From Volume 47, Issue 7, July 2020 | Pages 584-593
This paper, the last of a 4-part series, will discuss the impact of dental implant treatment on the health of the maxillary sinus. The need for assessment of maxillary sinus health and function, both clinically and radiographically, will be discussed. Strategies for implant planning that can reduce and mitigate complications will also be discussed, along with common surgical/post-surgery complications and the impact of these on patients.
In this fourth and final paper on the maxillary sinus and its importance for the Dental Team, the significance of the maxillary sinus, its structure, adjacent anatomical structures, and function will be looked at with regards to dental implant treatment in the atrophic maxillary alveolus. Dental implant treatment has become a popular treatment option for the replacement of missing teeth over the past two decades.1 Different areas of the mouth pose different challenges for prospective implant treatment. Planning and assessment of suitability for implants in the posterior maxillary area should include consideration of the maxillary sinus.2
While the proximity of the maxillary sinus is important in exodontia and endodontic treatment, a 3-dimensional understanding is vital when placing implants in the posterior maxilla. The shape and volume of the maxillary sinus is best viewed as a 3-sided, pyramidal-shaped cavity within the maxillary bone, often extending into the zygomatic bone, with the base of this pyramid on the medial aspect (lateral nasal wall), and the tip of the pyramid extending into the zygomatic bone. This is appreciated best in a colour atlas of cross-sectional anatomy.
The sinus is fully developed by 18–20 years, but will further increase in size following extraction of posterior maxillary teeth.3,4 In the anterior region, the maxillary sinus will generally extend towards the first premolar area, but can occasionally extend as far forward as the lateral incisor. The floor of the maxillary sinus generally passes downwards and inwards, and its lowest point is usually the maxillary first molar area.
The bony walls of the maxillary sinus may have septae projecting into the air space from any direction, and should be viewed as a variation of normal anatomy, rather than an abnormality that contributes to disease. The incidence is reported as 16%–58%, commonly taking the form of a single septum in one sinus.5,6 Generally, these do not have any influence on normal mucociliary clearance, but can cause significant technical difficulties during augmentation of the sinus floor during or before implant placement, and are the factor that contributes most to increased risk of perforation of the maxillary sinus lining during augmentation7 (Figures 1 and 2).
Identification of septae, particularly those involving the lateral wall prior to implant-related sinus surgery, is essential to assess the risk of perforation of the sinus lining. While septae can be imaged on Dental Panoramic Tomograms, they are best assessed using Cone Beam Computed Tomography (CBCT) (Figures 1 and 2).
The mucosal lining ranges from roughly 0.5 mm to 1.5 mm, and its thickness is significant as a thinner sinus lining may be more liable to tearing during sinus surgery. A history of chronic infection and tobacco smoking contributes to increased thickness.8 The thickness of the sinus lining can generally be identified using CBCT assessment, and identification of any disease can be acted upon.
The significance of variation of thickness of the maxillary sinus lining was discussed in Part 3 of this series. Maxillary sinus lining thickness is generally regarded as more of an immunological response to airborne irritants, rather than disease. Emphasis should be placed on normal function of the maxillary sinus airspace through muco-ciliary clearance and aeration of the airspace, rather than focusing on thickness of the lining in a particular area.
The maxillary sinus takes its blood supply from three significant arterial vessels:
The PSAA is the artery of significant concern in implant surgery as this can lead to significant peri-operative bleeding if damaged during sinus elevation. The average distance of the PSAA from the alveolar crest has been identified as approximately 16 mm.9,10 The development of high quality CBCT images in sinus grafting assessment has led to much easier identification of the PSAA risk factor in surgery (Figure 3).
The thickness of the lateral wall of the maxillary sinus is significant as an assessment tool in sinus surgery, as a thicker wall will potentially complicate surgery or prolong surgery from a patient's perspective, as it requires more time to cut a window carefully. A thinner wall must be treated with great care to reduce the risk of possible perforation (Figure 4).
The width of the maxillary sinus from lateral wall to medial wall (lateral nasal wall) may well determine complexity in the overall procedure. A smaller distance from lateral to medial wall will make surgery less challenging and application of instruments more straightforward. In general, the lateral medial measurement of greater than 20mm will increase the complexity of the procedure considerably, as there is more maxillary sinus lining to elevate carefully without tearing (Figure 3).
As with all surgical procedures, careful assessment of the patient's general health is essential in considering suitability for possible implant treatment in the posterior maxilla.
For patients where there is a risk of underlying chronic rhino-sinal disease, a specific assessment is essential, which is generally carried out early in the consultative process. The Sino-Nasal Outcome Test (SNOT-22) is a clinical questionnaire which is validated, and internationally recognized, for use in Ear, Nose and Throat (ENT) Surgery,11,12 where it is used for assessment of patients before and after paranasal sinus surgery, as a subjective measure of post-surgical improvement in symptoms. The use of the SNOT-22 questionnaire in dental implant surgery is not yet validated and, in consideration of the subjective nature of the assessment, Dental Surgeons should exercise caution in its use before dental implant placement, although it provides a useful list of symptoms to discuss with the patient. If there is suspicion of chronic rhinosinal inflammation, referral to an ENT surgeon through their General Medical Practitioner is recommended before proceeding to surgery.
For dental implant treatment in the posterior maxillary area, routine 2-dimensional radiographic examination using periapical and panoramic radiography is wholly acceptable, and to be recommended in the first instance.13 Although differing CBCT units have been found difficult to compare, it is generally accepted that CBCT doses range from approximately 27–1073 mSv.14 However, the potential increased dose from CBCT (compared to periapical radiographs) is outweighed by the detail of clinical information obtained, and how this can mitigate risk of complications (Figure 3).
Previously, residual alveolar height in the posterior region was thought to be significant in the overall survival and success of dental implants placed in the posterior maxilla. It is now thought that the ability to achieve primary stability through improving bone density, the use of tapered implants, or the use of collared implants, is more significant in the overall outcome than a specific residual height.15 Many clinicians still choose to place implants simultaneously, with sinus grafting only where greater than or equal to 5 mm of bone height exists, but some practitioners have found that this is not necessary and primary stability is the most significant factor.13 In many cases, dental implants can be placed simultaneously with sinus grafting, provided assessment deems this favourable and the operator is experienced enough to be able to carry out the procedure safely.
In poorly planned or executed dental implant surgery in the posterior maxilla, significant complications can arise. Implant survival following maxillary sinus floor elevation is well documented and is a reliable procedure to increase bone height in the posterior maxilla.13 Analysis of 4,800 patients, with almost 15,000 dental implants placed at sites of sinus augmentation, demonstrated implant survival rates which were comparable to implants placed in non-sinus grafted sites.13 However, failure to plan or execute cases appropriately can lead to significant complications.
Perforation of the maxillary sinus lining during implant placement is reported to show minimal complications (within a reasonable perforation diameter16,17) (Figure 4). Perforation of the maxillary sinus lining during elective sinus floor elevation is reported to occur in 10% of cases on average (4.8%–56% range in literature).18 If identified, small perforations of the maxillary sinus lining can be repaired by various techniques but most commonly by the use of a collagen membrane (Figure 5). This does not require the procedure to be halted and it can be continued as planned. In very large perforations, it may be necessary to halt the procedure and to allow the area to heal for a period of time, usually months, before re-attempting. This is reported in less than 1% of cases.18
On occasion, perforations of the maxillary sinus lining may not be identified during the surgical procedure and, as such, this can lead to a greater increase in the possibility of augmentation material passing into the sinus. Displaced augmentation materials, if not removed from the maxillary sinus via muco-ciliary clearance, will act as foreign bodies, causing inflammation, stasis and subsequent infection.
Implants with poor primary stability can become displaced into the maxillary sinus19,20 (Figure 6). With appropriate planning and surgical skill this complication can be minimized.
Significant bleeding from injured vessels during sinus surgery is reported to occur in between 2%–3% of cases.13,21,22 Any surgeon undertaking sinus floor surgery would be expected to have a means of controlling bleeding during sinus floor surgery. Apart from contributing to post-operative facial and cervical ecchymosis, problematic bleeding during sinus floor elevation obscures visual access and increases the risk of perforation of the maxillary sinus lining and subsequent augmentation. Diathermy is regarded as being the most effective method of controlling bleeding.
Aside from dental implant failure, which is reported to occur in 2.8%–6.3% of cases in the literature available,23 maxillary sinusitis is the most significant complication that can occur following sinus grafting procedures in implant dentistry. Post-operative maxillary sinusitis is reported to occur in approximately 2.5% of cases.18
In preparation of patients for elective posterior maxillary implant surgery, full and comprehensive assessment of patients is essential. This involves a detailed clinical examination, radiographic examination and discussion with the patient regarding the possible advantages and disadvantages of such surgery. This presents a wholly different situation from that of extraction of a maxillary tooth, which is often an emergency procedure.
Depending upon individual patient suitability, there are two possible techniques for sinus grafting:
1. A lateral window technique, which is similar to a high labial antrostomy approach in creating a window and elevating the membrane intact to allow implant placement with graft material (Figure 5).
2. A transcrestal approach, which involves the preparation of a short osteotomy site and the introduction of an instrument which is ‘tapped’ to raise the sinus floor. The transcrestal technique involves carrying out dental implant preparation ‘blind’ (Figure 7). Whilst being easier to perform, the transcrestal approach can lead to perforation of the membrane without visualization, and hence cause further complications. It is therefore vital that the transcrestal approach should only be used by surgeons who are also able to carry out a lateral window technique, and therefore repair any perforation which may occur during a transcrestal technique. Implant loss using transcrestal techniques has been recorded as 0–17% (4% on average).13
Various techniques exist to mitigate the possible complications of sinus surgery or sinus grafting to facilitate implant placement, as described below.
One approach to avoid the maxillary sinus is to utilize short implants in what remains of the maxillary alveolus. A short dental implant is defined as a device with a designed intra bony length of 8 mm or less.24 Systematic reviews in relation to the use of short dental implants support the use of short dental implants in partially edentulous patients, with an estimated failure rate of 0.01 per year.25 It is important to know that there is a slightly higher implant survival rate for rough surfaced implants in the mandible than in the maxilla. These may be a valid alternative to the classic positioning of a 10 mm greater length implant in the posterior maxilla requiring sinus grafting.26
The use of angled implants into large bony volumes in the premolar region have been used consistently in implant dentistry to avoid sinus augmentation. There is significant data now emerging to support the use of such restorations, particularly when splinted to axial dental implants in the anterior region in full arch reconstructions27 (Figure 8).
Cantilever restorations from maxillary pre-molar sites obviate the need for sinus involvement. A systematic review concluded that one cantilever, the size of a premolar, supported by two or more implants, is a valid treatment concept in partially edentulous patients with survival rates similar to a standard fixed dental prosthesis on implants.28 At present, there is limited evidence to support the use of cantilever restorations or bars on one implant.
Zygomatic implants and posterior maxillary implants, although advanced treatment options, can be utilized in an effort to avoid the unpredictability of sinus augmentation in patients where it is desirable to do so.29 Zygomatic implants do not avoid encroachment upon the maxillary sinus. The aim of a zygomatic implant is to utilize the dense bone of the zygoma, which has similar bone density to the mandible (Figure 9). Either the zygomatic implant can be placed passing directly through the maxillary sinus, or the sinus mucosa may be displaced to allow implant placement completely outside the sinus (Figure 10). Early research has demonstrated an increased incidence in maxillary sinus infection when zygomatic implants are placed through the maxillary sinus, as compared to those placed outside the maxillary sinus lining.30
Implants in the posterior maxilla, placed in the area between the maxillary sinus and pterygo-maxillary suture are known by a variety of names; tuberosity implant, pterygo-maxillary implant, pterygoid implant31,32 (Figure 11). A true pterygoid implant is placed into the pterygoid process across the pterygo-maxillary suture, engaging more dense bone than that available in the tuberosity area, but carrying with it the risk of bleeding from the pterygoid venous plexus or maxillary artery.
Unilateral maxillary sinus infection of odontogenic origin can arise as a complication of peri-implant infection. This particular complication should be viewed differently from acute post-operative infection that occurs immediately following sinus floor augmentation with implant placement. Peri-implant infection with soft tissue inflammation and bone loss occurs following initial osseo-integration and generally presents as a late complication, 2–3 years after implant placement.33,34 This particular complication is avoidable through regular review of hard and soft tissue implant health, and reinforcement of hygiene measures established before provision of implant surgery, and monitoring of occlusal forces35,36 (Figure 12).
Advances in dental implant treatment to restore the atrophic maxilla in patients who have lost teeth has resulted in a greater range of treatment options available, but equally increased risk of complication including failure. The Dental Team need to provide fully informed consent, giving consideration to realistic expectations, including possible complications and disadvantages of elective maxillary sinus surgery. Full and comprehensive clinical assessment of such patients must be undertaken and, where complications occur, these should be dealt with appropriately and where necessary by specialist individuals.
In this series of four papers maxillary sinus function and disease of relevance to the Dental Surgeon has been summarized. In Part 1, the differential diagnosis of orofacial pain and headaches was discussed with the aim of providing relief of patient symptoms and avoidance of unnecessary surgery or inappropriate antibiotic prescription. The techniques that can be used during removal of teeth to reduce the risk of oro-antral communication and subsequent fistula formation have been outlined in Part 2, along with careful endodontic technique to avoid displacement of materials into the maxillary sinus in Part 3. Lastly, in this paper, the provision of dental implant treatment in relation to maintenance of maxillary sinus health and function has been discussed.
