Clinical case of guided surgery by Doctor Marco Cernicchi. From computer design and model creation to the operation on the patient.
Stage 1 – Laboratory
After developing our model, it is acquired by means of a structured-light scanner. Once the master model has been acquired, the virtual processing starts with Exocad. When the 3D virtual model is obtained, the tooth library to be used on the model is selected and the virtual design phase starts. Checks are performed with the opposing arch to make sure that all teeth are correctly positioned. Once the virtual wax-up is complete with all the necessary requirements, it is sent to the centre that will create the surgical guide. At the end of the design phase, the production centre sends the model created with 3D printer back to the laboratory, so that lab analogs can be fitted on it. The latter simulate the position of the implants that will be inserted into the mouth. Then MUAs are fitted, at the indicated angles, as well as grade 5 titanium screws. At this stage, a new scanning is performed. This scan is reconstructed onto the initial diagnostic wax-up to obtain a functional model with precise aesthetical features. Once the framework has been fully designed, still virtually, a file is sent to the milling centre that will create a titanium framework. When the 3D model is sent back, the prosthetic components selected in the design phase are reassembled. After checking that the framework complies with the project, standard teeth are mounted on it, always complying with the initial project. The prosthesis is ready and consistent with the model, ensuring a correct dental occlusion and a good aesthetic appearance.
Stage 2 – Working plan
10 years ago, 3 implants were inserted in the lower arch of the patient concerned in this case: two of them to support the incisor group and one in the region of tooth 34. At that time, the patient had other teeth, but she has lost some of them over the years, including one of the inserted implants. Since it is necessary to remove all teeth to install a fixed final prosthesis, and considering the low bone density of the patient, it has been decided to perform a computer-assisted surgery. However, the main reason for this choice is the need to reposition the implant found in region 34 placing it in region 35, where the space available is limited and a great precision is required. When planning the positioning of implants, they have been set, respectively, in zones 35, 32, 42 and 45. 35 and 45 will be placed at the classic 30-degree angle. Then the diagnostic wax-up has been made in the laboratory and, based on it, implants have been set. At this point, the position of the 3 fastening pins is decided. All teeth will be removed, but tooth 33 will be left in place in a first moment because its stability will allow using it as a reference point for the surgical guide, before fixing the latter with the fastening pins. Only at this point, the tooth will be removed. The surgical guide is sent to the dental clinic from the laboratory and will allow a correct setting of all the elements necessary for the surgery (MUAs, pins). The guide features bushings which, besides providing the correct depth that the implant will reach when penetrating inside the bone, indicate, through notches, the exact position of the hexagon angles. EL implants by C-Tech, with tapered connection and internal hexagon, will be used. These implants will all measure 3.5×13 mm.
C-tech kit for guided surgery:
– Drill for side pins: it is used to insert side pins to stabilise the surgical guide
– Punch: instrument used to create the gingival operculum through which the various drills will pass.
– Lance-shaped drill: it is used to incise the cortical bone and create a hole for the other drills.
– Drills: drills are of different types with increasing diameters, from 2.1, 3.1, 3.5, up to, if required, dense bone drills. Since 3.5 implants are concerned in this case, drills will be used in sequence for each implant site (first 2.1, then 3.1 and finally 3.5).
– Implant Driver: device on which the implant is inserted to be positioned; it features an hexagon that must be aligned with the notches on the bushing. Apart from using the motorised mounter, implants can be inserted using a manual ratchet.
– Implant Mounts: used for a better stabilisation of the guide. They can be fastened after inserting the first implant, so that the guide is stabilised according to the position of the implant concerned.
The kit features two different parts: one for small 3.1 / 3.8 mm diameters and the other for larger 4.3 / 5.1 mm diameters.
Stage 3 – Surgery
Since in this case the patient has a complex occlusion and her arch still has teeth, sectional implants have been made at strategical points as a first step, in order to insert the prosthesis at a later stage. A post-extraction with immediate loading will be carried out with a computer-guided technique.
Implants have been removed from zones 32, 35 and 42, as well as the provisional implant and the remaining teeth. The tooth in zone 33 is kept in place to be used as a stable reference point.
Then, the surgical guide is applied and fastened using the side pins: at least 3 pins are required to ensure a good stability.
At this point, the opercula are created on the gingiva using a punch drill with low-speed rotation. Then a lance-shaped drill is inserted into the operculum to drill the cortical bone.
The first drill used measures 2.1 mm, the second one 3.1 mm and the last one 3.5 mm. In these phases it is important to perform an up/down movement to allow the cooling liquid to enter the bone and prevent the latter from overheating. Then the implant is inserted, at first with a motorised handpiece and then with a manual mounter, which will refine the insertion and make the implant reach the correct depth. The hexagon featured on the mounter must be aligned with the notches on the bushing. The implant insertion torque must range from 35 to 45 Newton. After inserting the implants, mounters are removed and the surgical part of the operation is completed.
The next step is the prosthetic phase. First of all, pins and guide are removed in order to allow the insertion of multi-unit abutments (MUAs). MUAs are tightened with a torque wrench at a torque of 25 Newton. MUAs in zones 32 and 42 are straight, while those in zones 34, 35 and 45 are angled (34 at 17 degrees and 35 and 45 at 30 degrees). After tightening the prosthetic screws, the last tooth left is removed and straight pillars are inserted onto the MUA “screws”, onto which the titanium prosthetic framework is glued. Lastly, the cement is applied, removing the excess material, and solidifies in 5 minutes. The prosthesis is then removed and sent to the laboratory, where laser micro-welding is performed between screws and prosthesis in order to reinforce the fastening obtained with the cement. The finished final prosthesis is positioned into the mouth and fixed to the implants. At last, the occlusion is checked and the holes for prosthetic screws are closed using filling material. The operation is now completed and the patient will be monitored over the following 4 months, after which a relining of the lower resin part will be performed.