Dental Clinical Articles
Posted: 17 May 2011
CBCT in implants - Planning your game
Relying on guesswork can have disastrous effects when placing implants. Julian Perry looks at why three-dimensional planning is essential before embarking on treatment
Implantology has advanced considerably since the mid 1950s, after the pioneering work by many implantologists including Per Ingvar Branemark. Unfortunately, though, there are still many clinicians carrying out sub-standard treatment, and for those who don’t know it already, the General Dental Council (GDC) now has a dedicated unit tasked with looking out for unacceptable treatment delivered to patients whose expectations have not been met.
Three-dimensional surgery in 2011 requires that three-dimensional planning take place, which includes full diagnostic wax up and surgical templates. However, I often meet colleagues who think they don’t need wax ups or stents to place their implants.
I accept that a skilled clinician can estimate the mid-point of a single tooth for implant placement, but not the placement of multiple implants in a free-end saddle situation or worse still, a full arch. Many get away with this unplanned approach because of the skill of their technician, but I doubt many of us would accept this haphazard guesswork if it was in relation to our own treatment.
If you ‘guess’ the first part of treatment, for example, placement in this case, you are stuck with the ‘guess’ as a legacy throughout the entire treatment. Poor placement causes a number of problems. Many are of course as a result of not meeting the patient’s expectations on aesthetics, but others are to do with food trapping, ridge-lapping and lip support, nerve damage, buccal dehiscence, sinus perforation, nasal floor perforation, lingual plate perforation, and sublingual haematoma, to name a few.
Cost is often an underlying concern and the less you spend on a job, the greater the profit. The problem comes when doing something too cheaply results in a poor outcome. Redoing or compensating for a poor placement costs a lot more than to have done it correctly the first time. For around £250, a laboratory can supply study casts, wax up, radioopaque stent and pilot guide.
Clinicians make stents in many different ways, and a simple radiographic stent is a good choice; a full tooth with the emergence point of the abutment marked out by a hole drilled in it (Figure 1).
The radiographic marker should look like Figure 1 in situ and sit ‘over’ the ridge of bone. If the patient is short of bone and you intend to graft the area, place the tooth in the final position. In this way, you will see on the scan the extent of the graft required.
This money isn’t wasted as it becomes a sales and communication tool for future prospective clients, as well as helping you do the job properly. Implant surgery is a three-dimensional process. As dentists, we see teeth three-dimensionally because all surfaces are visible. Bone is not visible and two-dimensional planning leaves us with a substantial void in our knowledge.
What can go wrong?
Today, with the advances in cone beam CT (CBCT) scanning and reduced doses of radiation, it is difficult to argue the case not to use three-dimensional planning for three-dimensional surgery. Let’s look at a case of poor planning when it comes to placing implants through a bilateral inferior dental canal (Figure 4). Without using CBCT, it is not possible to identify the inferior dental nerve position accurately, which resulted in bilateral anaesthesia/parasthesia.
Without the using CBCT scanning, the dentist mistook artefact for bone. The result - an implant placed in sinus tissue (Figure 5). Using CBCT would have helped enormously to avoid this situation.
In the case shown in Figure 6, the patient had received bilateral autogenous (hip bone) grafts in hospital. Had a CBCT been taken prior to placement, it might have been spotted that the graft had failed, was not attached and that the sinuses were full of inflammatory material (confirmed on re-entry).
As a result, one implant was placed straight into the sinus. This was later removed and the area re-grafted with Bio-Oss and a membrane, which also resulted in failure because of the residual inflammation. This then required a further operation to take everything out followed by three months of antibiotics, an oro-antral fistula and a very unhappy patient.
Normal non-pathological variation in anatomy can also be surprising (Figure 7). This section is through a lower first premolar site. Two things could cause a problem here:
1. The narrowing of the bone width which could result in lingual perforation if a sufficiently long implant was used
2. This slice is anterior to the mental foramen and yet the nerve is present in the slice reminding us of the anterior loop of the mental foramen.
In the next case (Figure 8), the OPG taken indicated that there was approximately 18mm of bone height. The CBCT of the 24 site showed that the anterior-medial portion of the sinus extended forward. The density of the buccal plate masked the sinus space giving the impression of adequate bone. The dentist concerned was initially thinking of placing a 14mm implant into this site. The clinician does not have experience carrying out sinus-lift procedures, so if he had not received this information, he may have found himself in some difficulty.
Figure 9 has been used to describe a finished case. If we look at this carefully, there are a number of potential issues. It would appear no stent was used, as the implants do not appear to be correctly placed. The anterior implant appears to be in contact with the root of the tooth in front, which also appears to be inadequately root filled and with a defective restorative distal margin. It may of course be that the implant is not quite touching, but there is no getting away from the fact it is in the wrong position and you would have to wonder about food packing to the anterior implant, and also between the posterior implant and the root-treated molar tooth. I wonder what will happen to the implant if and when the lower premolar tooth, which is inadequately root-filled, fails. And have you noted the relationship between the distal implant and the ID nerve?
It is not acceptable to find some bone and stick an implant in and then hope the technician can work a miracle. These days, implant work should always be carried out in partnership with the technician from the beginning, while making use of investigative and planning techniques which are now freely available.