archives of oral biology 53 (2008) 168–174
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/arob
Site specific mineral composition and microstructure of human supra-gingival dental calculus Junko Hayashizaki a,*, Seiji Ban b, Haruo Nakagaki a, Akihiko Okumura a, Saori Yoshii a, Colin Robinson c a
Department of Preventive Dentistry and Dental Public Health, School of Dentistry, Aichi-Gakuin University, Nagoya 464-8650, Japan Department of Biomaterials Science, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima 890-8544, Japan c Division of Oral Biology, Leeds Dental Institute, University of Leeds, Leeds LS2 9LU, UK b
article info
abstract
Article history:
Dental calculus has been implicated in the aetiology of several periodontal conditions. Its
Accepted 12 September 2007
prevention and removal are therefore desirable clinical goals. While it is known that calculus is very variable in chemical composition, crystallinity and crystallite size little is known about
Keywords:
site specific variability within a dentition and between individuals. With this in mind, a study
Dental calculus
was undertaken to investigate the comparative site specific nature and composition of human
Mineral contents
dental supra-gingival dental calculus obtained from 66 male patients visiting for their dental
Site-specificity
check-up using fluorescent X-ray spectroscopy, X-ray diffractometry and Fourier transform
Crystal phase
infrared spectroscopy. The supra-gingival dental calculus formed on the lingual surfaces of lower anterior teeth and the buccal surfaces of upper molar teeth were classified into four types based on calcium phosphate phases present. There was significant difference in composition of the crystal phase types between lower and upper teeth ( p < 0.01). There was no significant difference in crystal size between dental calculus on anterior or molar teeth of all samples. The degree of crystallinity of dental calculus formed on the upper molar teeth was higher than that formed on the lower anterior teeth ( p < 0.01). The CO32 contents in dental calculus formed on the lower anterior teeth were higher than on upper molar teeth ( p < 0.05) which might explain the difference in crystallinity. Magnesium and Si contents and Ca:P ratio on the other hand showed no significant difference between lower and upper teeth. It was concluded that the crystal phases, crystallinity and CO32 contents of human dental supra-gingival dental calculus is related to its location in the mouth. # 2007 Elsevier Ltd. All rights reserved.
1.
Introduction
Dental calculus which comprises mineralised dental biofilm1 is implicated in the progression of inflammatory periodontal disease.2 It is a predisposing factor in pocket development in that it provides a rough surface which can facilitate bacterial attachment.1 Therefore, good oral hygiene and frequent
professional care are necessary to minimise calculus formation. Dental calculus is usually classified by its location on a tooth surface in relation to the adjacent free gingival margin, that is, supra-gingival or sub-gingival.1 Calculus occurs most frequently on the lingual surfaces of lower anterior teeth and the buccal surfaces of maxillary first and second molars, opposite to the openings of the sublingual and parotid salivary glands ducts.
* Corresponding author at: 1-100 Kusumoto-cyo, Chikusa-ku, Nagoya 464-8650, Japan. Tel.: +81 52 2561x352; fax: +81 52 752 5988. E-mail address:
[email protected] (J. Hayashizaki). 0003–9969/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.archoralbio.2007.09.003
archives of oral biology 53 (2008) 168–174
The mechanism by which, mainly calcium and phosphate, minerals deposit from the saliva or gingival sulcus fluid and saliva into the biofilm matrix is still not completely understood.1 Recent research studies2,3 pointed to the possibility that calcification of dental calculus may involve similar phenomena to those of other pathological calcifications (such as urinary calculi). The chemical composition may in fact reflect different mechanisms of formation.4,5 This may explain why fluoride concentrations differ in different regions of dental calculus.5 In terms of mechanism, several different calcium phosphates have been suggested as both precursor phases and final phases in the both normal and pathological calcification.2,6 Human supra-gingival dental calculus can be up to 89% calcified and is reported to contain various calcium phosphates7 including calcium deficient apatite [(Ca(Ca, M)10(CO3, HPO4, PO4)6 (OH, X)2 (where M is another cation and X is Cl or F (AP)], dicalcium phosphate dihydrate CaHPO42H2O (DCPD), octacalcium phosphate Ca8H2(PO4)65H2O (OCP), whitlockite bTMCP(Ca, Mg)3(PO4)2 (TCP) and various short range order calcium phosphates. Dental calculus formation appears to begin with the deposition of DCPD and OCP within established dental plaque. With time these appear to transform by hydrolysis into AP and/or TCP, the latter appearing to be a primary constituent.8,9 The precise reasons for formation of specific calcium phosphates are still unclear with few reports in the literature. They most likely relate to local environment including pH, Ca:P ratio, and the contents of other minor ions probably related in turn to specific location in the mouth. This might also include the presence of specific organic components in the plaque of salivary or bacterial origin as well as the bacteria themselves. Minor inorganic components are very variable. Silica, for example, may have an important role in dental calculus formation in particular10, and apatite is less well crystallised and more unstable as magnesium or carbonate content increases.11,12 Damen and ten Cate13 reported that silica can act as a heterogeneous nucleation substrate, which stabilises growing calcium phosphate nuclei reducing the time needed for the formation of nuclei of stable size. In support of this, Gaare et al.14 revealed that the rate of formation of dental calculus was influenced by silica contained in foods, especially rice. Dental calculus composition, especially with regard to minor components is very variable and few studies have been reported dealing with the site specific mineral composition in human dental calculus. This study therefore was undertaken to clarify the site specificity of composition and mineral characteristics of human dental supra-gingival dental calculus from two specific sites obtained from male patients visiting for dental check-up using fluorescent X-ray spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).
2.
Materials and method
2.1.
Preparation of samples
The study was agreed with the Ethical Committee in AichiGakuin University, School of Dentistry and after obtaining
169
informed consents, human dental calculus was obtained from individuals chosen at random attending clinics for a dental check-up. As the check-ups were undertaken 6 months after the last dental cleaning, the age of the calculus samples was assumed to be up to 6 months. Samples of supra-gingival human dental calculus were removed from 55 lingual surfaces of lower anterior teeth and 11 buccal surfaces of upper molar teeth in each of 66 male patients (46.4 1.2 (S.E.) years) aged from 22 to 64 years for regular dental check-up in Nagoya, Japan from 2000 to 2002. Sites of dental calculus deposition is more frequent in lower anterior teeth than in upper molar teeth.15 Therefore, the numbers of samples obtained from lower anterior teeth was larger than of upper molar teeth. The samples were removed with a standard dental scaler, washed thoroughly in ethanol, allowed to air-dry for several days at room temperature, and were subsequently powdered using an agate mortar.
2.2.
Elemental analysis
Ten mg each of the powdered samples were attached to platinum plates (99.5% Pt) using 6 mm polypropylene seat (Rigaku regent). The samples were then analysed by fluorescent X-ray spectroscopy (RIX3001, Rigaku, Tokyo, Japan). The analysing crystals used were PET (pentaerythriol), Ge, LiF. After evacuating the chamber by rotary pump, samples were excited by a Rh anode X-ray tube (30 kV and 100 mA). Relative contents of Si and Mg were determined using calibration curves prepared as follows. Since calculus consists of a mixture of phases, appropriate mixtures of SiO2 (Sigma– Aldrich, USA) and stoichiometric hydroxyapatite powder (to give 0, 0.01, 0.02, 0.05, 0.1, 0.5 wt% SiO2) were used as standards for a Si calibration curve. The hydroxyapatite powder was synthesised by a wet method using H3PO4 and Ca(OH)2 aqueous solutions.16 The precipitate was washed 3 times with distilled water and then dried at 100 8C for 16 h. The dry precipitate was heated to 800 8C and subsequently sintered at 900 8C to produce crystalline hydroxyapatite. The calcium phosphate phases present were identified as stoichiometric hydroxyapatite using XRD and FTIR. Appropriate mixtures of Mg3(PO4)28H2O (Wako Pure Chemical Industries, Ltd., Osaka, Japan) to give 0, 0.1, 0.2, 0.4, 2.0 wt% Mg3(PO4)2, and Ca3(PO4)2 (Katayama Chemical Industries Co., Ltd., Osaka, Japan) were used as standards for a Mg calibration curve.
2.3.
Classification of crystal phases
The crystal phases of the samples were determined using Xray diffractometry (XRD) (Rigaku, Rotaflex RAD-rX, Tokyo, Japan) and Fourier transform infrared spectroscopy (FTIR, Diamond 20, JEOL, Tokyo, Japan) as follows. After pulverizing the dried dental calculus, the powder diffraction patterns were recorded in the 2u range 3–408 at a rate of 0.1 degree 2u/min using copper radiation (40 kV and 120 mA) and a curved graphite monochromator. The diffraction peak around 4.78 in 2u was used as a marker for the presence of OCP because this diffraction can be assigned to the (0 1 0) reflection of OCP which was the strongest peak in the standard chart (JSPDS No.26-1056). The diffraction around 31.08 in 2u was used as a marker for the presence of b-TCP which was because this
170
archives of oral biology 53 (2008) 168–174
diffraction can be assigned to the (1 0 0) reflection of b-TCP which was the strongest peak in the standard chart (JSPDS No.9-169). The diffraction around 31.88 in 2u was used as a marker for the presence of apatite because this diffraction can be assigned to the (2 1 1) reflection of hydroxyapatite which was the strongest peak in the standard chart (JSPDS No.9-432). FTIR spectra were measured using a KBr pellet method. After grinding 100 mg of dry IR-grade KBr to a fine powder in an agate mortar, 2 mg of specimen was added. The specimen was ground with the KBr until a uniform powder was formed, then 30 mg was pressed into a pellet. The solid KBr pellet was immediately placed into a sample holder and its transmission spectrum recorded in the wavenumber range 400–2000 cm 1 by FTIR spectrophotometer.
2.4.
Determination of carbonate
The approximate carbonate contents of the samples were determined from the FTIR intensities of the CO32 vibration bands.17–19 Appropriate mixtures of calcium carbonate and stoichiometric hydroxyapatite powder (to give 0, 10, 20, 30, 40 wt% CaCO3) were used as standards for a calibration curve. While this does not completely reproduce carbonate locations in specific calcium phosphate phases, it would be sufficiently accurate to detect relatively large differences in carbonate concentration. The ratio of the absorption intensities of CO3 and PO4 was taken from 870 cm 1 and 595 cm 1 for CO32 and PO43 , respectively. The carbonate contents of the samples were measured by using the calibration curve.
2.5.
Determination of Ca:P ratio
The relative calcium and phosphorus contents of dental calculus were determined using fluorescent X-ray spectroscopy. The method of determination of Ca:P ratio is simple and non-destructive. The Ca:P ratios of these samples were examined by using a calibration curve obtained as follows. The calibration curve was formed by mixtures of stoichiometric hydroxyapatite (Ca:P ratio = 1.67) as described above. These calcium phosphate were octa calcium phosphate, OCP (Ca:P ratio = 1.33) chemically synthesised20 from a suspension of DCPD and CaCO3, alpha tricalcium phosphate a-TCP (Ca:P ratio = 1.5) (Katayama Chemical Industries Co., Ltd., Osaka, Japan) and TTCP (Ca4(PO4)O) (Ca:P ratio = 2.0) (Wako Pure Industries Co., Ltd., Osaka, Japan).
2.6.
percentages of crystallinity were obtained by physically admixing different portions of an amorphous calcium phosphate (Ca:P ratio = 1.5) and stoichiometric sintered hydroxyapatite in an agate mortar. The splitting function (SF) was determined by the ratio of the two areas of the phosphate ion antisymmetric bending mode around 600 and 580 cm 1 in the spectra for the standard specimens. A plot of splitting function values against the percentage of sintered hydroxyapatite in the mixture was used as a calibration line for analysis of crystallinity.
2.7.
Statistical analysis
The difference of the composition of crystal phase in the locations of dental calculus formation was investigated using x2 test. The difference in the contents of CO32 , Mg, Si and the Ca:P ratio among the four calcium phosphate phases were analysed by one-way ANOVA and Scheffe´ test, and between the locations of dental calculus formation by Student’s t-test. Crystallite size and the degree of crystallinity in the locations of dental calculus formation were analysed by Student’s t-test.
3.
Results
3.1.
The classification of the crystal phases
Fig. 1 shows a typical diffraction pattern for the samples used. X-ray diffraction peaks at 25.98, 31.88, 32.28, 32.98 and 34.08 due to AP were observed in all the specimens. X-ray diffraction peaks at 4.78, 24.38, 26.08, 28.08, 31.58, 33.58 and 34.48 due to OCP were observed in some specimens together with HA. X-ray diffraction peaks at 27.88, 31.08 and 34.48 due to TCP were observed in some specimens together with HA.
Crystallinity of the supra-gingival dental calculus
Crystallite size (d-value, nm) in the c-axis direction and degree of crystallinity (%) of the samples were used as indices of crystallinity for these samples. Crystallite size in the c-axis direction is deduced from the diffraction peaks of the (0 0 2) reflection.21,22 In this study in order to approximate crystallite size of c-axis of each sample, peak breadths at half height were determined from the (0 0 2) reflection (2u = 25.88) of the XRD pattern using the Debye-Scherrer equation. The percentage of crystallinity (that is the percentage by weight of calcium phosphates found in the crystalline form) of the samples was determined following the method of Termine and Posner, using FTIR.23 Standard samples exhibiting varying
Fig. 1 – X-ray diffraction patterns of Types I–IV of the supragingival dental calculus.
171
archives of oral biology 53 (2008) 168–174
Fig. 2 shows typical FTIR spectra of each type samples. The FTIR spectra of all samples showed the broad PO43 bands around 590 cm 1 and 1040 cm 1 which was not clearly split. It also showed that all the samples with the CO32 bands around 1430 cm 1 and 870 cm 1 were contained carbonate-apatite with low crystallinity. Using X-ray diffraction and FTIR calcium phosphate phases in supra-gingival dental calculus samples were classified into four types as follows. Figs. 1 and 2 show the typical XRD diffraction patterns and FTIR spectra of these four types of samples. Type I, 48 samples, only produced XRD diffraction peaks due to AP. Type II, 1 sample, produced XRD diffraction peaks and FTIR spectra derived from AP and OCP. Type III, 11 samples, produced XRD diffraction peaks and FTIR spectra derived from AP and TCP. Type IV 6 samples, produced XRD diffraction peaks and FTIR spectra derived from AP, TCP and OCP. Figs. 1 and 2 show the typical XRD diffraction patterns and FTIR spectra of these four types of samples. The supra-gingival dental calculus formed on the lingual surfaces of lower anterior teeth was classified as Types I, III and IV. The buccal surfaces of upper molars, however, showed all four types. Table 1 shows the proportions of each mineral type in the samples. Type I occurred in the largest number of samples, followed by Types III, IV and II in order. There was significant difference in the composition of crystal phases between the locations of dental calculus formation ( p < 0.01).
3.2.
Fig. 2 – FTIR spectra of Type I–IV of the supra-gingival dental calculus.
Chemical compositions and Ca:P ratio
Table 2 shows the contents of CO32 , Mg, Si and the Ca:P ratio of the calcium phosphate in calculus Types I–IV. The CO32 content of the samples formed on the lingual surfaces of lower anterior teeth ranged between 3.5 and 9.5 wt% while that which formed on the buccal surfaces of upper molar teeth was between 3.0 and 7.0 wt%, respectively. The CO32 content of the dental calculus formed on the lower anterior teeth was significantly higher than that on the upper molar teeth ( p < 0.05). The CO32 content of the Type I samples, apatite, was higher than that of Type III formed on the buccal surfaces of upper molar teeth ( p < 0.05). It was not surprising perhaps since OCP and TCP have a much reduced capacity for CO32 uptake compared with apatite, this was also true for Type IV samples although results were not significant. The Si content of the samples formed on the lingual surfaces of lower anterior teeth varied between 20 and 2500 ppm, while that which formed on the buccal surfaces of upper molar teeth was between 50 and 1000 ppm. There was no significant difference between lower and upper teeth. However, the Si content of the Type III samples formed on lower anterior teeth was higher than that of Type I ( p < 0.05).
The Mg content of the Type I samples formed on the lingual surfaces of lower anterior teeth was significantly lower than that of Type III at the same site ( p < 0.01) again not surprising in view of the presence of TCP. The Ca:P ratio of all samples ranged between 0.9 and 1.4. The Ca:P ratio of dental calculus was not difference in the location of calculus formation.
3.3.
Crystallinity
The crystallite size of c-axis of the samples formed on the lingual surfaces of lower anterior teeth was 72.7 3.9 nm and that of the samples formed on the buccal surfaces of upper molar teeth was 76.1 9.8 nm. There was no significant difference in crystallite size between the sites of dental calculus formation. The degree of crystallinity of Type I samples formed on the lingual surfaces of lower anterior teeth was 17.2 0.6% and the samples formed on the buccal surfaces of upper molar teeth was 23.5 3.5%. The degree of crystallinity in dental calculus formed on upper molar teeth was significantly greater than that of lower anterior teeth ( p < 0.01).
Table 1 – Numbers of supragingival calculus classified types of crystal phases Site of calculus formation Lingual surface of lower anterior tooth Buccal surfase of upper molar tooth
Total sample no.
Type I (Apatite)
Type II (AP + OCP)
Type III (AP + TCP)
55 11
44 (80%) 4 (36%)
0 1 (9%)
8 (15%) 3 (27%)
Type IV (AP + TCP + OCP) 3 (5%) 3 (27%)
172
archives of oral biology 53 (2008) 168–174
Table 2 – Chemical compositions of supra-gingival dental calculus classified under the four types
L: lower anterior tooth; U: upper molar tooth, mean W S.E. (*p < 0.05: compared L and U). Values with the same superscript letter are significantly different between types of samples. (a: p < 0.05; b: p < 0.01).
4.
Discussion
The present study concentrated on supra-gingival calculus since this is the material considered to facilitate bacterial colonisation.1 Supra-gingival dental calculus is routinely removed during dental scaling and will most likely reflect the immediate environment. Supra-gingival dental calculus usually shows a white, creamy yellow appearance. Most frequent sites are on the lingual surfaces of submandibular anterior teeth and the facialbuccal surfaces of maxillary first and second molars. In this study, the chemistry and structure of human dental calculus was investigated at two different sites in the mouth (lower anterior teeth versus upper molar teeth). There were actually some imbalances between the sample numbers of male and female. We, therefore, analysed the male data only for preventing the imbalance of samples between males and females.
4.1.
Classification by calcium phosphate phases present
LeGeros6 reported that human dental calculus can contain a range of Ca–P phases, e.g., AP, DCPD, OCP and TCP. It was reported6 that DCPD was most frequently associated with 3–5day-old dental calculus, while AP and TCP were present mostly in older dental calculus. OCP was observed in both young and old dental calculus.8 Each individual sample used in the current investigation weighed more than 10 mg, suggesting that these samples were relatively old dental calculus. This was supported by the fact that, DCPD, often regarded as a precursor mineral was not detected while TCP and AP were
identified. OCP was also detected although this too has been considered as a precursor to apatite.24 Type I mineral (AP) occurred in the largest number of samples, followed in order by Type III, Type IV and Type II.
4.2.
CO32S content
While an admixture of compounds is not ideal as a reference for carbonate determination by FTIR, it was felt that the fundamental modes of vibration y2 observed at around 870 cm 1 are common spectra with all carbonate compounds25 and would give reasonably quantitative data. In addition, with regard to the ‘‘anomalous’’CO32 y2 doublet at 869 and 879 cm 1 in spectra of biological apatite, this was not observed in calculus samples. Therefore, the band at around 870 cm 1 was considered as reasonable for determination of carbonate content. The most likely location for carbonate in dental calculus is by its inclusion in hydroxyapatite. The effect of which is to decrease both crystallinity and crystallite size.12,26 Solubility of apatite is also affected: for example, at 3 wt% CO32 the solubility of apatite was 3 times higher than that of carbonatefree stoichiometric hydroxyapatite.27 The average CO32 contents of enamel, dentine and bone were reported to be 3.0, 4.8 and 4.8 wt%, respectively.24 The CO32 contents of supra-gingival dental calculus in this study on the other hand varied from 3.0 to 9.5 wt%. CO32 content of human dental calculus was therefore higher in average than that of other biological apatites, e.g., enamel, dentin and bone. Carbonate also showed a site specific variation. Dental calculus, on the lingual surfaces of lower anterior teeth contained more carbonate than that formed on the buccal
archives of oral biology 53 (2008) 168–174
surfaces of upper molar teeth. This was most likely due to the CO32 content of human submandibular saliva since the submandibular ducts exit close to the anterior lower teeth. Submandibular saliva also contains 4.0 mmol/l carbonate compared with that of parotid saliva which is 1.1 0.1 mmol/l.28 This is also likely to be related to flow rate since salivary flow rate and carbonate concentrations are directly related.
4.3.
dental calculus will be a reflection of the relative proportions of different phases (DCPD, TCP, OCP) present as well as the phases themselves. The lower Ca:P ratio in Type I dental calculus probably reflects the nonstoichiometric, nature of the apatite, being calcium deficient, impure and carbonatecontaining.3 Biological apatites are, however, non-stoichiometric containing many substituents such as carbonate and magnesium as well as vacancies and defects which by altering charge balance can also affect Ca:P ratios.
Si content 4.6.
Rølla et al.29 reported that dental calculus formed for a 5month period contained an average of 132 ppm silicon, whereas even older dental calculus contained up to 2000 ppm. Si contents in this study varied from 20 to 2500 ppm on lingual surfaces of lower anterior teeth and from 50 to 1000 ppm on buccal surfaces of upper molar teeth. The values in this study were thus somewhat higher than the data reported by Rølla.29 This can suggested that Si variations were large and the dental calculus used in this study had formed over periods of more than 5-month. Consequently, Gaare et al.14 found that dental calculus formation rates were higher in Asian populations which might originate in a high rice diet which is staple diet, for example, for Japanese. This was supported by the fact that samples removed from Japanese subjects who have a high rice containing diet had high silicon in their calculi.14 Si content was significantly different between Types I and III in the samples formed on the lingual surfaces of lower anterior teeth ( p < 0.05). The rate of growth of seeded hydroxyapatite crystals was markedly enhanced in the presence of silicon, but the presence of silicon and fluoride indicate different mechanisms of promotion of the precipitation of calcium apatite.13 Furthermore, it was suggested that the access of diet fluids to the upper molar vestibule is poor. Therefore, the reasons for this are not clear but Si was physically taken in calculus, and may relate to the presence of TCP on the lingual surfaces of lower anterior teeth, possibly, with the presence of many other elements such as fluoride.
4.4.
Mg content
Magnesium has a considerable effect on the deposition of calcium phosphates depending principally the Mg:Ca ratio.30 As Mg content increases, apatites became less well crystallised and more unstable.11 b-TCP on the other hand contains more Mg and its formation may be promoted by high Mg.8 The result of this study suggested that Types III and IV dental calculus which contained b-TMCP was promoted by high Mg. From the results of this study, Mg content of dental calculus tended to be higher in upper teeth than lower teeth. This, like carbonate, may be influenced by saliva since the Mg contents of resting submandibular and parotid saliva are 0.07 0.03 and 0.16 0.07 mmol/l, respectively.31
4.5.
173
Ca:P ratio
The calcium:phosphorus ratios of supra-gingival dental calculus varied from 0.9 to 1.4 almost certainly due to the presence of non apatitic calcium phosphates. The Ca:P ratio of
Crystal properties: size and crystallinity
In this study, the crystal size along the c-axis was measured from the diffraction peaks of the (0 0 2) reflection20,21 It was not possible to get any accurate results from reflections other than the (0 0 2) reflection, as intensities of the highly broadened (hk0) reflections were too low. Crystallite size was, as might be expected, very variable but larger than biological apatites of bone, enamel or dentine. This is consistent with the growth of calculus crystals lacking a degree of biological control compared to the above natural apatites.32 There was no significant difference with the crystal size along c-axis between upper or lower tooth sites. Crystallinity, however, differed significantly between the two sites being higher in the supra-gingival dental calculus. The most likely reason for this would be the lower carbonate content in dental calculus from the upper tooth samples. There was no significant correlation between Si content and crystallite size or crystallinity of the samples. However, there was significant correlation between Si content and degree of crystallinity in the samples formed on the lingual surfaces of lower anterior teeth. The broad conclusions which can be drawn from this study are that location is the mouth is related to calcium phosphate phases, crystallite size and crystallinity.
references
1. Wilkins EM. Clinical practice of the dental hygienist. 9th ed. Philadelphia: Lippincott Williams & Wilkins; 2004. p. 304–13. 2. ten Cate JM. Research on dental calculus: why? In: ten Cate JM, editor. Recent advances in the study of dental calculus. Oxford: IRL Press; 1989. p. 1–4. 3. LeGeros RZ. Apatite in biological systems. Prog Crystal Growth Charact 1981;4:1–45. 4. Okumura H, Nakagaki H, Kato K, Ito F, Weatherell JA, Robinson C. Distribution of fluoride in human dental calculus. Caries Res 1993;27(4):271–6. 5. Huang S, Nakagaki H, Okumura H, Morita I, Strong M, Robinson C, et al. Fluoride distribution in human dental calculus obtained from different sites on the tooth surface. J Periodontal Res 1996;31(2):149–56. 6. LeGeros RZ. Calcium phosphates in oral biology and medicine. New York: Karger; 1991. p. 130–41. 7. Glock GE, Murray MM. Chemical investigation of salivary calculus. J Dent Res 1938;17:258–64. 8. Schroeder HE, Bambauer HU. Stages of calcium phosphate crystallization during calculus formation. Arch Oral Biol 1966;11:1–14. 9. Driessens FCM, Verbeeck RHM. Possible pathways of mineralization of dental plaque. In: ten Cate JM, editor.
174
10. 11.
12.
13.
14.
15.
16.
17.
18.
19. 20.
archives of oral biology 53 (2008) 168–174
Recent advances in the study of dental calculus. Oxford: IRL Press; 1989. p. 7–17. Damen JJM, ten Cate JM. The effect of siclic acid on calcium phosphate precipitation. J Dent Res 1989;68:1355–9. Okazaki M, Takahashi J, Kimura H. Unstable behavior of magnesium-containing hydroxyapatite. Caries Res 1986;20:324–31. Okazaki M, Moriwaki Y, Aoba T, Doi Y, Takahashi J. Solubility behavior of CO3 apatites in relation to crysrallinity. Caries Res 1981;15:477–83. Damen JJM, ten Cate JM. Calcium phosphate precipitation is promoted by silicon. In: ten Cate JM, editor. Recent advances in the study of dental calculus. Oxford: IRL Press; 1989. p. 105–14. Gaare D, Rølla G, van der Ouderaa F. Comparison of the rate of formation of supra-gingival calculus in Asian and a European population. In: ten Cate JM, editor. Recent advances in the study of dental calculus. Oxford: IRL Press; 1989. p. 115–22. Schroeder HE. Investigations on supragingival calculus, Formation and inhibition of dental calculus. Stuttgart Vienna: Hans Huber Publishers Berne; 1969. p. 65–162. Ban S, Hasegawa J, Maruno S. Fabrication and properties of functionally gradient bioactive composite comprising hydroxyapatite containing glass coated Titanium. Mater Sci Forum vols 1999;308–311:350–5. Wiberley SE. Quantitative infrared analysis of solids in potassium bromide using an internal standard. Anal Chem 1957;29(2):210–3. Bradley KB, Potts WJ. The internally standardized nujol mull as a method of quantitative inflared spectroscopy. Appl Spectrosc 1958;3:77–80. LeGeros RZ, LeGeros JP. Carbonate analyses of synthetic, mineral and biological apatites. J Dent Res 1983;62:259. Ban S. Synthesis of octacalcium phosphates by reactions of dicalcium phosphate dehydrate and calcium carbonate. Phosphorus Res Bull 1991;1:155–60.
21. Carlstrom D. X-ray crystallographic studies on apatites and calcified tissue. Acta Radiol 1955;suppl:121. 22. Glas JE, Omnell KA. Studies on the ultrastructure of dental enamel. I. Size and shape of the apatite crystallites as deduced from X-ray diffraction data. J Ultrastruct Res 1960;3:334–46. 23. Termine JD, Posner AS. Infra-red determination of the percentage of crystallinity in apatitic calcium phosphates. Nature 1966;211:268–70. 24. Elliott JC. Structure and chemistry of the apatites and other calcium orthophosphates. London: Elsevier; 1994. p. 259– 63. 25. LeGeros RZ, LeGeros JP, Trautz OR, Klein E. Spectral properties of carbonate in carbonate-containing apatites. Dev Appl Spec 1970;7B:3–12. 26. LeGeros RZ, Trautz OR, LeGeros JP, Klein E. Carbonate substitution in the apatite structure. Bulletin de la socie´te´ chimoque de France 1968;1:1712–8. 27. Grøn P, Spinell M, Trautz O, Brudevold F. The effect of carbonete on the solubility of hydroxyapatite. Arch Oral Biol 1963;8:251–63. 28. Swift P. A method for the trace elemental analysis of dental tissues. Br Dent J 1967;123:326–7. 29. Rølla G, Gaare D, Langmyhr FJ, Helgeland K. Silicon in calculus and its potential role in calculus formation. In: ten Cate JM, editor. Recent advances in the study of dental calculus. Oxford: IRL Press; 1989. p. 97–103. 30. LeGeros RZ. Calcium phosphates in oral biology and medicine. New York: Karger; 1991. p. 52–59. 31. Tenovuo JO. Human saliva: clinical chemistry and microbiology. Tokyo: Issei Publising Co.; 1998. p. 64. 32. Smith LH. Abnormal Mineralization. In: Nancollas GH, editor. Biological mineralization and demineralization. Berlin, Heidelberg, New York: Springer-Verlag; 1982. p. 259– 70.
