Electronmicroscopy of Dental Calculus

Micro-Raman Spectroscopy Reveals the Presence of Octacalcium Phosphate and Whitlockite in Association with Bacteria-Free Zones Within the Mineralized Dental Biofilm

Through a correlative analytical approach encompassing backscattered electron scanning electron microscopy (BSE-SEM), energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy, the composition of the mineralized biofilm around a dental implant, retrieved due to peri-implantitis, was investigated. The mineralized biofilm contains two morphologically distinct regions: (i) bacteria-containing zones (Bact+), characterized by aggregations of unmineralized and mineralized bacteria, and intermicrobial mineralization, and (ii) bacteria-free zones (Bact-), comprised mainly of randomly oriented mineral platelets. Intramicrobial mineralization, within Bact+, appears as smooth, solid mineral deposits resembling the morphologies of dental plaque bacteria. Bact- is associated with micrometer-sized Mg-rich mineral nodules. The Ca/P ratio of Bact+ is higher than Bact-. The inorganic phase of Bact+ is carbonated apatite (CHAp), while that of Bact- is predominantly octacalcium phosphate (OCP) and whitlockite (WL) inclusions. Compared with native bone, the inorganic phase of Bact+ (i.e., CHAp) exhibits higher mineral crystallinity, lower carbonate content, and lower Ca/P, C/Ca, Mg/Ca, and Mg/P ratios. The various CaPs found within the mineralized dental biofilm (CHAp, OCP, and WL) are related to the local presence/absence of bacteria. In combination with BSE-SEM and EDX, micro-Raman spectroscopy is a valuable analytical tool for nondestructive investigation of mineralized dental biofilm composition and development.

A silicon cell cycle in a bacterial model of calcium phosphate mineralogenesis

The prokaryote Corynebacterium matruchotii produces calcium phosphate (bone salt) and may serve as a convenient model for examining individual factors relevant to vertebrate calcification. A factor of current clinical uncertainty is silicon. To investigate its possible role in biomineralisation advanced optical (digital deconvolution and 3D fluorescent image rendering) and electron microscopy (EDX microanalysis and elemental mapping) were applied to calcifying microbial colonies grown in graded Si concentrations (0-60mM). Cell viability was confirmed throughout by TO-PRO-3-iodide and SYTO-9 nucleic acid staining. It was observed that calcium accumulated in dense intracellular microspherical objects (types i-iii) as nanoparticles (5 nm, type i), nanospheres (30-50 nm, type ii) and filamentous clusters (0.1-0.5 μm, type iii), with a regular transitory Si content evident. With bacterial colony development (7-28 days) the P content increased from 5 to 60%, while Si was displaced from 60 to 5%, distinguishing the phenomenon from random contamination, and with a significant relationship (p<0.001) found between calcified object number and Si supplementation (optimum 0.01mM). The Si-containing, intracellular calcified objects (also positive for Mg and negative with Lysensor blue DND-167 for acidocalcisomes) were extruded naturally in bubble-like chains to complete the cycle by coating the cell surface with discrete mineral particles. These could be harvested by lysis, French press and density fractionation when Si was confirmed in a proportion. It was concluded that the unexplained orthopaedic activity of Si may derive from its special property to facilitate calcium phosphorylation in biological systems, thereby recapitulating an ancient and conserved bacterial cycle of calcification via silicification.

Electron microscopy of octacalcium phosphate in the dental calculus

The purpose of this study was to morphologically demonstrate the presence of octacalcium phosphate in the dental calculus by judging from the crystal lattice image and its rapid transformation into apatite crystal, as part of our serial studies on biomineral products. We also aimed to confirm whether the physical properties of octacalcium phosphate are identical with those of the central dark lines observed in crystals of ordinary calcifying hard tissues. Electron micrographs showed that crystals of various sizes form in the dental calculus. The formation of each crystal seemed to be closely associated with the organic substance, possibly originating from degenerated microorganisms at the calcification front. Many crystals had an 8.2-A lattice interval, similar to that of an apatite crystal. Furthermore, some crystals clearly revealed an 18.7-A lattice interval and were vulnerable to electron bombardment. After electron beam exposure, this lattice interval was quickly altered to about half (i.e. 8.2 A), indicating structural conversion. Consequently, a number of apatite crystals in the dental calculus are possibly created by a conversion mechanism involving an octacalcium phosphate intermediate. However, we also concluded that the calcification process in the dental calculus is not similar to that of ordinary calcifying hard tissues.

Demonstration of the central dark line in crystals of dental calculus

Using an electron microscope and Fourier transform infrared (FTIR) microspectroscopy, we studied the lattice images of crystallites of dental calculus to demonstrate the presence of the central dark line (CDL) in its crystallite and to compare this CDL with that of bone and synthetic hydroxyapatite crystals. Ultrastructural observations revealed clearly a number of crystallites, which displayed a proper lattice image and CDL similar to that of bone, in the dental calculus. FTIR microspectroscopy revealed that the dental calculus displayed a set of major spectra analogous to that of bone. These results suggest that the formation process of hydroxyapatite crystals with CDL in dental calculus, which is considered to be an unusual type of calcified structure in association with microorganisms, is basically similar to that of the ordinary calcifying hard tissues (bone, enamel, etc.).

Subgingival calculus: where are we now? A comparative review

OBJECTIVE

To critically analyse the formation, composition, ethnic variations and pathogenic potential of subgingival calculus in comparison with supragingival calculus.

DATA SOURCES

Using CD-ROM and index medicus, scientific papers relating to subgingival calculus or subgingival and supragingival calculus written in the English language since 1960 were considered, with the emphasis on more recent articles.

STUDY SELECTION

Studies were selected for their relevance and contemporary nature re:composition and formation of dental calculus and comparisons of ethnic groups with regard to dental calculus, especially subgingival calculus. Some similar studies were not included.

DATA EXTRACTION

Abstracts of studies were kept brief unless particularly important to the review. Population, methodology, statistics and accurate conclusions were used as important guides to the quality and validity of studies.

DATA SYNTHESIS

Similarities and differences between supragingival and subgingival calculus in composition and formation were shown. Different morphological types of subgingival calculus were demonstrated. There was evidence for an association between calculus formation and ethnicity with regard to supragingival and subgingival calculus, and an association between subgingival calculus composition and ethnicity was indicated.

CONCLUSIONS

An association between ethnicity and subgingival calculus formation and composition was found. Further research into the reasons for these ethnic differences in dental calculus and the role of the mineral constituents especially of subgingival calculus would be valuable.

Therapeutic mineral enrichment of dental plaque visualized by transmission electron microscopy

The form, location, and distribution of fluorhydroxyapatite deposited in dental plaque by a urease-mediated mineral enrichment process have been studied by transmission electron microscopy. Artificial plaque was formed in terylene gauze in the mouth of one subject and immersed for five min four times per day in a mineral-enriching solution. Contralateral control plaque remained untreated. The effect on natural plaque was studied in two subjects who withheld oral hygiene for four days and mouthrinsed with this solution for two min four times per day during the last two days. Mineral deposits were seen in all plaque samples exposed to the test solution. None was detected in any control sample. The deposits were scattered in the interbacterial matrix as needle-shaped crystals, the size and shape of apatite, together with amorphous material. The crystals appeared larger and more perfect, and the amorphous material less conspicuous, with longer in vivo rinsing periods. Platelet-shaped crystals of octacalcium phosphate were never seen. Mineral was also seen within the remnants of dead bacterial cells and within degenerating epithelial cells. Crystals were never seen within intact bacterial cells, as in calculus formation. The presence of a single crystal type and the relative absence of densely-mineralized foci are other differences between this mineral-enrichment process and supra-gingival calculus formation. A longer-term study is necessary to determine whether the solution promotes calculus by providing nucleation seeds.

Calculus revisited. A review

Although there is no doubt that gingivitis can develop in the absence of supragingival calculus, it is not clear to what extent the presence of mineralized deposit enhances gingival inflammation. Partial inhibition of plaque mineralization can be accomplished by chemical agents, but there has been no demonstration in humans of a reduction in gingivitis. It remains to be established what level of inhibition (if any) is required to have more than a cosmetic effect. Since the accepted scenario is that apical growth of supragingival plaque precedes the formation of subgingival calculus, there is no longer an issue of whether subgingival calculus is the cause or the result of periodontal disease. Subgingival mineralization results from the interaction of subgingival plaque with the influx of mineral salts that is part of the serum transudate and inflammatory exudate. This chronology, however, should not be the basis for relegating calculus to the ash heap. Morphologic and analytical studies point to the porosity of calculus and retention of bacterial antigens and the presence of readily available toxic stimulators of bone resorption. When coupled with the increased build up of plaque on the surface of the calculus, the combination has the potential for extending (beyond that of plaque alone) the radius of destruction and the rate of displacement of the adjacent junctional epithelium. The centrality of thorough scaling and root planing in the successful maintenance of periodontal health supports the view that subgingival calculus contributes significantly to the chronicity and progression of the disease, even if it can no longer be considered as responsible for initiation.

Purification of a protein component in extracts from supragingival dental calculus

In the present study supragingival dental calculus of unknown age was collected from the mandibular incisors of three individuals and solubilized by EDTA. The extracts were examined by gel filtration, ionic exchange chromatography and amino acid analysis. A protein component with similar characteristics to the main protein component of the acquired enamel pellicle was a regular constituent of the calculus extracts from the three subjects.

Crystallography of supragingival and subgingival human dental calculus

Selected area electron diffraction of sections and individual crystal fragments of human dental calculus has demonstrated that octacalcium phosphate, hydroxyapatite and whitlockite form the inorganic part of both supragingival and subgingival dental calculus. However, the major constituents in supragingival calculus are platelet-shaped crystals of octacalcium phosphate and needle-shaped crystals of hydroxyapatite, while bulk crystals of whitlockite is the predominant component in subgingival calculus. The subgingival samples seemed to be better crystallized than the supragingival ones. The results obtained by the electron optical and X-ray powder investigations are in good agreement.

Ultrastructure of nondecalcified supragingival and subgingival calculus

THE ULTRASTRUCTURE of nondecalcified supragingival and subgingival calculus was studied in mature deposits. To facilitate sectioning of the embedded material, a thin reinforcing film of plastic was painted on the block. A new film was applied for each section. Light microscopy showed that supragingival calculus was heterogeneous with islets of calcified material within the covering plaque and with noncalcified areas within the calculus. Under transmission electron microscopy supragingival calculus was heterogeneous, dominated by microorganisms, small needle-shaped crystals and large ribbon-like crystals. In the covering soft plaque small crystals were often scattered in the intermicrobial matrix. In the supragingival calculus itself noncalcified microorganisms were surrounded with densely packed small crystals. There were also rosettes and bundles of large crystals. Subgingival calculus was homogeneous in light microscopy. The covering plaque contained no calcified material and only calcified material was seen within the calculus itself. Transmission electron microscopy of subgingival calculus revealed crystals of small size only. Subgingivally very few noncalcified microorganisms were seen within the calculus. The bacterial cell wall seemed to be the structure that was last calcified, both supragingivally and subgingivally.

Salivary calculi: ultrastructural morphology and bacterial etiology

Ultrastructural morphology of 16 salivary calculi was studied by means of transmission and scanning electron microscopy. The external surface was mostly globular or coarse, and on high magnifications and features could be divided into four main groups: a) amorphic calcified deposits covering extensive areas, b) other areas covered with crystals in a variety of arrangements, c) heavy accumulations of calcified rod-like and filamentouslike microorganisms, and d) platelet crystals in juxtaposition to calcified microorganisms in several areas. In most calculi the split area was found to be laminated. It is suggested that microorganisms have an important role in the formation and growth of salivary calculi.

Proteolipid and calculus matrix calcification in vitro

The initiator of calculus matrix calcification, in vitro, was isolated. Crude phospholipid, known to contain the factor, was separated into five fractions by column chromatography. A single protein-containing fraction induced apatite formation during incubation. The nucleating fraction was indentified as a proteolipid.

Scanning electron microscopy of dental calculus

The morphologic structure of anorganic dental calculus was studied by means of the scanning electron microscope. From surface observations, calculus is apparently composed of two components with distinguishable patters of calcification. One component is formed by the precipitation of minute calcific crystals on microorganisms and intermicrobial substances (plaque matrix). Such calcified masses, often spherical in shape, have a sponge-like appearance with empty spaces representing the former sites of entombed and degenerated organisms. Thus, intracellular calcification is not evident at this stage of calculus development. The other component, although having at least one common calcification front with the former, does not appear to be directly associated with microbial calcification. It exhibits a configuration of generally larger crystal growths of varying shapes and sizes. These two calcification patterns are comparable, both in distribution and size, to what has been observed by means of the transmission electron microscope, and what Schroeder has designated as "types A & B centers of mineralization," respectively. The calcific precipitation in type A centers have been identified by X-ray diffraction as hydroxyapatite. It is, therefore, speculated that the crystal patters in type B centers might represent other known forms of calcium phosphates present in calculus, such as octacalcium phosphate, whitlockite and brushite.

Lipid and calculus matrix calcification in vitro

Lipid is necessary for calcification of a calculus matrix. Matrix was prepared by decalcification of dental calculus. The matrix calcified when it was exposed to a metastable calcium phosphate solution. After extraction with chloroform-methanol, the matrix lost the capacity to calcify. The lipid extract was calcifiable.

The effect of neuraminidase on the properties of salivary proteins

Neuraminidase rapidly cleaves sialic acid residues and increases the turbidity of human saliva. The isotherm for the adsorption of salivary proteins to hydroxyapatite is unchanged by preliminary treatment of the saliva or the hydroxyapatite with neuraminidase. The data suggest that neuraminidase does not alter the adsorption behavior of salivary proteins.

Mineralization of Bacteria

A variety of viable and non-viable bacteria became mineralized with hydroxyapatite when implanted in dialysis bags in the peritoneal cavities of rats. The microscopic pattern of mineral deposition appeared analogous to that in the formation of oral calculus. Since nonviable organisms were mineralized at an accelerated rate, bacterial metabolic processes may not be essential for mineralization.