Ocular Complications of Zygomatic Dental Implants: A Systematic Review

Zygomatic implants are a form of dental implant that anchors in the zygomatic bone with potential for complications to the eye and orbit. This article presents a systematic review of the literature regarding ophthalmological complications of zygomatic implants to familiarize ophthalmologists with the potential complications and their treatment options. The review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Various searches using PubMed, Elsevier, and Google Scholar were used to search for articles using search terms including ‘zygomatic’, ‘dental’, ‘implant’, ‘complications’, ‘eye,’ and ‘orbit.’ Exclusion criteria included articles that were unavailable in English or written before 1980. Twenty-four articles were included in this review: nine case reports, one case series, nine cohort studies, one randomized controlled trial, and four review articles. The most common complication was infraorbital paresthesia, followed by intraoperative orbital penetration. Other complications included implants placed into the orbit, orbital hematomas, extraocular muscle damage, diplopia, subconjunctival hemorrhage, periorbital fistulae, infraorbital rim infections, and orbital emphysema. Of 41 cases, which included outcomes, 10 patients required further procedures, and five patients had irreversible damage. It is important for both oral and maxillofacial surgeons and ophthalmologists to recognize these complications for proper coordination of care and treatment.


Introduction And Background
Dental implants are a common dental procedure used to create support for prosthetic teeth.Although they are typically anchored by titanium rods placed in the maxilla, in cases of severe maxillary atrophy, there can be insufficient bone to create a stable attachment point for the implants [1].In the past, bone grafts were used to increase maxillary bone and create a stable implant.However, bone grafts require additional procedures for bone procurement, increasing morbidity, and require waiting months before implants can be placed [2].One alternative is the zygomatic implant.In zygomatic implants, additional longer zygomatic fixtures are placed to improve the stability of the implant and decrease reliance on bone grafts [1].These fixtures run through the maxilla to the anterior portion of the zygomatic bone, passing near the floor of the orbit [1].Although this technique has been in use for over 20 years, it remains a highly specialized technique due to the high degree of technical difficulty [3].One of the sources of this difficulty is the small area of dense zygomatic bone the implant must be placed in and its close proximity to the orbit, resulting in the potential for orbit penetration and ocular complications [1].Recently, computer-generated 3D models and dynamic navigational systems are being developed to make zygomatic implants easier to place, resulting in increased popularity of the procedure [3].
Although the theoretical complications of orbit penetration are often mentioned in the literature, the current literature of ophthalmologic complications of zygomatic implants consists of individual case reports and incidental findings in studies designed to find survival rates of zygomatic implants.This paper seeks to perform a systematic review of the current literature on eye and orbit complications from zygomatic implants.

Review Methods
This study was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.PubMed, Elsevier, and Google Scholar were used to search for articles written between 1980 and 2024 using the terms 'zygomatic', 'dental', 'implant', 'complications', 'eye,' and 'orbit' (last searched April 2024).Articles were screened out using title and abstract, followed by a full-text review by two reviewers to select articles to be included (Figure 1).Forward and backward citations were then checked for additional articles.The inclusion criteria were any articles that reported cases of damage to the eye or orbit as a result of zygomatic dental implants or implantation.Case reports, cohort studies, randomized controlled trials, and review studies were included.The exclusion criteria were articles not

Results
Twenty-four studies were found to contain cases of eye or orbit complications from zygomatic dental implants: nine case reports [5][6][7][8][9][10][11][12][13], one case series [14], nine cohort studies [15][16][17][18][19][20][21][22][23], one randomized controlled trial [24], and four review articles [25][26][27][28] (Table 1).After accounting for duplicates, 49 distinct patients were identified as having suffered ocular complications.Twenty-seven cases of infraorbital paresthesia, 11 cases of orbital penetration, four cases of orbital implantation, five cases of subconjunctival hemorrhage, four cases of periorbital hematoma, three cases of periorbital fistula formation, three cases of lateral rectus damage, two cases of inferior oblique damage, two cases of intraorbital hematoma, one case of recurrent orbital rim infection, one case of infraorbital nerve damage, one case of orbital compression syndrome, and one case of orbital wall defect with orbital emphysema.Symptoms included bleeding, restricted ocular range of motion, diplopia, esotropia, and proptosis, along with pain and swelling.Of the 49 patients who experienced ocular complications, outcomes were reported for 41 of them.Outcomes were generally favorable, with 88% (36/41) of patients experiencing full resolution of symptoms.Ten patients required surgical treatment, most commonly implant removal (4/10).Four patients experienced a permanent range of motion deficit and one patient experienced permanent sensory loss.

Discussion
Dental implants are a common procedure used in clinical practice to aid in the placement of dental prostheses.While most maxillary dental implants are placed in the alveolar ridge, edentulous patients experience bone atrophy and resorption, often leaving the maxilla unsuitable to support implants [1].As an alternative, the implantation of longer implants anchored in the zygomatic bone is an option that is increasing in popularity [3].These implants allow for immediate prosthesis placement and have a high survival rate ~98% [27].However, due to the technical difficulty of implantation, small area of dense zygomatic bone, and close proximity to the orbit, these implants come with the risks of improper drilling and implant placement, including the risk of rare but serious ocular complications.Orbital hematomas, perihematomas, emphysema, extraocular muscle damage, infraorbital infections, infraorbital nerve damage, and orbital fistulation, along with permanent ocular range of motion defects, diplopia, and esotropia, have been reported.

Orbital Penetration
The most severe ocular complication of zygomatic implant placement was orbital penetration.Ten cases of orbital penetration have been reported, with 30% (3/10) cases resulting in permanent ocular range of motion deficits [7,12,13].Due to the superolateral angle of drilling up from the maxilla, the orbit can be breached during drilling of the osteotomy in the inferolateral portion [15].Minor 'skirting' breaches of the orbital floor or lateral wall that occur by obliquely drilling through the superomedial portion of the zygomatic bone usually result in no long-term ocular consequences [15,18,19].More medial or deeper penetrations of the orbit can result in damage to the lateral or inferior rectus muscle and cause intraorbital adhesions resulting in ocular range of motion defects [13].Most cases of orbital penetration were discovered during or immediately after surgery [7,10,12,13,15].However, one case was found only on routine postoperative cone beam computed tomography (CBCT) [18].Orbital penetration was followed by orbital implant placement in 50% (5/10) of cases.Orbital implantation resulted in damage to the lateral rectus and/or inferior oblique in 60% (3/5) of cases, resulting in ocular range of motion loss, esotropia, or diplopia despite implant removal [3,7,9].However, some cases can have minimal consequences [18].There have been no reported cases of a ruptured globe; however, considering multiple cases of extraocular muscle damage have been reported, globe rupture remains a risk.
To decrease the risk of orbital penetration, Topilow et al. [13] suggested using a stainless steel plate (Bausch and Lomb E1069) placed in the inferior conjunctival fornix to protect the orbit and provide the surgeon immediate tactile feedback if the orbit is breached.Additionally, using the 'extrasinus technique' as opposed to an 'intrasinus technique' may allow for better visualization of the drill during the osteotomy preparation and decrease the risk of orbital penetration.The intrasinus technique typically involves starting the osteotomy from the residual maxillary alveolar ridge, transversing the maxillary sinus until penetration of the zygomatic bone [1].Due to the fact that the zygomatic implant transverses the maxillary sinus internally, visualization of the drill and implant is severely compromised.However, the 'extrasinus technique' utilizes a diamond barrel bur to create the initial osteotomy along the lateral wall of the sinus prior to entering the zygoma enabling better visualization [29].Zielinski et al. [30] suggested the use of a zygomatic orbital floor (ZOF) classification system to reduce the risk of orbital penetration.By measuring the difference in height from the most lateral to most medial portion of the zygomatic bone, practitioners can have a measure of the degree of undercut of the orbit to better plan surgery.Alternatively, dynamic navigation systems (DNS) have been proposed to decrease the difficulty of zygomatic implantation [3].By mapping current drill tip location to pre-surgically mapped 3D models, exact real-time drill location and direction can be determined.This allows the surgeon to control angulation during drilling to avoid the orbit.While these technologies are promising and becoming more available, no studies have determined their ability to decrease the risk of orbital penetration.Routine use of post-implantation CBCT may be useful in finding asymptomatic orbital penetration or implantation [15].
The incidence of orbital penetration during zygomatic implant placement is difficult to determine.Most cases are found as case reports, and no sufficiently large study has been done to determine its incidence.
Estimates therefore vary wildly with (5.9%-0.66%)[22,27,28].However, these are likely overestimates as studies that contain at least one case of orbital penetration are more likely to be included: leaving out the majority of studies which report none.Using the data obtained in a large-scale systematic review of the survival rates of zygomatic implants, of the 1,975 patients in cohort studies and randomized controlled trials for which complications were reported, two cases of orbital penetration were documented indicating the incidence to be roughly 0.1% [27].However, this method likely underestimates the incidence as these studies were not designed for analysis of orbital penetration, possibly resulting in some cases going unreported as complications.
Management for orbital penetration should be decided on a case-by-case basis.CBCT or CT is performed to visualize the location of the implant and orbital structures [7,10,12,13].If the implant was placed in the orbit, prompt removal was performed in all (5/5) cases.Other than removing the offending implant, treatment was limited to specific features, such as strabismus surgery for esotropia and drainage for hematomas [10,12,13].When esotropia remains despite implant removal, strabismus surgery should be considered as it resulted in improvement, although not resolution, of symptoms in all three cases [10,12,13].Zygomatic fistulation can occur secondary to zygomatic implants as a late-onset complication occurring months after implantation [9,14,25].Zygomatic implants can be a nidus for infection and inflammation, particularly when the implant penetrates through the zygomatic bone into subcutaneous tissue [6,9,31].

Other Ocular Complications
Implants should be placed with minimal penetration through the zygomatic bone to avoid complications, with greater penetration rectified by performing an implant apicoectomy [6,31].Alternatively, improper irrigation during surgery can lead to retained contaminated debris from the oral mucosa, resulting in chronic infection [9].Periorbital infection and fistulation can present with erythema, suppuration, and conjunctival chemosis.Treatment for fistulation includes antibiotics, implant apicoectomy, and fistulectomy reserved for refractory cases [9].Resolution of fistulas occurred in all reported cases following treatment, although one case reported contralateral fistulation months later [9].
Periorbital hematomas are commonly seen after a zygomatic implant procedure.Although only four cases are reported in the literature, this is likely due to their expected occurrence and benign course.The one study that reported periorbital hematomas found a 40% (4/10) incidence rate [21].All four cases occurred immediately or soon after surgery and resolved within one week.
Temporary infraorbital paresthesias are a common complication of zygomatic implantation.The paresthesia is usually self-limiting lasting between one week and three months after surgery [24,25]; however, some cases may be permanent [20].Davó et al. [24] found all 21 cases performed in one surgical center experienced some infraorbital paresthesia, while none did in other locations.They postulated that the use of wider mucoperiosteal flaps was used in this location to gain a better view of the maxilla and infraorbital region, which may have contributed to the high rate of infraorbital paresthesias.All patients in this study regained full sensation without paresthesias within three months after surgery.

Conclusions
Zygomatic dental implants are an effective method of securing dental prostheses for patients with severe maxillary atrophy; however, serious ocular complications can occur.The most common complication is infraorbital paresthesia, which often self resolves.Orbital penetration is the most severe complication and can result in permanent ocular range of motion restriction, esotropia, and diplopia.Other complications include hematomas, emphysema, infraorbital nerve damage, fistulation, and infection.Therefore, zygomatic implantation should only be undertaken by experienced surgeons trained in the procedure.Although multiple methods have been proposed to decrease the risk of ocular complications, including steel plate placement, extra sinus technique, zygomatic orbital floor measurements, and dynamic navigational systems, further research is necessary to test the efficacy of these methods in preventing orbital complications.