M. Marending

Comparative assessment of time-related bioactive glass and calcium hydroxide effects on mechanical properties of human root dentin

Suspensions of micro- or nanoparticulate SiO(2)-Na(2)O-CaO-P(2)O(5) bioactive glasses could potentially be used as dressings in traumatized front teeth with open apices as an alternative to Ca(OH)(2). These materials have a disinfecting capacity similar to Ca(OH)(2), but bear the advantage of bioactivity. However, because bioactive glasses initially act as alkaline biocides just as Ca(OH)(2) does, they may also negatively affect mechanical dentin properties over time. This was assessed in the current study using standardized human root dentin bars. Specimens were immersed in 1:20 (wt vol(-1)) suspensions of nanometric bioactive glass 45S5 or calcium hydroxide for 1, 10, or 30 days. Control specimens were immersed in pure saline for 30 days (n = 20 per group). Subsequently, modulus of elasticity (E) and flexural strength (FS) of the specimens were determined. Results were compared between groups using one-way anova and Scheffés post-hoc test. Ca(OH)(2) caused a significant (P < 0.001) 35% drop in mean flexural strength values compared to the control treatment after 10 days. No further change was observed between 10 days and 30 days. Bioactive glass caused a 20% drop in mean flexural strength as compared to the control after 10 days. However, this difference did not reach statistical significance (P > 0.05). No effects of either material on dentin modulus of elasticity values were observed. It was concluded that the calcium hydroxide suspension affected the dentin more than the bioactive glass counterpart; however, the effect was self-limiting and probably restricted to superficial dentin layers, as suggested by the mere decrease in flexural strength but not in modulus of elasticity values.

Stabilizing sodium hypochlorite at high pH: effects on soft tissue and dentin.

INTRODUCTION When sodium hypochlorite solutions react with tissue, their pH drops and tissue sorption decreases. We studied whether stabilizing a NaOCl solution at a high pH would increase its soft-tissue dissolution capacity and effects on the dentin matrix compared with a standard NaOCl solution of the same concentration and similar initial pH. METHODS NaOCl solutions were prepared by mixing (1:1) a 10% stock solution with water (standard) or 2 mol/L NaOH (stabilized). Physiological saline and 1 mol/L NaOH served as the controls. Chlorine content and alkaline capacity of NaOCl solutions were determined. Standardized porcine palatal soft-tissue specimens and human root dentin bars were exposed to test and control solutions. Weight loss percentage was assessed in the soft-tissue dissolution assay. Three-point bending tests were performed on the root dentin bars to determine the modulus of elasticity and flexural strength. Values between groups were compared using one-way analysis of variance with the Bonferroni correction for multiple testing (α < .05). RESULTS Both solutions contained 5% NaOCl. One milliliter of the standard and the stabilized solution consumed 4.0 mL and 13.7 mL of a 0.1-mol/L HCl solution before they reached a pH level of 7.5, respectively. The stabilized NaOCl dissolved significantly more soft tissue than the standard solution, and the pH remained high. It also caused a higher loss in elastic modulus and flexure strength (P < .05) than the control solutions, whereas the standard solution did not. CONCLUSIONS NaOH-stabilized NaOCl solutions have a higher alkaline capacity and are thus more proteolytic than standard counterparts.

Apical fit of initial K-files in maxillary molars assessed by micro-computed tomography.

AIM To two- and three-dimensionally assess the fit of the first K-file binding at working length after a crown-down canal procedure. METHODOLOGY Twelve maxillary molars with fully developed roots and four separate root canals were selected. Canals were pre-flared using ProFile 0.04 instruments to three quarters of estimated working length (WL). WL was electronically determined using an ISO 06 K-file. Progressively larger K-files were inserted passively to WL. The first binding file was termed initial apical file (IAF). On micro-computed tomography (microCT) scans, cross-sectional areas of IAFs and canals and the largest and smallest root canal diameters were measured 1 mm from instrument tips. Volumes of the apical 2 mm of the instruments and corresponding root canal sections were calculated, and file binding was assessed. RESULTS IAF sizes ranged from ISO-size 0.08-0.30 and were lowest in second mesiobuccal and highest in palatal canals. Files bound in the apical 2 mm in 96% of the canals. The mean canal area filled by the instruments 1 mm from the tip was below 40% in all canal types, the filled volume below 50% (anova, P > 0.05). The mean ratio (+/-SD) between largest and smallest canal diameter was 3.0 +/- 2.6 for first mesiobuccal, 3.3 +/- 2.6 for second mesiobuccal, 4.1 +/- 3.5 for distobuccal and 1.6 +/- 0.4 for palatal canals, indicating oval to flattened cross-sections. CONCLUSIONS Two- and three-dimensional analysis of microCT scans revealed that whilst IAFs bound in the apical area, their fit was poor, because their shape does not correspond to maxillary molar canal anatomy.

Primary assessment of a self-adhesive gutta-percha material

AIM To evaluate a prototype gutta-percha material (Bio-Gutta), which is claimed to work without sealer because of its incorporated ultrafine bioactive glass particles, in terms of its induction of pH and calcium phosphate (CaP) precipitates, and its self-adhesiveness in root canals. METHODOLOGY Bio-Gutta was compared with conventional gutta-percha (GP, composition: 70 wt% ZnO, 30 wt% polyisoprene). Test and control materials (N = 3) were immersed in phosphate-buffered saline (PBS) at 37 °C for 30 days. The pH in the solution was monitored. Apparent CaP formation was assessed using scanning electron microscopy (SEM). The root canals of 33 single-rooted teeth were filled by vertical compaction of heated Bio-Gutta, 33 control canals were filled with vertically compacted GP without sealer. Push-out bond strengths associated with the filling materials in root cross-sections from middle root thirds was determined 1, 8, and 30 days after root filling (N = 11 per group). These values were compared between groups using one-way anova (α < 0.05). RESULTS Bio-Gutta induced a high pH in the PBS solution, which plateaued at values between 11.4 and 11.8. Apparent CaP crystals covered the Bio-Gutta material after 30 days of immersion in PBS, whilst no such structures were observed on GP. Both materials under investigation had similar initial push-out bond strength values (P > 0.05). The adherence of Bio-Gutta increased from day 1 to 8 and was significantly higher than that of conventional GP at 8 and 30 days (P < 0.05). CONCLUSIONS The experimental gutta-percha material under investigation was alkaline and caused CaP precipitates on its surface. It improved its adherence to the root canal wall within 1 week.

Initial apical fit of K-files versus LightSpeed LSX instruments assessed by micro-computed tomography

AIM To compare the apical fit in two dimensions of the first K-file versus the first Lightspeed LSX instrument binding at working length after an initial crown-down preparation. METHODOLOGY Twenty maxillary molars with fully developed roots and four separate root canals were selected. Canals were pre-flared with ProFile.04 taper instruments to three quarters of estimated working length. Working length was electronically determined using a size 06 K-file. Progressively larger K-files were inserted passively to working length. The first binding K-file was termed initial apical file (IAF). Then, the first binding LSX initial apical lightspeed-instrument (IAL) was determined. Teeth were scanned with and without instruments in place using micro-computed tomography. Cross-sections of the apical part of the root canals were analysed as follows: the largest and smallest diameters of the root canal and the diameter of the instrument were calculated and related to each other. Statistics were performed using Kruskal-Wallis test and Wilcoxon test. The alpha-type error was set at 0.05. RESULTS Initial apical file sizes ranged from 8 to 30 and were lowest in second mesiobuccal and highest in palatal canals. IAL sizes ranged from size 20 to 40. The apical large canal diameter was assessed more accurately by the LSX instruments (P < 0.0001). However, the smallest available LSX instrument (i.e. size 20) did not reach working length in 39 of 80 canals. CONCLUSIONS Instruments with a flat widened tip were found to determine apical cross-sectional diameter better than round, tapered instruments.