How to make a silicone index that works for you
One of the biggest game changers in dentistry for many practitioners is starting the use of a silicone index in the anterior composite work. The palatal silicone index is an impression of the wax-up intended for transferring that information into the mouth during treatment. It allows the practitioner to fully focus on the application of the composite layers, as both the sagittal dimensions are already perfectly defined: the length and the incisal edge position of the desired final result, as well as the mesial and distal angles, the incisal thickness, the facial curvature of the restoration; you can completely rely on the matrix to guide you in making what your patient wants. Because it is that exact shape, form and length the patient approved during the mock-up phase which has been transferred to the mouth via the silicone index. In a layering case, most of the times a lot of attention and time is put in the dynamic incisal third of a tooth. By not using the patient-approved index the situation will occur in many cases that the patient asks for shortening of the just applied restoration. Thereby asking for removal of all preciously applied character of the incisal third. Using the silicone matrix based on the wax-up, that was patient approved on mock-up, guarantees the operator that the final occlusal and esthetic adjustments will be minor and fast. The characterization of the incisal third will be kept alive. But how to exactly make the guide to serve you best? This article will go through the steps.
Img. 1 – Initial situation shows a worn dentition with failing discoloured composite restorations on all anterior teeth. Patient had already started orthodontic treatment of the lower arch because of crowding and rotations. Orthodontic treatment in the upper jaw was started to improve the gingival architecture and manage space before restoring the teeth with composite.
Img. 2 – Before starting orthodontics most of the old composite that was once applied to close diastemas was removed to allow the orthodontist to divide the space equally.
Img. 3 – The length of tooth #2.1 was significantly decreased because of wear patterns in the patient articulation and occlusion. Typical sign is the dropped gingiva level but same level of the incisal edge. Orthodontic relevelling is the preferred treatment avoiding surgical bone corrections.
Img. 5 – Diagnostic study casts were made and the use of direct composite was the method of choice to restore the teeth. A wax-up of teeth #1.3 up to and including tooth #2.3 was created to ameliorate the length/width ratio of the teeth and to close the diastemas.
Img. 6 – The first step of making a palatal silicone index is choosing the right material to do so. Most commonly used material is a vinyl polysiloxane, also referred to as PVS. What should be the material properties? High reproduction of detail and a high final hardness are major. Shore hardness is a scale for measuring the hardness of materials like rubber, elastomers et cetera. The higher the harder. For example Shore A 45 is relatively soft and Shore A 90 hard. The material used has a final hardness Shore 85 which is excellent for its purpose.
Img. 7 – This is the average amount of catalyst gel mixed in. Already spread over the whole surface for better mixing.
Img. 8 – But always try to work in Style!
Img. 9 – The mixture will turn into blueberry yogurt ice cream if it is not mixed fast enough. And even more unwanted, folds will develop. This is unsuitable for an accurate impression of the wax-up at this point.
Img. 10 – Mixing within 30 seconds using a very fast-paced motion of thumbs and fingers results in a mouldable ball with a homogenous colour that is ready to be used on the wax-up with a remaining working time of two minutes.
Img. 11 – The ball is positioned on the palatal and pressure is put in palatal and frontal direction.
Img. 12 – The material is softly pushed on top of the incisal edges making sure they are completely covered until just over the edges. Pressure is only exerted on top: no finger pressing against the labial side. That way the final cutting of the edges is easier because of better visibility.
Keeping the layer of material very thick ensures the stability of the silicone matrix intraorally.
Img. 13 – The desired extension of the material depends on which tooth or teeth are treated. The matrix always rests on the occlusal plane of teeth that will not be treated in order to have the stability of the matrix guaranteed during treatment. In this case the matrix is extended over the premolars until the mesial of the first molar.
Img. 14 – Occlusal aspect of the silicone on the model. Setting time of the material used is 6 minutes. Patience is mandatory before starting the refining with a scalpel. Precise cutting in unset material is difficult.
Img. 15 – The silicone matrix is carefully removed from the wax-up avoiding any damage to the vulnerable wax. First adjustments have to be made to enable proper seating of the matrix during treatment while the rubberdam is place.
Img. 16 – Close-up of the incisal edges in the material. In this picture especially on tooth #1.1 and #2.1 just labial of the incisal edge a shadow can be observed. That is where the scalpel will cut away any material that is overlapping the labial of the teeth.
Img. 17 – All material that is unnecessary for stability of the matrix can also be removed. To cut away the excess material a #1.1 scalpel is used.
Img. 18 – The complete palatal part is cut away along the cervical to make sure there is no rubberdam interference with the seating of the index.
Img. 19 – The most important cut is the one along the incisal edge. Bear in mind that the incisal edge has a certain thickness. The first layer of composite applied within the index will be the palatal with the incisal edge included. It is like the shape of a hockeystick. Do not cut away the crimp at the end. The use of a magnification loupe can be beneficial.
Img. 20 – By checking on the wax-up it can be determined whether enough PVS material has been removed. Here the central incisor is cut precisely, but the labial of the right lateral incisor is still partly covered and needs some more adjustment.
Img. 21 – Slicing away little excess remaining. A very sharp, new scalpel can be helpful.
Img. 22 – The scalpel is held parellel to the palatal surface of the teeth while cutting the edges.
Img. 23 – Special attention is to be given to the cuspid. Because of its more rounded anatomy in most cases the cuspid edge cannot be cut in one go, but has to be unwrapped in two cuts. The first starting from the approximate to the middle.
Img. 24 – Then turning the scalpel slightly and cutting away the rest from the middle towards the approximal.
Img. 25 – The unwrapped cuspid.
Img. 26 – The matrix shows the rounded form of the cuspid and the change of directions of the cuts to unveil the incisal edge of the cuspid.
Img. 27 – The silicone index is put in the mouth. Intraorally the matrix is not sustained by the wax-up. Emphasizing the need of the extension of the matrix to the (pre)molar area. And the importance of the use of a PVS material with a high Shore hardness to lower the compressive deformation. After the bonding procedure the first layer of composite can be applied within the matrix. Creating the palatal shape, form of the mesial and distal angles and the position of the incisal edge. Further layering will complete the restoration. In the finishing stage the silicone index will be used again according to the article The Power of Pencil to remove any surplus of composite that might have thickened the incisal edge.
Img. 28 – Final result in close-up. The index has guided the composite layering treatment, the incisal edge postion, the facial curvature and the shape of the angles and embrasures. The teeth look unworn, rich in enamel and vibrant again.
Img. 29 – Initial situation.
Img. 30 – Final result. Comparing to the initial situation all the old composites are replaced, the gingival architecture is improved, the tooth are restored in form and colour and the diastemas are closed.
Thanks to dental technician Ronald Mak for the laboratory work.
In every restorative treatment a lot of aspects have to be controlled at once. For example shape, occlusion and incisal edge position. The use of the silicone index ensures excellent control over many aspects during treatment. An accurate transfer of the wax-up information to the mouth is therefore guaranteed. If teeth are built up with a layering technique the silicone index will guide the layering. All final adjustments of occlusion at the palatal or the incisal edge are minor. This reduces the finishing time of the treatment drastically, but perhaps even more important is the fact the incisal 1/3 stays perfectly intact in the finishing stage because no significant length reduction will be asked by the patient. The length was already patient approved by mock-up. The restoration will keep its vibrancy and life-like appearance. Making and cutting the index precisely ensures it will perform precisely.