Fluoride uptake by hydroxyapatite formed by the hydrolysis of ?-tricalcium phosphate

Abstract

Although there is interest in forming synthetic analogs of hard tissues at physiologic temperature, significant gaps in knowledge exist with respect to the mechanisms by which precursor solids convert to apatites and also with respect to the apatite compositions that may be formed. In this study calcium-deficient HAp [Ca9(HPO4)(PO4)5OH] was prepared by hydrolysis of tricalcium phosphate (TCP), alpha-Ca3(PO4)2. The kinetics of HAp formation were studied as a function of temperature by isothermal calorimetry. TCP hydrolyzed completely within about 12 h, and the hydrolysis reaction evolved 133 kJ/mol of HAp formed. Although the kinetics of hydrolysis exhibited a strong temperature dependence, the mechanistic path taken appeared independent of temperature. The fluoridation of hydroxyapatite compositions having Ca/P ratios higher than 1.59 previously has been investigated. However, little work has been done on the fluoridation of more calcium-deficient hydroxyapatite. Ca9(HPO4)(PO4)5OH was formed at temperatures between 37.4 degrees and 55 degrees C to vary its morphology. These preparations then were reacted in NaF solution and the kinetics of fluoride incorporation studied. Solution chemical analyses were used to determine the amounts of fluoride incorporated. The extent of hydroxyl replacement by fluoride ranged from 17 to 72% and correlated with the surface area of the parent HAp.

Low temperature formation of calcium-deficient hydroxyapatite-PLA/PLGA composites

“…The corresponding extent of CDHAp formation in the precomposites was calculated using an enthalpy of reaction of 133 kJ/mol for the hydrolysis of phase pure TCP. 37 XRD data given in Figure 2 also show incomplete reaction for the composites prepared with PLA(1) and PLA (2). The XRD pattern of the composite containing the higher mo- lecular weight PLA indicates CDHAp with greater crystallinity.…”

“…The formation of HAp by a cement-type reaction of calcium phosphate precursors affords the possibility of a synthetic hard tissue developing its properties in vivo. 36,37 In particular, the hydrolysis reaction of particulate ␣-TCP (hereafter referred as TCP) results in the formation of hardened HAp monoliths. 38,39 This is critical if HAp is to be formed in vivo using TCP as a precursor.…”

“…The horizontal line at 133 kJ/mol represents the enthalpy of reaction for ␣-TCP → CDHAp as reported previously 37. …”

Clinical Effect of a Fluoride Varnish Including Tri-Calcium Phosphate on Relieving Dentin Sensitivity

“…22,23 Flor serbestlemesinin geleneksel flor verniklerine göre daha fazla olduğu bildirilen formülasyonda bu etkinin, koruyucu bariyerle kaplı kalsiyum bileşiğinin tükürükle aktivasyonu sonucunda florla birlikte ortama salınmasından kaynaklandığı ileri sürülmektedir. 19 Materyalin erken beyaz nokta lezyonlarının tamirini sağlayan bu koruyucu etkisinin yanı sıra dentin hassasiyetini de azalttığı bildirilmektedir. Yüzeyde bulunan yüksek derecede mineralize ve asit-rezistan koruyucu tabaka aynı zamanda açığa çıkmış dentin tü-büllerine penetre olup, örterek tübüler blokaj sağlar ki bu sayede dentin hassasiyeti azalır.…”

“…Bu multimineral kompleksin etken ajanlarından biri olan trikalsiyum fosfat (a-TCP veya Ca 3 (PO 4 ) 2 ) kalsiyum hidroksiapatit formasyonu için kullanılan yegâne hızlı hidrolize olabilen katı kalsiyum fosfattır. 19 Sodyum, flor iyonu varlığında fonksiyonalize trikalsiyum fosfata (f-TCP) dönüşüp minenin flor alımını arttırır. 20,21 Materyalin aynı zamanda diş yüzeyine ve diş aralarına akabilme özelliğinin olduğu, uygulandığı yere yapışıp uzun süre kaldığı ve 24 saate uzayan sürekli kalsiyum ve flor serbestlemesi gerçekleşti-rebildiği iddia edilmektedir.…”