In order to address the prevention of MSDs caused by forced postures, we need to have a clear understanding and global vision of human biomechanical design understood as a total active system. There are some basic principles of biomechanical design that rule posture and movement and it is essential to know these.
Dental professionals can use their hands with exquisite control and sensitivity, mastering extraordinary complex and subtle skills. However, none of those professional skills would be possible if we as a species had not evolved towards an erect posture.
Evolution has brought a vertical support system (bipedal erect posture) for the specific actions we do with our hands and when it is working in accordance with its design, those actions can be done effortlessly and with maximum efficiency. This wider vertical support system is the basic system all the other systems like breathing or the use of hands rely on.
If we take breathing for instance: we can do specific exercises to get some improvement but unless we understand correctly the total design breathing is based on, we will be working at a disadvantage because this wider “vertical support system” is the driving factor. A dentist with a very bent over posture will not be able to do much about breathing unless the posture is improved such that this “vertical support system” is activated.
In the case of lower back discomfort: there are many approaches to improvement, including methods and procedures such as stretching exercises to lengthen, strengthen and release muscles. However, back muscles are intrinsically linked to the erect posture. So, in order to make a specific muscle group move properly, it must do it in accordance with this wider system.
If we look at it from the perspective of evolution, one can see how the fish spine, being the first vertebrates and our ancestors, helps them to move forward towards food and how sensory organs and their processor, the brain, developed on the front end to get information from the environment and to direct the necessary motor activity to survive. All movements are organised in relation to the head and the spine, so any movement requires a shift forward horizontally.
In four-legged vertebrates, this brain-body relationship gets more complex in an evolutionary sense, because terrestrial animals must get up from the ground in order to move forward, as gravity feels stronger out of water.
In humans, the head and the spine are not arranged horizontally according to the sense of movement. However, we must still work against gravity using our head to guide our body, and we still move according to the sensory information we get through our eyes, ears and nose. The head is not arranged as per the direction of movement, but it is set high up, allowing us to move in any chosen direction. So, even within vertical functioning humans, the relationship between the head and the spine is the basic and primary coordinator of posture and movement, as it is in any other vertebrate.
If we go a bit deeper regarding the relationship of the head and the spine or torso, we must point out first that in terrestrial vertebrates, muscles have a double function: they produce movement and they also provide postural support against gravity.
That postural function of the muscles is so essential that we cannot talk about movement without considering it. In order to perform a specific movement, the muscle system must keep the whole of the skeleton stable relative to gravity: with the head balanced on top of the spine in a vertical position.
The primary muscles that give this anti-gravity support to humans are the back and leg extensors.
The flexors bend the trunk and extremities through the joints, the extensors spread extremities and offer support against gravity. The most important extensors are the neck and back muscles. The back has 5 layers of muscle, the upper layers move the ribs and the shoulders and are not involved directly in supporting the trunk upwards. The two deepest layers that are along the spine are the ones forming the trunk extensors.
The first layer is made of a series of small muscles located between the spine vertebrae from the sacrum to the cranium base. Their role is to keep the length and support the spine. The second layer is made of long muscles that extend in wads alongside the back (spine erectors), also from the sacrum to the cranium base. Their function is to keep the trunk stable in order to avoid it falling forward.
As opposed to what it seems, the cranium is not centred in relation to the spine, so as the superior part is the heaviest, the “natural” tendency is that the head is inclined forward from the atlanto-occipital joint. This forward weight causes stretching of the back of the neck extensor muscles and this balances the tendency of these muscles to shorten and contract, it reduces the pressure towards the bottom of the cranium above the spine and has a lengthening effect on it.
This spine lengthening is crucial for the proper functioning of the deepest muscles that support its posture. Vertebrae are cushioned by discs filled with fluid having hydraulic properties that sustain the spine. Some common postures observed in dentists like moving the head backwards or bending the thorax forwards, tend to create pressure on the discs so they lose that support capacity and that can lead to MSDs.