Endoosseous oral implantation has proven to be a successful approach for dental rehabilitation. This procedure often requires alveolar bone reconstruction in the maxillary and mandibular regions. Of the various procedures used for alveolar bone augmentation, guided bone regeneration (GBR) using autogenous bone, is well documented1-4).

Various graft materials has been used during the GBR procedure. Recently, various growth factors and cytokines have been studied to use for accelerating regeneration5-7). However, Autogenous bone is still considered as the gold standard during the GBR procedure due to its high biocompatibility and healing potential8,9). Autogenous bone in particulate form could be collected using hand chisels, burs, or bone collectors. Several studies showed bone debris obtained from implant drilling sites could be effective for covering exposed implant threads10-13).

The quality of bone debris could be influenced by the drilling conditions, such as, the drilling speed, the drilling time, the drill configuration (pressure, diameter, blade positioning, and angulation) and the coolant delivery system. Particle size of autogenous bone could influence on the induction of vital osteoblasts12). Zaner and Yukna14) concluded that a particle size between 300 µm and 500 µm is appropriate for periodontal surgery. Although bone debris obtained from implant drilling was used in many studies, little is known about the relationship between drilling speed and bone debris particle size during implant surgery. The aim of the study is to evaluate the effect of implant drilling speed on the composition of particle size of collected bone debris in an in vitro bovine model.

Sufficient width and depth of alveolar ridge are important in implant placement. Sometimes, implant fixtures were not completely covered by bony architecture. In cases only small size of dehiscence is found, a localized autogenous bone graft using implant drilling debris is recommended rather than performing major surgery using autogenous bone from the mandibular ramus or chin11-13).

When bone debris is collected for this purpose, every possible factor should be considered to achieve appropriate graft material. Several recent studies have focused on the risk of osseous damage at elevated drilling speeds during implant surgery16-18). Also, the possibilities of bone necrosis of drilling debris by mechanical manipulation, pressure, and temperature have been investigated19). A drilling speed of less than 2000 rpm with an irrigation system was not found to generate excessive heat during drilling20,21). Furthermore, Reingewirtz et al.22) recommended the use of less than 800 rpm in dense bone to prevent overheating. Anitua et al.23) suggested that drilling at a speed of only 50 rpm could reduce damage to the host tissue and obtain a mass of living bone.

Based on above evidence, drill speeds of 1,500 rpm (Group A) and 800 rpm (Group B) were selected in this experiment. No significant difference was found between the two groups in the total weight and volume of collected debris. In this study, mean dry volume per site in Groups A and B was 0 .173 ± 0 .025 mL (1.73 ± 0.25/10 drillings) and 0.163 ± 0.018 mL (1.63 ± 0.18/10 drillings) respectively. In Savant's study24), 0.195 ± 0.099 mL of implant debris dry volume was obtained per site. These differences came from the use of different drilling depth and collecting devices. In Savant's study, drilling depth was longer than this study and they used bone collector which could not collect small size of bone debris.

Many studies suggested that the particle size of the grafting material could effect on the osteogenic ability. Lee et al.25) suggested that the autogenous drilling dusts showed better results in regeneration for dehiscence-type defects. Zaner and Yukna14) argued that the appropriate particle size of graft material for periodontal surgery was 300 to 500 µm. Moreover, Mellonig26), in an in vitro study, concluded that particle sizes between 250 and 1,000 µm are significantly better than particle sizes of ≤ 250 µm in terms of bone growth rate. Shapoff et al.27) studied the relation between particle size and enhanced osteogenesis and concluded that; (1) particle sizes between 125 µm and 1,000 µm had increased surface area, which promotes bone formation, (2) an increase in surface area, with an increase in osteoclastic activity, could result in enhanced osteogenic induction, and (3) graft particles in the range of 125 to 1,000 µm could stimulate osteogenesis by increasing the number of pores. It was also suggested that an increase in particle surface-to-volume ratio increases bone morphogenic protein levels. Sampath and Reddi28) reported that the subcutaneous implantation of coarse powders (74 to 420 µm) of demineralized bone matrix results in the local differentiation of bone, whereas the implantation of a 44 to 77 µm sized particles does not. In the present study, total wet volume was not different in two groups. However, the percentage of >250 µm particle was higher in 800rpm than in 1500 rpm significantly.

The results of the present study showed that wet volume was greater than dry volume only in the LP fractions (> 500 µm) of both groups. In a previous clinical study, wet-conditioned bone particles were found to have a larger volume than dry bone particles24). These volumetric changes must be considered during the use of commercial xenograft or allograft products because graft material was soaked in saline for easy handling during the GBR procedure.

Despite of the small number of bone samples and small amount of acquired bone debris, this study showed that the drilling speed influenced the composition of particle size in collected drilling bone debris. The drilling in 800 rpm produced the more percentage of large particles than the drilling in 1,500 rpm. However, the drilling speed didn't effect on total volume of and weight of bone debris. Further, other factors, i.e. drill's shape, dillt's sequential procedure, should be investigated under in vitro and in vivo.