Preoperative Evaluation and Treatment Planning. Zygomatic Implant Critical Zone (ZICZ) Location

Key points

  • A systematic preoperative evaluation is an essential basis to identify challenges, risks, and limitations to establish an accurate treatment plan.

  • The understanding of anatomic differences provides the framework for the treatment planning design.

  • A complete treatment planning, including the visualization and prevention of late complications, constitutes the strategy for predictable, functional, and esthetic outcomes.


Maxillary atrophy usually represents the final outcome of multiple failed conservative dental treatments, regenerative approaches, or rehabilitation procedures such as grafting or implant placement. The rehabilitation of the severely atrophic edentulous maxilla entails both a huge challenge for the practitioner and the last opportunity for the patient to have a fixed set of teeth, to recover esthetics and masticatory function. ,

Clinicians face several important decisions in the planning and delivery of oral rehabilitation anchored on zygomatic implants. Nevertheless, this surgery demands, in addition to a high level of surgical experience and skills, a meticulous patient-centered evaluation to :

  • Address the patient’s concerns and goals

  • Minimize risks and adverse events

  • Reduce the treatment duration and the financial cost

  • Adequately inform the patient of the potential benefits and risks of this treatment

  • Provide the patient with an understanding of appropriate treatment alternatives

  • Simplify treatment when possible.

This treatment should be performed knowing one’s own limitations and seeking consultation whenever appropriate.

These goals are achieved using a systematic preoperative evaluation of the implicit risks and a profound knowledge of the maxilla anatomy. Only based on these elements, one can set up a centered patient’s welfare, anatomy-guided treatment planning.

Anatomic considerations

Profound knowledge of the anatomy is required, including the following structures ( Fig. 1 ):

  • Alveolar process of the maxilla

  • Maxillary anterior wall

  • Zygomatic process of the maxilla

  • Maxillary left and right, anterior ethmoidal, posterior ethmoidal, sphenoidal, frontal sinuses, and ostium

  • Tuberosity/pterygoid process

  • Zygomatic bone

  • Proximal soft tissues susceptible to being damaged during the drilling procedure or flap raising

Fig. 1
Maxillary bone ( green line ). Zygomatic process of the maxilla ( orange ). Located at the separation of the maxilla and zygoma surfaces. Its geometry and curvature are crucial parameters to determine the antrostomy location in an extramaxillary placed implant. Residual alveolar process ( yellow ) architecture is a key factor to plan where the ZICZ will be located.

The zygoma anatomy-guided classification

When planning the osteotomy for a zygomatic implant, it is crucial to understand that a zygomatic implant may adopt different trajectories. This will depend on the location of the coronal entrance, and on adapting the surgical procedures and implant designs to each patient’s anatomic characteristics. This is aimed at reducing early and late complications.

Based on a cross-sectional study of 200 sites, a classification system comprising 5 basic anatomic groups named from ZAGA 0 to 4 was proposed by Aparicio. Five basic skeletal forms of the zygomatic buttress and alveolar crest complex and implant trajectories were identified. Anatomic intraindividual patient differences were found in 58% of the population ( Fig. 2 ). It is believed that the proposed system is useful for classifying zygomatic implant cases for therapy planning and scientific follow-up purposes and case discussion.

Fig. 2
ZAGA Classification for the posterior zygomatic implant. The ZAGA Concept implies that in accordance to the amount of residual alveolar bone and anatomic characteristics the implant path will vary from the total intrasinus one ( A ) to the more or less partially intrasinus ( B,C ); the intra-alveolar, extramaxillary wall ( D ); or the extra-alveolar and extramaxillary wall ( E ).

The zygomatic implant critical zone

The knowledge and familiarity of the surgeon with anatomic characteristics of the structures that the oblique plane of the planned osteotomy intersects are of utmost importance. Therefore, it is relevant to study in more detail the implant trajectory in several zones of the osteotomy. For didactic purposes, we suggest distinguishing 3 main zones on the zygomatic implant trajectory:

  • the “Zygomatic Implant Critical Zone”

  • the “Antrostomy Zone”

  • the “Anchor Zone.”

Preventing late complications will be closely related to the understanding of the physiology, and function(s) of each of the 3 zones.

The authors of this article propose the name of “ Zygomatic Implant Critical Zone” (ZICZ) to define the complex formed by maxillary bone, soft tissue, and the zygoma implant at the coronal level where the first contact with maxillary bone occurs ( Figs. 3 and 4 ). The essentials for the localization of the ZICZ and implant osteotomy/trajectory can be found in the ZAGA Concept and will be discussed in a more detailed manner in a specific chapter. Residual alveolar bone and soft tissue preservation at the coronal level of the zygomatic implant are critical to prevent oral-sinus or oral-nasal fistula and soft tissue dehiscence, which are the most common late complications ( Figs. 5–25 ). Bone and soft tissue maintenance at the ZICZ should be one of the main goals of our surgical procedure. In this regard, a series of protocols, tools, interventions, and procedures are proposed to reach appropriate bone and soft tissue stability on the ZICZ ( Table 1 ).

Fig. 3
The ZAGA zones.

Fig. 4
The zygomatic Implant Critical Zone (ZICZ) is determined by the relationship between the implant alveolar bone and covering soft tissue.

Fig. 5
Case 1. 1- H.CH- R Planning. The case of an atrophic posterior maxilla is illustrated. Instead of penetrating a thin sinus floor, the right implant path planning is being shifted to the buccal side.

Fig. 6
Case 1. 2- H.CH- L planning. The left side is also extremely atrophied. An extramaxillary path has been chosen.

Fig. 7
Case 1. 3- H.CH- R lateral osteotomy. After marking the coronal and the antrostomy spots A drill from is being used for a precise lateral cutting.

Fig. 8
Case 1. 4- H.CH- R lateral osteotomy 2. The Versah drill is being used in a clockwise direction to prepare a lateral channel on the alveolar bone and maxillary wall with total respect for the sinus lining.

Fig. 9
Case 1. 5- H.CH- R lateral osteotomy 3. Using a back and forward movement of the Versah Zygo drill, a notch has been performed on the zygomatic maxillary process.

Fig. 10
Case 1. 6- H.CH- R Sword antrostomy. To minimize eventual heating of the dense zygomatic bone, a “sword” type drill from is being used.

Fig. 11
Case1. 7-H.CH-R antrostomy. The Versah spear drill is used in the presence of hard Zygomatic bone as initial drill before the round bur. The spear drilling is stopped when reaching the second zygomatic cortical.

Fig. 12
Case 1. 8- H.CH- R round bur. The round bur tail may slide back and forward to bevel the bony at the antrostomy zone.

Fig. 13
Case 1. 9- H.CH- R twist drill. A stepped twist drill of 2.9 mm diameter from Straumann AG was used to enlarge the osteotomy.

Fig. 14
Case 1. 10- H.CH- R final lateral osteotomy. A specially designed lateral cutting drill, from Straumann AG, with progressive diameter, was used to enlarge the osteotomy until reaching 4 mm of channel diameter at the ZICZ.

Fig. 15
Case 1. 11- H.CH- R osteotomy. A ZAGA minimally invasive osteotomy has been achieved. Membrane transparency can be seen at the ZICZ.

Fig. 16
Case 1. 12- H.CH- R measuring. A hook-ended gauge is used to determine implant length.

Fig. 17
Case 1. 13- H.CH- R implant insertion. A Straumann ZAGA Flat zygomatic implant design, totally matching the prepared osteotomy, is being screwed on the zygomatic bone.

Fig. 18
Case 1. 14- H.CH- L lateral osteotomy. The left channel is being carved using a 2 mm diameter Versah Zygo drill.

Fig. 19
Case 1. 15- H.CH- L lateral osteotomy. Following the pencil marks, the 2.5 mm diameter Versah Zygo drill has prepared a smooth channel and the initial notch for the antrostomy.

Fig. 20
Case 1. 16- H.CH- L Spear antrostomy. The spear type zygo bur is used for a predrilling in dense zygomatic bone previous to the 2.9 mm diameter twist drill.

Fig. 21
Case 1. 17- H.CH- L round bur. As the diameter of the spear drill is thinner than the twist drill, the round bur is used for enlarging the cortical entrance so that a precise osteotomy direction can be maintained.

Nov 5, 2021 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Preoperative Evaluation and Treatment Planning. Zygomatic Implant Critical Zone (ZICZ) Location
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