Prosthetic screw detorque values in implants retained as cast bar superstructures or bars modified by the Cresco Ti Precision technique--a comparative in vivo study.
OBJECTIVE
This prospective clinical trial investigated the effect of different fabrication techniques on screw-joint stability in implant-retained frameworks.


METHODS
Seventy-nine dental implants (39 Brånemark System and 40 Straumann) were inserted into 20 patients with an edentulous mandible. One of two fabrication techniques was randomly chosen as a definitive restoration, either a cast bar or a bar superstructure modified with the Cresco Ti Precision (CTiP) technique. The patients were divided into four groups depending on the type of implant and prosthetic superstructure: Straumann-conventional (Sc), Straumann-Cresco (SCr), Brånemark-conventional (Bc), and Brånemark-Cresco (BCr). Initial torque values and removal torque values were recorded with a custom-made digital torque controller both 1 week (T1) and 3 months (T2) after clinical function.


RESULTS
Statistical analysis revealed significant differences in absolute detorque values at T1 (P = .002) with 4.51 Ncm (SD = 3.80) for the Sc group, 10.65 Ncm (SD = 4.42) for SCr, 11.24 Ncm (SD = 4.00) for Bc, and 9.02 Ncm (SD = 3.81) for BCr. At T2 (P = .000) the median values of lost torque were 5.08 Ncm (SD = 4.05) for the Sc group, 10.51 (SD = 3.00) for SCr, 7.50 (SD = 5.86) for Bc, and 9.41 Ncm (SD = 4.54) for BCr. However, when correlation of detorque values to initial torque values was performed, no statistical differences were found between groups or time points. The percentage of lost torque at T1 (P = .849) and T2 (P = .058) was 28.60% (SD = 21.80) and 32.85% (SD = 24.65), 30.04% (SD = 12.49) and 30.80% (SD = 8.66), 32.11% (SD = 11.37) and 21.03% (SD = 16.53), and 25.33% (SD = 10.69) and 27.83% (SD = 12.57) for the Sc, SCr, Bc, and BCr groups, respectively.


CONCLUSIONS
The screw-joint stability of passivated bars is not superior to cast superstructures. A general decrease of approximately 30% of initial torque values can be expected in clinical situations, independent of the implant system used.
Department of Prosthodontics, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany. johannes.schmitt@uk-erlangen.de
Johannes
J
Schmitt
Stefan
S
Holst
Stephan
S
Eitner
Andreas
A
Schlegel
Manfred
M
Wichmann
Jörg
J
Hamel
D003735:Dental Casting Technique; D003758:Dental Implantation, Endosseous; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D004867:Equipment Design; D006801:Humans; D007575:Jaw, Edentulous / Q000534:rehabilitation; D008334:Mandible / Q000601:surgery; D011446:Prospective Studies; D019415:Torque