A process of injecting a thermoplastic material (20) within an annulus fibrosus of a selected intervertebral disk. The thermoplastic material (20) is heated by an injection device to a predetermined high temperature to provide flow of the thermoplastic material from a needle into the annulus fibrosus of the disk upon injection. After injection, the thermoplastic material is cooled by the body temperature of the patient for setting of the thermoplastic material in a non-flowing state while retaining a suitable resilience to provide desired cushioning. The thermoplastic material (20) may also be injected into an abnormal curvature of the spine to correct the abnormal curvature. The preferred thermoplastic material is gutta percha or a gutta percha compound.