There is little difference in the alignment between 32 teeth and 28 teeth, or even 24. What matters is where they are in the face. In my view the Indicator Line is the determining factor.
Most orthodontists feel they must achieve straight teeth and many adopt the “plaster on the table” approach to tooth positioning which has to fit certain ‘rules’ of angulation and hight. Arch width appears more important than arch length.
Orthotropic ‘rules’ are different. For men they aim to encourage forward growth of both teeth and jaws to achieve an Indicator Line of 38 millimetres with a secondary objective of an intermolar width of 44 millimetres. Women may be about two millimetres less. This will almost certainly create an attractive forward growing face and dentition.
Forward growth can be measured with a Gnathiometer which measures the position of the Gnathion (the point of the chin) relative to the forehead. Gnathion should lie just ahead of a straight line joining the Nasion (where your spectacles rest) and point ‘F’ on the forehead 50 millimetres above ‘N’ which should be extended down to the chin.
If the chin is 5 millimetres back from this line there may be slight crowding of the lower incisors. If it is 10 millimetres back there will be obvious dental crowding and shortage of room for the wisdom teeth. 15 millimetres back and there are likely to be jaw joint problems and impacted wisdom teeth. 20 millimetres of retrusion will be associated with severe malocclusion and sleep apnoea while 25 millimetres will result in severe sleep apnoea.
All these are estimates but they are affected by the patients muscle tone.
In my experience many orthotropists finish their patients with Indicator Lines higher than 38 millimetres, often over 42. This is just a matter of degree, but it does make a difference. There is less room for the wisdoms, re-crowding is more likely and some teeth may need extracting. Of more importance to most patients the faces do not look as good.
Most orthotropists try to follow these rules, some more assiduously than others. To reduce the Indicator Line they need to take the upper incisors forward and the further they do so the more forward growth they achieve but also the longer it takes. Time is money and not only does it take longer to procline the incisors but it also takes longer to bring the mandible further forward.
So we are faced with a choice; reduce the indicator line to 38 or only 40 or perhaps 42. Four millimetres may not sound much but you can clearly see the difference. Quite apart from that if the subconscious posture is not correct the result will relapse.
My concern is for the patient. How can they tell if the clinician has taken a short cut or not. In times past, the Doctor knew best, but now many patients are better informed from the media than the clinician. They can see the difference between a 38mm Indicator Line and a 42mm result also they can measure the intermolar width themselves. A good result is not an absolute, there is nothing wrong with offering an Indicator Line of 42 especially in an older patient. However these matters must be discussed with the patient so they too can balance time and money against quality. Ultimately the clinician can decide the level of results they wish to achieve but the patient must be allowed to make the choice.