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Histological examination of drill sites in bovine rib bone after grinding in vitro with eight different devices
British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
Histological examination of drill sites in bovine rib bone after grinding in vitro with eight different devices F.G. Draenert a,∗ , R. Mathys Jr. b , M. Ehrenfeld a , Y. Draenert c , K. Draenert c a b c
Clinic for Craniomaxillofacial Surgery, University of Munich, Lindwurmstr. 2a, 80336 Munich, Germany Dr. h.c. Robert Mathys Stiftung, G¨uterstr. 5, 2544 Bettlach, Switzerland Center for Orthopaedic Research (ZOW), Gabriel-Max-Str. 3, 81545 Munich, Germany
Accepted 20 December 2006 Available online 6 February 2007
Abstract The way in which bone is processed may affect the quality of the specimen and how much information may be gleaned on histological examination. We investigated eight widely used rasps and drills and compared the results. All large chip cutters damaged the bed and marrow of the bone. The tool that caused the least damage was the wet grinding diamond tool. © 2007 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Diamond; Bone cutter; Drill bit; Bone processing; Non-demineralized histology
Introduction The processing of bone is standard. Indications include biopsy specimens, preparation for implantation, and transplantation. The collection of samples of bone for histological examination requires undamaged pieces of tissue that allow microtopographic orientation and examination. Open resection and suitable cutting devices are therefore necessary. The first tools for this indication were manual trocars, trepans, and chisels.1,2 Powered instruments like drills, oscillating saws, and ultrasound cutters that result in less damage to bone samples were developed subsequently,4,3 yet these powered instruments often led to damage from heat and mechanical lesions at both the donor site and in the sample. The most common use of drill bits today is the preparation of bony recipient sites for such devices as dental implants, screws for osteosyntheses, or artificial joints.5–7 The genera∗ Corresponding author at: Clinic for Cranimaxillofacial Surgery, Lindwurmstr.2a, 80337 Munich, Germany. Tel.: +49 89 5160 2911; fax: +49 89 5160 2925. E-mail address: [email protected] (F.G. Draenert).
tion of an exact bed for the implant with limited tissue damage is most important. Cylindrical grafts have also been used to generate transplants for pressure fixation at a recipient site.8–10 The harvesting of these bone transplants demands that the structural integrity of the material must be perfect throughout. Mechanical tissue damage in the form of fractures and abrasions at the explantation or implantation sites, including the cylindrical graft itself, yield a high risk of non-union or delayed healing. Similarly the pressure fixation of an implant is considerably impaired; a precise grinding process is therefore desirable.8–11 Various drill designs have been developed to optimise the quality of the drilling. We presume that bone should be processed by a wet grinding process and extended water cooling if exact and minimally damaged donor sites and samples are desired. A diamond-coated cylinder drill with an internal water irrigation system for the optimised grinding of bone was developed. The purpose of the study was to investigate eight different rasps and drills including the newly developed wet-grinding diamond drill to process the bony bed for transplants or implants.
0266-4356/$ – see front matter © 2007 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bjoms.2006.12.007
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
549
Table 1 Cutter heads examined No.
Type
Diameter (mm)
Pilot drilling (mm)
1 2 3 4 5 6 7 8
Broach (conic rasp) Straight drill-bit Twinned drill-bit with chip-break-notch Twinned drill-bit Three-bladed sharp drill Cylindrical hollow drill Diamond-coated cylindrical hollow drill Burckhardt spindle drill
63 63 63 63 63 63 63
57 57 57 57 57 0 0
Materials and methods The grinding properties of eight different cutter heads were tested on bovine rib bone under standard conditions in vitro. The damage to cortical and cancellous bone was investigated by microradiographs and non-demineralised histological examination. Pieces 8 cm long were cut from 20 bovine fourth ribs from the Munich slaughter house 15 cm from the vertebral joint. These blocks of bone were kept at 20 ◦ C under moist conditions for immediate use in the experiments.
Eight different cutter heads were examined (Table 1, Fig. 1). The specimens were sampled with a stationary, rotationspeed-controlled drilling machine, and the bovine rib bone was fixed in a vice and submerged in a water bath at 20 ◦ C. The devices 2–8 were mounted on the drilling machine using an adapter with a quick coupling system. The experiments with these drills were done at 600 rpm (revolutions per minute) with a grinding pressure of 20 N. For the diamond cutting head an internal rinsing water supply at 4 bar was also used. A guiding hole (diameter 57 mm) was prepared for all except numbers 7 and 8. The broach (1) is a manual device with an attached handle. It was applied manually with the same pressure of 20 N, as the machine-driven devices. It was attached to the rack of the drilling machine and a weight of 2 kg was attached before manual drilling. Minor shear stress could not be avoided. The drill hole specimens in the bovine ribs were cut with a diamond hollow grinder (inner diameter 20.05 mm). These parts were fixed by immersion for 4 weeks, block-stained with alkaline fuchsin, and embedded in polymethylmethacrylate. Sequences of slices 500 m thick were generated and ground to 140 m, microradiographed, and further ground to 60 m for light microscopy (Leitz Orthoplan, Leica Microscopes GmbH, Wetzlar). Results
Fig. 1. The eight cutter heads that were compared.
The bone samples from the drill sites were morphologically analysed for mechanical damage, including the bone marrow, microfractures, and defects in the bone (Fig. 2). The broach (conic rasp) is a manual instrument, and was the only one that damaged the cortical bone samples. The examination of both imaging techniques showed deep and assymetrical defects. The spongiosa shows defects in the soft tissue of up to 0.7 mm and also fractures of the bone and defects on microradiography. Pieces of bone marrow over 1 mm2 in size had been ripped out of the cancellous bone at several sites, leaving empty areas in the bone trabeculae. The straight drill-bit is closely related to devices 3 and 4. There were no defects in the cortical bone. The defects in the tissue of the cancellous bone samples were the smallest among numbers 2, 3, and 4 with a defect in the soft tissue of up to 0.8 mm deep. There were no extensive bone defects on
550
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
cellous bone around the drill hole that had not been ripped out as with numbers1–4, but were pressed against the margin of the defect. The diamond-coated cylindrical hollow drill created a defect with no fractures or defects at the margin of the bone marrow. Micro-debris from ground bone was pressed into the marrow space, and the surrounding cancellous bone showed slight demineralisation up to a depth of 30 m indicated by fuchsin staining. The Burckhardt spindle drill resulted in longitudinal pieces of broken bone in the direction of grinding similar to drill 6. Defects in bone marrow were larger, similar to numbers 1–4. All large-chip cutters damaged the bone bed, bone marrow, and vasculature with microfractures and rupturing of whole bone segments. These devices resulted in imprecise implant beds. Acceptable but not perfect precision was found with numbers 5, 6, and 8. The only precise defect was processed using the wet grinding diamond tool. These results were not analysed statistically, as bone is considered a tissue with non-repeating structures.
Discussion
Fig. 2. The drill hole generated with the various instruments: left, drill design; (a) cortical bone; (b) microradiography of cancellous bone; (c) cancellous bone; (d) marking of defect in bone marrow.
microradiography, but there was a little debris at the drilling site. The twinned drill-bit with chip-break-notch showed similar results to number 2, but there were severe bony defects on microradiography. The results showed larger defects up to several mm2 in size around the drill margin in the cancellous bone as well as the other defects described for number 2. The depth of the defect in the soft tissue was largest among numbers 2, 3, and 4, being 0.9 mm deep. The twinned drill-bit showed similar results to number 3. Damage to the bony bed and the bone marrow was about the same, and the soft tissue defect was only slightly less at 0.8 mm deep. The three-bladed sharp drill caused less damage in all sections. It had a different cutting pattern with mainly sharp margins and minor bony defects. Only a few cancellous bone trabeculae were broken. The soft tissue damage was of a similar depth to the other drills. Microradiography showed bony debris at the margins of the drill site. The sharp drill is difficult to guide and the lack of balance results in a more elliptical shape of the drill hole. The cylindrical hollow drill resulted in similar soft tissue damage to number 5. There were broken trabeculae of can-
We examined eight drill designs in a standard in vitro model of bovine rib. The samples were analysed histomorphologically. Our goal was to compare the grinding quality of the new diamond hollow grinder with seven other drills. Only number 1 resulted in cortical bone damage in addition to severe damage to cancellous bone. This manual rasp could not be used without shear stress, which may have contributed to these bad results. All drills except number 7 (diamond hollow grinder) caused defects in the bone marrow, which are often accompanied by fractures and other defects in cancellous bone. Number 7 had sharp drill hole margin, no fractures, and no soft tissue defects. Micro-debris and slight demineralisation were unique to this device. Numbers 5, 6, and 8 showed only disseminated tissue damage and a sharp overall margin. The use of fresh animal or human bone samples for the testing of new drilling devices and subsequent histological examination is an accepted standard procedure.12–15 The water bath at a temperature of 20 ◦ C provided comparable conditions for the eight drills under investigation, and did not reflect the physiological conditions in the body. It is, however, not likely that the drilling quality would have been significantly different at 37 ◦ C in physiological saline. That experimental setting would have been more difficult to provide constantly. The drilling speed of 600 rpm reflects the current clinical practice in dental implantology. This is the most sensitive indication for the drilling of bone. Straumann recommends 800 rpm for its ITI Implant system, which is similar to the recommendations of other manufacturers (product information, Straumann AG, Waldenburg, Switzerland). Higher and lower drilling speeds between 280 and
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
30,000 rpm were used in other experiments and for clinical applications such as osteosyntheses screws and Kirschner wires.12,16–21 A maximum drilling pressure applied by surgeons of between 6 and 24 N was described in an older study.22 More recent experiments have mentioned values of 20 N, 12 N, and 24 N.14,20 We chose 20 N to reflect the most unfavourable peaks during drilling. Tissue damage such as fractures, loss of trabeculae from cancellous bone and soft tissue defects are common results of grinding bone. They occur at the drilling site or within an explanted sample for transplantation or for biopsy and they may result in complications such as loss of the implant and aseptic necrosis.23 That the quality of specimens of bone tissue for histopathological examination is good is essential,24 yet mechanical damage of the edges of the bone sample alone are considered a minor problem as the histopathological examination is not usually affected by this. The advantage of superior cutting quality is less traumatic for the patient. This was shown for number 7, and to a lesser extent for numbers 6 and 8. Short term implants such as screws for osteosyntheses or Kirschner wires are more likely to be affected by heat damage; mechanical lesions alone are a minor issue.15,18,25 Permanent implants demand an optimised implant bed for pressure fixation and primary bone healing. Related clinical fields are dental implantology and orthopaedic joint replacement.5,6 Cylindrical bone transplants for the dowelling and fusion of bony segments, bone-cartilage composite grafts for resurfacing joints, and bone-tendon-bone grafts for repair of ligaments demand exact cutting of both graft and bony bed.8–11 Current powered drills and large-chip cutters, cannot be considered to be suitable instruments.9 The diamond hollow grinder is the only instrument that we investigated that is suitable for all three indications. Devices 6 and 8 gave acceptable drill sites but there was a large amount of debris if they were used to obtain cylindrical transplants or biopsy specimens. Number 5 caused bone chips that made it unsuitable for transplantation en bloc or biopsy. The cutting efficiency in surgical practice can differ widely from this experimental setting for several reasons including uneven bones and the manual handling of the drill by the surgeon. Temperatures above 50 ◦ C and the resulting heat damage are also common when drilling bone.13,25 Because our experiments were all done in a water bath with completely submerged samples it was not appropriate to evaluate heat damage. In contrast, Allan et al. described partly submerged samples with non-submerged drilling sites.17 The wet grinding process does not damage bone as it is known from most sharp drills and trephines. This can provide a more precise implant bed for dental implants or pressure transplants and could result in lower immediate implant losses and faster healing. The micro-debris in the sur-
551
rounding bone marrow space can improve bony healing and direct ossification with its highly mineralised matrix environment, collagen, and released growth factors, and is quickly resorbed.23 Further mechanical tests could include a study of an isotropic material (such as artificial hydroxyapatite) with statistical analysis of the drilling damage, reproducibility, and accuracy in vitro. This is not possible with bone because of its anisotropic nature.
Acknowledgement This work was supported by a grant from Dr. Robert Mathys Stiftung, G¨uterstr. 5, 2544 Bettlach, Switzerland.
References 1. Craig FS. Vertebral-body biopsy. J Bone Joint Surg 1956;38(A):93–102. 2. Siffert RS, Arkin AM. Trephine biopsy of bone with special reference to the lumbar vertebral bodies. J Bone Joint Surg 1949;31(A):146–9. 3. Eggers G, Klein J, Blank J, Hassfeld S. Piezosurgery® : an ultrasound device for cutting bone and its use and limitations in maxillofacial surgery. Br J Oral Maxillofac Surg 2004;42:451–3. 4. Deeley TJ. The drill biopsy of bone lesions. Clin Radiol 1972;23:536–40. 5. DeBoer DK. Advantages of milling versus broaching the proximal femur. Orthopedics 2005;28(Suppl.):s1041–4. 6. Koch JP, Dunson B. Factors affecting bone healing following implant surgery. J Oral Implantol 1996;22:7–11. 7. Saha S, Pal S, Albright JA. Surgical drilling: design and performance of an improved drill. J Biomech Eng 1982;104:245–52. 8. Kordas G, Szabo JS, Hangody L. The effect of drill-hole length on the primary stability of osteochondral grafts in mosaicplasty. Orthopedics 2005;28:401–4. 9. Evans PJ, Miniaci A, Hurtig MB. Manual punch versus power harvesting of osteochondral grafts. Arthroscopy 2004;20:306–10. 10. Cloward RB. Treatment of acute fractures and fracture dislocations of the cervical spine by vertebral body fusion. A report of 11 cases. J Neurosurg 1961;18:201–9. 11. Moholkar K, Taylor D, O’Reagan M, Fenelon G. A biomechanical analysis of four different methods of harvesting bone-patellar tendon-bone graft in porcine knees. J Bone Joint Surg 2002;84(A):1782–7. 12. Chacon GE, Bower DL, Larsen PE, McGlumphy EA, Beck FM. Heat production by 3 implant drill systems after repeated drilling and sterilization. J Oral Maxillofac Surg 2006;64:265–9. 13. Ercoli C, Funkenbusch PD, Lee HJ, Moss ME, Graser GN. The influence of drill wear on cutting efficiency and heat production during osteotomy preparation for dental implants: a study of drill durability. Int J Oral Maxillofac Implants 2004;19:335–49. 14. Cordioli G, Majzoub Z. Heat generation during implant site preparation: an in vitro study. Int J Oral Maxillofac Implants 1997;12:186–93. 15. Natali C, Ingle P, Dowell J. Orthopaedic bone drills-can they be improved? Temperature changes near the drilling face. J Bone Joint Surg 1996;78(Br):357–62. 16. Federspil PA, Plinkert B, Plinkert PK. Experimental robotic milling in skull-base surgery. Comput Aided Surg 2003;8:42–8. 17. Allan W, Williams ED, Kerawala CJ. Effects of repeated drill use on temperature of bone during preparation for osteosynthesis self-tapping screws. Br J Oral Maxillofac Surg 2005;43:314–9. 18. Piska M, Yang L, Reed M, Saleh M. Drilling efficiency and temperature elevation of three types of Kirschner-wire point. J Bone Joint Surg 2002;84(Br):137–40.
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19. Benington IC, Biagioni PA, Crossey PJ, Hussey DL, Sheridan S, Lamey PJ. Temperature changes in bovine mandibular bone during implant site preparation: an assessment using infra-red thermography. J Dent 1996;24:263–7. 20. Brisman DL. The effect of speed, pressure, and time on bone temperature during the drilling of implant sites. Int J Oral Maxillofac Implants 1996;11:35–7. 21. Harris BH, Kohles SS. Effects of mechanical and thermal fatigue on dental drill performance. Int J Oral Maxillofac Implants 2001;16:819–26.
22. Hobkirk JA, Rusiniak K. Investigation of variable factors in drilling bone. J Oral Surg 1977;35:968–73. 23. Draenert K, Draenert Y. Eine neue Methode fuer Knochenbiopsien und Knorpel-Knochentransplantation [A new procedure for bone biopsies and cartilage and bone transplantation]. Sandorama 1987;3:254–69. 24. Bain BJ. Bone marrow trephine biopsy. J Clin Pathol 2001;54:737– 42. 25. Matthews LS, Green CA, Goldstein SA. The thermal effects of skeletal fixation-pin insertion in bone. J Bone Joint Surg 1984;66(A):1077–83.
INTERESTING CASE: Craniofacial dematiaceous fungal infection A 48-year-old man with no history of immunosuppressive illness presented with generalised facial ulceration and crusting throughout the lower and middle face (Fig. 1). He had previously had a Curvularia infection of the left turbinate. After an endoscopic examination of the maxillary sinus and incisional biopsy of the facial skin, extensive debridement, and treatment with itraconazole 600 mg daily, orally for four weeks he was considerably better. Curvularia is a saprobic dematiaceous mould that is often associated with human infections of the paranasal sinus, skin, and soft tissue. Antifungal treatment with itraconazole has been reported to be successful.
Kishore Shetty Available online 21 June 2007
Histological examination of drill sites in bovine rib bone after grinding in vitro with eight different devices F.G. Draenert a,∗ , R. Mathys Jr. b , M. Ehrenfeld a , Y. Draenert c , K. Draenert c a b c
Clinic for Craniomaxillofacial Surgery, University of Munich, Lindwurmstr. 2a, 80336 Munich, Germany Dr. h.c. Robert Mathys Stiftung, G¨uterstr. 5, 2544 Bettlach, Switzerland Center for Orthopaedic Research (ZOW), Gabriel-Max-Str. 3, 81545 Munich, Germany
Accepted 20 December 2006 Available online 6 February 2007
Abstract The way in which bone is processed may affect the quality of the specimen and how much information may be gleaned on histological examination. We investigated eight widely used rasps and drills and compared the results. All large chip cutters damaged the bed and marrow of the bone. The tool that caused the least damage was the wet grinding diamond tool. © 2007 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Keywords: Diamond; Bone cutter; Drill bit; Bone processing; Non-demineralized histology
Introduction The processing of bone is standard. Indications include biopsy specimens, preparation for implantation, and transplantation. The collection of samples of bone for histological examination requires undamaged pieces of tissue that allow microtopographic orientation and examination. Open resection and suitable cutting devices are therefore necessary. The first tools for this indication were manual trocars, trepans, and chisels.1,2 Powered instruments like drills, oscillating saws, and ultrasound cutters that result in less damage to bone samples were developed subsequently,4,3 yet these powered instruments often led to damage from heat and mechanical lesions at both the donor site and in the sample. The most common use of drill bits today is the preparation of bony recipient sites for such devices as dental implants, screws for osteosyntheses, or artificial joints.5–7 The genera∗ Corresponding author at: Clinic for Cranimaxillofacial Surgery, Lindwurmstr.2a, 80337 Munich, Germany. Tel.: +49 89 5160 2911; fax: +49 89 5160 2925. E-mail address: [email protected] (F.G. Draenert).
tion of an exact bed for the implant with limited tissue damage is most important. Cylindrical grafts have also been used to generate transplants for pressure fixation at a recipient site.8–10 The harvesting of these bone transplants demands that the structural integrity of the material must be perfect throughout. Mechanical tissue damage in the form of fractures and abrasions at the explantation or implantation sites, including the cylindrical graft itself, yield a high risk of non-union or delayed healing. Similarly the pressure fixation of an implant is considerably impaired; a precise grinding process is therefore desirable.8–11 Various drill designs have been developed to optimise the quality of the drilling. We presume that bone should be processed by a wet grinding process and extended water cooling if exact and minimally damaged donor sites and samples are desired. A diamond-coated cylinder drill with an internal water irrigation system for the optimised grinding of bone was developed. The purpose of the study was to investigate eight different rasps and drills including the newly developed wet-grinding diamond drill to process the bony bed for transplants or implants.
0266-4356/$ – see front matter © 2007 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bjoms.2006.12.007
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
549
Table 1 Cutter heads examined No.
Type
Diameter (mm)
Pilot drilling (mm)
1 2 3 4 5 6 7 8
Broach (conic rasp) Straight drill-bit Twinned drill-bit with chip-break-notch Twinned drill-bit Three-bladed sharp drill Cylindrical hollow drill Diamond-coated cylindrical hollow drill Burckhardt spindle drill
63 63 63 63 63 63 63
57 57 57 57 57 0 0
Materials and methods The grinding properties of eight different cutter heads were tested on bovine rib bone under standard conditions in vitro. The damage to cortical and cancellous bone was investigated by microradiographs and non-demineralised histological examination. Pieces 8 cm long were cut from 20 bovine fourth ribs from the Munich slaughter house 15 cm from the vertebral joint. These blocks of bone were kept at 20 ◦ C under moist conditions for immediate use in the experiments.
Eight different cutter heads were examined (Table 1, Fig. 1). The specimens were sampled with a stationary, rotationspeed-controlled drilling machine, and the bovine rib bone was fixed in a vice and submerged in a water bath at 20 ◦ C. The devices 2–8 were mounted on the drilling machine using an adapter with a quick coupling system. The experiments with these drills were done at 600 rpm (revolutions per minute) with a grinding pressure of 20 N. For the diamond cutting head an internal rinsing water supply at 4 bar was also used. A guiding hole (diameter 57 mm) was prepared for all except numbers 7 and 8. The broach (1) is a manual device with an attached handle. It was applied manually with the same pressure of 20 N, as the machine-driven devices. It was attached to the rack of the drilling machine and a weight of 2 kg was attached before manual drilling. Minor shear stress could not be avoided. The drill hole specimens in the bovine ribs were cut with a diamond hollow grinder (inner diameter 20.05 mm). These parts were fixed by immersion for 4 weeks, block-stained with alkaline fuchsin, and embedded in polymethylmethacrylate. Sequences of slices 500 m thick were generated and ground to 140 m, microradiographed, and further ground to 60 m for light microscopy (Leitz Orthoplan, Leica Microscopes GmbH, Wetzlar). Results
Fig. 1. The eight cutter heads that were compared.
The bone samples from the drill sites were morphologically analysed for mechanical damage, including the bone marrow, microfractures, and defects in the bone (Fig. 2). The broach (conic rasp) is a manual instrument, and was the only one that damaged the cortical bone samples. The examination of both imaging techniques showed deep and assymetrical defects. The spongiosa shows defects in the soft tissue of up to 0.7 mm and also fractures of the bone and defects on microradiography. Pieces of bone marrow over 1 mm2 in size had been ripped out of the cancellous bone at several sites, leaving empty areas in the bone trabeculae. The straight drill-bit is closely related to devices 3 and 4. There were no defects in the cortical bone. The defects in the tissue of the cancellous bone samples were the smallest among numbers 2, 3, and 4 with a defect in the soft tissue of up to 0.8 mm deep. There were no extensive bone defects on
550
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
cellous bone around the drill hole that had not been ripped out as with numbers1–4, but were pressed against the margin of the defect. The diamond-coated cylindrical hollow drill created a defect with no fractures or defects at the margin of the bone marrow. Micro-debris from ground bone was pressed into the marrow space, and the surrounding cancellous bone showed slight demineralisation up to a depth of 30 m indicated by fuchsin staining. The Burckhardt spindle drill resulted in longitudinal pieces of broken bone in the direction of grinding similar to drill 6. Defects in bone marrow were larger, similar to numbers 1–4. All large-chip cutters damaged the bone bed, bone marrow, and vasculature with microfractures and rupturing of whole bone segments. These devices resulted in imprecise implant beds. Acceptable but not perfect precision was found with numbers 5, 6, and 8. The only precise defect was processed using the wet grinding diamond tool. These results were not analysed statistically, as bone is considered a tissue with non-repeating structures.
Discussion
Fig. 2. The drill hole generated with the various instruments: left, drill design; (a) cortical bone; (b) microradiography of cancellous bone; (c) cancellous bone; (d) marking of defect in bone marrow.
microradiography, but there was a little debris at the drilling site. The twinned drill-bit with chip-break-notch showed similar results to number 2, but there were severe bony defects on microradiography. The results showed larger defects up to several mm2 in size around the drill margin in the cancellous bone as well as the other defects described for number 2. The depth of the defect in the soft tissue was largest among numbers 2, 3, and 4, being 0.9 mm deep. The twinned drill-bit showed similar results to number 3. Damage to the bony bed and the bone marrow was about the same, and the soft tissue defect was only slightly less at 0.8 mm deep. The three-bladed sharp drill caused less damage in all sections. It had a different cutting pattern with mainly sharp margins and minor bony defects. Only a few cancellous bone trabeculae were broken. The soft tissue damage was of a similar depth to the other drills. Microradiography showed bony debris at the margins of the drill site. The sharp drill is difficult to guide and the lack of balance results in a more elliptical shape of the drill hole. The cylindrical hollow drill resulted in similar soft tissue damage to number 5. There were broken trabeculae of can-
We examined eight drill designs in a standard in vitro model of bovine rib. The samples were analysed histomorphologically. Our goal was to compare the grinding quality of the new diamond hollow grinder with seven other drills. Only number 1 resulted in cortical bone damage in addition to severe damage to cancellous bone. This manual rasp could not be used without shear stress, which may have contributed to these bad results. All drills except number 7 (diamond hollow grinder) caused defects in the bone marrow, which are often accompanied by fractures and other defects in cancellous bone. Number 7 had sharp drill hole margin, no fractures, and no soft tissue defects. Micro-debris and slight demineralisation were unique to this device. Numbers 5, 6, and 8 showed only disseminated tissue damage and a sharp overall margin. The use of fresh animal or human bone samples for the testing of new drilling devices and subsequent histological examination is an accepted standard procedure.12–15 The water bath at a temperature of 20 ◦ C provided comparable conditions for the eight drills under investigation, and did not reflect the physiological conditions in the body. It is, however, not likely that the drilling quality would have been significantly different at 37 ◦ C in physiological saline. That experimental setting would have been more difficult to provide constantly. The drilling speed of 600 rpm reflects the current clinical practice in dental implantology. This is the most sensitive indication for the drilling of bone. Straumann recommends 800 rpm for its ITI Implant system, which is similar to the recommendations of other manufacturers (product information, Straumann AG, Waldenburg, Switzerland). Higher and lower drilling speeds between 280 and
F.G. Draenert et al. / British Journal of Oral and Maxillofacial Surgery 45 (2007) 548–552
30,000 rpm were used in other experiments and for clinical applications such as osteosyntheses screws and Kirschner wires.12,16–21 A maximum drilling pressure applied by surgeons of between 6 and 24 N was described in an older study.22 More recent experiments have mentioned values of 20 N, 12 N, and 24 N.14,20 We chose 20 N to reflect the most unfavourable peaks during drilling. Tissue damage such as fractures, loss of trabeculae from cancellous bone and soft tissue defects are common results of grinding bone. They occur at the drilling site or within an explanted sample for transplantation or for biopsy and they may result in complications such as loss of the implant and aseptic necrosis.23 That the quality of specimens of bone tissue for histopathological examination is good is essential,24 yet mechanical damage of the edges of the bone sample alone are considered a minor problem as the histopathological examination is not usually affected by this. The advantage of superior cutting quality is less traumatic for the patient. This was shown for number 7, and to a lesser extent for numbers 6 and 8. Short term implants such as screws for osteosyntheses or Kirschner wires are more likely to be affected by heat damage; mechanical lesions alone are a minor issue.15,18,25 Permanent implants demand an optimised implant bed for pressure fixation and primary bone healing. Related clinical fields are dental implantology and orthopaedic joint replacement.5,6 Cylindrical bone transplants for the dowelling and fusion of bony segments, bone-cartilage composite grafts for resurfacing joints, and bone-tendon-bone grafts for repair of ligaments demand exact cutting of both graft and bony bed.8–11 Current powered drills and large-chip cutters, cannot be considered to be suitable instruments.9 The diamond hollow grinder is the only instrument that we investigated that is suitable for all three indications. Devices 6 and 8 gave acceptable drill sites but there was a large amount of debris if they were used to obtain cylindrical transplants or biopsy specimens. Number 5 caused bone chips that made it unsuitable for transplantation en bloc or biopsy. The cutting efficiency in surgical practice can differ widely from this experimental setting for several reasons including uneven bones and the manual handling of the drill by the surgeon. Temperatures above 50 ◦ C and the resulting heat damage are also common when drilling bone.13,25 Because our experiments were all done in a water bath with completely submerged samples it was not appropriate to evaluate heat damage. In contrast, Allan et al. described partly submerged samples with non-submerged drilling sites.17 The wet grinding process does not damage bone as it is known from most sharp drills and trephines. This can provide a more precise implant bed for dental implants or pressure transplants and could result in lower immediate implant losses and faster healing. The micro-debris in the sur-
551
rounding bone marrow space can improve bony healing and direct ossification with its highly mineralised matrix environment, collagen, and released growth factors, and is quickly resorbed.23 Further mechanical tests could include a study of an isotropic material (such as artificial hydroxyapatite) with statistical analysis of the drilling damage, reproducibility, and accuracy in vitro. This is not possible with bone because of its anisotropic nature.
Acknowledgement This work was supported by a grant from Dr. Robert Mathys Stiftung, G¨uterstr. 5, 2544 Bettlach, Switzerland.
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INTERESTING CASE: Craniofacial dematiaceous fungal infection A 48-year-old man with no history of immunosuppressive illness presented with generalised facial ulceration and crusting throughout the lower and middle face (Fig. 1). He had previously had a Curvularia infection of the left turbinate. After an endoscopic examination of the maxillary sinus and incisional biopsy of the facial skin, extensive debridement, and treatment with itraconazole 600 mg daily, orally for four weeks he was considerably better. Curvularia is a saprobic dematiaceous mould that is often associated with human infections of the paranasal sinus, skin, and soft tissue. Antifungal treatment with itraconazole has been reported to be successful.
Kishore Shetty Available online 21 June 2007