Abstract
AimTo study the influence of time and volume of 2% sodium hypochlorite (NaOCl) on biofilm removal and to investigate the changes induced on the biofilm architecture. Steady‐state, dual‐species biofilms of standardized thickness and a realistic contact surface area between biofilms and NaOCl were used.Methodology Streptococcus oralis J22 and Actinomyces naeslundii T14V‐J1 biofilms were grown on saliva‐coated hydroxyapatite discs within sample holders in the Constant Depth Film Fermenter (CDFF) for 96 h. Two per cent NaOCl was statically applied for three different time intervals (60, 120 and 300 s) and in two different volumes (20 and 40 μL) over the biofilm samples. The diffusion‐driven effects of time and volume on biofilm disruption and dissolution were assessed with Optical Coherence Tomography (OCT). Structural changes of the biofilms treated with 2% NaOCl were studied with Confocal Laser Scanning Microscopy (CLSM) and Low Load Compression Testing (LLCT). A two‐way analysis of variance (2‐way anova) was performed, enabling the effect of each independent variable as well as their interaction on the outcome measures.ResultsOptical coherence tomography revealed that by increasing the exposure time and volume of 2% NaOCl, both biofilm disruption and dissolution significantly increased. Analysis of the interaction between the two independent variables revealed that by increasing the volume of 2% NaOCl, significant biofilm dissolution could be achieved in less time. Examination of the architecture of the remaining biofilms corroborated the EPS‐lytic action of 2% NaOCl, especially when greater volumes were applied. The viscoelastic analysis of the 2% NaOCl‐treated biofilms revealed that the preceding application of higher volumes could impact their subsequent removal.ConclusionsTime and volume of 2% NaOCl application should be taken into account for maximizing the anti‐biofilm efficiency of the irrigant and devising targeted disinfecting regimes against remaining biofilms.
Highlights
The oxidizing properties and reactivity of sodium hypochlorite (NaOCl) with organic matter account for its antibacterial and dissolving effect (McDonnell & Russell 1999, Estrela et al 2002), rendering it a suitable anti-biofilm root canal irrigant (Chavez de Paz et al 2010, Tawakoli et al 2015)
Biofilm dissolution The main effect of ‘Time’ was statistically significant (P = 0.001), meaning that when ‘Volume’ was not taken into account in the 2-way ANOVA, the results revealed that increasing time resulted in the reduction of the coherent biofilm layer; 300 s exposure to 2% NaOCl led to significantly more biofilm removal compared to 60 s (P < 0.001) and 120 s (P = 0.003) (Table 1)
Biofilm disruption The main effect of ‘Time’ was significant (P = 0.001), meaning that when ‘Volume’ was not taken into account in the 2-way ANOVA, the results showed that increasing time resulted in increasing biofilm disrupted layer; 300 s exposure to 2% NaOCl led to significantly more biofilm disruption compared to 60 s (P < 0.001) and 120 s (P = 0.015) (Table 1)
Summary
The oxidizing properties and reactivity of sodium hypochlorite (NaOCl) with organic matter account for its antibacterial and dissolving effect (McDonnell & Russell 1999, Estrela et al 2002), rendering it a suitable anti-biofilm root canal irrigant (Chavez de Paz et al 2010, Tawakoli et al 2015). The factors that affect the reactivity and subsequent dissolving capacity (chemical efficacy) of NaOCl have been primarily investigated on pulp tissue samples, artificial organic films and dentine (Rosenfeld et al 1978, Moorer & Wesselink 1982, Zehnder et al 2002, Sirtes et al 2005, Huang et al 2008, Macedo et al 2010, 2014a,b, Jungbluth et al 2011). This makes extrapolation of these findings on biofilm dissolution difficult. Using clinically relevant multi-species biofilms of standardized composition and maturity is required when the anti-biofilm efficacy of NaOCl is investigated
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