Dentine caries in vivo. Combined scanning electron microscopic and microradiographic investigation

Impact of biomineralization on resin/biomineralized dentin bond longevity in a minimally invasive approach: An "in vitro" 18-month follow-up

OBJECTIVES

To determine the impact of treating caries-affected dentin (CAD) with: 0.2% sodium fluoride (NaF), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP/MI Paste™) or peptide P₁₁-4 (Curodont™ Repair) on the longevity of resin/CAD interface at storage times of 24 -h, 6- and 18-month.

METHODS

255 caries-free third molars were used, and CAD was produced by a biological method. The teeth were randomly distributed into: G1- Sound dentin (SD); G2- CAD; G3- CAD + 0.2% NaF (CAD/NaF); G4- CAD + CPP-ACP (CAD/ACP); G5- CAD + Curodont™ Repair (CAD/P₁₁-4). The Filtek Z350 composite resin block was bonded to dentin using Adper™ Single 2 (4 mm/height). Resin/dentin blocks were stored in a solution of Simulated Body Fluid at 37 °C, pressures were modified to simulate natural pulpal pressures. Specimens were investigated by microtensile bond strength (μTBS) (n = 8), Scanning Electron Microscopy (to assess the failure mode) (n = 8), nanoinfiltration (to assess the interface sealing) (n = 3), in situ zymography (to assess the gelatinolytic activity) (n = 3) and micro-computed microtomography (μ-CT) (to assess the mineralization) (n = 3). Data from μTBS, μ-CT and, nanoinfiltration and hybrid layer formation/degradation were submitted to two-way ANOVA and Tukey tests, and failure patterns and in situ zymography to Kruskal-Wallis and Dunn tests (α = 5%).

RESULTS

The highest mineral density change by μ-CT, smallest silver nitrate infiltration and proteolytic activity in the adhesive layer were obtained significantly for the groups SD, CAD/ACP and CAD/P₁₁-4, with most mixed fractures at 18-month (p < 0.001). CAD/NaF showed significantly similar values to CAD, CAD and CAD/NaF which presented a high percentage of adhesive fracture (p < 0.001) at all time periods.

SIGNIFICANCE

Treating caries-affected dentin with remineralizing agents CPP-ACP and Curodont™ Repair, has the potential to be a clinically relevant treatment protocol to increase the longevity of adhesive restorations.

Clinical assessment of non carious cervical lesion using swept-source optical coherence tomography

Non-carious cervical lesions (NCCLs) involve various forms of tooth loss with different etiologies. This study aimed to utilize swept-source optical coherence tomography (SS-OCT) at 1300 nm wavelength range in vitro and in vivo to evaluate and clarify the mechanism of NCCLs. In the in vitro phase, a dentin attenuation coefficient (μt ) derived from the SS-OCT signal at NCCL was compared with mineral loss obtained from transverse microradiography (TMR) to determine a μt threshold to discriminate demineralization of cervical dentin in vivo. In the clinical study, 242 buccal surfaces were investigated in 35 subjects. Presence and dimensions of NCCLs, cervical cracking and the degree of demineralization at the exposed cervical dentin were determined using SS-OCT. Dentin demineralization was observed in 69% of NCCLs. SS-OCT results confirm that dentin mineral loss and occlusal attrition were associated with larger NCCLs, and can be considered as an etiological factor in formation and progress of these lesions. (A) We determined the attenuation coeffcient (μt ) threshold of SS-OCT signal for the detection of demineralization (1.21) from in vitro study. DEM: demineralized dentin, sound: sound dentin. (B) Using the μt threshold, we observed NCCLs in vivo to detect the demineralization in cervical dentin. SS-OCT scanning was performed along the red line. (C) SS-OCT image obtained along the red line in B. In SS-OCT, brightness of dentin beneath the NCCL was increased (arrow) compared with intact zone. The cervical dentin was slightly demineralized (μt : 1.25). e: enamel, d: dentin, g: gingiva.

Matrix metalloproteinases and other matrix proteinases in relation to cariology: the era of 'dentin degradomics'

Dentin organic matrix, with type I collagen as the main component, is exposed after demineralization in dentinal caries, erosion or acidic conditioning during adhesive composite restorative treatment. This exposed matrix is prone to slow hydrolytic degradation by host collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins. Here we review the recent findings demonstrating that inhibition of salivary or dentin endogenous collagenolytic enzymes may provide preventive means against progression of caries or erosion, just as they have been shown to retain the integrity and improve the longevity of resin composite filling bonding to dentin. This paper also presents the case that the organic matrix in caries-affected dentin may not be preserved as intact as previously considered. In partially demineralized dentin, MMPs and cysteine cathepsins with the ability to cleave off the terminal non-helical ends of collagen molecules (telopeptides) may lead to the gradual loss of intramolecular gap areas. This would seriously compromise the matrix ability for intrafibrillar remineralization, which is considered essential in restoring the dentin's mechanical properties. More detailed data of the enzymes responsible and their detailed function in dentin-destructive conditions may not only help to find new and better preventive means, but better preservation of demineralized dentin collagenous matrix may also facilitate true biological remineralization for the better restoration of tooth structural and mechanical integrity and mechanical properties.

Finite-element modeling and analysis in nanomedicine and dentistry

This article aims to provide a brief background to the current applications of finite-element analysis (FEA) in nanomedicine and dentistry. FEA was introduced in orthopedic biomechanics in the 1970s in order to assess the stresses and deformation in human bones during functional loadings and in the design and analysis of implants. Since then, it has been applied with great frequency in orthopedics and dentistry in order to analyze issues such as implant design, bone remodeling and fracture healing, the mechanical properties of biomedical coatings on implants and the interactions at the bone–implant interface. More recently, FEA has been used in nanomedicine to study the mechanics of a single cell and to gain fundamental insights into how the particulate nature of blood influences nanoparticle delivery.

Effect of loading and pH on the subsurface demineralization of dentin beams

It is important to understand subsurface dentin demineralization and caries from the clinical perspective as dentin properties are modified under acidic conditions and mechanical loading. This study was conducted to observe the subsurface demineralization of dentin beams at three different pH levels under tension and compression. Bovine dentin beams (10 x 3.75 x 1.45 mm) were fixed at one end and immersed in 0.1 M lactic acid solution at pH levels 4.5, 7, and 10 for 5 days under a load of 6.5 N (663 g), and the subsurface demineralization depth was measured using a polarized light microscope. The mean subsurface demineralization depth was more subjacent to the surface under compression than that under tension at pH 4.5 and decreased as the distance from the fixed end increased. No subsurface demineralization was observed at pH 7 or 10. It was concluded that both stress and low pH are associated with increased subsurface demineralization at the fixed end of the beam.

Reduced antigenicity of type I collagen and proteoglycans in sclerotic dentin

Antigenic alterations to the dentin organic matrix may be detected by an immunohistochemical approach. We hypothesized that alterations in the antigenicity of type I collagen and proteoglycans occur in sclerotic dentin under caries lesions. Transverse sections were prepared from carious teeth in the sclerotic zone and normal hard dentin. A double-immunolabeling technique was performed on these sections, with anti-type I collagen and anti-chondroitin 4/6 sulfate monoclonal primary antibodies. We used gold-conjugated secondary antibodies to visualize the distribution of intact collagen fibrils and proteoglycans by high-resolution SEM. For sclerotic dentin, labeling densities were 19.57 +/- 3.01/microm2 for collagen and 9.84 +/- 2.62/microm2 for proteoglycans. For normal hard dentin, values were 35.20 +/- 2.73/microm2 and 17.03 +/- 1.98/microm2, respectively. Distribution of intact collagen fibrils and proteoglycans in sclerotic dentin was significantly lower than in normal hard dentin. Reductions in antigenicity from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential of intrafibrillar remineralization.

Microhardness and Ca:P ratio of carious and Carisolv™ treated caries-affected dentine using an ultra-micro-indentation system and energy dispersive analysis of x-rays — A pilot study

BACKGROUND

This study aimed to evaluate microhardness and chemical analysis of carious and caries-affected dentine. The hypothesis tested was that calcium:phosphorous (Ca:P) ratios correlate with microhardness values.

METHODS

Four carious human third molars were sectioned through the caries lesion in the mesiodistal longitudinal plane. One half of each lesion underwent carious dentine removal using Carisolv gel. The cut surfaces were polished, microhardness tested using an Ultra-Micro-Indentation System (UMIS) and elemental analysis performed using energy dispersive analysis of x-rays (EDAX).

RESULTS

The microhardness of carious dentine decreased gradually towards the cavity floor, but that for caries-affected dentine showed more variation with depth, having a mean hardness of (0.63 +/- 0.18) GPa. Ca:P ratios of carious dentine varied among the four specimens. The mean Ca:P ratio of caries-affected dentine was 1:2.03 +/- 0.08. The hypothesis was accepted for active lesions.

CONCLUSIONS

The use of Carisolv to excavate carious tissue can be as effective as rotary instrumentation.

Relationship between large tubules and dentin caries in human deciduous tooth

The purpose of this study was to elucidate the relationship between large tubules and dentin caries by using human deciduous incisors that showed various levels of attrition but no macroscopical lesions resulting from caries. The teeth were cut longitudinally in the mesio-distal direction and the exposed surfaces observed with a high-resolution field emission scanning electron microscope. The inside of each large tubule showed dense collagen fibers running parallel to its long axis and small spherical bodies of aggregated crystals, but no marked attrition. In teeth where attrition had exposed dentin at the incisal edge, oral bacteria had infiltrated the large tubules. Furthermore, in teeth with advanced attrition, it was difficult to distinguish between the large tubules and the surrounding dentin matrix, and numerous bacteria were observed in both areas. These findings support the hypothesis that large tubules play a role in the pathway of caries formation in coronal dentin when incisal dentin is exposed by attrition. This suggests that early treatment of exposed dentin surfaces might be effective in preventing dental caries.

Characterising the micro-mechanical behaviour of the carious dentine of primary teeth using nano-indentation

A better appreciation of the properties of carious dentine would be of clinical advantage in carious assessment and management. The aim of this study is to understand the deterioration of the mechanical properties of carious dentine as a result of bacterial demineralising process as well as change in dentine structures observed under scanning electronic microscope. Eight primary molar teeth with untreated carious dentine were axially sectioned and fine polished for nano-indentation. On each specimen, six lines of indentation, evenly distributed through the lesion, were made from the pulp to lesion cavity floor parallel to tubule direction using nano-indentation (Ultra Micro Indentation System, UMIS-2000), while another two indentation lines were made on an adjacent region of sound dentine in the same manner. All tests were conducted on hydrated specimens. Hardness and elastic modulus decreased significantly and progressively toward the cavity floor varying from 0.56 to 0.001 GPa and 14.55 to 0.015 GPa, respectively. The change in mechanical properties was in a specific pattern as a function of lesion depth, in which the hardness could be fitted to an exponential function, while the variation of the elastic modulus across the entire lesion was fitted to a power law relationship. More critical evaluation of the elastic modulus data indicated that two distinct exponential functions provided an excellent fit to the results. These changes in elastic modulus also matched the structural changes seen across a lesion, which were associated with a change from primarily peritubular to intertubular dissolution.

Influence of hydration and mechanical characterization of carious primary dentine using an ultra-micro indentation system (UMIS)

The conditions under which mechanical properties of dentine are tested influence the values recorded. The aims of this study were to examine the effect of hydration on the mechanical properties of primary carious dentine and to provide information on changes in hardness and modulus of elasticity change caused by the demineralizing caries process in dentine. Three primary molar teeth with untreated carious dentine were prepared for nano-indentation tests under both wet and dry conditions. Further tests were conducted on eight primary molars with untreated carious dentine under hydrated conditions. The mechanical properties of dehydrated carious dentine increased approximately 10-fold for hardness and 100-fold for the modulus of elasticity compared with hydrated dentine. The hardness and elastic modulus of the carious primary dentine deteriorated progressively toward the lesion cavity floor, ranging from 0.001 to 0.52 GPa and from 0.015 to 14.55 GPa, respectively, and could be fitted to a simple linear relationship when plotted in logarithmic scale vs. distance. The total depth of dentine affected was around 1100 microm parallel to the tubule direction. This depth was significantly greater than observed subjectively, implying that the demineralization process is more advanced than might be suspected on simple clinical examination.

Effect of dentinal pretreatments on coronal dentin primary carious lesions: a field emission SEM study

The aim of the study was the morphological analysis of coronal dentin caries and the modifications induced by different pretreatments with phosphoric acid or sodium hypochlorite. Carious dentin specimens were obtained from human molars affected by carious lesions. Specimens were divided in four groups and submitted to: (1) untreated; (2) 35% phosphoric acid for 15 s; (3) 35% phosphoric acid for 15 s and 5% sodium hypochlorite for 2 min; (4) sodium hypochlorite for 5 min. Specimens were observed under high-resolution SEM. Different areas were identified within the carious lesion: a deeper, inner region revealing closed highly mineralized tubules, and a more superficial outer layer showing an increasing demineralization rate toward the surface of the lesion. Phosphoric acid followed by NaOCl treatment removed all collagen fibrils from greatly altered carious outer-dentin layer. The 5-min treatment with sodium hypochlorite affected both inner and outer dentin, removing all collagen fibrils and increasing the porosities of deeper intertubular hypermineralized dentin. FEISEM analysis confirmed that only inner carious dentin after phosphoric acid treatment may be considered a suitable substrate for dentinal bonding system. On the contrary, the outer dentin is an unstable substrate for any type of bonding systems and must be avoided/removed from any surface before conditioner application.

Effect of perfusion with water on demineralization of human dentin in vitro

Dentinal fluid rarely features in caries studies of dentin. The mutual effects of in vitro perfusion and dentin demineralization were investigated. The correlation between the remaining dentin thickness and demineralization was also analyzed. Buccal cervical dentin windows in human tooth segments were demineralized either with or without perfusion with water at 3.14 kPa. Transverse microradiography revealed that dentin perfusion reduced the amount of mineral loss from the lesions by 22 vol%; the reduction in lesion depth was 8%. Perfusion rate, which was measured throughout the demineralization process by means of a fluid transport model, did not change significantly. Lesions formed closer to the pulp exhibited increased mineral loss and lesion depth. In conclusion, dentinal fluid flow offers some protection against demineralization. For a better approximation of clinical reality, therefore, in vitro studies on dentinal caries should consider the effect of dentinal fluid flow.

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.

Structural evidence of a sealed tissue interface with a total-etch wet-bonding technique in vivo

The resin-dentin interface of in vivo specimens restored with the All-Bond 2 system by use of a total-etch wet-bonding technique on vital deep human dentin was investigated by: (a) SEM examination of cryofractured specimens; (b) SEM examination of acid-rinsed, highly polished, embedded specimens; and (c) TEM examination of demineralized ultrathin sections. Ultrastructural features that were pertinent to the formation of an effective clinical seal were characterized. It is suggested that the establishment of an effective seal of the patent dentinal tubules following total etching is accomplished by: (1) the formation of an outer zone of a solid resin plug surrounded by a circumferential cuff of resin-impregnated dentin; and (2) the formation of an inner zone of a hollow resin sheath with resin globules along the internal walls of the tubules, closely adapting to the odontoblast process. The structural appearance and functional implications of these two zones were strikingly similar, with the sealing of exposed dentinal tubules in arrested carious lesions or cervical abfraction lesions. It appeared that there is a common denominator in physiologic isolation defense mechanisms and the total-etch, wet-bonding technique in the All-Bond 2 system in preserving the biological and morphological integrity of the pulpo-dentinal complex.

Theoretical model for the scattering of light by dentin and comparison with measurements

A theoretical model of the scattering of light by dentin is presented. The model that results is a superposition of several scattering contributions, i.e., scattering by mineral crystals, collagen fibrils, and dentinal tubules. These tubules are oriented so that they cause an asymmetrical scattering process. The angular intensity functions are calculated for planes that are parallel or perpendicular to the plane of the tubules. The shape of the measured intensity function in the plane perpendicular to the tubules and the values of the scattering coefficient can be explained by the model that we present.

Cariostatic effect and fluoride release from a visible light-curing adhesive for bonding of orthodontic brackets

This study was designed to investigate the cariostatic potential in vivo of a visible light-curing adhesive for the bonding of orthodontic brackets. The fluoride release of the adhesive in water and saliva was also measured. Ten orthodontic patients with premolars to be extracted participated. One bracket with Heliosit-Orthodontic (no fluoride) was positioned on the buccal surface of one premolar (control), and another bracket with Orthodontic cement VP 862 (containing fluoride) was positioned on the experimental contralateral premolar. The adhesives were cured with a Heliolux II lamp, and the teeth were extracted after 4 weeks. The patients used a fluoride toothpaste during the experiment. The mineral content of the enamel adjacent to the brackets was determined by quantitative microradiography. The fluoride release from disk-shaped plates of the fluoride adhesive was measured in water for a 6-month period and in human saliva for 24 hours. The fluoride adhesive reduced lesion depths by about 48% than the nonfluoride adhesive (P less than 0.05, t test). The largest release of fluoride from the plates in water was observable within the first week. However, a significant amount of fluoride was still released after 6 months. The fluoride release in saliva was significantly lower in human saliva at pH 7 than in water (P less than 0.01, t test). When salivary pH was lowered to 4, to mimic a cariogenic challenge, the amount of fluoride released increased up to the value measured in water. It was concluded that the regular use of fluoride toothpastes is insufficient to inhibit lesion development around orthodontic brackets.(ABSTRACT TRUNCATED AT 250 WORDS)

Intra-oral models for studying de- and remineralization in man: methodology and measurement

A wide range of different methodologies and measurement techniques has been employed in laboratories around the world for the study of de- and remineralization of enamel and dentin in intra-oral systems. These different approaches are summarized and discussed in relation to the nature of the different research questions to be studied by means of the intra-oral model.

A review of quantitative methods for studies of mineral content of intra-oral caries lesions

Modern prospective caries studies require the measurement of small changes in tooth mineral content. Quantitative measurements of changes in mineral content in a single caries lesion is desirable. Quantitative methods can be either destructive or non-destructive. The latter type permits longitudinal studies to be conducted. Various methods available for the analysis of lesion parameters are reviewed. The basic principle of each method is summarized, and its characteristics are discussed. For each method, the correlation between the measured parameter and mineral loss, the useful range of mineral loss, the discrimination threshold, and the repeatability, are presented. Where such quantities were not available in the original papers, they were calculated from literature data. A comprehensive table of specifications of all methods is given.

Angular dependence of HeNe-laser light scattering by bovine and human dentine

The scattering phase functions for HeNe-laser light of dentine sections 10-20 micron(s) thick were measured. The functions perpendicular to the tubules had first-order maxima at angles of 4 degrees for bovine dentine and 5 degrees for human dentine; those parallel to the tubules showed no first-order maxima. Several corrections were made before the asymmetry factors g for intertubular dentine were determined; the average values are for bovine dentine g = 0.37 and for human dentine g = 0.44.