B.T. Amaechi

In vitro remineralisation of eroded enamel lesions by saliva

OBJECTIVES It is speculated that saliva, with its mineral content, may possess a reparative effect on an early erosion which is characterised by softened surface and slight subsurface demineralisation in addition to a crater. This study aimed to determine the possible remineralisation of early enamel erosion by saliva. METHODS Eroded lesions were produced in bovine incisors by 1-h immersion in orange juice. Control sections and three experimental slabs were produced from each tooth. The three slabs were assigned randomly to one of three remineralising agents: clarified natural saliva (NS), artificial saliva (AS) and remineralising solution (RS). All solutions had a pH of 7.2, a fluoride concentration of 0.022 ppm, and were changed daily. NS was collected daily from the same individual at the same time of day. The specimens were exposed to their respective remineralising agents for 28 days. Using microradiography and image analysis, the mineral loss (Delta z) and lesion depth (ld) were quantified in sections cut from the control and experimental slabs. RESULTS A significant (p<0.001) amount of mineral was gained following exposure to each remineralising agent. Significantly less Delta z and ld were observed for the experimental groups compared with the control group (p<0.001; paired t-test). This effect was greatest with RS and least with AS. Inter-group comparison (Duncan multiple tests) showed no significant difference in Delta z among the experimental groups, however ld was significantly higher for AS (p<0.001) compared with RS and NS, and no difference was observed between RS and NS. CONCLUSION Saliva as well as remineralising solutions can remineralise early enamel erosion.

Eroded enamel lesion remineralization by saliva as a possible factor in the site-specificity of human dental erosion

The composition and flow of saliva, which determine its functions, vary within intraoral sites and among individuals. Also, the susceptibility to tooth erosion reportedly varies among individuals and within the dental arches. A possible effect of saliva on early-eroded lesions may be a contributory factor. The aims here were firstly to determine the remineralization of eroded enamel lesions by saliva, and secondly to investigate any variation of this remineralization within the dental arches and among individuals. Early enamel erosion was produced on human premolars using orange juice. Control sections and two test slabs were cut from each tooth. The two slabs from the same lesion were bonded with composite resins to the palatal surface of upper right lateral incisor teeth and the lingual surface of the lower right lateral incisor teeth of volunteers, who then chewed a sugar-free gum four times daily. After 28-day intraoral exposure, mineral loss (DeltaZ) and lesion depth (ld) were quantified using microradiography and the data analysed by paired t-test (n=10, alpha=0.05). Mean DeltaZ was significantly lower in the group of slabs positioned palatally (P<0.001) and lingually (P<0.001) when compared with the control group, and in the lingually placed group when compared with the palatally positioned (P<0.01). A significantly lower ld was observed in the group of slabs positioned palatally (P<0.05) and lingually (P<0.001) when compared with the control group, and in the lingually positioned group when compared with the palatally placed (P<0.05). It was concluded that saliva can remineralize early enamel erosion, and that the degree of remineralization varies within intraoral sites and may be responsible for the differing susceptibility to erosion within the dental arches.

Enamel demineralization in situ with various frequencies of carbohydrate consumption with and without fluoride toothpaste.

There is little information in the literature on the relationship among the frequency of carbohydrate consumption, the use of fluoride toothpaste, and enamel demineralization. The aim of this investigation was to compare the extent of demineralization of enamel slabs in situ, with a sugar-based solution, consumed in constant amounts but with various frequencies in subjects both with and without the use of fluoride (F) toothpaste. Eight subjects wore removable mandibular appliances carrying an enamel slab cut from white-spot lesions. The subjects were required to drink 500 mL of a 120-gm/L sugar solution either once, 3, 5, 7, or 10 times/day for 30 sec on each occasion, for a period of 5 days while brushing their teeth twice daily with either a F (1450 ppm NaF) or a F-free toothpaste. Mineral analysis revealed that when the subjects used a F toothpaste, net demineralization was evident only with the seven- and 10-times/day regime (ns). When F-free toothpaste was used, statistically significant demineralization was observed when the frequency exceeded 3 times/day. This study demonstrates the importance of F-containing toothpaste in enamel re-/demineralization by varying the frequency of carbohydrate challenge in situ.

Factors affecting the development of carious lesions in bovine teeth in vitro

This study aimed to determine the effect of temperature, duration of exposure, position on enamel surface, and type of demineralization solution on the production of caries-like lesions in bovine enamel in vitro, and to establish the conditions for the formation of artificial caries in bovine enamel. Caries-like lesions were produced in incisal, middle and cervical sites on enamel samples, with either an acidified hydroxyethylcellulose gel system or a partially saturated acidic buffer solution at either 20 degrees C or 37 degrees C for 3, 4, or 5 days. Lesion variables (mineral loss/lesion depth) were quantified. Regular subsurface lesions were produced in all specimens in acidic buffer solution within 3 days at either temperature. In gel, caries-like lesions were produced in 62% of the specimens at 37 degrees C and in 49% at 20 degrees C, while the remaining specimens were either eroded or softened. Mineral loss and lesion depth were significantly greater with buffer than with gel, and with increased length of exposure in either solution. There were no significant differences in either variable with position or temperature in either solutions, though numerically both variables were greater at the cervical site, and at 37 degrees C in either solution. It was concluded that caries-like lesions can be consistently produced in bovine enamel with a partially saturated acidic buffer solution at 20 degrees C or 37 degrees C within 3 days.

Use of Transverse Microradiography to Quantify Mineral Loss by Erosion in Bovine Enamel

The aim of the present study was to develop transverse microradiography (TMR) in order to quantitatively assess the influence of artificial saliva and orange juice on the erosion of bovine enamel. Bovine incisors were sectioned sagittally into two equal halves. Each half was coated with acid-resistant nail varnish except for a rectangular enamel window on the labial surface of the tooth. While both halves of each tooth were immersed in pure orange juice 6 times daily for a period of 5 min at each occasion making a total of 30 min per day, one half was stored in artificial saliva and the other half in deionized distilled water between exposures to orange juice and for the remaining 12 h overnight, for 24 days making a total of 12 h of exposure to orange juice. Sections bearing intact and eroded enamel surfaces were cut from each specimen and ground to 80 μm thickness, and TMR of the sections was made. Mineral loss was quantified from the microradiographs using two-step image analysis. Mineral loss was significantly greater in those specimens cycled in orange juice and de-ionized distilled water. TMR was used successfully to quantify the mineral loss by erosion in vitro, and it is envisaged that it will be useful for specimens used in intra-oral appliances during in situ trials. Artificial saliva saturated with respect to calcium and phosphate salts can possibly remineralize an erosive lesion and may reduce the degree of erosion.

Efficacy of Sterilisation Methods and Their Effect on Enamel Demineralisation

The aim of this project was to determine the effectiveness of sterilisation methods for dental enamel for use in intra–oral cariogenicity tests, and their possible effect on the degree of demineralisation of enamel. Bovine incisors were cut vertically into five portions and each assigned to one of five groups. Group 1 was used as a control while the other four groups were subjected, respectively, to gamma irradiation (≅25kGy), steam autoclaving (121°C for 15min), sodium hypochlorite (12% w/v for 24h) and povidone–iodine (7.5% w/v for 24h). Total viable counts of microorganisms remaining following sterilisation of the specimens were performed following incubation of the specimens for 24h at 37°C. Caries–like lesions were produced in each specimen using an acidic buffer solution (pH4.5). Sections were cut from each specimen, ground to 80–μm thickness, and microradiographed. Mineral loss and lesion depth were quantified using transverse microradiography. Statistical analysis was by ANOVA. Dunnetts and Tukeys tests. Microbial growth (Staphylococcus aureus and bacilli) was observed only in control specimens in both brain heart infusion broth and on blood agar plates. The sterilisation methods affected the enamel surface as follows: gamma irradiation (cream discolouration), NaOCl (bleaching), and povidone–iodine (white spot–like lesion). Compared with the control, there was no significant difference in mineral loss and lesion depth with any of the groups, but the numerical values of mineral loss and lesion depth in groups can be ranked as follows: gamma irradiation <povidone–iodine <control <autoclave <NaOCl. In conclusion, the four sterilisation methods were all effective to sterilise enamel, but gamma irradiation proved the most acceptable method for enamel to be used in cariogenicity tests having the least adverse effect.

The influence of xylitol and fluoride on dental erosion in vitro

The aim was to determine the effect of xylitol, fluoride and xylitol/fluoride combined on the erosion of dental enamel by pure orange juice in vitro. Freshly extracted bovine incisors were sectioned vertically into four equal portions. Each portion was then coated with an acid-resistant nail varnish except for an enamel window on the labial surface of the tooth. These were then divided into four groups with each group containing one portion of each tooth selected randomly. Four erosive agents were prepared as follows: (A) pure orange juice only; pure orange juice plus either (B) xylitol (25% w/v) or (C) fluoride (0.5 parts/10(6)) or D) xylitol/fluoride (25% and 0.5 parts/10(6) respectively). Each group was assigned to one of the erosive agents and immersed six times daily for a period of 5 min on each occasion and stored in artificial saliva between exposures and for 12 hr overnight, for 24 days making a total of 12 hr of exposure to the assigned erosive agent. Sections were cut from each enamel specimen ground to a thickness of 80 microns and microradiographed. Mineral loss was quantified by a two-step image analysis. Mineral loss was significantly lower (p < 0.05) in group D (xylitol/fluoride) only when compared with group A (pure orange juice only). The numerical values of mineral loss could be ranked as follows: group D < group C < group B < group A. It was concluded that xylitol and fluoride have an additive effect in the reduction of dental erosion by pure orange juice in vitro.

Diagnosis of dental caries using quantitative light-induced fluorescence

Current dental diagnostic methods can detect caries but cannot quantify the mineral status of the lesion. Quantitative Light-induced Fluorescence (QLF) measures the percentage fluorescence radiance change of demineralised enamel with respect to surround sound enamel, and related it directly to the amount of mineral lost during demineralisation. Demineralisation of teeth to produce caries-like lesions and the subsequent remineralisation of the lesions were monitored quantitatively and longitudinally with QLF. The influence of factors such as presence of plaque or saliva, lesion staining, lesion magnification, tooth thickness and developmental hypomineralisation, on the reproducibility of QLF imaging and analysis were investigated, Results showed that the integrated fluorescence change (hence the mineral loss) increased linearly with demineralisation time and decreased with increasing remineralisation time. Caries detection was limited by saliva or plaque, but enhanced by staining. QLF could not discriminate between developmental hypomineralisation and caries. Neither the variation in tooth thickness nor lesion magnification within the limit of a sharp image made a significant difference in QLF analysis. It was concluded that QLF could detect and quantitatively monitor the mineral changes in an incipient caries on a longitudinal basis, however detection may be limited by the presence of saliva or plaque or enhanced by staining.

Use of quantitative light-induced fluorescence to monitor tooth whitening

The changing of tooth shade by whitening agents occurs gradually. Apart from being subjective and affected by the conditions of the surroundings, visual observation cannot detect a very slight change in tooth color. An electronic method, which can communicate the color change quantitatively, would be more reliable. Quantitative Light- induced Fluorescence (QLF) was developed to detect and assess dental caries based on the phenomenon of change of autofluorescence of a tooth by demineralization. However, stains on the tooth surface exhibit the same phenomenon, and therefore QLF can be used to measure the percentage fluorescence change of stained enamel with respect to surrounding unstained enamel. The present study described a technique of assessing the effect of a tooth-whitening agent using QLF. This was demonstrated in two experiments in which either wholly or partially stained teeth were whitened by intermittent immersion in sodium hypochlorite. Following each immersion, the integrated fluorescence change due to the stain was quantified using QLF. In either situation, the value of (Delta) Q decreased linearly as the tooth regained its natural shade. It was concluded that gradual changing of the shade of discolored teeth by a whitening agent could be quantified using QLF.

En-face OCT technology for high-resolution imaging of tissue

En-face optical coherence tomography (OCT) technology is employed to produce high resolution images from the retina, cornea, skin and teeth. Longitudinal (B-scan) and transversal (C-scan) images are demonstrated using en-face scanning method. The main advantage of the en-face imaging is that the C-scan images permit a straightforward comparison with the images produced by confocal microscopy. Other developments are also presented as the generation of 3D imaging of different tissue using stacks of en- face OCT images collected at different depths.