.016 reverse curve archwire in .018 pre-adjusted slots

The reverse curve .016 nickel titanium archwire exerts little or no intrusive force on the incisors and/or cuspids when placed in the pre-adjusted edgewise slots. The narrow vertical opening of the edgewise slot in conjunction with the wide mesial distal dimension flattens out the archwire. The slight distal tip of the cuspids further flattens out the anterior bow of the reverse curve archwire. Note: The archwire is not touching the brackets on the centrals and laterals.

.016 reverse curve archwire in .035 interactive slots

The reverse curve .016 nickel titanium archwire placed in the interactive slot clearly exerts an intrusive force on the incisors and the cuspids. The interactive slot is narrow mesial/ distal (.055) and the vertical opening is .035. The distally tipped cuspid has no effect on the archwire.

Illustration 2 : When a greater magnitude of force is needed.

A .016 steel archwire is used in the interactive slot with bi-lateral gable bends in the archwire between the cuspid and the bicuspid, as near to the bicuspid as possible. This archwire will produce an extrusive force on the posterior teeth and an intrusive force on the six anterior teeth. No rotating force on canines. Bite opening and cuspid class II correction is accomplished much faster. The same archwire configuration can be used in the mandibular arch. A .016 or .018 steel archwire can be used depending upon the forces required to open the bite.

Illustration 3:   Bite Opening with the interactive slot.

Maxillary Arch: .016 steel archwire inserted into interactive slots with bi-lateral gable bends between bicuspids and cuspids, initial archwire placement.

Mandibular Arch: Flat .014 nickel titanium archwire in edgewise slot.

Six weeks Later

Bite Opening: Correcting Anterior Rotations

In those cases where there is minimal horizontal overbite with significant vertical overbite, bite opening should be accomplished first before proceeding with rotational corrections in the mandibular anterior teeth. Both the maxillary and mandibular anterior teeth are thicker in the labial-lingual dimension at the gingival junction than they are at the incisal edge. Many times just opening the bite gives the necessary space to align the mandibular anterior teeth.

Illustration 4: Bite Opening and Rotation Corrections

A.  Closed Bite with no anterior-posterior space to properly align mandibular anterior teeth.

B.  Opening bite generates anterior-posterior space between the facial surface of the mandibular incisors and the lingual surface of the maxillary incisors.

Arch Leveling: As Relates to "Torque" (Base inclination)

The bite should be leveled to the point whereby a straight archwire will pass through the edgewise slot of the bicuspids, cuspids, laterals and centrals in both arches without being deflected in an occlusal direction. If a .018 x 25 archwire must be deflected toward the incisal to engage into the brackets on the central and laterals, the full base inclination built into the central and lateral brackets by the manufacturer will not be realized.

Illustration 5: Arch leveling and "Torque"

There is 10 degrees of "torque" not realized due to the arch not being level. Lines C and D are parallel. If the archwire is deflected toward the gingival, the "torque" angle would be increased in proportion to the degree the archwire is deflected.

The flexible nickel titanium archwire is a good addition to the types of archwires available to the practitioner when correcting rotated or maligned teeth. However, due to its flexibility the nickel titanium archwire is not the archwire of choice for arch leveling. The use of a steel archwire in the interactive slot with gable bends between the cuspids and bicuspids, in conjunction with a nickel titanium archwire in the pre-adjusted slot can be used to leveling the arch.

Rotational Corrections

The advent of the new more flexible archwires has open up new possibilities in the mechanics of rotating teeth. The more flexible ones have made it easier to engage the archwire into the edgewise slot. However, the major problem associated with correcting rotated teeth with the edgewise slot has not changed. The major problem has not been the engagement of the archwire into the bottom of the edgewise slot of the bracket on the rotated tooth, but rather keeping it there. Steel ligatures are very often used to hold the wire in the edgewise slot, but more often than not the pressure against the tie by the archwire results in the tie stretching so that the archwire does not stay at the bottom of the edgewise slot. Elastomeric "O" rings are not usually strong enough to hold the archwire in the bottom of the edgewise slot. Too often, the bracket on the rotated tooth is dislodged in the effort to set up a force system to align the rotated tooth.

Illustration 6: .016 nickel titanium in the interactive slot

The Cannon Ultra Bracket System establishing a force system to align a rotated tooth by inserting a flexible, small gauge archwire in the interactive slot of the brackets and buccal tubes. This process is much easier than employing steel ties, rotating wedges or springs. With metal to metal contact between the archwire and the bracket there is no possibility of the rotating force dissipating due to the stretching of the steel tie or the "O" ring. Power chain was added to speed up rotation.

Differential Resistance

It is generally accepted that it requires considerable more force to move a tooth in a bodily fashion, than it does to tip a tooth. The greater force required for bodily movement will present a greater drain on the anchorage system. The greater force needed is due in part to the friction of the bracket against the archwire. Since the Cannon Ultra Bracket System has both a pre-adjusted edgewise slot for bodily movement and a interactive slot for tipping, differential resistance can be set up by simply selecting the edgewise slot for the anchorage teeth and selecting the interactive slot for the teeth to be moved. Differential resistance being defined as two separate units being acted upon by the same force and the result being that one unit is the primary movement unit. This can be accomplished either intra-arch or inter-arch. An example of intra-arch differential resistance would be in an extraction case where the anterior teeth need to be retracted posteriorly. The archwire is engaged into the edgewise slot in the posterior teeth and into the interactive slot in the anterior teeth. An example of inter-arch differential resistance would be in a case where the maxillary teeth need to be distalized but with little or no anterior movement of the teeth is desired in the mandibular arch. The mandibular teeth would have the archwire engaged into the edgewise slot and the maxillary arch would have the archwire engaged into the interactive slot. Still another example would be a case where the maxillary posterior teeth need to be moved forward.

Non-Extraction Treatment

These are usually very simple cases to treat.  The important thing is to determine why the cuspids are in a class II relationship.  The mandibular anterior teeth could be in retro-version or the maxillary anterior teeth could be flared, or a combination of both.

Illustration 7:  Combination of flared maxillary anterior teeth and retro-version of the mandibular anterior teeth.                                                  

Molar class I, Cuspids class II

Apical base class I (Wits = -2mm to +3mm)

The initial archwires were .016 nickel titanium inserted into the interactive slots to correct rotations and and align in the facial/lingual plane.  The second set of archwires were .016 steel inserted into the pre-adjusted edgewise slots in the maxillary arch and in the interactive slots in the mandibular arch.  The .016 steel archwire in the mandibular arch has bi-lateral gable bends between the cuspids and bicuspids to open the bite by intruding the mandibular incisors.  Class II elastics were employed at this stage of treatment. The third set of archwires were .018 x .025 nickel titanium inserted into the pre-adjusted slots in both arches to finish the case.  Light class II elastics were continued.

Molar Class II; Cuspids class II or non-erupted 
Apical base class I (Wits = -2mm to +3mm)

These type cases usually present with molar class II as a result of the maxillary molars being positioned anteriorly. The canines can be non-erupted or crowded out to the labial or, if the four incisors are flared, there can be sufficient arch length for the canines to be fully erupted but class II. The teeth in the mandibular arch are usually in rather good alignment. The key to successful treatment is the distal movement of the maxillary posterior teeth, thereby making enough arch space for the proper alignment of the maxillary anterior teeth and establishing a class I occlusion. Great care should be taken not to move the mandibular teeth anteriorly.

Anchorage Preparation in the Mandibular Arch

The arch should be leveled with all teeth up-righted and all rotations corrected. A .018 x .025 archwire should be placed in the pre-adjusted edgewise slots in the mandibular arch. The mandibular arch will become the anchorage arch. Once the above is accomplished, up to 4 oz. of class II elastic force can be utilized bilaterally, in association with a sliding yoke on the maxillary archwire, to move the maxillary posterior teeth distally without forward movement of the mandibular teeth.

Procedures for the Maxillary Arch

Brackets are placed only on the four incisors with buccal tubes only on the first molars. If the cuspids are fully erupted brackets should also be placed on them. While preparing the mandibular arch as the anchorage arch, align the maxillary arch so that a .018 steel archwire can be inserted into the interactive slot of the brackets and into the occlusal component of the buccal tubes. The .018 archwire is inserted through the eyelets of the sliding yokes and then the assembly is placed in the maxillary arch. (See illustrations 7 and 8) The archwire is allowed to project out from the distal surface of the buccal tubes as much as possible without causing irritation once turned in toward the molar. Depending on the amount of distal movement of the molars it may be necessary to replace the .018 archwire to allow for more distal movement of the molars. If the canines are erupted but crowded out to the labial adjust the .018 archwire is shaped to allow for the maligned canines. The distal movement of the molars will not be bodily. Some degree of tipping occurs. Over-correction of molar class I is necessary to allow for slight mesial movement of the crowns of the molars later in treatment. Approximately 4 oz of bilateral elastic force is attached from the elastic hook on the buccal tube to the hook on the sliding yoke to distalize the molars. Once the molars have been distalized to an over-corrected class I, the brackets are placed on the bicuspids and canines, if erupted, and begin the finishing alignment of the maxillary arch. Care should be taken to insure that the maxillary molars are not tipped but up-right and in a good class I relationship.

Cases with flared anterior teeth usually presents with considerable horizontal overbite. Not only do the molars and bicuspids have to be move distally, the anterior teeth have to be move distally as well. The sliding yokes, along with the .018 steel archwire, are used in the same manner as discussed previously to distalize the maxillary molars.  As the molar move distally the transseptal fibers tend to move the bicuspids distally as well. Do not try to move the anterior teeth distally at the same time as moving the molars. Once the molars are in an over-corrected class I, reduce the bi-lateral elastic force on the sliding yokes to two ounces of force and place an equal amount of force on the anterior teeth. This can be accomplished by holding the anterior teeth together with a wide power chain and hooking the elastic to the canine “T” hooks. Once the canines are in class I and the horizontal overbite is corrected, place the brackets on the bicuspids and proceed with finishing the case.

Fabrication of Sliding Yoke

The sliding yoke is fabricated from .022 stainless steel wire. An eyelet is formed at one of the wire. The eyelet is then bent at a 90 degree angle from the long axis of the wire. A second eyelet is formed a measured distance from the first eyelet. The distance from the mesial end of the first molar buccal tube to the canine region and the distance between the two eyelets should be the same. The second eyelet is then bent 90 degrees from the long axis of the wire to the same side as the first eyelet. After the second eyelet is fabricated, continue bending the wire to form a hook in the shape of a fish hook. The shaft of the hook should be as long as possible without causing occlusal interference and the end of the hook should be bent in such a fashion as to accept an elastic without causing tissue irritation. The hook is positioned to the facial side of the sliding yoke. Therefore, there are left and right sliding yokes. The fabrication of the sliding yoke is such that the elastic hook is positioned near the occlusal plane not gingival to the canine bracket. This design will greatly reduce the vertical component of force of the class II elastics and thereby reduce the extrusion force on both the mandibular molars and the maxillary anterior teeth.

Illustration: 8: Sliding Yoke

Illustration 9: Yoke in place

Pre-distalization                           Post-distalization

APICAL BASE DISCREPANCY CASES  

Apical base discrepancy cases can present with a concave profile, a convex profile, or even a straight profile. The parameters for apical base discrepancy is; a Wits of more than + 3 mm is considered an apical base class II, and a Wits of less than - 2 mm is considered an apical base class III. A secondary measure helpful in determining apical base relationships is the linear distance between Porion and Pt B, compared to the linear distance between Porion and Pt A.  If Porion to Pt B is less than 8 mm longer than Porion to Pt A, this would be further evidence of an apical base class II.  If Porion to Pt B is as much as 14 mm longer than Porion to Pt A, this would be further evidence of an apical base class III. With apical base class III cases, it appears that the steepness of the OP - SN angle is a major determining factor as to the shape of the profile.  The low OP - SN angle cases usually present with a prognathic mandible, concave profile, and generally require surgery to correct the apical base class III.  Surprisingly, a large number of high OP - FH angle cases present with basically a straight profile which precludes surgery, since going from a straight profile to a convex profile would be unacceptable to the patient.   In the straight profile apical base class III cases, modification of the predetermined angles of the pre-adjusted edgewise brackets must be done to produce quality orthodontic treatment results.

The case demonstrated in illustration 9 is of a case where quality orthodontic treatment was achieved without surgery or extractions by simply establishing custom "torques" for the maxillary and mandibular incisors, and custom "angulations" for the maxillary and mandibular canines and bicuspids (dental compensation). This case was treated exclusively with continuous archwires in the interactive slot/tube.  Segmental archwires were utilized in the edgewise slots of the brackets on the maxillary and mandibular four incisors to correct angulations. Pre-treatment: UI - FOP = 61 degrees and LI - FOP = 83 degrees.  Post-treatment: UI - FOP = 55 degrees and LI - FOP = 79 degrees. 

Illustration 10: Apical base class III discrepancy
Wits = minus 4.0 mm 
Porion to Pt A/Pt B difference = 15 mm

In illustration 9 dental compensation was utilized to accomplish maximum interdigitation between the teeth in this case, however, it is up to the practitioner to decide how far to carry the concept of dental compensation.   In general, the higher the OP - FH angle, the higher negative Wits can be treated by dental compensation in apical base class III cases.   The ability to easily utilize dental compensation to treat borderline apical base class II and III cases is definitely an advantage.  Also, perhaps in conjunction with extractions, it gives the possibility to at least greatly improve those cases where surgery is the preferred treatment, but the family simply cannot afford the cost of surgery. 

DENTAL COMPENSATION FOR APICAL BASE DISCREPANCY

The concept of using pre-adjusted edgewise brackets that establish a single set of predetermined angles between the teeth and the functional occlusal plane simply is not adequate for apical base class II and III discrepancy cases.  These predetermined angles are adequate for cases that finish with an apical base class I relationship between the arches.  However, in cases that finish with either an apical base class II or III discrepancy between the maxilla and the mandible, these predetermined angles of the pre-adjusted edgewise bracket systems must be customized.  Not only does the "torque" in the brackets for the maxillary and mandibular four incisors need customizing, but the "angulation" in the brackets for the cuspids and bicuspids need to be customized for individual cases as well. This can be accomplished by the utilization of the interactive slot/tube component of the brackets and buccal tubes.  The interactive slot has no pre-determined "torques" and/or "angulations" built into the slot.  By utilizing an archwire in the interactive slots of the maxillary and mandibular arches, in conjunction with appropriate triangular elastics, class II or III, dental compensation can be easily accomplished.  The dental compensation can occur primarily in one arch or in both arches.
Illustration 11: Apical base class III, Wits = -4.6

    UI - FOP = 58 deg. / LI - FOP = 80 deg.    

UI - FOP = 50 deg. / LI - FOP = 76 deg.
             

 EXTRACTION TREATMENT

Bodily en masse retraction of the anterior teeth with the pre-adjusted edgewise appliance can be difficult, requiring sophisticated closing loop configurations and external anchorage. If a retraction force, in conjunction with a continuous archwire, is used at such a magnitude that results in the gingival bowing of the archwire in the extraction site, the maxillary cuspids will tip distally, the second bicuspids will tip mesially and the maxillary incisors will be extruded proportionally to the degree of the tipping of the cuspids.  The bowed archwire will actually decrease the “torque” angle of the centrals and laterals incisors and extrude them which will close the bite.

Illustration 12: Effects of a gingival bowing archwire in the extraction sites

En Masse retraction with the Cannon Ultra System 

Utilizing the interactive slot in conjunction with the pre-adjusted edgewise slot, bodily en masse retraction of the six anterior teeth can be accomplished with the Cannon Ultra Bracket System without the mesial tipping of the bicuspids and the distal tipping of the cuspids which results in bite closure.

Illustration 13A:  Typical archwire setup for bodily en masse retraction

Note:  The same archwire setup is used in both the maxillary and mandibular arches. 

Illustration 13 demonstrates a typical en masse retraction archwire set up for a dental class I bi-maxillary protrusion case with second molar attachments for anchorage.  Second molar attachments are usually needed only in extreme bi-maxillary protrusion cases.

Before beginning the retraction of the anterior teeth, the teeth in both arches should be aligned so that a .018 x .025 nickel titanium archwire can be inserted into the pre-adjusted edgewise slots and a .018 steel archwire into the interactive slots of the Cannon Ultra System.  The .018 steel archwire is referred to as the Vertical Stabilization (VS) archwire.  It has a gable bend distal to each cuspid to a degree that if laid on a flat surface the apex of the gable bent projects approximately three to four millimeters above the surface, approximately 25 degree bends.  The steepness of the gable bends can be adjusted for individual cases.  If during en masse retraction, the bite begins to close, the steepness of the gable bends should be increased.  If during en masse retraction the bite becomes open, the steepness should be decreased. The VS archwire is always inserted into the interactive slots/tubes of the Cannon Ultra Bracket System.  During en masse retraction of the anterior teeth the VS archwire is used in conjunction with a .018 x.25 nickel titanium archwire that is inserted into the pre-adjusted edgewise slots of the Cannon Ultra Bracket System. This .018 x .025 nickel titanium archwire is referred to as the Universal Auxiliary (UA) archwire.   The function of the VS archwire is to maintain the bite open during any procedure that results in extrusive forces being exerted on the anterior teeth.  It also prevents distal tipping of the cuspids and mesial tipping of the bicuspids and first molars.  The function of the UA archwire is to establish and/or maintain the proper "torques" and "angulations" of the teeth during tooth movement.  As previously stated, if the cuspids tip distally the four incisors will extrude.  The VS archwire with the gable bends will nullify any extrusive force on the incisors. 

Illustration 13 B: Demonstrates the bowing action of the VS archwire on the UA archwire.

A.  Flat UA archwire   B.  Bowing of the UA archwire by the VS archwire  C.  Degree of bowing

Since the steel VS archwire is more rigid than the nickel titanium UA archwire, the arch will take on the shape of the VS archwire.  As the arch takes on the shape of the VS archwire the softer UA archwire will be deformed into a rocking chair shape.  As the anterior and posterior portions of the UA archwire bend upwards in a gingival direction, there will be a distal root torque exerted on the six anterior teeth, and a distal crown torque on the posterior teeth.  This torque force prevents the retraction force from tipping the six anterior teeth distally, thereby resulting in bodily movement.  The distal crown torque on the posterior teeth improves anchorage, and prevents excessive loss of posterior anchorage.  Power chain is used from molar to molar as the retraction force.  Class II or III elastics can be used if needed to maintain a class I relationship between the arches.

Illustration 14: En masse retraction completed.

Illustration 15:  Bodily en masse retraction for bi-maxillary protrusive, dental class I, apical base class I cases.

Step by step treatment can be view in Case Review at the Home Page

EN MASSE RETRACTION CONTROLLED TIPPING IN MAXILLARY ARCH

Illustration 16:  Four second bicuspid extractions

  Dental class II; Apical base class I

 No external anchorage was employed.  The second molars had not erupted.  The only anchorage was the mandibular first molars.  The anchorage arch was a .018 x .018 steel archwire with bi-lateral "V" bends, approximately 20 to 25 degrees, between the first bicuspids and the first molars.  The archwire was inserted into the pre-adjusted edgewise slots.  In the last phase of treatment a second archwire, .018 steel, with bilateral "V" bends between the cuspids and first bicuspids was inserted in to the interactive slot to increase anchorage. The controlled tipping arch in the maxillary arch was a .016 steel archwire with bi-lateral gable bends, approximately 25 to 30 degrees, between the cuspids and the first molars.  The archwire was inserted into the vertical slots.  

In dental class II cases with severe maxillary anterior protrusion the cuspids can become distally tipped while establishing a cuspid class I relationship. If this occurs, the initial VS archwire can be as small as .016 steel and the initial UA archwire could be as small as .016 nickel titanium; however, to establish proper "torques" and "angulations" the finishing VS archwire must be .018 steel.  The finishing UA must be .018 x .025 nickel titanium.  The controlling factor that determines the size of the initial UA archwire is the degree that the bicuspids and/or cuspids are tipped. 

Illustration 17: Vertical stabilization archwire to prevent bite closure

Step by step treatment procedures can be view in Case Review at Home Page.

Summary

The discussion has been about four common types of malocclusions which have an apical base class I relationship between the arches.  

 Non-extraction; Molar Class I, Cuspid Class II

What must be determined is why are the cuspids in class II?  If the maxillary anterior teeth are flared, the mandibular arch should be the anchorage arch.  That is, the archwires should be inserted into the pre-adjusted edgewise slots in the mandibular arch, and get to a .018 x .025 archwire as soon as possible.  The maxillary anterior teeth need to be retracted. This is eaisly accomplished by the utilization of a .016 steel archwire in the interactive slots in conjunction with light class II elastics.  If the bite needs opening place a 20 degree bi-lateral gable bend between the cuspids and first bicuspids.  If the mandibular anterior teeth are in retro-version, the maxillary arch becomes the anchorage arch and the anterior teeth in the mandibular arch are the teeth that needs to be moved in a labial direction.  In many cases just correction the crowding and rotations will bring the mandibular anterior teeth forward into position.  If not, insert a .016 steel archwire in the interactive slots and utilize light class II elastics.  If the bite needs opening place bilateral gable bends in the .016 archwire between the cuspid and first bicuspid.

Non-extraction; Molar Class II, Cuspid Class II or non-erupted

There are two very important points to establish before beginning treatment on these type cases.  The case must be an apical base class I and the molar class II correction must be  accomplished by distalization of the maxillary posterior teeth.  The mandibular arch is the anchorage arch.  The anchorage archwire should be a .018 x .025, either nickel titanium or steel.  Approximately 4 oz. bilateral class II elastic pressure.  The molar class II correction must be over corrected.  There will be some mesial movement of the first molar crown when finishing the case due to some distal tipping of the first molar.  There are several devices that will correct molar class II by distalizing the maxillary molars; however, they all require additional work and are not an integral part of the conventional orthodontic strap-up.

Four Bicuspid Extraction; Molar and Cuspid Class I

In bi-maxillary protrusion cases the anterior teeth usually require either a .016 or .018 nickel titanium archwire to aligned the anterior teeth.  Once the teeth are aligned or if a .016 steel archwire can be inserted initially, utilize a .016 steel archwire for the retraction of the anterior teeth until a good visual axial inclination is achieved.   This is accomplished with a .016 steel archwire in the interactive slot utilizing power chain. The cuspid brackets are good guides. When the pre-adjusted slot of the cuspids appear to be parallel with the occlusal plane insert the .018 steel VS archwire in the interactive slots in conjunction with a .018 x .025 nickel titanium in the pre-adjusted edgewise slots.  Utilize power chain to close the remaining extraction sites.  If needed elastics, either class II or III can be used to maintain a class I relationship between the teeth. Once the extraction spaces have been closed, remove the .018 steel archwire and finish with the .018 x .025 nickel titanium archwire.

Four Bicuspid Extraction; Molar and Cuspid Class II

All rotations are corrected utilizing small gauge archwires inserted into the interactive slots.  In the mandibular arch, once all rotations are corrected, the archwire placement should transition to the pre-adjusted edgewise slots. If the cuspids are tipped distally a VS archwire of at least .016 steel should be inserted into the interactive slots in conjunction with a .018 x .018 nickel titanium archwire in the pre-adjusted edgewise slots.  The VS archwire will prevent the bite from closing and will enhance anchorage. If the mandibular anterior teeth are flared power chain from first molar to first molar can be utilized. In the maxillary arch a .016 steel archwire with bi-lateral gable bends of 20 to 25 degrees between the cuspid and bicuspid should be inserted into the interactive slots for the controlled distal tipping of the maxillary anterior teeth.  These archwire configurations should establish a cuspid and molar class I relationship between the arches.  In the mandibular arch, the cuspids should not be tipped distally, therefore the VS archwire can be removed and finish the case in the pre-adjusted edgewise slots.  There should be very little or no extraction space remaining.  In the maxillary arch, watch the pre-adjusted edgewise slot of the cuspids.  When the pre-adjusted edgewise edgewise slot becomes parallel with the occlusal plane stop the controlled tipping of the maxillary anterior teeth.  By this time, in most cases, a cuspid class I relationship has been established.  If the extractions spaces are closed or within 2mm of being closed and a molar class I relationship has been achieved, finish case in pre-adjusted edgewise slots with standard rectangular archwires. If the extraction space is greater than 2mm, insert a .018 x .018 steel archwire into the pre-adjusted edgewise slots with a bi-lateral gable bend of 20 degrees between the cuspid and the bicuspid and close remaining extraction space.  In those cases with severe horizontal overbite, the cuspids may become tipped distally by the time a cuspid class I relationship is established.  If this occurs, use a .016   VS steel archwire, .018 if possible, in the interactive slots in conjunction with an .018 x .018 nickel titanium archwire in the pre-adjusted edgewise slots.  This will allow the cuspids to upright without bite closure.  Class II elastics should be utilized.  Once the cuspids have uprighted finish the case in the pre-adjusted edgewise slots.