XbowTM
Dolphin Aquarium TM Crossbow Movie
XbowTM shown with ForsusTM Fatigue Resistant Device EZ2 Module with 22 mm pushrods and Gurin Locks from 3M Unitek and Spring Caps from Comfort Solutions Inc.
Gurin Lock is rotated 180 degrees.
New protocol for Forsus EZ2 module and 22 mm pushrod:
The 22 mm pushrod keeps the spring compact and decreases the chance of sores. We also routinely rotate the Gurin Lock 180 degrees after completely tightening it and then rotate it a few degrees either way to positon the anterior spring (with cap) about 1 or 2 mm off the gingiva. The rotated Gurin Lock acts like a cam against the pushrod loop. We routinely use a straight 22 mm pushrod without adjustments. If the anterior spring or cap still impinges on the gingiva bend the pushrod buccally.
There is a greater chance for interference between the thicker clip and the lower molar solder joint. This may cause the upper molar bracket weld to fail or the band to tear. In this case it is better to expand the maxilla before you place the springs or remove the anti rotation arm. (See photo below.)
EZ2 with anti-rotation arm removed, 22 mm pushrod, and Gurin lock rotated 180 degrees.
Shorty or mesial hookup (22 mm pushrod and "L" pin inserted from the mesial of the headgear tube. This hookup is used if the distal end of the spring impinges posteriorly.)
shorty hookup initial
shorty hookup after 5 months, day of spring removal,
note small amount of Gurin lock movement to acheive first bicuspid movement from half cusp Class II to half cusp Class III
After settling
29 mm pushrods with bayonet bend, missing lower second bicuspids
29 mm pushrods with bayonet bend, missing lower second bicuspids
The XbowTM Class II Corrector is protected by the following patents:
3M Unitek's Orthodontic Perspectives has an article on Xbow and one on ForsusTM by Dr. Bob Miller.
Volume XIII, No. 2, Invitation to Efficiency
Great Lakes Orthodontics, LTD. has the exclusive license to fabricate Xbows in the United States.
Integral Dental Lab has been given a license to fabricate Xbows in Canada. The address is #1402-805 West Broadway, Vancouver, British Columbia, V5Z 1K1. Phone (604)872-6656.
Preferred Ortho Dental Laboratory has been given a license to fabricate Xbows in Canada. The address is #207, 14065 Victoria Trail, Edmonton, Alberta, T5Y 2B6. Phone (780)490-6585.
A hybrid appliance called “XbowTM”( “CrossbowTM”) has been developed that connects a maxillary expansion appliance to a mandibular lingual arch with the ForsusTM Fatigue Resistant Device for phase one treatment in the late mixed dentition or early permanent dentition. It is an alternative to the HerbstTM Appliance for the treatment of Class II malocclusions in children and adolescents.
Once the dust clears it looks like there are only two things that help a corrected Class II malocclusion remain Class I (other than indefinite retention with a "passive activator") They are: 1. The fact that the mandible outgrows the maxilla, and, 2. A socked-in buccal occlusion, and more importantly, socked-in first bicuspids. Dr. Herbst had it figured out by 1905.
In Dr. Casko's 1 landmark cephalometric study he showed wide ranges of dental and skeletal variation in individuals with untreated ideal occlusions. He showed that when the ANB angle is high (up to 8 degrees), the incisors are normally more upright in the maxilla (down to 93 degrees) and more protrusive in the mandible (up to106 degrees).
Fixed or non-compliance Class II correctors such as the Herbst and Xbow have a much lower failure-to-complete rate than removable appliances. In O'Brien's 11 randomized clinical trial invloving 215 patients the Twin-block appliance resulted in a 33.6% failure-to-complete rate. This is such a problem that some clinicians are cementing Twin-block appliances in their patient's mouths. This results in a bulky appliance that makes speaking, eating, and oral hygiene difficult compared to Herbst or Xbow.
It appears that mandibular propulsive appliances offer no significant advantages over other appliances.
Dr. Carlos Flores-Mir, a
Clinical Associate Professor
at the University of Alberta Orthodontic Graduate Program, and Director, Cranio-facial
& Oral-health Evidence-based Practice Group (COEPG) (http://www.uofaweb.ualberta.ca/ortho/nav02.cfm?nav02=27929&nav01=10601),
states: "As shown in a published systematic review 15,
the effects produced by the bonded Herbst appliance are significantly
dentoalveolar. Some "headgear effect" and changes in mandibular length were
reported but they are not likely clinically significant. No good evidence was
reported for long term changes.
In systematic reviews of the effects of fixed 16 and removable 17 functional appliances, there were no profile soft tissue changes when normal
expected facial growth was factored out.
Xbow is an appliance system based on:
1. Targeting a Class I first bicuspid relationship by overcorrecting the maxillary first bicuspids from Class II to a half cusp Class III and utilizing the bite-catching effect of the first bicuspids as the distalized teeth rebound mesially and occlusally. The key is waiting for the first bicuspids to erupt before beginning treatment.
2. Use of the Forsus Fatigue Resistant Device for automatic/non-compliance Class II correction to shorten treatment time in phase one and phase two.
3. Incorporating maxillary sutural expansion and mandibular “e” space preservation with Class II correction.
4. Opening space for the maxillary canines without proclining the maxillary incisors.
5. Preventing maxillary occlusal canting that occurs when a unilateral Forsus device is used with a full edgewise appliance in asymmetric Class II cases. The tipping of the buccal segment occlusal plane with Xbow encourages the bite-catching effect of the first bicuspids.
6. Preventing buccal tipping of the maxillary molars and the posterior openbite that occurs when Forsus is used with a full edgewise appliance. A posterior openbite occurs in some Xbow cases but it settles before the second phase is begun. Do we want this side effect in phase one or relatively late in phase two?
7. Reducing the time in full edgewise appliances and especially the time that the upper incisors are retracted with edgewise appliances to reduce root resorption 2,5 and decalcification.
The stages of treatment are: 1. increase maxillary width, if necessary. 2. maxillary incisor alignment, if necessay. 3. primary arch coordination including distalization of the maxillary bicuspids and molars to open space for maxillary canines and achieve Class I first bicuspids, 4. secondary arch coordination including alignment and space closure using a full edgewise appliance.
If treatment is postponed until the placement of a full edgewise appliance in the permanent dentition, including second molars, and Class II correction is not started until after the placement of rectangular archwires there is the strong possibility of missing out on growth modification and the headgear effect, especially in early maturing females or late eruption. There is also the risk of prolonged treatment time with a full edgewise appliance, leading to the possibility of root resorption, decalcification, and patient burnout.
With Xbow there is temporary over-proclination of the lower incisors over a short treatment time of approximately three to five months, after which the lower incisors are allowed to upright, and the tension in the periodontium is reduced. The gingival tissues are monitored closely during this time of rapid tooth movement. Pancherz 12 has shown that proclination of the lower incisors with the Herbst appliance does not cause gingival recession. This has also been the author's experience with Xbow.
The advantages that the Xbow has over the Herbst are:
1. The use of six ordinary bands instead of crowns or reinforced bands. This is possible because of a consistent force from the Forsus device that bands can withstand and the fact that the Forsus device acts as a stress breaker.
2. The Forsus device allows measurable forces of approximately 200 grams or less to be placed on the teeth on one or both sides for as long as it takes to achieve the desired overcorrection. This is handy in asymmetrical Class II cases where the Forsus device is left on one side for a longer time.
3. Forsus devices can be placed in cases with a full cusp Class II molar and little overjet where the canines are blocked out.
4. The Forsus device allows the mandible to function in centric relation with the condyles seated.
The advantages that the Xbow has over maxillary first bicuspid and Nance anchorage to distalize maxillary first molars are:
1. The maxillary first bicuspid is distalized with the Xbow and mesialized with maxillary first bicuspid and Nance anchorage.
2. Space is opened for the maxillary canines with the Xbow and closed with maxillary first bicuspid and Nance anchorage.
3. With maxillary first bicuspid and Nance anchorage once the maxillary molars are distalized, you must "maintain the gain". This requires placing a Nance to the molars, waiting for the first bicuspids to relapse distally, placing full edgewise appliances, opening space for the maxillary canines, and finally, removing the Nance and using anchorage such as headgear, Class II elastics or Forsus devices to retract the maxillary incisors. Why not use the Forsus device on a Xbow in the first place?
Xbow Related Research
The orthodontic graduate students at the University of Alberta, University of Toronto, and University of Western Ontario are treating patients with Xbow.
Flores-Mir et al 21 from the University of Alberta analyzed the lateral cephalograms of 67 consecutively started Xbow patients and compared them to non-treated controls. The mean treatment time was 4.5 months. The T2 cephs were taken 6.4 months after Forsus removal on average. The following are the results after growth was factored out. SNA was reduced by an average of 1.0 degree and "A" point came back 0.5 mm. The upper incisors came back 1.8 degrees and 0.5 mm (not significant). The maxillary first molar was distalized 2.0 mm. The mandibular plane angle opened 1.0 degree. The lower incisors proclined an average of 3.8 degrees and came forward 1.2 mm. The mandibular first molar came forward 0.6 mm. The overjet was reduced an average of 2.4 mm. The ANB angle was reduced an average of 0.8 degrees. No other appliance was used. This compares favorably to Herbst treatment.
Dr. Carlos Flores-Mir has begun a prospective randomized clinical trail using a 3D dental, skeletal, and facial volumetric analysis of Xbow patients.
Dr. Bob Miller compared 8 two phase Herbst cases with 7 two phase Xbow cases and 7 single phase Forsus cases.
Herbst (two phase) Xbow (two phase) Forsus on arch wire (single phase)
Clinical Use of the Xbow Appliance
The Xbow is made up of a maxillary expansion appliance, the Triple "L" ArchTM, the 3M Unitek Forsus Fatigue Resistant Device with "L" pins or EZ2 Modules, 22 mm Direct Push Rods, and Gurin locks (3M Unitek large size Order #560-400). Don't forget to order a Gurin lock wrench.
Ask for the Dentaurum "Variety" two leg expansion screw. There is less chance of palatal impingement with distal tipping and intrusion of the first molars than with a two leg screw design. If the patient has a posterior crossbite or a narrow maxilla, expand the maxilla first. It makes it easier in a patient with a narrow maxilla to attach the Forsus device if you expand the maxilla first. If more than 12 mm of expansion is necessary use a SuperScrew. Band the upper 6’s and the upper 4’s. Control of the upper first bicuspids is important if the goal is overcorrection and the bite-catching effect of the first bicuspids. If the treatment plan involves serial extraction of all four first bicuspids, band the upper e’s or 5’s, and 6’s.
Fit the bands and take an alginate impression. Place the bands in the impression and secure with sticky wax. Pour the impression and check the band position before sending the case to the lab.
Dr. Bob Miller places compound material over the bands before taking the alginate impression. This method ensures that the band placement in the impression is correct.
The next most accurate method is to fit the bands but remove them before taking the impression. Pour the model and send with the bands separately. The lab will place your bands on the model. Don't forget to replace the separators.
Another method is to place separators for a week, remove the separators, take impressions, and replace the separators. Send the models (or impressions) to the lab. The lab will fit bands on the models.
You can use VPS impression material if you want the lab to pour the model . Don't try to take an impression of the bands on the teeth with VPS. It's difficult enough trying to get those impressions out of the mouth WITHOUT bands.
Use occlusal headgear tubes on the upper 6’s to attach the Forsus device springs.
Once space is gained from the expansion, use upper 2x4 mechanics, if necessary. After alignment, segment the archwire to maintain the incisors. This allows over-correction of the Class II buccal segments without over-retraction of the upper incisors.
If the upper incisors are well aligned and the maxilla doesn't need expanding initially, cement the maxillary expander and the Triple "L" Arch at the same time and place the springs immediately or one week later. If you need to expand the maxilla first, wait to cement the Triple "L" Arch until you are ready to attach the springs.
Microetch the bands and occlusal rests just before cementation. We use the UnitekTM Multi-Cure Glass Ionomer Band Cement from 3M Unitek. This powder-liquid cement has a long working time and on demand light cure. We rarely have a loose band. Bond the occlusal rests with Transbond™ Supreme LV Low Viscosity Light Cure Adhesive. If the upper second molars have erupted bond an occlusal rest to prevent the first molars from intruding too much. Occlusal rests for the maxillary second molars can be placed even if they are just erupting and still mostly covered with soft tissue. The rest can be placed at the level of the soft tissue so that when the second molar erupts further the rest will contact the occlusal surface. It is not necessary to bond the rest in this case.
If there is an interference between an upper tooth and the lower labial bow or Gurin Lock, bond Transbond™ Plus Light Cure Band Adhesive to the occlusal surface of the lower first molars to open the bite.
If the labial bow is too close to the gingiva of the lower incisors use a three prong plier posteriorly to raise it. If the buccal section of the labial bow is too close to the teeth and the pushrod is hung up then use the three prong from the occlusal on the spot with the least clearance to bow out the wire.
To open the pushrod loop enough to place it on the labial bow simply push a bird beak far enough into the loop and squeeze the tips together through the opening. To remove the rod from the labial bow take the end with your fingers and flip it anteriorly so that the labial bow passes through the loop opening.
See the patient every six weeks and overcorrect the maxillary first bicuspid to a half cusp Class III.
Half cusp overcorrection of first bicuspids after 4 months Xbow
"Bite-catching" by first bicuspids after rebound (7 months post Forsus)
The use of the Forsus device causes rapid over-correction, usually in four to five months for a full cusp Class II. Fully compress the springs by distalizing the Gurin locks with the Gurin lock wrench. If you don't keep the spring compressed it will flop around, wing out buccally causing sores, and increase the chances of the patient biting on it and causing distortion. A properly compressed spring will also stay active longer as the patient opens. A fully compressed Forsus device has 200 grams of force and looses 20 grams for every 1 mm of deactivation. If you run out of length on the labial bow to reactivate the spring then you can either replace the pushrod with a longer one or use a "shorty" hook-up.
Once overcorrection has been achieved remove the springs and Gurin locks and start maxillary expansion, if necessary. Test the stability of the Class II correction for a couple of months and replace the springs on one or both sides, if necessary. The goal is a socked-in Class I first bicuspid so the best time to start is after the first bicuspids erupt. If the lower e's have not exfoliated cut the labial bow and occlusal rests off with a high speed.
We overcorrect maxillary expansion depending on the amount of constriction. If there is a complete bilateral crossbite we overcorrect the upper molars into a buccal crossbite. If the crossbite is unilateral we overcorrect the non-crossbite side into a buccal crossbite. If there is a crossbite tendency as a result of Class II correction we overcorrect the molars until the lingual cusp tip of the upper molar contacts the buccal cusp tip of the lower molar on one side. We leave the RME in place to retain the expansion for an additional five months. This gives us the opportunity to check for Class II relapse two months after completing expansion and replacing the Forsus device on one or both sides.
Xbow Comfort
To address the issue of comfort, I went to Sandra Ipsen of Comfort Solutions. Orthodontists are contacting Comfort Solutions after their patients experience sores. I recommend that you start with anterior and posterior spring caps and have Spi-Wrap on hand. Spi-Wrap is spiral cut tubing that works well for sores from the lower labial bow as well as transpalatal arches. Comfort Solutions offers these items together in a Xbow kit (Order #4201). Great Lakes Orthodontics will supply the end caps if you check the option on the lab prescription.