The treatment of root surfaces in periodontal lesions with mechanical instruments is becoming more and more popular as an alternative to the conventional treatment with curets. In this in-vitro study a phantom head with a simulated periodontitis was used. The aim of this investigation was to determine the percentage of the subgingival non-treated root surfaces after treatment with different instruments and by different persons. Newly developed mechanical file instruments (Rootshape) were tested. Hand curets served as control group. The treatment of the teeth was carried out by three groups, each including 4 people. Group one were dental hygienists (DH), group two dentists with (Spez) and group three dentist without (Zaz) experience in the therapy of periodontal diseases. They were asked to perform a scaling and root planing on six teeth (16, 21, 24, 36, 41, 44) both with curets and Rootshape files. The size of the non-treated areas was subsequently determined planimetrically and expressed as percentage of the entire subgingival root surface. Independent of the group the percentage after file treatment was significantly lower (mean 9.85 +/- 7.78%) than that after curet-treatment (mean 14.74 +/- 10.20%). Significant differences were found when the three groups were compared after treatment either with files or curets (DH 9.61 +/- 8.02%, Spez 12.11 +/- 8.01%, Zaz 15.18 +/- 11.01%; p < 0.001). Zaz working with files achieved as good results as DH or Spez with curets (p < or = 0.05). The results indicate that the files represent an alternative to hand instruments concerning the accessibility of root surfaces.