Prosthetic Rehabilitation with Zygomatic Implants after Maxillectomy: A Systematic Review

TABLECREATED

Table 3: Details of the included studies.

Surgery

Reconstruction was performed in 8 patients and consisted of the use of soft-tissue flaps (temporalis muscle: 2; latissimus dorsi: 1; fasciocutaneous radial forearm: 1; fat pad: 2; skin flap: 1; and type not available: 1). For 9 patients, the type of flap was not clearly stated.

Radiotherapy

Radiotherapy was performed after implant placement in 17 patients, with radiation doses ranging from 50 to 63 Gy, when available. For the 16 remaining patients, there no radiotherapy was provided, or it was not mentioned in the articles.

Number of implants

Eighty-six ZIs were placed on the resected side of the maxilla; 8 ZIs were lost; and 1 ZI was associated with biomechanical complications. Of the 78 remaining implants, 4 [11] were custommade subperiosteal implants supported by the zygoma, and 2 were placed using a “reverse” technique [7].

Type of prosthesis

A maxillary obturator prosthesis was placed in 12 patients, a fixed (screwed) prosthesis in 10 patients and a removable denture in 4 patients. The type of prosthesis was unclear in 10 patients (removable or obturator prosthesis). The types of attachments used for patients who underwent rehabilitation with removable dentures (obturator or not) were screws for fixed prostheses or a prosthetic bar (combined or not with Locator^®) in 11 patients, a specific anchoring system in 1 patient, and magnetic attachments in 3 patients.

Quality of the studies-risk of bias

The level of evidence of the articles was low, as only case reports or short case series were included. Therefore, no meta-analysis could be performed. Nonetheless, as the aim of the study was to collect data for therapeutic decisions, the review resulted in a more consistent series.

Several biases were identified. First, the number of patients had to be reinterpreted, as Ozaki published twice the same case (in 2016 and 2018) [9,13]. In one study [14], some patients were treated with zygomatic implants due to an extremely resorbed maxilla and were not after maxillectomy, so the number of ZIs had to be cautiously interpreted. In 2 studies [14,16], the types of prostheses and attachments remained unclear, as the authors mentioned either obturation of the defect by a flap or by an obturator prosthesis. However, these factors have little influence on the ZI success rate, occlusal force and prosthetic durability. Some missing data could have influenced the interpretation of the results: there was a lack of data concerning radiotherapy; a lack of data concerning the time of radiotherapy (before or after ZI placement, time interval between radiotherapy and ZI placement); and a lack of data concerning the types of prostheses or attachments. In these cases, photos of the patients had to be used when available to assess the types of attachments used. Additionally, data regarding oral hygiene (which might have compromised the ZI success rate) were not reported.

Conclusion

Number of implants required

In this study, Pellegrino’s classification was preferred for the classification of defects because it proposed a defect classification related to prosthetic rehabilitation with zygomatic implants, depending on the size of the defect [3]. Pellegrino proposes a 3-class classification system with 3 subclasses. Class I represents a bilateral maxillectomy, requiring 4 ZIs. Class IIA represents a partial maxillectomy with remaining dentures, requiring 1 or 2 ZIs on the resected side and 1 on the contralateral side. Class IIB represents a partial maxillectomy in an edentulous patient, requiring 2 ZIs in the resected part and 2 conventional implants contralaterally. Class IIC represents a partial maxillectomy in edentulous patients with bone atrophy, requiring 2 ZIs on the resected side and 1 ZI on the opposite side. Class III represents an anterior maxillectomy, requiring either ZIs if there is bone atrophy or conventional implants if the bone volume is sufficient [3]. This classification and recommendation system for ZIs has also been preferred by Salvatori [12]. For classes IIa and b, the lack of precision in the number of patients is due to a lack of precision regarding the remaining dentures in the study by Atalay [14] and of the conversion between Brown’s and Pellegrino’s classifications in the study by Butterworth [10].

Success rate and specific risks of failure

The ZI success rate ranges from 95.8% to 99.9% [2]. In this review, the success rate was 96.38%, but the follow-up times differed from one study to another.

Most ZI failures appeared within the 6-month surgical period, which occurs during the second-stage period, consistent with the results of Chranovic [2]. The main features of conventional ZIs are sinusitis, fistula, soft-tissue infection, paresthesia, and oroantral fistula, leading to loss of osseointegration. Smoking, radiotherapy, and cantilever force also increase the failure risk [19]. In this series, 39 ZIs were reported to be immediately placed at the time of reconstruction and 19 ZIs with secondary placement. There were 4 ZI failures: 3 in the 6-month postoperative period and 1 at a later time. Immediate placement seemed to be preferred.

Overloading of zygomatic implants could be one of the causes of implant loss [13,14]. Special care regarding biomechanical forces is required [5], especially in maxillectomy patients where no alveolar bone anchor is available. Akay [20], in a finite element analysis study, highlighted that the placement of 2 ZIs on each side of the maxilla was better than using conventional implants on the nonoperated side. Furthermore, increasing the number of implants was not mandatory. Occlusal forces should be given great attention on the nonoperated side [20]. In contrast, Atalay [14] preferred using conventional implants on the nonresected side.

External radiotherapy is also known to increase the risk of implant failure [16]. Schmidt [16] proposed ZI placement at the time of resection and at the beginning of radiation therapy within 2 to 3 weeks. In cases of secondary placement, implant loading often has to be delayed. In this series, 6 of 28 cases of ZI placement failed, of which 5/6 implants were placed in irradiated patients. Boyles- Varley [21] reported a series of 20 ZI patients in which 6 patients were irradiated without any cases of failure after an 18-month followup. The optimal time interval between implant placement and the beginning of radiotherapy ranges from 2 to 3 weeks [16] to 8 weeks [21]. Analysis of the cases following Pellegrino’s classification and recommendation was performed and showed some differences between Pellegrino’s recommendations and the number of implants placed. In most cases, the authors tried to remain in accordance with Pellegrino’s recommendations. Differences could be explained by local constraints such as the number of remaining teeth, patient’s sleight, or anatomical constraints. One author [16] who published results before Pellegrino seemed to have placed more implants than the number found in recent studies. It has been proven that the number of implants is not a major biomechanical factor for implant survival [20].

Flap closure

Using flap closure allows the closure of the defect and isolates zygomatic implants from the oral cavity [6]. Local or locoregional flaps such as temporalis muscle flaps or fasciocutaneous free flaps such as radial forearm flaps [10] allow separation between the sinus and the oral cavity, restoring etancheity [3,12]. Soft-tissue flaps can be placed in vascular compromised patients and/or in elderly patients [10]. Nonetheless, conventional implants cannot be placed with these flaps. Butterworth [10] suggested a ZI-perforated microvascular softtissue flap for the rehabilitation of maxillectomy patients, which is of great interest by Brown for class 2B patients [9] – i.e., class IIa or b according to Pellegrino’s classification. No correlation could be found between reconstruction (or not) and the type of defect or between the type of flap and the type of defect. Flap overgrowth (over ZI emergence) was observed, and Butterworth [10] proposed the placement of a small polythene disk around the ZI to prevent this overgrowth. Without flap closure, ZIs allow simple postoperative observations [13].

Chronology of the treatment

Despite some heterogeneity in the different studies, the immediate placement of zygomatic implants during resection and flap reconstruction seemed to allow a better success rate [10,19], especially if postoperative radiotherapy was mandatory. Indeed, placement allowed primary osseointegration before radiotherapy [12], which limited the possible adverse effects of implant placement on osseointegration. Furthermore, placement of the zygomatic implants when performing the maxillectomy allowed direct vision of the zygoma, thus making it easier to place the implants [12]. The use of computer-aided systems and planification remain mandatory for better predictability [3]. Immediate loading is possible due to the high initial stability of ZIs. Immediate versus secondary loading is controversial; some authors think that it is preferable, whereas others [14] admit that the relationship between the loading and success rates is unclear. It seems that immediate loading is preferable in cross arch rehabilitations, with solidarization of the ZI, whereas it must be discussed in unilateral rehabilitations [8], especially in oncologic patients.

Screwed retention bars can be associated with fasteners [8]. Between ZI placement and loading, small polyethylene disc cuts surrounding the implants can be placed to prevent flap overgrowth [9].

Prosthetic considerations

Prosthetic management depends on the number of implants placed, the presence or absence of reconstruction, the number of residual teeth, and the type of bone defect. A trapezoid prosthesis basal design should be preferred [22]. Obturator prostheses may have a high score in terms of quality of life and functional results [9]; however, the results highly depend on the extent of the resection, particularly in its horizontal component, which influences the stabilization and retention of the prosthesis [8] and on the eventual remaining teeth needed to support the prosthesis [9]. The use of implants and ZIs has dramatically increased the effectiveness of the prosthesis in these cases.

Different attachments are described in the literature: magnetic, telescope or screwed prostheses [19]. To overcome the increased failure risk due to overloading, the use of magnetic attachments with weak forces can be proposed [9,13]. Maintenance is easier than with ball attachments, with however the remaining problem of the lateral forces that may mobilize the prosthesis. Thus, magnetic attachments can be used in cases of obturator prostheses because the obturator provides lateral stabilization of the prosthesis. Stabilization of the obturator prosthesis with ZIs avoids the superior displacement of the prosthesis in the maxillectomy cavity [19]. However, the risks of implant fracture and peri-implantitis remain.

Temporary prostheses are often necessary because of the need for flap monitoring in the immediate postoperative period [10,21]. Fitting is recommended during a 4- to 6-week postoperative period [10].

Quality of life

Quality of life seems to be comparable between ZI-supported obturator prostheses and fixed prostheses [19]. Primary closure of the defect should be preferred over obturator prostheses [12]. Obturator prostheses are easy to remove and allow easy local followup [11]; cleaning of the flap and prosthesis is easier. For conventional implants, the surgeon must keep in mind the final goal, which is the prosthesis, and thus place “prosthesis-driven implants “[11]. Several quality of life studies have compared obturator prostheses and free flap reconstruction and have not shown any significant differences [23,24].

Outcomes

Regarding the review of the literature, in maxillectomy patients who are noncandidates for free flap reconstruction, the rehabilitation proposal should first answer the following question: is the patient a candidate for soft-tissue rehabilitation? In addition to surgical criteria, the size of the defect, patient prognosis and patient sleight can help answer this question. Depending on the decision of soft-tissue defect closure, additional criteria should be considered for the prosthetic decision: the number of implants and their distribution, which allows different biomechanical conditions; the number of remaining teeth; oral hygiene, which is more difficult in cases of fixed prostheses; and aesthetic considerations, especially in cases of anterior defects (class III of Pellegrino’s classification). Figure 2 summarizes the different prosthetic treatments proposed in the case of maxillectomy regarding Pellegrino’s classification.

    

    

    Figure 2: Decision tree for prosthetic treatment regarding general and secondary criteria and Pellegrino’s classification.