The potential for dental plaque to protect against erosion using an in vivo-in vitro model--a pilot study

BACKGROUND: Tooth erosion is a problem for professional wine tasters (exogenous erosion from frequent exposure to wine acids) and for people with gastro oesophageal reflux disease (GORD) and bulimia who experience frequent reflux of gastric contents into the mouth (endogenous erosion from mainly HCl). The objective in this study was to determine whether plaque/pellicle could provide teeth with any protection from two common erosive acids, using an in vivo-in vitro technique. METHODS: Tiles of human tooth enamel and root surfaces were prepared from six extracted, unerupted third molar teeth and sterilized. Mandibular stents were prepared for six volunteer subjects and the tiles bonded to the buccal flanges of these stents. They were worn initially for three days to permit a layer of pellicle and plaque to form over the tile surfaces, and for a further 10 days of experimentation. Following cleaning of the plaque/ pellicle layer from the tiles on the right side flange, all the tiles were submerged in either 0.06M HCl or white wine for an accumulated time of 600 and 1500 minutes, respectively. Depths of erosion were determined using light microscopy of sections of the enamel and root tiles. SEM of the lesion surfaces was carried out to investigate the nature of erosive damage and of plaque/pellicle remnants. RESULTS: Retained plaque was found to significantly inhibit dental erosion on enamel, from contact with both HCl and wine, compared with that resulting following its removal. However, it was found to provide no significant protection on root surfaces. SEM analysis of the tile surfaces revealed marked etching of enamel on the cleaned surfaces, and considerable alteration to the appearance of remaining plaque and pellicle on most surfaces. CONCLUSION: Within the limitations of numbers of specimens, dental plaque/pellicle provided a significant level of protection to tooth enamel against dental erosion from simulated gastric acids and from white wine, using an in vivo-in vitro model. It was unable to provide any significant protection to root surfaces from these erosive agents. Possible reasons for this difference are explored.     

Protective effect of the in situ pellicle on dentin erosion - an ex vivo pilot study

AIM: The acquired pellicle is well known as an anti-erosive proteinaceous layer on enamel, but its protective properties on dentin have not been investigated in detail until now. The aim of the present ex vivo study was to evaluate the erosive effects on pellicle coated dentin. METHODS: Bovine dentin slabs were exposed to the oral cavity of one subject for 120 min for in situ pellicle formation. Subsequently, the slabs were incubated with HCl (pH 2.3) in vitro for 5 min and erosive calcium-release was measured photometrically. In addition, the acid treated specimens were evaluated by transmission electron microscopy (TEM). Pellicle free samples served as controls. RESULTS: Calcium erosion from the pellicle coated dentin slabs amounted to 23.5+/-2.9 microg Ca/min (pellicle free samples: 32.2+/-4.2 microg Ca/min). The difference was statistically significant (p < or = 0.05). In pellicle coated as well as in uncoated dentin samples, TEM-evaluation showed a demineralised dentinal surface layer which thickness ranged between 3 and 6 microm. The pellicle itself was partially dissolved but not removed by hydrochloric acid treatment. CONCLUSION: The protective properties of the acquired pellicle against an erosive challenge of the dentinal surface are limited. The dentinal pellicle functions like an ion permeable network rather than a barrier.     

In situ evaluation of the erosive potential of orange juice modified by food additives

The aim of this study was to evaluate the erosive potential of orange juice modified with food-approved additives: 0.4 g/l of calcium (Ca) from calcium lactate pentahydrate, 0.2 g/l of linear sodium polyphosphate (LPP) or their combination (Ca+LPP) were added to a commercially available orange juice (negative control, C-). A commercially available calcium-modified orange juice (1.6 g/l of calcium) was the positive control (C+). These juices were tested using a short-term erosion in situ model, consisting of a five-phase, single-blind crossover clinical trial involving 10 subjects. In each phase, subjects inserted custom-made palatal appliances containing 8 bovine enamel specimens in the mouth and performed erosive challenges for a total of 0 (control), 10, 20, and 30 min. Two specimens were randomly removed from the appliances after each challenge period. Enamel surface microhardness was measured before and after the clinical phase and the percentage of surface microhardness change (%SMC) was determined. Before the procedures, in each phase, the subjects performed a taste test, where the juice assigned to that phase was blindly compared to C-. Overall, C+ showed the lowest %SMC, being the least erosive solution (p < 0.05), followed by Ca+LPP and Ca, which did not differ from each other (p > 0.05). LPP and C- were the most erosive solutions (p < 0.05). Taste differences were higher for C+ (5/10 subjects) and Ca (4/10 subjects), but detectable in all groups, including C- (2/10 subjects). Calcium reduced the erosive potential of the orange juice, while no protection was observed for LPP.     

Protective effect of the in situ formed short-term salivary pellicle

Salivary pellicle, as previously investigated, protects the enamel surface after certain processes of maturation against the influence of acidic agents. The aim of the present study was to investigate the protective effect of the short-term salivary pellicle formed in situ over periods of 3, 60 and 120 min. Six human volunteers used intraoral acrylic splints with bovine enamel samples fixed at the buccal and palatal sites of the maxillary first molars and second premolars. Enamel specimens (n = 252) with and without pellicle were immersed for 60 s in 1.0% citric acid solution under agitation. Knoop surface hardness (KHN) of uneroded polished enamel was measured as a baseline and estimated immediately after erosive treatment reflecting the microhardness loss (DeltaKHN). The amounts of calcium dissolved from the eroded enamel surface were analysed by atomic absorption spectroscopy and scored in mg/l per 10 mm2 of enamel surface area. In addition, the scanning electron microscope was used for the micromorphological examination of the erosive alterations of the enamel surface. The average microhardness loss values after erosion of the enamel samples with buccally/palatally formed pellicle layers were measured as 139.1/144.9 DeltaKHN for 3 min pellicle, 145.9/146.9 DeltaKHN for 60 min pellicle and 141.7/138.6 DeltaKHN for 120 min pellicle. Calcium release values from the specimens with buccal/palatal pellicles were amounted to 15.0/14.9, 16.5/15.9 and 15.3/17.4 mg/l per 10 mm2 for 3, 60 and 120 min-old pellicles, respectively. No significant differences were related to the pellicle formation time and intraoral site (buccal or palatal) in all tested series (ANOVA, P < 0.05). However, significant protection of the enamel surface provided by the pellicle layer was observed on all pellicle-covered surfaces if compared to the non-covered enamel samples (calcium release: 25.6 mg/l per 10 mm2; microhardness loss 187.0 DeltaKHN). These data were in accordance with the morphologic alterations caused by citric acid on the pellicle-covered and pellicle non-covered specimens. It could be concluded that salivary pellicle formed in situ within a period of 3 min offers protection of enamel against citric acid. However, pellicle does not completely inhibit the erosive action of citric acid under the conditions of the present study.     

Thickness of acquired salivary pellicle as a determinant of the sites of dental erosion

Dental erosion shows a typical distribution pattern within the dental arches. Tooth protection from erosion by salivary pellicle has been shown in vitro, but the hypothesis that pellicle may differ quantitatively at sites of erosion has not been investigated. This study aimed to determine the thickness of acquired salivary pellicle within the dental arches, investigate the possible relationship of this thickness to the distribution and severity of erosion within the arches, and confirm the protective effect of pellicle against dental erosion. Eight enamel blocks were produced from each of 5 bovine incisors assigned to five volunteers. Each block was further cut into 2 slabs, producing control and experimental slabs. Pellicle developed on experimental slabs located on 8 intra-oral sites after 1 hr of exposure was stained by "sheep anti-human IgGAM-FITC". Slabs were then visualized, and pellicle thickness measured, by confocal laser scanning microscopy. Eroded enamel lesions were produced in experimental and control slabs by means of pure orange juice. The degree of erosion was quantified by transverse microradiography. Pellicle thickness varied significantly within the dental arches and among individuals. An inverse relationship (r = -0.96, p<0.001) was observed between the degree of erosion and pellicle thickness. Significant differences in erosion were observed between slabs with and those without pellicle. This study has shown that the thickness of acquired salivary pellicle varies within the dental arches, which may be responsible for the site-specificity of dental erosion, and that pellicle does protect the teeth from erosion.     

Toothbrushing before or after an acidic challenge to minimize tooth wear? An in situ/ex vivo study

PURPOSE: To evaluate whether patients should be advised to perform toothbrushing before or after an acidic challenge to minimize enamel and dentin wear by brushing abrasion. METHODS: The study was a two-period crossover design (A and B, each 14 days) in which three enamel and dentin specimens were fixed in intraoral appliances of 10 volunteers. The following regimens were performed three times a day with at least 4 hours in between: A: 20-second brushing treatment in an automatic brushing machine, 5 minutes intraoral exposure of the specimens, extraoral erosion of enamel and dentin specimens for 40 seconds or B: Extraoral erosion for 40 seconds, 5 minutes intraoral exposure of the specimens, 20-second brushing treatment in an automatic brushing machine. Enamel and dentin loss at the end of each 14-day regimen was assessed by profilometry and statistically analyzed by t-test. RESULTS: For all volunteers, mean enamel and dentin wear was significantly lower when brushing treatment was performed before erosion (A: enamel: 2.3 +/- 1.0 microm, dentin: 4.1 +/- 1.6 microm) than when brushing was applied after erosion (B: enamel: 6.4 +/- 3.0 microm, dentin: 15.3 +/- 6.8 microm). It was concluded that patients awaiting an erosive attack should perform toothbrushing prior to rather than after an acidic challenge to minimize enamel and dentin wear.     

Impact of acquired enamel pellicle modification on initial dental erosion

The acquired enamel pellicle that forms on the tooth surface serves as a natural protective barrier against dental erosion. Numerous proteins composing the pellicle serve different functions within this thin layer. Our study examined the effect of incorporated mucin and casein on the erosion-inhibiting potential of the acquired enamel pellicle. Cyclic acidic conditions were applied to mimic the erosive environment present at the human enamel interface during the consumption of soft drinks. One hundred enamel specimens were prepared for microhardness tests and distributed randomly into 5 groups (n = 20) that received the following treatment: deionized water, humidity chamber, mucin, casein, or a combination of mucin and casein. Each group was exposed to 3 cycles of a 2-hour incubation in human saliva, followed by a 2-hour treatment in the testing solution and a 1-min exposure to citric acid. The microhardness analysis demonstrated that the mixture of casein and mucin significantly improved the erosion-inhibiting properties of the human pellicle layer. The addition of individual proteins did not statistically impact the function of the pellicle. These data suggest that protein-protein interactions may play an important role in the effectiveness of the pellicle to prevent erosion.     

Scanning electron microscopic study of the effect of salivary pellicle on enamel erosion

A bovine tooth model system was used to study the effect of experimental salivary pellicle on enamel erosion. Test blocks with varnish-covered control surfaces in each specimen were immersed into an acidic cola beverage (pH 2.6) for 120 min, either with or without the pellicle which was grown for 7 days by using clarified human saliva. After immersion, the pellicle was removed from some specimens with 10% sodium hypochlorite (20 h at 20 degrees C) and ultrasonic bath (60 s) to study its effect on erosion. All specimens were then studied in the scanning electron microscope. The specimens without pellicle (positive controls) showed gross erosion with prism core dissolution in all study blocks. The specimens with pellicle showed occasionally a film-like integument covering the apparently intact test surfaces with adjacent enamel surfaces slightly eroded. The erosion, however, was not of the same magnitude as in the positive controls. After removing the pellicle, the enamel surfaces showed pitted appearance of the prism heads; the demineralization seemed to attack more the prism sheath areas. Thus, salivary pellicle was found to protect the underlining enamel from erosion in vitro.     

Protective influence of experimentally formed salivary pellicle on enamel erosion. An in vitro study

The purpose of this study was to evaluate dental erosion in 0.1 and 1.0% citric acid in vitro by several different methods and to assess the protective potential of experimentally formed salivary pellicle (24 h in vitro). Bovine enamel slabs were embedded in epoxy resin and polished. Erosion was performed in citric acid for 1, 5 or 10 min and recorded as microhardness loss, as changes of surface roughness (R(a), R(t) and R(zDIN)) and as calcium release. Additionally, erosive alterations were observed with scanning electron microscopy. Significant microhardness loss on non-pellicle-covered specimens was measured after 1-min exposure to 0.1% citric acid. Microhardness loss was time- and concentration-dependent. Salivary pellicle significantly inhibited both microhardness loss, except after 10-min immersion in 1.0% citric acid, and significantly reduced the increase of surface roughness. There were, however, no significant differences in calcium release between pellicle-covered and non-covered enamel. The results support the general conclusion that salivary pellicle effectively protects enamel surface against short-term erosion in organic acids.     

In vitro salivary pellicles from adults and children have different protective effects against erosion

Objectives

We aimed at analyzing the protective effects of salivary pellicles, formed with saliva from adults or children, on enamel from permanent or deciduous teeth.

Materials and methods

Ninety human enamel specimens (45 permanent premolars and 45 deciduous canines) were ground, and the outer 200 μm of enamel was removed. We divided the teeth into three further subgroups: no salivary pellicle (control), adult salivary pellicle (AP), and child salivary pellicle (CP). We collected stimulated saliva from adults and children and placed 160 μl of either saliva on enamel specimens from AP and CP, respectively. Control specimens received no saliva. Specimens were stored at 37 °C for 2 h and then submitted to an erosive challenge (10 mL; 1 % citric acid; pH 3.6; 25 °C, 1 min). Pellicle formation and erosion was repeated for a total of 4 cycles. After every cycle, relative surface reflection intensity (rSRI) and surface microhardness (rSMH) were calculated.

Results

On permanent enamel, AP presented significantly better protective effects, with less rSMH loss (p?<?0.001) and less rSRI loss (p?<?0.001). On deciduous enamel, CP presented significantly better protective effects than AP and control (p?<?0.05), for both measured parameters.

Conclusion

We conclude that pellicles from adults and children promote different erosion protective effects, where adult pellicle provides better protection for permanent enamel, and child pellicle promotes better protection on deciduous enamel.

Clinical relevance

The present results provide a better understanding toward the protective effect of salivary pellicle against dental erosion and brings light to one more factor involved in the erosion of deciduous teeth.

     

The effect of red wine in modifying the salivary pellicle and modulating dental erosion kinetics

This study investigated the potential of red wine in modulating dental erosion kinetics in the presence or absence of salivary pellicle. Polished human enamel specimens were used in two conditions; presence or absence of acquired enamel pellicle; and subdivided according to exposure: red wine, orange juice, apple juice, or citric acid. The specimens were incubated in clarified whole human saliva (presence of acquired enamel pellicle) or in a humid chamber (absence of acquired enamel pellicle) for 2 h at 37°C, then in the test substances for 1 min, at 25°C, under shaking. This was repeated four times. Surface hardness was measured initially and after each cycle and surface reflection intensity was measured initially and after all cycles. In the presence of acquired enamel pellicle, red wine caused the least surface hardness loss, followed by orange juice, apple juice, and citric acid. Statistically significantly less surface reflection intensity loss was observed for red wine and orange juice than for apple juice and citric acid. In the absence of acquired enamel pellicle, red wine and orange juice caused less surface hardness loss than apple juice and citric acid. Orange juice showed the least surface reflection intensity loss, followed by red wine, citric acid, and apple juice. The polyphenol composition of these drinks can notably modulate the erosion kinetics.     

Pathogenesis and modifying factors of dental erosion

Dental erosion is caused by acidic solutions which come into contact with the teeth. Because the critical pH of dental enamel is approximately 5.5, any solution with a lower pH value may cause erosion, particularly if the attack is of long duration, and repeated over time. Saliva and salivary pellicle counteract the acid attacks but if the challenge is severe, a total destruction of tooth tissue follows. Ultrastructural studies have shown that erosive lesions are seen in prismatic enamel as characteristic demineralization patterns where either the prism cores or interprismatic areas dissolve, leading to a honeycomb structure. In aprismatic enamel the pattern of dissolution is more irregular and areas with various degrees of mineral loss are seen side by side. In dentin the first area to be affected is the peritubular dentin. With progressing lesions, the dentinal tubules become enlarged but finally disruption is seen also in the intertubular areas. If the erosion process is rapid, increased sensitivity of the teeth is the presenting symptom. However, in cases with slower progression, the patient may remain without symptoms even though the whole dentition may become severely damaged. Regarding the role of causative agents, present data does not allow the ranking of different acids with regard to their potential of causing erosion. Neither is there consensus as to how effective fluorides are in preventing the progression of erosive lesions, or how the chemical and structural factors of tooth tissue in general might modify this pathological process.     

Acquired pellicle as a modulator for dental erosion

Dental erosion is a multifactorial condition that can result in the loss of tooth structure and function, potentially increasing tooth sensitivity. The exposure of enamel to acids from non-bacterial sources is responsible for the progression of erosion. These erosive challenges are counteracted by the anti-erosive properties of the acquired pellicle (AP), an integument formed in vivo as a result of selective adsorption of salivary proteins on the tooth surface, containing also lipids and glycoproteins. This review provides an in-depth discussion regarding how the physical structure of the AP, along with its composition, contributes to AP anti-erosive properties. The physical properties that contribute to AP protective nature include pellicle thickness, maturation time, and site of development. The pellicle contains salivary proteins embedded within its structure that demonstrate anti-erosive properties; however, rather than individual proteins, protein–protein interactions play a fundamental role in the protective nature of the AP. In addition, dietary and synthetic proteins can modify the pellicle, enhancing its protective efficiency against dental erosion. The salivary composition of the AP and its corresponding protein-profile may be employed as a diagnostic tool, since it likely contains salivary biomarkers for oral diseases that initiate at the enamel surface, including dental erosion. Finally, by modifying the composition and structure of the AP, this protein integument has the potential to be used as a target-specific treatment option for oral diseases related to tooth demineralization.     

Exposure time of enamel and dentine to saliva for protection against erosion: a study in vitro

Previous research, mainly on enamel, supports a protective role for salivary pellicle against erosion. Pretreatments have tended to be lengthy (24 h or more) and of questionable relevance to the regular intake of acidic food and drink by many individuals. The aim of this study in vitro was to determine the protective effect of salivary pellicle formed on enamel and dentine over time periods up to 4 h. Flattened, polished human enamel and dentine specimens were pretreated with unstimulated human saliva from a single donor for 2 min, 30 min (enamel only), 1, 2, or 4 h. Controls were exposed to water for the same times. Specimens were then exposed to 0.3% citric acid, pH 3.2 for 10 min with stirring. This cycle was carried out 12 times. Tissue loss was measured by profilometry after 3, 6, 9 and 12 cycles. For enamel, statistically significant protection was found at >or=1 h. For dentine, significant protection was achieved at 2 min. Salivary pellicle offered proportionately greater protection to enamel than dentine. Cautiously extrapolating these in vitro data suggests that pellicle should offer erosion protection to individuals who imbibe acidic drinks at frequencies of 1 h or less.     

Influence of in vivo formed salivary pellicle on enamel erosion.

This study assessed the protective effect of the salivary pellicle formed in vivo during 24 h or 7 days against demineralization of bovine enamel caused by citric acid. In addition, the influence of acid treatment on the behavior of the pellicle was investigated. Enamel specimens with and without in vivo pellicles were immersed in citric acid (0.1, 1.0%) over 30, 60, and 300 s, and processed for scanning (SEM) and transmission electron microscopy (TEM), as well as for measurement of surface microhardness (SMH). Specimens coated with the in vivo formed pellicles revealed less extensive erosive demineralization of the enamel surface compared to uncovered enamel specimens. SEM analysis and SMH results did not indicate distinct differences between erosive surface alterations on enamel slabs covered with 24-hour pellicles and on those covered with 7-day pellicles. TEM analysis showed that the pellicle layer was dissolved in part from the enamel surface due to acid exposure. However, pellicle residues could be detected by TEM in all specimens, even after 5-min exposure to 1.0% citric acid. It is concluded that the in vivo salivary pellicle can resist the acidic action to some extent and provides protection to the underlying enamel surface against erosive destruction caused by short-term action of citric acid.     

Scanning electron-microscopic study of pellicle and plaque formation on tetracycline-impregnated dentin

Previous experiments have shown that tetracyclines may react with hydroxyapatite, e.g. in enamel and dentin, without losing their antimicrobial capacity. The present paper examines the pattern of pellicle and plaque formation on doxycycline-treated dentin by the use of scanning electron microscopy (SEM). From newly extracted human teeth were prepared standardized dentin slabs, half of which were soaked in aqueous solutions of doxycycline HCl, 10 mg/ml (pH 2.5) for 10 min. Seven volunteers carried doxycycline-impregnated specimens ligated to the buccal surface of a maxillary molar for 2 h, 8 h, 24 h and 120 h, respectively. Untreated control specimens were ligated to the contralateral teeth. After removal from the oral cavity, the dentin slabs were briefly rinsed in water, allowed to air dry and processed for SEM. SEM assessment of the specimens showed that doxycycline-impregnation resulted in a superficial etching of the dentin, a reduced rate of pellicle formation as well as an impairment of pellicle adhesion, and a retarded bacterial plaque formation on the dentin surfaces.     

Scanning electron-microscopic study of pellicle and plaque formation on tetracyclineimpregnated dentin

Abstract — Previous experiments have shown that tetracyclinecs may react with hydrosyapatite, e.g. in enamel and dentin, without losing their antimicrobial capacity. The present paper examines the pattern of pellicle and plaque formation on doxycycline-treated dentin by the use of scanning electron microscopy (SEM). From newly extracted human teeth were prepared standardized dentin slabs, half of which were soaked in aqueous solutions of doxycycline HC1, 10 mg/ml (pH 2.5) for 10 min. Seven volunteers carried doxycycline-impregnated specimens ligated to the buccal surface of a maxillary molar for 2 h, 8 h, 24 h and 120 h, respectively. Untreated control specimens were ligated to the contralateral teeth. After removal from the oral cavity, the dentin slabs were briefly rinsed in water, allowed to air dry and processed for SEM. SEM assessment of the specimens showed that doxycycline-impregnation resulted in a superficial etching of the dentin, a reduced rate of pellicle formation as well as an impairment of pellicle adhesion, and a retarded bacterial plaque formation on the dentin surfaces.     

Resistance of two dentin-bonding agents and a dentin densensitizer to acid erosion in vitro.

OBJECTIVES: To determine the resistance of two dentin-bonding agents (DBAs) and a dentin desensitizer to simulated dental erosion. METHODS: Twenty teeth in each of three groups of selected premolars, with exposed cervical dentin, were treated with one of three dentin surface treatment systems: Gluma Desensitizer (Heraeus Kulzer (UK) Ltd), One Coat Bond (Whaledent (UK) Ltd), and Optibond FL (Kerr (UK) Ltd) and exposed to water (control) and an erosive challenge (Coca Cola) for 14 days. Sequential tracings of the specimens were taken, superimposed and the mean reduction in densensitizer or DBA thickness and or tooth loss determined. RESULTS: A mean loss of 77 microns (s.d. 14.6 microns) of tooth tissue over the untreated sites following 14 days exposure to Coca Cola was observed. The application of DBAs, as opposed to Gluma Desensistizer alone, over exposed dentin surfaces afforded substantial protection against erosion by Coca Cola over the period of study. The mean change in vertical profile of teeth treated with a DBA was 20 microns (s.d. 14.7 microns), almost four times less than that seen over untreated sites. SIGNIFICANCE: With the exception of Gluma Desensitizer, which was lost completely, One Coat Bond and Optibond FL demonstrated levels of acid dissolution resistance, which would be of potential value clinically.     

Saliva and dental erosion

Dental erosion is a multifactorial condition. The consideration of chemical, biological and behavioral factors is fundamental for its prevention and therapy. Among the biological factors, saliva is one of the most important parameters in the protection against erosive wear.

Objective

This review discusses the role of salivary factors on the development of dental erosion.

Material and Methods

A search was undertaken on MEDLINE website for papers from 1969 to 2010. The keywords used in the research were "saliva", "acquired pellicle", "salivary flow", "salivary buffering capacity" and "dental erosion". Inclusion of studies, data extraction and quality assessment were undertaken independently and in duplicate by two members of the review team. Disagreements were solved by discussion and consensus or by a third party.

Results

Several characteristics and properties of saliva play an important role in dental erosion. Salivary clearance gradually eliminates the acids through swallowing and saliva presents buffering capacity causing neutralization and buffering of dietary acids. Salivary flow allows dilution of the acids. In addition, saliva is supersaturated with respect to tooth mineral, providing calcium, phosphate and fluoride necessary for remineralization after an erosive challenge. Furthermore, many proteins present in saliva and acquired pellicle play an important role in dental erosion.

Conclusions

Saliva is the most important biological factor affecting the progression of dental erosion. Knowledge of its components and properties involved in this protective role can drive the development of preventive measures targeting to enhance its known beneficial effects.     

Laser-activated fluoride treatment of enamel as prevention against erosion

BACKGROUND: Erosion is the loss of dental hard tissues from an acidic challenge, often resulting in exposure of dentinal tubules and hypersensitivity to environmental stimuli. Laser-activated fluoride (LAF) therapy with 488nm laser energy has been shown previously to increase the resistance of human enamel and dentine to acid dissolution. The aims of this study were to investigate the action spectrum of LAF in protecting tooth enamel from softening in response to an erosive challenge, and to examine for any temperature change with the treatment. MATERIALS AND METHODS: Buccal and lingual surfaces of extracted sound molar and premolar teeth were used to prepare matched pairs of enamel slabs (N = 10 per group). After application of 1.23% neutral sodium fluoride gel (12 300ppm F ion), slab surfaces were lased with 488, 514.5, 532, 633, 670, 830 or 1064nm wavelength (energy density 15J/cm(-2); spot size 5mm), then exposed to an erosive challenge (1.0M HCI for five minutes). The Vicker's hardness number (VHN) was recorded before fluoride gel application and again following the acid challenge. Negative controls did not receive laser exposure. RESULTS: All wavelengths of laser light examined provided a protective LAF effect against softening, compared with the negative control surfaces. CONCLUSION: From these findings, we conclude that the action spectrum of the LAF effect extends across the visible spectrum, providing protection to dental enamel from an erosive challenge.