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. 1987;Hahnetal. (SPSS Inc., Chicago, IL, USA). eliminated from the image. The measuring 1992; Kneissel et al. 1994; Ulm et al. 1995, field area, the bone area and the bone per- 1999). imeter were assessed for the subsequent Additionally, on the histological speci- Results calculations. A programmed dilation of the mens the maximum anterior-posterior trabeculae was carried out with a median length (distance between the middle of the The female specimens ranged in age from filter to calculate the trabecular bone pat- cortical layer of the maxillary sinus and 57 to 91years (81.60∫11.38 years), the tern factor (TBPf). This dilation resulted in the most peripheral point of the specimen), male specimens from 70 to 89 years a thickening of all trabecular margins by the maximum medio-lateral width of the (78.47∫6.58years). The differences in age 1pixel (Hahn et al. 1992; Ulm et al. 1999). zygomatic bones (distance between the were not statistically significant (PΩ0.11). Subsequently, a second measurement of medial and the lateral cortex tangent to the The results from the quantitative com- the bone area and the bone perimeter was cortical layer of the maxillary sinus), the puted tomography measurements and the performed. The following histomorpho- maximum thickness of the buccal cortical histomorphometric analysis are reported in metric parameters, which are based on the portion and the estimated maximum im- Tables1 and 2. The trabecular bone min- plate-like trabeculae model, were calcu- plant length within the zygomatic bones in eral density (BMD) was slightly higher for lated: the plane of the intended implant direction the male than for the female group The trabecular bone volume (Ωtrabecu- (distance between the middle of the cor- (398.94∫89.11 mg/cm3 and 369.95∫ lar bone volume per tissue volume ΩBV/ tical layer of the maxillary sinus parallel to 188.80 mg/cm3, respectively, PΩ0.23). TVΩevaluation of the stained cancellous the crista zygomaticoalveolaris) were as- The histomorphometrically assessed tra- bone, as compared to the total area of the sessed (Fig.4). All histological specimens becular bone volume (BV/TV) was lower image detail; %); were checked for the occurrence of the for the female than for the male specimens The cortical bone volume (Ωcortical nervus zygomaticofacialis. (19.99∫7.60%and27.32∫9.49%, respec- bone volume per tissue volumeΩevalu- tively). However, the values did not differ ation of the stained cortical bone, as com- Statistics significantly (PΩ0.06). The trabecular pared to the total area of the image detail; Multiple measurements per sample at bone pattern factor (TBPf) showed a sig- %); identical points of time were aggregated nificant difference between male and fe- The trabecular bone pattern factor prior to analysis using the mean as aggre- male specimens (1.2¿10ª2 ∫1.28mmª1 (TBPf), which describes the extent of the gation measure. Mean values are given and 1.02∫0.96mmª1, respectively, PΩ intertrabecular connectivity. The trabecu- with standard deviation. For comparison of 0.045). The cortical bone volume did not lar bone pattern factor is based on the idea continuous variables in unpaired small differ for both of the groups (female that the connectedness of cancellous bone samples, the Mann–Whitney-test was 83.18∫8.87%, male 83.68∫6.35%, PΩ structures in a two-dimensional section used. The Spearman correlation coefficient 0.90).

Table 1. Results of quantitative computed tomography and histomorphometry Sex n Mean age Bone mineral density of Trabecular bone volume Trabecular bone Cortical bone volume (years) the trabecular portion (BV/TV,%) pattern factor BVCORT (BMD, mg/cm3) (TBPf, mmª1) (%)

Female 15 81.60 ∫ 11.38 369.95 ∫ 188.80 19.99 ∫ 7.60 1.02 ∫ 0.96 83.18 ∫ 8.87 Male 15 78.47 ∫ 6.58 398.94 ∫ 99.11 27.32 ∫ 9.49 1.2 ¿ 10ª2 ∫ 1.28 83.68 ∫ 6.35 P-value / 0.11 0.23 0.06 0.045 0.90

Table 2. Morphometric analysis Sex n Anterior-posterior Medio-lateral Thickness of the Estimated implant length length (mm) thickness (mm) lateral corticalis (mm) within the zygomatic bone (mm)

Female 15 25.40 ∫ 2.64 7.60 ∫ 1.45 1.71 ∫ 0.52 14.00 ∫ 3.10 Male 15 24.93 ∫ 4.67 8.00 ∫ 2.26 1.75 ∫ 0.66 16.53 ∫ 4.55 P-value / 0.92 0.98 0.98 0.08

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Table 3. Analysis of correlation according to Spearman

Age BMD TBPf BV/TV BVCORT

Age Female Spearman’s correlation coefficient 1.000 0.284 0.018 0.147 0.199 significance (two-way) / 0.305 0.949 0.600 0.476 Male Spearman’s correlation coefficient 1.000 ª 0.336 ª 0.271 0.864 0.004 significance (two-way) / 0.221 0.328 0.328 0.990 BMD Female Spearman’s correlation coefficient 0.284 1.000 ª 0.668 0.775 / significance (two-way) 0.305 / 0.007 0.001 / Male Spearman’s correlation coefficient ª 0.336 1.000 ª 0.034 0.395 / significance (two-way) 0.221 / 0.904 0.145 / TBPf Female Spearman’s correlation coefficient 0.018 ª 0.668 1.000 ª 0.821 / significance (two-way) 0.949 0.007 / Ͻ 0.0005 / Male Spearman’s correlation coefficient ª 0.271 ª 0.034 1.000 ª 0.749 / significance (two-way) 0.328 0.904 / 0.001 / BV/TV Female Spearman’s correlation coefficient 0.147 0.775 ª 0.821 1.000 / significance (two-way) 0.600 0.001 Ͻ 0.0005 / / Male Spearman’s correlation coefficient 0.048 0.395 ª 0.749 1.000 / significance (two-way) 0.864 0.145 0.001 / /

BVCORT Female Spearman’s correlation coefficient 0.199 / / / 1.000 significance (two-way) 0.476 / / / / Male Spearman’s correlation coefficient 0.004 / / / 1.000 significance (two-way) 0.990 / / / /

BMDΩtrabecular bone mineral density, TBPf Ωtrabecular bone pattern factor, BV/TVΩtrabecular bone volume, BVCORT Ωcortical bone volume.

Table 4. Analysis of correlation according to Pearson

Age BMD TBPf BV/TV BVCORT

Age Female Pearson’s correlation coefficient 1.000 0.218 ª 0.023 0.141 0.143 significance (two-way) / 0.436 0.935 0.617 0.612 Male Pearson’s correlation coefficient 1.000 ª 0.413 ª 0.345 0.100 ª 0.085 significance (two-way) / 0.126 0.208 0.722 0.763 BMD Female Pearson’s correlation coefficient 0.218 1.000 ª 0.625 0.779 / significance (two-way) 0.436 / 0.013 0.001 / Male Pearson’s correlation coefficient ª 0.413 1.000 ª 0.204 0.359 / significance (two-way) 0.126 / 0.465 0.189 / TBPf Female Pearson’s correlation coefficient ª 0.023 ª 0.625 1.000 ª 0.855 / significance (two-way) 0.935 0.013 / Ͻ 0.0005 / Male Pearson’s correlation coefficient ª 0.345 ª 0.204 1.000 ª 0.821 / significance (two-way) 0.208 0.465 / Ͻ 0.0005 / BV/TV Female Pearson’s correlation coefficient 0.141 0.779 ª 0.855 1.000 / significance (two-way) 0.617 0.001 0.000 / / Male Pearson’s correlation coefficient 0.100 0.359 ª 0.821 1.000 / significance (two-way) 0.722 0.189 Ͻ 0.0005 / /

BVCORT Female Pearson’s correlation coefficient 0.143 / / / 1.000 significance (two-way) 0.612 / / / / Male Pearson’s correlation coefficient ª 0.085 / / / 1.000 significance (two-way) 0.763 / / / /

BMDΩtrabecular bone mineral density, TBPf Ωtrabecular bone pattern factor, BV/TVΩtrabecular bone volume, BVCORT Ωcortical bone volume.

Spearman’s rank correlation coefficient male PϽ0.0005, male PΩ0.001). However, Pearson’s correlation coefficient was was used to assess relationships between the trabecular bone mineral density (BMD) used to determine whether different par- the different measured parameters. A sig- and the trabecular bone pattern factor ameters can be predicted by one another. nificant correlation was found between the (TBPf) correlated only for the female speci- In the female group the trabecular bone trabecular bone volume (BV/TV) and the mens (female PΩ0.007, male PΩ0.904) mineral density (BMD) can be used to pre- trabecular bone pattern factor (TBPf) (fe- (Table3). dict the trabecular bone volume (BV/TV)

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The classic anatomic sites for implant maxilla is difficult to achieve according to placement in the mandible and maxilla the current literature. Only HU can be ob- have been studied extensively by histo- tained (Yilderim et al. 1998). However, due morphometry (Razavi et al. 1995). How- to the described problem of calibration ever, information concerning bone quality their use seems not to be reasonable, when and quantity of the zygomatic bone is dif- different measurements have to be com- ficult to achieve (Triepel 1922). To date, an pared. Therefore, at the moment a com- anatomic site evaluation of the zygoma parison of the trabecular bone mineral den- with state-of-the-art techniques is not sity assessed in the present study to the Fig.5. Nervus zygomaticofacialis (arrow) within the zygomatic bone (Trichrome-Masson-Goldner-stain- available. Therefore, the aim of the present maxilla is not possible. ing, original magnification ¿5). study was to assess morphology and micro- Histomorphometrically, structures are architecture by quantitative computed described in general by their porosity, den- and the trabecular bone pattern factor tomography and histomorphometry. sity, and the configuration of several struc- (TBPf) (PΩ0.001 and PΩ0.013, respec- Bone density is one of the decisive fac- ture elements. Many parameters for the es- tively). Moreover, the trabecular bone pat- tors that influence the survival rate of den- timation of bone structure have been es- tern factor (TBPf) can be used to predict the tal implants. The measurement of this par- tablished. However, the most important trabecular bone volume (BV/TV) and vice ameter is an important tool in the diagnos- parameter is still the bone volume (BV/TV) versa (PϽ0.0005). In the male group only tic evaluation of patients to assess the (Parfitt et al. 1987). Measurement and cal- the trabecular bone pattern factor (TBPf) skeletal status. The techniques of measur- culation of this value are easy and essential can be used to predict the trabecular bone ing bone mineral density have been im- for the understanding of osteopenias and volume (BV/TV) and vice versa (PϽ0.0005) proved significantly over the recent years. other pathological conditions. Neverthe- (Table4). Quantitative computed tomography is less, by using it, a complete characteriza- The average anterior-posterior length considered the method of choice, because tion of the trabecular lattice is impossible. was the same for female and male speci- it provides a high precision (McClean et al. Early changes in the trabecular bone struc- mens (female 25.40∫2.64mm, male 1990; Klemetti & Vainio 1993; Moegelin ture, such as small perforations, cannot be 24.93∫4.67mm, PΩ0.92). The medio-lat- et al. 1993; Kalender et al. 1995). While detected. Only progressive disturbances in eral thickness was less pronounced for the daily quality control and constancy checks the trabecular bone structure can be dem- female group (female 7.60∫1.45mm, male have been addressed appropriately by each onstrated. The degree of connectivity of 8.00∫2.26mm, PΩ0.98). The average single manufacturer, problems still exist in spongy bone is determined mainly by the thickness of the lateral corticalis showed the comparability of results obtained from number of perforations. A perforation is no differences between male and female different CT units. There are no generally the complete, osteoclastic penetration of group (1.75∫0.66mm and 1.71∫0.52mm, accepted calibration standards and there plate- or rod-like trabeculae. Therefore, the respectively, PΩ0.98). The estimated im- are no agreed procedures for measurements trabecular bone pattern factor has been in- plant length within the zygomatic bone of patients and evaluation of images. troduced to quantify the connectedness of was higher for the male specimens (male Therefore, when quantitative computed the trabecular bone. The lower the value, 16.53∫4.55mm, female 14.00∫3.10mm). tomography is applied, the decisive factor the higher the stability of the bone (Hahn However, a statistically significant differ- is the use of a calibration phantom et al. 1992). This assumption is supported ence could not be found (PΩ0.08). In 11 of (Cann & Genant 1980). This serves to con- by the results of the present study, which the male and eight of the female specimens trol the apparatus stability and to provide show a correlation between trabecular the nervus zygomaticofacialis was encoun- a calibration standard for conversion of CT bone mineral density (BMD) and the tra- tered (Fig.5). numbers, measured in Hounsfield units becular bone pattern factor (TBPf). Ulm (HU), into density values, usually ex- et al. (1999) found values of pressed in mg/cm3. Calcium hydroxyapa- 0.123∫1.68mmª1 for female and Discussion tite is used as bone-equivalent material. ª0.708∫1.72mmª1 for male specimens The aim is to obtain quantitative results in the region of the first premolar of the The use of the zygomatic bone as an im- independent of scan parameters or scanner maxilla. Compared to these investigations plant site in conjunction with ablative sur- condition and to compare results obtained the values for the trabecular bone pattern gical procedures has been described several on different scanners (Kalender & Suess factor of the zygomatic bone were higher times before (Parel et al. 1986; Vuillemin 1987). Reference values for spongiosa den- (female specimens 1.02∫0.96mmª1, male et al. 1990; Izzo et al. 1994; Roumanas sities have been reported in a large number specimens 1.2¿10ª2 ∫1.28mmª1, et al. 1994; Evans et al. 1996; Weischer of trials on quantitative computed tomo- Table 1), i.e. less favourable for implant et al. 1997). Recently, this implant site has graphy studies (Block et al. 1989; Kalender placement. been adopted for patients with extremely et al. 1989). However, BMD-values for the The dependence of bone density on sex resorbed maxillae. The clinical use of zygo- zygomatic bone cannot be find in the has been shown before (Parfitt et al. 1983; matic bone implants has been established literature. The study reveals values that are Klemetti & Vainio 1993; Kneissel et al. successfully (Reichert et al. 1999). The aim lower than measurements for the mandible 1994; Ulm et al. 1994, 1995). However, in of this procedure is to avoid shortcomings as determined by Moegelin et al. (1993). the present study this relationship could arising from grafting procedures. Quantitative computed tomography of the not be found for the measured parameters.

76 | Clin. Oral Impl. Res. 14, 2003 / 72–79 Nkenke . Zygomatic bone for dental implants

Although more favourable values were for providing the zygomatic specimens, measured for the male zygomatic bones, and Brigitte Kart and Christian Dittmann the differences were not statistically sig- for the preparation of the figures. nificant. It seems that reduction of bone density and rarefication of trabeculae, which are normally more pronounced in Re´sume´ women, affect both sexes to the same ex- tent where zygomatic bone of edentulous Trente zygomatiques de cadavres(15 femmes [82∫ 11 individuals is concerned. ans], 15 hommes [78∫7ans]) ont e´te´ examine´s par tomo- The determination of the dimensions of graphie quantitative par ordinateur et histomorphome´tri- quement. Le but de cette e´tude a e´te´ d’e´valuer la densite´ the zygomatic bone showed a medio-lat- mine´rale, le volume d’os trabe´culaire et le facteur de mo- eral thickness of 7.60∫1.45mm for the fe- de`le d’os trabe´culaire. De plus, les dimensions ante´ro- male and 8.00∫2.26mm for the male poste´rieures et me´dio-late´rales et la longeur implantaire specimens (Table2). Therefore, the place- estime´e dans l’os zygomatique ont e´te´ de´termine´es. Pour la tomographie quantitative par ordinateur les spe´cimens ment of a zygomaticus implant of 4.5mm e´taient balaye´savecunosdere´fe´rence. La densite´ mine´- in diameter should leave more than 1mm rale osseuse e´tait ensuite calcule´edansleplandeladirec- of bone around the implant. However, the tion voulue du placement de l’implant. Ensuite par la study of Jensen et al. (1992) reveals the de- technique de sciage et d’usure les spe´cimens ont e´te´ pre´- Fig.6. Implant placement through the fossa infratem- pendence of the medio-lateral thickness on pare´sdanslemeˆme plan pour l’histomorphome´trie. La poralis (arrow). densite´ mine´rale osseuse trabe´culaire e´tait de the race of the patients. They examined the 370∫189mg/cm3 chez les femmes et de 399∫99mg/cm3 zygomatic bones of Indian people and chez les hommes (pΩ0,23). Le volume osseux trabe´culai- found average values of 4.4mm, which The result is the use of four cortical por- re chez l’homme montrait une valeur de 27∫9% et chez seem to be critical for implant placement. tions compared to one or a maximum of la femme de 20∫8%(pΩ0,23). Le facteur de mode`le d’os trabe´culaire e´tait de 1,2x10ª2∫1,3mmª1 chez l’homme When the amount of bone provided by two cortical portions with conventional et de 1,02∫0,96 mmª1 chez les femmes (pΩ0,045). Cette the zygomatic complex is confined, the implant placement in the maxilla. The en- e´tude re´ve`le que l’os zygomatique consiste en de l’os tra- computer-assisted insertion of the zygo- gagement of as much cortical bone as poss- be´culaire avec des parame`tres qui sont de´favorables pour maticus implants has been proposed. Based ible has been advocated as a decisive factor le placement des implants. Cependant, le succe`s des im- on spiral computed tomography data, a for the success of dental implants, because plants place´s dans l’os zygomatique est se´curise´ par l’uti- lisation d’au moins quatre portions corticales. navigation system can be installed for the it provides more stability than a larger preoperative planning and intraoperative amount of less dense trabecular bone (Hes- control of insertion of the implants. The sling et al. 1990; Ivanoff et al. 1996). There- Zusammenfassung preoperative planning is supported by 3D- fore, to gain additional stability of the zygo- visualization of the anatomic sites and vir- maticus implants a modification of their Präparate von 30 Jochbeinen (15 weibliche{81.60π/-11.38 tual positioning of the implants. By guiding placement has been proposed by Jensen Jahre}, 15 männliche {78.47π/-6.58 Jahre}) wurden mittels the drill in the intended direction, the clin- et al. (1992). By the insertion of the im- quantitativer Computertomographie und Histomorpho- ical procedure of the implant placement plants through the fossa infratemporalis in metrie untersucht. Das Ziel der Studie war die Ermitt- can be carried out with an improved pre- the zygomatic arch, two additional cortical lung der Knochenmineraldichte, des trabekulären Kno- chenvolumens und des Faktors des trabekulären Kno- cision (Schramm et al. 2000). layers can be employed (Fig.6). Although chenmusters. Zudem wurden die anterio-posterioren und In the histological specimens of the pres- muscles in the fossa infratemporalis may medio-lateralen Dimensionen und die geschätzte Implan- ent study the nervus zygomaticofacialis is be perforated, complications or sequelae tatlänge innerhalb des Jochbeinknochens bestimmt. encountered frequently. Therefore, it arising from this procedure have not been Für die quantitative Computertomographie wurde die seems that during the clinical procedure of encountered (Jensen et al. 1992). Proben zusammen mit einen anthropomorphischen Phantom, mit welchem Knochen imitiert werden kann, implant placement a damage of this nerve In conclusion, it seems that despite the eingelesen. Die Knochenmineraldichte der Proben wurde is likely to occur. Sensitivity disorders of unfavourable microarchitecture of the in der Ebene der geplanten Implantatrichtung berechnet. the malar skin following implant place- zygomatic bone, implants can be placed in Daraufhin wurden die Proben mit der Säge- und Schleif- ment in the zygomatic bone have been re- patients with extremely resorbed maxillae technik in derselben Ebene für die Histomorphometrie aufgearbeitet. ported. (Reichert et al. 1999). with good clinical success when it is poss- Die trabekuläre Knochenmineraldichte betrug 369.96π/- Success rates of 65%to75% have been ible to achieve a multicortex stabilization. 188.80mg/cm3 bei den weiblichen und 398.94π/- described for implants placed solely in the The latter seems to be more important for 99.11mg/cm3 bei den männlichen Präparaten (pΩ0.23). zygomatic bone after ablative tumour a long-lasting success of the zygomaticus Das männliche trabekuläre Knochenvolumen zeigte einen surgery of the maxilla (Weingart et al. implants than the structure of the trabecu- Wert von 27.32π/-9.49%, während die weibliche Gruppe einen Wert von 19.99π/-7.60%(pΩ0.23) erreichte. Der 1992). However, when zygomaticus im- lar bone. Faktor des trabekulären Knochenmusters betrug plants are installed in patients with ex- 1.2x10ª2π/-1.28mmª1 bei den männlichen und 1.02π/- tremely resorbed maxillae, success rates of AcknowledgementsThe authors thank 0.96mmª1 bei den weiblichen Präparaten (pΩ0.045). over 80% hav been reported (Reichert et al. Tony Simpson, Jochen Lennerz and Prof. Die Studie zeigt, dass das Jochbein trabekulären Knochen mit ungünstigen Voraussetzungen für eine Implantation 1999). The reason seems to be that in such Dr Winfried Neuhuber of the Anatomy enthält. Jedoch wird der Erfolg von Implantaten, welche in cases the palatinal alveolar crest and the Institute I of the University of Erlangen- den Knochen des Jochbeins gesetzt werden, durch die Ver- sinus floor become part of the implant site. Nuremberg (Head: Prof. Dr W. Neuhuber) wendung von mindestens 4 kortikalen Anteilen gesichert.

77 | Clin. Oral Impl. Res. 14, 2003 / 72–79 Nkenke . Zygomatic bone for dental implants

Resumen valor de 27.32∫9.49 %, mientras que en el grupo de las mujeres alcanzo´ un valor de 19.99∫7.60 %(pΩ0.23). El factor del patro´n de hueso trabecular fue de Se examinaron por tomografı´a computarizada e histomor- 1.2x10ª2∫1.28mmª1 para los hombres y 1.02∫0.96 fometrı´a 30 especimenes o´seos zigoma´ticos humanos (15 mmª1 para los especimenes de las mujeres (pΩ0.045). femeninos [81.60∫11.38], 15 masculinos [78.47∫6.58 El estudio revela que el hueso zigoma´tico consiste en ´ an˜ os]). La intencion del estudio fue valorar la densidad hueso trabecular con para´metros que son desfavorables mineral del hueso, el volumen trabecular del hueso y el para la colocacio´n de implantes. De todos modos, el e´xito ´ ´ ´ factor de patron trabecular oseo. Ademas, se determina- de los implantes colocados en el hueso zigoma´tico esta ron las dimensiones antero-posterior y medio-lateral y la asegurado por el empleo de al menos 4 porciones corti- ´ longitud estimada del implante dentro del hueso zigoma- cales. tico. Se escanearon los especimenes junto con un fantomas de referencia de imitacio´n antropomo´rfica por tomografı´a computarizada cuantitativa. Se calculo´ la densidad mine- ral del hueso para los especimenes en el plano de la direc- cio´nenlaquesetienelaintencio´n de colocar el implan- te. Subsecuentemente, con la te´cnica de corte y desgaste se prepararon los especimenes en el mismo plano para histomorfometrı´a. La densidad del mineral del hueso trabecular fue de 369.95∫188.80 mg/cm3 para las mujeres y 398.94∫99.11 mg/cm3 para los especı´menes de los hombres (pΩ0.23). El volumen trabecular o´seo de los hombres mostro´ un

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