J Periodontol • September 2000 Morphology and Elemental Composition of Subgingival Calculus in Two Ethnic Groups Elizabeth A. Roberts-Harry,* Valerie Clerehugh,* Roger C. Shore, † Jennifer Kirkham, † and Colin Robinson † 1401 Background: The aim of the present study was to compare the morphology and elemental composition of subgingival cal- culus between Indo-Pakistani and Caucasian patient groups. Methods: Extracted teeth from 14 Indo-Pakistani and 19 Cau- casian subjects were collected. Of these, 12 Indo-Pakistani and 10 Caucasian teeth had sufficient subgingival calculus for analy- sis. Subgingival calculus present on the 22 teeth was classified into six morphological types: 1) crusty/spiny/nodular; 2) ledge/ ring; 3) thin, smooth veneers; 4) finger/fern-like; 5) individual islands/spots; or 6) supramarginal on submarginal. Subgingival calculus was zoned: coronal, mid, and apical. A sample obtained from each zone was subdivided to allow 3 separate analyses: transmission electron microscopic (TEM) x-ray microanalysis for elemental composition, fluoride analysis, and carbonate analysis. Results: Crusty/spiny/nodular, ledge/ring, and thin, smooth veneers were more commonly found in the Indo-Pakistani group; individual islands were more prevalent in the Caucasian subjects. Supramarginal on submarginal calculus was found only in the Indo-Pakistani group. No finger/fern-like deposits were found. No differences within or between the two ethnic groups were found with regard to calcium:phosphate ratios, fluoride, or carbonate content. However, the Indo-Pakistani group showed significantly lower levels of sodium in apical samples than in coronal sam- ples (ANOVA, F 1,16 = 5.98, P = 0.03), and significantly lower levels of sodium (ANOVA, F 1,12 = 4.75, P = 0.05) and magne- sium (ANOVA, F 1,12 = 5.16, P = 0.04) in apical samples than in those from Caucasians. After adjusting for smoking, the magnesium results remained significant (ANOVA, F 2,11 = 4.64, P = 0.05). Conclusions: Subgingival calculus demonstrated differences in morphology between these two ethnic groups and differences in elemental composition, which may influence its overall solu- bility and contribute to its greater accretion in the Indo-Pakistani subjects. J Periodontol 2000;71:1401-1411. KEY WORDS Comparison studies; dental calculus/chemistry; ethnic groups; dental calculus/physiology; dental calculus/ ethnology. * Department of Periodontology, Leeds Dental Institute, Leeds, UK. † Department of Oral Biology. S ubgingival calculus has been researched less than supragingival calculus, 1-4 yet moreso than sup- ragingival calculus, it has been associ- ated with periodontal destruction and breakdown. 5-8 Early research papers tended to report on dental calculus as a whole rather than differentiate between supragingival and subgingival types. As the role of plaque and the mineralization process in the formation of dental cal- culus became better understood, it became clear that the origins of the inor- ganic constituents of supragingival and subgingival calculus differed. The min- eral ions of supragingival calculus appeared to derive from salivary con- stituents, while those of subgingival cal- culus appeared to come from the serum transudate that is present when a peri- odontal pocket occurs. In addition, dif- ferent morphological types of subgingi- val calculus have been identified. 9 There is also growing evidence for racial dif- ferences in the formation of dental cal- culus, with some populations apparently suffering to a greater degree than others in respect to high levels of supragingival and subgingival calculus accretions and associated periodontal breakdown. 10-15 Why these differences occur is not clear, but it is possible that the nature of the calculus itself in terms of its composi- tion and structure may have a significant role. The aims of this study were therefore to 1) compare the morphology and ele- mental composition of subgingival cal- culus at different locations on the root