Emeka Nkenke Anatomic site evaluation of the Michael Hahn Michael Lell zygomatic bone for dental implant Jörg Wiltfang placement Stefan Schultze-Mosgau Beate Stech Martin Radespiel-Tröger Friedrich Wilhelm Neukam Authors’ affiliations: Key words:bone mineral density; trabecular bone pattern factor, trabecular bone volume; Emeka Nkenke, Jörg Wiltfang, Stefan Schultze-Mosgau, Beate Stech, zygomatic bone; zygomaticus implant Friedrich Wilhelm Neukam, Department of Oral and Maxillofacial Surgery, University of Abstract:Thirty human zygomatic bone specimens (15 females mean age 81.60 ∫ 11.38 years, Erlangen-Nuremberg, Erlangen, Germany Michael Hahn, Department of Bone Pathology/ 15 males, mean age 78.47 ∫ 6.58 years) were examined by quantitative computed tomography Center Biomechanics, University of Hamburg, and histomorphometry. The aim of the study was to assess the bone mineral density, the Hamburg, Germany Michael Lell, Department of Diagnostic trabecular bone volume and the trabecular bone pattern factor. Moreover, the anterior- Radiology, University of Erlangen-Nuremberg, posterior and the medio-lateral dimensions and the estimated implant length within the Erkangen, Germany zygomatic bone were determined. For quantitative computed tomography the specimens Emeka Martin Radespiel-Tröger, Institute of Medical Informatics, Biometry and were scanned together with a bone mimicking anthropomorphic reference phantom. The Epidemiology, University of Erlangen- bone mineral density was calculated for the specimens in the plane of the intended Nuremberg, Erlangen, Germany direction of the implant placement. Subsequently, with the sawing and grinding technique, Correspondence to: the specimens were prepared in the same plane for histomorphometry. The trabecular bone Dr Dr Emeka Nkenke mineral density was 369.95 ∫ 188.80 mg/cm3 for the female and 398.94 ∫ 99.11 mg/cm3 for Department of Oral and Maxillofacial Surgery University of Erlangen-Nuremberg the male specimens (P Ω 0.23). The male trabecular bone volume showed a value of 27.32 ∫ Glückstr. 11 9.49%, while the female group reached a value of 19.99 ∫ 7.60% (P Ω 0.23). The trabecular 91054 Erlangen bone pattern factor was 1.2 ¿ 10ª2 ∫ 1.28 mmª1 for the male and 1.02 ∫ 0.96 mmª1 for Tel: π49 9131 8534221 Fax: π49 9131 8534219 the female specimens (P Ω 0.045). The study reveals that the zygomatic bone consists of e-mail: trabecular bone with parameters that are unfavourable for implant placement. However, / emeka.nkenke mkg.imed.uni-erlangen.de the success of implants placed in the zygomatic bone is secured by the employment of at least four cortical portions. The use of endosseous implants has be- developed to increase the bone volume. come a standard procedure in the treat- Autogenous bone grafts, guided bone re- ment of complete and partially edentulous generation, allogenic material and combi- patients. Rehabilitation of the masticatory nations of these procedures are used in or- function with dental implants can be der to overcome insufficient bone volume. achieved with predictable success in vari- These techniques have in common that Date: ous clinical situations. However, the prob- they require an additional operation site or Accepted 12 November 2001 lem of insufficient height and width of the that an increased number of infections are To cite this article: Nkenke E, Hahn M, Lell M, Wiltfang J, Schultze- alveolar ridge at the implant site remains. likely to occur (Schlegel et al. 2000). Espe- Mosgau S, Stech B, Radespiel-Tröger M, Neukam Inadequate bone volume is caused by re- cially bone grafting is a common procedure FW. Anatomic site evaluation of the zygomatic bone for dental implant placement sorption following extraction, trauma, in- to increase the bone volume. The grafts Clin. Oral Impl. Res, 14, 2003; 72–79 fection, pneumatization of the maxillary can be harvested from different intra- and sinus and ablative tumour surgery (Von extraoral regions. The donor sites are often Copyright C Blackwell Munksgaard 2003 Arx & Kurt 1998). related to complications such as sensitivity ISSN 0905-7161 Several surgical procedures have been disorders, haematomas and postoperative 72 Nkenke . Zygomatic bone for dental implants pain (Nkenke et al. 2001). Moreover, to ob- tain high success rates, a two-stage pro- cedure with delayed implant placement is recommended (Lundgren et al. 1999). The result is an increased number of oper- ations, which reduce the patients’ comfort. Therefore, the use of alternative implant sites for the masticatory rehabilitation of the maxilla has been advocated to reduce the necessity of bone grafting procedures. The placement of dental implants in the Fig.3. Computed tomography section in the intended zygomatic bone is well known from pre- plane of the implant placement with the region of prosthetic surgery following ablative tu- interest bordered by a black line. mour surgery (Vuillemin et al. 1990;Izzo et al. 1994; Roumanas et al. 1994; Evans et al. 1996; Weischer et al. 1997). The clin- ical use in patients with severely resorbed Fig.1. Zygomatic complex. a) Facial surface (black posterior maxillae has been described (Re- line: plane of the intended direction of the implant ichert et al. 1999). The zygomaticus im- placement). b) Medial surface. 1) Infraorbital rim. 2) plant passes through the sinus close to the Foramen of the nervus zygomaticofacialis. 3) Pro- crista zygomaticoalveolaris. It is placed cessus zygomaticofrontalis. 4) Zygomatic arch. 5) Crista zygomaticoalveolaris. 6) Maxillary sinus. slightly palatal in the region of the second premolar and its apex perforates the cor- tical portion of the zygomatic bone close Fig.4. Histologic specimen sliced in the intended to the angle between the zygomatic arch plane of the implant placement (Trichrome-Masson- and the processus frontalis (Stella & Warn- Goldner-staining, original magnification ¿1.25). 1) er 2000). Anterior-posterior length. 2) Medio-lateral thickness. To date, there is a lack of information on 3) Estimated implant length within the zygomatic the dimension and the microstructure of bone. the zygomatic bone. Therefore, the aim of the present study was to evaluate quantity and quality of bone of the zygomatic com- covered an area of 75mm2. A high resol- plex in human specimens by means of ution kernel (AH 70) was used. A recon- quantitative computed tomography and struction increment of 1mm was applied. histomorphometry. In the computed tomography images the region of interest was marked in the axial slices bordering the trabecular bone por- Material and methods tion (Fig.3). Two slices were added together and the Hounsfield units (HU) computed. In all, 30 left zygomatic bones (15 male, 15 Fig.2. European forearm phantom (EFP). From the Hounsfield units measured for female) were examined (Fig.1). The age of the reference phantom, a regression line the deceased subjects ranged from 57 to was calculated, which was used to assess 91years (mean age 80.47∫9.30years). ally defined anthropomorphic structures the corresponding values for the trabecular They had bequeathed their bodies to the (Fig.2). Water-equivalent plastics are used bone mineral density in mg/cm3 of the Anatomic Institute I of the University of together with calcium hydroxyapatite, zygomatic bones (Moegelin et al. 1993). Erlangen-Nuremberg for medical-scientific which simulates bone tissue. Cortical and After fixation in Schaffer’s solution (two research and training purposes. The reason spongiosa densities and thicknesses are parts 96% ethanol, one part 37% formalde- for death was unknown. All patients were varied from section to section, offering a hyde) 5-mm-thick sections were sawn in edentulous. range of spongiosa densities from 50 to the region of the second premolar perpen- For quantitative computed tomography 200 mg hydroxyapatite/cm3. The true dicular to the crista zygomaticoalveolaris the specimens were scanned in a Spiral CT values for all measured quantities are well in the plane of the intended direction of (Somatom Plus 4, Siemens, Erlangen, Ger- defined (Kalender & Suess 1987; Kalender implant placement. The undecalcified sec- many) in the plane of the intended direc- et al. 1989, 1995). tions were embedded in Technovit 7200 tion of implant placement. The samples The zygomatic bones were scanned con- VCL (Heraeus Kulzer, Wehrheim, Ger- were placed in water together with a refer- tiguously with a 1-mm slice thickness. many). Ground sections 30mm thick were ence phantom. This phantom (European 1.5mm pitch, 170 mA, 120kV, and a field produced with a diamond band-saw and a Forearm Phantom, EFP) is composed of of view (FOV) of 75 mm were chosen. The microsectioning system (Exakt-Apparate- three sections, each containing geometric- rotation time was 1.5s. The field of view bau, Norderstedt, Germany) (Donath 73 | Clin. Oral Impl. Res. 14, 2003 / 72–79 Nkenke . Zygomatic bone for dental implants 1988). A Trichrome-Masson-Goldner-stain- can be described by the relation of convex was calculated for evaluation of a possible ing was performed (Fig.4). With a video- to concave surfaces. Concave surfaces rep- association between continuous covariates camera, images were assessed at a magni- resent a well connected spongy lattice, without assumption of normal distri- fication of ¿12.5. The images were trans- while convex surfaces indicate a poorly bution. A multiple linear regression was ferred into an automatic image analysing connected trabecular lattice. The calcu- performed for evaluation of a possible pre- system (IBAS 2000, Kontron-Zeiss, lation formula (bone perimeterªdilated dictability of mineral bone density by Munich, Germany). They were transform- bone perimeter/bone areaªdilated bone measuring the CT bone density. P-values ed into binary images. Measuring field area; mmª1) reveals that the intertrabecu- equal to or smaller than 0.05 were con- boundaries of the trabecular bone were de- lar connectivity is the higher, the lower the sidered significant. All calculations were fined and artefacts such as air bubbles value of the trabecular bone pattern factor made using SPSS Version 10 for Windows within the plastic resin or scratches were (Parfitt 1962; Parfitt et al.