Efficacy of an Organic Solvent and Ultrasound for Filling Material Removal

The Novel Role of Solvents in Non-Surgical Endodontic Retreatment

Non-surgical endodontic retreatment is a reliable conservative option for managing post-treatment apical periodontitis. However, effective microbial control, based on the maximization of filling removal and disinfection protocols, is not yet predictable. Traditional gutta-percha solvents, which are indistinctively used for both the core and sealer filling materials, became obsolete due to unprecedented advances in endodontic technology. Nonetheless, microtomography, scanning electronic microscopy findings, and histobacteriological analysis tend to confirm the persistence of filling materials and the lack of association between root canal enlargement and superior disinfection. There is a controversy regarding the most suitable clinical protocols surrounding the shaping procedures and the supplementary disinfection steps. Based on the literature and the previous work of the team, the authors aimed to summarize the current knowledge regarding specific solvent formulations that target filling materials. Additionally, the advantage of an additional irrigation step to optimize disinfection was highlighted. This adjunctive procedure serves a dual role in the dissolution of filling materials, and in conferring an antibiofilm effect. Further research is needed to understand the novel contribution of these strategies upon clinical practice outcomes.

Critical analysis of research methods and experimental models to study removal of root filling materials

Despite enjoying high favourable outcome rates, root canal treatment is not always successful. Root canal retreatment is a widely practised option for managing a non-healing root treated tooth. A basic distinction between retreatment and initial treatment is the requirement to remove the existing root filling material occupying the root canal space. Only then, can the technical deficiencies and possible causes of failure be addressed. Hence, the successful removal of the root filling material is critical to achieving the objectives of retreatment. Many different materials and techniques have been used for root canal filling, which have been documented in a plethora of studies; these are mainly laboratory studies investigating the removal of root filling materials. To help guide future research, which may then better inform clinical practice in relation to retreatment procedures, the focus of this narrative review is on the research methods and experimental models employed to study the removal of root filling materials. The current available literature demonstrates great variation in the research methodologies used to study the removal of root filling material, including direct visualization by splitting tooth samples or clearing, three-dimensional radiographic imaging including using microcomputed tomography or cone-beam computed tomography, and a combination of these techniques. Depending on the research method employed, variation also exists in quantification of root filling material removal; these include measurements of surface area, volume or weight, and criteria-based (semi-quantitative) assessment. Experimental models, using human teeth or resin models, differ with respect to standardization techniques and replication of the clinical scenario including initial sample preparation, canal filling, allocation and technical aspects of retreatment procedures. Future models should replicate, as closely as possible, the clinical scenario. Currently, microcomputed tomography provides a highly detailed, non-invasive and non-destructive method of objectively assessing and quantifying root filling removal.

Effect of a novel laser-initiated photoacoustic activation of a solvent or sodium hypochlorite in the removal of filling remnants after retreatment of curved root canals

BACKGROUND

This study aimed to evaluate the effect of Er:YAG laser-initiated shockwave-enhanced emission of photoacoustic streaming (SWEEPS®) and passive ultrasonic irrigation (PUI) combining thymol-based solvent or sodium hypochlorite (NaOCl) in the removal of filling remnants from curved canals.

METHODS

Forty-eight curved root canals were instrumented and filled with an epoxy-resin-based sealer and gutta-percha. The canals were retreated with a Wave One Gold primary file (tip size 25; variable taper) and sodium hypochlorite (NaOCl). After the retreatment, the samples were randomly divided into four groups according to the additional irrigation protocol: PUI/NaOCl, PUI/solvent, SWEEPS®/NaOCl or SWEEPS®/solvent. The volume of filling material in root canal was measured after root canal filling, after mechanical retreatment, after final irrigation protocol and after additional irrigation protocol, using micro-CT. The results were analyzed using Kruskal-Wallis test with the post-hoc Mann-Whitney U test and Wilcoxon test (α=0.05).

RESULTS

In the PUI group, irrigation with the solvent or NaOCl resulted in similar filling reduction (p = 0.224). In the SWEEPS® group, irrigation with NaOCl resulted in a significantly greater filling reduction compared to the solvent (p = 0.021). The SWEEPS®/NaOCl group was more effective than the PUI/NaOCl group (p = 0.008). No significant differences were found between PUI/solvent and SWEEPS® groups (p>0.05) and PUI/NaOCl and SWEEPS®/solvent group (p>0.05).

CONCLUSION

Although all tested protocols improved the removal of filling remnants from curved root canal, the SWEEPS® was more successful than PUI when NaOCl was used. Both tested techniques showed similar efficacy when in combination with the solvent.

The use of solvents for gutta-percha dissolution/removal during endodontic retreatments: A scoping review

This scoping review study aimed to map the evidence about solvents' use for gutta-percha dissolution and removal during endodontic retreatments. The study protocol followed the Joanna Briggs Institute guidelines, available online (https://osf.io/5vy8n/). Reporting was based on PRISMA Extension for Scoping Reviews. We selected dentistry studies that considered the effectiveness of solvents in gutta-percha dissolution in endodontic retreatments and compared their performance to the use of instrumentation techniques without solvents. The search and study screening were performed in PubMed and Scopus databases by two independent researchers. A descriptive analysis considered the study design, method/technique used for obturation, method/technique used for instrumentation during retreatment, solvent solutions tested, exposure time, and main findings. A total of 41 studies were included. Despite that, most studies suggested that solvents' use may complicate root canal cleanliness, regardless of the type of instrumentation used, and facilitate the presence of gutta-percha remnants in the root surface. Thus, the use of solvents should be avoided and its use should only be considered if the previous working length was not possible to access without it. Despite that, high heterogeneity was observed, further studies are still encouraged comparing the performance and effects of different solvents in different clinical scenarios.

Filling Material Removal with Reciprocating and Rotary Systems Associated with Passive Ultrasonic Irrigation

Objective:

The purpose of this ex vivo study was to evaluate the filling material removal ability, and the time required to perform this procedure, of reciprocating and conventional rotary systems when associated with passive ultrasonic irrigation.

Methods:

The palatal roots of 40 maxillary molars were submitted to root canal preparation and filling. The desobturation of root canals was initially performed with Largo burs in the coronal portion (4 mm) to drill the gutta-percha and to facilitate the action of the instruments used then. Next, the palatal roots were randomly distributed (n=10) according to the systems and irrigation protocols used for filling material removal: ProTaper universal retreatment (PTR), PTR+passive ultrasonic irrigation (PUI) (PTR+PUI), Reciproc system (RS), and RS+PUI. Passive ultrasonic activation was performed in the root canals completely filled with 2.5% sodium hypochlorite solution using a smooth and straight ultrasonic tip, coupled to a low-power (20%) ultrasonic device for 1 min (3 cycles of 20 s). After retreatment, the roots were longitudinally sectioned to the remaining filling material quantification using an operating microscope. Environmental scanning electron microscopy (ESEM) micrographs at 97, 105, and 250 X magnifications were also taken to evaluate the quantity of filling material present at the apical portion of the palatal roots.

Results:

The RS group presented greater quantity of filling material attached to the root canal walls than the other groups (P>0.05). PTR+PUI and RS+PUI groups were statistically similar (P>0.05). Reinstrumentation of root canals using RS was faster than PTR, irrespective of the irrigation protocol used (P>0.05).

Conclusion:

The association between PUI and the different systems for reinstrumentation yielded greSater filling material removal. The reciprocating system was faster.

Evaluation of Capacity of Essential Oils in Dissolving ProTaper Universal Gutta-Percha points

PURPOSE

Solvents may be used to remove the filling materials. The purpose of this in vitro study was to evaluate and compare the efficacy of formulated orange oil, orange oil and formulated eucalyptol in dissolving F3 ProTaper Universal Gutta-percha points.

MATERIAL AND METHODS

200 samples were used and divided into four groups, further divided in fifty samples for each solvent. The samples were weighed on an analytical balance before being subjected to the action of solvents. Subsequently, they were put onto watch glasses, 7X45mm in length, and immersed into solutions for the following times: 5, 10, 20, 25 and 30 minutes. The loss of mass was recorded by weighing samples after every minute of action of the solvent on the points. Data were statistically analyzed by Kruskal-Wallis test at a significance level of 5%.

RESULTS

All solvents showed that the first five minutes of action was the period of greatest dissolving power. In terms of immersion time, xylol (control group) exhibited a markedly superior ability in dissolving the gutta-percha points compared to other solvents and, also, showed statistically significant differences. A continuous dissolution was observed in all groups. Formulated orange oil presented a markedly superior solvent effect on filling materials compared to orange oil and formulated eucalyptol; however, there were no statistically significant differences.

CONCLUSION

Considering the results obtained and methodology employed, it can be concluded that xylol was the most effective solvent in dissolving gutta-percha points, followed by formulated orange oil, orange oil and formulated eucalyptol oil.

Evaluation of three different rotary systems during endodontic retreatment - Analysis by scanning electron microscopy

Background

Endodontic therapy is considered a series of important and interdependent steps, and failure of any of these steps may compromise the treatment outcome. This study aimed to evaluate the effectiveness of three different rotary systems in removing obturation materials during endodontic retreatment using scanning electron microscopy (SEM) analysis.

Material and Methods

Thirty-six endodontically treated teeth were selected and divided into 3 groups of 10 and 1 control group with 6 dental elements. The groups were divided according to the rotary system used for removing gutta-percha, as follows: G1: ProTaper system; G2: K3 system; G3: Mtwo system; and G4: Control group. Thereafter, the roots were split and the sections were observed under SEM, for analysis and counting of clear dentinal tubules, creating the variable “degree of dentinal tubule patency” (0: intensely clear; 1: moderately clear; 2: slightly clear; 3: completely blocked). The data were subjected to the Friedman and Kruskal-Wallis statistical tests.

Results

No differences were observed in the “degree of dentinal tubule patency” neither between the root thirds (to each evaluated group) nor between the groups (to each evaluated third). Nevertheless, when the three root thirds were grouped (providing evaluation of all root extension), the “degree of dentinal tubule patency” was lower in G1 than in G3 (p<0.05), but showed no differences neither between G1 and G2 nor G2 and G3.

Conclusions

No technique was able to completely remove the canal obturation material, despite G1 having shown better results, although without significant difference to G2

Key words:Scanning electron microscopy, NiTi, retreatment.