Clinical and Histological Analysis of Sinus Floor Elevation and Alveolar Bone Augmentation Using an Interconnected Superporous Hydroxyapatite With Beta-Tricalcium Phosphates: Preliminary Results

The placement of dental implants in highly atrophic alveolar bone continues to be a major challenge in implant dentistry. Sinus floor elevation and guided bone regeneration (GBR) involves augmenting the bone with grafting materials to provide adequate support for implants. From the various materials available for the bone augmentation, autogenous bone is considered the gold standard because of its high osteoconductive, osteoinductive, and osteogenic potential. However, the collection of autogenous bone requires an extra surgical site for bone harvesting, which increases the risks of morbidity and discomfort. To avoid these problems, various bone substitute materials have been used in GBR, including freeze-dried bone allografts, xenografts, and synthetic ceramics such as hydroxyapatite (HA) or beta-tricalcium phosphates (bTCP). Among them, inorganic bovine bone has been widely used and recommended for bone augmentation purposes¹⁾. Recently, a novel superporous HA was approved for dental use in Japan. A highly porous HA with three-dimensionally interconnected pores is expected that bone ingrowth is deeper and fast into the material than conventional HA. Although highly porous, the HA material itself is very slow resorption during the remodeling process²⁾. On the other hand, bTCP provides a resorbable interlocking network to implant within a bone defect and promote healing. In this clinical case report, to evaluate new bone formation after sinus floor elevation and alveolar bone augmentation using an interconnected superporous HA with bTCP by means of clinical and histological examination of human biopsies.

An interconnected superporous HA (Apaceram-AX, Japan) has 85% porosity and contains macropores more than 100 μm in diameter that are spherical and interconnected. In addition, it has micropores ranging from several hundred nanometers to several micrometers in diameter that create a rough surface on the macropores²⁾. A composite of 90% HA granules and 10% bTCP (Cerasorb, Germany) granules were placed on the augmented region and covered by means of an e-PTFE membrane (Cytoplast, USA) for GBR. Implant placements were used simultaneously or 2-staged (5 months after the augmentation) approach. The membrane was removed after 6 weeks. The specimens obtained after 5 months were analyzed histologically and histomorphometrically with special focus on bone remodeling within the residual bone and the augmented region. Quantitative and qualitative bone assessment of augmented bone was analyzed using cone-beam computed tomography (CBCT). All patients gave written informed consent before surgery, in accordance with the principles of the Declaration of Helsinki.

This case study revealed that newly formed bone with the vascularization which covered over the implant was already observed at the point of membrane removal. CBCT image showed that the calcified area of the augmented region with the composite bone substitutes gradually increased from the residual bone with time. Histological sections revealed that the newly formed bone with bone marrow was observed around Apaceram-AX granules. Furthermore, the pores seem to be fusing suggesting mild resorption of the material and slow degradation of its structure. However, Cerasorb was almost degraded and replaced new bone at the augmented region.

The results also showed that bTCP granules promoted bone remodeling in the early period, and the interconnected superporous hydroxyapatite granules provided continuous natural bone remodeling.  It can be used with success as a bone substitute composite in the bone augmentation to provide adequate support for implants.

References

1) Clin Oral Implants Res 2008; 19:19-25

2) Arch Orthop Trauma Surg 2012;132:1603-1610.