Autogenous fresh demineralized tooth graft prepared at chairside for dental implant

Although autogenous bone is considered the gold standard among graft materials, donor site morbidity may be an associated problem. Allogenic, xenogenic, and alloplastic graft materials have been used as alternatives, but they have a number of drawbacks compared with autologous grafts, such as decreased function, the potential risk of infectious disease, an unsatisfactory resorption pattern, a prolonged healing time, and high cost [1]. An ideal bone graft material should stabilize the blood clot; provide a biomechanical scaffold for cell migration, proliferation, and differentiation; contain functional proteins and peptides, such as growth factors; and exhibit appropriate resorption and remodeling during new bone formation. Materials based on collagen, particularly type I collagen, have attracted attention because of their ability to improve the cellular responses of osteogenic lineages, thus ensuring better bone regeneration [2]. However, the mineral component providing the biomechanical backbone remains an important factor for cell differentiation, nidus of calcification, and space maintenance during new bone formation [3]. Considering the hierarchical structure of bone, a mineralized collagen matrix with functional proteins and proper fibrillar arrays for biomechanics may be suitable as a natural bio-inspired graft material in bone tissue engineering [4].

The tooth is increasingly attracting attention as a material for alveolar bone regeneration. It is composed of an organic matrix and an inorganic reinforcing phase of hydroxyapatite. Radial arrays of dense type I collagen fibrils, which account for 90% of the organic matrix, and noncollagenous acidic proteins play an important role in calcification [5]. The chemical composition of dentin is very similar to that of bone. The inorganic content is 70%–75%, organic content 20%, and water content 10%. In alveolar bone, these components are present in proportions of 65%, 25%, and 10%, respectively [6]. However, tooth has much lower fat content and no marrow compared to bone, which make it easier to be changed into graft material [7]. A raw tooth cannot easily induce new bone formation because of its high mineral content, high crystallinity, and low porosity, which may interfere with migration, attachment, and proliferation of vascular and mesenchymal cells. The osteogenic capacity of a demineralized tooth was verified as early as 1967 [8], and it has been generally accepted that autogenous and allogenic demineralized teeth are osteoinductive or osteoconductive graft materials [9].

Commercial materials based on demineralized teeth have recently been used in human trials [1]. However, several shortcomings limit the popularity of these materials, including a long preparation time, limited productivity for commercial preparation, a consequent increase in cost, and dehydration that decreases the commercial shelf life. Some efforts to decrease the demineralization time did not satisfy the requirements for the simplicity of these materials and easy availability of different graft forms (block, chips, and powder) in the clinic [10].

This prospective study aimed to evaluate the clinical usefulness of autogenous fresh demineralized tooth (auto-FDT) graft prepared at the chairside immediately after extraction and used as a bone graft material for dental implant placement and to assess the potential of this material as an alternative for autologous bone and other graft materials.

According to search of the Pubmed database, the first use of demineralized dentin for bone regeneration in humans dates back to 1975; in that case, an allogenic source was used [11], whereas an autogenous source was first used only in 2003 [12]. The present study is likely to be the first human trial of auto-FDT prepared at the chairside and implanted on the day of extraction. Placement of a tooth into an alveolar socket after treatment is called “tooth replantation” or “tooth transplantation”. Auto-FDT grafting for alveolar bone regeneration can be referred to as a “tooth osteoplantation”. Demineralization is a crucial step in tooth grafting. Although a nondemineralized form of tooth powder showed good results [13], demineralization of bone and teeth increases the bioavailability of matrix-associated noncollagenous proteins such as osteocalcin, osteonectin, bone sialoprotein, phosphophoryn, and bone morphogenetic protein; these may enhance new bone formation [14-16]. Considering the higher mineralization and crystallinity of the tooth compared with those of bone, a decrease in mineral components and crystallinity may be more important for tooth-based graft materials [17]. Tooth demineralization is time consuming (usually 2–6 days), thus limiting the use of FDT as a graft material. Nevertheless, FDT has shown great potential in alveolar bone regeneration [18,19]. Another drawback of demineralization is that prolonged acid exposure may negatively affect noncollagenous proteins involved in new bone formation [20]. Murata et al. reported a device and method to decrease the demineralization time for tooth graft material, but this method only provides the powder type and uses an organic acid, which is not recommended for processing. In addition, these authors did not describe a specific final sterilization method for the graft material [10].

To overcome these limitations, we adopted a modified ultrasonic technology. The preliminary tests revealed that a regular ultrasonic cleaner does not dramatically decrease the processing time because the tooth is comprised of numerous microsized dentinal tubules surrounded by peritubular dentin, which is more sclerotic than intertubular dentin [21]. Periodic negative pressure can eliminate ultrasonic pocketing and the implosion loss of cavitation, which decrease the efficacy of ultrasound, and allows deep penetration of the cavitation energy and reagents into the dentinal tubules [22,23]. A thermoelectric cooler prevents the temperature increase caused by strong ultrasonic power and maintains the temperature under 40°C. These advances facilitate quicker demineralization and prevent thermal damage to the tooth proteins. The short duration of the entire process enables grafting on the same day of extraction and also increases the clinical availability of auto-FDT, because the block form of the graft can be trimmed or easily converted into chips or powder depending on the condition of the bone defect during surgery.

Implant stability was confirmed by a radio frequency device and histological examination in this study. The ISQ of all implants was satisfactory for final prosthesis placement. Histological examination revealed appositional bone growth around the auto-FDT graft, and its resorption implies that the demineralized tooth was osteoconductive with a remodeling characteristic. The interesting histological features observed in this study included the appearance of fusion-like integration between two matries of the graft and new bone at the interface with an undistinguishable border and new bone formation in the auto-FDT graft (Figure 3). This implies that dentinal tubules provide niches for cells involved in osteogenesis. Possible reasons for the good results in this study include the high biocompatibility of autogenous tissue, its collagen-based porous structure that is beneficial for cell function, minimal changes in the structure of mineralized collagen without dehydration (freeze drying), and rehydration procedures and preservation of beneficial noncollagenous proteins involved in mineralization. This study strongly supports the view that auto-FDT grafts provide a useful biological scaffold comprising three-dimensional macro- and microarchitecture with osteopromotive osteoconduction suitable for new bone formation [24].

The use of auto-FDT prepared at the chairside as bone graft material on the day of tooth extraction can be convenient for both patients and clinicians. Within the limitations of this study, the results indicate that auto-FDT graft prepared within 2 h of extraction can effectively restore alveolar bone defects in humans. We conclude that the availability of auto-FDT graft would have a strong positive effect on the clinical use of the tooth as a bone graft material in implant surgery. Further studies should be performed to confirm the osteogenic effects and biological safety of this tooth-based graft material.