The theory and practice of internal 'tunnel' restorations: a review of the literature and observations on clinical performance over eight years in practice.

The tunnel or 'internal' restoration to restore an approximal caries lesion was first described in 1984. The technique allows the operator to conserve the important external anatomical features of the tooth, thereby saving considerable clinical time while leaving relatively little of the material externalized. The development of a new generation of glass-ionomer materials with higher flexural and compressive strengths appears to satisfy the main objective of carious dentine replacement facilitated by a 'keyhole' internal preparation. The long-term clinical evaluation of these materials is difficult since new formulations are being continually developed. The literature was reviewed. Clinical cases restoring approximal caries lesions in permanent molars and premolars were observed in a private practice. Over the course of eight years 60 tunnel restorations were placed in 48 regularly attending patients. The materials used in both total and partial tunnel restorations were Ketac Silver, Hi-Dense and Fuji IX. At eight years a failure rate of 15% was seen in the 50 restorations observed at last dental examination. The findings suggest that modern tunnel techniques may offer a restorative technique worthy of consideration in treating primary approximal caries lesions.