The bone particles collected during osteotomy could be used as autogenous bone graft materials for implant placement surgery. This study examined the effect of drill design on the quantity and size of bone collected during the preparation of implant sites. Bone was collected during the in vitro preparation of bovine bone using three different implant system drills: parallel shape (Group 1), tapered shape (Group 2), and tapered and stepped shape (Group 3). Bone particles were sieved. The wet volume and dry weight were measured. The mean total wet volume collected per osteotomy was 0.199 ± 0.0445 ml and the dry weight was 0.0477 ± 0.0087 g. In all three groups, bone particles >500 μm were harvested in larger amounts than particles 250–500 and <250 μm. Group 3 drills produced smaller bone particles than Group 1 and 2 drills. The size differences were significant when Group 3 particles were compared with the particles produced by Group 1 drills. The differences in total dry weight of bone collected by the three drilling systems were not statistically significant. Drill design significantly influenced the size of bone particles collected during the preparation of implant sites.
The autogenous bone graft is considered the ideal graft material because of its superior osteogenicity, osteoconductivity, and osteoinduction . To harvest an intraoral autogenous bone block or particles, patients require a second operation at the donor site and can suffer from surgical complications. Collecting bone during osteotomy for implant fixture is advantageous for patients because it avoids the additional surgery and discomfort at the wound site.
Bone particles collected during implant site preparation consist of a mixture of cortical bone and cancellous bone, and have histologically well-preserved structures with a large number of osteocytes in a calcified matrix . In an animal study, C oradazzi et al. found collected bone resorbed more rapidly and showed higher osteoinductive potential than particulated bone in the early healing stages . When the collected bone particles were grafted onto the dehiscence or fenestration bone defects of the implant site, new bone formation was successful and stable results were maintained .
Particle size and available bone volume are important factors for graft material. In general, small particles might be preferable because of more rapid resorption, greater surface area, and enhanced osteogenesis , but particles that are too small lack the space for the migration and proliferation of cells, vessels and bone. A pore size of at least 100 μm is necessary. Z aner et al. and others recommend that an appropriate particle size would be 300–500 μm . U rist et al. report that decalcified freeze-dried bone (DFDBA) ranging in size from 250 to 420 μm resulted in better bone induction than DFDBA ranging in size from 1000 to 2000 μm . S hapoff et al. reported that bone particles 125–1000 μm had greater osteogenic activity than particles <125 μm . Bone particles 0.5–1 mm showed more new bone formation than larger particles after 4 weeks . The optimal bone graft particle size might be in the range of 250–1000 μm.
Among the factors affecting the particle size of graft materials, low speed drilling resulted in graft particles of 527.0 ± 360.2 μm, larger than graft particles obtained with a high speed bur (351.1 ± 213.7 μm) . The effect of drill design on the particle size of the collected bone was not fully assessed.
This study hypothesized that the implant drill design could affect the bone particle size and three different implant drilling systems (parallel shape, tapered shape, and tapered and stepped shape) were selected for analysis. Each drill design of three different systems was examined and the effect of drill design on the size of bone particles collected during osteotomy was evaluated.
Material and methods
In vitro experiment
The experiment protocol was designed by modifying a previously described in vitro experiment for bone collection . Implant drilling for collection of bone particles was performed on two lateral portions of dead bovine mandibles. Periosteum was elevated with periosteal elevators to expose the mandibular body. Drills from three different implant systems were used ( Fig. 1 ). Group 1 included implant fixture with parallel shape: Brånemark system ® (Nobel Biocare AB, Göteborg, Sweden); round bur, 2 mm twist drill, 3 mm pilot drill, 3 mm twist drill. Group 2 included implant fixture with tapered shape: Endopore ® (Innova, Toronto, Canada); round bur, 2.5 mm pilot drill, 3.4 mm sizing drill. Group 3 included implant fixture with tapered and stepped shape: Frialit-2 ® (Friadent, Mannheim, Germany); round bur, 2.0 mm twist drill, 3.4 mm stepped drill. The description of each drill is summarized in Table 1 .
|Implant fixture design||Shape of the final drill||Flute number|
|Group 1: Brånemark system ® (3 mm twist drill)||Parallel||Twist||2|
|Group 2: Endopore ® (3.4 mm sizing drill)||Tapered||Straight||4|
|Group 3: Frialit-2 ® (3.5 mm stepped drill)||Tapered + stepped||Twist||4|
Each drilling site was prepared to a depth of 10 mm, and drilling sites were randomly selected. One bony surface of bovine mandible had 50 drilling sites. Drilling procedures were performed with a KaVo INTRAsurg 300 plus ® system (KaVo, Lake Zurich, IL, USA). Drilling speed was 2000 rpm in Group 1 and 1000 rpm in Groups 2 and 3, according to the manufacturers’ instructions. Bone particles were collected in a small bowl after drilling procedures using saline irrigation. After 10 osteotomies per group, the bone particles collected were sieved twice with a 250 μm and a 500 μm pore diameter sieve (Chunggye Co., Seoul, South Korea). The bone particles were divided into three fractions: bone particles sized <250, 250–500, or >500 μm. Similar to the study by K ainulainen et al., bone particles were packed into a 2 ml syringe, and the wet volume of the bone particles was measured . The dry weight of the bone particles was measured after drying for 72 h at room temperature. A MX microbalance electronic-scale ® (Mettler-Toledo Co., Greifensee, Switzerland) was used for measuring dry weight. These procedures were repeated 10 times for statistical power.
Measurements of drill geometry
Figure 2 shows the photographs taken with a Cannon D1x ® digital camera (Cannon Inc. Tokyo, Japan). The drill geometry related to bone chip formation is illustrated in Fig. 3 . The diameter of web, thinning and flute width were directly measured on each drill with callipers. The helix angle (rake angle) was measured on the photographs.
Statistical analysis was performed using a computer program (SAS, Chicago, IL, USA). The wet volume and dry weight of the collected bone particles were tested using the paired t -test with Bonferroni’s correction. A P -value of <0.05 was considered statistically significant.
Table 2 shows the measurements of three different system drills, including the drill geometry affecting the bone chip formation ( Fig. 3 ). The 2-mm and 3-mm twist drills in Group 1 were two-flute parallel shaped twist drills. A thinning of the drill web for reducing fraction during the drilling formed on only the 3 mm twist drill. The 2.5 mm twist drill in Group 2 had two flutes (1.6 mm width) and two thinnings on the edge. The 3.5 mm bur in Group 2 was a tapered and straight shaped four-flute drill. The 2.0 mm pilot drill and a 3.5 mm stepped drill in Group 3 were four-flute twist drills, and there were no thinnings on the drill edge. The 3.5 mm stepped drill was a tapered and stepped shaped drill, and steps at intervals of 2.5–3 mm were formed. The web diameters of the drills in Group 1 were smaller than those of the drills in Groups 2 and 3, and the flute of the drills in Group 1 was wider than the others.
|Drill shape||Flute number||Web (mm)||Thinning||Flute (mm)||Rake angle|
|Group 1: 2 mm twist drill||Parallel, twist||2||0.2||No||1.5||15|
|Group 1: 3 mm twist drill||Parallel, twist||2||0.8||2||2||15|
|Group 2: 2.5 mm twist drill||Parallel, twist||2||1.5||2||1.6||13|
|Group 2: 3.4 mm sizing bur||Tapered, straight||4||1.5||4||1.2–1.8||0|
|Group 3: 2 mm twist drill||Parallel, twist||4||1.0||No||1.0||15|
|Group 3: 3.5 mm stepped drill||Tapered, stepped, twist||4||2.0||No||1.5||10|
Among the bone debris collected after drilling, the wet volume of >500 μm sized bone particles was greater than that of bone particles with sizes 250–500 and <250 μm in all three groups ( Table 3 ). In Groups 1 and 2, the wet volume of bone particles >500 μm was significantly different from the wet volume of bone particles sized 250–500 and <250 μm (Group 1: P < 0.0001, Group 2: P = 0.0003). Among bone particles >500 μm in all three groups, the wet volume of Group 1 was significantly greater than that of Groups 2 and 3 ( P = 0.0027, P < 0.0001, respectively). The wet volume of the bone particles 250–500 and <250 μm in Group 3 was greater than that in Group 1 ( P = 0.0373, P = 0.0037, respectively). The total wet volume of bone particles was the greatest in Group 1. The difference in the total wet volume between Groups 1 and 3 was statistically significant ( P = 0.0413). The percentage of wet volume of bone particles >500 μm in size was 82% in Group 1 and 68% in Group 2. The wet volume of bone particles in Group 3 was distributed more evenly, with the percentage of bone particles >500, 250–500, and <250 μm at 47%, 22%, and 31%, respectively.
|>500 μm||250–500 μm||<250 μm||Total|
|Group 1||1.845 ± 0.275 * , #||0.195 ± 0.080||0.200 ± 0.053||2.240 ± 0.286|
|Group 2||1.145 ± 0.369 * , #||0.240 ± 0.070||0.280 ± 0.098||1.665 ± 0.375 †|
|Group 3||0.970 ± 0.347 * , †||0.465 ± 0.194 †||0.645 ± 0.250 †||2.075 ± 0.490|