RN-Sagittal Appliance

The RN-Sagittal appliance was developed by Dr. Dennis Nordstrom and modified by Dr. Francois Rossouw. (See fig.#1)

 

fjrossouw@me.com

Francois J. Rossouw, B. Ch D. (Pret)

Darick Nordstrom B.S., D.D.S.

d@nordstromdds.org

The modification made by Dr. Rossouw was the addition of springs to the maxillary cuspids. The key to understanding this modification is that these springs must remain passive during the initial activation of the appliance. If the springs are activated prior to developing the maxilla they lock the appliance. (See fig.#2)

Fig.#2

The RN-Sagittal appliance can develop the width of the maxilla, the length of the maxilla, and correct a dental Division Two. It can also be used in conjunction with a Reverse Pull Head Gear to advance the position of the maxilla in the prepubertal patient. (See fig.#3)

Fig.#3

The first decision in the fabrication of the appliance is the design of the trans palatal arch (TPA). If the omega loop in the TPA opens anteriorly the effect is to distalize the maxillary buccal segments. This design is called a Class II TPA. If the omega loop in the TPA opens posteriorly the effect is to mesalize the maxillary buccal segments. This design is called a Class III TPA. (See. Fig.#4)

Class II TPA Class III TPA

Fig #4

The use of the RN-Sagittal depends upon the eruption of the maxillary first bicuspids for the placement of the cribs. The younger patient is usually treated with one of the various designs of the maxillary Schwartz appliance.(See fig.#5)

3-Screw Schwarz 3D-Schwarz

Fig #5

Placement & Activation of the RN-Sagittal Appliance

The clinician should first check the fit of the appliance. The crescent wires on the cribs may require adjusting in terms of their length and their retention.

Composite ledges are placed on the palatal of the maxillary cuspids to increase retention for the springs. The patient is instructed on the placement and removal of the appliance. The clinician releases the maxillary sutures on the older patient and then replaces the passive appliance. There is no activation of the appliance for the first four weeks of treatment. The tongue presses against the appliance when the patient swallows which in turn activates the appliance.

After four weeks the appliance is activated in the correct series of arch development. The load in the appliance is approximately 3mm from its passive position and is maintained at 3mm. The correct sequence is as follows:

1. Treat an asymmetrical premaxilla which corrects the upper skeletal midline shift as well as the asymmetrical dental Division Two. This step requires maximum anchorage within the maxilla which is easy to attain if this correction is addressed first. (See fig.#6)

Fig. #6

1. Correct the now symmetrical dental Division Two until a sagittal over jet starts to develop. The adjustment is made using the fingers. This prevents any loss of anchorage within the appliance which could distalize the maxillary buccal segments and starts to decompress the TMJs. (See fig.#7)

Fig. #7

1. Continue the symmetrical sagittal correction and start the transverse maxillary development. The adjustment is again made with the fingers. This begins to eliminate the transverse entrapment of the maxilla on the mandible and further decompresses the TMJs. (See fig.#8)

Fig. #8

1. When a transverse overjet of the maxilla to the mandible occurs the TMJs have decompressed. The night Reverse Pull Head Gear can now be added to the RN-Sagittal appliance if the maxilla is retrognathic and the patient is prepubertal.

It is at this point the transverse development of the lower arch also begins.

Many skeletal Class II patients have a “V” shaped maxilla. In this situation the posterior portion of the maxilla becomes correct, but the anterior portion still requires additional development. In this situation the Class II TPA is activated with a flat on flat pliers allowing the appliance to work like a fan. (See fig.#9)

Fig. #9

The anterior acrylic portion of the appliance moves to the palatal when the appliance is activated transversely. (See fig.#10) The clinician has three options for adjusting this acrylic.

Fig. #10

1. It is activated first if the patient is a dental Division Two.
2. It is placed back into passive contact with the maxillary incisors in a dental Division One.
3. It remains out of contact in a Dental Division Three. This allows the pressure from the upper lip to start to reduce the dental protrusion.

It is important to understand that the optimal orthopedic load for the RN-Sagittal appliance is 3mm in any direction. The patient is seen every four weeks. After the initial 3mm load the appliance is measured intraorally and again extra orally. The difference between the two measurements indicates the amount of load remaining in the appliance from the previous adjust. The objective of the new adjustment is to return the total load to 3mm. (See fig.#11)

Fig.#11

Cuspid Springs

It is extremely important that the cuspid springs in the RN-Sagittal remain passive until the maxilla is fully developed. Activating the springs prematurely can lock the appliance or cause the appliance to create asymmetries in the maxilla. If the cuspids require additional development the springs are activated as the final step in the treatment. (See fig.#12)

Fig.#12

A Segmented Arch & RN-Sagittal

Early alignment of the maxillary anterior teeth can frequently speed the treatment. This is especially true if the patient is a severe dental Division Two. A cuspid to cuspid .020 x.020 thermal Niti segmented arch using Delta Force brackets can be placed as the maxilla is developing creating space for the incisors. The segmented arch wire is advanced into.019 x .025 thermal Niti to complete the anterior torque. If any anterior spacing occurs this usually indicates the maxillary lateral incisors are microdontic and will require bonding to balance the Bolton relationship. (See fig.#13)

Fig.#13

Modification of the RN-Sagittal appliance

The appliance can be modified with occlusal coverage on acrylic if the patient has an anterior cross-bite. The patient eats I the appliance then the occlusal coverage of acrylic is usually removed once the anterior cross-bite has been corrected.

The appliance can be modified for the patient who has an anterior tongue thrust. This modification includes occlusal coverage of acrylic and also incorporates tongue guards and a palatal tongue spinner. The patient eats in the appliance and has myofunctional swallowing therapy. (See fig.#14)

Fig.#14

When the patient has a deep bite the RN-Sagittal is modified with an anterior bite ramp and vertical elastic hooks on the first molar cribs. Vertical elastics, 1/8” 4.5oz, are used at the first molars to open the deep bite.

If the patient is also a skeletal Class II elastic hooks are added to the cribs on the first bicuspids. Class II elastics, 3/16” 4.5oz, are used to hold the mandible forward into the anterior bite ramp. The vertical elastics can be used at the beginning of treatment. The Class II elastics cannot be used until the lower arch is prepared as an anchor unit to prevent the loss of lower arch length. Occlusal pads are used on the second molars to support the mandibular condyles on the articular disks in the post pubertal patient. (See fig.#15)

Fig.#15

Another common modification of the RN-Sagittal appliance is an omega loop or a screw to recover lost “E” space. This modification works well until the second molar erupts into the arch. If the first molar rotated to the palatal as it drifted forward the omega loop is used to both distalize and counter rotate the first molar. If the first molar is forward but not rotated the screw is the better option to distal drive the first molar and not create an unwanted rotation. (See fig.#16)

Omega Loop Screw

Fig. #16

Critical Anchorage

Critical anchorage in a light wire appliance means that there is something in the occlusion that creates an anchor unit that causes the appliance to produce asymmetrical movement. The critical anchorage must be eliminated first before the light wire appliance can be used. The three most common critical anchorage situations are posterior dental cross-bites, the posterior skeletal cross -bite, and an internally rotated maxilla.

The posterior dental cross-bites are corrected with 3/16” 4.5oz cross-bite elastics. Separating elastics are used to open the contacts of the tooth or teeth actually in the cross-bite. This allows them to move back into the arch. (See fig.#17)

Fig. #17

The posterior skeletal cross-bite is corrected with a rigid appliance such as a Schwarz or a fixed expander. (See fig.#18)

Fig. #18

The internally rotated maxilla is corrected with a modified Schwarz appliance that engages cross arch anchorage and unilaterally develops the maxilla. (See fig.#19)

Fig.#19