Abstract:
An orthodonic archwire and method of making same. The archwire through a unique combination of physical and material properties can be activated for providing a variety of teeth corrective forces simultaneously. The archwire is provided with a pair of loop structures substantially equidistant from the center line of the arch form., The posterior sections of the archwire are curved in two directions so as to provide both toe in forces, for rotation of the posterior teeth, and forces for extrusion of the posterior teeth and bite opening. The method of manufacturing the archwire is such that substantially no residual torque is present in the finally formed archwire.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to appliances used in dentistry and, more particularly, to an orthodontic archwire used in applying corrective forces to maloccluded teeth. 
     In the practice of orthodontia, various appliances are used to correct the malocclusion of teeth in the mouth of the patient. During this corrective procedure, it is often necessary to impart a variety of forces to the teeth so as to move the teeth to their final desired position. Typically this is achieved through the use of a variety of different appliances, either simultaneously or consecutively. One of the most common appliances used in orthodontics is an orthodontic archwire which is secured to orthodontic brackets which in turn are attached to the teeth of a patient. Typical prior art orthodontic archwires have been limited with respect to the amount of movement that can take place and the type of forces which can be applied. It is often necessary to frequently change the archwire or to use other auxillary-type appliances to move the teeth to their final position. Elastic chains and coil metal springs are used as retraction mechanisms by attaching them in tension between fixed anchor points in the mouth and the tooth desired to be moved. Springs have been built into the archwire itself, however, this is difficult for the orthodontist to fabricate, and requires considerable non-productive time on the part of the orthodontist. 
     In accordance with the present invention, Applicants have developed an orthodontic archwire which through a unique combination of material properties and shape can be activated for retraction of anterior teeth, provide intrusion of anterior teeth, provide extrusion and bite opening of the posterior section, as well as mesial ligually rotation of posterior teeth simultaneously thereby eliminating or minimizing the need for several wire changes which will reduce the treatment time and provide a cost savings for the doctor by using fewer wires and having to see the patient fewer times. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, there is provided an orthodontic appliance having a force-imparting archwire for applying corrective force to a tooth. The archwire has a generally U-shaped configuration with a pair of loop structures disposed therein, one loop structure is disposed on each side of the mesial center line. Each of the loop structures comprise a pair of substantially vertically extending legs placed substantially adjacent each other which form a substantially closed loop section at their upper end. The orthodontic archwire has a central anterior section and a pair of posterior sections extending on either side of the anterior section. The posterior sections of the archwire are shaped so as to have a reverse curvature of spee and toe in curvature. 
     In another aspect of the present invention, there is provided a method of making an orthodontic archwire made of a titanium molybdenum alloy comprising the steps of: 
     a) forming a generally U-shaped archwire from a continuous length of wire having a central anterior section and a pair of posterior sections extending from both ends of the anterior section, partially forming a pair of loop structures in the archwire and forming the anterior sections with toe in curvature; 
     b) completing the forming of the loop structure in the archwire; 
     c) forming a reverse curvature of spee in the posterior sections. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to FIG. 1, there is illustrated a top plan view of an orthodontic archwire made in accordance with the present invention; 
     FIG. 2 is a front elevational view of FIG. 1; 
     FIG. 3 is a side elevational view of the orthodontic archwire of FIG. 1 as taken along line 3--3; 
     FIG. 4 is an enlarged view of a portion of the archwire of FIG. 2 taken along line 4--4 illustrating one of the loop structures formed in the archwire; 
     FIG. 4A is a view similar to FIG. 4 illustrating the loop structure having a step formed therein for intrusion of the teeth; 
     FIG. 4B is a view similar to FIG. 4 illustrating the loop structure activated for providing retraction of the teeth; 
     FIG. 5 is an enlarged cross-sectional view of FIG. 4 taken along line 4--4 illustrating the cross configuration of the archwire; 
     FIG. 6 is a front elevational view of an orthodontic archwire made in accordance with the present invention as placed on the upper jaw of a patient; 
     FIG. 7 is a side elevational view of FIG. 6; 
     FIG. 8 is a part bottom plan view of the teeth of FIG. 6 as taken along line 8--8; and 
     FIG. 9 is a top plan view of the archwire of figure after initial formation of the loop structures but before forming the reverse curvature of spee in the posterior section. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-5 and 9, illustrated an orthodontic archwire 10 made in accordance with the present invention, and FIGS. 6-8 illustrate archwire 10 as mounted on the upper teeth of a patient. The orthodontic archwire 10 has a unique configuration and is made of a material having bendability and ductility properties that will enable the orthodontist to perform a variety of different functions and provides a large working range over which orthodontic forces can be maintained. In particular, the archwire 10 is made from a material having a flexural modulus in the range of about 3 to 15 million psi, preferably in the range of 6 to 10 million psi. Applicants have also found that the set angle of the orthodontic archwire should be less than 75°, preferably less than 70° as measured by a Tinius Olsen Bending Machine with 1/4 inch span wherein the wire has been subjected to a 90° bend. Applicants have found that an orthodontic wire made out of a titanium molybdenum alloy is capable of providing the desired physical properties. U.S. Pat. No. 4,197,643 disclose some alloys of the general type suitable for the present invention. In order to maintain the appropriate ductility required for an archwire made in accordance with the present invention, the wire should be made of a material having a body centered cubic structure having a maximum of 30% alpha phase form. Applicants have found the following alloy composition to be suitable: 
     
         ______________________________________         % By Weight______________________________________Mo (Molybelenum)           11.5% ± 2%Zr (Zirconium)  6.0% ± 2%Sn (Tin)        4.5% ± 2%Ti (Titanium)   balance______________________________________ 
    
     The above alloy can be manufactured to provide the following properties: a modulus of elasticity in the range of about 5 to 15 million psi, a set angle of about 70° and a flexural modulus in the range of 6 to 10 million psi. 
     The orthodontic archwire 10 is provided with a pair of loop structures 12 which are formed at a point substantially equally distant from the mid line 14 at the apex of the archwire 10. In the preferred embodiment illustrated, loop structures 12 are integrally formed as part of archwire 10 through opposite bending operation integrally formed on the archwire 12, thus, the archwire is a single continuous element without any welds. In the preferred embodiment, the archwire 10 has a substantially rectangular cross sectional shape, having a width W and a thickness T. The thickness T ranging from about 0.0l6 to 0.0l9 inches (0.406 mm to 0.48 mm) and W ranges from about 0.022 to 0.025 inches (0.558 mm to 0.635 mm). However, the cross sectional shape and size of archwire 10 may be varied as discussed. In the particular embodiment illustrated, each loop structure 12 comprises a pair of substantially vertically extending legs 16,17 which are preferably placed adjacent each other so that no space is present between legs 16,17. The legs 16,17 form a substantially closed loop section 18 at the upper end. In the particular preferred embodiment, loop structure 12 has a substantially T-shaped configuration. The loop structures 12 each have a height H as measured from the main section of archwire 10. The legs 16,17 having a length L. The height H, width W and length L may be varied to provide the desired force and a width W. While in the preferred embodiment loop structures 12 are substantially T-shaped, it is to be understood that the loop structures 12 may have a variety of other configurations, for example such as P-shaped. What is important with regard to the loop structures 12 is that each loop structure 12 is provided with two vertical legs 16,17 closely adjacent to each other and form some a generally closed loop section 18 spaced from the main body section of the archwire 10, which provides the loop structure with the ability of setting the legs in a position relative to each other as illustrated in FIGS. 4A and 4B to provide the desired forces. The portion of archwire 10 generally between the two loop portions 12 is considered the anterior portion 20 of the orthodontic archwire 10 and the portions extending on either side of the anterior section toward the rear of the orthodontic archwire 10 are typically referred to as the posterior sections of the archwire 10. The particular point at which the anterior and posterior sections 20,22 meet may vary in accordance to that typically found in the prior art. Applicants have found that the anterior section 22 generally ranges from about 22 mm to about 42 mm in the central section of the archwire 10. 
     As best seen in FIG. 3, the posterior section of orthodontic archwire 10 has a reverse curvature of spee as represented by the radius R. The amount and shape of the reverse curvature of spee is selected in accordance with desired shapes that are well known in the orthodontic field. In the particular embodiment illustrated, the reverse curvature of spee has a radius R, which typically ranges from about 1 to 3 inches (2.54 cm to 7.62 cm). Additionally, the radius R may be a single radius or a compound radius as desired by the orthodontist. The reverse curve of spee provides forces which result in extrusion of teeth and bite opening. 
     For intrusion of the teeth, a step 24 may be placed in the anterior section 20 of the archwire 10 with respect to the loop structure 12 as illustrated in FIG. 4A. Typically, the size of step 24 ranges between 1 and 3 mm. However, the step 24 may be provided as large or small as desired and may be placed at a point appropriate for providing the desired amount of intrusion. 
     The T loop structures 12 can also be activated for retraction of the anterior teeth. This is accomplished by separating the legs 16 of the loop structure 12 in a mesial distal direction as shown in FIG. 4B. The loop structure in FIG. 4B having a generally reverse V-shaped configuration. 
     As is best seen in FIG. 1 and 9, the posterior sections of archwire 10 are curved inwardly (toed in), each having a radius R 1 . The radius R 1  is preferably in the range of 1.0 inches to about 1.5 inches (2.54 cm to 3.81 cm). Preferably, as is also illustrated, radius R 1  is a compound curve with the smaller radius being located at the outer end of the posterior section of archwire 10. The toed in configuration provides for the mesial ligual rotation of molar teeth. 
     The orthodontic archwire 10 can be used to provide several separate functions which were required to be performed independently and typically at different times. The material properties of the archwire 10 are selected such that various forces can be applied to the teeth at the same time and over substantial distances. The present invention allows various orthodontic procedures to occur simultaneously and more efficiently over large working distances, thus reducing the treatment time and provide a cost savings for the doctor by using fewer wires and having to see the patient fewer times. In testing of archwires made in accordance with the present invention, the number of wire changes have averaged 50% less than typical prior art procedures, and time periods for the procedures have been reduced approximately 60%. 
     The orthodontic archwire 10 is made by first selecting the desired raw material having the desired physical, chemical and mechanical properties. For example; by taking a length of straight wire 30 having a rectangular cross section made from a material having the desired characteristics. Archwire 10 with loop structures are made from a continuous length of wire which is wrapped around a spool having a predetermined diameter. In the manufacture of archwire 10, a 6 inch (15.24 cm) diameter spool is used; however, a diameter as low as 3 inches (9.62 cm) has been found suitable. 
     The manufacturing process involves the partial formation of the loops structure 12, the anterior and posterior curvatures, followed by a secondary operation which will finish the loop formation as well as completing the general U-shaped/horseshoe shaped arch form. In the final operation the reverse curves of spee are formed. 
     It is important that no residual torque be present in the archwire. Applicants have found that forming the archwire with a Torin spring mandrel or a four slide apparatus provides an archwire without any subustantial residual torque. 
     It is to be understood that various changes and modifications may be made without departing from the scope of the present invention. The present invention being defined by the following claims.