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J Oral Maxillofac Surg 59:1193-1198, 2001 Measurement of the and Zygoma as an Aid in Installing Zygomatic Implants Yuki Uchida, DDS, PhD,* Masaaki Goto, DDS, PhD,† Takeshi Katsuki DDS, PhD,‡ and Toshio Akiyoshi, MD, PhD§

Purpose: This study used maxillary and zygomatic measurements to obtain information for installing zygomatic implants. Patients and Methods: Angular and linear distances between the maxilla and the zygoma were measured in 12 cadavers (n ϭ 22 sides) classified into short and tall groups by height (140 to 159 cm and 160 to 180 cm, respectively). Results: Based on mean and standard deviation values, the installation angle of zygomatic implants was between 43.8° and 50.6°. The distance between the crest of the maxillary alveolar near the palate and the jugale (Ju) point of the zygoma was between 44.3 and 54.3 mm. The minimum distance between the most lateral corner of the and the Ju point was 6.41 mm, and the minimum anteroposterior length of the zygoma was 5.68 mm in the shorter group. Conclusions: When the installation angle of zygomatic implants is 43.8° or less, perforation of the maxilla and the zygoma or the must be avoided. When the angle is 50.6° or more, perforation of the orbital floor must be avoided. Special attention is needed to ensure osseointegration in shorter patients, because the distance between the most lateral corner of the antrum supporting the zygomatic implant and the Ju point is 10 mm or less. The apex of the implant is 3.75 mm in diameter, and the thickness of the zygoma must be 5.75 mm or more. The threads of the implant must not be exposed from the zygoma in shorter patients. © 2001 American Association of Oral and Maxillofacial Surgeons

Bone grafting is performed to place endosseous im- grafting, has recently been developed.1,2 Zygo- plants in patients with maxillary defects resulting matic implants are inserted from the crest of the from tumor resection or in patients with severe bone (at a position in the second resorption of the maxillary alveolar process. How- region of the maxillary alveolar process and in a ever, oral and maxillofacial surgeons may serious slightly palatal position), along the lateral wall of the problems in managing patients if the bone graft is maxillary sinus into the zygoma. In such cases, stable rejected or the procedure fails. The zygomatic im- retention of the prosthesis can be achieved by placing plant (Nobel Biocare AB, Go¨teborg, Sweden), which 2 or more implants (standard type) in the anterior is expected to eliminate or minimize the need for maxilla in addition to 1 or 2 zygomatic implants.2,3 It is important for oral and maxillofacial surgeons to clearly understand the detailed anatomy of the maxilla Received from the Saga Medical School, Nabeshima, Saga, Japan. and the zygoma before undertaking surgery for the in- *Research Fellow, Department of Oral and Maxillofacial Surgery; stallation of zygomatic implants.2 However, there have Private Practice, Uchida Dental Clinic, Chihaya, Higashi-ku, been no fully satisfactory anatomic studies of the maxilla Fukuoka, Japan. and the zygoma for the installation of zygomatic im- †Associate Professor, Department of Oral and Maxillofacial Sur- plants. The purpose of this study was to obtain anatomic gery. information to ensure the safe installation of zygomatic ‡Professor and Chairman, Department of Oral and Maxillofacial implants by measuring angular and linear distances of Surgery. the maxilla and the zygoma in cadavers. §Honorary Professor, Department of Anatomy. Address correspondence and reprint requests to Dr Uchida: Uchida Dental Clinic, 2-27-1 Chihaya, Higashi-ku, Fukuoka 813- Patients and Methods 0044, Japan; e-mail: [email protected] © 2001 American Association of Oral and Maxillofacial Surgeons PATIENTS 0278-2391/01/5910-0011$35.00/0 Twelve cadaver heads (22 hemimaxillae and hem- doi:10.1053/joms.2001.26725 izygomata) from the collection of the Department of

1193 1194 MEASUREMENT OF THE MAXILLA AND ZYGOMA

FIGURE 1. Landmarks and measurements on the nasal, maxillary, and zygomatic defined as aids in installing zygomatic implants (frontal and axial views). The midsagittal plane (Md) plane is defined as the plane passing through three points: 1) the midpoint of the superior margin of the (nasion) (N), 2) the deepest point shifted from the inferior anterior margin of the toward the anterior surface on the alveolar process of the maxilla (subspinale) (Ss), and 3) the . The plane through the bilateral infraorbital foramina (IF) perpendicular to the Md plane is also defined as PTBIF. Point A is defined as the point corresponding to the starting point for the insertion of the zygomatic implant, which is shifted 5 mm toward the palate from the most inferior point of the alveolar process that crosses the line passing through the parallel to the Md plane. The jugale (Ju), corresponding to the endpoint reached by the implant, is defined as the point on the zygomatic lateral surface at the most depressed point of the transitional region from the lateral margin of the zygomaticofrontal process to the upper margin of the zygomaticotemporal process. Point B is a point located at the most lateral corner of the posterosuperior roof of the maxillary sinus. An angle (the angle between the PTBIF and the A-Ju) and linear distances (A-Ju and B-Ju) were measured.

Anatomy of Saga Medical School were used. The body cular tissues in the and infratemporal fossa can heights of the cadavers ranged from 140 to 180 cm be damaged. Obtaining precise information concern- (159 Ϯ 14.2 cm), with the height unavailable for 2 ing the installation angle and length of the average cadavers (4 sides). The cadavers were divided into 2 zygomatic implant before surgery should contribute groups based on the height distribution of samples: a to safer and smoother surgical procedures. For this shorter group (n ϭ 11) (140 to 159 cm height) and a reason, point A and the jugale (Ju) point related to the taller group (n ϭ 7) (160 to 180 cm body height). Of angle and distance for installed zygomatic implants the 22 sides, molars were present on 10 sides. In (Fig 1) were defined. Point A was defined as the point these 10 sides, the positional relationship between corresponding to the starting point for installation of the infraorbital foramen and the maxillary teeth was the zygomatic implant, which is shifted 5 mm toward evaluated. Criteria for exclusion from the study in- the palatal side from the most inferior point of the cluded specimens from cadavers whose medical alveolar process that crosses a line passing through records showed diseases involving the zygoma, max- the infraorbital foramen parallel to the Md plane. The illa, or maxillary sinus; specimens from cadavers Ju, corresponding to the endpoint reached by the showing marked facial asymmetry; and specimens implant was specified as a point on the lateral surface from cadavers in which thickening of the antral mem- of the zygoma at the most depressed point of the brane was found when the maxillary sinus was ex- transitional region from the lateral margin of the zy- posed. In each specimen, the region from the orbit to gomaticofrontal process to the upper margin of the the maxilla was detached from the head and the nasal zygomaticotemporal process. bone, the maxilla, and the zygoma were exposed. The stability of bone support for the zygomatic implant depends on the how well the apical portion LANDMARKS of the implant engages with the . In The midsagittal (Md) plane was defined as the plane other words, the distance of penetration by the zygo- passing through 3 points: 1) the midpoint of the matic implant between the most lateral corner of the superior margin of the nasal bone (nasion) (N), 2) the maxillary sinus and the zygoma is very important deepest point shifted from the inferior anterior mar- information in ensuring osseointegration. To obtain gin of the anterior nasal spine to the anterior surface this information, point B at the most lateral corner of of the alveolar process of the maxilla (subspinale) the maxillary sinus penetrated by the apical portion of (Ss), and 3) the incisive foramen. The Md plane of the the implant was specified (Fig 1). Point B was defined specimen was set to a vertical line on the experimen- as the point at the most lateral corner of the postero- tal table (Figs 1, 2). The plane through the bilateral superior roof of the sinus. Using a round diamond bar, infraorbital foramina (PTBIF) perpendicular to the Md a window measuring approximately 10 ϫ 10 mm was plane was also defined (Figs 1, 2). opened adjacent to the lateral wall of the sinus close If a zygomatic implant is installed in an incorrect to the infrazygomatic crest, and the maxillary sinus direction, important internal structures or neurovas- mucosa was removed to determine point B. UCHIDA ET AL 1195

FIGURE 2. Landmarks and measurements for the anteroposterior lengths on the maxilla and zygoma, which are defined as aids in installing zygomatic implants (frontal and axial views). Point C is the point where the line passing through the corner of the inferior crest of the (CICZP) parallel to the Md plane crosses the PTBIF and is defined as a point on the anterior surface of the maxillary zygomatic process. Point D is defined as the point on the posterior surface of the zygomatic process corresponding to point C where the maxillary anteroposterior length is minimum. Point E is the point where the line passing through the most inferior point of the maxillary zygomatic suture (Zm) parallel to the Md plane crosses the PTBIF, which is defined as a point on the zygomatic lateral face. Point F is defined as the point on the zygomaticotemporal face corresponding to point E where the zygomatic anteroposterior length is minimum. Point G is the point where the line parallel to the Md plane passing through the Ju crosses the PTBIF and is defined as a point on the zygomatic lateral face. Point H is the point on the zygomaticotemporal face corresponding to point G where the zygomatic anteroposterior length is minimum. Anteroposterior lengths (C to D, E to F, and G to H) were measured.

It is also essential to determine the mean antero- tween the PTBIF and the A-Ju), a protractor was used posterior length of the maxillary zygomatic process for measurement. The distance between the crest of and zygoma to avoid exposure of the threads on the the maxillary alveolar process near the palate and the anteroposterior side after installation of the zygomatic zygoma (A-Ju) was measured using calipers (Mitsu- implant. Thus, points C to H were defined for mea- toyo, Kanagawa, Japan). The distance between the surement of the anteroposterior length of the maxil- most lateral corner of the maxillary sinus and the Ju lary zygomatic process and zygoma (Fig 2). Point C is (B-Ju) and the maxillary zygomatic process and zygo- the point where the line passing through the corner matic anteroposterior lengths (C to D, E to F, and G to of the inferior crest of the zygomatic process (CICZP), H) were measured using an external dial caliper gauge parallel to the Md plane, crosses the PTBIF, and is (Mitsutoyo, Kanagawa, Japan). All measurements defined as a point on the anterior surface of the were performed by the same researcher to minimize maxillary zygomatic process. Point D is defined as the error. point on the posterior surface of the zygomatic pro- cess corresponding to point C where the maxillary MEASUREMENT ERRORS anteroposterior length is minimum. Point E is the The reproducibility of the measurements obtained point where the line passing through the lowest point was evaluated by randomly selecting a specimen used on the zygomatic maxillary suture (zygomaxillare) in the study, measuring an angle and 5 linear distances (Zm), parallel to the Md plane, crosses the PTBIF, using the methods previously described, and obtain- which is defined as a point on the zygomatic lateral ing these measurements again 1 week later. The mea- face. Point F is defined as the point on the zygomat- surement errors obtained, which were calculated as icotemporal face corresponding to point E, where the the difference between corresponding measure- zygomatic anteroposterior length is minimum. Point ments, were expressed in terms of s(i) values as fol- G is the point where the line parallel to the Md plane, lows: passing through the Ju point crosses the PTBIF, and is ͸͑ Ϫ ͒2 Xa Xb defined as a point on the zygomatic lateral face. Point s͑i͒ ϭ ͱ H is the point on the zygomaticotemporal face corre- 2N sponding to point G where the zygomatic anteropos- terior length is minimum. STATISTICAL ANALYSIS In the statistical analysis, Excel 2000 (Microsoft Co, ANGULAR AND LINEAR MEASUREMENTS Redmond, WA) was used, and the mean and standard Based on the points previously defined, an angle deviation of each measurement were obtained for all and 5 linear distances were measured (Figs 1, 2). To specimens and height groups. In addition, the Stu- determine the installation angle (ie, the angle be- dent’s t-test was used to identify measurement differ- 1196 MEASUREMENT OF THE MAXILLA AND ZYGOMA ences between the 2 height groups. For measure- zygoma (A-Ju), which was the sum of the mean and ments in which significant differences (P Ͻ .05) were standard deviation values, was between 44.3 and 54.3 observed between height groups, the Pearson corre- mm. The minimum length was found in the shorter lation coefficient between the height and measure- group, and the maximum length was found in all ment value was obtained. specimens. No significant differences were recog- nized between height groups (P Ͼ .05). Results DISTANCE BETWEEN THE MOST LATERAL CORNER POSITIONAL RELATIONSHIPS BETWEEN THE OF THE MAXILLARY SINUS AND THE JU (B-JU) INFRAORBITAL FORAMEN AND THE MAXILLARY The mean distance between the most lateral corner TEETH of the maxillary sinus and the Ju (B-Ju) was 10 mm or For dentate maxillae with molars (10 sides), a line less only in the shorter group. The minimum value, parallel to the Md plane and passing through the which added the mean and standard deviation, was infraorbital foramen crossed the second premolar of 6.41 mm in the shorter group. Significant differences, the maxilla on 9 sides. In the remaining specimen, the were recognized between height groups (P Ͻ .0005). line crossed the proximal surface between the max- The correlation coefficient between height and the illary second premolar and the first . B-Ju line was ␥ ϭ 0.81.

RELIABILITY OF MEASUREMENTS MAXILLARY ZYGOMATIC PROCESS AND Measurement error was 0.20° or less for the angle ZYGOMATIC ANTEROPOSTERIOR LENGTHS and 0.15 mm or less for linear distances. (CTOD,ETOF,ANDGTOH)

ANGLE AND LINEAR MEASUREMENTS OF THE The mean value of G-H was the smallest of the 3 MAXILLA AND THE ZYGOMA measurements in each group. The G-H line, which was the sum of the mean and standard deviation The mean values and standard deviations for all values, was smallest in the shorter group at 5.68 mm. specimens and height groups, respectively, are No significant differences were recognized between shown in Table 1. height groups (P Ͼ .05). INSTALLATION ANGLE The range of installation angles defined as the angle Discussion between the PTBIF and the A-Ju, which was the sum of the mean and standard deviation values, was be- In this study, the Frankfort plane could not be used tween 43.8° and 50.6°. The maximum value was as a standard plane, because only the region from the found in the shorter group, and the minimum value orbit to the maxilla was detached from the head of the was found in the taller group. Significant differences cadaver. Therefore, the Md plane and the PTBIF, were recognized between the height groups (P Ͻ which can be determined in either edentulous or .005). The correlation coefficient between height and dentate and are not affected by severe resorption the installation angle was ␥ ϭϪ0.76. of the alveolar process, were used as standard planes in this study. Under such conditions, measurement DISTANCE BETWEEN THE CREST OF THE MAXILLARY error in the angular and linear distances of the maxilla ALVEOLAR PROCESS NEAR THE PALATE AND THE and the zygoma was 10% or less in terms of standard ZYGOMA(A-JU) deviation for all specimens (n ϭ 22) (Table 1). There- The range of the distance between the crest of the fore, the measurement method used in this study is maxillary alveolar process near the palate and the considered precise and reliable.

Table 1. ANGLE AND LINEAR DISTANCES OF THE MAXILLA AND ZYGOMA

Installation Angle (°) A-Ju (mm) B-Ju (mm) C–D (mm) E–F (mm) G–H (mm) Group Mean Ϯ SD Mean Ϯ SD Mean Ϯ SD Mean Ϯ SD Mean Ϯ SD Mean Ϯ SD All (n ϭ 22) 47.5 Ϯ 2.32 50.2 Ϯ 4.13 12.2 Ϯ 5.53 11.6 Ϯ 1.78 9.67 Ϯ 1.77 7.79 Ϯ 1.59 Height 140 to 159 cm (n ϭ 11) 49.3 Ϯ 1.27* 49.0 Ϯ 4.72 8.94 Ϯ 2.53† 11.9 Ϯ 1.70 9.92 Ϯ 2.17 7.87 Ϯ 2.19 160 to 180 cm (n ϭ 7) 45.7 Ϯ 1.89* 49.9 Ϯ 1.44 18.8 Ϯ 4.41† 10.8 Ϯ 1.77 9.23 Ϯ 1.56 7.64 Ϯ 0.74 * P Ͻ .005. † P Ͻ .0005 UCHIDA ET AL 1197

The starting point for the installation of a zygomatic dard deviation for individual differences in this dis- implant is the position in the second premolar region tance preoperatively when determining the length of the maxillary alveolar process and in a slightly of the zygomatic implant, which should ensure a palatal position.2,3 However, when zygomatic implant smoother surgical procedure. The minimum value installation is planned, patients are frequently eden- (A-Ju line), based on the mean and standard deviation tulous or lack molars. The position of the second values, was 44.3 mm in the shorter group. The mini- premolar can be estimated from the infraorbital fora- mum value was 46 mm or more in all specimens, as men based on the results of anatomic studies.4,5 In well as in the taller group. Zygomatic implants are almost all specimens with dentate maxillae (9 sides) available in lengths from 30 to 50 mm in 5-mm examined in our study, the plane parallel to the steps.2,3 Accordingly, a 40-mm zygomatic implant may Md plane passing through the infraorbital foramen be appropriate for patients who are less than 159 cm crossed the maxillary second premolar. The infraor- in height. In patients who are 160 cm or more in bital foramen can easily be identified by exposing the height, a longer zygomatic implant of 45 or 50 mm is lateral surface of the maxilla by an incision in the oral more appropriate. vestibule. Accordingly, the infraorbital foramen is a A zygomatic implant is supported by osseointegra- useful anatomic landmark for the installation of zygo- tion in both the maxillary alveolus and the zygoma. In matic implants. particular, the zygoma is in close proximity to the After the starting point for the installation of a defect in the maxillary alveolar bone, which has sat- zygomatic implant is determined based on the infraor- isfactory bone quality. Consequently, the distance be- bital foramen, the installation angle of the implant tween the most lateral corner of the maxillary sinus through the maxillary sinus into the zygoma must be and the outer cortical layer of the zygoma engaged by carefully determined. This will avoid damage to im- the zygomatic implant is essential information for portant anatomic structures, nerves, and blood ves- ensuring proper osseointegration. The mean distance sels in the orbit and infratemporal fossa after perfora- between the most lateral corner of the maxillary sinus tion of the maxilla and zygoma. Furthermore, the and the Ju point measured in this study was 10 mm or installation angle is determined preoperatively to pre- less only in the shorter group. In addition, the mini- vent interference with the osseointegration process mum was 6.41 mm in the shorter group, taking into because of contact between soft tissues and the zy- consideration the mean and standard deviation for gomatic implant. The zygomatic implant developmen- individual differences among the measured values. tal team,1 which has been working with Brånemark,2 The results of a previous study6 revealed that the reported that the key to successful placement of a long-term clinical outcome is not favorable when a zygomatic implant is to determine the correct angle standard Brånemark implant 3.75 mm in diameter and for installation of the implant. In short, determination 10 mm or less in length is installed in the posterior of the installation angle is the most important factor in maxilla. Therefore, special attention must be given to the procedure. The installation angle measured in our achieve good osseointegration of the zygomatic im- study ranged from 43.8° to 50.6°, taking into consid- plant, because the distance between the most lateral eration the mean and standard deviation for individual corner of the maxillary sinus and the Ju point is likely differences among the measured values. Therefore, to be 10 mm or less in patients less than 159 cm in perforation into the lateral side of the maxilla and the height. Moreover, the distance between the most zygoma, or the infratemporal fossa, is possible if the lateral corner of the maxillary sinus and the Ju point installation angle is 43.8° or less with the PTBIF de- showed statistically significant differences between fined as a standard plane, and penetration into the the height groups, and a strongly positive correlation orbital floor is possible when the installation angle is with height was observed (␥ ϭ 0.81). Consequently, 50.6° or more. Furthermore, a comparison of the the distance between the lateral corner of the maxil- installation angle between the height groups showed lary sinus and the Ju point is probably dependent on a statistically significant difference, with a strongly the patient’s height: the greater the height, the longer negative correlation between the installation angle the distance, the shorter the height, the shorter the and height (␥ ϭϪ0.76). Accordingly, the optimal distance. installation angle is presumably dependent on the It is essential to determine the mean anteroposte- patient’s height: the greater the height, the smaller rior length of the maxillary zygomatic process and the angle; the shorter the height, the larger the angle. zygoma preoperatively to avoid exposure of the Once the installation angle has been determined, threads after installation of the zygomatic implant. the distance between the starting point of installation The mean anteroposterior length at 3 points from the and the apex of the zygomatic implant reaching the maxillary zygomatic process to the zygoma through outer cortical layer of the zygoma is determined. It is which the zygomatic implant passes laterally was useful to take into consideration the mean and stan- gradually decreased in this study, and the G-H was the 1198 MEASUREMENT OF THE MAXILLA AND ZYGOMA shortest. Taking into consideration the mean and stan- guidelines for the selection of patients for zygomatic dard deviation for individual differences among the implants and recommend that the zygomatic implant measured values, the minimum G-H was 5.68 mm in procedures be performed based on the measurements the shorter group. Triplett et al3 reported that the obtained in the present study. apical portion of a zygomatic implant installed in the zygoma is 3.75 mm in diameter. Frodel et al7 reported References that the bone surrounding an osseointegrated implant 1. Darle C: Minimized treatment for maximal predictability: A new should be at least 1-mm thick. In other words, the procedure for rehabilitating the severely resorbed maxilla. Talk thickness of the zygoma around the apical portion of of the Times 4 (ed 1). Go¨teborg, Sweden, Nobel Biocare AB, 1999, p 5 the implant should be at least 5.75 mm. Therefore, 2. Brånemark P-I: Surgery and Fixture Installation. Zygomaticus oral and maxillofacial surgeons should be very careful Fixture Clinical Procedures (ed 1). Goteborg, Sweden, Nobel Biocare AB, 1998, p 1 to avoid exposure of the threads of the implant from 3. Triplett RG, Schow SR, Laskin DM: Oral and maxillofacial sur- the zygoma when zygomatic implants are installed in gery advances in implant dentistry. Int J Oral Maxillofac Implants patients less than 159 cm in height. 15:47, 2000 4. Archer WH: A Manual of Dental Anesthesia (ed 2). Philadelphia, With regard to the selection of candidates for zygo- PA, Saunders, 1958, p 104 matic implants, Reichert et al8 investigated this point 5. Bennett CR: Monheim’s Local Anaesthesia and Pain Control in by installing 18 implants in 12 patients and recom- Dental Practice (ed 6). St Louis, MO, Mosby, 1978, p 74 6. Li KK, Stephens WL, Gliklich R: Reconstruction of the severely mended the use of zygomatic implants as supports for atrophic edentulous maxilla using Le Fort I with prostheses in patients with maxillary defects resulting simultaneous bone graft and implant placement. J Oral Maxillo- from tumor resection, severe resorption of the poste- fac Surg 54:542, 1996 7. Frodel JL, Funk GF, Capper DT, et al: Osseointegrated implants: rior maxilla, or unsuccessful autogenous bone grafts, A comparative study of bone thickness in four vascularized bone as well as in patients who refuse autogenous bone flaps. J Plast Reconstr Surg 92:449, 1993 8. Reichert TE, Kunkel M, Wahlmann U, et al: Das Zygoma-Implant- grafting, according to the indications of the zygomatic Indikationen and erste klinische Erfahrungen. Z Zahnarztl Im- implant developmental team.1 We agree with these plantol 15:65, 1999