April 10, 2012
This 61 year old male patient was referred after losing his upper right first molar tooth. The initial OPG showed a shortage of bone height into which a dental implant could be placed.
When missing teeth are replaced with dental implants, it is of course essential that sufficient height and width of bone exists to accommodate the implant fixture. In the upper molar region, enlarged maxillary sinuses can mean that insufficient bone height exists, particularly if it has been some time since the teeth were extracted and the sinuses have ‘pneumatised’. A technique pioneered back in 1985 called a ‘sinus lift’ allows bone volume to be increased in the sinus floor enabling a longer implant to be placed.
Traditionally the window for the sinus graft was created using rotary surgical burs and extreme care would be needed to remove the bone without breaching the underlying sinus membrane. A variation on the original technique is to place the implant fixture at the same time as the sinus lift and this can be done if 4mm or more bone is available for primary implant stability.
The process begins with referring the patient for a low dose Cone Beam CT scan (CBCT) so that the three dimensional anatomy of the sinus can be seen. This will show pathology as well as structures such as septae, which occur in 33% of sinuses. Fortunately 77% of septae are in the anterior region so the further back we go the less chance of these being present. Interestingly more septae occur on the left side by a ratio of 3:1. The CBCT scan will also show thickened sinus membranes, which can occur in the presence of chronic infection. Active periodontitis around the teeth underlying the sinus is a common cause of this and would contra-indicate sinus surgery until the teeth are treated or removed and a further scan confirmed resolution of the sinus membrane.
The implant placement can also be planned at this stage and calculations made as to how much bio-material is required for the sinus graft itself. Some planning software will work out the volume of graft material required and this can be very useful especially given the high cost of these products.
Pre-operative antibiotics are given and these must be broad spectrum ones as we are working within the sinus, an area with significant infection potential. Amoxycillin 500mg tds for 7 days pre-operatively can be used, alternatively cephalexin 500mg qds 3 days or clarithromycin 500mg bd for 3 days. Clindamycin has been shown to be ineffective in prevention and treatment of sinus infections and is thus not used.
The sinus is accessed via a window on the buccal wall known as the Caudwell-Luc approach. Particular care is taken when retracting flaps for sinus lifts around the infra-orbital foramen as damage to the neurovascular bundle can occur due to the extent of the flap design in gaining access to the bony wall.
I now choose to predominantly use DASK is used to simultaneously remove the bone and using internal saline irrigation, push the sinus membrane away so that it is not torn. This technique has superseded the traditional surgical bur Caudwell Luc approach, which risked tears in the membrane. There are many surgeons that use Piezon systems very well and I have in the past. In my hands however the DASK presents much less tear risk than the Piezon.
The main anatomical concerns are the arteries that run along and within the buccal sinus walls, particularly the posterior superior alveolar artery. This runs within the bony wall in the majority of people but fortunately at an average height of 22.75mm from the alveolar crest. Only 20% of these arteries are below 15mm from the alveolar crest and around 60% show on the CBCT scan. As there is still a risk of rupturing this major vessel, the osteotomy must be completed slowly and carefully so that if rupture does occur, it does so before entrance to the sinus is made.
Once the window is created and the membrane checked for lack of tears and this is by observing the movement of the membrane as the patient breaths in and out. If the membrane does not move during breathing, a tear is likely and a collagen membrane would then be placed into the sinus to form a pouch with the membrane above it. The bio-material is then placed beneath the elevated sinus membrane mixed with some autogenous bone scrapings to increase the ostegenic potential of the graft. It is important that there is some venous bleeding at this stage into the graft as it will be this blood clot that forms the start point for osteogenesis.
Opinions differ of the exact choice of bio-material but it has to be remembered that the process of bone growth occurs not because of the material itself but due to the spacer effect that it has by keeping the sinus membrane away from the bony sinus floor and containing the blood clot between. In this case I have used Osteon sinus as it is presented in easy to use syringes that nicely fit the window created by the DASK bur system.
The sinus membrane is gently held out of the way whilst the implant osteotomy is prepared. This stage is the most delicate as a tear to the Schneiderian membrane is all too easy. This membrane if healthy measures only 0.13 to 0.5mm in thickness so extreme care is required. Anecdotally ex-smokers are easier to work with as their membranes are thicker however I would insist that a smoker had stopped for over 3 months prior to surgery so that the healing potential improved. The smooth sided sinus instruments are used help to minimize the tear risk. I always work with loupes and 3.8x magnification when working on sinus grafts and find this helps enormously.
If a tear does occur the treatment will depend upon the extent:
After completing the osteotomy, part of the sinus is filled with Bio-material and carefully packed towards the medial wall using wide flat ‘elephants foot’ instruments. This ensures that this area is filled well as it cannot be accessed after the implant has been placed. The packing must be done very carefully and slowly as the particles themselves are quite sharp and may pierce the membrane if excess force is used. Large particle sizes are preferred as this provides that largest spaces for blood clot formation and thus better osteogenesis.
The implant is now placed and the Bio-material hydraulically pushes the membrane upwards leaving a further space which is filled with more material. I typically use an engine driver but on a very slow rotation.
The exact volume of bio-material required will depend upon the planned implant length and the dimensions of the sinus however the sinus should not be filled as a rule beyond 15mm from its floor as occlusion of the ostium may occur. There should be no reason to do this as long implants will confer no additional support than standard sizes. The ostium semilunaris is an incredibly important landmark to protect as lymph drainage of 2 litres per day occurs through this from the sinus. I have observed the results of a surgeon occluding the ostium with an excessive volume of bio-material and it was truly awful.
Finally a collagen membrane is placed over the window and the site sutured up.
It is essential that clear post-operative instructions are given particularly warning against activities that may create pressure changes or movement in the sinus for 4 weeks. These include refraining from…
The latter two are difficult ones as coughs and colds can be caught at any time. The pre-operative antibiotics regiemes mentioned at the start will help prevent sinus infections however.
A post-operative OPG shows the implant in place and the bio-material surrounding it. This will be left buried for around 6 months allowing the patients bone to grown into the graft. After this time the implant can be restored in the normal way. There should be no reason for a further CBCT scan if healing is uneventful.