Comparison of Calcium/Phosphorus Analysis, Longitudinal Microradiography and Profilometry for the Quantitative Assessment of Erosive Demineralisation

Effect of combining aminomethacrylate and fluoride against erosive and abrasive challenges on enamel and dentin

This study evaluated the effect of solutions containing aminomethacrylate copolymer (AA) and sodium fluoride (F; 225 ppm F-) or fluoride plus stannous chloride (FSn; 225 ppm F-, 800 ppm Sn2+) against enamel and dentin erosion/abrasion. Solutions F, FSn, AA, F+AA, FSn+AA, and deionized water as negative control were tested. Bovine enamel and dentin specimens (n = 13/solution/substrate) underwent a set of erosion-abrasion cycles (0.3% citric acid [5 min, 4×/day], human saliva [1 h, 4×/day], brushing [15 s, 2×/day], and treatments [2 min, 2×/day]) for each of five days. Initial enamel erosion was evaluated using Knoop microhardness after the first and second acid challenge on day 1, and surface loss with profilometry after day 5. KOH-soluble fluoride was assessed. Data were analyzed with ANOVA/Tukey tests. The combination of fluoride and AA resulted in higher protection against enamel erosion, whereas this was not the case for the combination of AA and FSn. All treatments protected against enamel and dentin loss. The lowest surface loss values were observed with F+AA and FSn+AA. The polymer did not significantly influence the KOH-soluble fluoride formation on enamel/dentin specimens. The aminomethacrylate copolymer effectively enhanced the efficacy of sodium fluoride against initial erosion and improved the control of enamel and dentin wear of F and FSn solutions.

Assessment of demineralized tooth lesions using optical coherence tomography and other state-of-the-art technologies: a review

Tooth demineralization is one of the most common intraoral diseases, encompassing (1) caries caused by acid-producing bacteria and (2) erosion induced by acid of non-bacterial origin from intrinsic sources (e.g. stomach acid reflux) and extrinsic sources (e.g. carbonated drinks). Current clinical assessment based on visual-tactile examination and standardized scoring systems is insufficient for early detection. A combination of clinical examination and technology is therefore increasingly adapted. This paper reviews various procedures and technologies that have been invented to diagnose and assess the severity of tooth demineralization, with focus on optical coherence tomography (OCT). As a micron-resolution non-invasive 3D imaging modality, variants of OCT are now available, offering many advantages under different working principles for detailed analytical assessment of tooth demineralization. The roles, capabilities and impact of OCT against other state-of-the-art technologies in both clinical and research settings are described. (139 words).

Characterization of dynamic process of carious and erosive demineralization - an overview

To review the analytical methods for carious and erosive demineralization an initial search of peer-reviewed scientific literature from the digital library database of PubMed/Medline indexed journals published up to early 2022 was carried out based on keywords relevant to the topic criteria including bibliographic citations from the papers to gather the most updated information. This current review aims to provide an updated overview of the advantages, limitations, and potential applications of direct and indirect research methods available for studying various dynamic stages of carious and erosive demineralization in enamel and dentin. This paper categorizes and describes the most suitable, frequently adopted and widely used quantitative and qualitative techniques in in vitro/in vivo research which are well-established, emerging, or comparatively novel techniques that are being explored for their potential validation.

A novel non-destructive technique for qualitative and quantitative measurement of dental erosion in its entirety by porosity and bulk tissue-loss

OBJECTIVE

To explore the potential of combining non-contact profilometry (NCP) and confocal laser scanning microscopy (CLSM) data to measure the entire erosive process non-destructively and to validate findings using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and surface microhardness (SMH) using the same samples throughout.

METHODS

Polished bovine enamel samples (n = 35) were divided into groups (7/group) with similar SMH values. Samples underwent individual erosive challenges (1 % citric acid, pH3.8) for 1, 5, 10, 15 or 30 min under stirring and aliquot extracts were analysed for Ca and P by ICP-AES. SMH was used to measure erosive softening. Profilometry was used to assess bulk volume loss (BVL). Images were captured by SEM. Samples were stained with rhodamine-B (0.1 mM, 24 h) and images captured by CLSM. Image processing was used to determine changes in fluorescent volume for the first 10 μm (ΔFV₁₀) for each enamel sample which were combined with BVL to calculate total lesion volume (TLV). ANOVA, linear regression and Pearson correlation analysis were used where applicable.

RESULTS

Surface softening, [Ca], [P], BVL and ΔFV_10μm increased with acid erosion duration which were significant by 10 min (P < .01). The Ca:P ratio increased to 1.57 then decreased after 5 min erosion suggesting a sub/surface phase change, which was observed by SEM and CLSM showing significant changes to the enamel surface and subsurface morphology with time. Combination of BVL and ΔFV₁₀ as TLV strengthened the significant correlations with [Ca], [P], and SMH (P < .01).

CONCLUSION

This novel combination of CLSM and NCP allows for concurrent non-destructive quantification of the entire erosive process by mineral loss, and qualitatively characterise microstructural changes during dental erosion.

Monitoring of Erosive Tooth Wear with Intraoral Scanners In vitro

Intraoral scanners (IOS) have been used to quantify tooth wear, but so far they have not been systematically validated for monitoring of tissue loss. The aim of this in vitro study was to investigate whether progression of tissue loss can be detected with an IOS and whether IOS values agree with those obtained with noncontacting profilometry (PRO) serving as a standard method. Model jaws were mounted in a phantom head positioned in a dental chair. Flattened areas were prepared on the non-load-bearing cusps of the first molars (model teeth; n = 16) in order to fix flat enamel samples with an experimental area and a reference area. After baseline PRO and IOS, the experimental enamel area was stepwise etched with 35% H3PO4 gel (4 × 30 s and 4 × 15 s). After each etching, PRO and IOS was performed and the vertical tissue loss between the reference and experimental areas was measured, each at the same 3 measurement points. Furthermore, cupped cusps were simulated by stepwise preparation of the load-bearing cusps of the model teeth with a spherical diamond bur, and the maximum vertical depth after each preparation step was measured only by IOS. Trios3 (3Shape, Denmark), Carestream CS3600 (Carestream, USA) and an optical profilometer (MicroProf, Fries, Germany) were used to measure the flat areas of the enamel samples, whereas only IOS were used to measure curved surfaces on the load-bearing cupped cusps of the model teeth. The IOS data were analyzed with an external software (GOM Inspect, Germany) and with the respective internal IOS software. PRO revealed a mean (±SD) tissue loss of 17.1 ± 4.7 µm after 30-s etching steps and 10.1 ± 5.1 µm after the 15-s etching steps. IOS and software types were able to detect the progression of tissue loss after each etching step (p ≤ 0.001 each); Bland-Altmann plots revealed good agreement with PRO regardless of the order of tissue loss, and no systematic difference was found. Increasing cupped lesion depths were detected by all IOS, with no significant differences between IOS and analysis methods. IOS were able to detect small amounts of tissue loss under simulated clinical conditions and seem to be a promising tool for monitoring even initial erosive tooth wear.

In vitro and In vivo evaluation of resin composites fluorescence

This study aimed at comparatively evaluate, by visual method, the fluorescence intensity in vitro and in vivo of six resins composed of different classifications and viscosities compared to natural enamel. For the in vitro study, seventy specimens were prepared and for the in vivo study, a restoration was performed on the cervical portion of the buccal face of 6 anterior maxillary teeth, which under ultraviolet light were compared to the dental structure. The specimens and restorations were photographed only under the illumination of an ultraviolet lamp. The photographic record was performed, with standardized parameters for all photographs (ISO 100). After visual analysis of the images by three evaluators calibrated in the in vitro study and by ten evaluators calibrated in the in vivo study, numerical values were assigned to resins without fluorescence (zero), medium fluorescence (1) and high fluorescence (2). The evaluations were submitted to the Kruskal-Wallis and Dunn test, which among the limitations of this study and according to the employed methodology, it was found that there was no statistical difference in fluorescence intensity among the composite resins evaluated, since all types of resins achieved fluorescent metamerism with dental enamel.

Influence of Erosive and Abrasive Cycling on Bonding of Different Adhesive Systems to Enamel: An In situ Study

This study evaluated the impact of orange juice on the bond strength (BS) of dentin bonding systems (DBSs) to enamel surface after simulation with an in situ/ ex vivo erosive cycling. One hundred and ninety two bovine enamel fragments (4x4x2mm) were obtained and randomized regarding superficial microhardness and distributed to palatal devices for 8 volunteers, in three phases (one for each DBS), containing 8 blocks, which were, allocated in 4 pairs. Daily, these pairs were subjected extraorally to the following conditions: CONT- neither erosive nor abrasive challenge; ERO- erosive challenge only; ABR- abrasive challenge only and ERO + ABR- with erosive and abrasive challenges. Erosive cycles (immersion in orange juice, 3 times/day/5 min/5 days) or/and abrasive challenges (electric toothbrush, 3 times/day/1 min/5 days) were performed. After these cycles, all specimens were restored with the adhesive systems Adper Scotchbond Multi Purpose (MP), Adper Single Bond 2 (SB) or Clearfil SE Bond (SE), and the composite resin Filtek Z250. After 7 days, sticks (area ≅1 mm2) were obtained and subjected to the microtensile bond strength test (μTBS) at 0.5 mm/min. Data was statistically analyzed by ANOVA and Tukey tests (a=0.05). Failure modes were determined using a digital microscope (40´). DBS was the only statistical significant factor. SE was the unique DBS not affected in any challenge, whereas MP and SB performed according to the scenario. The adhesive and mixed failures were predominant in all groups. Overall performance suggested that BS to enamel after erosive /abrasive challenged by orange juice was not affected and it was material-dependent.

Comparison of the microhardness of primary and permanent teeth after immersion in two types of carbonated beverages

OBJECTIVES

The consumption of carbonated beverages is one of the etiological factors that cause dental erosion. The purpose of this research was to compare changes in the microhardness of permanent and primary teeth after immersion in two types of carbonated beverages.

MATERIALS AND METHODS

This investigation was done on 30 healthy permanent molars and 30 healthy primary canines. Each group of primary and permanent teeth was subdivided into three groups of 10 teeth. The teeth was immersed in 40 ml of each of the three beverages for 5 min. One subgroup was immersed in water (as a control). The next was immersed in Lemon Delster and the last subgroup was immersed in Coca-Cola. The microhardness of enamel was measured using the Vickers method before and after immersion. Finally, the data was analyzed by paired t-test, one-way analysis of variance, and t-test.

RESULTS

Microhardness reduction in the primary teeth was significant in both the Lemon Delster and Coca-Cola groups (P < 0.05). This reduction was also statistically significant in the permanent teeth (P < 0.05). A comparison of the enamel changes in the primary teeth with permanent teeth after immersion in both beverages showed a greater microhardness reduction in the primary teeth in both the experimental groups.

CONCLUSIONS

Coca-Cola and Lemon Delster caused a significant reduction of microhardness in tooth enamel. This reduction was greater in primary teeth than in permanent teeth, and was also greater after immersion in Coca-Cola than after immersion in Lemon Delster.

A new hand-held optical reflectometer to measure enamel erosion: correlation with surface hardness and calcium release

In the present study, the surface reflection intensity (SRI) was measured from enamel with different induced erosion degrees using a hand-held pen-size reflectometer (Hand-Held) and a Table-Top reflectometer. To validate the Hand-Held reflectometer, we correlated its optical signals with the change of surface microhardness (SMH), and amount of calcium released from the enamel samples during erosion. We used 124 tooth enamel specimens that were exposed to an erosive challenge of either 1, 2, 4, 6, 8, or 10 minutes. SRI and SMH were measured before and after the erosive challenge and we also measured the amount of calcium released to the citric acid. Relative SRI loss (rSRI_loss) and relative SMH loss (rSMH_loss) were calculated. rSRI_loss from the Hand-Held and the Table-Top reflectometers were similar and significantly correlated to rSMH_loss and calcium release. The regression analyses showed a significant association between rSRI_loss from both reflectometers and rSMH_loss and calcium, showing that both reflectometers can be used to measure erosive demineralization of enamel. The Hand-Held reflectometer is capable of assessing in vitro erosion, correlating to other commonly used methods. It is small, easy to handle and provides fast measurement, being a possible candidate to measure erosion in clinical studies.

The effect of air-abrasion on the susceptibility of sound enamel to acid challenge

OBJECTIVE

To evaluate the effect of air-abrasion using three abrasive powders, on the susceptibility of sound enamel to an acid challenge.

METHODS

40 human enamel samples were flattened, polished and assigned to 4 experimental groups (n=10); a: alumina air-abrasion, b: sodium bicarbonate air-abrasion, c: bioactive glass (BAG) air-abrasion and d: no surface treatment (control). White light confocal profilometry was used to measure the step height enamel loss of the abraded area within each sample at three stages; after sample preparation (baseline), after air-abrasion and finally after exposing the samples to pH-cycling for 10 days. Data was analysed statistically using one-way ANOVA with Tukey's HSD post-hoc tests (p<0.05). Unique prismatic structures generated by abrasion and subsequent pH cycling were imaged using multiphoton excitation microscopy, exploiting strong autofluorescence properties of the enamel without labelling. Z-stacks of treated and equivalent control surfaces were used to generate non-destructively 3-dimensional surface profiles similar to those produced by scanning electron microscopy.

RESULTS

There was no significant difference in the step height enamel loss after initial surface air-abrasion compared to the negative control group. However, a significant increase in the step height enamel loss was observed in the alumina air-abraded samples after pH-cycling compared to the negative control (p<0.05). Sodium bicarbonate as well as BAG air-abrasion exhibited similar enamel surface loss to that detected in the negative control group (p>0.05). Surface profile examination revealed a deposition effect across sodium bicarbonate and BAG-abraded groups.

CONCLUSION

This study demonstrates the importance of powder selection when using air abrasion technology in clinical dentistry. Pre-treating the enamel surface with alumina air-abrasion significantly increased its susceptibility to acid challenge. Therefore, when using alumina air-abrasion clinically, clinicians must be aware that abrading sound enamel excessively renders that surface more susceptible to the effects of acid erosion. BAG and sodium bicarbonate powders were less invasive when compared to the alumina powder, supporting their use for controlled surface stain removal from enamel where indicated clinically.

Enamel demineralization after different methods of interproximal polishing

OBJECTIVES

The aim of this in vitro study was to investigate the demineralization rate in human enamel after interproximal polishing (IPP) and to detect possible correlations with the IPP method used, with special emphasis on the surface characteristics of the enamel being treated.

MATERIALS AND METHODS

This in vitro study tested five IPP systems (Profin Directional System®, Intensiv ProxoStrip®, OS discs®, ARS Safe-Tipped Bur Kit® and Ortho-Strips Set®) that are currently available on the market. Each of the five examination groups comprised 12 randomly selected teeth, while the control group consisted of six teeth. The teeth were placed in an artificial model for each group. The proximal contacts were then resolved by IPP. To allow detection of any surface characteristics, one surface was not further processed after IPP, while the other side was additionally polished. After IPP, the teeth were exposed to a pH-cycling model with alternating phases of demineralization and remineralization. Substance loss was analyzed using optical emission spectrometry. Data were subjected to simple analysis of variance (ANOVA) performed with Tukey's test. Comparison between the groups with and without polishing was conducted using the t test for independent samples. The significance level was set at p < 0.05.

RESULTS

Demineralization significantly increased after IPP. The rates of demineralization differed significantly among the examination groups, with the greatest loss of substance being produced with Sheridan's Air-Rotor Stripping® system (ARS; 145.34 ± 20.37 μm). In all of the examination groups, subsequent polishing of the surfaces did not significantly reduce the amount of demineralization (polished 119.64 ± 28.61 μm; unpolished 114.16 ± 28.61 μm).

CONCLUSION

No correlation between surface morphology and the degree of susceptibility of human enamel was detected. However, it must be taken into consideration that there was no potential bacterial colonization in this in vitro erosive set-up. Thus, in contrast to previous explanations, the outermost fluorapatite layer and the individual composition of the enamel may have a greater impact on the solubility of the enamel and the amount of enamel loss after IPP than the type of system used and the resulting surface texture.

CLINICAL RELEVANCE

Whenever the outermost layer of enamel is reduced, the practitioner must expect an increase in demineralization. Subsequent polishing does not appear to affect the amount of demineralization.

Comparison of four methods to assess erosive substance loss of dentin

Erosion of dentin results in a complex multi-layered lesion. Several methods have been used to measure erosive substance loss of dentin, but were found to have only limited agreement, in parts because they assess different structural parameters. The present study compared the agreement of four different methods (transversal microradiography [TMR], Confocal Laser Scanning Microscopy [CLSM], Laser Profilometry [LPM] and modified Knoop Hardness measurement [KHM]) to measure erosive substance loss in vitro. Ninety-six dentin specimens were prepared from bovine roots, embedded, ground, polished and covered with nail-varnish except for an experimental window. Erosion was performed for 1 h using citric acid concentrations of 0.00% (control), 0.07%, 0.25% and 1.00% (n = 24/group). Adjacent surfaces served as sound reference. Two examiners independently determined the substance loss. After 1 h erosion with 1% citric acid solution, substance losses (mean±SD) of 12.0±1.3 µm (TMR), 2.9±1.3 µm (LPM), 3.9±1.3 µm (KHM) and 17.0±2.6 µm (CLSM) were detected. ROC curve analysis found all methods to have high accuracy for discriminating different degrees of erosive substance loss (AUC 0.83–1.00). Stepwise discriminatory analysis found TMR and CLSM to have the highest discriminatory power. All methods showed significant relative and proportional bias (p<0.001). The smallest albeit significant disagreement was found between LPM and KHM. No significant inter-rater bias was detected except for KHM. LPM is prone to underestimate erosive loss, possibly due to detection of the organic surface layer. KHM was not found suitable to measure erosive loss in dentin. TMR and CLSM detected the loss of mineralised tissue, showed high reliability, and had the highest discriminatory power. Different methods might be suitable to measure different structural parameters.

Trimodal detection of early childhood caries using laser light scanning and fluorescence spectroscopy: clinical prototype

There is currently a need for a safe and effective way to detect and diagnose early stages of childhood caries. A multimodal optical clinical prototype for diagnosing caries demineralization in vivo has been developed. The device can be used to quickly image and screen for any signs of demineralized enamel by obtaining high-resolution and high-contrast surface images using a 405-nm laser as the illumination source, as well as obtaining autofluorescence and bacterial fluorescence images. When a suspicious region of demineralization is located, the device also performs dual laser fluorescence spectroscopy using 405- and 532-nm laser excitation. An autofluorescence ratio of the two excitation lasers is computed and used to quantitatively diagnose enamel health. The device was tested on five patients in vivo as well as on 28 extracted teeth with clinically diagnosed carious lesions. The device was able to provide detailed images that highlighted the lesions identified by the clinicians. The autofluorescence spectroscopic ratios obtained from the extracted teeth successfully quantitatively discriminated between sound and demineralized enamel.

Measuring enamel erosion: a comparative study of contact profilometry, non-contact profilometry and confocal laser scanning microscopy

OBJECTIVES

To compare three instruments for their ability to quantify enamel loss after acid erosion.

METHODS

6 randomized parallel groups of bovine enamel samples were subjected to citric acid (higher acidity) or orange juice (lower acidity) erosion and remineralisation in a cycling model. Two protected shoulders were created on each of the samples using tape, to serve as reference for analysis. The time of exposure to each acid was varied, along with presence or absence of agitation. After treatment, samples were measured on 3 instruments capable of measuring step height: a contact profilometer (CP); a non-contact profilometer (NCP); and a confocal laser scanning microscope (CLSM) by three different examiners. Additionally, 3D (volume) step height was also measured using the CLSM.

RESULTS

Increasing acid concentration and exposure time resulted in greater erosion, as did agitation of samples while in acid solution. All instruments/methods identified the same statistically significant (p<0.05) pair-wise differences between the treatments groups. Further, all four methods exhibited strong agreement (Intra-class correlation ≥ 0.96) in erosion level and were highly correlated, with correlations of 0.99 or higher in all cases.

SIGNIFICANCE

All instruments/methods used in this study produced very similar conclusions with regard to ranking of enamel loss, with data showing very high agreement between instruments. All instruments were found to be equally suited to the measurement of enamel erosion.

Spectrally enhanced imaging of occlusal surfaces and artificial shallow enamel erosions with a scanning fiber endoscope

An ultrathin scanning fiber endoscope, originally developed for cancer diagnosis, was used to image dental occlusal surfaces as well as shallow artificially induced enamel erosions from human extracted teeth (n=40). Enhanced image resolution of occlusal surfaces was obtained using a short-wavelength 405-nm illumination laser. In addition, artificial erosions of varying depths were also imaged with 405-, 404-, 532-, and 635-nm illumination lasers. Laser-induced autofluorescence images of the teeth using 405-nm illumination were also obtained. Contrast between sound and eroded enamel was quantitatively computed for each imaging modality. For shallow erosions, the image contrast with respect to sound enamel was greatest for the 405-nm reflected image. It was also determined that the increased contrast was in large part due to volume scattering with a smaller component from surface scattering. Furthermore, images obtained with a shallow penetration depth illumination laser (405 nm) provided the greatest detail of surface enamel topography since the reflected light does not contain contributions from light reflected from greater depths within the enamel tissue. Multilayered Monte Carlo simulations were also performed to confirm the experimental results.

Diagnostic accuracy of proximal enamel subsurface demineralization and its relationship with calcium loss and lesion depth

OBJECTIVE

The aim of this study was to determine the relationship between the amount of calcium loss, lesion depth, and the accuracy of storage phosphor plate (SPP) and film radiographs for the detection of artificial proximal demineralization.

METHODS

Standard enamel windows of extracted premolars were exposed to a demineralizing solution for 60 h, 80 h, 100 h and 120 h. Solutions were analysed for calcium concentration by atomic absorption spectrometer and the lesion depths were calculated by a specific formula. All teeth were radiographed with SPPs and F-speed films before and after acid application. Images were evaluated by five observers. Stereomicroscopic and scanning electron microscopic (SEM) observations were carried out to visualize enamel surfaces after acid exposure. Receiver operating characteristic analysis was used for diagnostic accuracy (A(z)). A(z)s were compared with factorial analysis of variance and t-tests. The relationship between A(z)s and lesion depths was determined with Pearson's correlation test.

RESULTS

Strong positive correlation was found between A(z)s of both radiographic methods and lesion depths. No difference was found between the A(z)s of two radiographic systems for any of the demineralization durations (p > 0.05). Pair-wise comparisons revealed no significant difference in A(z)s of SPPs (p > 0.05), while significant differences were obtained for the A(z)s of films for different demineralization periods (p < 0.05). Stereomicroscopic and SEM observations confirmed demineralizations from superficial to deeper layers of enamel.

CONCLUSION

Subsurface enamel demineralization was not accurately detectable with either storage phosphor plates or F-speed films. The amount of calcium loss and the depth of demineralization have a strong relationship with diagnostic accuracy with a significant effect particularly on F-speed films.

Application of the specular and diffuse reflection analysis for in vitro diagnostics of dental erosion: correlation with enamel softening, roughness, and calcium release

We present assembly and application of an optical reflectometer for the analysis of dental erosion. The erosive procedure involved acid-induced softening and initial substance loss phases, which are considered to be difficult for visual diagnosis in a clinic. Change of the specular reflection signal showed the highest sensitivity for the detection of the early softening phase of erosion among tested methods. The exponential decrease of the specular reflection intensity with erosive duration was compared to the increase of enamel roughness. Surface roughness was measured by optical analysis, and the observed tendency was correlated with scanning electron microscopy images of eroded enamel. A high correlation between specular reflection intensity and measurement of enamel softening (r(2) ≥ -0.86) as well as calcium release (r(2) ≥ -0.86) was found during erosion progression. Measurement of diffuse reflection revealed higher tooth-to-tooth deviation in contrast to the analysis of specular reflection intensity and lower correlation with other applied methods (r(2) = 0.42-0.48). The proposed optical method allows simple and fast surface analysis and could be used for further optimization and construction of the first noncontact and cost-effective diagnostic tool for early erosion assessment in vivo.

Clinical studies of dental erosion and erosive wear

We define erosion as a partial demineralisation of enamel or dentine by intrinsic or extrinsic acids and erosive tooth wear as the accelerated loss of dental hard tissue through the combined effect of erosion and mechanical wear (abrasion and attrition) on the tooth surface. Most experts believe that during the last decade there has been a significant increase in the prevalence and severity of erosive tooth wear, particularly in adolescents. Even when erosive wear occurs in its milder forms, this is a matter of concern, as it may compromise the integrity of an otherwise healthy dentition in later life. The erosive wear process is complicated and modified by many chemical, behavioural and associated processes in the mouth. If interventions are to be developed it is therefore important that in vivo methods are developed to assess the outcomes of the erosion and erosive wear processes and the effects of interventions upon them. This paper discusses potential methods of investigating erosion and erosive wear in vivo and the difficulties associated with clinical studies.

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.

Efficacy of a tin/fluoride rinse: a randomized in situ trial on erosion

Concentrated tin- and fluoride-containing mouthrinses are effective erosion inhibitors in enamel and dentin. To test whether this is also true for solutions with lower concentrations, we conducted a randomized double-blind three-cell crossover in situ study with extra-orally performed erosive impacts (citric acid, 6 x 5 min/day) and an intra-oral rinsing protocol (1 x 30 sec/day) in 24 volunteers. The mouthrinses were a placebo, a NaF (500 ppm F⁻), and an amine fluoride (AmF)/NaF/SnCl₂ mouthrinse (500 ppm F⁻, 800 ppm Sn(2+)). Compared with the placebo, the NaF mouthrinse reduced substance loss by 19% in enamel and 23% in dentin (p ≤ 0.01 each); the AmF/NaF/SnCl₂ mouthrinse reduced this parameter by 67% in enamel and 47% in dentin (p ≤ 0.001 each). AmF/NaF/SnCl₂ was significantly more effective than NaF in both tissues (p ≤ 0.01). The mouthrinse containing Sn and F exhibited good efficacy, even under severe erosive conditions.

Effects of toothbrushing force on the mineral content and demineralized organic matrix of eroded dentine

Eroded dentine has a complex histological structure, and its organic fraction becomes increasingly exposed as a result of the continual action of acids. The present study sought to investigate the effects of brushing forces up to 4 N on mineralized and organic dentine fractions. The study was a cyclic demineralization and remineralization experiment (carried out over 9 d). Erosion was performed with HCl (6 x 2 min d-1), pH 1.6. Samples exposed to erosion alone served as controls; test samples were eroded and brushed with a powered toothbrush (2 x 15 s d-1), applying forces of 2, 3, or 4 N. Samples were analysed (using profilometry and longitudinal microradiography) before and after the removal of superficial organic material with collagenase. Randomly selected samples were subjected to scanning electron microscopy. Demineralized organic material was present on all samples regardless of brushing force. Loss values (determined using profilometry) after erosion only, and after brushing with forces of 2, 3, and 4 N, were 11.7 +/- 5.1, 13.6 +/- 11.2, 30.7 +/- 19.0, and 25.5 +/- 20.3, respectively, before treatment with collagenase, and 111.7 +/- 11.6, 122.0 +/- 11.8, 121.9 +/- 15.7, and 123.0 +/- 12.0, respectively, after treatment with collagenase. Microradiography confirmed the results. Significant effects of brushing force were only found on the demineralized organic fraction, and mineral loss was unaffected. The notion that eroded dentine is particularly prone to abrasion should be reconsidered.

Insights into preventive measures for dental erosion

Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear, high-concentrated fluoride applications are recommended. Currently, little information is available about the efficacy of other preventive strategies, such as calcium and laser application, as well as the use of matrix metalloproteinase inhibitors. Further studies considering these factors are required. In conclusion, preventive strategies for patients suffering from erosion are mainly obtained from in vitro and in situ studies and include dietary counseling, stimulation of salivary flow, optimization of fluoride regimens, modification of erosive beverages and adequate oral hygiene measures.

Influence of beverage composition on the results of erosive potential measurement by different measurement techniques

The influence of beverage composition on the measurement of erosive potential is unclear. The aim of this study was to evaluate whether beverage composition influences the measurement of erosive potential and to evaluate the influence of exposure in small and large volumes. Eleven beverages were included: water (control), 3 alcopops, 2 beers and 5 soft drinks. For each beverage 15 bovine enamel samples were used: 5 for chemical and 10 for profilometric analysis. After exposure to the beverages (63 min) the resulting solutions were analyzed for Ca and inorganic phosphorus (P(i)) content. The samples for optical profilometry were submersed sequentially in 500 ml or in 1 ml of the drinks for 3, 6, 9, 15 and 30 min (total 63 min). For some of the beverages high baseline concentrations of Ca (energy drink) or P(i) (cola drink, cola lemon drink, beer, beer lemon) were found. Some of the beverages showed a good correlation between the chemical methods. Profilometry (both for 1 and 500 ml) showed generally lower enamel losses than the chemical methods. Lower enamel losses were found for the profilometry 1 ml compared to the profilometry 500 ml only for the cola drinks. It can be concluded that the composition of the beverages had a significant effect on the determination of the erosive potential with chemical analyses. Drink composition also influenced the effect of small versus large exposure volumes, indicating the need for standardization of exposure parameters.

Evaluation of a profilometrical method for monitoring erosive tooth wear

The in vivo monitoring of erosive wear is difficult because lesions mostly progress relatively slowly and reliable reference points are difficult to obtain. To date, only a few methods for clinical monitoring of erosive loss have been described, which either require extensive equipment or do not provide sufficient sensitivity. The aim of the present study was to evaluate, using study models (epoxy resin material), a procedure that permits the reliable and accurate monitoring of erosive substance loss within acceptable observation periods. The method is the profilometric measurement of erosive tissue loss using acid-resistant markers, which represent both a reference area and a structure for the defined retracing of a given erosive lesion surface. The study model magnified values slightly (2.8%; not significant), the precision was < 4 microm, and the repeatability was good (95% limits of repeatability ranging from -4.7 to 5.2 microm). The estimated detection threshold for erosive loss is 15 microm, which appears to be adequate for monitoring. The method is indicated for special dental care in cases of severe dental erosion (e.g. eating disorders) and for clinical studies.

Effect of pepsin on erosive tissue loss and the efficacy of fluoridation measures in dentine in vitro

OBJECTIVES

In dentine, erosive lesion progression and efficacy of fluoridation measures for symptomatic therapy of dental erosion are both dependent on the presence of the organic matrix. In patients with eating disorders in combination with chronic vomiting, the demineralized organic matrix can be degraded by gastric enzymes. The aim of this study was to investigate the effect of pepsin on erosion progression and the efficacy of fluoride in dentine.

MATERIAL AND METHODS

Human dentine specimens were prepared and randomly divided into 4 groups of 20 specimens each. They were subjected to a cyclic de- and remineralization procedure for 9 days. For demineralization (6 x 2 min per day), an HCl solution (pH 1.6) was used in all groups. In two groups, pepsin (1.5 mg mL(-1)) was added to the demineralization solution. Fluoridation was performed in two groups 6 x 1 min per day with a mouth rinse (Olaflur/SnF(2); 250 ppm F(-)) after demineralization with both the HCl solution and the pepsin containing solution. Degradation of collagen was quantified by analyzing hydroxyproline and tissue loss was determined microradiographically. SEM images were taken in addition.

RESULTS

In the pepsin group, 1.72 (0.26) microg mL(-1) (mean (SD)) hydroxyproline per day was detected, and in the pepsin-fluoride group 1.95 (0.50) microg mL(-1). Tissue loss after 9 days in the control group was similar to that in the pepsin group (122.2 (53.4) microm and 122.2 (38.0) microm, n.s., respectively). Fluoridation reduced tissue loss after demineralization (98.8 (30.2) microm) but not after pepsin treatment (125.2 (34.2) microm; p< or =0.05).

CONCLUSION

Under the conditions used, pepsin had no influence on tissue loss, but altered the efficacy of fluoridation measures.

Effects of toothbrushing on eroded dentine

It is an established assumption that eroded dental hard tissues are particularly prone to toothbrush abrasion. Only a few studies have aimed to show this for dentine and, if so, disregarded the complex histological structure of this tissue. Therefore, the present study sought (i) to investigate the effects of toothbrushing on eroded dentine and (ii) to analyze how the organic matrix influences the outcome of established methods for quantifying dental hard tissue loss. The effects of brushing were investigated by optical (P-O) and mechanical (P-M) profilometry, by longitudinal microradiography (LMR), and by scanning electron microscopy (SEM). The SEM images showed that a demineralized organic layer had developed, which was unaffected by brushing. For substance loss, there was no significant difference between eroded and eroded/abraded samples. Considerable differences occurred, however, when results from the different methods were compared. P-O yielded the lowest (7.0 +/- 3.4 microm) and LMR the highest (109.8 +/- 10.7 microm) substance loss values. When the organic material was removed enzymatically, all methods gave comparable results. The results of this study do not lend support to the notion that brushing increases substance loss of eroded dentine. Profilometry was not suitable for measuring mineral loss, unless the organic material was removed.

Efficacy of Waiting Periods and Topical Fluoride Treatment on Toothbrush Abrasion of Eroded Enamel in situ

The aim of this study was to investigate the effectiveness of both waiting periods between acid exposure and tooth brushing and fluoride applications in preventing toothbrush abrasion of acid-softened enamel surfaces. The study, on 5 subjects, had an in situ crossover design with experimental periods of 5 days each. Human enamel samples were recessed in mouth appliances and at the end of each experimental period, enamel loss was determined profilometrically. Specimens were eroded extraorally (2 x 20 min per day; 0.05 M citric acid), standardized brushing (2 x 30 s per sample per day; powered toothbrush) was performed in situ. The groups were: (1) erosion only, (2) brushing with fluoride-free toothpaste directly after, (3) 2 h after, or (4) before erosion; fluoride application was either (5) brushing with a fluoride toothpaste or (6) brushing with a fluoride toothpaste or gel, and rinsing with a fluoride mouth rinse. Enamel loss was (1) 45.2 +/- 10.8, (2) 79.3 +/- 7.8, (3) 81.7 +/- 9.5, (4) 69.7 +/- 13.8, (5) 51.5 +/- 13.0, and (6) 41.2 +/- 1.8 microm. Brushing without fluoride increased the enamel loss significantly (p < or = 0.001), waiting for 2 h had no protective effect, and brushing before erosion decreased enamel loss values only by 12% (n.s.). In the fluoride groups, enamel loss was significantly lower than after brushing with the fluoride-free toothpaste and comparable to values after erosion only (n.s.). Waiting periods had only a minor effect, whilst the application of fluoride appeared promising.

Effect of stannous fluoride toothpaste on erosion-like lesions: an in vivo study

It has recently been shown that stannous fluoride (SnF(2)), in the form of aqueous solutions and as toothpaste, can reduce the dissolution of enamel in erosive acids in vitro and in situ. The aim of this study was to compare the effect of toothpastes containing SnF(2) or NaF on enamel dissolution using an in vivo model. Four healthy anterior teeth in each subject (n = 20) were exposed to diluted citric acid (100 mmol l(-1) or 10 mmol l(-1)) applied using a peristaltic pump (5 ml @7 ml min(-1)) and the acid was collected in a test tube before and after application of the respective toothpastes (etch I and etch II). Toothpaste was applied to the labial surfaces with a soft brush (four applications, each of 1-min duration), with gentle water rinsing between applications. Each subject had one pair of teeth treated with each of the test toothpastes. Enamel dissolution was examined by assessment of calcium content in the citric acid applied before and after the treatment with toothpaste. The results indicate that the SnF(2) toothpaste markedly reduced the dissolution of teeth in vivo (etch II < etch I), whereas the NaF toothpaste provided no protection (etch II > etch I). Toothpaste appears to be an acceptable vehicle for SnF(2) and maintains the dissolution-reducing effect exhibited by aqueous solutions of this fluoride salt.