Evaluation of the zygomatic bone prior to the quad zygoma surgery: virtual implant placement study on cone-beam computed tomography

Abstract

Background

The objectives of our study were to evaluate zygomatic implants placed according to quad zygoma protocol in the severely absorbed maxilla on cone-beam computed tomography (CBCT) scans using virtual implant placement program and to compare the variables according to gender. The secondary objectives were to examine the intra and extra-sinus pathways of anterior and posterior implants.

Materials and methods

56 zygomatic bones from 28 patients were examined using CBCT scans. A total of 112 zygomatic implants were evaluated to zygomatic bone-implant contact (zBIC) lenght, the relationship zygomatic implants between the maxillary sinus and zygomaticofacial foramen (ZFF) were compared and analyzed by gender on virtually placed anterior and posterior implants on the three-dimensional reconstruction images.

Results

The average zBICs length in males was found to be 11.77 ± 3.47 mm, in females 11.23 ± 2.61 mm. Although the zBIC lenghts of anterior implants were reported to be higher than those of posterior implants, no significant differences were found, respectively (p > 0.05). Among the anterior and posterior zygomatic implants classified according to ZAGA classification, ZAGA 3 (%55,3) and ZAGA 4 (%50) were most common reported, respectively. ZFF contact was significantly higher in implants with an anterior exit profile (p < 0.05). No statistically significant differences were found between gender-related parameters that were investigated (p > 0.05).

Conclusion

BIC length was not affected by gender or implant position. Most of the zygomatic implants were placed extrasinus trajectory. Anteriorly placed zygomatic implants presented high risk for ZFF contact.

Trial registration

Not applicable.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-025-06910-6.

Background

Rehabilitation of extremely resorbed maxilla poses a difficult challenge with serious limitations for conventional implant placement and frequent complications, morbidity, and a high rate of resorption with time for extensive bone grafting reconstruction [1]. In addressing these issues, recent trends favour the use of short, angled, and zygomatic implants as preferable alternatives to complex grafting procedures for cases involving severely atrophic maxilla [2]. Notably, the utilization of zygomatic implants in maxillary reconstruction has demonstrated an impressive long-term survival and success rate, ranging from 94.2 to 100%, establishing them as a reliable alternative [3].

The quad zygoma protocol involves the placement of four zygoma implants strategically to distribute forces in the antero-posterior direction, particularly in cases where patients exhibit inadequate bone structure in this dimension of the maxilla [4]. Although the quad zygoma technique is effective and well documented in literature, it has some limitations. The most frequently reported complications in anteriorly placed zygomatic implants, due to patient-related anatomical factors, include orbital cavity penetration, mucosal recession and infraorbital nerve damage [5, 6].

Quad zygoma surgery is a complex procedure that demands a comprehensive evaluation of various anatomical, radiological, clinical, and prosthodontic parameters. Prior to implant placement, a thorough radiological analysis of the zygomatic bone, orbita, infratemporal fossa, nasal cavity, and maxillary sinus is imperative [7]. Given the challenges posed by soft and hard tissues in severely atrophic maxilla, meticulous preoperative planning becomes crucial to optimize results and mitigate potential complications. Current data remains insufficient to precisely determine the position and trajectory of the quad zygoma implant. The inclusion criteria for the few studies that exist are not clear. There are deficiencies such as the mixed examination of dentate and edentulous patients, the lack of clear information according to the Cawood Howell classification as an indication for quad zygoma procedure.

Defining the precise position of the implant within the oral cavity, considering factors such as bone-implant contact (BIC) rate and its relationship to the maxillary sinus, is essential [8]. Newer software technologies uses CBCT scans to assist in surgical planning and in creation of a surgical drilling guides, which helps in limiting the depth of drill and the degree of trajectory by stabilising the drilling process during the installation of dental implants.

Numerous authors have conducted extensive research on the necessary zygomatic bone length for optimal implant placement [9–11].

The zygomaticofacial foramen (ZFF) is the point where the zygomaticofacial nerve emerges, responsible for innervation of the skin in the zygomatic region [12]. In the quad zygoma procedure, the apex of the anterior zygomatic implants receive anchorage from the lateral margin of the orbital cavity. It is important to consider that the presence of vessels and nerves in this region may cause complications, such as nerve damage or hematoma, during surgical procedures.

However, current data remains insufficient to precisely determine the position, trajectory, BIC lenght and ZFF contact of the quad zygoma procedure [7]. The objectives of this study were to investigate the difference in zBIC length, maxillary sinus and zygomaticofacial foramen and the relationship between zygomatic implants in patients with an indication of quad zygoma.The secondary objectives were to examine the intra- and extra-sinus pathways of anterior and posterior implants according to zygoma anatomy-guided approach (ZAGA) classification,

Methods

Patients

This retrospective study received approval from the Non-Interventional Clinical Research Ethics Committee of İzmir Katip Çelebi University, decision IRB No: 0512. The research involved a comprehensive review of cone-beam computed tomography (CBCT) scans, which were originally recorded for implant surgery planning and other diagnostic purposes. These images were sourced from the archives of the Department of Oral and Maxillofacial Radiology. Clinical trial number: not applicable.The article adheres to the guidelines outlined in the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) directives, ensuring transparent and comprehensive reporting of the study. Additionally, ethical considerations were maintained, following the principles outlined in the Helsinki Declaration of 1964 and its subsequent revisions. A consent report was obtained from the dental department, authorizing the evaluation and utilization of human data.

The study group comprised patients meeting specific inclusion criteria:

1. Absence of maxillofacial traumas,

2. No history of cysts/tumors on the maxilla and zygomatic bones,

3. No medication affecting bone structure,

4. Clear visibility of the orbita and zygomatic bones on CBCT,

5. Alveolar bone resorption classified as either Class V or Class VI according to the Cawood & Howell resorption classification [13].

Exclusion criteria;

1. Anatomical abnormalities in the maxilla or zygoma,

2. Severe facial asymmetry.Severe facial asymmetry.

3. Alveolar bone resorption classified from level I to IV according to the Cawood & Howell classification.

These criteria were carefully selected to ensure a homogenous and relevant study population for the investigation.

The sample size for the present study was calculated using G* power 3.1.2 software. Based on the effect size 0.739, α error 0.05, the total sample size was estimated to be 28 patients with actual power of 80%.

CBCT standardization

In this study, the New Tom 5G (QR srl, Verona, Italy) CBCT was utilized to collect data. The following parameters were employed during the data acquisition process: 90 kV, 10 mA, and a duration of 36 s, with a Field of View (FOV) set at either 15 × 12 or 18 × 16 cm. The scan ranged from supraorbital edge to mandibular base was taken into consideration. Patients assumed a standing position during the scanning process, with their heads held perpendicular to the sagittal and vertical planes and parallel to the orbitomeatal plane. The CBCT device completed a 360-degree rotation around the patient during the scanning procedure.The isotropic voxel dimension was set to 0.3 mm, and the section thickness on the obtained images was 0.40 mm. Following the scan, the acquired Digital Imaging and Communications in Medicine (DICOM) data from the CBCT were imported into DTX Studio™ (Nobel Biocare, Zürich, Switzerland) for further analysis and interpretation.

Classification of alveolar bone resorption level

A total of 248 edentulous patients, meeting the criteria for quad zygoma indication based on the Cawood-Howell classification, were selected from the archives for this study. This classification, which defines alveolar bone atrophy using the incisive foramen for the anterior and greater palatine foramen for the posterior as fixed points, was employed in this selection process. For this study, the highest point of the alveolar crest for the anterior and posterior aspects was identified, and measurements were taken between these points.Cases exhibiting insufficient width and a height of less than 5 mm in flat crest formations were categorized as Class V alveolar bone atrophy, while Class VI was identified as basal bone and class V and VI patients were included in the study. Subsequently, zygomatic bone width measurements were conducted among these patients to provide relevant data for the investigation. This systematic approach ensures a focused examination of patients with specific alveolar bone conditions, contributing to the precision and applicability of the study’s findings.

To assess the width of the zygomatic bone, a line was delineated from the point where the inferior and lateral rims of the orbit intersect, extending down to the lower edge of the zygomatic bone. This line was drawn perpendicular to the long axis of the implants. A total of 28 patients were enrolled in this study, meeting the criterion of having a zygomatic bone width between 18 and 20 mm, as defined by Davo and David [5] for quad zygoma implant surgery. This specific inclusion criterion ensures a homogeneous study group for the investigation of zygomatic bone dimensions relevant to the quad zygoma implant procedure.

Virtual implant planning

The acquired DICOM data from the CBCT scans of 28 patients were imported into DTX Studio™ (Nobel Biocare, Zürich, Switzerland). This software was employed for the virtual placement of quad zygoma implants. A total of 112 virtual implants were placed on 56 zygomatic bones. The placement of the virtual implants was guided by both anatomical and prosthodontic considerations based on previous studies. The entrance points of the implants into the alveolar bone and their exit angles on the zygomatic bones were planned using anatomical placement guides developed by [14] and [15].

Implant site selection

The program employed an algorithm to automatically generate a three-dimensional image, allowing each section to be visible to the viewer. In the application, an occlusal plane curve was formed to identify potential implant locations, with lateral incisors in the anterior and the second premolar or first molar in the posterior. The occlusal plane, location within the zygomatic bone, and the relationship to the maxillary lateral wall were determined to complete the virtual surgery (Fig. 1). A meticulous evaluation ensured that none of the implant apexes were in contact, determining the optimal location within the occlusal prosthodontic plane. According to previous studies of [15] and Bertos et al. [16], the apexes of anterior and posterior implants were positioned. The distance between two implants should be a minimum of 5 mm, and anterior implants should be positioned at least 3 mm away from the infraorbital nerve were controlled during planning.

Fig. 1.

The planning of quad zygome protocol was performed in a software based on three dimensional images from patient’s preoperative cone-beam computed tomography

The quad zygoma implants were labelled as follows: Z1 and Z3 for anterior implants, positioned around the location of the maxillary second incisor or the maxillary canine tooth, and Z2 and Z4 for posterior implants, located around the position of the maxillary second premolar or the first molar tooth (Fig. 2). For the anterior implants, the insertion point was identified at the lowest point of the alveolar crest, around the lateral-canine tooth (A1). The exit point of the anterior implants was positioned at the lowest point of the lateral border of the orbita socket (A2).

Fig. 2.

Z1 and Z3 for anterior implants, positioned around the location of the maxillary second incisor or the maxillary canine tooth, and Z2 and Z4 for posterior implants, located around the position of the maxillary second premolar or the first molar tooth

Regarding the posterior implants, the insertion point was determined at the junction between the lateral border of the infraorbital foramen and the alveolar crest, around the second premolar and the first molar (B1). The exit point of the posterior implants was located between the lowest point of the lateral border of the orbita socket and the lowest point of the zygomaticomaxillary suture, approximately one-third closer to the orbita side (B2) (Fig. 3).

Fig. 3.

Insertion and exit point of anterior implants ‘’A1, A2’’ and posterior implants ‘’B1, B2’’

Measurements and data collection

Various measurements, such as implant length and diameter, contacts, and distances with important anatomical landmarks, were determined using the measurement tools within the program. Specific investigations included assessing zBIC lenght, the relationship between the zygomatic implant and the maxillary sinus, and zygomaticofacial foramen. In this study, the relationship between zygomatic implants and maxillary sinus was evaluated according to the ZAGA classification [14]. According to this protocol, the position of zygomatic implant is determined by the anatomical circumstances of the maxillary-zygomatic complex for each individual patient, with the aim of achieving a crestal emergence of the zygomatic implant, thus aligning with prosthetic goals. The specific position of the ZI can vary, either inside or outside the sinus, depending on factors such as the curvature of the maxillary wall and the extent of alveolar atrophy. This position can be categorized as intra-sinus, lateral wall of the maxilla, or extra-sinus (ZAGA 0–4) (Fig. 4).

Fig. 4.

The optimal occlusal prosthodontic plane, location within the zygomatic bone, and the relationship to the maxillary lateral wall, as per the Zygomatic Anatomy-Guided Approach (ZAGA) classification, were determined to complete the virtual surgery. Maxilla anatomy is in ZAGA type 2 in this figure

BIC length is a linear measurement protocol. The BIC was the average value of zygomatic BIC length on the facial and the temporal sides in the facial -temporal cross section (Fig. 5). The distance from the insertion points on the zygomatic bone to the point where the implant exits the zygomatic bone was calculated using the implant enter view tool (Fig. 6).

Fig. 5.

The linear measurement of zygomatic bone implant contact (zBIC, red length bar) length from the insertion points on the zygomatic bone to the point where the implant exits the zygomatic bone was calculated using the implant enter view tool

Fig. 6.

3D and 2D images illustrating the anatomic features of an eventual zygomatic implant trajectory in the approximate position of the upper left canine. Extrasinus planning in a ZAGA type 3 maxilla

Statistical analysis

Descriptive statistics were utilized to define continuous variables. The comparison of two variables, which were independent and did not show a normal distribution, was conducted using the Mann-Whitney U test. The analyses were performed using MedCalc Statistical Software version 12.7.7 (MedCalc Software bvba, Ostend, Belgium; http://www.medcalc.org; 2013). In our study, the length of intraosseous implants throughout the course of virtual implantation, the relationships of implants with the maxillary sinus and the zygomaticofacial foramen were investigated. Additionally, a comparison was made between male and female patients. P value < 0.05 was considered statistically significant for the present study.

Results

A total of 28 patients with severely atrophic maxilla met the inclusion criteria for fixed oral rehabilitation anchored on four zygomatic implants. In our study, 112 zygomatic implants were placed virtually in all patients, including 16 female (57.1%) and 12 male (42.9%) patients. The average age of the patients is 60.75 ± 10.86 and varies between 45 and 83.

The zBIC lenght, the relationship between the zygomaticofacial nerve and the implant, and the relationship of the implants with the maxillary sinus were compared depending on gender at different points on the virtually placed anterior and posterior implants on the CBCT images.

Table 1 shows the average zBICs lenght for each implant and the differences in zBIC lenght according to gender.

Table 1.

The average zygomatic bics Lenght (mm) for each implant and virtual implant Lenght (mm) in anterior (Z1,Z3) and posterior (Z2,Z4) implants

	Entire cohort (n = 28)			Male (n = 12)			Female (n = 16)
	Mean ± SD	Min	Max	Mean ± SD	Min	Max	Mean ± SD	Min	Max
Zygomatic BIC lenght (mm) of Z1	12.08 ± 2.72	5.4	17.4	11.55 ± 2.95	5.4	15.2	12.44 ± 2.58	8.5	17.4
Zygomatic BIC lenght (mm) of Z2	10.41 ± 3.3	5.2	19.2	11.78 ± 4.01	5.2	19.2	9.39 ± 2.29	6.1	14
Zygomatic BIC lenght (mm) of Z3	12.76 ± 3.14	5.8	22.7	12.33 ± 2.98	5.8	17	13.08 ± 3.31	8.9	22.7
Zygomatic BIC lenght (mm) of Z4	10.62 ± 3.12	4.9	18.4	11.42 ± 3.95	4.9	18.4	10.03 ± 2.27	7.4	15.4
Zygomatic BIC lenght (mm) of anterior implants (Z1,Z3)	12.42 ± 2.93	5.4	22.7	11.94 ± 2.96	5.4	17	12.76 ± 2.94	8.5	22.7
Zygomatic BIC lenght (mm) of posterior implants (Z2,Z4)	10.51 ± 3.21	4.9	19.2	11.6 ± 3.98	4.9	19.2	9.71 ± 2.28	6.1	15.4
Virtual implant lenght (mm) of anterior implants (Z1,Z3)	48.34 ± 5.15	42.50	52,50	49.47 ± 2.36	45.00	52.50	47,72 ± 2.21	42.50	52.50
Virtual implant lenght (mm) of posterior implants (Z2,Z4)	40,74 ± 4.61	35.00	45.00	41.13 ± 2.42	37.50	45.00	40.36 ± 2.12	35.00	45.00

Abbreviation: BIC bone implant contact, Z1 Z3 anterior positioned zygomatic implants, Z2 Z4 posterior positioned zygomatic implants

In our study, the average zBICs length in males was found to be 11.77 ± 3.47 mm, in females 11.23 ± 2.61 mm, with an overall average of 11.46 ± 3.14 mm. However, no statistically significant difference was found (p > 0.05). Although the BIC lenghts of anterior implants were reported to be higher than those of posterior implants, no significant difference was found (p > 0.05).

The average anterior zygomatic implants length in males was found to be 49.47 ± 2.36 mm, in females 47.72 ± 2.21 mm and the posterior zygomatic implants length in males was found to be 41.13 ± 2.42 mm, in females 40.36 ± 2.12 mm which showed a statistical insignificance of P > 0.05 (Table 1).

Table 2 shows the distribution of zygomatic implants placed in the anterior and posterior regions according to gender and ZAGA classification. There is no significant difference according to gender. (p > 0.05). Among the 56 implants with an anterior exit profile (Z1-Z3), 1.7% were classified as ZAGA 0, 7.2% as ZAGA 1, 16.1% as ZAGA 2, 55.3% ZAGA 3and 19.7% as ZAGA 4. For implants with a posterior exit profile (Z2-Z4), 7.2% were classified as ZAGA 0, 7.2% as ZAGA 1, 21.4% as ZAGA 2, 14.2% as ZAGA 3, and 50.0% as ZAGA 4.

Table 2.

Relationship between the maxillary sinus (ZAGA classification) and zygomatic implants according to gender

		Male		Female
		N	%	N	%	p
Relationship between maxillary sinus and Z1	ZAGA 0	0	0.0%	1	6.3%	0.088
	ZAGA 1	1	8.3%	1	6.3%
	ZAGA 2	3	25.0%	2	12.5%
	ZAGA 3	6	50.0%	9	56.3%
	ZAGA 4	2	16,7%	3	18.7%
Relationship between maxillary sinus and Z2	ZAGA 0	0	0.0%	2	12.5%	0.059
	ZAGA 1	1	8.3%	1	6.3%
	ZAGA 2	2	16.7%	4	25.0%
	ZAGA 3	3	25.0%	2	12.5%
	ZAGA 4	6	50.0%	7	43.7%
Relationship between maxillary sinus and Z3	ZAGA 0	0	0.0%	0	0.0%	0.509
	ZAGA 1	1	8.3%	1	6.3%
	ZAGA 2	1	8.3%	3	18.7%
	ZAGA 3	7	58.4%	9	56.3%
	ZAGA 4	3	25.0%	3	18.7%
Relationship between maxillary sinus and Z4	ZAGA 0	1	8.3%	1	6.3%	0.666
	ZAGA 1	1	8.3%	1	6.3%
	ZAGA 2	3	25.0%	3	18.7%
	ZAGA 3	2	16.7%	1	6.3%
	ZAGA 4	5	41.7%	10	62.5%

Abbreviation: Z1 Z3 anterior positioned zygomatic implants, Z2 Z4 posterior positioned zygomatic implants

There is no statistically significant difference in the relationship between the ZFF contact and the implant according to gender (p > 0.05). (Table 3) However, it was found that the ZFF contact was significantly higher in implants with an anterior exit profile (Z1-Z3) compared to implants placed posteriorly (p < 0.05) (Z1: 35.7%, Z3: 46.4%).

Table 3.

Relationship between zygomaticofacial foramen (ZFF) and zygomatic implants according to gender

		Male		Female
		N	%	N	%	p
Relationship between ZFF and Z1	Non-contact	7	58.3%	13	72.3%	0.105
	Contact	5	41.7%	5	27.7%
Relationship between ZFF and Z2	Non-contact	11	91.7%	16	100%	0.627
	Contact	1	8.3%	0	0.0%
Relationship between ZFF and Z3	Non-contact	6	50.0%	11	61.1%	0.226
	Contact	6	50.0%	7	38.9%
Relationship between ZFF and Z4	Non-contact	12	100.0%	15	93.7%	0.407
	Contact	0	0.0%	1	6.3%

Abbreviation: Z1 Z3 anterior positioned zygomatic implants, Z2 Z4 posterior positioned zygomatic implants

Discussion

The use of three-dimensional imaging techniques, along with virtual surgical planning, enables a comprehensive analysis of anatomical structures. This approach helps in precisely visualizing the patient’s unique anatomy, optimizing implant placement, and reducing the likelihood of damage to critical structures. Ultimately, preoperative planning plays a vital role in achieving successful quad zygoma surgery and forming the basis for an ideal prosthodontic rehabilitation [17].

In their studies, Davo and David [4], and Malo et al. [18], have focused that quad zygoma surgery is indicated for patients classified under Class V-VI. According to their research, for quad zygoma surgery, the zygomatic bone width should be at least 1.8–2 mm, the distance between two implants should be a minimum of 5 mm, and anterior implants should be positioned at least 3 mm away from the infraorbital nerve. Upon reviewing the literature, it has been observed that in some studies, these criteria were not consistently adhered to. In our study, we examined the CBCT scans of a total of 248 completely edentulous patients, and 28 patients meeting the aforementioned criteria were included in the study.

The contact surface between the zygomatic bone and the surface of the zygomatic implant is referred to as Bone-Implant Contact (BIC). It is well-documented that a high BIC value is crucial for the success and survival of implants [11]. A review of the literature revealed that preoperative and postoperative measurements of contact surface between zygomatic bone and implant have been conducted.

In a study by Bertos et al. [16], virtual quad zygoma implants were placed on CBCT data from 23 patients. A total of 92 implants were compared based on the implant length within the zygoma and the levels of atrophy (Class IV and Class V). They calculated the zBIC length as 16,95 ± 4,73 mm. Pellegirino et al. [19], in their study, reported zBIC measurements for zygomatic implants placed in different virtual trajectories to be 17.92 ± 6.92 mm. On the other hand, Huang et al. [20] reported zBIC measurements of 16.70 ± 4.18 mm in their study. In post-operative BIC measurement studies after zygomatic implant surgery, Balshi et al. [21] found an average BIC of 16.95 ± 4.73 mm.

In our study, the average intra-zygomatic implant length in males was found to be 11.77 ± 3.47 mm, in females 11.23 ± 2.61 mm, with an overall average of 11.46 ± 3.14 mm. However, no statistically significant difference was observed (p > 0.05). Although the BIC values of anterior implants were reported to be higher than those of posterior implants, no significant difference was found (p > 0.05). The differences between our findings and the results of these studies may be attributed to our study group comprising patients with severe atrophy of the maxilla, the higher BIC length of single zygoma implants, and deviations in post-operative tomographic measurements of zygomatic implants. Also, Huang et al. [20] focused on an Asian demographic. Conversely, [16] conducted their research on a European cohort, examining the influence of alveolar bone resorption on the BIC of quad ZIs, the volume of implant-engaged zygoma bone, and its correlation with the maxillary sinus. In our opinion, demographic differences across studies may account for the different results. Also, Additionally, our measurements were taken when the zygomatic implant was completely within the zygomatic bone. No measurements were taken from the area where the implant partially penetrated the zygomatic bone. Therefore, we believe our measurements are shorter than those reported in the literature.

Aparicio et al. [22], in 2011, developed the Zygoma Anatomy-Guided Approach (ZAGA) classification system based on the skeletal form of the zygomatic and alveolar crest complexes and the implant trajectory that can be utilized according to these forms. According to the ZAGA concept, placement of the zygomatic implant is Guided by the anatomic and prosthetic requirements. The osteotomy goals are to achieve maximum primary stability, optimal anteroposterior distribution and implant trajectory and position that prevent potential long-term complications. ZAGA types 0–2 present more intraoperative challenges. A small window is created in the lateral wall of the maxilla. Direct visualization of the zygomatic bone is difficult. Because the implant passes through the maxillary sinus, sinusitis and oroantral fistulas are more common occured than other types. In ZAGA types 3 and 4, the zygomatic bone is directly accessed. However, because the implant trajectory is outside the maxilla, soft tissue dehiscences may occur.

In their updated classification for quad zygoma patients in 2021, [23] described an approach like the previous system for osteotomy techniques and positioning of implants for anterior and posterior implants. For the updated classification for quad zygoma patients, the ratio of implants placed in the anterior maxilla (ZAGA-A) corresponding to each of the five osteotomy paths was as follows: for type 0, 2.9%; type 1, 4.5%; type 2, 19.7%; type 3, 55.7%; and type 4, 17.2%. Additionally, implants placed posteriorly were named from ZAGA P-0 to P-4. Percentages for each class were as follows: for type 0, 5.7%; type 1, 10.2%; type 2, 8.2%; type 3, 18.4%; and type 4, 57.4%.In our study, among the 56 implants with an anterior exit profile (Z1-Z3), 1.7% were classified as ZAGA 0, 7.2% as ZAGA 1, 16.1% as ZAGA 2, 55.3% ZAGA 3and 19.7% as ZAGA 4. For implants with a posterior exit profile (Z2-Z4), 7.2% were classified as ZAGA 0, 7.2% as ZAGA 1, 21.4% as ZAGA 2, 14.2% as ZAGA 3, and 50.0% as ZAGA 4. This classification in our study shows similarity with Aparicio’s work.

Most common complication reported after zygomatic implant surgery was sinusitis followed by paraesthesia. [2] In a systematic review by [24], 15 paraesthesia cases were reported on the infraorbital and zygomaticofacial nerves. The reason for these complications could result from intra-operative subperiosteal dissection or zygomatic implant placement. ZFF is an important anatomical structure that should be considered in quad zygoma procedure. ZFF is the point where the zygomaticofacial nerve emerges, responsible for innervation of the skin in the zygomatic region In particularly, the presence of ZFF at the anchor point of the anterior zygomatic implant is a condition that should be examined as a pre-operative. Contact between the zygomatic implant and the nerve and blood vessels results in temporary paraesthesia and hematoma. The ZFF contact with the anterior zygomatic implant seen in pre-operative planning will be useful to inform the patient about possible complications. In a morphological study conducted by [25], it was found that in the examined 287 macerated skulls, the zygomaticofacial foramen (ZFF) was absent in approximately 16.8% of females and 18.2% of males. It was determined that one ZFF was present in 52.1% of females and 53.3% of males, two ZFFs in 24.7% of females and 22% of males, three ZFFs in 5.3% of females and 5.4% of males, and four ZFFs in 1.1% of females and 1.1% of males. There was no statistically significant was observed between genders. In this study, it was found that the contact to ZFF was significantly higher in implants with an anterior exit profile (Z1-Z3) compared to implants placed posteriorly (p < 0.05) (Z1: 35.7%, Z3: 46.4%). This study holds the distinction of being the first to examine the relationship between implants and the zygomaticofacial foramen in limited virtual planning studies in the field of quad zygoma procedure.

The limitations of the study were: smaller sample size and clinical placement of zygomatic implants were not performed after virtual planning of the quad zygoma. However, it gives a broader picture about the radio-anatomical characteristics of the zygomatic bone for the planning and placement of quad zygomatic implants. BIC measurement was base on linear instead of area measurement, and these may be different from actual clinical practice. The classification of the edentulous residual ridge was based on ridge height measurements, suggesting that a more precise classification system is needed for future research. Virtual planning for placement of zygoma implants in quad approach would be a feasible requirement as it ensures to provide a definitive angulation in a coarse zygomatic bone with precise determination of the distance and length of implants. It also enables the surgeon to take precautions before the operation, depending on whether the implants are in the extra-sinus, intra-sinus or lateral wall of the maxilla or eases out the surgeon’s practice and prevents the possibilities of causing intrusion complications intraoperatively.

Conclusion

Zygomatic bone has an irregular structure and varies from person to person. According to the results of our study conducted using a virtual implant program before quad zygoma surgery, gender does not affect the BIC lenght, the relationship between the zygomatic implant and the maxillary sinus, and ZFF contact. The BIC values of anterior implants were reported to be higher than those of posterior implants, however there is no significant difference was found. ZFF contact was significantly higher in implants with an anterior exit profile compared to implants placed posteriorly. The ZFF contact with the anterior zygomatic implant seen in pre-operative planning will be useful to inform the patient about possible complications. Particularly, examining the anatomy of the region with three-dimensional imaging techniques before quad zygoma surgery and conducting surgical rehearsals with programs that allow virtual surgery are crucial to prevent potential complications and ensure an ideal prosthetic rehabilitation. The goal of future studies is to obtain data from larger sample groups and demonstrate the accuracy of these data through clinical application.

Authors’ contributions

OŞ contributed to conception and design, mentored the project, drafted and critically revised the manuscript, analyzed the data, approval of the submitted and final versions; DA contributed to conception, design, analyzed data and critically revised the manuscript approval of the submitted and final versions; İDK contributed to conception and design and drafted and analyzed and critically revised the manuscript approval of the submitted and final versions; MH contributed to conception and design and drafted and analyzed and critically revised the manuscript approval of the submitted and final versions; FR contributed to conception and design and drafted and analyzed and critically revised the manuscript approval of the submitted and final versions EA contributed to conception, design, analyzed, performed the zygomatic implant lenght measurements and critically revised the manuscript, approval of the submitted and final versions. All authors gave final approval and agreed to be accountable for all aspects of the work.

Funding

Not applicable.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Ethical approval was obtained from the Non-Interventional Clinical Research Ethics Committee of İzmir Katip Çelebi University, decision No.: 0512. Written and informed consent was obtained from all participants prior to their inclusion in the study.

Consent for publication

Not Applicable.

Competing interests

The authors declare no competing interests.