Matthias Zehnder

Soft Tissue Dissolution Capacity of Currently Used and Potential Endodontic Irrigants

Necrotic soft-tissue remnants in root canals may provide a source of nutrition for surviving microbiota after root-canal therapy. This study assessed the necrotic tissue dissolution capacity of some popular and some potential root-canal irrigants: 1% (wt/vol) sodium hypochlorite (NaOCl), 10% chlorhexidine, 3% and 30% hydrogen peroxide, 10% peracetic acid, 5% dichloroisocyanurate (NaDCC), and 10% citric acid. Standardized necrotic tissue samples obtained from pig palates were incubated in these solutions, and their weight loss was measured over time. None of the test solutions except sodium hypochlorite had any substantial tissue dissolution capacity. It was concluded that this might be important when considering the use of irrigants other than NaOCl.

Antimicrobial Effect of Nanometric Bioactive Glass 45S5

Most recent advances in nanomaterials fabrication have given access to complex materials such as SiO2-Na2O-CaO-P2O5 bioactive glasses in the form of amorphous nanoparticles of 20- to 60-nm size. The clinically interesting antimicrobial properties of commercially available, micron-sized bioactive glass 45S5 have been attributed to the continuous liberation of alkaline species during application. Here, we tested the hypothesis that, based on its more than ten-fold higher specific surface area, nanometric bioactive glass releases more alkaline species, and consequently displays a stronger antimicrobial effect, than the currently applied micron-sized material. Ionic dissolution profiles were monitored in simulated body fluid. Antimicrobial efficacy was assessed against clinical isolates of enterococci from persisting root canal infections. The shift from micron- to nano-sized treatment materials afforded a ten-fold increase in silica release and solution pH elevation by more than three units. Furthermore, the killing efficacy was substantially higher with the new material against all tested strains.

Effects of ethylenediaminetetraacetic, etidronic and peracetic acid irrigation on human root dentine and the smear layer

AIM To evaluate the effects of ethylenediaminetetraacetic (EDTA), etidronic (EA) and peracetic acid (PA) when used in conjunction with sodium hypochlorite (NaOCl) as root canal irrigants on calcium eluted from canals, smear layer, and root dentine demineralization after instrumentation/irrigation. METHODOLOGY Single-rooted human premolars were irrigated as follows (n = 12 per group): (1) 1% NaOCl during instrumentation, deionized water after instrumentation, (2) 1% NaOCl during, 17% EDTA after instrumentation, (3) a 1 : 1-mixture of 2% NaOCl and 18% EA during and after instrumentation, and (4) 1% NaOCl during, 2.25% PA after instrumentation. Irrigant volumes and contact times were 10 mL/15 min during and 5 mL/3 min after instrumentation. The evaluated outcomes were eluted calcium by atomic absorption spectroscopy, smear-covered areas by scanning electron microscopy in secondary electron mode and apparent canal wall decalcifications on root transsections in backscatter mode. For the smear layer analysis, sclerotic dentine was taken into consideration. Results were compared using appropriate parametric and nonparametric tests, alpha = 0.05. RESULTS The statistical comparison of the protocols regarding calcium elution revealed that protocol (1) yielded less calcium than (3), which yielded less than protocols (2) and (4). Most of the instrumented canal walls treated with one of the decalcifying agents were free of smear layer. Protocols (1) and (3) caused no decalcification of root dentine, whilst (2) and (4) showed substance typical demineralization patterns. CONCLUSIONS The decalcifying agents under investigation were all able to remove or prevent a smear layer. However, they eroded the dentine wall differently.

Hard-Tissue Debris Accumulation Analysis by High-Resolution Computed Tomography Scans

INTRODUCTION Hard-tissue debris accumulation is a potential side effect of root canal instrumentation that has not been systematically investigated. In the current communication, a method to assess this debris using high-resolution microcomputed tomography (microCT) is presented. METHODS Based on prescans, mandibular molars with joining mesial root canals and isthmuses between these were selected (n = 6). The mean volume filled with apparent hard-tissue debris after instrumentation without irrigation was calculated over 2 mm of the mesial canal system by multiplying the voxel volume with the number of voxels representing acquired radiopaque material. Backscattered electron imaging was used to compare the calcium-phosphorus content of this material with that of the root dentin in the same specimen. RESULTS Backscatter scans showed that the accumulated debris viewed in the microCT scans was consistent with root dentin. In the selected canal segments, 29.2% +/- 14.5% of the original canal volume was filled with accumulated debris, which represented a significant change from the preoperative scan (p < 0.01, one-sample t test against zero). Three-dimensional reconstructions of the microCT images visualized the accumulated hard-tissue debris in the whole canal system. CONCLUSIONS The current method appears suitable to quantitatively compare different instrumenting/irrigating regimens on dentin debris accumulation.

Microtomography-based comparison of reciprocating single-file F2 ProTaper technique versus rotary full sequence.

INTRODUCTION A preparation technique with only 1 single instrument was proposed on the basis of the reciprocating movement of the F2 ProTaper instrument. The present study was designed to quantitatively assess canal preparation outcomes achieved by this technique. METHODS Twenty-five extracted human mandibular first molars with 2 separate mesial root canals were selected. Canals were randomly assigned to 1 of the 2 experimental groups: group 1, rotary conventional preparation by using ProTaper, and group 2, reciprocate instrumentation with 1 single ProTaper F2 instrument. Specimens were scanned initially and after root canal preparation with an isotropic resolution of 20 μm by using a micro-computed tomography system. The following parameters were assessed: changes in dentin volume, percentage of shaped canal walls, and degree of canal transportation. In addition, the time required to reach working length with the F2 instrument was recorded. RESULTS Preoperatively, there were no differences regarding root canal curvature and volume between experimental groups. Overall, instrumentation led to enlarged canal shapes with no evidence of preparation errors. There were no statistical differences between the 2 preparation techniques in the anatomical parameters assessed (P > .01), except for a significantly higher canal transportation caused by the reciprocating file in the coronal canal third. On the other hand, preparation was faster by using the single-file technique (P < .01). CONCLUSIONS Shaping outcomes with the single-file F2 ProTaper technique and conventional ProTaper full-sequence rotary approach were similar. However, the single-file F2 ProTaper technique was markedly faster in reaching working length.

Accumulated hard tissue debris levels in mesial roots of mandibular molars after sequential irrigation steps

AIM To investigate the impact of sequential irrigation procedures on accumulated hard tissue debris (AHTD) levels in canal systems in mesial roots of human mandibular molars after instrumentation. METHODOLOGY Based on pre-scans in a micro-computed tomography (μCT) system, 20 extracted human mandibular molars with joining mesial root canals and an isthmus between these were selected. Canals were instrumented using the ProTaper rotary system until the F3 instrument reached working length. A 1% NaOCl solution was applied during instrumentation, followed by a final 5-mL flush to working length. Subsequently, canals were irrigated with 5 mL of 17% EDTA. Thereafter, passive ultrasonic irrigation (PUI) was performed using 1% NaOCl on three occasions each for 20 s. Percent values of total canal system volume filled with AHTD were calculated based on high-resolution scans after each irrigation step. Data was compared using repeated measure anova followed by paired t-test for individual comparisons. Bonferronis correction was applied for multiple testing; the alpha-type error was set at 1%. RESULTS Instrumentation of the root canals in conjunction with 1% NaOCl irrigation left 6.9 ± 4.2 vol.% of the total canal system volume filled with AHTD. This value was significantly (P < 0.01) reduced to 4.9 ± 3.6 vol.% after EDTA irrigation. Subsequent PUI resulted in a further significant (P < 0.01) reduction to 3.7 ± 2.8 vol.%. CONCLUSIONS In this quantitative study on AHTD reduction, a significant effect of EDTA and PUI was shown. However, approximately half of the debris that accumulated during instrumentation remained in the canal system.

Do bioactive glasses convey a disinfecting mechanism beyond a mere increase in pH

AIM To test whether bioactive glasses kill microbiota via mineralization or the release of ions other than sodium. METHODOLOGY Flame-spray synthesis was applied to produce nanometric glasses of different sodium content and constant Ca/P ratio: 28S5, 45S5 and 77S. Calcium hydroxide and nanometric tricalcium phosphate (TCP) were used as controls. Apatite induction was monitored by Raman spectroscopy. Bovine dentine disks with adherent Enterococcus faecalis cells were exposed to test and control suspensions or buffered solutions for 1 h, 1 day and 1 week. Colony-forming units were counted and disks were inspected using scanning electron microscopy. Suspension supernatants and solutions were analysed for their pH, osmolarity, calcium and silicon content. RESULTS Sodium containing glasses induced pH levels above 12, compared with less than pH 9 with sodium-free 77S. Calcium hydroxide, 45S5 and 28S5 killed all bacteria after 1 day and lysed them after 1 week. TCP caused the highest apatite induction and substantial calcification on bacteria adhering to dentine, but did not reduce viable counts. 77S achieved disinfection after 1 week without visible apatite formation, whilst the buffer solution at pH 9 caused only minimal reduction in counts. CONCLUSION Bioactive glasses have a directly and an indirectly pH-related antibacterial effect. The effect not directly linked to pH is because of ion release rather than mineralization.

The mysterious appearance of enterococci in filled root canals.

In this narrative review, the potential reasons for the high occurrence of enterococci in filled root canals are explored. The pulpless root canal appears to be a habitat for these bacteria, particularly for Enterococcus faecalis. However, re-surveying the literature in caries research, it can be concluded that, contrary to earlier belief, enterococci are rare if ever found at the advancing front of dentinal lesions. The same is the case for true primary endodontic infections, but some uncertainty remains, because the coronal seal and the history of teeth harbouring enterococci have rarely been accurately investigated. Furthermore, from longitudinal studies with a known infection at the initiation of treatment, which was carried out under controlled asepsis, it is questionable whether enterococci are as difficult to eliminate from the canal system as is commonly held. A more likely explanation for the high occurrence of enterococci in filled root canals is that they enter after treatment, but from which source? The intriguing finding in this context is that enterococci do not appear to be colonizers of the oral cavity. They are merely transient oral bacteria, unless there is a predilection site such as the unsealed necrotic or filled root canal. The origin of this infection is most likely food. Using the example of enterococci in filled root canals, this paper highlights the possible importance of transient microorganisms in the oral cavity and changes in a microenvironment that can create favourable conditions for infection.

Necrotic pulp tissue dissolution by passive ultrasonic irrigation in simulated accessory canals: impact of canal location and angulation.

AIM To evaluate whether passive ultrasonic irrigation (PUI) of 2.5% NaOCl would dissolve necrotic pulp tissue from simulated accessory root canals (SACs) better than passive placement of the irrigant, when temperature was equilibrated between the two treatments. METHODOLOGY Transparent root canal models (n = 6) were made from epoxy resin. SACs of 0.2 mm diameter were placed at defined angles and positions in the mid-canal and apical area. SACs were filled with necrotic bovine pulp tissue. PUI was performed five times for 1 min each with irrigant replenishment after every minute. Main canal temperature was measured after each minute, and a digital photograph was taken. In control experiments, mock treatments were performed with the same set-up without activation of the file using heated NaOCl to mimic the temperature created by PUI. Experiments were repeated five times. Digital photographs were analysed for the distance of dissolved tissue into the SACs in mm. Overall comparison (sum of dissolved tissue from all five accessory canals) between treatments was performed using paired t-test. Differences between SAC angulation and position after PUI were investigated using anova/Bonferroni (alpha < 0.05). RESULTS Passive ultrasonic irrigation caused a rise in irrigant temperature in the main canal to 53.5 +/- 2.7 degrees C after the fifth minute. PUI dissolved a total of 6.4 +/- 2.1 mm, mock treatment controlled for heat: 1.4 +/- 0.6 mm (P < 0.05). No significant influence of SAC position or angulation was found. CONCLUSIONS Passive ultrasonic irrigation promotes positive tissue-dissolving effects beyond a rise in irrigant temperature.

Acoustic Hypochlorite Activation in Simulated Curved Canals

INTRODUCTION It was the goal of this study to compare different NaOCl activation schemes regarding a desired and an untoward outcome. Ultrasonic tips and a currently marketed sonic system were used in conjunction with a 2.5% sodium hypochlorite solution. Necrotic pulp tissue dissolution in simulated accessory canals and transportation of the main canal were assessed. METHODS Epoxy resin models (10 per group) with a curved simulated main root canal and two simulated accessory canals filled with necrotic bovine pulp tissue were irrigated passively with one of three ultrasonic setups (straight stainless steel files, prebent stainless steel files, or nickel-titanium tips) or a sonic device in conjunction with a plastic tip. Activation was performed four times for 30 seconds with replenishment of the NaOCl solution in between. All the files/tips had a 2% taper and a 0.15-mm tip diameter according to the manufacturer. Data from superimposing and analyzing digital photos before and after treatment were statistically analyzed using one-way analysis of variance followed by Bonferronis correction for multiple comparisons (alpha < 0.05). RESULTS Passive ultrasonic irrigation (PUI) in all the groups dissolved significantly more tissue than sonic activation (p < 0.05). No detectable canal transportation with sonic activation was observed. The difference in this outcome was not significant compared with ultrasonically activated nickel-titanium tips, whereas the straight stainless steel files caused significantly more ledging compared with these setups (p < 0.05). CONCLUSION Under the current conditions, PUI with a nickel-titanium tip promoted superior tissue-dissolving effects over sonic irrigant activation while maintaining simulated canal anatomy.