Implant stability is critical to implant success, and the amount of available bone is vital to achieving that end. Because of low-lying maxillary sinuses, adequate alveolar height on the posterior maxilla is often lacking in many patients in need of implant replacement. This chapter reviews both the traditional lateral sinus lift maxillary approach to achieve vertical augmentation as well as the transcrestal osteotome intraoral approach. A discussion of osseodensification will also be mentioned as an alternative approach.
Over time, the maxillary sinus undergoes a process called pneumatization.
Over time, the alveolar bone of the posterior maxilla will undergo resorption.
Augmentation of the maxillary sinus can be performed by using a transcrestal sinus lift or a lateral approach.
A common clinical finding facing the implant surgeon when planning for implant placement in the posterior maxilla is lack of adequate bone height either due to low lying maxillary sinus or due to atrophy of the alveolous following extraction. Augmentation of the site can be performed by using a transcrestal sinus lift or a lateral approach. Both techniques are discussed in this chapter.
Anatomy of the maxillary sinus
The maxillary sinus is an air space that occupies the maxilla bilaterally and is surrounded by the nasal cavity mesially, the maxillary tuberosity laterally, the orbit superiorly, and the alveolar bone inferiorly. The volume of the maxillary sinus is approximately 20 mL and is usually present at birth completing its development at 18 years of age.
The maxillary sinus is also lined with ciliated pseudostratified epithelium, and there are cilia lining the membrane of the maxillary sinus as well, the purpose of which is to clear the paranasal sinus cavity of pathogens and debris that are continually inspired in normal respiration.
The maxillary sinus is robustly supplied by multiple arteries, which include the infraorbital artery, greater palatine artery, lesser palatine artery, sphenopalatine artery, and the posterior superior alveolar artery.
Over time, the maxillary sinus undergoes a process called pneumatization. This process occurs when an individual loses their posterior maxillary teeth and in response to this loss of teeth the maxillary sinus will enlarge and encompass a larger portion of the posterior maxillary alveolous. Pictured in Fig. 1 is a pneumatized maxillary sinus. Over time, the alveolar bone of the posterior maxilla will undergo resorption. The pneumatization of the maxillary sinus and resorption of the maxillary alveolar bone results in difficulty placing dental implants in the maxillary sinus. A maxillary sinus lift is conducted in order to facilitate the placement of dental implants in an environment with diminished vertical bone height. In order to have a successfully integrated dental implant, the recommendation is to place at least a 10-mm long implant with a width of 3 mm.
The diagnostic and surgical workup for those patients who may require a sinus lift begins as most other surgical workups do, beginning with obtaining the following needed information: chief complaint, medical history, medications, allergies past surgical history, and dental history. A patient who may require a maxillary sinus lift may indicate that they lost their maxillary posterior teeth many years ago and have trouble eating. Other patients with big smiles may indicate that they do not smile as much as the missing posterior teeth are noticeable.
An important part of the medical history is for the practitioner to ascertain that the patient does not have a history of bleeding problems. This is especially important as one of the complications of a maxillary sinus lift is perforation of the maxillary sinus intraoperatively, which can lead to bleeding, which would be worse in a patient with a history of bleeding problems. A patient with a history of bleeding problems may report a history of frequent nose bleeds, heavy menstrual bleeding (in females), easy bruising, and a history of prolonged bleeding after a wisdom tooth extraction. A patient on blood thinners such as Warfarin or PO Heparin is also prone to excessive bleeding intraoperatively.
Another important factor relevant to the medical questionnaire is learning about a possible history of rhinosinusitis. Rhinosinusitis is associated with nasal congestion, postnasal drip, headaches, and sore throat, and evidence of rhinosinusitis may be seen on dental imaging. Later in this text, the author will discuss the implication of radiographic findings associated with the maxillary sinus.
Following the medical history, a physical examination must be conducted. The author recommends starting the examination with a complete head and neck examination to rule out any gross abnormalities followed by the intraoral examination. Specifically, it is important to note the buccal/palatal width of the maxillary alveolar bone, presence of keratinized tissue, and intraocclusal distance for the final prostheses. In order to place an implant of 3 mm diameter the buccal palatal length of the maxillary bone must be 4 mm.
Following completion of the physical examination a radiographic examination is performed. Generally, a panoramic imaging study is adequate; however many practitioners may include a cone beam computed tomography (CBCT) study as well in order to accurately assess a patient. The 3-dimensional CBCT allows one to obtain information necessary information about the buccal/lingual width of the maxillary alveolar bone, and one can also determine the exact distance from the crest of the alveolar bone to the maxillary sinus. In addition, the CBCT study can also reveal whether there are septa within the planned sinus surgical site. Normally, septa with low height (less than 2 mm) do not require further attention because the membrane can usually be elevated without difficulty. However, high septa with partial or complete separation of the sinus cavity may involve the preparation of 2 windows during sinus lift surgery. Finally, the clinician can observe possible sinus mucosal thickening, sinus polyps, and air fluid levels. This chapter, in a later section, discusses the implications of these findings on the success of a maxillary sinus lift and ultimately, the placement of a dental implant.
A maxillary sinus augmentation is recommended when there is less than 10 mm of space available from the alveolar crest to the maxillary sinus, and the clinician and patient wish not to use small implants to reconstruct the area. As part of the discussion with the patient, the length of treatment time should be discussed with the understanding that the patient may or may not have a single stage or possible 2-stage implant procedure.
In a 1-stage implant placement, the implant can be placed at the same appointment as the sinus augmentation, whereas in a 2-stage implant placement, the sinus augmentation is performed first and the dental implant is placed 4 to 6 months later. Later in this chapter, the recommendations based on evidence-based medicine for one procedure versus the other are discussed.
During this appointment, the risks, benefits, and alternatives to the procedure must also be discussed with the patient, and it is recommended that a formal consent be obtained and signed by the patient as well.
Abnormal radiographic findings
Upon review of the imaging studies, the practitioner may notice abnormal maxillary sinus findings including, but not limited to, mucosal thickening, sinus polyps, mucosal perforation, opacification of the maxillary sinus, and obstruction of the osteomeatal complex. The reported rate of incidental radiologic sinus abnormalities in asymptomatic patients is as high as 60%.
An air fluid level would be the most typical imaging finding of mucosal thickening ( Fig. 2 ). A sinus polyp would be viewed as a hypodensity in the maxillary sinus ( Fig. 3 ). Opacification as the name suggests would be seen as an opacified maxillary sinus ( Fig. 4 ). Lastly, the obstruction of an osteomeatal complex would be seen as opacification of the maxillary sinus.
If any of these pathologies are viewed on the patient’s radiograph, additional discussion with the patient is warranted. This discussion should rule out any history of rhinosinusitis. Rhinosinusitis can be divided into acute and chronic states, with acute being defined as symptoms lasting less than 4 weeks. These symptoms include nasal mucopurulent drainage, facial pressure and/or feeling of fullness, nasal congestion, and possible loss of sense of smell, whereas chronic rhinosinusitis is defined as symptoms lasting greater than 4 weeks.
If a patient denies any symptoms of rhinosinusitis, the radiographic findings can be considered to be incidental findings and is not a contraindication to performing maxillary sinus augmentation. The most common augmentation complication is maxillary sinusitis and has been reported in 27% of cases. Incidental radiographic findings with no clinical symptoms do not increase the risk of developing maxillary sinusitis. It is important to note that patients who do have symptoms of acute or chronic sinusitis should be referred to an ear, nose, and throat doctor for possible treatment, as these patients are at possible increased risk for postaugmentation maxillary sinusitis.
Bone grafting materials
During the maxillary sinus augmentation technique, bone grafting material is placed inferior to the sinus membrane. Before this, the sinus membrane is elevated on the medial and lateral walls. The options of bone graft materials available include the following:
.Autograft—bone graft from the patient
.Allograft—bone graft from the same species (but not from the patient)
.Alloplast—a graft material that is engineered, it is derived from a nonanimal source
.Xenograft—bone graft from a different species
The graft material that is the gold standard and has the highest success rate is the autogenous bone graft. In situations where large amounts of bone graft is required, the anterior iliac crest is an option. From this site, one can obtain approximately 50 cc of corticocancellous bone ; however, if even more bone graft is required the options are either anterior iliac crest or the posterior iliac crest. If a small amount of bone is needed, there are several options. These include the maxillary tuberosity, mandibular ramus, or mandibular symphysis.
As an alternative to autogenous bone grafting, nonautogenous bone grafts are also a viable option and are advantageous because there is no associated donor site morbidity, they are associated with good success rates, are easily obtained, and are easy to use.
A lateral maxillary window sinus lift is generally performed on patients who require more than 3 mm of augmentation. Generally, when a large amount of bone is required to place an implant, the lateral window sinus lift is recommended rather than a transcrestal sinus lift.
An incision is made over the alveolar crest from the maxillary midline to where the implant osteotomy site is planned. The incision should extend past the osteotomy site so that the incision can be closed on sound bone. While making the osteotomy, one should keep principles of surgical access and good visualization in mind. A dental bur or a piezoelectric device is used to create an oval or rectangular osteotomy over the lateral maxillary sinus wall ( Fig. 5 ). It is important to not perforate the sinus membrane during this step. Once the lateral window has been made, the sinus membrane is teased off the floor of the sinus and from the surrounding walls ( Fig. 6 ). The bone graft is then placed under the sinus membrane. The practitioner should aim for having 12 mm of bone after the sinus lift is completed, keeping in mind that the length of the implant will be at least 10 mm. The few extra millimeters of bone are in order to account for bone resorption during the healing process. Once the bone graft has been placed, the incision is primarily closed with resorbable sutures.