Electron microscopy of octacalcium phosphate in the dental calculus

Abstract

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.

Calcium orthophosphates (CaPO 4 ): Occurrence and properties

“…OCP is of a great biological importance because it is one of the stable components of human dental and urinary calculi (Chow and Eanes 2001;Kakei et al 2009). OCP was first proposed by W. E. Brown to participate as the initial phase in enamel mineral formation and bone formation through subsequent precipitation and stepwise hydrolysis of OCP (Brown 1962(Brown , 1966Brown et al 1962).…”

“…According to the data available (Poloni and Ward 2014), the unwanted depositions could consist of many substances and all of them always lead to various diseases. Regarding the unwanted depositions of CaPO 4 , they are found in soft tissue calcification (in damaged joints, blood vessels, dysfunctional areas in the brain, diseased organs, scleroderma, prostate stones) (Reid and Andersen 1993;Scotchford and Ali 1995;P'ng et al 2008;Brancaccio and Cozzolino 2005;Goff and Reichard 2006;Bittmann et al 2003;Molloy and McCarthy 2006;Giachelli 2004;Kazama et al 2007), kidney (Giannossi and Summa 2012;Mukherjee 2014) and urinary (Zhu et al 2014;Huo et al 2015;Selvaraju et al 2015) stones, dental pulp stones and dental calculus (Kakei et al 2009;Kodaka et al 1988Kodaka et al , 1998Ç iftçioglu et al 1998;Hayashizaki et al 2008), salivary stones (Zelentsov et al 2001;Luers et al 2014), gall stones (Qiao et al 2013;Hussain and AlJashamy 2013), pineal gland calcifications (Güney et al 2013), atherosclerotic arteries and veins (Ortlepp et al 2004;Tomazic 2001;Marra et al 2006;Kurabayashi 2013), coronary calcification (Fitzpatrick et al 2003;Matsui et al 2015), damaged cardiac valves (Suvorova and Buffat 2005), calcification on artificial heart valves (Giachelli 2001; Pettenazzo et al 2001;...…”

Ultrastructure of Apatite Crystals Formed During Vascular Calcification in Humans

“…However, the development of both these types of crystals is not common in bone or in other normal calcified hard tissues. Given the assumption that either crystals with or without CDLs should be present, the difference in the ultrastructure of these 2 crystal types may indicate that a different mechanism is at work for the formation of apatite crystals 28,32) . In the case of dental calculus, we morphologically demonstrated that octacalcium phosphate (OCP) is involved in the formation of crystals without CDLs 32) .…”

“…Given the assumption that either crystals with or without CDLs should be present, the difference in the ultrastructure of these 2 crystal types may indicate that a different mechanism is at work for the formation of apatite crystals 28,32) . In the case of dental calculus, we morphologically demonstrated that octacalcium phosphate (OCP) is involved in the formation of crystals without CDLs 32) . Similarly, the appearance of crystals without CDLs may indicate the involvement of OCP in ectopic calcification, as has been pointed out by many researchers [33][34][35][36] .…”

“…Furthermore, with regard to the process of crystal formation, we observed that unusual calcification occurred in dental calculus, but by a very different process. In addition, we found that dental calculus was composed of crystals of various sizes both with and without CDLs 31,32) .…”