each of the potential inhibitors and tested for their antibacterial activity against E. faecalis, strain A197A. Surviving bacteria were sampled after 1 and 24 h of incubation. Dentin matrix and heat-killed microbial cells were the most effective inhibitors of chlorhexidine, whereas dentin pretreated by citric acid or EDTA showed only slight inhibition. Dentin and skin collagen showed some inhibition at 1 h but not after 24 h. Iodine potassium iodide was effectively inhibited by dentin, dentin matrix, and heat-killed microbial cells. Skin collagen and dentin pretreated by EDTA or by citric acid showed little or no inhibitory effect on iodine potassium iodide. Different components of dentin are responsible for the divergent patterns of inhibition of the antibacterial activity of chlorhexidine digluconate and iodine potassium iodide. Chemical treatment of dentin before applying the medication into the root canal may alter the antibacterial effect of the medication.