In-vitro assessment of the Periotest M device as a means of measuring temporary anchorage device stability: a pilot study

Introduction: The movement of teeth orthodontically can be complicated by the undesired movement of the structures being utilized as anchors. A relatively new means of using the skeleton as an anchor in tooth movement has come from the development of temporary anchorage devices (TADs), sometimes referred to as orthodontic mini-screws. They are small screws that are placed in the upper or lower jaws that aid in facilitating tooth movement. However, premature loss of the TADs due to a loss of stability has plagued providers who use them. The purpose of this study is to establish a protocol by which the stability of a TAD can be measured via the Periotest M device, and to investigate the validity of such data, in preparation for data collection in patients, via data collection the donated mandibles (lower jaws) of two pigs.

Materials and Methods: In each mandible, sites were prepared on opposite sides of the mandible, with one site having bone removed from the lingual (interior) side of the mandible. Four TADs were placed within the sites, two TADs being placed in one mandible from the VectorTAS system, and two being placed in the other mandible from the Bioray TAD system. A series of measurements using the Periotest M device were obtained by two separate operators at various angles. The TADs were then removed one turn at a time, with new Periotest measurements taken after each turn. Values obtained by the first and second operators were compared, as well as values obtained at different angulations. The Periotest values of all TADs as they were removed were also graphed for comparison.

Results: There was found to be a significant difference in the values obtained by Operator 1 compared to Operator 2. Throughout all variations of device angulation, holding the device parallel to the ground appears to produce the most consistent measurements. As the TADs were removed, Periotest values indicated a steady decrease in TAD stability for each TAD, although other influences on these values likely exist. Periotest value variances of TADs placed in fully intact bone and sites where some bone was removed yielded conflicting results, with small sample size making it difficult to draw conclusions.

Conclusions: Data collected within this study indicate that the Periotest device may be a useful means of assessing the stability of TADs in patients, but technique and TAD designs must be considered when assessing Periotest value.