Ask a formulator what fraction of a toothpaste can be hydroxyapatite and the reflex answer traces back to one number: the ~10% used in remineralisation trials and blessed by the EU’s safety opinion for nano grades. A team at Hasanuddin University in Makassar asked a different question: what if the mineral is not an additive on top of the formula, but the abrasive base itself?
How much hydroxyapatite can a formula carry?
Their material came from an unglamorous local source — bones of Sardinella fimbriata, a fish processed at scale in Indonesia. The characterisation was respectable for a biogenic powder: the bone ash ran to 60.25% calcium oxide with 39.66% phosphorus pentoxide by XRF, and “the XRD of the natural fish bone hydroxyapatite compound has a crystallinity of 82.9%.”
Then the formulation step, and the interesting move: “F1, F2, and F3 contained 30, 40, and 50 parts of hydroxyapatite, respectively, replacing an equivalent amount of the standard abrasive (calcium carbonate).” Not a 2% actives sprinkle — the mineral as the body of the paste. The formulations passed their physical tests, and the conclusion was direct: the fish-bone hydroxyapatite “can be incorporated into toothpaste formulated with F3, which includes a 50% hydroxyapatite concentration.”
Did anyone want to brush with it?
That was the sharper result. In the sensory evaluation, “the average hedonic test liked each toothpaste formula, but the F3 formula was preferred in color, aroma, taste, and texture.” The highest mineral loading won on all four counts. Whatever intuition says a chalky biogenic powder ruins mouthfeel at high doses, ten Indonesian panellists disagreed.
The abrasive framing also changes what “quality” means. An active at 2% is judged on biology; an abrasive at 40 or 50% is judged on hardness, particle-size distribution, and how it wears both stains and enamel — properties this study leaves for the dentifrice standards to police. That checklist is what any buyer would run before moving a biogenic powder from the actives column to the base column. What the Makassar data establishes is narrower and still useful: nothing about consumer acceptance forbids trying.
The honest limits: ten panellists is a pilot, not a market study; the paper measured no remineralisation or caries endpoint; and one calcination temperature was tested — the authors themselves call for comparative work. And this is micron-scale fish-bone material replacing an abrasive, a different regulatory question from nano grades with biological claims.
What does this change for a buyer?
The ceiling assumption. If biogenic hydroxyapatite can serve as half the formula — as the abrasive system, at commodity loading — then the relevant comparison is not hydroxyapatite versus other actives at 5%, but hydroxyapatite versus calcium carbonate at 40%, where the volumes and the price sensitivity are entirely different. That reframing favours exactly the routes this blog keeps returning to: eggshell and other biogenic feedstocks, whose economics work at bulk, and whose consistency question — which lot, which feedstock, which firing — becomes the commercial question the moment the loading multiplies by ten.
At 2% an inconsistent powder is a variance. At 50% it is the product.
Sources
Anwar AI, Ruslin M, Marlina E, et al. “Physicochemical analysis and application of sardinella fimbriata-derived hydroxyapatite in toothpaste formulations.” BMC Oral Health, 2025;25 (open access) — pmc.ncbi.nlm.nih.gov/articles/PMC11806528.