PRIASE 2021 guidelines for reporting animal studies in Endodontology: explanation and elaboration

Laws and ethics require that before conducting human clinical trials, a new material, device or drug may have to undergo testing in animals in order to minimize health risks to humans, unless suitable supporting grandfather data already exist. The Preferred Reporting Items for Animal Studies in Endodontology (PRIASE) 2021 guidelines were developed exclusively for the specialty of Endodontology by integrating and adapting the ARRIVE (Animals in Research: Reporting In Vivo Experiments) guidelines and the Clinical and Laboratory Images in Publications (CLIP) principles using a validated consensus-based methodology. Implementation of the PRIASE 2021 guidelines will reduce potential sources of bias and thus improve the quality, accuracy, reproducibility, completeness and transparency of reports describing animal studies in Endodontology. The PRIASE 2021 guidelines consist of a checklist with 11 domains and 43 individual items and a flowchart. The aim of the current document is to provide an explanation for each item in the PRIASE 2021 checklist and flowchart and is supplemented with examples from the literature in order for readers to understand their significance and to provide usage guidance. A link to the PRIASE 2021 explanation and elaboration document and PRIASE 2021 checklist and flowchart is available on the Preferred Reporting Items for study Designs in Endodontology (PRIDE) website (http://pride-endodonticguidelines.org/priase/).

PRIASE 2021 guidelines for reporting animal studies in Endodontology: a consensus-based development

Animal testing is crucial in situations when research on humans is not allowed because of unknown health risks and ethical concerns. The current project aims to develop reporting guidelines exclusively for animal studies in Endodontology, using an established consensus-based methodology. The guidelines have been named: Preferred Reporting Items for Animal Studies in Endodontology (PRIASE) 2021. Nine individuals (PD, VN, AK, PM, MN, JF, EP, JJ and SJ), including the project leaders (PD, VN) formed a steering committee. The steering committee developed a novel checklist by adapting and integrating their animal testing and peer review experience with the Animals in Research: Reporting In Vivo Experiments (ARRIVE) guidelines and also the Clinical and Laboratory Images in Publications (CLIP) principles. A PRIASE Delphi Group (PDG) and PRIASE Online Meeting Group (POMG) were also formed. Thirty-one PDG members participated in the online Delphi process and achieved consensus on the checklist items and flowchart that were used to formulate the PRIASE guidelines. The novel PRIASE 2021 guidelines were discussed with the POMG on 9 September 2020 via a Zoom online video call attended by 21 individuals from across the globe and seven steering committee members. Following the discussions, the guidelines were modified and then piloted by several authors whilst writing a manuscript involving research on animals. The PRIASE 2021 guidelines are a checklist consisting of 11 domains and 43 individual items together with a flowchart. The PRIASE 2021 guidelines are focused on improving the methodological principles, reproducibility and quality of animal studies in order to enhance their reliability as well as repeatability to estimate the effects of endodontic treatments and usefulness for guiding future clinical studies on humans.

Electrokinetic transport and distribution of antibacterial nanoparticles for endodontic disinfection

AIM

To assess a novel, noninvasive intervention capable of mobilizing charged antibacterial nanoparticles to the apical portions of the root canal system, utilizing the principles of electrokinetics.

METHODS

Experiments were conducted in three stages. Stage-1: A computer model was generated to predict and visualize the electric field and current density distribution generated by the proposed intervention. Stage-2: Transport of chitosan nanoparticles (CSnp) was evaluated qualitatively using a transparent microfluidic model with fluorescent-labelled CSnp. Stage-3: An ex vivo model was utilized to study the antimicrobial efficacy of the proposed treatment against 3-week-old monospecies E. faecalis biofilms. Scanning electron microscopy (SEM) was also utilized in this stage to confirm the deposition of CSnp.

RESULTS

The results of the computer simulations predicted an electric field and current density that reach their maxima at the apical constriction of the root canal. Correspondingly, the microfluidic experiments demonstrated rapid, controlled CSnp transport throughout the simulated root canal anatomy with subsequent distribution and deposition in the apical constriction as well as periapical regions. Infected root canals when subjected to the novel treatment method resulted in a mean bacterial reduction of 2.1 log CFU. SEM analysis revealed electrophoretic deposition of chitosan nanoparticles onto the root canal dentine walls in the apical region.

CONCLUSION

The findings from this study demonstrate that the combination of cationic antibacterial nanoparticles with a low-intensity electric field results in particle transportation (electrophoresis) and deposition within the root canal. This results in a synergistic antibiofilm efficacy and has the potential to enhance root canal disinfection.

Efficacy of bioactive nanoparticles on tissue-endotoxin induced suppression of stem cell viability, migration and differentiation

AIM

To characterize a lipopolysaccharide (LPS)-treated dentine tissue model (LPS dentine) to analyse the efficacy of polycationic chitosan nanoparticles (CSnp) and/or dexamethasone conjugate chitosan nanoparticles (Dex-CSnp) on the viability/differentiation potential of stem cells from apical papilla (SCAP) when exposed to LPS dentine. A further aim was to understand the effect of macrophage-dependent inflammation on SCAP migration in the presence of LPS dentine.

METHODOLOGY

A total of 88 dentine slabs were used. TOF-SIMS analysis was performed amongst the LPS-treated and untreated dentine groups (n = 2/group). The study was conducted using four dentine groups: no treatment (control); LPS treatment only; LPS treatment followed by CSnp conditioning; and LPS treatment followed by Dex-CSnp conditioning groups. SCAP adherence, viability, differentiation and biomineralization potential on dentine from different groups were studied using fluorescent and scanning electron microscopy. Inflammation by macrophages in response to LPS dentine was quantified, and effect on SCAP migration was analysed. Statistical analysis was performed using Student's t-test with a significance level of P < 0.05.

RESULT

TOF-SIMS analysis confirmed LPS contamination. LPS dentine affected SCAP viability but not adherence to dentine (P < 0.001). Conditioning of LPS dentine with either nanoparticles improved SCAP viability (P < 0.01) and rescued other LPS related adverse effects on SCAPs, such as F-actin disruption, decrease in differentiation/biomineralization potential. IL-6 produced by macrophages in response to LPS-treated dentine impeded SCAP migration (P < 0.001), diminished on CSnp and Dex-CSnp conditioning groups (P < 0.01).

CONCLUSION

This study developed an LPS-dentine model and highlighted the ability of CSnp and Dex-CSnp to promote stem cell viability, migration, differentiation potential and reduce inflammation, providing an environment conducive for tissue regeneration/repair.

Alternative model for cathepsin K activation in human dentin

OBJECTIVE

To evaluate the protease activity in dentin matrices subjected to lactic acid (LA) in comparison to polyacrylic acid (PAA) challenge model at cathepsin K (CT-K) optimum pH 5.5 to assess effectiveness of inhibitors in dentin collagen degradation.

METHODS

Dentin disks measuring 0.5mm prepared from human molars were completely demineralized in 10% H₃PO₄. Demineralized dentin disks were challenged with 0.1M LA, 1.1mM PAA, artificial saliva (AS), or deionized water (C) for 24h or 7-days. Dentin collagen properties were tested by measurement of %dry mass change, and ultimate tensile strength (UTS). Degradation of dentin type I collagen was measured by telopeptide assays measuring the sub-product release of C-terminal cross-linked telopeptides (ICTP) and C-terminal peptide (CTX) in the incubation media in relation to total protein concentration, which correlates with matrix metalloproteinases (MMPs) and CT-K activities.

RESULTS

Gravimetric analysis showed statistically significant difference between C and other groups (p<0.04) at 24h. LA specimens showed significantly higher weight loss from 24h to 7-days (p=0.02). UTS revealed statistically significant difference between AS and LA at 24h and 7-days. UTS at 24h and 7-days for C and AS had significantly higher mean values compared to LA and PAA. Telopeptide assays reported that CTX_tp results showed that LA at 24h had significantly higher mean values compared to C and AS.

SIGNIFICANCE

LA has the ability to activate endogenous CT-K in dentin as measured by the release of CTX (CT-K specific telopeptide). This LA based model has the potential application for further investigations on the activity and possible inhibitors of CT-K in human dentin.

Preferred Reporting Items for Animal Studies in Endodontology: a development protocol

The regulated use of animals in endodontic research is often necessary to investigate the biological mechanisms of endodontic diseases and to measure the preclinical efficacy, biocompatibility, toxicology and safety of new treatments, biomaterials, sealers, drugs, disinfectants, irrigants, devices and instruments. Animal testing is most crucial in situations when research on humans is not ethical, practical or has unknown health risks. Currently, there is a wide variability in the quality of manuscripts that report the results of animal studies. Towards the goal of improving the quality of publications, guidelines for preventing disability, pain, and suffering to animals, and enhanced reporting requirements for animal research have been developed. These guidelines are referred to as Animals in Research: Reporting In Vivo Experiments (ARRIVE). Henceforth, causing any form of animal suffering for research purposes is not acceptable and cannot be justified under any circumstances. The present report describes a protocol for the development of welfare and reporting guidelines for animal studies conducted in the specialty of Endodontology: the Preferred Reporting Items for Animal Studies in Endodontology (PRIASE) guidelines. The PRIASE guidelines will be developed by adapting and modifying the ARRIVE guidelines and the Clinical and Laboratory Images in Publication (CLIP) principles. The development of the new PRIASE guidelines will include a five-step consensus process. An initial draft of the PRIASE guidelines will be developed by a steering committee. Each item in the draft guidelines will then be evaluated by members of a PRIASE Delphi Group (PDG) for its clarity using a dichotomous scale (yes or no) and suitability for its inclusion using a 9-point Likert scale. The online surveys will continue until each item achieves this standard, and a set of items are agreed for further analysis by a PRIASE Face-to-face Consensus Meeting Group (PFCMG). Following the consensus meeting, the steering committee will finalize and confirm the PRIASE guidelines taking into account the responses and comments of the PFCMG. The PRIASE guidelines will be published and disseminated internationally and updated periodically based on feedback from stakeholders.

Inflammatory potential of monospecies biofilm matrix components

AIM

To assess the inflammatory potential of biofilm matrix constituents of Enterococcus faecalis and Pseudomonas aeruginosa monospecies biofilms on macrophages.

METHODOLOGY

In vitro biofilms of E. faecalis and P. aeruginosa were grown (7 days) in aerobic and anaerobic conditions. The biofilm matrix components: exopolysaccharides (EPS) and extracellular DNA (eDNA) were extracted and quantified. The inflammatory potential of EPS and eDNA was assessed on macrophage cell lines (RAW 267.4) using nitric oxide (NO), and enzyme-linked immunosorbent assay for tumour necrosis factor (TNF-α) and interleukin-6 (IL-6) expressions. LPS from P. aeruginosa and planktonic bacteria were positive controls. One-way analysis of variance and the Tukey post hoc test were used for statistical analysis.

RESULTS

Extracted EPS from both biofilm strains was associated with higher levels than eDNA in both growth conditions (P < 0.05). The biofilm components had less inflammatory potential compared to planktonic bacteria and LPS. EPS produced higher levels of inflammatory response compared to eDNA for both strains (P < 0.05). IL-6 and TNF-α, and NO expression showed no difference for E. faecalis EPS (P ≥ 0.05). In contrast, P. aeruginosa EPS and eDNA had significant levels of IL-6 compared to TNF-α and NO (P < 0.05).

CONCLUSIONS

Monospecies biofilm matrix EPS and eDNA from the bacterial strains tested had the ability to induce a low-grade inflammatory response when compared to planktonic bacteria and LPS. This study highlights the potential of biofilm matrix/components, devoid of bacteria to induce low-grade chronic inflammation.

Biomechanical studies on the effect of iatrogenic dentin removal on vertical root fractures

Introduction

The aim of this study was to understand the mechanism by which iatrogenic root dentin removal influences radicular stress distribution and subsequently affects the resistance to vertical root fractures (VRF) in endodontically treated teeth.

Materials and Methods

The experiments were conducted in two phases. Phase 1: freshly extracted premolar teeth maintained in phosphate-buffered saline were instrumented to simulate three different degrees of dentin removal, designated as low, medium, and extreme groups. Micro-Ct analyzes were performed to quantitatively determine: (a) the amount of dentin removed, (b) the remaining dentin volume, and (c) the moment of inertia of root dentin. The specimens were then subjected to thermomechanical cycling and continuous loading to determine (a) the mechanical load to fracture and (b) dentin microcracking (fractography) using scanning electron microscopy. Phase 2: Finite element analysis was used to evaluate the influence of dentin removal on the stress distribution pattern in root dentin. The data obtained were analyzed using one-way ANOVA and Tukey's post hoc test (P < 0.05).

Results

Phase 1: A significantly greater volume of dentin was removed from teeth in extreme group when compared to low group (P < 0.01). The mechanical analysis showed that the load to fracture was significantly lower in teeth from extreme group (P < 0.05). A linear relationship was observed between the moment of inertia and load to fracture in all experimental groups (R² = 0.52). Fractography showed that most microcracks were initiated from the root canal walls in extreme group. Phase 2: The numerical analysis showed that the radicular stress distribution increased apically and buccolingually with greater degree of root canal dentin removal.

Conclusions

The combined experimental/numerical analyses highlighted the influence of remaining root dentin volume on the radicular bending resistance, stress distribution pattern, and subsequent propensity to VRF.

Characterizing bubble dynamics created by high-intensity focused ultrasound for the delivery of antibacterial nanoparticles into a dental hard tissue

Hig hintensity focused ultrasound (HIFU) has been applied for drug delivery in various disease conditions. Delivery of antibacterial-nanoparticles into dental hard tissues may open up new avenues in the treatment of dental infections. However, the basic mechanism of bubble dynamics, its characterization, and working parameters for effective delivery of nanoparticles, warrants further understanding. This study was conducted to highlight the basic concept of HIFU and the associated bubble dynamics for the delivery of nanoparticles. Characterization experiments to deliver micro-scale particles into simulated tubular channels, activity of ultrasonic bubbles, and pressure measurement inside the HIFU system were conducted. Subsequently, experiments were carried out to test the ability of HIFU to deliver nanoparticles into human dentine using field emission scanning electron micrographs (FESEM) and elemental dispersive X-ray analysis (EDX). The characterization experiments showed that the bubbles collapsing at the opening of tubular channels were able to propel particles along their whole length. The pressure measured showed sufficient negative and positive pressure suggesting that the bubble grew to a certain size before collapsing, thus enabling the particles to be pushed. The FESEM and EDX analysis highlighted the ability of HIFU to deliver nanoparticles deep within the dentinal tubules. This study highlighted the characteristics and the mechanism involved of the bubbles generated by the HIFU and their capability to deliver nanoparticles.

Bioactivity of novel carboxymethyl chitosan scaffold incorporating MTA in a tooth model

AIM

To characterise the bioactivity of a novel carboxymethyl chitosan (CMCS) scaffold with and without incorporating mineral trioxide aggregate (MTA) in a tooth model.

METHODOLOGY

Cross-linked CMCS scaffold (CaC) and MTA-coated CaC (CaMT) scaffold were prepared by freeze-drying. The bioactivity of the scaffolds was tested in vitro in four different mineralisation solutions (bulk system) and ex vivo in simulated body fluid (SBF) in the tooth model. After mineralisation, the mineral deposits on the scaffolds were analysed using scanning electron microscopy, energy dispersive X-ray, and inductively coupled plasma mass spectroscopy. All data were statistically analysed using the two-sample t-test (P < 0.05).

RESULTS

Hydroxyapatite (HAP) deposition was observed on CaC and CaMT scaffolds after 1 week of mineralisation in the tooth model and in the bulk system. The deposition was significantly higher (P < 0.05) on CaMT scaffold than that on CaC scaffold. The amount of HAP formed in the tooth model was significantly lower (P < 0.05) than that in the bulk solution.

CONCLUSIONS

The CMCS scaffolds are bioactive and capable of biomineralisation by forming HAP within a tooth model ex vivo. The bioactivity of the CMCS scaffold can be enhanced by incorporating MTA.

Light activated disinfection: an alternative endodontic disinfection strategy

BACKGROUND

An improved light activated disinfection technique utilizing a specific photosensitizer formulation, liquid optical-conduit, oxygen-carrier and light energy of appropriate wavelength has been introduced recently. This study tested the efficacy of this improved light activated disinfection on ex vivo biofilms of Enterococcus faecalis at two different stages of maturation.

METHODS

Eighty-five tooth sections were prepared and endodontic biofilm of E. faecalis were grown within the root canal. In stage 1, conventional light activated disinfection (LAD), chemical disinfectant (sodium hypochlorite) and improved LAD were tested on four-day-old (immature) biofilms. In stage 2, conventional LAD, improved LAD and chemomechanical disinfection (alone and in combination with improved LAD) were tested on four-week-old (mature) biofilms.

RESULTS

Sodium hypochlorite and improved LAD showed the ability to significantly inactivate bacteria in four-day-old biofilms when compared to the control and LAD (p < 0.05). Inactivation of bacteria from deeper dentine was higher in improved LAD than sodium hypochlorite. In four-week-old biofilms, a combination of chemomechanical disinfection and improved LAD produced significant bacterial killing compared to either chemomechanical disinfection or improved LAD alone.

CONCLUSIONS

This study highlighted the potential of improved LAD to kill bacteria within dentinal tubules. In combination with chemomechanical preparation, the improved LAD significantly inactivated four-week-old biofilm bacteria.

Hydromechanics in dentine: Role of dentinal tubules and hydrostatic pressure on mechanical stress–strain distribution

OBJECTIVES

This investigation is to understand the role of free water in the dentinal tubules on the mechanical integrity of bulk dentine.

METHODS

Three different experiments were conducted in this study. In experiment 1, three-dimensional models of dentine with gradient elastic modulus, homogenous elastic modulus, and with and without hydrostatic pressure were simulated using the finite element method. Static compressive loads of 15, 50 and 100 N were applied and the distribution of the principal stresses, von Mises stresses, and strains in loading direction were determined. In experiment 2, experimental compression testing of fully hydrated and partially dehydrated dentine (21 degrees C for 72 h) was conducted using a Universal testing machine. In experiment 3, Fourier transform infrared spectroscopic analysis of hydrated and partially dehydrated dentine was carried out.

RESULTS

The finite element analysis revealed that the dentine model with simulated hydrostatic pressure displayed residual tensile stresses and strains in the inner region adjacent to the root canal. When external compressive loads were applied to the model, the residual stresses and strains counteracted the applied loads. Similarly the hydrated specimens subjected to experimental compression loads showed greater toughness when compared to the partially dehydrated specimens. The stress at fracture was significantly higher in partially dehydrated specimens (p=0.014), while the strain at fracture was significantly higher in hydrated dentine specimens (p=0.037).

SIGNIFICANCE

These experiments highlighted the distinct role of free water in the dentinal tubules and hydrostatic pressure on the stress-strain distribution within the bulk dentine.

Digital moiré interferometric investigations on the deformation gradients of enamel and dentine: an insight into non-carious cervical lesions

OBJECTIVES

The objective of this study was to evaluate the biomechanical basis of non-carious cervical lesions by examining the patterns of deformation (strain) in the enamel and dentine.

METHODS

The digital moiré interferometry is optics based non-destructive, whole-field experimental technique that provides whole-field strain information. Diffraction gratings (with a frequency of 1200 lines/mm) were transferred onto sagittal sections of human teeth, which were subsequently loaded compressively for loads ranging from 10 to 200 N at the incisal edge of the tooth. The acquired digital moiré fringe patterns were used to determine the in-plane deformation pattern in the enamel and the dentine in the direction parallel to the long axis (axial direction) and in the direction perpendicular to the long axis (lateral direction) of the tooth.

RESULTS

It is observed that the enamel displayed marked strain gradients in the lateral direction, while the coronal dentine experienced marked strain gradients in the axial directions during compression. With the increase in applied loads, the strains in the enamel increased at the cervical edge (above the cemento-enamel junction) on the facial side, while the strains in the dentine increased below the cemento-enamel junction on the facial side.

CONCLUSION

The enamel and dentine displayed unique in-plane deformation patterns in the axial and the lateral directions of the tooth. These experiments support the hypothesis that occlusal loading will contribute to cervical loss of dental hard tissues.

Enterococcus faecalis-mediated biomineralized biofilm formation on root canal dentinein vitro

Enterococcus faecalis is the most predominant bacteria in teeth with failed root canal therapy and is found to survive harsh conditions prevailing in the root canals of endodontically treated teeth. This study aims to investigate the interaction between E. faecalis and root canal dentine substrate. Towards this end, tooth specimens were prepared and divided into two groups. The tooth specimens in group 1 were incubated with E. faecalis for periods of 2-, 4-, and 6-week intervals and the chemical composition of the biofilm was determined using X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. The tooth specimens in group 2 were incubated with E. faecalis for a period of 6 weeks and the topography and ultrastructure of the biofilm were examined using scanning electron microscopy (SEM), light microscopy, and laser confocal scanning microscopy. The sediments formed from the bacterial interaction on the dentine (in group 1) were also examined by SEM and FTIR. These experiments highlighted different stages in the interaction of E. faecalis with root canal dentine. Further, a bacterial-induced apatite reprecipitation on mature biofilm was also observed. This ability of E. faecalis to form such calcified biofilm on root canal dentine may be a factor that contributes to their persistence after endodontic treatment.

The Role of Environmental Changes on Monospecies Biofilm Formation on Root Canal Wall by Enterococcus faecalis

Biofilm mode of growth is a strategy in microorganisms to survive harsh growth conditions. Although previous studies have established the ability of Enterococcus faecalis to survive postendodontic environmental conditions, the effect of such conditions on the ultrastructural and physiochemical features of E. faecalis biofilm has received less attention. This study aims to evaluate the effect of different growth conditions on the characteristics of E. faecalis biofilm on root canal, and the penetration of E. faecalis into dentinal tubules. Forty-five intact noncarious human maxillary molars were experimented under nutrient-rich, nutrient-deprived, aerobic, and anaerobic conditions for a period of 21 days. Scanning Electron Microscopy with Energy Dispersive X-ray microanalysis, Laser Confocal Scanning Microscopy and Light microscopic examinations were carried out. The microscopic analysis highlighted a distinct variation in the ultrastructure of the biofilms formed under different experimental conditions. The EDX microanalysis showed a significant increase in the levels of Calcium (Ca) in the biofilm structures formed under anaerobic nutrient-deprived condition (p < 0.001). The depth of bacterial penetration was significantly greater in nutrient-rich condition (p < 0.001). This study demonstrated distinct ultrastructural and physiochemical properties of the biofilms formed and dentinal tubular penetration of E. faecalis under different conditions.

Periapical biomechanics and the role of cyclic biting force in apical retrograde fluid movement

AIM

To investigate the stress distribution pattern in the periapical region caused by biting forces and to study the role of cyclic biting loads on periapical fluid movement.

METHODOLOGY

In the first part, a digital photoelastic experiment was conducted to study stress distribution in the periapical region. In the second, 20 maxillary central incisors were selected and divided into three main groups: normal intact teeth (group 1), tooth specimens in which the root canal was enlarged and maintained wet (group 2), and tooth specimens in which the root canal was enlarged and maintained dry (group 3). The tooth specimens were placed in a polycarbonate support with a cavity filled with a sponge soaked in methylene blue solution to simulate a periapical defect with exudate. During testing, the specimens were placed in a water bath at 37 degrees C, and were loaded cyclically with a load of 20 N, at a rate of 72 cycles min(-1), to a maximum of 20,000 cycles. The specimens were then sectioned and evaluated for retrograde fluid movement using light microscopy. The data were analysed using one-way anova (post hoc tests).

RESULTS

Digital photoelastic experiments showed that the compression of teeth produced bending stresses in the periapical region. Testing with cyclic loads demonstrated retrograde fluid movement into the apical portion of the root canal and extraradicular region in all groups. There was a significant difference amongst the apical retrograde fluid movement displayed by different groups (<0.01). Group 2, in which the root canal was enlarged and maintained wet showed maximum retrograde fluid movement, whilst group 3, in which the root canal was enlarged and maintained dry showed the least retrograde fluid movement.

CONCLUSIONS

Biting forces would cause bending of the periapical bone and cyclic biting forces would contribute to retrograde fluid movement into the root canal space and extraradicular region.

Experimental investigation on the role of water in the mechanical behavior of structural dentine

Dentine is a porous hydrated composite structure that forms the major bulk of the human tooth. The aim of this study was to investigate the role of free water on the in-plane, mechanical strain response in dentine structure. A digital moire interferometry was used for this purpose. It was observed from this experiment that structural dentine demonstrated distinct strain gradients in the axial (perpendicular to the dentinal tubules) and lateral (parallel to the dentinal tubules) directions. The hydrated dentine displayed significant increase in strain with stress in the direction perpendicular to the dentinal tubules, and this response was characteristic of a tough material. On the contrary, the dehydrated dentine, which was dehydrated at 24 degrees C, 55% relative humidity for 72 h showed a strain response characteristic of a brittle material. The strains formed in the direction parallel to the dentinal tubules for hydrated dentine were consistent and did not vary much with increase in applied loads. Upon dehydration, the outer dentine experienced higher strains, and the difference between the outer and inner dentine became more conspicuous with increase in loads. This experiment highlights hydration-induced, distinct in-plane strain gradients in the directions perpendicular and parallel to the dentinal tubules in the dentine structure.

Photomechanical investigations on the stress-strain relationship in dentine macrostructure

In this study photomechanical experiments were carried out to examine the relationship between macroscopic mechanical stress and strain gradients within the root dentine structure. Three-dimensional digital photoelasticity was used to study the stress distribution patterns in tooth models, while digital moire interferometry was used to study the strain gradients within the natural teeth. The stress analysis showed a distinct bending stress distribution, along faciolingual plane in the coronal and cervical regions of the tooth. There was a reduction in bending towards the apical third of the tooth model. The strain analysis displayed strain gradients in the axial (along the long axis of the tooth) and lateral (perpendicular to the long axis of the tooth) directions in dentine. There was a conspicuous reduction in strains from the cervical to the apical third of the root dentine. The root dentine displayed uniform distribution of normal strains. Although there was a steep increase in stresses from the inner core region to the outer surface of an isotropic tooth model, there were more uniform strain gradients in the natural dentine structure. It is apparent from these observations that complex organization of material properties facilitated distinct strain gradients in dentine structure during mechanical functions.

Chairside sensor for rapid monitoring of Enterococcus faecalis activity

In this study, optical spectroscopy was used to monitor a chromogenic, enzyme-substrate reaction for the rapid identification of Enterococcus faecalis. The detection system, comprising a miniature spectrophotometer and an accompanying data acquisition system, was placed in an incubator. During testing, a 3-ml test sample was placed in a cuvette within the spectrophotometer. This permitted online, real-time, and remote analysis of spectral signature needed to monitor the bacteria. It was observed that the absorption peak intensity increased conspicuously 3.5 h after inoculation and through the entire period of testing. A linear-regression analysis demonstrated a significant correlation between the increase in absorption peak intensity at 610 nm (r = 0.9389) and 653 nm (r = 0.9387) with the formation of colony-forming units. Optical spectroscopy-based sensing systems can pave the way for rapid, nonlaboratory-based approaches to monitor microbial status quantitatively and qualitatively from clinical samples.

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol-gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be rho=-0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.

Total protein measurement using a fiber-optic evanescent wave-based biosensor

A novel method and instrumental system to determine the total protein concentration in a liquid sample is described. It uses a fiber optic total protein sensor (FOPS) based on the principles of fiber optic evanescent wave spectroscopy. The FOPS applies a dye-immobilized porous glass coating on a multi-mode optical fiber. The evanescent waves at the fiber optic core-cladding interface are used to monitor the protein-induced changes in the sensor element. The FOPS offers a single-step method for quantifying protein concentrations without destroying the sample. The response time and reusability of the FOPS are evaluated. This unique sensing method presents a sensitive and accurate platform for the quantification of protein.

Scanning electron microscopic and energy dispersive spectrometric investigations on the effect of XeCl excimer laser on human dentin with smear layer

The purpose of this study was to study the effect of XeCl excimer laser on smear layer covered dentine of extracted human teeth. Twenty-four freshly extracted human molar teeth were collected and randomly divided into one control group and three experimental groups of six teeth each (groups A-D). The teeth in the experimental groups were irradiated with XeCl 308-nm excimer laser at a fluence of 0.4 J cm-2 and a constant pulse repetition rate of 25 Hz. Group A was used as the control, while groups B, C and D were irradiated at different exposure times of 3, 5 and 7 s, respectively. Subsequently these teeth specimens were subjected to scanning electron microscopic (SEM) examination and energy dispersive X-ray (EDX) spectrometric analysis. The SEM examination revealed melting of the smear layer covered dentin to conceal the underlying dentinal tubules. At a longer exposure time (7 s), dentin melted to form large grains and this resulted in non-uniform closure of underlying dentinal tubules. Under the conditions of this study, it is concluded that the pulsed XeCl 308-nm excimer laser at a fluence of 0.4 J cm-2, with an exposure time of 5 s uniformly occluded exposed smear layer covered dentine with no conspicuous variation in chemical structure.

Photomechanical investigations on post endodontically rehabilitated teeth

An investigation of the stress distribution patterns in post-core restored teeth and the behavior of dentin material to fracture propagation was conducted using experimental techniques such as digital photoelasticity (on photoelastic models), mechanical testing and scanning electron microscopy (SEM) (on extracted teeth). Digital photoelastic experiments showed that endodontic post-core restoration resulted in regions of high tensile stress and of stress concentrations in the remaining dentin structure. It was observed from mechanical testing that the fracture resistance in post-core restored teeth is significantly lower (p<0.0001) than that in intact tooth. There was a significant correspondence between the plane of stress concentrations identified in the photoelastic models and in those of the plane of fracture exhibited by the rehabilitated tooth specimens. While the fracture of post-core rehabilitated teeth was consistent, that of control teeth was not as distinct. The SEM highlighted varying dentin response to fracture propagation at the inner core and the outer regions. The fractographs showed brittle and ductile response to fracture propagation in the outer and inner core dentin, respectively. These photomechanical studies highlighted that the stress concentrations, high tensile stress and loss of inner ductile dentin associated with post endodontic rehabilitation diminished their resistance to fracture.

Approaching biomimetics in dental restorations via photonics

It is established that a natural system balances functional requirements with the anatomical optimizations it has achieved. Though such process of functional adaptation is recognized in bone tissue, any mode of functional adaptation in dental tissue is yet to be understood. In this study a three-dimensional digital photoelasticity is conducted to evaluate the nature of stress distribution in the sagittal aspect and the cross-sections of the dentine structure. Later, a fluoroscopic X-ray microscopic analysis and a microindentation experiments, are performed on different sections obtained from the sagittal and cross-sections of the dentine. These experiments aided in correlating the multi-plane pattern of mineralization and the spatial gradients in elastic modulus in the original dentine structure with the three-dimensional stress distribution in photoelastic models. This study highlights dentine structure as a biologically graded structure to functional loads.

Analysis on the nature of thermally induced deformation in human dentine by electronic speckle pattern interferometry (ESPI)

OBJECTIVE

To examine the in-plane and out-of-plane response of human dentine to thermal loads in real time.

METHODS

An Electronic Speckle Pattern Interferometry (ESPI) system sensitive to both the in-plane and out-of-plane displacements was configured and used in conjunction with an advanced fringe processing technique. Specimens were prepared from freshly extracted lower central incisor teeth and were separately mounted on a thermal block to apply thermal loads from room temperature (25 degrees C) to 60 degrees C. The real time speckle patterns were acquired using a digital camera. These digital fringe patterns were subjected to further image processing to enhance the quality of fringes. The resultant images were later analyzed to study the out-of-plane and in-plane displacement gradients in the facio-lingual plane of the dentine.

RESULTS

The out-of-plane deformations were observed in the plane perpendicular to the long axis of the tooth, while the in-plane deformations occurred in the plane parallel to the long axis of the tooth.

CONCLUSION

The ESPI analysis revealed whole-field and distinct thermal response in human dentine in-plane and out-of-plane. The cervical dentine experienced distinct and conspicuous displacement to the temperature changes.

Investigations of thermal property gradients in the human dentine

An investigation of the adaptation of dentine to temperature variation was conducted with the aid of digital moiré interferometry and thermomechanical analysis. The moiré interferometric patterns provided direct evidence of two major phases of thermally involved deformation in dentine. An initial phase of expansion was followed by contraction at higher temperatures. Significant gradients in thermal strain and the coefficient of thermal expansion were identified. Close agreement was found between the response of dentine to thermal changes as observed by moiré interferometry and that detected by thermomechanical analysis. This study highlights the biological adaptation of dentine to thermal variations.

Advanced digital photoelastic investigations on the tooth-bone interface

The purpose of this study was to investigate the behavior of the tooth-bone interface on the nature of stress distribution in the tooth and its supporting alveolar bone for various occlusal loads using an advanced digital photoelastic technique. A digital image processing system coupled with a circular polariscope was used for the stress analysis. The phase shift technique and a phase unwrapping algorithm was utilized for fringe processing. This aids in obtaining qualitative and quantitative information on the nature of stress distribution within the dento-osseous structures. The experiments revealed bending stresses within dento-osseous structures. However, the compressive stress magnitude was larger than the tensile stress. Zero stress regions were also identified within the dento-osseous structures. The results suggest that the geometry of the dento-osseous structures and the structural gradients at the tooth-bone interface play a significant role in the distribution of stresses without stress concentrations. Further, the application of an advanced image-processing system with the circular polariscope showed notable advantages and could be applied in other biomechanical investigations.

Stress distribution in the dento-alveolar system using digital photoelasticity

Past research has confirmed that the governing factors in cellular modelling and remodelling adhere to sound principles of engineering mechanics. Hence studies of stress distributions would provide better understanding of the functional adaptation of dental supporting structures. Photoelasticity is an established experimental tool to study whole-field stress distribution in structures subjected to forces. However, it has certain limitations that make its application in biological specimens tedious. In this investigation an advanced digital photoelastic system is used to visualize and study the nature of the stress distribution in dental supporting structures. These digital fringe patterns are analysed using a phase-shift technique. The present biomechanical study shows that dental supporting structures exhibit a characteristic stress distribution, promoting structural adaptation based on needs. Furthermore, the advantage of using a digital image processing system along with the circular polariscope is discussed.

Experimental studies on the nature of property gradients in the human dentine

We conducted an investigation into the nature of dentine mineralization and mechanical property gradients with the aid of experimental techniques such as the fluoroscopic X-ray microanalysis and instrumented microindentation, respectively. It was found that the tooth adapts to a complex structure with significant gradients in properties. We observed a significant correlation between the degree of mineralization within the dentine and the mechanical properties. The natural gradation in mechanical properties is explained by the stress analysis within anatomical-sized tooth specimens done using digital photoelasticity. These results are explained within the context of the functional requirements that are imposed on the tooth. This study highlights tooth structure as a biologically adapted, functionally graded material.

A strain gauge and photoelastic analysis of in vivo strain and in vitro stress distribution in human dental supporting structures

Strain gauge and photoelastic experiments have been workhorses of experimental stress analysis for over 50 years. In this study, both were used to analyse the nature of stress distribution from the tooth root surface to the supporting alveolar bone. Such studies help in understanding the behaviour of dental supporting structures under physiological function. In the strain gauge experiment, the mechanical strains were measured on the supporting bone surface and the root surface of the tooth under applied bite force. It was found that higher strains were distributed along the cervical region of the supporting bone and the root surface. The photoelastic study was also done to evaluate the stress distribution pattern from the root surface to the supporting bone under clinical conditions. The stress patterns were found to decrease from the cervical to the apical region of the root surface. These studies highlight the role of the periodontium in stress distribution and bone remodelling.

Biomechanics of endodontic endosseous implants--a comparative photoelastic evaluation

Dental biomechanics is an interdisciplinary study wherein engineering principles are used for the better understanding of clinical dentistry. The present biomechanical study was done to understand the mechanism by which an endodontic implant transmits occlusal forces to the surrounding bone. In this experimental study, photoelastic techniques were utilized to compare stress distribution patterns in the supporting bone of an intact tooth, a tooth with supporting bone loss, and a tooth stabilized using an endodontic endosseous implant. It was concluded that there were distinct variations in the biomechanics underlying various dental clinical conditions. Further, the implant did not appear to improve the stress distribution.