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Novel Assessments of Early Enamel Erosion

Chew, Hooi Pin

[Thesis]. Manchester, UK: The University of Manchester; 2013.

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Abstract

Dental erosion has been defined as a chemical process that involves the dissolution of enamel and dentine by acid(s) not derived from bacteria when the surrounding aqueous phase is under-saturated with tooth mineral. Clinically however, dental erosion hardly ever occurs exclusively from the other modes of tooth wear such as abrasion and attrition. Hence the term erosive wear has been proposed and used to describe erosion-facilitated wear.With the prevalence of erosive wear being reported to be on the rise among children and adolescents in many countries, a plethora of oral health products such as dentifrices and mouth rinses had been put forward with claims of increasing the resistance of the enamel and / or dentine from being demineralised. However, the efficacy of these oral health products is still widely questionable as the studies carried out were mainly in vitro and / or in situ studies and the contradictory results were reported by different groups of researchers.The above mentioned discrepancies are often due to non-standardised in vitro and in situ study designs of erosion studies. Parameters such as type of acid used, concentration of acid used, duration of acid exposure, inclusion or exclusion of abrasion in the study model, ex vivo or in vivo acid challenge, ex vivo or in vivo treatment with oral health product and the nature of pellicle on the specimen are often varied.The availability of an detection tool which could be used to measure demineralisation on natural tooth surface in vivo would exclude many of the inevitable variability in in situ and in vitro study design, such as the simulation of the intra oral conditions in which the erosion challenge and intervention take place and the nature of the pellicle formed on the specimens. Hence with an in vivo detection tool, it is hopeful that the efficacy of any interventions would be evaluated more accurately and its results expounded to a wider context. It would be useful if the tool was sensitive to the very early stages of the erosion process as this would entail shorter and more economical study designs. Arising from the problems discussed above, potential non-invasive assessment methods that could be used clinically to measure demineralisation were explored and it was found that two optical methods, Optical Coherence Tomography (OCT) and Quantitative Light-induced Fluorescence (QLF) were potential methods for the tasks.The studies described in this thesis were divided into three main big sections; the first being the in vitro validation work of the two optical methods (Chapter 5 and 6), the second, validation of these methods in situ (Chapter 7) and finally the assessment of the efficacy of a high fluoride dentifrice on early enamel erosion using these two methods (Chapter 8).In the in vitro validation (Chapter 5), it was demonstrated that both QLF and OCT were able to detect erosion-interval related changes in natural surface samples eroded with orange juice for 60 minutes. However, results of Multiple Linear Regression and Paired t test suggest that QLF was more sensitive than OCT in the detection of demineralisation changes in this particular experimental setting. QLF demonstrated a R2 value of 0.590 while the best of the OCT outcome measure demonstrated a R2 value of 0.319.Further in vitro study (Chapter 6) was performed to explore the use of a moistened-exposed surface as a reference method for both OCT and QLF as it was felt that it would be beneficial if a coated reference area which posts as an additional step for error could be done away with. Results of this study showed that the moistened-exposed surface could be used a reference method for QLF only but not for OCT. Furnished with the findings of the above mentioned in vitro validation studies, an in situ validation of both the optical methods was performed (Chapter 7). It was found that OCT and QLF were able to longitudinally measure in situ demineralisation on polished and natural surfaced enamel which were subjected to 150 minutes of in vivo exposure to orange juice. Similar to the results of the in vitro study, QLF was found to be more sensitive than OCT in the detection of demineralisation changes on natural surfaced enamel. The last in situ study (Chapter 8) was to evaluate whether there was a protective effect of treating human enamel with a high-concentrated fluoride dentifrice during an active erosion phase and whether OCT and QLF were able to detect the protective effect. It was found that treating natural surface enamel with a 5000ppm NaF dentifrice increased its resistance against concurrent in vivo erosive challenge with an orange juice challenge. QLF was able to detect the protective effect of the 5000ppm NaF dentifrice on natural surface enamel against early in vivo erosion with an orange juice challenge regime while OCT did not.

Layman's Abstract

Dental erosion is defined as a chemical process that involves the dissolution of enamel and dentine by acid which is not derived from bacteria when the surrounding aqueous phase is under saturated with tooth mineral. The acids may be of intrinsic or extrinsic origin. Intrinsic acid is acid regurgitated from the stomach and extrinsic acids can be from consumption of food and drinks such as soft drinks, citrus fruit juices and pickles. When the acid is in contact with enamel, it causes dissolution of the enamel hydroxyapatite crystals. The process of erosion starts to take place within the prism sheath area and then spreads to the prism core, leaving a honey comb appearance of the interprismatic areas when viewed microscopically. Eventually, fresh and unionised acid will then diffuse into the interprismatic areas of enamel and further dissolve mineral in the subsurface region. This dissolution process extends a few micrometers below the surface and has is known as softening . Over time, as softening progresses further into the enamel, dissolution in the most superficial enamel will reach a point where the softened layer of enamel is permanently lost. This process, if not diagnosed and curbed in its early stages can quickly deteriorate and result in severely worn teeth that require complex restorations. In order to prevent or stop the process, several attempts have been made to evaluate the erosive potency of acidic beverages and the protective efficacy of modified beverages and dental health products. These evaluations have mainly been performed by assessing the degree of softening or roughening of the early eroded surface using nano or micro hardness techniques, or measuring the amount of tooth structure loss evident of advanced erosion using surface profilometry. The use of these techniques is limited to extra-oral use and hence the study designs of these investigations had to be either in vitro or in situ. Profilometry has been widely used to detect the later stages of dental erosion following surface tissue loss and more recently the introduction of a non-contact profilometer has been preferentially used. A non-contact profilometer provides a 3D image of an area to be measured by means of a white light probe that is split to the full spectral field. Each colour frequency is allocated to a certain height and the light that is reflected back represents the individual height and is converted into an image. Once an image has been obtained, the difference in height from an unexposed control area and the eroded channel is calculated. The advantages of this profilometry technique is that it has a resolution as low as 0.01 µm and is non destructive so does not damage the softened surface in the same way that a stylus on a contact profilometer does. Optical Coherence Tomography (OCT) is an optical technique that has been developed for the investigation of various biological tissue and its use has been particularly well established in ophthalmology for detecting retinal detachments. This optical technique enables non-invasive ‘optical biopsies’ to be taken from samples by illuminating them with a broadband light source and collecting the reflected light for image processing. The increased porosity of demineralised enamel, compared to sound enamel, results in a change in optical property, resulting in a difference of intensity of the reflected light, which can be quantified and analysed. Previous studies have looked into using OCT to characterise both sound and carious enamel and dentine and evaluate the enamel restoration interface in laboratory settings. In vivo work has also been carried out on the detection of early caries and periodontitis. The results of these studies indicate a positive potential for the use of OCT in detecting and quantifying demineralisation in vivo.Quantitative Light Fluorescence (QLF) is also a non-invasive optical technique and had initially been developed for in-vivo measuring of early tooth decay and demineralisation. It has since been extensively used for the investigation of caries and fluorosis. QLF works by illuminating the enamel surface with blue light. The emitted fluorescent light (normally green light) from dentin is then collected by filtering out the incident light to form an image. Loss of fluorescence is normally observed in demineralised areas of the teeth. The aim of this study is to investigate the sensitivity of OCT and QLF in detecting early erosion in an in situ setting before progressing onto using it in a true in vivo situation. The sensitivity of OCT and QLF will be compared to the more established technique of measuring erosion using non-contact profilometry

Bibliographic metadata

Type of resource:
Content type:
Form of thesis:
Type of submission:
Degree type:
Doctor of Philosophy
Degree programme:
Research programme in the School of Dentistry
Publication date:
Location:
Manchester, UK
Total pages:
317
Abstract:
Dental erosion has been defined as a chemical process that involves the dissolution of enamel and dentine by acid(s) not derived from bacteria when the surrounding aqueous phase is under-saturated with tooth mineral. Clinically however, dental erosion hardly ever occurs exclusively from the other modes of tooth wear such as abrasion and attrition. Hence the term erosive wear has been proposed and used to describe erosion-facilitated wear.With the prevalence of erosive wear being reported to be on the rise among children and adolescents in many countries, a plethora of oral health products such as dentifrices and mouth rinses had been put forward with claims of increasing the resistance of the enamel and / or dentine from being demineralised. However, the efficacy of these oral health products is still widely questionable as the studies carried out were mainly in vitro and / or in situ studies and the contradictory results were reported by different groups of researchers.The above mentioned discrepancies are often due to non-standardised in vitro and in situ study designs of erosion studies. Parameters such as type of acid used, concentration of acid used, duration of acid exposure, inclusion or exclusion of abrasion in the study model, ex vivo or in vivo acid challenge, ex vivo or in vivo treatment with oral health product and the nature of pellicle on the specimen are often varied.The availability of an detection tool which could be used to measure demineralisation on natural tooth surface in vivo would exclude many of the inevitable variability in in situ and in vitro study design, such as the simulation of the intra oral conditions in which the erosion challenge and intervention take place and the nature of the pellicle formed on the specimens. Hence with an in vivo detection tool, it is hopeful that the efficacy of any interventions would be evaluated more accurately and its results expounded to a wider context. It would be useful if the tool was sensitive to the very early stages of the erosion process as this would entail shorter and more economical study designs. Arising from the problems discussed above, potential non-invasive assessment methods that could be used clinically to measure demineralisation were explored and it was found that two optical methods, Optical Coherence Tomography (OCT) and Quantitative Light-induced Fluorescence (QLF) were potential methods for the tasks.The studies described in this thesis were divided into three main big sections; the first being the in vitro validation work of the two optical methods (Chapter 5 and 6), the second, validation of these methods in situ (Chapter 7) and finally the assessment of the efficacy of a high fluoride dentifrice on early enamel erosion using these two methods (Chapter 8).In the in vitro validation (Chapter 5), it was demonstrated that both QLF and OCT were able to detect erosion-interval related changes in natural surface samples eroded with orange juice for 60 minutes. However, results of Multiple Linear Regression and Paired t test suggest that QLF was more sensitive than OCT in the detection of demineralisation changes in this particular experimental setting. QLF demonstrated a R2 value of 0.590 while the best of the OCT outcome measure demonstrated a R2 value of 0.319.Further in vitro study (Chapter 6) was performed to explore the use of a moistened-exposed surface as a reference method for both OCT and QLF as it was felt that it would be beneficial if a coated reference area which posts as an additional step for error could be done away with. Results of this study showed that the moistened-exposed surface could be used a reference method for QLF only but not for OCT. Furnished with the findings of the above mentioned in vitro validation studies, an in situ validation of both the optical methods was performed (Chapter 7). It was found that OCT and QLF were able to longitudinally measure in situ demineralisation on polished and natural surfaced enamel which were subjected to 150 minutes of in vivo exposure to orange juice. Similar to the results of the in vitro study, QLF was found to be more sensitive than OCT in the detection of demineralisation changes on natural surfaced enamel. The last in situ study (Chapter 8) was to evaluate whether there was a protective effect of treating human enamel with a high-concentrated fluoride dentifrice during an active erosion phase and whether OCT and QLF were able to detect the protective effect. It was found that treating natural surface enamel with a 5000ppm NaF dentifrice increased its resistance against concurrent in vivo erosive challenge with an orange juice challenge. QLF was able to detect the protective effect of the 5000ppm NaF dentifrice on natural surface enamel against early in vivo erosion with an orange juice challenge regime while OCT did not.
Layman's abstract:
Dental erosion is defined as a chemical process that involves the dissolution of enamel and dentine by acid which is not derived from bacteria when the surrounding aqueous phase is under saturated with tooth mineral. The acids may be of intrinsic or extrinsic origin. Intrinsic acid is acid regurgitated from the stomach and extrinsic acids can be from consumption of food and drinks such as soft drinks, citrus fruit juices and pickles. When the acid is in contact with enamel, it causes dissolution of the enamel hydroxyapatite crystals. The process of erosion starts to take place within the prism sheath area and then spreads to the prism core, leaving a honey comb appearance of the interprismatic areas when viewed microscopically. Eventually, fresh and unionised acid will then diffuse into the interprismatic areas of enamel and further dissolve mineral in the subsurface region. This dissolution process extends a few micrometers below the surface and has is known as softening . Over time, as softening progresses further into the enamel, dissolution in the most superficial enamel will reach a point where the softened layer of enamel is permanently lost. This process, if not diagnosed and curbed in its early stages can quickly deteriorate and result in severely worn teeth that require complex restorations. In order to prevent or stop the process, several attempts have been made to evaluate the erosive potency of acidic beverages and the protective efficacy of modified beverages and dental health products. These evaluations have mainly been performed by assessing the degree of softening or roughening of the early eroded surface using nano or micro hardness techniques, or measuring the amount of tooth structure loss evident of advanced erosion using surface profilometry. The use of these techniques is limited to extra-oral use and hence the study designs of these investigations had to be either in vitro or in situ. Profilometry has been widely used to detect the later stages of dental erosion following surface tissue loss and more recently the introduction of a non-contact profilometer has been preferentially used. A non-contact profilometer provides a 3D image of an area to be measured by means of a white light probe that is split to the full spectral field. Each colour frequency is allocated to a certain height and the light that is reflected back represents the individual height and is converted into an image. Once an image has been obtained, the difference in height from an unexposed control area and the eroded channel is calculated. The advantages of this profilometry technique is that it has a resolution as low as 0.01 µm and is non destructive so does not damage the softened surface in the same way that a stylus on a contact profilometer does. Optical Coherence Tomography (OCT) is an optical technique that has been developed for the investigation of various biological tissue and its use has been particularly well established in ophthalmology for detecting retinal detachments. This optical technique enables non-invasive ‘optical biopsies’ to be taken from samples by illuminating them with a broadband light source and collecting the reflected light for image processing. The increased porosity of demineralised enamel, compared to sound enamel, results in a change in optical property, resulting in a difference of intensity of the reflected light, which can be quantified and analysed. Previous studies have looked into using OCT to characterise both sound and carious enamel and dentine and evaluate the enamel restoration interface in laboratory settings. In vivo work has also been carried out on the detection of early caries and periodontitis. The results of these studies indicate a positive potential for the use of OCT in detecting and quantifying demineralisation in vivo.Quantitative Light Fluorescence (QLF) is also a non-invasive optical technique and had initially been developed for in-vivo measuring of early tooth decay and demineralisation. It has since been extensively used for the investigation of caries and fluorosis. QLF works by illuminating the enamel surface with blue light. The emitted fluorescent light (normally green light) from dentin is then collected by filtering out the incident light to form an image. Loss of fluorescence is normally observed in demineralised areas of the teeth. The aim of this study is to investigate the sensitivity of OCT and QLF in detecting early erosion in an in situ setting before progressing onto using it in a true in vivo situation. The sensitivity of OCT and QLF will be compared to the more established technique of measuring erosion using non-contact profilometry
Thesis main supervisor(s):
Thesis advisor(s):
Language:
en

Institutional metadata

University researcher(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:191941
Created by:
Chew, Hooi Pin
Created:
11th April, 2013, 15:32:58
Last modified by:
Chew, Hooi Pin
Last modified:
25th July, 2013, 10:27:21

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