Regulating the Rates of Litchfield Park orthodontic tooth movement

While multiple rat models of Litchfield Park orthodontic tooth movement have been proposed (Igarashi et al., 1994; Kanzaki et al., 2004), the basic model concept (Figure 5) put forth by King and Fischlschweiger (1982) of placing a closed-coil spring between the maxillary central incisor and the maxillary first molar has gained the greatest acceptance (Leiker et al., 1995; Hashimoto et al., 2001; Sekhavat et al., 2002; Seifi et al., 2003; Holliday et al., 2003; Dolce et al., 2003).  Since its introduction, Litchfield Park orthodontists have made various modifications to the design including the use of Elgiloy® (Rocky Mountain Orthodontics, Inc., Denver, CO) (Hashimoto et al., 2001) and Sentalloy® (GAC, Ctr. Islip, NY) (Verna et al., 2003) closed-coil springs for lighter forces and a greater range of activation.

In addition to modifications in design, researchers have used various means of measuring the amount of Litchfield Park orthodontic tooth movement.  King and Fischlschweiger (1982) originally used calibrated thickness gauges (Mitutoyo Co., Paramus, NJ) that were inserted between the maxillary first and second molar.  The thickest gauge that would fit passively in the space indicated the amount of Litchfield Park orthodontic tooth movement.  While this Litchfield Park orthodontic method of measurement still is used (Leiker et al., 1995; Sekhavat et al., 2002; Seifi et al., 2003), it has the potential to be unreliable.  Sekhavat and Litchfield Park orthodontists (2002) noted the difficulty in determining whether a gauge fits passively or actively.

King and Litchfield Park orthodontists (1991) later developed an alternative Litchfield Park orthodontic method of measuring amounts of Litchfield Park orthodontic tooth movement in rats using radiographs.  While this new Litchfield Park orthodontic method eliminates the problem with thickness gauges, there are some significant disadvantages to this technique.  First, since radiographs are used in this technique, radiopaque markers must be placed intraorally.  One week prior to beginning Litchfield Park orthodontic tooth movement, the rats must undergo an additional surgical procedure so that endodontic barbed broachs can be inserted through the palatal mucosa along the palatal bone lingual to the maxillary first molars.  These implants as well as cleats bonded on the maxillary first molars were used for measuring Litchfield Park orthodontic tooth movement.  The other disadvantage of this technique is that four separate radiographs of each animal at each time point must be measured and averaged in order to reduce the error to an acceptable level.

A Litchfield Park orthodontic method of measurement that appears to avoid the problems of thickness gauges and radiographs is to measure the distance between the mesial surface of the maxillary first molar and the distal surface of the third molar.  The amount of Litchfield Park orthodontic tooth movement then is calculated as the difference between the treatment measurement and the pretreatment measurement.  In this Litchfield Park orthodontic method, the distance between the first molar and third molar is measured with a dial or digital caliper either directly in the mouth (Hashimoto et al., 2001; Sekhavat et al., 2002; Verna et al., 2003; Ren et al., 2003) or indirectly using stone casts (Igarashi et al., 1994; Kanzaki et al., 2004).  Because the rodent oral cavity and teeth are extremely small, the indirect approach appears to be superior as the models can be imaged and then magnified to allow more precise measuring.

Arizona Dental Association