Advanced Zygomatic Implants: The ZAGA Concept

1

Origins of the ZAGA Concept

Carlos Aparicio

Rehabilitating patients with severe maxillary atrophy has remained a consistent challenge for clinicians. In select cases, a complete or partial dental rehabilitation anchored with zygomatic implants can be an excellent option. In practice, though, the historical long-term unpredictability of such procedures means that some clinicians still opt for conventional methods, even though they can be more complex, time-consuming, and costly for the patient. As is true of techniques for placing standard implants in different situations, zygomatic implant placement practices have evolved over the years, from the original Brånemark technique to the slot, extrasinus, and extramaxillary approaches, and now the zygoma anatomy-guided approach (ZAGA). As zygomatic implant placement systems have evolved, so have the implants, tools, technology, and thinking behind them.

Thirty years ago, zygomatic implants were uncharted territory for the vast majority of clinicians. Today, zygomatic implant therapy represents a milestone of progress in the genesis of oral implantology. As it has become more commonplace, a substantial body of evidence has grown to support it. The technique has been well documented over the long term, with success rates that compare favorably with conventional treatment using dental implants and bone grafting. Changes in zygomatic implant design have occurred over the past 20 years, and with these changes, surgical protocols have also evolved. This chapter examines the evolution of oral rehabilitation with zygomatic implant–supported prostheses, from its origins to the present.

Technique Evolution

Brånemark’s original technique: The beginning of the ZAGA story

In the early 1990s, several reports were published on the possibility of anchoring implants into the zygomatic bone for both nasofacial1 and dental prostheses.2 In 2004, Brånemark et al published a long-term follow-up study on onlay bone grafting and the simultaneous placement of zygomatic implants,3 and zygomatic implants were accepted into the scientific implantology community. In this study, 52 zygomatic implants and 106 conventional implants were placed across 28 patients. Bone grafting was performed in 17 patients. All patients were followed closely for 5 to 10 years. The procedure for placing the zygomatic implants consisted of performing a window antrostomy in the upper lateral quadrant of the anterior maxillary wall. The sinus mucosa was then reflected, and no special effort was made to keep it intact.3

According to Brånemark, the direction of the zygoma fixture was selected to provide optimal stability against prosthetic requirements, meaning the implant path had a more-or-less palatal point of entry, depending on the curvature of the maxillary wall.3 This implant path was said to achieve an intrasinus trajectory (Fig 1-1). Due to the palatal positioning of the zygomatic implants, the palatal flap had to be thinned and the fat tissue eliminated to prevent any soft tissue inflammation around the final abutments. However, despite the palatal positioning of the implant head, no patient discomfort or speech difficulties were reported in the initial study.

FIG 1-1 This clinical photograph shows some of the features of the original surgical technique, such as palatal entry and the opening of an anterior window to visualize the implant path.

The results

In the long term, there were three reported zygomatic implant failures, reflecting a survival rate of 94.2%. Overall, the prosthetic restoration success rate at 5 years was 96%. At least 96 conventional implants between 10 and 20 mm in length were placed. The success rate for the original conventional implants was about 71%. In 2 of the 28 patients, one of the two zygomatic implants installed was disconnected from the prosthesis due to suppuration at the palatal entry point of the implant combined with sinus infection. Recurrent sinusitis affected four patients within the follow-up time (Fig 1-2). The treatment of these four cases was identical: an antrostomy of the inferior meatus with satisfactory results. An additional four patients were found to have radiographically diagnosed sinusitis with clinically symptom-free maxillary sinuses. In those cases, no treatment was considered necessary. According to the definition of Lanza and Kennedy,4 the percentage of cases that developed clinical sinusitis was 21%. If we also apply the radiologic criteria of Lund and Mackay,5 the percentage of rhinosinusitis would rise to 35.7%.

FIG 1-2 (a) Tomographic section of the maxillary sinus taken 1 year after placement of the zygomatic implant through the thin palatal wall. Note the transparency of the maxillary sinus. (b) After a period of 3 years, the patient was diagnosed with rhinosinusitis with radiologic occupation of the sinus with no apparent cause.

In 2010, Bedrossian reported a retrospective follow-up of 36 patients treated with the immediate loading protocol over a period of 5 to 7 years. The survival rate was 97.2%.6 Following this in 2012, Aparicio et al reported on a prospective study with a minimum 10-year follow-up of 22 consecutive patients.7 In this study, the original Brånemark two-stage protocol was used along with the original titanium-turned zygomatic implants. In year 9, two stable zygomatic implants from one patient were removed due to a peri-implant infection in conjunction with recurrent sinusitis, resulting in a cumulative overall survival rate of 95.12% over 10 years.

Concerns with the original technique

When first marketed in 1998, the original Brånemark zygomatic implant was fully threaded and machined. Its head had a 45-degree angulation. The implant transporter and then the abutment were fixed to the implant with a screw that went completely through the head of the implant. The implant was initially designed with an external hex connection so that clinicians could effectively use the components of the Brånemark system. Passing the implant through the maxillary sinus via a palatal perforation did not appear to cause any serious negative sinus reactions, provided the implant was stable and the antral cavity was sealed, as evaluated in a sinuscopy study of 14 patients.8

However, Brånemark’s 2004 study found that 6 of 28 patients (21%) experienced clinical symptoms of acute sinusitis, 4 of whom experienced recurrent acute sinusitis.3 An additional four patients (14%) experienced only radiologic findings of sinusitis (chronic rhinosinusitis), resulting in an overall prevalence of sinusitis of 35%. The occurrence of a relatively high percentage of infectious sinus problems was initially attributed to causes such as poor sealing of the antrum near the palatal area caused by implant micromovement or imprecise surgical technique. Other clinicians attributed these infections to the design of the abutment and implant head screw attachment, through which bacterial microleakage and a consequent inflammatory response with bone destruction could have occurred.

Significantly, most of the studies that include follow-ups of zygomatic implants placed according to the original technique do not mention the prevalence of sinus problems or complications. When rhinosinusitis infections were reported, they appeared to occur at a rate similar to those obtained by Hirsch et al and Malevez et al in 2004, who reported the occurrence of sinusitis in 2.3% to 13.6% of all treated sinuses.9,10 This is in contrast to studies by Brånemark et al,3 Becktor et al,11 and Farzad et al,12 in which the incidences of sinusitis were 35%, 29%, and 31.8%, respectively. Becktor et al had to remove 3 of 31 implants due to recurrent sinusitis, although the implants were clinically stable.11 Again, the two explanations proposed for these problems were, first, that the internally threaded abutment screw chamber in the zygomatic implant head may have created an oroantral communication leading to sinusitis and, second, that there may have been a lack of osseointegration at the marginal level in the palatal area, resulting in transverse mobility of the zygomatic implant and a pump effect during function.

It is noteworthy that very few studies have been as detailed as Brånemark’s with respect to patient follow-up, especially sinus status. Additionally, at the time the original technique was first being performed, there was a lack of consensus on how to report a diagnosis of sinusitis in the dental literature, so information on the prevalence of sinus infection problems should be taken with caution. In most studies with a focus on zygomatic implants, the term used to describe sinus pathology is sinusitis, without clarifying the type, associated signs and symptoms, or whether CT or endoscopy was performed to confirm the diagnosis. Furthermore, sinusitis can be diagnosed years after zygomatic implant surgery.

In summary, oroantral fistulas and subsequent sinusitis are typical late complications associated with zygomatic implants,13 and there are different hypotheses for their etiology—one being lengthy resorption of the thin bone surrounding the neck of the implant when it crosses the palate. There may also be other factors affecting the resorption process, like overly extensive preparations, fracture of the thin alveolar ridge during implant placement, history of periodontitis, and oral hygiene procedures.

In 2016, the Nobel Zygoma with a TiUnite surface implant (Nobel Biocare) replaced the original Brånemark System Zygoma TiUnite implant. It came with a new, nonperforated implant head, a complete rough surface, and the need for a specific zygomatic implant abutment. But even in a recent multicentric study by Felice et al in 2020, sinusitis was cited as the most frequent complication.14 Thus, the risk of soft tissue problems and sinusitis should not be underestimated.

In addition to causing sinus concerns, the original technique is a two-stage procedure, which increases the total treatment time and the number of surgical procedures. The process also allows for less than optimal prosthetic management during the healing period. Therefore, some authors suggested using an immediate loading protocol, placing a definitive abutment, and avoiding abutment changes in a single-stage procedure.15,16 It is proposed that these factors could decrease the risk of oroantral communication by establishing a better soft tissue barrier.

Another drawback of the original technique was the palatal emergence of the implant head that often occurred as a result of keeping the implant body within the boundaries of the maxillary sinus. This process commonly resulted in a prosthesis with a bulky palatal aspect that caused tongue discomfort and poor phonetics and prevented correct oral hygiene (Fig 1-3). Furthermore, zygomatic implant placement with an intrasinus path may not even be possible in patients with highly pronounced buccal concavities at the lateral aspect of the maxillary sinus because the implant would emerge close to the midpalate.

FIG 1-3 Occlusal photograph of a fixed prosthesis with four standard anterior implants and two zygomatic implants with a palatal placement in the posterior sector according to the original technique. Note that there were no angled abutments to correct the direction of the prosthetic screws at the time the original technique was being developed.

Tribute to Per-Ingvar Brånemark

The drawbacks of the original technique have been described with the healthy pride of a disciple who humbly accepts and follows the master and then intuits that he can evolve the knowledge garnered and improve the results. Step by step, measuring the consequences of each individual change to the original technique, Brånemark’s students have been able to make the seed he planted grow. I think this is the best tribute and the best reward a teacher might have.

After all, when we were first starting to think about rehabilitating partially edentulous spans with several implants, Brånemark was already looking for places distant from the alveolar bone to anchor fixtures—he did not like to call them implants—to fix dental restorations. Not only was he the forefather of zygomatic implant placement, but he was also a pioneer in placing implants into the septum that separates the maxillary sinuses and the nasal cavity (Fig 1-4). With the exception of a few visionary professionals, the placement of implants taking advantage of the nasal bone is something that we seem to be discovering only very recently (see chapter 11).

FIG 1-4 This radiographic image taken from the 2004 study by Brånemark et al shows the placement of an implant in the nasal septum (white circle) . (Reprinted from Brånemark et al. 3 )

The slot technique

Despite the reported success of the original Brånemark technique, it was clear there were problems that needed to be overcome. To eradicate excessive palatal implant head emergence and to reduce postoperative discomfort, Stella and Warner first described the slot technique in a technical note in 2000.17 First, a crestal incision was preferred to the vestibular Le Fort incision recommended in the original technique. The latter can be challenging to manage as it places the flap closure over the antrostomy. The authors proposed raising a flap only as far as the inferior part of the infraorbital nerve and up to the medium-inferior part of the zygomatic process of the maxilla. Unlike the original technique, they did not uncover the angle formed by the frontal and temporal processes of the zygomatic bone because, in theory, this groove gave them the direction of the implant. Wisely, the authors also questioned the need for the extensive antrostomy prescribed in the original technique when the problem is advanced atrophy of the maxilla. Instead, they proposed to perform a narrow slot in the previously imaged direction of the implant to help visualize implant angulation. The most significant contribution of this new technique, however, was to question the need for palatal implant entry, which results in bulky prostheses. Instead, Stella and Warner proposed a crestal entry to achieve superior anatomical prostheses. Local anesthesia and intravenous (IV) sedation were also introduced, and it was suggested that a better controlled slot approach with a reduced antrostomy and a careful implant path through the sinus would be favorable for healing and enhanced prosthetic positioning of the implant head.

The process

After flap raising, a slot is drilled prior to zygomatic implant placement following a preplanned implant path. First, a hole is prepared in the lateral wall of the maxillary sinus using a tungsten carbide drill. This is made at the extreme upper contour of the zygomatic buttress. Then, a zygomatic implant depth gauge is placed in the hole and positioned to simulate the angled approach of the implant twist drill. A second hole is then made on this trajectory 5 mm above the crest of the ridge. Finally, a slot connects the two holes (Fig 1-5). A rounded drill is first used to mark the implant anchoring zone on the maxillary crest at the first molar level. Then, a 2.9-mm drill is introduced, directly visualized through the preprepared sinus slot, and aimed superiorly toward the junction of the lateral orbital rim and zygomatic arch. In the same way, a pilot drill and a 3.5-mm twist drill are directed through the center of the sinus slot. The correct depth of the preparation is again confirmed using an implant depth gauge, and the appropriate length of implant is selected.

FIG 1-5 Intraoperative photograph showing the slot technique. Note that the fit of the groove with the implant itself is not optimal because the groove is made before placing the implant. (Courtesy of Dr M. Peñarrocha.)

The results

Despite the lack of data, the use of the sinus slot technique was reported by Peñarrocha et al.18 Just five patients were followed, requiring 10 zygomatic implants, 2 pterygoid implants, and 16 standard implants. Zygomatic implants could not be placed at the alveolar ridge position in 2 of the 10 sites, thus requiring palatal displacement. Follow-up lasted between 12 and 18 months, during which the remaining implants and prostheses on all patients remained stable and in function.

Although the slot technique represents an improvement in prosthesis design and minimizes the antrostomy, the method is not without drawbacks. The authors did not provide any specific criteria for adopting variations within this process to avoid, for example, oroantral communication caused by penetrating the sinus through an alveolar ridge that is too thin. Nor did they define the path of the implant for different anatomical situations. Because the slot antrostomy is performed before implant placement, it does not always match the shape of the implant. For the same reason, the slot may not be necessary in the presence of considerable concavities in the maxillary wall. In other words, the ability to seal the maxillary wall with the implant is limited.

The extrasinus/externalized approach

The next step in the evolution of the original technique occurred when Aparicio’s group presented a 1-year follow-up of a new technique for zygomatic implant placement at the 2005 EuroPerio meeting. This new technique, indicated in cases of maxillary wall concavity, used an external approach to the maxilla to place zygomatic implants (Fig 1-6). The 1-year study for this new technique was first published in the English literature by Aparicio’s group in 2006.19 Migliorança et al, also in 2006, described a similar approach in Portuguese, which they called the externalized technique.20 In this approach, priority is given to the fabrication of anatomical prostheses so the entry of the implant occurs in the maxillary ridge. Depending on the concavity of the anterior wall, the implant will have a more-or-less aerial path. By placing the implants partially outside the wall, sinus perforation at the crestal level is avoided, and the need for a window antrostomy or the creation of a slot before surgery is eliminated. Moreover, according to Corvello et al, this technique achieves greater implant contact at the zygomatic bone level21 (Fig 1-7). This approach has fewer surgical steps, is less invasive, is more precise (because the osteotomy fully matches the shape of the implant), minimizes operating and recovery time, and can be used with anatomical prostheses without overhang because the implant emerges directly from the alveolar ridge.

FIG 1-6 Radiographic section showing the concavity of the anterior maxillary wall. The white arrow indicates the partially extramaxillary path proposed for the implant.

FIG 1-7 Illustrated representation of the work of Corvello et al. 21 Superimpositions on the tomographic slice showing two possible implant paths: (a) The implant is placed according to the original technique. (b) The implant is placed according to the externalized technique. The red arrows indicate the different lengths of osseous contact at the zygomatic level achieved by both techniques.

The process

According to Aparicio, the key indication for using the extrasinus or exteriorized technique is buccal concavities in the lateral wall of the maxillary sinuses. The situation initially described for the use of the exteriorized technique is equivalent to the later so-called ZAGA Type 3. The rationale for this process is to avoid perforation of the sinuses in a position close to the crest, thus preventing infectious sinus complications. The extrasinus technique also allows placement of the implant head close to the top of the alveolar ridge in this type of anatomy. A slightly palatal crestal incision is used together with releasing incisions in the areas of the tuberosities and at the level of the anterior nasal spine. After raising an extensive flap that includes separation of the periosteum at the superior angle formed by the temporal and frontal processes of the zygoma, drilling is performed from the palatal side of the remaining alveolar bony ridge toward the zygomatic arch. Thus, there is no need to prepare a window or slot in the maxillary sinuses, and the integrity of the sinus membrane is preserved (Fig 1-8).

FIG 1-8 Intraoperative image showing two zygomatic implants placed in the presence of a concave maxillary wall without removal of the alveolar bone remnants, according to the externalized technique proposed by Aparicio et al in 2008. 22

The results

In a 3-year prospective study first published online in 2008,22 Aparicio et al reported the results of placing 36 zygomatic implants in an extrasinus position in a total of 20 consecutive patients recruited between October 2004 and October 2005. The minimum follow-up was at least 3 years. As in the original technique, Nobel Biocare zygomatic implants with turned threads were used.

The study reported good stability, individually measured, of the 36 implants placed. No signs of maxillary sinus infection were detected, and no soft tissue dehiscence was reported during the 3-year follow-up period. In addition, the extrasinus technique resulted in better positioning of the zygomatic implant head closer to the maxillary alveolar bony ridge.

One of the concerns with this new technique was the long-term effect of the exposed threads placed directly next to the soft tissues on the lateral aspect of the zygomatic implants. However, all patients had healthy mucosal coverage. One explanation can be found in the fact that this technique was used in patients with concave maxillary lateral walls (ZAGA Type 3) and the alveolar bone around the implant was preserved. This remnant of alveolar bone provides an anchorage zone for soft tissue connective fibers that prevents posterior dehiscence.

In 2011, Migliorança et al retrospectively reported the results of 75 patients treated with conventional implants and 150 zygomatic implants, all placed external to the maxillary sinuses.23 To place the implants, a supracrestal incision joining both tuberosities was made, along with two vertical releasing incisions. A mucoperiosteal flap was reflected, and osteotomies for the zygomatic implants were initiated using a round bur, which penetrated the residual ridge near its superior aspect from the palatal side. This, in turn, transfixed the ridge and emerged from the buccal side external to the maxillary sinuses until reaching the zygomatic bone without the creation of a preliminary sulcus or window in the anterior maxillary wall.

The authors evaluated clinical conditions at all follow-up appointments every 3 months during the first year and semiannually thereafter. Patients were examined via periodontal probing, radiographs, and intraoral and extraoral photographs. For biofilm control, all patients were instructed to use interdental brushes, dental floss, and an oral hygiene system based on twice-daily, high-pressure water spraying.

The study does not provide information on dropouts, but it is reported that all implants were followed up for at least 1 year. The survival rate was estimated at 98.7%. Despite the systematic use of pressurized water that could eventually damage the hemidesmosomes of the implant with the soft tissue, only two implants showed mild soft tissue dehiscence with no inflammation. Although not specified in the paper, the exteriorized technique thus described would be conservative only with respect to the integrity of the near-ridge sinus membrane. In other words, in cases where the maxillary wall is concave, the amount of remaining alveolar bone allows it to be penetrated without direct perforation of the sinus membrane. Yet as shown in the case photographs from Migliorança et al, when the maxillary wall is not concave, perforation of the sinus membrane near the crest and the consequent risk of sinus complication is possible with this method. However, no oroantral fistulas or sinus infections were described in any patient.

The extramaxillary approach

In 2008, Maló et al introduced a double modification to the extrasinus/exteriorized approach, which they called the extramaxillary technique.24 First, the indication for this technique is universal, not for use only in maxillae with a concavity in the anterior wall but for all patients. Second, the extramaxillary technique prescribes the systematic reduction of the residual alveolar bone to achieve exclusive anchorage in the zygomatic bone. When the wall of the maxillary sinus was convex, the membrane was inevitably perforated because it was in the direction of the drill. Of the 18 patients who underwent 1-year follow-up, 4 had a sinus infection (22% sinusitis if dropouts are taken into account).

In an extension of the study in 2012, and following the extramaxillary modification, Maló et al retrospectively reported on the 3-year follow-up of 5-mm-diameter zygomatic implants placed in 39 consecutive patients between January 2006 and October 2009.25 Emulating the initial pilot study protocol, the maxillary bone was prepared to allow direct drill access to the inferior zygomatic border but was not used to anchor the extramaxillary implant. No dropout data is given, but a reported six patients experienced sinus complications (18%).

In an extension of previous studies, Maló’s group reported a 6-month to 7-year follow-up of the extramaxillary technique in a study originally published online in 2013.26 This time, 352 consecutive patients were followed from January 2006 to July 2012. The increase of patients reported in the literature at this time was remarkable: from 39 patients between January 2006 and October 2009 (3 years and 10 months) to 352 patients in July 2012 (313 new patients in 2 years and 9 months). This new study reported better long-term outcomes with respect to sinus infections (8%) compared to previous work (18% to 22%).

Although the decrease in sinus infections is not explained, a possible interpretation of this improvement is found in the use of methodologic variations. One example is the introduction of the channel osteotomy, as used with other techniques, to avoid damaging the sinus membrane during implant placement. Another possibility for the improvement in sinus health could be the abandonment of alveolar ridge bone recontouring, which was prescribed in the beginning. Additionally, the exclusive use of 5-mm-diameter zygomatic implants was abandoned in the last studies.

According to the surgical protocol described by Maló’s group, the extramaxillary implants achieved zygomatic anchorage without mandatory alveolar contact. This approach may have affected the distribution of functional forces. As Freedman et al stated in 2015, occlusal stresses are higher in models with zygomatic anchorage and no alveolar support.27 In addition, due to the larger implant diameter (5 mm) used in the Maló studies, the space for implant placement is reduced. Implants with a wide diameter tend to be positioned parallel to one another instead of converging apically, which considerably increases the anteroposterior (AP) overhangs (Fig 1-9). These two facts could explain the high incidence of mechanical problems found in 156 patients (44%) in the Maló et al study.26 Despite the placement of implants outside the maxilla, however, none of these cited studies reported complications related to soft tissue dehiscence or recession around zygomatic implants.

FIG 1-9 (a) The apical convergence of narrow implants. (b) The relation between implant diameter, zygoma size, and the possibility of achieving a good AP distribution of forces. The larger the implant diameter, the greater the bone destruction and the more parallel the placement will have to be, resulting in worse AP distribution with longer cantilevers.

The ZAGA Concept

The concept of the zygoma anatomy-guided approach (ZAGA) was described by Aparicio as a refinement of his extrasinus technique. This technique represents the natural evolution of the original Brånemark technique and the slot and extrasinus approaches summarized in Fig 1-10.

FIG 1-10 Graphic representation of the advantages and disadvantages of the three techniques described so far. Three different implant paths can be used to treat the same patient via either the original (red) , slot (yellow) , or extrasinus (gray) technique.

Prior to the ZAGA concept, techniques for placing zygomatic implants offered a universal application for all patients. The ZAGA concept differs in that it seeks to provide patient-specific treatment. With this technique, multiple treatment factors can be varied between patients: the type of incision depending on the gingival phenotype and amount of soft tissue, the surgical protocol for positioning and design of the osteotomy, the type of drilling with a lateral or perpendicular cut depending on the type of osteotomy projected, the procedures and recommendations to better preserve the bone and soft tissue in the zygomatic implant critical zone (ZICZ), different instruments such as drills used to facilitate the surgery, and even the choice of implant for each site. In other words, instead of forcing the patient’s anatomy to adapt to a particular process and/or implant, the ZAGA concept is used to select strategies and tools that will complement the patient’s anatomy. The placement of each zygomatic implant is guided by an anatomical and prosthetic approach with a set of well-defined criteria to assist the clinician in decision-making. This is achieved when the clinician appreciates both interindividual and intraindividual anatomical differences.

Following specific prosthetic, biomechanical, and anatomical criteria, the following chapters describe the most suitable places to position the entry or first contact of the implant with the alveolar ridge, the zygomatic entry point, and/or the antrostomy site. The ideal implant trajectory based on the vertical and horizontal resorption of the alveolar/basal process, the curvature of the anterior maxillary wall, and the architecture of the zygomatic bone are also described. Ultimately, understanding the ZAGA concept helps the clinician make better use of the available crestal and maxillary wall bone. The ZAGA concept can also be used to achieve better soft tissue control for predictable coverage of zygomatic implants compared to an exclusively extramaxillary technique. In this way, the implant will have an intrasinus path when the alveolar bone remnant, evaluated according to the ZAGA protocol, is considered sufficient to be crossed and preserved in a predictable way. In other cases, when the amount of bone forming the floor of the nose or maxillary sinus is classified as insufficient, the implant will have an extrasinus path. The ZAGA anatomical evaluation also takes into account other intermediate anatomies, where the implant will have a more-or-less externalized path (Fig 1-11).

FIG 1-11 From top to bottom, the figure shows first the ZAGA classification of the different types of anatomy found in the path of the posterior zygomatic implant. Next, we find the different types of paths that the implant can adopt according to the anatomy found. The lower portion shows the recommended implant design according to the type of osteotomy chosen, whether tunnel or channel.

Case Studies

The following cases illustrate the application of the ZAGA concept in patient-specific scenarios.

Case 1

Case 1 illustrates a completely edentulous patient indicated to receive four zygomatic implants and a fixed restoration with immediate loading. The clinical and radiologic photographs illustrate two different ways of designing the osteotomy specifically adapted to the patient’s anatomy according to the ZAGA concept. The location of the anterior implant makes it possible to take advantage of part of the residual bone crest, helping to prevent complications. There is less residual bone in the more distal implant location, so the osteotomy was moved to the maxillary external area. Note that in addition to two different osteotomy patterns, different implant designs were used. The anterior implant (Straumann ZAGA Round) has a round section with threads in its neck to maintain the residual bone around it. The posterior implant (Straumann ZAGA Flat) has a circumferential arch section, and its neck has microthreads only in the part that will contact the bone. Comparing the preoperative radiographs with those taken upon delivery of the final prosthesis, the sinus response is positive.

Case 1 (1) Virtual planning for the left anterior implant. (2) Virtual planning for the left posterior implant. (3) Process of marking the ZAGA zones (white circle s; see chapter 3 ). This marking is essential so that the surgeon can know and remember the path of the implants during the surgery. (4) A round bur is used to cut through the thin alveolar ridge. Once on the buccal side, it will be used to carve a canal from the vestibular alveolar outlet (white circle) to the sinus entrance. (5) A twist drill is used to complete the zygomatic osteotomy. The osteotomy goes through the alveolar bone (white circle) . >>

Case 1 cont. (6) In the posterior zone, the osteotomy is prepared in the external zone to avoid perforation of the sinus membrane at that level. The osteotomies thus prepared are considered minimally invasive because only the bone necessary to place the implant is removed. (7) Following the round bur, a 2.9-mm-diameter twist drill was used to complete the drilling. Abundant irrigation of both the bone and the drill with cold saline is mandatory. (8) Two osteotomies have been performed according to the minimally invasive ZAGA concept using only a round bur and a twist drill. Next, a drill with multiple helical blades and an inactive tip is used to widen the entry and accommodate the implant neck without fracturing the remaining alveolar bone. (9) Insertion of a Straumann ZAGA Flat zygomatic implant in the second premolar area. (10) The posterior implant was placed first, followed by the anterior implant. The final positions of the implants are oriented according to the prosthetic emergence. (11) The two implants are in place. The white circles highlight the differences in design and location of the osteotomies. (12) Control CBCT slice taken before delivery of the final prosthesis. The DTX Studio Implant software shows the position of the anterior left implant and its path. If we compare this slice with 1 , we can see that the health status of the sinus has been maintained. (13) Control CBCT slice taken before delivery of the final prosthesis. The DTX Studio Implant software shows the position of the posterior left implant and its path. If we compare this CBCT with 2 , we can see that the health status of the sinus has been maintained.

Case 2

This second clinical case illustrates a third variation in the design and location of a minimally invasive osteotomy according to the ZAGA concept (Case 2). This is a patient with missing premolars and molars with numerous bone defects after tooth extractions. In this case, the placement of four standard implants was indicated in the anterior sector along with two zygomatic implants. This was followed by a fixed restoration with immediate loading. As in the first case, the location of the implants makes it possible to take advantage of part of the residual bony ridge. This, as explained in later chapters, helps to avoid complications and should be the first choice of placement under the right conditions. Once again, the surgeon makes an effort to be minimally invasive in this case, manifested in two patterns: (1) No preliminary osteotomy or antrostomy in the form of a window or slot was performed, and (2) only special osseocondensation drills were used in order to minimize bone removal at the alveolar level and facilitate osseointegration of the implant.

Case 2 (1) Radiographic section showing the virtual planning for the implant in the right premolar position. After a study of the architecture and measurement of the residual ridge, a ZAGA 0 osteotomy was decided. The antrostomy will be placed just across the sinus floor. (2) A Versah drill from the pilot study for the development of zygomatic drills, rotating counterclockwise. Because the remaining alveolar bone is minimal in width and height, it was decided to optimize its use by moving it laterally according to the osteocondensation drilling technique. (3) Another Versah drill with a larger diameter, also from the initial development group, is used to complete the osteocondensation of the ridge. (4) The circular ZAGA tunnel osteotomy was completed by condensing the alveolar bone with Versah drills. The yellow circle highlights the characteristic white color of the osseocondensed area. Note the outer line drawn on the maxillary wall that serves as a guide for drilling. >>

Case 2 cont. (5) A Straumann ZAGA Round implant is used to close the circular section tunnel osteotomy. (6) After studying the measurements and architecture of the maxillary bone, the anatomy is classified as ZAGA 0. Note that only one and not two osteotomies is performed prior to implant placement. Therefore, no bone was removed from the maxillary wall to see the drill path, either in the form of a window or a slot. Only the minimally invasive osteotomy necessary for implant placement was performed. The image shows the hexagonal platform of the Straumann ZAGA Round implant. (7) On the left, a CBCT slice shows the planned path for the zygomatic implant in the position of the right second premolar. Measurement of the remaining alveolar bone revealed more than 4 mm in height in this oblique section. Therefore, it was decided to place the implant through the alveolar bone and stabilize it in the zygoma. On the right, the final position of the implant can be seen. In this ZAGA 0 case, the maxilla has not been opened in its anterior part. Note the transparency of the sinus 1 year after the placement of the Straumann ZAGA Round implant.

Initial Results of the ZAGA Concept

In 2014, Aparicio et al presented the long-term results of a comparative study between a group of patients treated with the original technique (control group) and another treated according to the ZAGA concept (test group).28 The study included data on survival rate, implant stability, sinus conditions, prosthesis design, and soft tissue sealing. The original control group consisted of 22 consecutive patients rehabilitated with zygomatic implants using the original technique, all with at least 10 years of follow-up. The test group consisted of 80 consecutive patients rehabilitated with zygomatic implants according to the ZAGA concept. The observation period of the patients treated according to the ZAGA philosophy lasted from January 2004 to October 2009, with a mean follow-up of 4.62 years. All patients in the ZAGA group had at least 3 years of prospective follow-up. Both groups participated in a free maintenance program that included two annual visits. Remarkably, the same type of Nobel Biocare zygomatic implant, made of titanium with a threaded surface obtained by turning a grade 4 titanium bar, was used in both groups.

All patients were contacted for a final radiologic and clinical evaluation including a CBCT and were also invited to answer two specific questionnaires to evaluate the clinical status of their sinuses and their degree of satisfaction with the treatment received.

Within the limits of the study, the results presented by Aparicio et al showed that the procedures obtained similar results in terms of long-term implant survival. However, the ZAGA concept had several advantages over the original technique: Rehabilitation was immediate (in less than 48 hours), the risk of sinus pathology was minimized (76% of ZAGA patients had negative Lund-Mackay and Lanza-Kennedy tests compared to 54% of those treated with the original technique), and finally, the prostheses were less bulky, more comfortable, and easier to clean. The main points to remember when performing a ZAGA procedure are summarized in Box 1-1.

Box 1-1 >> Fundamental principles of the ZAGA concept

1. Maximize bone-to-implant contact (BIC) along the entire length of the implant, especially in the area where the implant first contacts the alveolar bone and in the zygomatic anchorage zone and, if possible, in the medial zone. Maximizing BIC effectively contributes to the initial stability of the implant and the achievement of a bony seal of the antral cavity. This, in turn, facilitates immediate loading of the implant and decreases the possibility of micromovement that would facilitate the creation of fistulas and sinus contamination or cellulitis that could extend into the orbit.

2. Maximize implant stabilization in the zygomatic area by following criteria for the appropriate number and design of implants. It is the anatomy of the zygomatic bone that should guide the precise preparation of the four cortices through which the implants are inserted.

3. ZAGA criteria should be used to prevent intraoperative complications, such as zygomatic bone fracture and lack of sufficient anchorage, and late complications, such as bone or sinus infection, oroantral communication, and soft tissue dehiscence.

Conclusion

Rehabilitation techniques for the atrophic maxilla using zygoma-supported prostheses have come a long way in the past 3 decades. The ZAGA concept, with its approach fully focused on achieving predictable and durable individualized rehabilitation, truly honors the Brånemark legacy. A long-term observation period is mandatory for any new technique, however, and even more so with this technique. An understanding of the ZAGA concept should be thoroughly developed and clinical experience gained before variations are introduced. From there, a minimum of 3 years should be allowed for comparative observation of the advantages or disadvantages of subsequent modification because complications, especially late ones, will be very difficult or impossible to resolve. The ZAGA concept aims to overcome the pitfalls of earlier approaches by standardizing surgical procedures and providing clinicians with the rationale to determine the ideal zygomatic implant position in every case.

References

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