Immediate Oral Rehabilitation With Quad Zygomatic Implants: Ultrasonic Technique vs Conventional Drilling

A severely resorbed edentulous maxilla represents a unique challenging condition when inserting conventional dental implants. Excessive bone resorption combined with poor bone quality, insufficient bone height, and pneumatization of the maxillary sinus are the major limiting factors for anchoring dental implants.^1–3  As an alternative to grafting techniques, several treatment modalities such as short implants, tilted implants, and zygomatic implants (ZIs), have been proposed in the literature.

In the 1990s, ZIs were introduced as implants that are anchored into the zygomatic bone.^4–9  Initially, ZIs were proposed for the prosthetic rehabilitation of patients with extensive defects of the maxilla caused by tumor resections, trauma, or congenital defects, as well as for patients who are edentulous and have severely atrophic maxilla.^4,7  Since Brånemark first described ZIs, many surgical protocols and guidelines have been proposed for ZIs, along with improvements and variations.^4–6,10  This kind of surgery has become more popular since patients are increasingly demanding a therapy that can offer good final results with reduced costs and time.¹¹  Zygomatic implants give surgeons the possibility to obtain a firm anchorage to the zygomatic bone with 2 to 4 implants.^12,13  Total treatment time decreases dramatically, especially when ZIs are loaded immediately after placement, which represents a favorable condition for patients seeking esthetics, function, and comfort.⁶  However, the placement of ZIs is a major surgical procedure associated with some risks and difficulties because of neighboring critical anatomic structures, such as the infraorbital nerve, orbit, and infratemporal fossa. Additionally, major complications, such as oral-antral communication, sinusitis, paresthesia, mucositis, peri-implantitis, penetration of the orbital cavity during the drilling protocol, cutaneous fistula, and failure of the implants, can be associated with the ZIs.^14–18 

The major limitations in ZI surgery are related to the reduced surgical visibility and instrument control. Currently, most of the surgical drilling protocols described in the literature use long drilling burs, which may be a limitation to the precise control of the axial preparation of the implant site.

As an alternative to conventional instruments, piezoelectric devices were developed for the atraumatic cutting of bone with ultrasonic vibrations. There has been extensive research on indications of piezosurgery in the fields of oral surgery, periodontology, and implantology. Piezosurgery permits more precise bone cutting with improved intraoperative management. Better control of osteotomies can be performed compared with traditional procedures that use bone burs and saws.^19–23 

In 2015, the research group of this study published preliminary results of a surgical technique with quad ZIs, which included the use of ultrasonic device; a 100% survival rate was reported with no adverse events.²¹  This pilot study showed that ultrasonic implant-site preparation for ZIs can be a feasible alternative to the conventional drilling technique.

The primary aim of this study was to compare the outcomes and postoperative complications of the rehabilitation of extremely edentulous maxillae with quad ZIs, using traditional drilling technique vs ultrasonic preparation. The secondary aim was to evaluate operative time and surgical difficulty from the operator's perspective.

The study was designed as a prospective clinical case-control study with a total of 92 patients who were referred to the 2 dental offices in Turin and Viareggio, Italy, between September 2015 and June 2017. Patients were treated according to the principles of the World Medical Association Helsinki Declaration of 1975 for biomedical research involving human participants, as revised in 2000. All patients received information about the study protocol and signed an informed consent form before being enrolled in this study. The study protocol was approved by the institutional review board of the Orthopedic Institute Galeazzi.

Initially, the patients were radiologically evaluated with preoperative panoramic radiographs and cone beam computerized tomography scans. The latter were obtained to assess the size and form of the zygomatic and maxillary bone and to exclude maxillary sinus pathologies.

The inclusion criteria were total edentulous maxilla requiring total fixed rehabilitation together with any of these following situations: (1) severe atrophy (Class IV or V Cawood and Howell²⁴ ) with less than 5 mm in all regions of the maxilla, (2) inability to place standard implants in the maxilla without prior bone grafting, and (3) patients not willing to undergo a grafting procedure.

The exclusion criteria for the use of ZIs were the following: uncontrolled coagulation disorders, uncontrolled metabolic disease (eg, diabetes mellitus, bone pathologies), acute myocardial infarction within the previous 6 months, radiotherapy to the head or neck within the previous 24 months, past or present treatment with intravenous bisphosphonates, immunosuppressed or immunocompromised status, acute sinusitis, poor oral hygiene and motivation, pregnant or lactating, and inability to return for standard follow-up controls up to 5 years.

Based on the aforementioned criteria, 92 patients (50 women and 42 men) with a mean age of 60.6 ± 6.3 years (range = 48–71) were included. All the patients underwent the placement of 4 ZIs. A total of 368 ZIs NobelZygoma (Brånemark System, Nobel Biocare) were placed and immediately loaded with fixed full-arch prostheses. The ZIs used were either fully or partially threaded (with an unthreaded implant body to interface with soft tissue, and a threaded apical end).

Patients were divided into 2 groups: 47 patients were treated with ultrasonic preparation (test group with 188 implants), and 45 patients were treated with conventional drilling technique (control group with 180 implants). The surgical approach, presurgical procedure, prosthetic procedure, and follow-up protocol were the same as described in a 2015 article published by the same research group.²¹ 

A careful examination and surgical planning were done for each patient using the radiologic documentation by a 3-dimensional (3D) reconstruction of the entire maxilla (Figure 1a and b). Localization of the quad ZIs was planned before surgery using the NobelGuide program (Nobel Biocare) and was simulated on a 3D reconstruction model (Figure 2a and d: test group; Figure 3a and d: control group). Preoperative photographs for the esthetic analysis were obtained, and preliminary impressions were made. A customized guide was fabricated to identify the best implant positioning over the crest for a correct alignment with the prosthesis. The same guide was then used at the end of the surgery to take the impression and verify the occlusal position for immediate loading and prosthesis finalization.

A blood test, electrocardiography, and chest radiography were performed to evaluate the patients' general health status. One week before surgery, a professional oral hygiene session was given to each patient. Patients underwent oral rinses with chlorhexidine digluconate 0.2% mouthrinses 3 days before the surgery. All patients were prescribed pre- and postoperative antibiotics: amoxicillin/clavulanate potassium (Augmentin, GlaxoSmithKline) at a dosage of a 1-g tablet every 8 hours for a total of 6 days, starting the evening before the surgery, or erythromycin (Klacid, Abbot) at a dosage of 500-mg tablets for 7 days, when an allergy to penicillin was declared.

All surgeries were performed by the same surgeon (M.M.) under general anesthesia with blood pressure, pulse, and oximetric parameters monitored by an anesthesiologist. Consecutive patients were alternately assigned randomly to the test or control group.

After flap reflection, in the control group, all bone surgeries and the implant-site preparation were performed using a standard drilling technique (Figure 4). In the test group, such procedures were performed using the ultrasonic technique with the SURGISONIC MOTO System (Esacrom SRL) (Figure 5). The latter consisted of an ultrasonic hand piece with a functional frequency from 22 000 to 35 000 Hz. The implant site preparation and groove osteotomy were performed with the Surgisonic ZYGOMAKIT by Esacrom working tips. All zygomatic fixtures were carefully inserted at a low speed (20–40 rpm), with a torque of 50 Ncm, followed by the final stabilization performed manually with an extraoral screwdriver. The ZIs were anchored in the zygomatic bone with stabilization at the level of the maxillary alveolar process. The anterior implants that emerged from the canine to the lateral incisor region were always the first to be inserted (Figure 6a through e).

In brief: 202 ZIs were inserted with the extrasinus technique (Figure 7), 77 ZIs were inserted with the sinus slot technique,²⁵  and 89 ZIs were inserted with the Brånemark technique (Table 1). The wounds were closed with continuous resorbable sutures (Vicryl, Ethicon FS-2, Johnson & Johnson).

At the end of surgery, panoramic radiographs were taken to have a general overview and to assess implant positioning (Figures 8 and 9). The total surgical time from flap incision to suturing was recorded. After each surgery, the surgeon filled in a visual analogue scale (VAS) assessing the surgical difficulty. For this evaluation the surgeon was asked to score feelings about surgical stress on a 10-cm VAS scale, with 0 cm reflecting no stress and 10 cm reflecting the worst stress possible.²⁶ 

The prosthetic procedure followed the protocol previously described by Mozzati et al.^27,28  Light-curing acrylic resin was used to connect the temporary cylinders to the resin customized guide using a vinylpolysiloxane precision impression material. Healing caps were screwed on the multiunit abutments to prevent soft tissue closure during the provisional prosthesis restoration. Complete arch acrylic resin provisional prostheses reinforced with metal connections laser welded to the titanium temporary multiunit cylinders (Nobel Biocare) were inserted 3 to 5 hours after surgery.

Postoperative control radiograms were taken at the same day of the surgery. The patients were recalled for clinical follow-ups after 3 days, 1 week, 2 weeks, 1 month, 3 months, and 6 months. Patients were then enrolled in an oral hygiene program, with recall visits every 6 months. At each visit, the oral hygiene level and condition of the soft tissue surrounding the ZIs were assessed by evaluating the full-mouth plaque score (FMPS) and the full-mouth bleeding score (FMBS). These parameters were evaluated at the mesial, vestibular, distal, and palatal aspects of the implant.²⁹  Both implant and prosthesis stability were also assessed at each visit. Occlusion was assessed carefully at the delivery of the final prostheses and at the follow-ups. (Figure 10 a through d).

Implant and prosthesis survival were evaluated as a primary outcome in this study. The definition of implant survival was based on a modification of clinical and radiologic criteria described by Albrektsson and colleagues.³⁰  Criteria of success for ZIs were as follows: 1. absence of clinically detectable implant mobility; 2. no evidence of peri-implant radiolucency; and 3. absence of pain, infections, neuropathy or paresthesia.³⁰ 

The definition of prosthesis survival was based on full functionality of the prosthesis. Additional outcome evaluation was the incidence of any biological and mechanical complications. Secondary outcomes of this study were as follows: operative time, taken from the first incision to flap closure by suturing; the surgeon's stress related to the difficulty of the surgical procedure; and periodontal parameters (FMPS and FMBS).

Descriptive statistics were done using mean values and SDs for quantitative variables normally distributed. Qualitative variables and non-Gaussian quantitative variables were presented as median and 95% CIs. Normality of distributions was assessed using the d'Agostino and Pearson omnibus test. Homogeneity of the groups for gender, age, atrophy grade, and type of opposing dentition was checked using the Pearson χ² test. Comparison between groups for the main outcome variables was done using parametric (Student t-test) or nonparametric test (Mann-Whitney test), as appropriate. The number of implant failures and complications in the 2 groups were compared using the Fisher exact test, given the low number of such events in the follow-up period. The significance level was P = .05). The software GraphPad Prism 5.03 (GraphPad Software, Inc) was used for statistical analysis.

The main characteristics of the patients are shown in Table 2. Forty-one patients had Class IV atrophy and 51 had Class V according to the classification of Cawood and Howell.²⁴  The opposing arch exhibited natural dentition in 27 patients and implant-supported fixed denture in 14. Thirteen patients had a combination of natural dentition and implant-supported fixed prostheses, while 38 patients had an overdenture in the opposing arch. There was no between-group difference regarding the opposing dentition and degree of atrophy.

No implant failure occurred in the test group, while 2 implants failed in 2 patients of the control group, without compromising prosthesis function, yielding a survival rate of 98.9% for this group. There was no between-group difference regarding the opposing dentition and the degree of atrophy.

There were 4 postoperative complications in the test group: 1 case of sinusitis that resolved with antibiotic and corticosteroid therapy; 2 patients with persistent pain and swelling (up to 20 days) that resolved with macrolide therapy (Zitromax 500 mg; Pfizer) 2 times per day for 6 days; and 1 patient with transient hypoesthesia, which resolved with corticosteroid therapy for 5 days. In the control group, 5 postoperative complications were recorded: persistent pain and swelling in 2 patients, resolved with macrolide therapy (Zitromax 500 mg) 2 times per day for 6 days; 1 patient with green-stick fracture of the zygomatic bone (prosthetic load was suspended until complete healing of the fracture); 1 case of peri-implantitis in a patient with thin periodontal biotype (connective tissue grafting was performed); and 1 patient with transient hypoesthesia that resolved with corticosteroid therapy for 5 days. As a result, the between-group difference for complications was not statistically significant (Table 2).

The time required for the surgical procedure was significantly higher (by approximately 10% over 2 hours' surgery) for the group using ultrasonic instruments (P < .01). The surgical stress evaluation of the surgeon showed that stress associated with the test group was significantly lower than for the control group (P < .05).

The FMPS and FMBS improved significantly throughout the study (P < .001 in both groups). These parameters were slightly but significantly higher in the control group than the test group at baseline. They decreased significantly and there was no significant difference at the 24-month follow-up period (Table 2).

Although it is regarded as a gold standard, autogenous bone grafting raises concerns due to the morbidity at the harvesting site and delay in the final treatment. This fact triggered the development of techniques without grafting as alternatives for the treatment of patients with atrophic edentulous jaws.³¹ 

Zygomatic implants were introduced for the oral rehabilitation of patients with severe and extended defects of the jaws caused by postoncological resections, trauma, or congenital malformations, or by long-term edentulism.^4–7  Over the years, ZIs have proven to be a valid treatment option with high success rates. In a study with 10 years of follow-up, Tolman et al³²  reported a 96% success for ZIs. Similarly, Brånemark et al³³  showed a survival rate for ZIs of 97% in 81 patients with a follow-up up of 12 years.

A recent systematic review, based on 38 studies on immediately loaded ZIs with at least 12 months of follow-up, reported a success of implants and prostheses ranging from 96% to 100%.³⁴  Another systematic review based on 15 studies reporting on 1541 ZIs with at least 2 years of follow-up estimated an implant survival rate of 97.86% after 36 months of function.³⁵  It was reported that failures occurred mostly in the first year and were related to clinical complications, such as acute and chronic sinusitis.³⁵ 

However, zygomatic surgery is a rather demanding technique and is not risk free due to neighboring anatomic structures such as the infraorbital nerve, orbit, and infratemporal fossa. Additionally, various postoperative complications have been reported in the literature, such as; sinusitis, soft tissue infection around the implants, paresthesia of the infraorbital or zygomaticofacial nerves, and formation of oroantral fistula.^14,15  Complications related to the positioning of ZIs were also described, including implant failures, implant fracture, abutment and prosthetic screw loosening, speech difficulties, hygiene difficulties, and chronic rhinosinusitis.^34,35  These complications are not only associated with surgical difficulty but also with reduced visibility and instrument control when preparing the implant site in the zygomatic arch through the maxillary sinus. To reduce these complications, the current study team proposed a new surgical technique for rehabilitation with quad ZIs, which included the use of an ultrasonic device.²¹  Ten consecutive patients with severely atrophic maxilla were treated with quad ZIs and immediate complete arch acrylic resin provisional prostheses. The patients were followed up for 30 to 32 months with 100% implant and prosthetic success rate. The incidence of complications was very low.²¹  Within the limitations of that preliminary study, the data indicated that the ultrasonic technique can be a good alternative to the drilling technique. In the present study, implants placed with the ultrasonic technique showed no failures and fewer complications compared with conventional drilling, although results were not statistically significant between the 2 groups due to the extremely low event rate.

Recently, Esposito and colleagues³⁶  published a split-mouth randomized controlled trial with 20 edentulous patients to compare conventional drills and piezoeletric surgery for rehabilitation with 4 immediately loaded ZIs. The patients received 4 ZIs, 2 for each side. One side was done with the drilling technique, the other side with piezoelectric surgery preparation. Both drilling techniques achieved similar clinical results, but conventional drilling was found to be more aggressive.³⁶  This finding also supports the data of the present study regarding surgical stress, which suggested a significant advantage associated with ultrasonic instrumentation. The latter, in fact, due to its safer handling compared with traditional high-speed drilling devices, makes the surgeon more comfortable and less stressed in performing demanding surgical procedures like the placement of ZIs. This may compensate for the slightly longer duration of the surgical procedures when using ultrasonic devices.

Piezosurgery instruments have been used in dental implant surgery and offers several advantages.^22,23  Piezoelectric surgery is a safe, reliable, and advantageous method from an intraoperative technical point of view for the surgeon.²³  It is less traumatic, is more secure, and provides more intraoperative comfort and a better postoperative course.^22,23  In terms of biological advantages, ultrasonic devices offer a less traumatic surgery with greater visibility. There is reduced thermal stress on tissues with better healing and less postoperative pain and edema of the soft tissues.²³  However, the piezoelectric preparation is usually associated with a significative increase in operative time compared with conventional instruments.²²  On the other hand, ultrasound instruments applied to the implant site preparation can provide a bone surgery with fewer risks related to operative maneuvers and greater comfort for the patient and surgeon.^22,23  Scarano et al²²  and Maglione et al²³  compared ultrasonic and conventional drill implant-site preparation in observational clinical studies. According to their results, osteotomies with piezoelectric surgical instruments created fewer intraoperative risks and more comfortable surgical time for the patient. Additionally, postoperative swelling and pain were less, although there was a significant increase in operative time compared with traditional drills.^22,23 

Despite the high success rates reported in the literature,^34,37  insertion of ZIs should be performed with caution and should not be considered the first treatment choice in edentulous maxilla patients who are seeking oral rehabilitation. Risks and benefits should be discussed with the patient and indications should only be for limited cases as a last option whenever an alternative is not feasible.

One of the strong points of this study was that all the operations were done by the same highly experienced surgeon. This must be taken into consideration when discussing the excellent implant survival rates observed, and readers must be aware that zygomatic surgery should not be underestimated. The results may differ in another setting with less experienced surgeons. Therefore, one limitation of this study may be the limited generalization of the results. A hospital setting providing general anesthesia is also crucial for the comfort of the surgeon and the patient during the whole procedure. Additionally, although ultrasonic instruments are safer in terms of possible damage to neighboring anatomic sites than conventional drills, they can prolong the drilling time. Thus, in our view, one surgeon might feel more surgical stress while another might feel less stress, as surgical stress is a rather subjective outcome.

In conclusion, the data from this study indicate that the ultrasonic technique can be an alternative to conventional drilling during zygomatic surgery. Because of the severe complications associated with ZI surgery, in order to provide safer and more simple treatments, further research should be conducted comparing ultrasonic preparation with other methods, such as modern guided ZI insertion.

Abbreviations

3D:

3-dimensional

FMBS:

full-mouth bleeding score

FMPS:

full-mouth plaque score

VAS:

visual analogue scale

ZI:

zygomatic implant

The authors wish to thank Dr Marta Giovannardi, visiting professor of the Università degli Studi di Milano, for independently reviewing the study methodology and the statistical analysis of the results.

The authors declare that they have no conflicts of interest.