Study protocol

This was a prospective observational clinical study on the treatment of patients with a severely atrophic maxilla. All subjects underwent surgical implant placement and immediate prosthesis delivery at a private dental office in Lisbon, Portugal, performed by one surgeon (EA) with experience in full-arch rehabilitations and immediate loading procedures. The final prostheses were made in Bollate, Italy, by a small group of clinicians with experience in full-arch rehabilitations and prosthetic protocols. The investigation was conducted in accordance with the principles of the Declaration of Helsinki, as revised in 2004, and was approved by an independent ethics committee (Ethics Committee for Health, Lisbon, Portugal).

At the preliminary visit, detailed information regarding the nature of the study and any possible alternative treatment was provided to all patients. Written informed consent was obtained before enrolment. A total of 15 patients (13 female and two male) were treated consecutively between October 2008 and April 2010. The mean age on the day of surgery was 62 years (range 46–70 years). All patients were followed for a minimum of 6 years (range 73–91 months, average 85.04 ± 7.23 months).

Inclusion and exclusion criteria

Inclusion criteria were the following: patient of any race and sex; fully edentulous maxilla with severe resorption of the posterior ridges preventing implant placement in the pterygoid area or conventional fixtures without prior sinus grafting (Cawood and Howell class 5 or 6 ); inadequate bone volume up to the canine region to place implants of at least 3.3 mm diameter and/or 10 mm in height; good general health condition; and physically and psychologically able to undergo a surgical procedure under general anaesthesia (American Society of Anesthesiologists (ASA) class 1 or 2) and subsequent restorative procedures chair-side.

The following exclusion criteria were applied: the presence of active infection or inflammation at the sites intended for implant placement, in the maxillary sinus or in the osteomeatal complex; presence of systemic disease (i.e. haematological disease, uncontrolled diabetes, serious coagulopathies, or disease of the immune system); irradiation to the head and neck region within 60 months before surgery; treatment with bisphosphonates at any time; heavy smoking habit (more that 20 cigarettes/day); severe bruxism or clenching; emotional instability or unrealistic aesthetic expectations; poor oral hygiene; and poor motivation to return for scheduled follow-up visits. Twelve subjects were excluded because of the presence of at least one of the aforementioned conditions.

Preoperative evaluation

Preliminary screening was performed using panoramic radiographs, radiography of the skull in lateral view, and a computed tomography (CT) scan, with imaging including the zygoma and osteomeatal complex. A clinical examination was conducted with particular attention to the amount of keratinized gingiva and to all prosthetic references, such as the occlusal vertical dimension, smile line, lip support, and inter-arch relationships (vertical and horizontal overlap). If an improper vertical dimension was noted, a denture with a new dimension was delivered for 6 months, and any sign of temporomandibular joint pathology or patient discomfort recorded.

Surgical planning was based on CT scan observations, although the final decision concerning the implant configuration was made intraoperatively. According to bone availability, two options were considered: four zygomatic implants (All-on-4 Extra-Maxilla, or All-on-4 Double-Zygoma; Nobel Biocare AB, Göteborg, Sweden) or two zygomatic implants in combination with two conventional fixtures in the anterior maxilla (All-on-4 Hybrid; Nobel Biocare AB), as described previously . The zygoma implants used in this study had a straight head ending with an external hex, a 5-mm diameter body, and a narrow tip with active threads for the engagement of the zygomatic bone. The threads were not present in the coronal half of the implant and the whole surface was anodically oxidized (TiUnite; Nobel Biocare AB). The available lengths ranged between 30 mm and 50 mm.

Surgical and prosthetic protocol

Antibiotics were given 1 h prior to surgery and daily for 6 days thereafter (2 g of amoxicillin 875 mg + clavulanic acid 125 mg, Clavamox DT 1 g; Bial Laboratory, S. Mamede de Coronado, Portugal). It was recommended that chlorhexidine digluconate 0.20% mouthwash be used three times a day starting 3 days before surgery and continuing for 7 days postoperative (EludrilPerio; Pierre Fabre Laboratory, Lisbon, Portugal). All surgeries were performed under general anaesthesia in an operating room. Articaine chlorhydrate 4% with epinephrine 1:100,000 (Artinibsa c/EPI; Laboratórios Inibsa S.A., Sintra, Portugal) was used, providing local infiltration in the vestibular area of the maxilla up to the zygoma, followed by bilateral block of the greater palatine nerve. In order to control the inflammatory response, corticosteroid medication (Meticorten; Schering-Plough Farma Lda, Agualva-Caćem, Portugal) was given daily with a tapering dose (15 mg at surgery, 10 mg on the first 2 days postoperative, and 5 mg on days 3 and 4 postoperative). Anti-inflammatory medication (ibuprofen 600 mg; Ratiopharm Lda, Carnaxide, Portugal) was administered every 12 h on days 4 through 8 postoperative and an analgesic (Clonix 300 mg; Janssen-Cilag Farmaceutica, Barcarena, Portugal) was given postoperatively for the first 3 days if needed.

A linear incision was made slightly towards the palate, from the molar area to the contralateral side, with two vertical incisions over the zygomatic process. A mucoperiosteal flap was raised in the same way as for a Le Fort I exposure, giving direct vision of the piriform rim and of the body of the zygomatic bone with its inferior edge. Isolation of the infraorbital nerve and identification of the masseter muscle insertion were conducted, these representing the superior and inferior limits for the zygomatic fixtures. The palatal mucosa was also reflected to avoid interference during the drilling phase. When necessary and depending on the morphology of the residual alveolar process, regularization of the ridge was performed with bony forceps and rotary instruments to remove knife edge ridges.

Patients were treated with the All-on-4 Extra-Maxilla or All-on-4 Hybrid protocols based on the preoperative evaluation and the intraoperative decision of the surgeon. The zygomatic implants were placed following the protocol described previously by Maló et al. , and with the aim of optimizing the primary stability of the fixtures. Implant insertion was driven by local anatomical conditions, respecting the integrity of the infraorbital nerve, the orbit, and the infraorbital fossa. The osteotomy was conducted as posterior as possible, keeping a safe 3-mm distance from the posterior vertical edge of the zygomatic bone. When the path of the zygomatic implant had been visualized, surgical burs were used to create a channel starting from the residual crest and proceeding on the buccal surface of the maxillary body. Once the sinus membrane had been exposed, manual instruments were used to gently push it inwards with the aim of preserving its integrity and to make space for the drills ( Fig. 1 ). The zygomatic implants were placed in a space created between the membrane and the zygomatic bone, with their body located in the sinus cavity. The apico-coronal position of the platform relative to the residual crest was determined by the surgeon according to prosthetic needs.

One of the key aspects of the extramaxillary approach is the anchorage gained in the zygomatic bone, with the fixture inserted external to the Schneiderian membrane, thereby maintaining its integrity. A diamond bur is used at the beginning of the osteotomy, to start the preparation of the surgical site tangent to the maxillary bone. Once the membrane is exposed, it is pushed gently inwards into the cavity to gain sufficient space for the drills.

With the All-on-4 Extra-Maxilla protocol, the posterior zygomatic implant usually emerged at the level of the second premolar, while the head of the anterior fixture was located at the level of the lateral incisor ( Figs 2 and 3 ). With the All-on-4 Hybrid protocol, in addition to one zygoma fixture on each side, two standard implants (NobelSpeedy Groovy; Nobel Biocare AB) were positioned close to the midline ( Figs 4–6 ). In order to compensate for implant inclination, abutments angulated at 30° (Nobel Biocare AB) were placed on the zygomatic fixtures in such a way as to obtain a suitable emergence of the prosthetic screw. Abutments angulated at 17° or straight abutments were positioned on standard implants.

Surgical placement of four zygoma implants in a completely resorbed maxilla. Threads are only present in the apical part of the fixture that has anchorage within the zygoma, while the first half of the implant body has a rough surface that will be covered by soft tissue.

Radiograph of the skull showing the distribution of zygomatic and conventional fixtures in the treatment of a case of advanced edentulism.

The extramaxillary approach allows the clinician freedom in the apico-coronal positioning of the zygomatic implants. Anchorage is guaranteed by the mechanical engagement of the zygomatic bone. The zygomatic fixture on the left side has been positioned subcrestally to reduce the buccopalatal extension of the final prosthesis.

The 30° angulated abutment and more apical position of the zygomatic implant platforms allows the delivery of a fixed prosthesis that does not invade the space for the tongue, even in the case of centripetal resorption of the posterior maxilla.

Panoramic radiograph showing the rehabilitation of a severely atrophic maxilla with a fixed prosthesis, supported by one zygomatic fixture on each side and two conventional anterior implants.

The flap was subsequently sutured trying to create a collar of keratinized gingiva around each fixture. A custom open tray and silicon polyvinylsiloxane putty was used for impression, and a full acrylic prosthesis containing 10 teeth was delivered within 3 h. Occlusion was limited from canine to canine without any interference in lateral excursion.

The patients were instructed to avoid brushing or any trauma to the surgical site for 2 weeks. Cold food was recommended for the first day and a soft diet for the first week. Six months after the surgery, computer-aided design and computer-aided manufacturing (CAD/CAM) Procera titanium prostheses with acrylic or ceramic teeth were constructed according to the patient’s selected choice and based on the opposing dentition (Procera Implant Bridge; Nobel Biocare AB).

Data collection and follow-up

Patients were scheduled for weekly postoperative control in the first month. Prosthetic functionality and tissue healing were assessed at each appointment. The level of oral hygiene was evaluated by a graduate dental hygienist every 3 months in the first year and then twice a year. A panoramic radiograph was taken every 6 months for the first 2 years and yearly thereafter. Peri-apical films were obtained only for the standard implants because of difficulties in achieving a proper film alignment due to the lack of palatal concavity in almost all cases.

Bone level measurements were performed by calculating the distance between the fixture and the most coronal point of the peri-implant bone, on both the mesial and distal side, using the implant–abutment junction as a reference point. To adjust for dimensional distortion and enlargement on the radiographs, the actual sizes of the implants were compared to the measured implant dimensions on the radiographs. At the 1-year follow-up visit and then annually, the prostheses were unscrewed and any screw loosening was recorded. The stability of each implant was tested clinically with the pressure of two opposing instruments. The torque of the abutment screw was checked for every implant. Any complication with the prosthetic components was also recorded.

Every time the restoration was removed, the plaque index and bleeding index were evaluated. A plastic periodontal probe (Perio-Probe; Kerr Corporation, Bioggio, Switzerland) was gently inserted 1 mm apical to the mucosal margin. Each implant was examined on four aspects (mesial, distal, buccal, and palatal), and any site where plaque could be detected with the naked eye or with a probe accounted for 6.25% (1/16), with a possible total score of 100%. The same was done for the bleeding index: any site that showed bleeding during the examination was considered positive. At the same visit, the probing pocket depth was assessed at four sites for each conventional fixture and at the mesiopalatal and distopalatal aspects for the zygomatic implants. Probing depths equal or superior to 4 mm were recorded.

Primary outcome measures

The outcome measures for this study were prosthetic success, implant success, and biological complications.

Prosthetic success was defined as a prosthesis that was in function, without mobility or pain, even if one or more implants were lost. Prosthesis stability was tested by means of pressure between two opposing instruments. The prosthesis was judged as a failure if the implants on one side of the arch were lost.

Implant success was defined according to the following criteria : (1) the implant fulfilled its function as support for the reconstruction; (2) it was stable when individually and manually tested upon removal of the prosthesis; (3) no signs of persistent pain or infection were observed; (4) no radiolucent areas indicative of an encapsulation were observed around the implants, as evaluated on peri-apical radiographs or panoramic films. If an implant did not fulfil all of these requirements but remained in situ, it was considered an implant that had survived. In the case of implant removal, this was considered a failure.

Biological complications, such as sinus membrane perforation, peri-implant mucositis, peri-implantitis, soft tissue recession with oral exposure of the implant rough surface, maxillary sinus infection, paresthesia, fistula or abscess, or any mechanical or prosthetic complications, such as fracture of the implant or of any prosthetic component, were recorded.

Secondary outcome measures

For conventional fixtures, marginal peri-implant bone level changes were measured on peri-apical films, as described previously. After removal of the prosthesis at the annual visit, the plaque index, bleeding index, and probing depth were recorded as mentioned above. The sites at which plaque or bleeding could be detected were scored as positive or negative. Sites with a probing pocket depth equal or superior to 4 mm were noted.

Patient satisfaction with function, aesthetics, and phonetics was assessed by means of a questionnaire before surgery, at 6 months after surgery (just before delivery of the final prosthesis), and then at 1, 3, and 6 years of follow-up . The answers were based on a 5-point Likert-type scale, ranging from 1 (‘poor’) to 5 (‘excellent’).

Statistical analysis

SPSS 11.5.0 software (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. The plaque index and bleeding index scores were reported as the mean ± standard deviation values.