Sir, I agree with Bob Chate (Dental appliances with inadequate occlusal coverage; BDJ 2011; 210: 109–110) that it can be dangerous to use part coverage splints but even the full coverage splints and intrusion wires he recommends have their dangers. A broad band of evidence tells us that in the long-term changing the occlusion usually reduces muscle tone, weakens lip seal, and increases vertical height1,2 and an equally broad band suggests that this in turn may reduce arch length, worsen dental crowding and increase the risk of TMD or sleep apnoea.3,4,5,6 Adjusting the occlusion is fraught with danger.

In one way it is simple: all dentists know that unopposed teeth continue to erupt. Why then don't all patients have full occlusal contact; surely the contact should self correct? The answer is 'not unless the teeth are in contact enough'. The correct balance seems to be four to eight hours of light contact in 24 which will ensure an ideal occlusal height for all humans.7 The complex bit is generating enough muscle tone to restore a satisfactory occlusion; there is no other way.

If the muscle tone is weak the teeth over-erupt, premature contacts develop and bite splints fail to work unless they are five or more millimetres high, which risks permanent facial lengthening. As a result of weak muscle tone most civilised humans have their maxilla ten or more millimetres too far down and back from its ideal relationship with the cranial vault. If this is not corrected before the child is 9-years-old they will be stuck with palliative treatment and life-long retention.