Facebow mounting

 Today I made a few errors when recording and mounting a facebow record. Each facebow system works on the principle of providing 3 reference points to mount the maxillary cast. The anterior reference point is the occlusal plane of the maxilla and the 2 posterior points are the temperomandibular joints. There is a This approximates the position of the maxilla in relation to the terminal hinge axis but this can be any point in the arc. Due to this, another point is chosen in each facebow system to control where in the arc the model will be mounted. In this case there is a reference point at the infraorbital notch. This position will roughly place the models in the centre of the articulator in a vertical position. 

In this case I forgot to use this fourth reference point and had the arm of the earpieces a tad too high. I was sure to make the ear piece bar parallel to the interpupillary line as this will give a realistic appraisal of any anterior occlusal cants on the mounted models. However, due to my incorrect positioning, the maxillary model was positioned quite high in the articulator. I discovered this during the mounting procedure and realised my next mistake when I had mixed the plaster and tried to close the articulator to mount the maxillary model. 

The base of the model was quite thick and the upper member of the articulator didn't actually close all the way down to the 0 position on the pin. Initially I thought that the plaster had set too fast and I was trying to force it closed but after removing the plaster I realised the problem. I was contemplating just leaving the pin open but I thought that the facebow record would only be accurate when the model was mounted at the correct position relative to the upper member. However on contemplation it would probably have been fine and the only difference is the default position would be + a few millimeters instead of at 0mm. However, if there is stone contact between the maxillary model and the upper member of the articulator hindering complete seating then the weight of the articulator may move the facebow record and the plaster might not be thick enough to have strength to hold the model on. I quickly remedied this by removing the plaster, grinding the model back and remounting it. However I forgot to add in the indicies on the model base after grinding it down and so if the model falls off it will be difficult to relocate it. I will probably grind in some indices at the seam line and fill that with plaster to ensure it will be possible to remount. 

The last issue is that I dropped the facebow record on the table as I was attempting to screw it onto the articulator. I tightened it pretty well but I am at this point unsure if the record itself was altered. Be careful with these records as they are easily damaged and hold them with a steady hand. Dropping it as well as roughly handling it to try and seat the upper member may have distorted the record and will introduce inaccuracies. Instead, mix plaster, close the upper member till it is supprted by the upper member, put your hand under the facebow record to supprt it and tap the upper member with a metal instrument to make the thixotropic plaster flow. This way you won't put any downward force that could distort the position of the facebow fork.