In vitro evaluation of the early erosive lesion in polished and natural human enamel.

OBJECTIVE: This study evaluated the capability of profilometry, microhardness, Optical Coherence Tomography (OCT) and Tandem Scanning Confocal Microscopy (TSM) in characterising the early erosive lesion in polished and natural human enamel in vitro. METHODS: Polished (n=60) and natural (n=60) human enamel surfaces, were immersed and agitated in 0.3% citric acid erosion at 0s, 10s, 30s, 60s, 120s, and 300s (n=10). Changes in the surface were measured with 3D-step height change (µm), surface roughness (µm), surface microhardness (KHN), and images were assessed qualitatively with OCT and TSM. RESULTS: Mean (SD) 3D-step height change (µm) was measurable for polished enamel at: 60s (0.24±0.1), 120s (1.16±0.71), 300s (2.01±0.47; p<0.05); a step height change was not detectable on acid challenged natural enamel surfaces. Mean (SD) surface roughness (µm) of polished enamel was detected at 10s (0.270±0.013; p<0.05) and all erosion periods; and in natural enamel detected after 120s (0.830±0.125) and 300s (0.800±0.140; p<0.005). Polished enamel Mean (SD) microhardness (KHN) statistically significantly decreased at all time points (p<0.001); this was unmeasurable for natural enamel. Qualitative image analysis of both surface types indicated erosive change at the surface level, with progression after increasing erosion time. SIGNIFICANCE: The early erosive lesion in polished enamel could be characterised quantitatively surface roughness and microhardness and qualitatively using OCT and TSM; whilst in natural enamel only surface roughness could be utilised. Further investigation of early erosion in natural enamel is required to develop new more clinically relevant models.

Effects of tooth-brushing force with a desensitising dentifrice on dentine tubule patency and surface roughness.

OBJECTIVES: To investigate the effects of a 5% NovaMin containing dentifrice on dentine tubule patency and surface roughness at 100g and 400g tooth brush abrasion forces. METHODS: 75 polished human dentine samples were prepared and randomly allocated into one of five groups; control (1), Na2PFO3 100g abrasion force (2), NovaMin 100g (3), Na2PFO3 400g (4) and NovaMin 400g (5). The control group underwent two 2-min cycles of artificial saliva (AS), one 2-min erosion cycle; the rest underwent two toothbrush abrasion cycles in an AS/dentifrice slurry and one 2-min erosion cycle. All samples were imaged at baseline and post intervention using Tandem Scanning Microscopy and Profilometry to analyse tubule patency and roughness. RESULTS: Mean tubule patency increased significantly between baseline and post intervention in groups 1,2 and 4 and decreased significantly post intervention in groups 3 and 5 (p<0.01). Post intervention, there were statistically significant differences in mean patent tubules between NovaMin and the Na2PFO3 and control groups (p<0.001). Surface roughness increased for all groups between baseline and post interventions (P<0.001); mean (SD) roughness increases for groups 1, 2, 3, 4 and 5 were 0.14 (0.05) µm, 0.18 (0.04) µm, 0.16 (0.06) µm, 0.19 (0.07) µm and 0.21 (0.02) µm respectively. Differences between group 1 and 5 were significant (p<0.01). CONCLUSIONS: Brushing with NovaMin resulted in significant dentine tubule occlusion at 100g and 400g, but brushing with Na2PFO3 resulted in increased tubule patency. Surface roughness increased significantly at 400g brushing with NovaMin. There was no correlation between tubule patency and surface roughness. CLINICAL SIGNIFICANCE: A NovaMin desensitising dentifrice resulted in tubule occlusion even at high brushing forces. There was minimal increase in surface roughness at the lower (100g) brushing force.

Efficacy of sodium and stannous fluoride mouthrinses when used before single and multiple erosive challenges.

BACKGROUND: Application of fluoride mouthrinse before an acidic challenge may decrease enamel erosion. This paper compares the efficacy of stannous (SnF2 ) and sodium (NaF) fluoride when facing single and multiple erosive cycles in vitro. METHODS: Human enamel samples (N = 60) were randomly assigned to groups testing SnF2 and NaF mouthrinses (225 p.p.m.) and a water control. Samples were allocated into subgroups testing one or five erosive cycles. Samples were immersed in test solution for 1 min prior to citric acid immersion (0.3%, pH 3.2, 10 min), and the cycle repeated either one or five times. Analysis was done using profilometry and microhardness change. RESULTS: After one cycle, SnF2 resulted in least step height followed by NaF and water (1.3 µm (0.63), 2.3 µm (0.39), 4.3 µm (0.41) respectively; P < 0.0001). After five cycles SnF2 continued to reduce step height but pre-application of NaF was no different to water (4.6 µm (0.7), 10.5 µm (1.1) and 11.1 µm (0.38) respectively; P < 0.0001). There were no statistical differences in microhardness change between fluorides. After one erosive cycle, fluoride application resulted in statistically softer enamel compared with water. CONCLUSIONS: Both SnF2 and NaF reduced erosion after one cycle. After five cycles, SnF2 continued to offer protection whereas NaF was statistically comparable with water. Softening of enamel may not imply less erosion has occurred.

Confocal laser scanning microscopy and area-scale analysis used to quantify enamel surface textural changes from citric acid demineralization and salivary remineralization in vitro.

OBJECTIVES: This paper investigates the application of confocal laser scanning microscopy to determine the effect of acid-mediated erosive enamel wear on the micro-texture of polished human enamel in vitro. METHODS: Twenty polished enamel samples were prepared and subjected to a citric acid erosion and pooled human saliva remineralization model. Enamel surface microhardness was measured using a Knoop hardness tester, which confirmed that an early enamel erosion lesion was formed which was then subsequently completely remineralized. A confocal laser scanning microscope was used to capture high-resolution images of the enamel surfaces undergoing demineralization and remineralization. Area-scale analysis was used to identify the optimal feature size following which the surface texture was determined using the 3D (areal) texture parameter Sa. RESULTS: The Sa successfully characterized the enamel erosion and remineralization for the polished enamel samples (P<0.001). SIGNIFICANCE: Areal surface texture characterization of the surface events occurring during enamel demineralization and remineralization requires optical imaging instrumentation with lateral resolution <2.5 µm, applied in combination with appropriate filtering in order to remove unwanted waviness and roughness. These techniques will facilitate the development of novel methods for measuring early enamel erosion lesions in natural enamel surfaces in vivo.

Comparison of the possible protective effect of the salivary pellicle of individuals with and without erosion.

The acquired pellicle adheres to tooth surfaces and has been suggested to provide differing degrees of protection against acidic erosion. This study investigated whether pellicle formed on enamel blocks in patients suffering dietary dental erosion modified the effect of an in vitro simulated dietary challenge, in comparison with pellicle formed on enamel blocks in healthy subjects and to no-pellicle enamel samples. Sixty subjects recruited from dental erosion clinics were compared to healthy age-matched controls. Subjects wore a custom-made maxillary splint holding human enamel blocks for 1 h during which the acquired enamel pellicle was formed. Enamel blocks were removed from the splints and a simulated dietary erosive challenge of 10 min was performed. In addition the challenge was performed on 30 enamel samples without pellicle. Profilometry showed no statistical difference between samples from the erosion subjects with a mean step height of 1.74 µm (SD 0.88) and median roughness (Sa) of 0.39 µm (interquartile range, IQR 0.3-0.56) and the controls with 1.34 µm (SD 0.66) and 0.33 µm (IQR 0.27-0.38), respectively. The control samples without pellicle had Sa of 0.44 µm (IQR 0.36-0.69) and these differences were statistically significant compared to those from the healthy subjects (p = 0.002). Mean (SD) microhardness reduction with a 100-gram load for the erosion group was 113.5 (10) KHN, for healthy subjects was 93 (15.4) KHN and for the enamel samples without pellicle 139.6 (21.8) KHN and all groups were statistically different. The microhardness and roughness data suggested the pellicle influenced erosion under these study conditions.

Occlusal tooth wear in Chinese adults with shortened dental arches.

To assess associations between occlusal tooth wear and shortened dental arches (SDA) in Chinese 40 years and older subjects. From a sample of 1462 urban and rural adults, those presenting with SDA (n = 150) were compared with a control group of 65 randomly selected subjects with complete dentitions (CDA). Occlusal wear was assessed using a modified Smith and Knight index - the occlusal tooth wear index (OWTI) - and analysed using multivariate (logistic) regression. There was no significant effect from SDA on severe occlusal wear (OTWI score 3 or 4: OR = 2.016; 95% CI = 0.960-4.231; P = 0.064). Higher age was associated with severe occlusal wear (P values ≤0.007) and with higher mean OTWI scores; urban had less often severe occlusal wear than rural residents (OR = 0.519; P = 0.008). Higher mean OTWI scores were associated with rural residents, except for anterior teeth. Females had lower mean OTWI score for anterior teeth (effect = -0.153; P = 0.030). Premolars in SDA had higher mean OTWI scores compared with those in CDA (effect = +0.213; P = 0.006). In SDA, more posterior occluding pairs (POPs) were associated with lower mean OTWI sores for anterior teeth (effect: -0.158; P = 0.008) and higher scores for molars (effect: +0.249, P = 0.003). Subjects with SDA or CDA presented comparable occlusal wear, but premolars in SDA tend to have higher probability for having occlusal wear. Fewer numbers of POPs were associated with more wear in anterior teeth.

Prevalence of tooth wear on buccal and lingual surfaces and possible risk factors in young European adults.

To assess the prevalence of tooth wear on buccal/facial and lingual/palatal tooth surfaces and identify related risk factors in a sample of young European adults, aged 18-35 years. Calibrated and trained examiners measured tooth wear, using the basic erosive wear examination (BEWE) on in 3187 patients in seven European countries and assessed the impact of risk factors with a previously validated questionnaire. Each individual was characterized by the highest BEWE score recorded for any scoreable surface. Bivariate analyses examined the proportion of participants who scored 2 or 3 in relation to a range of demographic, dietary and oral care variables. The highest tooth wear BEWE score was 0 for 1368 patients (42.9%), 1 for 883 (27.7%), 2 for 831 (26.1%) and 3 for 105 (3.3%). There were large differences between different countries with the highest levels of tooth wear observed in the UK. Important risk factors for tooth wear included heartburn or acid reflux, repeated vomiting, residence in rural areas, electric tooth brushing and snoring. We found no evidence that waiting after breakfast before tooth brushing has any effect on the degree of tooth wear (p=0.088). Fresh fruit and juice intake was positively associated with tooth wear. In this adult sample 29% had signs of tooth wear making it a common presenting feature in European adults.

Tooth wear with an erosive component in a Mediaeval Iceland population.

OBJECTIVES: Dental erosion is generally thought of as a modern phenomenon, but there is emerging evidence that the condition has always been present in the human dentition to some degree. The aim of this study was to quantitatively evaluate the severity of tooth wear observed in skeletal material from a mediaeval population of the farm at Hofstaðir, Mývatnssveit, in northeast Iceland. METHODS: The teeth were examined and tooth wear was quantified using the Smith and Knight Tooth Wear Index. All surfaces of the teeth were examined by a single trained examiner from 53 adult skulls available (24 males and 29 female). The majority of the skulls were examined at the stores of Þjóðminjasafn Íslands (The National Museum of Iceland) using good lighting and magnification. RESULTS: There were a total of 1696 possible teeth and 6784 surfaces, and from this 69.5% were scored. There was a higher overall rate of wear in the mandibular dentitions and that the highest wear rates were seen on the occlusal/incisal surfaces of the 1st and 2nd molars and the premolars. For the group, and from those surfaces available for scoring, dentine was exposed on 1464 surfaces (31%). There was no evidence of cervical wear. CONCLUSION: High levels of tooth wear were observed in this Icelandic assemblage and the appearance was characteristic of both chemical and physical wear.

A preliminary investigation into the use of denture adhesives combined with dietary advice to improve diets in complete denture wearers.

OBJECTIVES: To investigate how nutritional advice and denture adhesives may be associated with eating healthier foods. METHODS: 35 edentulous subjects (13 males and 22 females, mean age 73.9 years (55-84 years)), wearing complete dentures more than one year old, completed validated questionnaires analysing saturated fat, protein, Vitamin C, the number of servings of fruit/vegetables. In addition subjects completed the NDNS and OHIP Edent questionnaires. At baseline, nutritional information and the use of denture adhesive was provided. Subjects returned after 30 consecutive days and the questionnaires were repeated. A Wilcoxon signed rank test was used to test the effect of the denture adhesive on diet and on quality of life measures. RESULTS: The subjects increased mean intake from 2.2 portions of fruit/vegetables a day to 3.6. Fat and saturated fats were reduced from 23.2g to 11.3g and Vitamin C intake increased by 34.4mg. All were statistically significant (p<0.0001). There was a statistically significant improvement over the 30-day treatment period in subjects' ability as measured by using OHIP Edent scores to bite (p=0.017) and chew a range of foods (p=0.007). CONCLUSION: Within the confines of the study, use of simple dietary advice and denture adhesives improved diet. CLINICAL SIGNIFICANCE: The results of this pilot study suggest that denture fixatives may improve dietary behaviour of complete denture wearers.

A method to evaluate profilometric tooth wear measurements.

OBJECTIVES: To test the accuracy of measurements of tooth wear using a non-contacting laser profilometer (NCLP) and surface matching software. METHODS: The accuracy and repeatability of the NCLP and software in measuring length was assessed by repeatedly scanning a calibrated 25 mm engineering steel gage block. Volumetric measurements were assessed after scanning commercially pure titanium frustums of varying volume. The accuracy and repeatability of the systems in measuring step height and volume after surface matching were assessed using a custom built model with cemented engineering slip gages and cemented onlays of super-plastically formed titanium. The overall effect on the uncertainty of measurement of repeated superimpositions of the same cast, repeated impressions of the same patient and using step-over distances smaller than the laser spot size were also quantified. RESULTS: The accuracy and repeatability were 1.3 µm and 1.6 µm in measuring length. The system was accurate for volumetric measurement with coefficients of variation <5%. Measurements using the model with cemented engineering slip gages and cemented super-plastically formed titanium onlays varied slightly (23.07 µm and 1.6 mm(3)). Scanning and superimposing the same model introduced mean error of 2.7 µm (SD=0.7). Scanning and superimposing separate casts from repeated impressions of a patient introduced mean error of 14.8 µm (SD=2.8). Decreasing step-over distances reduced measurement error (p<0.05). SIGNIFICANCE: The methodologies described here served to assess sources of error in tribology studies using surface mapping and surface matching technologies. The results optimized data interpretation. Study supported by Guy's and St. Thomas' Charity and the Royal College of Surgeons of England.

In vivo measurements of tooth wear over 12 months.

The aim of this study was to measure the progression of tooth wear in a cohort of 63 patients, 43 males and 20 females with a mean age of 39.1 years. Recruitment followed referral from general practice to Guy's Hospital for advice/management of tooth wear. Addition silicone impressions were taken at 6-month intervals for a total of 12 months; impressions were subsequently poured in type IV gypsum. Casts were scanned using a non-contacting laser profilometer and then superimposed using Geomagic® Qualify 11. Wear was measured in µm by tooth per time interval. A questionnaire highlighting dietary, parafunctional and gastric risk factors was obtained from each participant. Clustered multiple regression analysis was used to determine the relationship between tooth wear progression and risk factors. Maximum follow-up times were 6 months for 63 participants and 12 months for 30 participants. The measurement error was 15 µm. At the tooth level, 72.2% of 1,078 teeth wore <15 µm over a 6-month period. At the subject level, 77.7% of 63 participants showed median wear <15 µm over a 6-month period. There was a statistical trend towards tooth wear progression being associated with gastric risk factors (p < 0.05). The lower molars and the upper anterior teeth were the most commonly affected teeth; the lower molars and the upper central incisors were the most severely affected teeth. Tooth wear progression was slow in this cohort, suggesting that tooth wear may be cyclical and inactive in the majority of participants.

The association of tooth wear, diet and dietary habits in adults aged 18-30 years old.

OBJECTIVE: The association of acidic foods and drinks to the development of erosive tooth wear was investigated in a single cohort of adults aged 18-30 years. METHOD: A tooth wear index was recorded on 1010 participant's who had a mean age of 21.9 years (SD 0.1) and of which 70% were female and 30% males. Participant's completed a previously validated questionnaire containing 50 questions about current and historical dietary habits. Data were analysed at the tooth level using odds ratio. RESULTS: Tooth wear was statistically significantly associated to acidic foods and drinks with high titratable acidity and dietary habits, including drinking from a glass and holding drinks, (OR 5 and 6.5 respectively). A history of heartburn was statistically significantly associated to palatal dentine exposure (p≤0.05 and OR 7.6). CONCLUSION: In this sample of adults, tooth wear was associated to a number of acidic dietary products and drinking habits.

A qualitative and quantitative investigation into the effect of fluoride formulations on enamel erosion and erosion-abrasion in vitro.

OBJECTIVES: To investigate the effect of a single application of highly concentrated SnF(2) and NaF solutions and a NaF/CaF(2) varnish on human enamel subjected to hydrochloric acid erosion and tooth brush abrasion. METHODS: Forty enamel samples were prepared from human third molars and NaF (9500ppm, pH 8.0), SnF(2) (9500ppm, pH 2.6) solutions; Bifluorid10(®) varnish (42,500ppm, NaF 5%, CaF(2) 5%) and deionized water (control) was applied to the enamel. Following this three, six and nine cycles of erosion [1 cycle=erosion (0.01M HCl, pH 2.2, 2min)+artificial saliva (1h, pH 7.0)] and erosion-abrasion [1 cycle=erosion (0.01M HCl, pH 2.2, 2min)+artificial saliva (1h, pH 7.0)+abrasion (120 linear strokes in artificial saliva from Tepe medium soft brushes 200g loading)] were carried out. The fluoride treated enamel was analysed using Knoop microhardness, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). RESULTS: For erosion alone, there was significantly less microhardness reduction in the Bifluorid10(®) group after three and six cycles of erosion (P<0.05), however no other groups showed statistically different hardness (P>0.05). The EDS analysis showed that only the Bifluorid10(®) group had any detectable fluorine following erosion and erosion-abrasion (0.1wt.% and 0.2wt.% fluorine respectively). The surface fluorine was found to have been removed after erosion and erosion-abrasion for all other surface treatments. Although precipitates were observed after application of the surface treatments, following erosion-abrasion, no visible surface effects from any fluoride preparation remained. CONCLUSIONS: Enamel surface precipitates from application NaF, SnF(2) solutions appear to not be able to provide protection against gastric erosion and tooth brush abrasion. The NaF/CaF(2) varnish provided limited protection against erosion but the role for such varnishes in gastric erosion and tooth brush abrasion remains uncertain.

An experiment on the attrition of acid demineralized dentine in vitro.

BACKGROUND: A laboratory investigation was designed to test the hypothesis that acids increase the rate of wear caused by attrition on dentine. METHODS: Dentine sections from 10 teeth were polished, cleaned in an ultrasonic bath and divided into 8 equally sized areas. The occlusal tip of a tooth, placed vertically in a wear machine and loaded at 150 N, was moved against each dentine section for 5000 return strokes with artificial saliva acting as a lubricant. Each dentine section was divided into 8 sections and half randomly immersed in a 1% citric acid solution (pH 2.3) for 20 minutes. The wear regime produced 8 wear scars in total per dentine sample. The volume of each wear scar was measured using a contacting digitizing profilometer. RESULTS: A total of 80 wear scars were produced with 40 treated with acid and 40 acting as controls. The mean for wear volume of the dentine scars with acid was 4.84 µm(3) (1.38) and for the non-acid surface 2.95 µm(3) (0.86). This difference was statistically significant (p < 0.05). CONCLUSIONS: These results support the hypothesis that acids increase the rate of wear caused by attrition on dentine.

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro.

OBJECTIVES: To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro. METHODS: Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm x 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n=10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle=artificial saliva (2h, pH 7.0)+erosion (0.3% citric acid, pH 3.2, 5 min)+fluoride/control (5 min)+attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in mum was measured using optical profilometry. RESULTS: When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences. CONCLUSIONS: The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine.

Systematic review of the prevalence of tooth wear in children and adolescents.

Data on the prevalence of tooth wear among children and adolescents are inconsistent. Given the impact of extensive tooth wear for over a lifetime, evidence on the extent is required. The aim was to systematically review the literature on the prevalence of tooth wear in children and adolescents. A PubMed literature search (1980-2008) used the keywords 'tooth' AND 'wear'; 'dental' AND 'attrition' AND 'prevalence'; 'dental' AND 'wear' AND 'prevalence'; 'erosion AND prevalence' AND 'abrasion AND prevalence'. Following exclusion criteria, 29 papers were reviewed using established review methods. There was a total of 45,186 subjects (smallest study 80 and largest study 17,047 subjects) examined from thirteen multiple random clusters, eight multiple convenience clusters and eight convenience clusters. Nine different tooth wear indices were used, but the common denominator among studies was dentin exposure as an indicator of severe wear. Forest plots indicated substantial heterogeneity of the included studies. Prevalence of wear involving dentin ranged from 0 to 82% for deciduous teeth in children up to 7 years; regression analysis showed age and wear to be significantly related. Most of the studies in the permanent dentition showed low dentin exposure, a few reported high prevalence (range 0-54%); age and wear were not related (regression analysis). The results of this systematic review indicate that the prevalence of tooth wear leading to dentin exposure in deciduous teeth increases with age. Increase in wear of permanent teeth with age in adolescents up to 18 years old was not substantiated.

The effect of casein phosphopeptide-amorphous calcium phosphate on erosive enamel and dentine wear by toothbrush abrasion.

OBJECTIVE: In addition to its role as a remineralizing agent in preventing dental caries, calcium product (CPP-ACP) delivered as a mousse (Tooth Mousse, TM) can reduce erosion of enamel and dentine. The aim of this study was to determine whether CPP-ACP could also reduce erosive tooth wear involving toothbrush abrasion. METHODS: Flat, polished enamel and dentine specimens (n=72) were subjected to 10 wear regimes, with each regime involving erosion in 0.3% citric acid (pH 3.2) for 10 min followed by toothbrush abrasion in a slurry of fluoride-free toothpaste and artificial saliva (1:3 ratio by weight) under a load of 2N for 200 cycles. The specimens were immersed in artificial saliva for 2h between wear regimes. In the experimental group 1, TM (containing CPP-ACP) was applied at the beginning of each wear episode for 5 min whereas TM- (without CPP-ACP) was applied in the experimental group 2. No mousse was applied in the control group. RESULTS: TM significantly reduced enamel wear (mean+/-S.E., 1.26+/-0.33 microm in the experimental group 1 vs 3.48+/-0.43 microm in the control group) and dentine wear (2.16+/-0.89 microm in the experimental group 1 vs 10.29+/-1.64 microm in the control group), and dentine wear was significantly less in the experimental group 1 than in the experimental group 2 (5.75+/-0.98 microm). CONCLUSION: The finding that TM reduced erosive tooth wear involving toothbrush abrasion, probably by remineralizing and lubricating eroded tooth surfaces, may have implications in the management of tooth wear.

The microhardness of bleached dentine and its bond strength to a dentine bonding agent.

The aim of this study was to measure the hardness of a bleached dentine surface and its bond strength to a dentine-bonding agent. Thirty teeth were randomly divided into a test and control group. The teeth were hemi-sectioned, the cut surfaces ground flat and the test surfaces bleached with a 10% aqueous solution of carbamide peroxide continuously for 4 days. Hardness was determined using a Vickers microhardness test. The bond between Coltene 'One Coat Bond' and bleached and unbleached dentine was evaluated by measuring shear bond strength using an Instron machine. The mean hardness of dentine before and after bleaching was 62.5 (10.2) and 53.6 (7.3) and this difference was statistically different (p<0.001). For the controls immersed in water the hardness was before 60.8 (standard deviation: 7.2) and after 59.6 (8.2) respectively. The mean shear bond strength for the unbleached was 5.5MPa (1.6) and for the bleached samples was 3.3MPa (1.8) and this difference was statistically significant (p<0.002). Under these study conditions the Vickers hardness and bond strength to dentine was reduced by bleaching.

Effect of resin coating on dentine compared to repeated topical applications of fluoride mouthwash after an abrasion and erosion wear regime.

OBJECTIVES: The role of fluoride in preventing erosion and abrasion on dentine remains unclear. The aim of this study was to investigate the effect of repeated applications of a 0.05% fluoride mouthwash and an adhesive on wear of dentine using stainless steel discs reference points and a laser profilometer. METHODS: Small stainless steel discs were bonded to 60 caries free extracted molars which had previously been sectioned horizontally. The teeth were equally divided and subjected to four modalities in an erosion and abrasion laboratory model. Step heights were measured from the metal discs using a non-contacting laser profilometer at 100, 500, 1000, 2500 and 5000 cycles. RESULTS: The results after 5000 cycles showed that dentine coated with a dentine adhesive (0.015 microm, S.D. 0.090) had statistically less wear than fluoride (0.127 microm, S.D. 0.150), abrasion and erosion (0.182 microm, S.D. 0.150) or abrasion only (0.096 microm, S.D. 0.090) (p<0.001). CONCLUSION: In conclusion dentine surfaces coated with a resin-based adhesive provided more protection against erosion and abrasion than a fluoride mouthrinse. There were no statistical differences between the modalities for cycles less than 5000.