Fourteen days after orthodontic appliances were removed, levels of a bone-forming enzyme in the group of rabbits receiving a special combination injection reached a peak of 0.789 ± 0.039 U/mg, far exceeding those of the untreated control group. The number may seem small on paper, but its significance is substantial: the bone surrounding the recently moved teeth was actively rebuilding itself rather than reverting to its original state.
This was the central finding of a study published in AIP Conference Proceedings (2018) by a research team from the Faculty of Dentistry, Universitas Gadjah Mada. The study was initiated by Ananto Ali Alhasyimi together with Prof. Dr. drg. Pinandi Sri Pudyani, SU., Sp.Ort(K), from the Department of Orthodontics; Widya Asmara from the Faculty of Veterinary Medicine; and Ika Dewi Ana from the Department of Biomedical Sciences, Faculty of Dentistry, Universitas Gadjah Mada.
The Old Enemy of Orthodontic Patients
Orthodontic relapse is more than an aesthetic disappointment. It is a longstanding clinical challenge in orthodontic practice. Teeth that have been painstakingly moved over two to three years can gradually shift back towards their original positions—even without the patient realising it—because of incomplete remodelling of the alveolar bone.
The biological key lies in an enzyme called alkaline phosphatase (ALP). This enzyme is a marker of osteoblast activity—the activity of cells responsible for forming new bone. The higher the ALP level in gingival crevicular fluid (the fluid occupying the space between the gums and teeth), the more active the bone formation process. The problem is that on the compression side of a recently moved tooth, ALP levels tend to decline after the orthodontic appliance is removed—and this is where relapse can occur.
The question that followed was: could ALP levels be artificially stimulated in a safe and controlled manner?
Two Weapons Combined
The UGM research team proposed an answer through a combination of two materials: carbonated hydroxyapatite (CHA) in hydrogel form and advanced platelet-rich fibrin (aPRF).
CHA is not an unfamiliar material in dentistry. Its structure resembles the inorganic component of cancellous bone, with an interconnected porous structure capable of gradually releasing calcium and phosphate ions—the primary building blocks for new bone formation. In this study, CHA functioned not only as a bone scaffold but also as a controlled drug delivery system.
aPRF itself is a newer generation of platelet concentrate. It was prepared from the experimental rabbits' own blood—making it autologous—and centrifuged at a lower speed and for a longer duration than standard methods, producing a platelet concentration 4.78 times higher than that of whole blood. It contains several growth factors, including VEGF, PDGF, IGF, EGF, and TGF—a biological cocktail that promotes osteogenesis, angiogenesis, and tissue healing.
The concept was simple yet clever: allow CHA to act as a “vehicle” that carries aPRF to the appropriate location, releases it gradually, and maintains its effects longer than a conventional injection can.
“CHA hydrogel incorporating aPRF is expected to retain growth factors until they reach the target area, gradually degrade, and release growth factors in a controlled manner to prevent relapse.” — Alhasyimi et al., AIP Conference Proceedings, 2018
Evidence from the Gingival Sulcus
The study involved 45 male New Zealand rabbits divided into three groups: an untreated control group, a CHA-only group, and a CHA-aPRF group. The lower incisors of each rabbit were moved distally for one week using a nickel-titanium open-coil spring and then retained for two weeks. During the retention period, intrasulcular injections were administered every seven days.
Gingival crevicular fluid was collected using sterile paper points inserted 1 mm into the gingival sulcus. ALP levels were then measured using a UV-Vis spectrophotometer at a wavelength of 405 nm. Measurements were taken on days 0, 3, 7, 14, and 21 after removal of the orthodontic appliance.
The results were consistent and statistically significant. The CHA-aPRF group showed a significant increase in ALP levels on days 7 and 14 compared with both the control group and the CHA-only group. The peak occurred on day 14—a time that biologically coincides with the final phase of tooth movement, when tissue hyalinisation occurs and osteoclast activity on the compression side begins to decline.
The mechanism underlying these findings involves VEGF contained in aPRF. This growth factor is known to induce osteocyte differentiation and migration while directly increasing ALP activity. CHA, meanwhile, contributes by increasing the local concentrations of calcium and phosphate ions, thereby promoting bone conduction and induction.
From Rabbit Cages to the Dental Chair
Naturally, there remains a substantial gap between an animal model and clinical practice. The researchers themselves emphasised the need for further molecular and cellular studies, including additional parameters such as RANKL, OPG, and type I collagen, to confirm the long-term effectiveness of CHA-aPRF.
Nevertheless, the direction indicated by this study is promising. At present, prevention of orthodontic relapse relies heavily on retainers—devices whose success depends greatly on patient compliance. If biomaterial-based therapy such as CHA-aPRF proves effective in humans, it could become a complementary intervention that works from within: strengthening the bone rather than merely holding the teeth in place from the outside.
Ultimately, teeth that have moved to a new position may need more than braces to stay comfortably where they belong.
Source DOI: https://doi.org/10.1063/1.5023953
Authors: Nanda Ayu; drg. Achmad Zam Zam Aghasy, M.Kes.
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