The trend of radiographic healing after root canal treatment in teeth with apical periodontitis based on cone-beam computed tomography: A 4-year longitudinal study.

OBJECTIVES: The aim of this study was to observe the radiographic healing of periapical lesions after root canal treatment via volumetric measurements based on cone-beam computed tomography (CBCT) over 4 years. METHODS: In total, 162 single-root teeth from patients with chronic periapical periodontitis who underwent primary root canal treatment were included in this retrospective study. Follow-up visits were scheduled at 1, 2, and 4 years after treatment. The volume of radiolucency at pretreatment and follow-up were measured, and the radiographic outcomes were classified into 4 categories: absence, reduction, uncertain or enlargement. Reduction or enlargement was considered when the volumetric change in radiolucency was 20 % or more. RESULTS: During the 4-year follow-up period, 128 teeth were reviewed at least once, including 3 extracted teeth. Of the remaining 125 teeth, the volume of radiolucency was reduced in 116 teeth (90.6 %), uncertain in 5, and enlarged in 4 teeth during 1 to 4 years after treatment. Among the 43 teeth with reduced radiolucency at 1 year after treatment, 42 (97.7 %) had continuing reduced lesions at 4 years. In the 2 teeth with enlarged radiolucency at 1 year, the volume of radiolucency doubled at 4 years. Cox regression analysis revealed that the preoperative radiolucency size was a risk factor for persistent periapical radiolucency. CONCLUSIONS: The efficacy of root canal treatment for apical periodontitis was predictable. When the radiolucency changed by 20 % or more in volume on CBCT scans at 1 year after treatment, reversal of the radiographic healing tendency was rare. CLINICAL SIGNIFICANCE: The volumetric changes in radiolucency on CBCT could reflect trends in the healing process and may foster early clinical decision-making.

Radiographic healing after a root canal treatment performed in single-rooted teeth with and without ultrasonic activation of the irrigant: a randomized controlled trial.

INTRODUCTION: The aim of this study was to compare the outcome of a root canal treatment with and without additional ultrasonic activation of the irrigant. METHODS: Single-rooted teeth with radiographic evidence of periapical bone loss were randomly assigned to 2 treatment groups. In both groups syringe irrigation was performed, and in one group the irrigant was also activated by ultrasound. Ten to 19 months after treatment, the teeth were examined by using periapical radiography (PA) and cone-beam computed tomography (CBCT). Area and volume of the periapical lesions were measured, and the outcome was presented in 4 categories: absence, reduction or enlargement of the radiolucency, or uncertain. Lesions were classified as reduced or enlarged when the change in size of the radiolucency was 20% or more. RESULTS: The recall rate was 82%, and 84 teeth were analyzed. CBCT detected significantly more post-treatment lesions than PA (P = .038), but the percentages of absence and reduction of the radiolucency together revealed by CBCT and PA were similar (P = .383). The CBCT results showed that absence of the radiolucency was observed in 16 of 84 teeth (19%) and reduction of the radiolucency in 61 of 84 teeth (72.6%), but there was no significant difference between the results of the 2 groups (P = .470). Absence and reduction of the radiolucency together were observed in the ultrasonic group in 39 of 41 teeth (95.1%) and in the syringe group in 38 of 43 teeth (88.4%). CONCLUSIONS: Root canal treatments with and without additional ultrasonic activation of the irrigant contributed equally to periapical healing.

Sodium chloride and potassium sorbate: a synergistic combination against Enterococcus faecalis biofilms: an in vitro study.

Incomplete disinfection of the root canal system is a major cause of post-treatment disease. This study aimed to investigate the disinfecting property of organic acid salts and sodium chloride (NaCl), in a double-hurdle strategy, on Enterococcus faecalis biofilms. First of all, the high-throughput resazurin metabolism assay (RMA) was used to test a range of organic acid salts. Then, to gain more insight into the efficacy of sorbate salt solutions, 48-h E. faecalis biofilms were evaluated in colony-forming unit (CFU) assays. Chlorhexidine (CHX) and calcium hydroxide [Ca(OH)(2) ] were tested in parallel as controls. Sorbate salt produced the largest and most significant reduction of fluorescence intensity in the RMA assay. Neither NaCl nor potassium sorbate (KS) alone induced a clinically relevant reduction of CFU counts after 1 h. Surprisingly, the combination of the two in a single solution had a synergistic effect on the inactivation of E. faecalis. Potassium sorbate amplified the efficacy of NaCl. Of the salts tested, NaCl with KS eradicated E. faecalis biofilms within 1 h. This study showed that the double-hurdle strategy indeed leads to synergistic efficacy and is a possible next step in the complete disinfection of endodontic infections.

Comparison of the cleaning efficacy of different final irrigation techniques.

INTRODUCTION: The aim of this study was to evaluate the removal of dentin debris from artificially made grooves in standardized root canals by 6 different final irrigation techniques. METHODS: Conventional syringe irrigation, manual dynamic activation (MDA) with tapered or nontapered gutta-percha (GP) cones, the Safety Irrigator system, continuous ultrasonic irrigation (CUI), and apical negative pressure (ANP) irrigation were tested ex vivo in 20 root canals with a standardized, debris-filled groove in the apical portion of one canal wall. After each irrigation procedure, the groove was photographed, and the residual amount of dentin debris was scored. RESULTS: There was no significant difference between the MDA with a nontapered GP cone, the Safety Irrigator, and the ANP irrigation. These techniques produced better cleaning efficacy than syringe irrigation (P < .005) but significantly worse than the MDA with a tapered cone (P < .05). CUI was significantly better than all the other techniques tested in this study (P < .001). CONCLUSIONS: CUI was the most effective technique in dentin debris removal from the apical irregularities, and syringe irrigation alone was the least effective. MDA technique was more effective with a tapered GP cone than with a nontapered one.

Irrigant flow beyond the insertion depth of an ultrasonically oscillating file in straight and curved root canals: visualization and cleaning efficacy.

INTRODUCTION: The purpose of this study was to evaluate the influence of the insertion depth of an ultrasonically oscillating file on the ability to remove dentin debris from simulated canal irregularities in an extracted tooth model of a straight root canal and its influence on the flow of irrigant in both straight and curved canals. METHODS: A tooth model with artificial depressions in 1 canal wall at 0.5, 2, 4, and 6 mm from the working length was used. Ultrasonic-activated irrigation was performed with the file inserted 1, 2, 3, 4, or 5 mm short of the working length. Dye penetration and high-speed recordings of the flow in straight and curved canals showed the static and dynamic behavior of the flow during ultrasonic activation. RESULTS: The overall cleaning efficacy decreased with increasing distance between the file and the apex, with the depressions next to the file and within 3 mm in front of the file being the cleanest. The flow observed from the visualization experiments matched this distance, suggesting a direct relation between flow and cleaning. The observed flow depth increased with increasing power setting; the curvature of the root canal had no influence on the flow depth. High-speed imaging showed a start-up phase with deeper fluid activation than in the steady phase afterward. CONCLUSIONS: The ultrasonically oscillating file could remove dentin debris up to 3 mm in front of the file tip, coinciding with the extent of the observed flow. The root canal curvature had no influence on the irrigant flow.

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles.

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip.

The influence of the ultrasonic intensity on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: It is not clear whether increasing the ultrasonic intensity would enhance the cleaning efficacy of passive ultrasonic irrigation (PUI) inside a root canal. The aim of this study was to evaluate the effect of the ultrasonic intensity on PUI to remove dentin debris and whether there is any lateral effect beyond the ultrasonic tip. METHODS: Each of 15 in vitro root canal models with four standard depressions in the apical part of one canal wall were filled with dentin debris and received PUI repeatedly. The most apical depression was localized apically from the ultrasonic tip. The highest intensity was applied in group 1, the lowest intensity was applied in group 3, and syringe irrigation was performed in group 4 as a control. Before and after irrigation, images of the canal wall with depressions were taken and compared. The removal of dentin debris in the depression was categorized as clean or not clean. The data were analyzed by means of the chi-square test. The oscillation amplitude of the ultrasonic file at each intensity was recorded in vitro using time-resolved high-speed imaging. RESULTS: Group 1 (highest intensity) exhibited significantly better cleaning than all the other groups (P < .05); no significant difference was found between the four levels of the depressions within any of the four groups. High-speed imaging showed that the amplitude of the oscillating file increased as the intensity went up, which leads to a higher velocity of the irrigant around the file. CONCLUSIONS: Higher ultrasonic intensity resulted in a higher amplitude of the oscillating file and, consequently, enhanced the cleaning efficacy of PUI.

Resazurin metabolism assay for root canal disinfectant evaluation on dual-species biofilms.

INTRODUCTION: Endodontic infections are caused by polymicrobial biofilms. Therefore, novel root canal disinfectants should be evaluated not only on single-species biofilms but also on dual- or mixed-species biofilms. A simple, high-throughput assay is urgently needed for this. In this study, the application of the resazurin metabolism assay was investigated for the evaluation of a root canal disinfectant on dual-species biofilms. METHODS: Enterococcus faecalis with or without Streptococcus mutans in biofilms were formed in an active attachment biofilm model for 24 hours. Subsequently, the biofilms were treated with various concentrations of NaOCl for 1 minute. After resazurin metabolism by both organisms was confirmed, treatment efficacies using 0.0016% resazurin were evaluated. RESULTS: During NaOCl treatments, resazurin metabolism displays a clear dose response, not only in single-species E. faecalis (or S. mutans) biofilms but also in dual-species biofilms. Notably, the assay revealed that the resistance of dual-species biofilms to NaOCl was 30-fold higher than in single-species E. faecalis biofilms. Viability counts on a selected NaOCl treatment (0.004%) confirmed this result and showed the increased resistance of E. faecalis in dual-species biofilms. CONCLUSIONS: Clearly, the high-throughput and low cost resazurin metabolism assay has a great potential for testing novel root canal antimicrobial agents in mixed-species biofilms.

An evaluation of the effect of pulsed ultrasound on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: Multiple activations of the irrigant by using pulsed ultrasound may enhance the removal of dentin debris because of repeated acceleration of the irrigant. The aim of this study was to evaluate the effect of pulsed ultrasound on passive ultrasonic irrigation (PUI) in its ability to remove artificially placed dentin debris from a simulated apical oval extension within standardized root canals. METHODS: Each of 20 in vitro root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either without pulsation (group 1) or with pulsation (730 milliseconds on/100 milliseconds off in group 2, 400 milliseconds on/400 milliseconds off in group 3, and 100 milliseconds on/670 milliseconds off in group 4), corresponding to duty cycles of 100%, 88%, 50%, and 13%, respectively. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by taking photographs of the groove and scoring. The irrigation procedures were also visualized in vitro using high-speed imaging performed in glass root canal models. RESULTS: The debris score was significantly lower only in group 3 (p = 0.023). The in vitro visualization showed increased streaming and cavitation during the start-up phase of each pulse. CONCLUSIONS: PUI with a pulsation pattern of 400 milliseconds on/400 milliseconds off and a duty cycle of 50% is more effective in removing dentin debris from a simulated apical oval extension in standardized root canals than continuous ultrasonic activation. Duty cycles of 13% and 88% showed no difference compared with continuous oscillation.

Influence of the oscillation direction of an ultrasonic file on the cleaning efficacy of passive ultrasonic irrigation.

INTRODUCTION: The cleaning mechanisms and characteristics of passive ultrasonic irrigation (PUI) are not yet completely understood. The aim of this study was to investigate whether the oscillatory direction of the ultrasonically driven file had an influence on dentin debris removal from artificially made grooves in standardized root canals. METHODS: Each of 20 ex vivo root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either with file oscillation toward the groove or with file oscillation perpendicular to the groove. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by photographs of the groove and by scoring. The oscillations of the ultrasonic file were also visualized in vitro by using high-speed imaging at a time scale relevant to the cleaning process, order 10 microseconds. RESULTS: A nonparametric analysis showed significantly more dentin debris reduction when the file oscillated toward the groove (P = .002). High-speed imaging showed that the oscillation of the file is in a single plane, resulting in high-velocity jets emanating from the file tip in the direction of the oscillations. CONCLUSIONS: Oscillation of the ultrasonically driven file toward the groove is more effective in removing dentin debris from the groove than oscillation perpendicular to the groove, which can be related to the fact that there is a high-velocity jet from the file tip in a single direction following the file oscillation and a relatively slow inflow in the perpendicular direction.

Evaluation of a sonic device designed to activate irrigant in the root canal.

INTRODUCTION: The aims of this study were to evaluate the removal of dentin debris from the root canal by sonic or ultrasonic activation of the irrigant and the physical mechanisms of sonic activation by visualizing the oscillations of the sonic tip, both inside and outside the confinement of the root canal. METHODS: Roots of 18 canines were embedded, split, and prepared into standardized root canals. A standard groove was cut on the wall of one half of each root canal and filled with the same amount of dentin debris before irrigation procedures. The removal of dentin debris was evaluated after different irrigation procedures. The oscillations of the sonic tip were visualized ex vivo by using high-speed imaging at a time scale relevant to the irrigation process, and the oscillation amplitude of the tip was determined under 20x magnification. RESULTS: After irrigation, there was a statistically significant difference between the experimental groups (P < .0001). Without irrigant activation, the grooves were still full of dentin debris. From the ultrasonic activated group, 89% of the canals were completely free of dentin debris, whereas from the sonic group, 5.5%-6.7% were (P = .0001). There was no significant difference between the sonic activation groups. CONCLUSIONS: Activation of the irrigant resulted in significantly more dentin debris removal; ultrasonic activation was significantly more efficient than sonic activation. The oscillation amplitude of the sonically driven tips is 1.2 +/- 0.1 mm, resulting in much wall contact and no cavitation of the irrigant.

Influence of Streptococcus mutans on Enterococcus faecalis biofilm formation.

INTRODUCTION: An important virulence factor of Enterococcus faecalis is its ability to form biofilms. Most studies on biofilm formation have been carried out by using E. faecalis monocultures. Given the polymicrobial nature of root canal infections, it is important to understand biofilm formation of E. faecalis in the presence of other microorganisms. METHODS: Eight clinical strains of E. faecalis were tested for biofilm formation on hydroxyapatite disks in the presence and absence of a Streptococcus mutans biofilm. RESULTS: Significantly more E. faecalis viable cells were found in biofilms in the presence of S. mutans. This phenomenon was, however, strain-dependent. Of the 8 strains tested, biofilm formation of strains AA-OR34, ER5/1, and V583 was not influenced by S. mutans biofilms. CONCLUSIONS: The results from this study, especially the strain difference, underline the importance of studying biofilm formation in a more realistic multispecies setting.