Biomedical subjects

A Kishen

Publications and source records attributed to A Kishen.

At least 19 recordsLinked to original sources

PubMed2007

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.

Biomechanical Phenomena↗

PubMed2006

Enterococcus faecalis-mediated biomineralized biofilm formation on root canal dentine in 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.

Biocompatible Materials↗

PubMed2006

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.

Compressive Strength↗

PubMed2005

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.

Dentin↗

PubMed2005

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.

Aerobiosis↗

PubMed2005

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.

Alveolar Process↗

PubMed2004

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.

Biosensing Techniques↗

PubMed2003

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.

Biosensing Techniques↗

PubMed2003

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.

Biosensing Techniques↗

PubMed2002

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.

Calcium↗

PubMed2002

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.

Biomechanical Phenomena↗

PubMed2001

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.

Dentin↗

PubMed2001

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.

Adult↗

PubMed2001

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.

Alveolar Process↗

PubMed2000

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.

Biomechanical Phenomena↗

PubMed2000

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.

Alveolar Process↗

PubMed2000

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.

Alveolar Process↗

PubMed1999

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.

Alveolar Bone Loss↗