Effect of proteolytic enzymes on caries lesion formation in vitro

Effects of a commercial whitening toothpaste containing hydrogen peroxide and citric acid on dentin abrasion and erosion

BACKGROUND

Hydrogen peroxide (HP) and citric acid (CA), key contributors to toothpaste acidity, can lead to dental loss. This study aimed to compare the amount of abrasion or loss of dentin based on pH, buffering, and concentration of HP and CA in commercial and experimental toothpastes after toothbrushing or immersion.

METHODS

Bovine dentin specimens were randomly assigned to nine solutions. The prepared solutions included two commercial toothpastes (whitening toothpaste [WT] with HP and CA; conventional toothpaste [CT] without HP and CA), reference slurry (RS), two CA solutions (1.92%, CAS1; 0.001%, CAS2), basic solution (7.16% sodium phosphate dibasic [SPDS]), CA phosphate buffer solution (3.58% SPDS and 0.96% CA [CAPB]), HP solution (4%, HPS), and distilled water (DW). Dentin specimens were performed in two treatments: one with only abrasion (10,000 brushings) and one with only immersion (1 h). After treatments, the amount of dentin loss and surface images were measured and observed using noncontact profilometry. Data were analyzed using an one-way analysis of variance and the Tukey test as a post hoc analysis (p < 0.05).

RESULTS

WT with pH 5.0 had lower dentin abrasion than CT and RS after brushing but had higher dentin loss than both after immersion. The dentin surfaces of CAS1, CAPB, and WT were damaged after immersion, whereas HPS, CAS2, CT, SPDS, RS, and DW remained intact after soaking. CAS2 and HPS, which had a pH of 5.0 like WT, did not significantly differ from those of DW after brushing.

CONCLUSIONS

WT containing HP and CA did not cause significant dentin abrasion but may cause additional dentin loss even without brushing. After brushing or immersion, the CA concentration may affect the dentin surface more than the HP concentration included in WT. The amount of abrasion or loss of dentin after brushing or soaking can vary based on the composition, concentration, and buffer in the solution, even if the pH of the solution is similar to pH 5.0.

Influence of Smoking Habits on the Prevalence of Dental Caries: A Register-Based Cohort Study

Objective This study aimed to evaluate the influence of smoking habit on the prevalence of dental caries lesions in a follow-up study.

Materials and Methods A total of 3,675 patients (2,186 females and 1,489 males) with an average age of 51.4 years were included. Outcome measures were the incidence of dental caries defined as incipient noncavitated, microcavitated, or cavitated lesions which had been diagnosed through clinical observation with mouth mirror and probe examination evaluating change of texture, translucency, and color; radiographic examination through bitewing radiographs; or secondary caries through placement of a new restoration during the follow-up of the study.

Statistical Analysis Cumulative survival (time elapsed with absence of dental caries) was estimated through the Kaplan–Meier product limit estimator with comparison of survival curves (log-rank test). A multivariable Cox proportional hazards regression model was used to evaluate the effect of smoking on the incidence of dental caries lesions when controlled to age, gender, systemic status, frequency of dental hygiene appointments, and socioeconomic status. The significance level was set at 5%.

Results Eight hundred sixty-three patients developed caries (23.5% incidence rate). The cumulative survival estimation was 81.8% and 48% survival rate for nonsmokers and smokers, respectively ( p < 0.001), with an average of 13.5 months between the healthy and diseased state diagnosis. Smokers registered a hazard ratio for dental caries lesions of 1.32 ( p = 0.001) when controlled for the other variables of interest.

Conclusion Within the limitations of this study, it was concluded that smoking habit might be a predictor for dental caries.

In vitro inhibition of bovine enamel demineralization by enamel matrix derivative

This study aimed to determine whether enamel matrix derivative (Emdogain) affects the demineralization of bovine enamel in vitro and to assess the agent's anti-caries potential. Bovine enamel blocks were prepared and randomly divided into three groups (n = 15 per group), which were treated with distilled water (negative control), NaF (positive control), or Emdogain. All three groups were pH-cycled 12 times over 6 days. The percentage of surface enamel microhardness reduction (%SMHR), calcium demineralization rate (CDR), surface roughness, lesion depth and mineral loss after demineralization were examined. Surface morphology of specimens was studied by scanning electron microscopy. The Emdogain and positive control groups showed similar surface roughness, lesion depths and mineral loss, which were significantly lower than those in the negative control group. In addition, the enamel surfaces of both the Emdogain and NaF groups showed much narrower intercrystalline spaces than the surfaces of the negative control group, which exhibited extensive microfractures along the crystal edges. %SMHR differed significantly among all three groups, with the smallest value in the Emdogain group and the greatest in the negative control group. These results indicate that enamel matrix derivative (Emdogain) can significantly inhibit demineralization of bovine enamel in vitro, suggesting that it has potential as an anti-caries agent.

Adhesive systems and secondary caries formation: Assessment of dentin bond strength, caries lesions depth and fluoride release

OBJECTIVES

The present study evaluated the microtensile bond strength and caries formation on adhesive/dentin interfaces before and after dynamic chemical formation of secondary caries.

METHODS

Restorations were prepared on the dentin surface of 80 bovine incisors using four adhesive systems: two fluoride-free (Single Bond and Clearfil SE Bond) and two fluoride containing (Optibond Solo Plus and Clearfil Protect Bond). The restored teeth were then sectioned into multiple slabs that were further trimmed at the bonded interface to a cross-sectional area of 1 mm2. Half of the slabs were subjected to secondary caries formation using a pH cycling model (treated groups); while the other half was used as the control group (no pH cycling). The specimens designated for bond strength evaluation were subjected to microtensile bond strength test (muTBS). Caries lesions formation was assesses by polarized light microscopy at different depths from the adhesive-dentin bonded interface. The fluoride ion concentration was evaluated using the de/remineralization solutions (De/Re).

RESULTS

No differences in muTBS were observed among the adhesive systems in both the control and treated conditions. Secondary caries significantly reduced the values of muTBS for all adhesives (p<0.05). Optibond Solo Plus presented the lowest caries formation at 5 microm depth. Fluoride concentrations present in the De/Re were less than 0.03 ppm, regardless of the adhesive system tested.

SIGNIFICANCE

Bond strength values significantly decreased after in vitro secondary caries formation. Fluoride present in adhesive systems is not capable of inhibiting secondary caries or maintaining bond strength values following caries formation.

Effect of 2% plain and fluoridated milk on root surface caries in vitro

The caries-protective effect of milk and fluoridated milk on enamel has been reported; however, few data are available concerning the role of milk and/or fluoridated milk on root surfaces. The aim of this study was to compare the effect of plain and fluoridated milk on root surface caries. Artificial root surface lesions were created, sectioned and analyzed using polarized light microscopy (PLM) and microradiography (MRG). The sections were covered except for the original surface and assigned to a treatment group. The samples were immersed in 2% plain milk or fluoridated milk for 40 hours and re-evaluated. Changes were measured and mean differences were compared with an unpaired t-test. Both techniques revealed a reduction in lesion depth for each milk group; however, a significantly greater reduction (p<0.05) was observed with the fluoridated milk. These results suggest that fluoridated milk may have a beneficial effect on the remineralization of root surface caries.

The continuum of dental caries--evidence for a dynamic disease process

The eventual outcome of dental caries is determined by the dynamic balance between pathological factors that lead to demineralization and protective factors that lead to remineralization. Pathological factors include acidogenic bacteria, inhibition of salivary function, and frequency of ingestion of fermentable carbohydrates. Protective factors include salivary flow, numerous salivary components, antibacterials (both natural and applied), fluoride from extrinsic sources, and selected dietary components. Intervention in the caries process can occur at any stage, either naturally or by the insertion of some procedure or treatment. Dental caries covers the continuum from the first atomic level of demineralization, through the initial enamel or root lesion, through dentinal involvement, to eventual cavitation. The dynamic balance between demineralization and remineralization determines the end result. The disease is reversible, if detected early enough. Since demineralization can be quantified at early stages, before frank cavitation, intervention methods can be tested by short-term clinical trials.

The effects of MMP inhibitors on human salivary MMP activity and caries progression in rats

Previous studies suggest that salivary and pulp-derived host enzymes, matrix metalloproteinases (MMPs), may be involved in dentin caries pathogenesis. To study the inhibition of acid-activated human salivary MMPs by non-antimicrobial chemically modified tetracyclines (CMTs), we used a functional activity assay with 125I-labeled gelatin as a substrate. To address the role of MMPs in the progression of fissure caries in vivo, we administered the MMP inhibitors CMT-3 and zoledronate to young rats per os for 7 weeks, 5 days a week. Caries lesions were visualized by Schiff reagent in sagittally sectioned mandibular molars. Marked reduction in gelatinolytic activity of human salivary MMPs was observed with CMT-3. CMT-3 and zoledronate, both alone and in combination, also reduced dentin caries progression in the rats. These results suggest that MMPs have an important role in dentin caries pathogenesis, and that MMP inhibitors may prove to be useful in the prevention of caries progression.

Molecular pathogenesis of root dentin caries

Human dentin has a higher content of organic matrix and more non-ideal hydroxyapatite than human enamel. Ultrastructural studies indicate that root caries involves both mineral dissolution and breakdown of the organic matrix. Factors involved in the root caries process seem more complicated than those in enamel caries. Moreover, the distinct roles of acids and enzymes and the sequence of events in the root caries process are not well-understood. Although Streptococcus mutans and Actinomyces viscosus are considered to be major pathogenic micro-organisms of root caries, their roles in degradation of the organic matrix components of root dentin need clarification. The purpose of this paper is to review the basic composition of root dentin and the roles of acids and both endogenous and bacterial enzymes in the root caries process.

The activation and function of host matrix metalloproteinases in dentin matrix breakdown in caries lesions

Matrix metalloproteinases (MMPs) are a family of enzymes which, in concert, are capable of degrading collagen. We investigated whether human MMPs could participate in the degradation of dentin organic matrix after demineralization. We performed Western blot analyses using MMP-specific antibodies to identify MMPs in human dental caries lesions. Enzymography and functional activity assays, with 125I-labeled gelatin as substrate or quantitating the degradation of type I collagen, were used to determine the activity of purified and salivary gelatinolytic (MMP-2 and MMP-9) and collagenolytic (MMP-8) enzymes with and without acid-activation in pHs relevant to caries. Respective analyses were done with caries-related bacteria. We performed electron microscope analyses to assess the degradative activity of sterilized salivary host MMPs on demineralized human dentin. Human MMP-2, MMP-8, and MMP-9 were identified in demineralized dentinal lesions. The latent purified forms of these enzymes were activated at low pH (4.5), followed by neutralization, mimicking the conditions during caries progression. Incubation of human saliva at low pH followed by neutralization resulted in a four-fold increase in the gelatinolytic activity. No gelatinolytic or collagenolytic activity was observed in bacterial samples. The activated enzymes in saliva degraded demineralized dentin organic matrix in vitro. These results demonstrate the pH-dependent activation mechanism of MMPs, which may have a distinct role in different physiological and pathological conditions. They further demonstrate that host MMPs, activated by bacterial acids, have a crucial role in the destruction of dentin by caries.

Denture plaque--past and recent concerns

OBJECTIVE

This paper critically reviews the history of denture plaque and identifies some concerns with the presence of Candida in the mouth.

DATA SOURCES

This review covers literature sources related to Candida albicans and its relationship to denture plaque.

STUDY SELECTION

The articles selected for this review are from referred journals and describe C. albicans and its relationship to oral, gastrointestinal and pleuropulmonary infections. The relationship to caries, root caries and periodontal disease is also covered.

CONCLUSIONS

Denture plaque containing Candida could cause not only oral candidiasis, like oral thrush or denture-induced stomatitis, but also caries, root caries and periodontitis of abutment teeth. However, there is only limited experimental evidence or information available on the cariogenicity of Candida. The continuous swallowing or aspiration of micro-organisms from denture plaque exposes patients, particularly the immunocompromised host or medicated elderly, to the risks of unexpected infections. The term, 'denture plaque' has been used throughout the review. However, the term 'plaque on denture' should be used because the microbial flora and its pathogenicity of denture plaque resembles those of plaque formed on the tooth surface, so called dental plaque. In addition, the term 'denture related stomatitis' would be preferable to 'denture induced stomatitis', since the inflammation of (palatal) mucosa is not induced by the denture, but by wearing the denture or by plaque on the denture.

Root-surface caries formation: effect of in vitro APF treatment

To determine the effect of one and four-minute acidulated phosphate fluoride, or APF (Oral-B Minute Gel, Oral-B Laboratories) treatments on artificial caries development in root surfaces, an in vitro study was conducted. The authors created a window of exposed root surface on extracted teeth by applying acid-resistant varnish to the remaining surface. APF treatment was administered and followed by a 24-hour deionized-distilled water rinse. A window of sound root surface that had been protected from the APF treatment was exposed and served as a control. Acidified gel was then applied to the exposed root surfaces to create the artificial caries. The authors found that APF treatment significantly enhanced resistance to demineralization of root surfaces from an in vitro acidogenic challenge. However, there was little difference in effectiveness between the one- and four-minute APF treatment times.

Modification of amino acid residues in carious dentin matrix

The Maillard reaction between sugar and protein has been postulated as the cause for the browning and arrestment of caries lesions. This reaction has been implicated as the cause for decreased degradability of collagen in vivo. The aim of the present study was to verify the occurrence of the reaction in vivo. Carious and sound dentin samples were taken from extracted human teeth and analyzed for the fluorescence characteristic of the Maillard reaction and oxidation and, by HPLC, for Maillard products. In addition, physiological cross-links were analyzed by HPLC. Oxidation- and Maillard reaction-related fluorescence increased in collagenase digests from carious dentin. Advanced Maillard products (carboxymethyllysine and pentosidine) increased, whereas furosine, a marker for the initial reaction, was not observed consistently. This implies no direct addition of sugars to protein, but rather the addi-tion of smaller metabolites and glycoxidation products. In addition, the physiological cross-links hydroxylysinonorleucine and dihydroxylysinonorleucine decreased in carious dentin. Also for hydroxylysylpyridinoline, a decrease was observed, but not consistently. In conclusion, the caries process modifies amino acids in dentin collagen, which can lead to increased resistance against proteolysis and ultimately to caries arrestment.

Effects of collagenase on root demineralization

The role of proteolytic enzymes in the root caries process remains unclear. The aim of this study was to investigate collagenase activity during tooth root demineralization and remineralization in an in vitro demineralization/remineralization pH-cycling model, Human tooth roots were subjected to pH cycling (alternating demineralization and remineralization) in one of two different time cycles for five days. Collagenase at 90, 180, or 360 micrograms per root was placed into either the demineralizing solution or the remineralizing solution in the pH-cycling system. The effects of additional exposure to collagenase before or after pH cycling were also studied. After the exposure, thin sections of the roots were examined histologically by polarized light microscopy. Changes of calcium and phosphate in the solutions were analyzed chemically. Surface erosion occurred only in the groups where collagenase was contained in the remineralizing solution and in which the root samples were exposed to severe demineralization. However, no differences among the control and experimental groups were found in calcium and phosphate changes in the pH-cycling solutions. These findings suggest that collagenase works during the remineralizing phase and predominantly attacks the organic matrix of the root after demineralization. Additional exposure to collagenase before or after pH cycling did not increase surface erosion except for exposure to collagenase in the absence of phosphate following pH cycling.

The application of in vitro models to research on demineralization and remineralization of the teeth

Progress in in vivo and in situ experimentation has led many researchers to speculate as to the relevance and importance of in vitro testing protocols in caries research. A Medline/Biosis search for the present review revealed well over 300 citations (since 1989) documenting in vitro tests associated with caries research on mineralization and fluoride reactivity. The present survey documents these recent applications of in vitro test methods in both mechanistic and 'profile' caries research. In mechanistic studies, in vitro protocols over the past five years have made possible detailed studies of dynamics occurring in mineral loss and gain from dental tissues and the reaction dynamics associated with fluoride anticaries activity. Similarly, in profile applications, in vitro protocols make possible the inexpensive and rapid--yet sensitive--assessment of F anticaries efficacy within fluoride-active systems, and these tests represent a key component of product activity confirmation. The ability to carry out single variable experiments under highly controlled conditions remains a key advantage in in vitro experimentation, and will likely drive even further utilization, as advances continue in physical-chemical and analytical techniques for substrate analysis in these protocols. Despite their advantages in vitro testing protocols have significant limitations, most particularly related to their inability to simulate the complex biological processes involved in caries.

The influence of the organic matrix on demineralization of bovine root dentin in vitro

The effect of matrix degradation on the rate of demineralization of dentin lesions was investigated. It was hypothesized that the demineralized matrix would inhibit the demineralization of the underlying mineralized dentin. Bovine root dentin specimens were alternately demineralized and incubated with either a bacterial collagenase or buffer (control). The demineralization was carried out under various conditions: Acetic acid solutions were used to form incipient and advanced erosive lesions, and lactic acid solutions containing a bisphosphonate were used to form incipient subsurface lesions. Under all conditions, the demineralization was found to be accelerated when the matrix was degraded by collagenase. This increase was more pronounced in advanced erosive lesions than in incipient lesions. Microscopic examination of collagenase-treated specimens revealed that the matrix of erosive lesions contained several layers of differently affected matrices, whereas the matrix of subsurface lesions appeared to be equally affected throughout the lesion. In conclusion, the matrix degradation was different in erosive and subsurface lesions but promoted the demineralization in both types of lesions.

Solubilization of dentin matrix collagen in situ

The effects of the oral environment on dentin matrix collagen were studied. In the partial prostheses of 12 participants, two completely demineralized dentin specimens were mounted covered by a Dacron gauze. After an experimental period of seven weeks, the specimens were transferred to a trypsin-containing buffer for determination of the amount of denatured collagen. Subsequently, the specimens were incubated with a bacterial collagenase for assessment of the amount of collagen. After the intra-oral exposure, there was a collagen loss varying between 1 and 47 wt%. This variation might be due to differences in proteolytic activity of the colonizing microflora. After exposure to the oral environment, only about 0.5 wt% of the available collagen was trypsin-degradable. This indicates a rapid solubilization of the denatured collagen from the specimens into the oral cavity. A separate group of specimens was examined by light microscopy and transmission electron microscopy. Various degrees of breakdown could be discerned. Some experimental specimens showed loss of surface integrity and tubules heavily infected with different types of micro-organisms. The lumens of the tubules were enlarged, sometimes creating caverns as a result of the loss of the intertubular collagenous matrix.