Abstract
Consequently, to the resorption of the alveolar process following tooth loss, vertical bone height in the posterior maxillary region is often insufficient to receive an implant.
Following dental extractions, the residual bone crest undergoes a complex resorption process.
Moreover, the loss of teeth may induce expansion of the maxillary sinus, which is probably caused by pneumatization the maxillary sinus (i.e. the positive air pressure created during breathing).
Thus, implant-supported prosthetic rehabilitation requires the use of surgical techniques to increase the sub-sinusal bone volume.
The surgical approach is done either by the lateral or by the crestal way. The filling of the sinuses can be done by autogenous bone, by allografts or by xenografts.
In this article we will describe two clinical cases illustrating two different surgical techniques allowing to raise the sinus floor in order to gain vertical height of the edentulous crest. A 4/10 standard implant was placed following the sinus elevation in both cases. Each of the surgical techniques presents its precise indications and a well-defined protocol.
In both cases we can easily obtain satisfactory aesthetic and functional rendering.
Key words: Sinus lift, sinus anatomy, crestal approach, lateral approach, osteotomy.
Introduction
In the posterior maxillary region, the vertical bone height is often insufficient to receive an implant. Following dental extractions, the residual bone crest undergoes a complex resorption process.
The pneumatization of the maxillary sinus causes a resorption in the coronary direction. Besides, the post-extraction alveolar resorption evolves a resorption in the apical direction.
So, implant placement in this region requires the use of surgical techniques to increase the sub-sinusal bone volume. 1, 10
For more than 30 years, sinus elevation has been the gold standard for increasing the vertical height of edentulous ridges in the posterior regions of the maxilla 2. The effectiveness and predictability of this procedure have been determined by numerous studies.
The surgical approach may be performed either laterally or from the crest 3. Thus, the elevation of the sinus membrane allows the placement of a filling material which may be autogenous bone, allografts or xenografts. 3
The aim of this work is to describe different sinus floor elevation techniques based on clinical cases, emphasizing the anatomical considerations and the preoperative evaluations to be taken into consideration.
Clinical Reports
Two surgical techniques are commonly used to treat bone defects in the posterior maxilla:
1. The lateral window approach.
2. The crestal approach.
A. PATIENT 1
Clinical examination
• Patient’s History: Patient aged 25 years in good general condition consulted for an implantsupported prosthetic rehabilitation of the 26 extracted for some years.
• Endobuccal examination: The alveolar crest showed a slight resorption in the vertical direction. It is covered by a well-healed mucosa with sufficient keratinized gingiva. (Figure 1.1) The mesiodistal space was reduced.
• Radiological examination: revealed a reduced vertical height of the edentulous ridge, less than 6 mm. The maxillary sinus was free from pathological signs.
Retro alveolar radiograph: confirms the observations found in the panoramic radiograph.
Scanner: Coronal oblique section showed that the vertical height is reduced, less than 6mm.
The vestibulo-lingual width is sufficient for a standard implant 4/10.
Therapeutic decision
Sinus floor elevation using lateral approach with simultaneous single implant placement:
Surgical procedure: (figure 3)
After infiltration of a local anesthetic, a supracrestal incision was made along the posterior maxillary edentulous ridge. It was complemented with two vertical release incisions anteriorly and posteriorly. A full-thickness flap with trapezoid base was reclined exposing the lateral wall of the maxilla.
A series of specially designed piezosurgery inserts and curettes were used to prepare the area for maxillary sinus grafting.
The delimitation of the lateral window, first described by Tatum 4, was performed with a round piezosurgery insert 5. Drilling was only made through the bone, avoiding laceration of the sinus membrane.
The osteotomy was done under constant irrigation for cooling at a speed of 800-1200 rpm. The maxillary sinus membrane was identified by bluish hue appearing through the thin bone. An oval shape is given to the lateral window to avoid sharp bone edges (Figure 1.2).
After the window has been carefully assessed, the lateral bone was gently removed as to prevent trauma to the membrane. At this stage, the bony flap remains bound to the membrane.
Horn shaped flat smooth insert with dull edges was used for displacing sinus membrane from the floor of maxillary sinus and the lateral flap connected to the membrane.
The sinus membrane was then carefully elevated from the sinus floor using the specially designed curettes. The curettes were used to detach the membrane from the anterior, inferior, and medial walls of the maxillary sinus cavity. The membrane was carefully elevated to be able to create a compartment for the grafting material.
Further to the confirmation of an intact sinus membrane and sufficient superior displacement, the implant site was prepared for a standard 4/10 implant (Figure 1.3).
The sinus cavity was then grafted with bone substitute using 250–1000 m particles of Anorganic Bovine Cancellous Bone (DirectOss) mixed with saline. After sinus filling, the lateral window was sealed with a resorbable collagen membrane at 18 weeks (Figure 1.4).
The flap was repositioned and sutured. (Figure 1.5)
Postoperative medications consisting of 500mg Amoxicillin 2 times per day for 1 week and 500mg of Paracetamol 3 times per day for 5 days were prescribed for the patient. The patient was examined 2 weeks after the surgery for suture removal, and no complications were noted. The patient revealed slight discomfort and swelling after the surgery.
B. PATIENT N°2
Clinical examination
• Patient’s History: A 35-year-old patient, in good general condition, consulted for an implantsupported prosthetic rehabilitation of the 16 extracted in recent years.
• Endobuccal examination: Absence of the 16 (Figure 2.2)
• Radiographic examination: the vertical height of the ridge was reduced but the mesiodistal distance was sufficient. (Figure 2.1)
Therapeutic decision:
Sinus floor elevation using crestal Approach with simultaneous single Implant placement:
Surgical procedure: (figure 4)
In the following clinical case the crestal approach 7,8 using the CAS-kit (Crestal Approach Sinus using hydraulic pressure) was applied, according to the operating protocol defined by the manufacturer 10. Once the oral cavity was disinfected, local anesthesia was performed.
A supra-crestal incision is made along the edentulous ridge. A flap of total thickness was elevated in the vestibular and slightly in the palatal so as to expose the entire width of the crest. The 2.0 mm diameter drill was used to drill up to 2.0 mm in the residual bone. For safe drilling, stops ranging from 2mm to 12mm were set up. The diameter of the drill was then increased gradually in function of the implant diameter which would be put in place later.
For safe drilling, stops ranging from 2mm to 12mm were set up 10. A standard 4/10 mm implant was placed in this case.
The blunt-ended depth gauge was used to measure the residual height of the bone beneath of the sinus floor and to check the elevation of the membrane after each drilling. It was connected to a stop to prevent the perforation of the Schneider membrane. The hydraulic lift was then inserted into the drilled site and 0.3 ml of saline were injected slowly with the 1.0 ml syringe to raise the maxillary sinus membrane. An aspiration and then a new injection were carried out gradually until complete detachment of the sinus membrane. Implant placement was performed at this stage (Figure 2.5).
The filling material consisting of 250–1000 m particles of Anorganic Bovine Cancellous Bone (DirectOss) was carried by the Bone Carrier to the drilling site and condensed by the Bone Condenser 10, 11.
Finally, the implant was placed and the site hermetically sealed.
Postoperative medications consisting of 500mg Amoxicillin 2 times per day for 1 week and 500mg of Paracetamol 3 times per day for 5 days were prescribed for the patient. The patient was examined 2 weeks after the surgery for suture removal, and no complications were noted.
Discussion
A thorough knowledge of sinus anatomy is mandatory for successful sinus lift surgery. The maxillary sinuses are pyramidal cavities excavated in the maxillary bones. They are located laterally to the nasal cavity, above the maxillary teeth, below the orbits and anterior to the infratemporal fossa (Fig. 5). 12
Maxillary sinus has four walls (upper, medial, postero-lateral and antero-lateral), a lower and a top edges. The upper wall corresponds to the floor of the orbit. It is traversed by the infra-orbital nerve. The medial wall is complex. It corresponds to the lateral wall of the nasal cavity, includes the ostium of the maxillary sinus and represents a communication between the maxillary sinus and the nasal cavity via the middle nasal meatus. The position of the maxillary ostium represents the upper limit of the sinus elevation. It must not be obstructed in any way to allow drainage of the secretions.
The posterolateral wall is located opposite to the 3rd molar and the tuberosity of the maxilla by separating the sinus from the infra-temporal fossa. The anterolateral wall corresponds to the lateral surface of the maxillary bone. This is the first surgical approach to a lateral approach. The evaluation of the thickness of this wall is essential before the realization of the lateral flap. The lower edge is narrow it corresponds to the sinus floor. It is formed by the alveolar process of the maxilla with projections corresponding to the dental alveoli. This is the crestal way first. The vertex corresponds to the zygomatic process of the maxillary bone.
The vascularization of the maxillary is complex. The blood supply is assured by numerous arterioles from the sphenopalatine artery and an anastomosis between the posterior superior alveolar artery and the infraorbital artery, also known as alveolar antral artery. It guarantees the blood supply to the sinus membrane, to the periosteal tissues, and especially to the anterior lateral wall of the sinus. 12, 14
The sinus cavity can be smooth and regular or it can present bony septa that rise vertically in a random manner leading to the formation of more or less important partitions. They are present in 37% of patients 12, 14. The presence and location of septa influences the therapeutic approach.
The maxillary sinuses are lined with a mucous membrane known as Schneider’s membrane, which includes a ciliated cylindrical pseudostratified epithelium (respiratory epithelium). 12
This mucosa is fine, fragile and very adherent to the underlying bone. Its thickness varies between 0.3 and 0.8 mm 13.
The pre-surgical assessment must be performed as part of a sinus filling. The panoramic radiograph provides a general view of maxillary and mandibular arches. Cone beam computed tomography (CBCT) provides high-quality images in three dimensions using low doses of irradiation compared with conventional computed tomography.
It can reveal information about residual bone volume, thickness of the lateral bone wall, presence of septa or pre-existing sinus pathologies 12. It can also reveal a significant thickening of Sinus membrane. Mucosal thickening may indicate an inflammatory condition, which must be treated before any intervention. 13
Local contraindications to sinus lifting should be noted. These may include:
– Maxillary sinus infections such as chronic sinusitis, or allergic rhinitis.
– Maxillary sinus aspergillosis of odontogenic origin – Sinonasal polyposis. When the polyps are multiple, it may be associated with other conditions and cause bilateral nasal obstruction.
– Smoking and alcohol are contraindications to this type of surgery such as any bone graft surgery.
The sinus lifting is indicated by the impossibility of placing implants with a minimum length of 8-10 mm 12, 13 in the planned implant sites. The choice of the method is based on Jensen’s classification 16. Measuring the height of the residual alveolar bone may help the surgeon to determine the choice of surgical technique and the appropriate filling material. Although other factors, such as marginal bone width, local intra-sinus anatomy, number of teeth to be placed and surgical experience, may have an impact.
The approach remains rather empirical, depending on the satisfactory results usually obtained by the practitioner. The evaluation of the original bone at the recipient site influences the choice of the graft type. The smaller the remaining bone is the more autogenous bone is required to achieve a good graft quality 17.
Each of the previously described techniques has its own indication. The lateral approach is mainly indicated for a vertical height of residual bone of less than 6 mm. A thorough clinical and, above all, radiological examination can be carried out to assess the thickness of the sinus membrane or the presence of sinus in relation to the surgical site. However, the successes obtained with the crestal approach are also satisfactory and make it possible to gain up to 3-5 mm of bone height.
For the lateral approach, the delimitation of the lateral flap, first described by Tatum 4, is carried out with a tungsten carbide or diamond cutter mounted on a contra-angle 5. This technique is still used when the side wall is thick. However, in the case of a thin lateral wall, the risk of perforating the Schneiderian membrane is high. This is the reason why some opt for the use of a piezo surgery ball insert 6. This osteotomy is done under constant irrigation.
The lateral window, often rectangular or oval in shape, is outlined with a size of approximately 10 mm x20 mm. 1
However, the oval shape may avoid sharp bone edges. The separation of the bone flap is also completed by a flat piezo surgery insert with a diamond base. The bone window can either be infracted with the membrane or removed for replacement after the augmentation. 1
The transcrestal sinus floor elevation technique has some advantages over the lateral sinus floor elevation procedure, such as less trauma 10, shorter operation time and less postoperative morbidity. Moreover, the implants are commonly placed simultaneously with the transcrestal sinus floor elevation procedure. It is indicated when the residual height below the maxillary sinus is around 5-8 mm and a dental implant exceeding that height is to be installed. The technique is particularly suitable for single tooth gaps with sufficient bone width but can be used for multiple implants. 1
There are two principally different techniques with regard to the perforation of the sinus floor preparation of the implant site starts according to the traditional drill protocol and is completed either with drills to the level of the sinus floor or by using an osteotome as part of the preparation. As the crestal approach is a ‘blind’ procedure 10, assessment of the condition of the membrane has to be performed through the osteotomy site. 1
After preparation of the site is complete, together with lifting of the sinus membrane, with or without additional bone material, the implant is installed.
The long-term clinical outcome for the procedure is good (a 97.2% survival rate of the implants followed up to 6 years compared with 93.7% for the lateral window approach) and complications are few. The clinician should, however, bear in mind that for a predictable outcome, namely a flat sinus floor without bone septa, an intact Sinus membrane is essential and membrane elevation must be performed with great care.
Conclusion
Sinus floor elevation has become a technique of choice for the treatment of insufficient bone height in the posterior maxillary region. And there is a wide range of techniques available for maxillary sinus augmentation. The choice of technique will largely depend on the characteristics of the edentulous site, which will either allow or prevent placement of implants simultaneous to the augmentation procedure.
Other therapeutic alternatives have been proposed such as short implants. These have proved to be effective in the short term, but there is a lack of studies on their longevity. So Although there are some contraindications to the procedure, there are almost no absolute contraindications. With experience, maxillary sinus floor elevation is a procedure that greatly benefits the patient, with a predictable outcome.
