Periodontal ligament fibres. Coloured scanning electron micrograph (SEM) of periodontal ligament fibres (green). These fibres, a specialised type of connective tissue, anchor the roots of the teeth to the jaw bone. The enamel, the hard outer covering of a tooth, does not contain any sensory cells, instead the periodontal ligaments do this job. The fibres contain sensors for tension, pressure, temperature and pain. They also help to provide a cushion around the teeth that prevents compression, for example from chewing, from damaging the bone.