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PubMed1998

Scanning microradiographic studies of rates of in vitro demineralization in human and bovine dental enamel.

The aim was to measure frequently and with precision the local integrated mineral loss through small areas of the natural surface of human and bovine enamel during in vitro demineralization using an X-ray photon-counting system (scanning microradiography). The method used was an adaptation of photographic longitudinal microradiography in which the attenuation of X-rays through the enamel is measured in the direction of acid attack, i.e., normal to the enamel surface. The mass of mineral (assumed to be hydroxyapatite) per unit exposed area was measured over 15 microm dia. circles at a series of positions as a function of time in blocks of human and bovine enamel immersed in 0.1 mol/l acetic acid buffered to pH 4.0 with NaOH. There was an initial period (approx. 45 h for human, approx. 75 h for bovine enamel) during which the mineral loss with time was sigmoidal, followed by a nearly linear loss for the remainder of the experiment, in some cases up to 500 h. The initial sigmoidal period may be due to properties of surface enamel or be associated with the development of a surface layer overlying subsurface demineralization. The essentially constant rate of mineral loss after the surface layer has formed confirms earlier observations and is consistent with a rate-limiting process occurring at the dissolving enamel surfaces of the advancing front, and not by transport of ions within the lesion. Small perturbations from a linear loss were seen, which were approximately periodic for human enamel. The slope of the linear period was rather constant within one human or bovine block, but variable between blocks without a clear distinction between human and bovine enamel.

Animals↗

PubMed1999

Demineralizing effect of dental cements on human dentin.

OBJECTIVE: This study was undertaken to verify the hypothesis that dentin surfaces are demineralized during placement of four kinds of chemically setting cements (zinc phosphate cement, luting glass-ionomer cement, restorative glass-ionomer cement, and zinc polycarboxylate cement). METHOD AND MATERIALS: Sixty cemented dentin disks were observed under scanning electron microscopy and with confocal laser scanning microscopy after use of an argon-ion etching technique. To determine the surface effects of the cements, 30 dentin surfaces were treated with 1 of 6 freshly mixed cements (5 per group) for 60 seconds. The disks were subjected to rinsing with a water spray and ultrasonic washing prior to scanning electron microscopic observation. RESULTS: Observation of cemented dentin specimens revealed that the dentin was not completely demineralized at the interface formed by the cement and dentin and that the extent and depth of demineralization along the interface tended to be nonuniform. Zinc phosphate cement caused the greatest demineralization of dentin, followed by luting glass-ionomer cement. The extent of demineralization with restorative glass-ionomer cement or zinc polycarboxylate cement was less discernible. Confocal laser scanning microscopy generally confirmed scanning electron microscopic observations and revealed that most of the specimens showed close adaptation of the cements to the dentin surfaces. CONCLUSION: Acid-containing cements have self-etching properties that are effective, to various degrees, in removing the smear layer and promoting close adaptation to dentin surfaces.

Acid Etching, Dental↗

PubMed2006

The role of matrix metalloproteinases (MMPs) in human caries.

The objective of this review is to summarize our understanding of the role of host matrix metalloproteinases (MMPs) in the caries process and to discuss new therapeutic avenues. MMPs hydrolyze components of the extracellular matrix and play a central role in many biological and pathological processes. MMPs have been suggested to play an important role in the destruction of dentin organic matrix following demineralization by bacterial acids and, therefore, in the control or progression of carious decay. Host-derived MMPs can originate both from saliva and from dentin. They may be activated by an acidic pH brought about by lactate release from cariogenic bacteria. Once activated, they are able to digest demineralized dentin matrix after pH neutralization by salivary buffers. Furthermore, the degradation of SIBLINGs (Small Integrin-binding Ligand N-linked Glycoproteins) by the caries process may potentially enhance the release of MMPs and their activation. This review also explores the different available MMP inhibitors, natural or synthetic, and suggests that MMP inhibition by several inhibitors, particularly by natural substances, could provide a potential therapeutic pathway to limit caries progression in dentin.

Dental Caries↗

PubMed1999

A double-blind crossover trial of Oral Balance gel and Biotene toothpaste versus placebo in patients with xerostomia following radiation therapy.

Following therapeutic irradiation of the head and neck, patients with profound xerostomia have complaints associated with oral dryness, effects upon use of oral prosthesis, speech, and taste. In addition, xerostomia may lead to risk of oral infections and rampant demineralization of teeth. The use of topical Oral Balance gel and Biotene toothpaste (Laclede Professional Products, Gardena, CA) versus carboxymethylcellulose gel and commercial toothpaste applications was assessed in a 2-week double-blind, crossover design. The palliative effects of Oral Balance gel and Biotene toothpaste were superior to the effects of a placebo. No effect on oral colonization by Candida species and cariogenic oral microflora was seen with use of the topical agents.

Adult↗

PubMed1996

Modeling the caries-inhibitory effects of dental materials.

The objectives of this review are to compare the models that are used to simulate the caries process in cardiology research and to suggest how these models might be used to assess caries-inhibitory properties of dental materials. Available caries-simulation models fall into the following classifications: 1) in vitro demineralization using acid buffers, 2) in vitro demineralization using bacterially generated acids, 3) in vitro demineralization/remineralization using a pH-cycling system, 4) an artificial mouth where a bacterially generated acid challenge is interspersed with a "saliva" treatment, 5) in vivo animal model (generally with rats), 6) in situ demineralization and/or remineralization using enamel or dentin blocks or slices in the human mouth, and 7) in vivo studies using teeth scheduled for extraction in the human mouth. Most dental materials studies have used simple in vitro demineralization models or component release experiments, each of which is inadequate to answer the questions that are being asked about the caries-inhibitory properties of the material being tested. Experimental methods must be chosen with care to ensure that the material to be tested is examined in an appropriate mode. The ultimate goal is to correctly predict clinical outcomes. The design or redesign of a model must eventually be tied to documented clinical outcomes to improve the model and allow for future successful development of new materials.

Animals↗

PubMed1995

Contact microradiography of dentine under wet conditions to prevent lesion shrinkage.

A considerable shrinkage of dentinal lesions is the result of desiccation of dentine sections during contact microradiography. We introduce a simple modification which allows the dentine to be wet during the microradiographic procedure. The volume stability of both sound and demineralized dentine sections microradiographed under wet conditions is compared to sections microradiographed while being exposed to the air. Under wet conditions no shrinkage could be detected of both sound and demineralized sections. Within 15 min exposure to the air, demineralized sections showed their lesion depth to be significantly reduced by 21%, resulting in an underestimation of the mineral loss of 44%. No shrinkage was observed in the air-dried sound dentine. Especially when high-resolution plates are used, which require an extended exposure time, microradiography of dentine sections under wet conditions is recommended. In longitudinal de- and remineralization studies, the use of water instead of impregnation with low-volatility liquids is to be preferred because of the possible effects of these liquids on the mineralization processes.

Absorptiometry, Photon↗

PubMed2000

Morphological changes in dental enamel after fluoride gel application in vitro.

INTRODUCTION: The investigations of in vitro models precede the clinical studies. Using these studied we can investigate the effect upon the enamel of different agents for local application. AIM: The purpose of this study was to investigate the ultrastructural changes in a normal and partially demineralized enamel after 0.42% fluoride gel application in vitro using scanning electron microscopy. MATERIAL AND METHODS: The experiment was performed on 20 premolars extracted for orthodontic indications. Symmetrical specimens were prepared, as one half served as a control, while the other one was treated with fluoride gel. The specimens were examined with electron microscope at different magnifications. RESULTS: The findings show that fluoride gel applications affect the processes of mineralization and remineralization. CONCLUSIONS: This gives us the ground for applying fluoride gel in the clinical practice for prevention and treatment of caries incipiens.

Dental Caries↗

PubMed1993

Protective effect of topically applied fluoride in relation to fluoride sensitivity of mutans streptococci.

The aim of the present in vitro experiments was to determine whether the protection of enamel by topically applied fluoride against demineralization by bacterial acids would depend on the fluoride sensitivity of the bacteria. Glucose-agarose gel suspensions of fluoride-sensitive and fluoride-resistant mutans streptococci were placed on bovine enamel specimens with different amounts of fluoride. One group of specimens was untreated, a second group had been pretreated with a F-lacquer, and a third group had been pretreated with the F-lacquer and rinsed subsequently with a KOH-solution, to remove deposited CaF2. After 22-hour incubations at 37 degrees C, the amounts of calcium and lactate and the pH of the agarose gels were determined. This procedure was repeated on three consecutive days. Two parent S. mutans strains, one parent S. sobrinus strain, and five fluoride-resistant derivatives were tested. Both pretreatments gave a significant protection to the enamel specimens. For the S. mutans strains, the degree of protection did not depend on the fluoride sensitivity of the strains. For the S. sobrinus strains, the results suggested a reduced protection against demineralization by the fluoride-resistant derivatives. Only from the second group of enamel specimens was enough fluoride released for inhibition of bacterial metabolism. Presumably, it was released by the dissolution of CaF2. It is concluded that a possible adaptation of mutans streptococci in dental plaque to frequent exposures to fluoride will not necessarily decrease the caries-preventive effects caused by topically applied fluoride agents.

Adaptation, Biological↗

PubMed1997

In vitro studies of laser fluorescence for detection and quantification of mineral loss from dental caries.

Laser fluorescence (LF) is thought to be a quantitative technique for the measurement of mineral loss from dental caries. These studies aimed to demonstrate the quantitative nature of LF, by means of transverse microradiography (TMR), in addition to the possible use of LF on small specimens suitable for in situ studies. Studies also aimed to determine the ability of LF to detect caries adjacent to amalgam restorations. The results demonstrated reasonable correlation between both the histological depth and mineral loss measured by TMR compared with the % change in mean fluorescence radiance measured by LF (r = 0.70 and 0.83, respectively). Studies with small specimens demonstrated that in vitro remineralization could be observed with LF for comparison of the demineralized specimen with an undemineralized reference. ANOVA showed significant mineral gain (p < 0.0001). The detection and quantification of mineral loss adjacent to amalgam restorations may have potential for the management of recurrent caries. Studies have demonstrated that LF can detect such mineral loss, and, with refinement of the image analysis system, LF was capable of detecting remineralization. Remineralization of such lesions is controversial, but it is suggested that LF may have a role in secondary caries management.

Analysis of Variance↗

PubMed1996

A scanning electron-microscopic study of solubility variations in human enamel and dentine.

Cut, polished surfaces of human teeth were exposed to acetate buffers, pH 5.2, with a background electolyte composition similar to plaque fluid and with - log10 (ion-activity product) for hydroxyapatite, pIHA, ranging from 55 to 62, at 37 degrees C under a 5% v/v CO2 atmosphere. Demineralization was assessed by scanning electron microscopy of the treated surfaces and of methacrylate replicas of subsurface pores. Intertubular dentine was slightly soluble at pIHA 55, while peritubular dentine was less soluble, dissolving at pIHA > or = 58. In enamel, dissolution of prism junctions occurred at pIHA > or = 55, but was slight in middle enamel. Demineralization of intraprismatic enamel was observed at pIHA > or = 56 in inner enamel and in a few places in outer enamel but did not occur in middle enamel and most of the outer enamel at pIHA < or = 58. The results support the conclusion that the bulk of enamel has the solubility properties of a slightly defective form of hydroxyapatite. The correlations between structure and solubility are likely to have a strong influence on the pattern of caries lesion formation.

Acetates↗

PubMed1993

The effect of fixed and functional appliances on enamel decalcifications in early Class II treatment.

The presence of enamel decalcifications before and after early Class II treatment was examined on 41 subjects and 164 permanent first molars. No new demineralization areas were found in patients wearing only a removable appliance. Of the maxillary molars 6% displayed decalcifications in patients wearing a headgear only: whereas of patients wearing a headgear and biteplate 25% displayed enamel lesions. Eighteen percent of white spot lesions diagnosed before treatment had shown a "reversal phenomenon," whereby the enamel appeared normal after treatment. This process only occurred in the functional appliance group indicating that remineralization was better achieved with an appliance that was capable of being removed from the oral cavity.

Activator Appliances↗

PubMed1995

Tensile properties of resin-infiltrated demineralized human dentin.

The ability of adhesive resins to restore the physical properties of demineralized dentin has not been well-documented. The unfilled resins that are used for adhesion have relatively low moduli of elasticity and limited ability to increase dentin stiffness, although they may increase the ultimate tensile strength of dentin. This study tested the hypothesis that resin infiltration of demineralized dentin can restore its tensile properties to those of mineralized dentin. Small (ca. 0.5 mm thick x 0.5 mm wide) specimens of demineralized human dentin were infiltrated with one of five different dentin bonding resins over many hours, to determine how these resins altered the tensile properties of dentin. Tensile stress and strain were measured in these and control (mineralized and demineralized) specimens until their ultimate failure. The results indicate that some adhesive resins, after infiltrating demineralized dentin, can restore and even exceed the ultimate tensile strength of mineralized dentin. These resins increased the modulus of elasticity of resin-infiltrated dentin to values equal to or greater than those of the resins but far below those of mineralized dentin. Although the conditions in this experiment were far removed from the manufacturer's recommendations or clinical practice, the results support the potential of resin infiltration for reinforcing dentin.

Acid Etching, Dental↗

PubMed1995

An ultrastructural evaluation of the effects of cysteine-proteinase inhibitors on osteoclastic resorptive functions.

This study was designed to evaluate the effects of specific and potent cathepsin inhibitors on osteoclastic resorptive functions in vitro by means of a novel ultrastructural assay system. Mouse bone marrow cell-derived osteoclasts were suspended on dentine slices and cultured for 48 hours in the presence of either E-64 (a generalized cysteine proteinase inhibitor) or Z-Phe-Phe-CHN2 (a selective cathepsin L inhibitor). After the removal of cultured osteoclasts, co-cultured dentine slices were examined using electron microscopy: backscattered (BSEM), scanning (SEM), and atomic force (AFM). In morphometric analyses of BSEM images, there were no significant differences in the areas of demineralized dentine surfaces between control and inhibitor-treated groups, suggesting that cathepsin inhibitors had no effect on dentine demineralization by cultured osteoclasts. However, in SEM and AFM observations, both inhibitors remarkably reduced to the same extent, the formation of deep resorption lacunae on dentine slices that had resulted from degradation of matrix collagen. In addition, Z-Phe-Phe-CHN2 treatment produced deeper, ring-like grooves with little collagen exposure in shallow resorption lacunae. These results strongly suggest that (1) cathepsins released by osteoclasts are involved in the formation of deep resorption lacunae, and (2) cathepsin L plays a key role in bone resorption.

Animals↗

PubMed2006

Effect of sucrose concentration on dental biofilm formed in situ and on enamel demineralization.

The relationship between sucrose concentration and cariogenic potential was studied in situ. Adult volunteers wore intraoral palatal appliances containing human dental enamel blocks, which were extraorally submitted 8 times a day for 14 days, to the treatments: deionized distilled water and sucrose solutions from 1 to 40%. The biofilm formed was analyzed with respect to acidogenicity and biochemical composition; enamel demineralization was evaluated by microhardness. The results showed that 1% sucrose is less cariogenic than 5% or higher concentrations, although sucrose solution at 40% was still able to increase the concentration of insoluble polysaccharide in the biofilm formed. The findings suggest that the threshold of sucrose solution concentration for the formation of a cariogenic biofilm is 5%, which provided the same cariogenic potential as that observed for 10 and 20% sucrose solution.

Adult↗

PubMed2003

Quantifying enamel demineralization from teeth with orthodontic brackets--a comparison of two methods. Part 2: validity.

This is Part 2 of an in vitro study investigating two techniques for recording and quantifying demineralization surrounding orthodontic brackets. In Part 1 the repeatability of computerized image analysis from digitally converted photographic slides and quantitative light-induced fluorescence (QLF) was explored. In Part 2 of the investigation the validity of each technique was examined. Thirty halved human molars, shaped to look like incisors and with an orthodontic bracket bonded to the buccal surface were used. A small area of each of the four edges of the bracket was variously exposed to a demineralizing gel for 0, 3, 7, or 14 days. Images of the teeth were taken and analysed using the two techniques. Repeat images and analysis were carried out blind. The sensitivity, specificity, positive, and negative predictive values were calculated. A negative result confirmed that there was no demineralization present in the majority of cases. A positive result was less reliable particularly for the occlusal and gingival regions. The 7- and 14-day demineralization patterns were detected every time using the photographic technique. The discrimination of the 0- and 3-day patterns was less reliable. The results of this study were extrapolated to allow for the prevalence of the condition following orthodontic treatment, and the implications of this for a putative clinical trial are discussed, together with the advantages and disadvantages of each method. Either technique would be applicable to use in a clinical trial.

Dental Bonding↗

PubMed1998

Combined effects of laser irradiation/solution fluoride ion on enamel demineralization.

OBJECTIVE: The effects of CO2 laser irradiation of dental enamel were evaluated in enamel demineralization experiments in partially saturated solutions (i.e., solutions containing both calcium and phosphate ions) with and without fluoride ions. SUMMARY BACKGROUND DATA: Previous studies had shown that a continuous-wave CO2 laser at an energy density of around 130 J/cm2 may induce an increased acid resistance in human dental enamel as assessed by exposure to severe demineralization conditions (0.1 mol/L acetate buffer, pH 4.5 and ionic strength 0.5 mol/L). METHODS: Enamel blocks were irradiated with a continuous-wave CO2 laser at a wavelength of 10.6 microns using energy densities of from 42.5 to 170.0 J/cm2. The blocks were then exposed to a partially saturated demineralizing solution with or without 0.2 ppm fluoride at a temperature of 30 degrees C for 24 hours. The demineralization was examined both qualitatively by light microscopy and quantitatively by microradiography. RESULTS: A comparison between the lased and the unlased portions of enamel showed increased acid-resistance with increasing laser energy density and, at the highest energy density of 170.0 J/cm2, there was little or no lesion development in the fluoride-free dissolution medium. The demineralization of enamel was reduced dramatically in the presence of 0.2 ppm fluoride for both lased and unlased enamel; there was only modest lesion development observed for unlased enamel and, at an energy density as low as 85.0 J/cm2, the surface of enamel was found to be completely protected. CONCLUSIONS: These findings are consistent with the mechanism that laser irradiation of dental enamel results in significant reduction of the effective solubility of enamel mineral and that there is a significant synergism between laser irradiation and solution fluoride with regard to this effect.

Carbon Dioxide↗

PubMed1996

Effects of acidic conditioners on dentine demineralization and dimension of hybrid layers.

OBJECTIVES: This study was aimed at investigating the relationships between dentine conditioning for different durations with different acids and (1) the resulting depth of dentinal demineralization and (2) the rebounding capacity of collapsed collagen due to primer and adhesive resin penetration. METHODS: Two commercial and four experimental acids were tested directly by light microscopic evaluation of the depth of decalcification of dentine, and indirectly by determination of the hybrid layer thickness and the total depth of demineralization effects on perpendicular sections through Gluma bonded composite resin specimens. RESULTS: Depths of demineralization increased by both acid concentrations and conditioning times following a logarithmic relationship. There was good agreement between the results of the direct and the indirect procedures. Thirty seconds' conditioning with 20% phosphoric-acid gel resulted in 10-microns hybrid layer thickness. This 20% compound was considered a suitable compromise as a uni-etch conditioner since 30-s etch duration also generated an effective enamel retentive pattern and at the same time a frosted enamel appearance for visual control of extent and efficacy of enamel conditioning.

Acid Etching, Dental↗

PubMed2003

Effect of smear layer on root demineralization adjacent to resin-modified glass ionomer.

The cariostatic effect of resin-modified glass ionomer (RMGI) on secondary root caries is well-documented. However, this beneficial effect may be dependent upon the mode of cavity surface treatment. To investigate this relationship, we studied 4 cavity surface treatments prior to the placement of RMGI: no treatment (None), polyacrylic acid (PAA), phosphoric acid (H(3)PO(4)), and Scotchbond Multi-Purpose adhesive (SMP) as a control. Specimens were aged for two weeks in synthetic saliva, thermocycled, and subjected to an artificial caries challenge (pH 4.4). Polarized light microscopy (PLM) and microradiography (MRG) showed significantly less demineralization with the H(3)PO(4) cavity surface treatment as revealed by ANOVA and Tukey's multiple comparisons (p < or = 0.05). Dentin fluoride profiles determined by electron probe microanalysis (EPMA) supported PLM and MRG findings. It may be concluded that removal of the smear layer with phosphoric acid provides significantly enhanced resistance to secondary root caries formation adjacent to RMGI restorations.

Acid Etching, Dental↗