HERBST APPLIANCE

INTRODUCTION HERBST APPLIANCE is a fixed inter maxillary

appliance used for correction of class ii malocclusion EMIL HERBST developed this appliance based on the idea of jumping the bite which was introduced by kingsley in 1880. The herbst appliance functions like a artificial joint between maxilla and mandible

The Herbst appliance generations

Gen. I Banded and crown Herbst Gen. II Herbst directly onto archwires Gen. III Cantilever Herbst Gen. IV The Ball joint attachments

Gen. I Banded and crown Herbst This is characterized by a fixing system to the

crowns or bands through the use of screws. This is the most common form. It is necessary to weld the pivots to the bands or crowns and then fix the tubes and plungers with the screws.

Gen. II Herbst directly onto archwires This has a fixing system that fits directly onto the

archwires through the use of screws. This method of application has the disadvantage of causing constant fractures in the archwires. The lack of flexibility together with the difficulty in lateral movements and the stress placed on the archwires through activation causes fractures, especially in the lower arch .

Gen. III Cantilever Herbst Fitted directly to the lower molar bands through a

cantilever arm. This system means that crowns have to be fitted to the upper and lower molars. The cantilever secured to the mandibular stainless steel crowns has a disadvantage in that the thickness of the screw mechanism can impinge on the patients cheek. The parts are available in kit form with pre-welded screw mechanisms and cantilever arms on crowns of seven different sizes.

Gen. IV The Ball joint attachments This has a fixation system with a ball attachment,

which allows greater flexibility and freedom of mandibular movement. It has a major disadvantage that in relation to other similar appliances it needs brakes to stabilize the joint. The brakes are small and difficult to fit. When a fracture occurs or a brake is lost, the appliance becomes loose.

Herbst designs Banded herbst design Cast splint herbst design Stainless steel crown herbst design

Acylic splint herbst design

Banded herbst Original design consists of a bilateral telescopic

mechanism attached to orthodontic bands on maxillary first permanent molars and mandibular first premolar which maintains the mandible in a continuous anterior jumped position If mandibular premolar has not erupted , permanent canines can be banded but there is an increased possibility of buccal mucosa ulceration at the corner of the mouth

PARTS OF HERBST A TUBE

A PLUNGER TWO PIVOTS TWO LOCKING DEVICES Pivot for tubes is soldered to maxillary first molar

band and pivot for plunger is soldered to mandibular first premolar band The tubes and plungers are attached to the pivot with locking screws and can freely rotate around their point of attachment.

Components of herbst:

The plunger should be as long as possible to

prevent its slippage out of the tube and to avoid damage of the appliance if the plunger gets jammed in the tube If plunger is too longer- extends behind the maxillary first molar irritates buccal mucosa Plunger too short- slips out oftube when patients open their mouth

The telescope can be extended using tubes or rings

sized from 1 to 7 mm to move the mandible forward step by step to reduce maxilary overjet and ending up with little overcorrection Band- 0.15mm or 0.010mm thickness prevents breakage allows increased extension in the occluso gingival direction to achieve adequate retention of the bands on the teeth

It permits small lateral movements in addition to

opening movements because of loose fit of the tube and plunger at the sites of attachment Lateral movements increased by widening the pivot openings of tubes and plungers If larger movements are desired herbst telescope with balls will allow wider freedom.

ANCHORAGE PARTIAL ANCHORAGE:

Maxillary: bands of maxillary first permanent

molar and first premolars are connected with a half round (1.5 x 0.75 mm) lingual or buccal sectional wire on each side Mandibular: bands of first premolars are connected with a half round or round 1mm lingual archwire touching the lingual surfaces of anterior teeth

Total anchorage Maxillary: Labial arch wire is ligated to the brackets on

the first premolar , cuspids and incisors . In addition trans palatal arch can be attached to the first molar bands Mandibular: bands are cemented on the first molars and connected to the lingual archwires which is extended lingually. In addition premolar to premolar rectangular labial arch wire can also be attached if arch wire in front section is 0.016x0.022 the lingual wire on the anterior mandibular segment is not needed It can be combined with maxillary expansion screw or

head gear

MECHANISM OF ACTION The telescopic mechanism of the herbst exerts a

posteriorly directed force on the maxilla and its dentition and anteriorly directed force on the mandible and its dentition The mandibular length is increased due to stimulation of condylar growth and the remodelling process in the articular fossa which can be attributed to anterior jumped position of mandible.

CAST SPLINT HERBST: Developed by pancherz in which bands are

replaced by cast splints Precisely covers the lateral segments which is fabricated from cobalt chromium alloy and is cemented with GIC Both the appliance produce similar effects on dentofacial structures Splinted is preferable to banded because more clinical and laboratory time needed to replace fractured or dislodged banded appliance

STAINLESS STEEL CROWN: Introduced by langford to avoid breakages of the

bands Advantage include resistance to the streses placed on the appliance, elimination of loose crowns or breakage during treatment avoidance of excessive protrusion of mandibular incisors

ACRYLIC SPLINT HERBST:(AM J ORTHOD DENTOFAC ORTHOP 1988;94:10-8.) FRAMEWORK FABRICATION The acrylic splint Herbst appliance is fabricated on upper

and lower work models, usually poured in stone from maxillary and mandibular alginate impressions. A construction bite also is provided, which postures the

mandible approximately 2 to 3 mm in an anterior direction and opens the bite approximately 3 mm incisally. The work models are trimmed with the construction

bite in place so that the posterior surfaces of the model are trimmed flush with one another.

MAXILLARY WORK MODEL: A length of 0.045inch Elgiloy wire is bent to fit

the maxillary work model . The palatal arch is formed by placing an omega loop in the center of the dental arch between the second premolar and the first permanent molar. A lateral bend is then made at the gingival margin of the upper first premolar, bringing it through the interproximal space. The wire is contoured posteriorly along the buccal surface of thecanines and first premolars. The wire is kept approximately 1 mm away from the tooth surfaces just above the gingival margin.

Mandibular wire framework: The framework for the lower splint is formed on

the mandibular work model by means of 0.040-inch Elgiloy wire that is contoured along the lingual surface of the six lower anterior teeth The wire then passes through the interproximal surface distal to the canine and passes distally along the buccal surfaces of the teeth. It then curves around the distal surface of the first molar and follows the lingual contour of the posterior dental segment

Articulation of the work models After the entire wire framework has been

completed,it is removed from the work models. Grooves are cut into the base of the work models and the models are placed in the construction bite Upper and lower models are articulated in a fixator with construction bite in position using plaster

Placement of the Herbst axles: Each wire framework is placed on its

respective work model and secured in place with dental compound If the screws and axles (pivots) have been predrilled to accept ligature wire, they must be kept separate by quadrant since these components are not interchangeable. The pivots are oriented in the correct horizontal, vertical, and angular positions and then are welded in place with two wire leads from a spot welder The axles and auxiliary attachments are

Placement of acrylic: The maxillary work model is soaked in water for 30 seconds and

then coated with an acrylic separating medium. The work model is placed into either the large (125mm) or small (95 mm) model holder with the gingival margin of the dental cast oriented horizontally Depending on the amount of bite opening produced in the construction bite, either 2- or 3-mm thick Biocryl* is used for construction. With the pressure chamber in the open position, a sheet of splint Biocryl is positioned according to the instructions of the manufacturer. The heating element is moved into position over chamber is rotated over the model holder and the handle is engaged. Air pressure is used to push the softened Biocryl onto the work model. Finally, a cone-shaped burr is used to define the gingival margins. With a diskshaped green stone, a pattern of serrations

HERBST BITE-JUMPING MECHANISM The maxillary and mandibular splints are replaced

on the work models and then placed in the fixator model holder. The occlusion is checked with articulating paper and even contact is established If necessary, acrylic can be added to build up areas and establish vertical contact, although the addition of excessive interocclusal acrylic is not recommended.

Fitting of the Herbst appliance The upper tube and lower plunger are placed on

the appropriate pivots. The maxillary tube length (which determines the amount of forward bite advancement) is sized so that it just contacts the base of the plunger when the upper and lower casts are articulated according to the construction bite. The plunger is trimmed either flush with the distal end of the opening of the maxillary tube in cases in which there is no second molar present or at the levelof the maxillary axle in cases in which the second molar is present.

KEY POINTS: 1. The amount of bite advancement should not be

excessive. Every effort should be made to restrict the amount of bite advancement from 2 to 4 mm at anyone time. 2. In most patients the dentition should be decompensated before the placement of a Herbst appliance. This is particularly important in a patient with a deep bite. A forward advancement of the mandible will result in the lower incisors being displaced downward and forward along the lingual aspect of the upper incisors. This movement will increase the vertical dimension of the patient and may result in a posterior open bite existing

3. The Herbst appliance should be used as a

removable appliance whenever possible. This will minimize the potential for decalcification. However, the appliance usually is bonded in cases in which the rapid palatal expander or an auxiliary arch wire is used. It also should be bonded when most of the teeth are deciduous because of the lack of retention inherent in theshape of these teeth.

Advantages Dislodgement never happens

Used with any age patients

Disadvantages

Thick screw impinge on cheek. Little discomfort

Indications

Dental class-II malocclusion Skeletal class-II mandibular deficiency Upper molar distalization Lower incisor advancement

Contra Indications

Case Prone to root resorption Dental and skeletal open bites Vertical growers Procumbent mandibular incisors Protrusive maxillary and normal mandibular positions

Mechanism of Action In a separate study, Pancherz delineated the

components of change responsible for class II correction in patients treated with the herbst appliance: 1. Maxillary growth inhibition 6% 2. increased mandibular growth 37% 3. distal movement of maxillary molar 42 % 4. mesial movement of mandibular molar 15%

Pancherz and Hagg in another study of

consecutively treated cases compared the somatic maturation level to the mechanism of Class II correction. They found that mandibular growth accounted for 61% of the overjet reduction when treatment occurred during the pre-peak period this percentage dropped 49% and if it occurred during the post-peak period, if fell to 34%. However,Class II correction was still obtained through