Abstract
The zygomatic implant is an alternative to bone grafting in extremely resorbed maxilla. This study evaluates the results of a consecutive cohort of 20 patients (mean age 56 years) with extremely resorbed maxillas provided with four zygomatic implants. The first 10 patients had a two-stage procedure, the next 10 next patients benefited from a one-stage surgical procedure and one of them had flapless guided surgery with Nobelguide ® in development and immediate function. The same surgical drilling protocol, according to B ranemark ‘s procedure, was applied to all the patients. Except for one patient who lost three implants, 18 patients received a fixed Procera ® implant bridge and another an overdenture retained by a screwed bar fixed on the four zygomatic implants. The cumulative survival rate after 40 months is 96%. Although bone augmenting procedures such as onlay grafts and sinus grafts are popular and well-documented, the four zygomatic implants procedure results in less morbidity, shorter delays between anatomical reconstruction and functional rehabilitation and can provide immediate or early loading with immediate function. Four zygomatic implants and a fixed bridge seem to be a valuable technique for the rehabilitation of extremely resorbed maxillas.
The rehabilitation of patients with an extremely atrophied maxilla is a challenge. Owing to the extreme resorption of the upper jaw, removable prostheses jeopardize masticatory function, speech and quality of life. Implant insertion and rehabilitation with fixed bridges are difficult in these patients because of the lack of bone.
Anterior alveolar bone resorption, pneumatization of the sinuses and limited bone volume in the posterior region reduce the possibility of inserting standard implants. For these reasons, many bone augmentation procedures have been proposed with high success rates and well-established protocols. Sinus lift, sinus graft or onlay grafts using various surgical approaches are commonly proposed with an overall success rate of 60–90% . Long-term results with apposition grafts with or without Le Fort I osteotomy have an 85–90% success rate . All of these techniques are well-documented.
Despite the good results, these techniques often require invasive and lengthy surgery, a long treatment time with delayed implant placement and some morbidity including sinusitis, contamination or exposure of the graft, risk of morbidity at the donor site and postoperative pain. Patients also have to wait for several months before being completely rehabilitated, and may have to remain edentulous without a removable prosthesis .
In the 1990s, B ranemark introduced an alternative to these bone grafting techniques : the zygomatic implant (Branemark system ® , Nobel Biocare, Goteborg, Sweden) called the zygomaticus fixture. The aim of this new implant was to obtain a steady anchorage in the zygoma bone for the posterior maxillary region bone quality type IV that does not allow insertion of standard implants, while adding two to four standard implants in the anterior region. The new protocol was first developed in a multicentre study and had a high success rate . Since then, several clinicians have used the same protocol and some have added modifications and guidelines. Bone volume in the anterior region can be sufficient to allowing the insertion of two to four standard implants, but not in the posterior region where two zygomatic implants add a posterior anchorage for supporting a fixed screwed prosthesis. If the bone volume is insufficient in the anterior region, small bone grafting can be added in the anterior region to allow for the insertion of two to four standard implants, two zygomatic implants being used for the posterior region . Bone anchorage of the zygoma is considered sufficient due to triple cortical strength even if trabecular bone density is unfavourable. The success of the zygomatic implants is related to the cortical strength of the zygoma bone .
Quality of life has been shown to increase with the use of zygomatic implants . The patient’s wishes should be evaluated by the clinicians. Even in complex cases such as maxillary defects, tumour resection and congenital disease , zygomatic implants can provide valuable rehabilitation for patients.
Soft tissue considerations should also be assessed. For anatomical reasons, zygomatic implants have some palatal outcome at the level of the second premolar. At this level, this parakeratinized epithelium surrounding the zygomatic implant, even if it is thicker (5 mm) than the crestal mucosa soft tissue, cannot be compared with periodontal pockets .
Several authors described oro-antral fistula that could be considered a severe complication needing antibiotics and/or aeration of the sinuses by meatotomies. Nevertheless the zygomatic implant technique simplifies the treatment of the severely atrophic maxilla, allows less invasive surgery, low cost hospitalisation, reduction of treatment time and pain with a success rate comparable with that of conventional implants .
The most common treatment uses two zygomatic implants and two to four anterior standard implants. The success rate obtained with the standard implants in the anterior region is 91–93% . Some maxillas are so resorbed that the insertion of standard implants is impossible.
Following the success rates obtained with zygomatic implants, and knowing that if there is insufficient bone height in the anterior maxilla, bone grafting is necessary and increases the length of rehabilitation, the authors have devised a procedure whereby four zygomatic implants are inserted to support the fixed prosthesis. The aim of this retrospective study in a cohort of 20 consecutive patients is to evaluate the results obtained with four zygomatic implants inserted in a severely resorbed maxilla with a fixed prosthesis screwed on top of them.
Material and methods
The patients’ general health was investigated clinically and radiologically. They were all edentulous in the upper jaw with extremely resorbed maxilla screened using panoramic radiography and spiral computed tomography (CT). The patients were given a choice between rehabilitation by means of bone grafting or the use of zygomatic implants; they chose zygomatic implants.
Postoperative controls were applied at 1 week, 1, 3, 6 and 9 months and then once per year after prosthesis placement. Prostheses were unscrewed and implants were separately tested for no pain, no mobility, and no infection.
Patients
All 20 patients (19 women; one man) with a mean age of 56 years (range: 35–75 years), were provided with four zygomatic implants from the Branemark System ® (Nobel Biocare, Goteborg, Sweden). The criteria used for proposing the four zygomatic implants were total edentulism in the upper jaw classes D and E according to the Lekholm classification, with a bone height of <5 mm in the anterior and posterior region due to the pneumatization of the sinus and alveolar bone resorption.
There was no possibility of placing standard implants in the anterior region without bone grafting because the alveolar rim lacked the height, thickness and arch perimeter. No patient was treated by chemotherapy or radiotherapy. Two patients had hypertension, two had diabetes, one had Sjögren’s syndrome and three were taking antidepressants. There were no smokers. The only contraindication was acute or recurrent sinusitis. The CT scan confirmed the integrity of the sinus; no sinusitis, polyps or any unusual pathology was discovered in any patient.
Pre-surgical procedures
All the patients had the same pre-surgical procedure. Radiological investigation consisted of orthopantomograms (OPGs) and spiral CT. The CT scan involved the zygomatic arch. A digitalized tridimensional reconstruction of the entire maxilla was carried out with Procera ® software (Nobel Biocare AB, Goteborg, Sweden). The dimensions and localisation of the zygoma implants were defined on computerized pictures before surgery ( Figs 1 and 2 ).
In one patient an additional impression was made for a surgical guide. The Nobelguide ® and teeth-in-an-hour ® procedures were used for one patient to make an ideal prosthesis regarding vertical dimension, phonetic and masticatory condition, occlusal balance, functional and aesthetic characteristics for the teeth before the surgery.
Surgical procedures
Surgery was carried out by two different surgeons (CM, PD). Eighteen patients followed the same surgical protocol. A customized guide was used for one patient. One patient received a Nobelguide ® and flapless surgery with immediate loading.
Preoperative treatment was 1 g of amoxicillin with clavulanic acid the day before and 3 h before surgery. All surgery was carried out under general anaesthesia in the 1-day clinic and all the patients received corticoids (methylprednisolone 32 mg) during surgery to prevent excessive swelling of the lips and face.
The incision, on the maxillary crest or 5 mm palatally to the crest, depending on the residual anatomy, went from one tuberosity to the contralateral tuberosity. A vertical releasing incision was performed bilaterally at the posterior end of the first incision as well as in the midline . The periosteal elevation of this flap exposed the entire maxillary process up to the zygomatic buttress. The infraorbital nerve was identified. With a round bur a horizontal bony window was made at the upper limit between the zygoma and the sinus to visualize the insertion of the zygoma implants in the zygoma bone. The classical protocol for drilling proposed by B ranemark was then followed . The implant length was verified with the depth indicator and the tip of the implant was observed by the surgeon at the top of the zygoma.
The anterior implant was first inserted with a low speed motor and with the manual driver to give the desired fixture head position in accordance with the prosthetic work. The emergence point of the first implant was at the level of the second incisor or canine. The posterior zygomatic implant was installed following the same sequence. The emergence point of the second implant was at the level of the second premolar–first molar. All the zygomatic implants were stable at the time of the placement.
After implant insertion, either a cover screw was placed on top of the implants and the soft tissue closed (two-stage procedure; 10 cases) or an abutment (one-stage procedure) for performing early or immediate loading (10 cases).
In the case in which the Nobelguide ® was used, no flap was raised following the Nobelguide ® protocol. The four zygomatic implants were inserted and a permanent prosthesis screwed on the implants on the day of surgery (teeth-in-an-hour ® ). The distribution lengths of implants was 30–52.5 mm.
All patients received antibiotic prophylaxis (2 g of amoxicillin with clavulanic acid per day for 4 days) and analgesics (codeine phosphate and paracetamol) to minimize postoperative pain. Patients had to rinse their mouths carefully with chlorhexidine after each meal.
In the two-stage procedure, the delays before the second stage were 2, 3, 4 and 5 months.
Prosthetic procedures
For the two-stage procedure (10 cases), the abutments were placed at the second-stage surgery and an immediate (same day) provisional fixed prosthesis was provided for seven patients. Three patients were not provided with provisional fixed prosthesis but with a removable re-adapted one for 2–3 months.
For those undergoing the one-stage procedure (10 cases), an acrylic provisional fixed prosthesis was provided the day of surgery or a couple of weeks later.
One patient received an immediate definitive prosthesis at the time of surgery with the teeth-in-an-hour ® concept (Nobel Biocare AB, Goteborg, Sweden).
All the patients benefited from a definitive fixed prosthesis with a titanium frame Procera ® implant bridge (Nobel Biocare AB, Goteborg, Sweden) and acrylic, except for one patient who received an overdenture retained by a rigid bar ( Fig. 3 ).
Follow-up procedures
OPGs ( Fig. 4 ) or X-rays were not taken systematically because they do not provide much information because of superimposition of the bony structures, deformation of the zygoma implants (OPG), and difficulty in standardising retroalveolar X-rays. Only clinical investigations were performed.
Clinical investigations to assess pain, infection, stability of the implant, control of plaque and inflammation, and occlusal adjustment were performed after 1 week, 1, 3, 6 and 9 months and 1 year during the first year and then once a year after prosthesis placement. Only survival rates were proposed because of the lack of information given by radiological examination.
Results
The survival rate of the implants after 3 years is 96% (77 implants of 80). The failure rate is shown in Table 1 . The cumulative failure rate was calculated using the following formula:
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