Rigid Fixed Functional Appliances – A Review

The number of Class II patients reporting to an Orthodontist’s office for treatment is quite significant. Mandibular retrusion contributes to a majority of these Class II malocclusions. For a post-pubertal patient orthodontic camouflage or surgical options were considered and modulating growth was considered improbable. However, studies on young adults by Pancherz [1] and co-workers have demonstrated the potential of condylar and glenoid fossa remodeling beyond the pubertal growth spurt using the Herbst appliance. Fixed functional appliances or more appropriately termed ‘non-compliant Class II inter-arch correctors’ have gained significant ground. 

The main advantages of combining Fixed functional treatment along with fixed appliance therapy is termed as “Telescoping treatment”. This refers to the combination of two treatment modalities to maximize the benefits whilst minimizing their individual drawbacks. To be more specific, the fixed appliance is aimed at targeting the dentition and providing the following dental corrections: a) facilitating mandibular advancement by eliminating dental interferences and b) consolidating the arches in order to minimize the adverse dental side-effects. This is in conjunction with the fixed functional appliance providing the impetus for anterior mandibular repositioning and optimizing growth.

The first fixed functional appliance namely, the Herbst appliance, was very rigid, suffered from breakages and could allow for only limited lateral movements. Operators had difficulties in placing the appliance and patients found it difficult to cope up with. Appliances similar to Herbst have been labeled as rigid fixed functional appliances. As an alternative, the Jasper Jumper [2] was subsequently introduced, which solved the issue of patient comfort but continued to break very often. This was mainly attributed to the curvilinear stresses generated when the spring of the Jasper was flexed intra-orally. Class II correctors belonging to this category have been branded as Flexible fixed functional appliances. The Jasper Jumper also showed more dento-alveolar changes in effecting the Class II correction and was considered a disadvantage in comparison to Herbst, which had demonstrated more orthopedic changes. This led to the evolution of the Hybrid fixed functional appliances or Inter-arch compression springs (Table 1). 

• Classification of Fixed Functional Appliances 

Table 1: Classification of Fixed Functional Appliances. 

Herbst Appliance: The Herbst appliance (Figure 1) is a fixed appliance which functions like an artificial joint between the maxilla and the mandible. The original design (banded Herbst design) consists of a bilateral telescopic mechanism attached to orthodontic bands on maxillary first permanent molars and on mandibular first premolars, which maintains the mandible in a continuous protruded position [1]. 

A more recent version of the Herbst appliance was developed by Pancherz, in which the bands are replaced by cast splints (cast splint Herbst design), which fit precisely and cover the teeth in their lateral segments, fabricated from cobalt-chromium alloy and cemented with glass ionomer cement to the teeth. Each of the telescopic mechanisms consists of a tube and a plunger which fit together, two pivots and two locking screws. The pivot for the tube is soldered to the maxillary first molar band and the pivot for the plunger to the mandibular first premolar band. The tubes and plungers are attached to the pivots with the locking screws and can easily rotate around their point of attachment. The bands on which the tube and the plunger are attached should be fabricated from at least 0.15 mm or 0.010′′ thick orthodontic material, which prevents any breakage during treatment with the Herbst appliance and also allows increased extension in the occlusocervical direction to achieve adequate retention of the bands on the teeth [3]. 

 Figure 1: Different views of the Herbst appliance 

• Variants of Herbst Appliance 

Acrylic Splint Herbst Appliance: The Acrylic Splint Herbst Appliance (Figure 2) consists of the telescopic mechanism which is attached to acrylic splints cemented or bonded on the maxillary and mandibular dentition. For the attachment of the bite-jumping mechanism, a wire framework is used, over which 2.5–3 mm acrylic is adapted. A transpalatal arch or, more usually, a rapid palatal expansion screw attached to the wire framework connects the left and right parts of the splint together. The acrylic maxillary and mandibular splints can also be removable. The appliance can be worn on a full-time basis and removed only for oral hygiene, or on a part-time basis. Mainly due to the fact that bonding of the acrylic splints increases the risk of decalcification [4]. 

Figure 2: Acrylic Splint Herbst Appliance - A through D, Trimmed Herbst appliance after final polish. In this case the acrylic extends only to the lingual surface of the upper canine, the design used when the maxillary splint is bonded. 

Goodman’s Modified Herbst Appliance: This appliance (Figure 3) consists of stainless steel crowns placed on the maxillary first permanent molars and, if additional anchorage is required on maxillary first deciduous molars, a transpalatal arch fabricated from 0.045′′ round wire connecting the crowns, bands on the mandibular first molars, frameworks for both mandibular and maxillary arches made of 14-gauge half-round wire, and the Herbst telescopic mechanism. The maxillary pivots are soldered to the most distobuccal points of the crowns, parallel to the distal and the occlusal surfaces, while the mandibular pivots are soldered to the wire framework on a level with the mesial surface of the first deciduous molars. A wax-bite in an edge-to-edge incisal position is taken and the cementation of the appliance follows after a trial procedure [5]. 

Figure 3: Small arrow shows 45° cut at end of arm extension, mesial to maxillary second molar. Large arrow shows screw where ratcheting may occur if parallelism is not achieved or patient makes repetitive, forceful lateral excursions. 

Mandibular Advancement Locking Unit (MALU): The Mandibular Advancement Locking Unit (Figure 4) was introduced by Schiavoni et al and consists of two tubes, two plungers, two upper “Mobee” hinges with ball-pins, and two lower key hinges with brass pins. Bands are placed on the maxillary first molars with 0.051′′ headgear tubes, while a palatal arch can be used in cases of overexpansion. Regarding the mandible, bands are placed on the mandibular first molars, while the anterior teeth are bonded from canine to canine with 0.022′′ brackets, and a 0.021 × 0.025′′ stainless steel archwire with labial root torque in the anterior section is used, bent back at the distal ends. The Mobee hinge is inserted into the hole at end of the MALU tube and secured to the first molar headgear with the ballpin, while the lower key hinge is inserted into the hole at the end of the plunger and locked to the mandibular base arch with the brass pin. The length of the tube–plunger assembly is specified by the amount of mandibular advancement required, and further advancements of 1–5 mm can be performed using spacers [6]. 

Figure 4: Mandibular Advancement Locking Unit - With upper and lower MALU components in place, length of tube-plunger assembly is adjusted according to desired mandibular protrusion. 

Magnetic Telescopic Device: According to Ritto, the Magnetic Telescopic Device consists of two tubes and two plungers with a semicircular section and with NdFeB magnets, which are positioned to exert a repelling force, while fitting is achieved using the MALU system. Its main advantages include the linking of a magnetic field on a functional appliance, while its disadvantages involve its thickness, the laboratory work necessary to prepare it, and the covering of the magnets [7]. 

Flip-Lock Herbst Appliance: The Flip-Lock Herbst Appliance (Figure 5) uses ball-joint connectors instead of screw attachments, and it needs no retaining springs. The ball-joint connectors are attached to stainless steel crowns on maxillary first molars and mandibular first premolars. Further, bands are placed on mandibular first molars and a lingual arch connects them with the crowns on first premolars. The rods have forked ends to be crimped onto the mandibular balls [8]. 

 Figure 5: Flip-Lock Herbst Appliance 

Hanks Telescoping Herbst Appliance: It consists of two tubes, a ball and socket joint, and a rod attached to the mandibular premolars or cantilever arms, and functions like a free-sliding radio antenna. The outer tube of the axle captures the middle tube and the middle tube slides inside the outer tube stopped at the mesial end of the outer tube. The rod is captured by the middle tube and slides inside the middle tube until it is stopped at the mesial end of the middle tube (Figure 6). The advantages of the Hanks Telescoping Herbst include one-piece design, which prevents disengagement, reduced ulcerations, greater lateral movements of the mandible because of the ball and socket joints, fewer emergency appointments, patient comfort and user friendly components [9]. 

 Figure 6: Hanks Telescoping Herbst 

Ventral Telescope: The Ventral Telescope is first intermaxillary appliance fabricated as a single unit and is fixed via ball attachments. The Ventral Telescope is available in two sizes and is activated by unscrewing the tube, thereby causing approximately 3 mm of activation. Its advantages include elimination of the risk of the appliance disassembling when maximum opening occurs, and easy and simple operation, while its disadvantages include thickness and fractures of the brake which stabilizes the joint [10]. 

Universal Bite Jumper: The Universal Bite Jumper (Figure 7) was introduced by Calvez and is similar to the Herbst appliance but smaller and more adaptable, while an active coil spring can be added when needed. The jumper is fitted in the mouth and cut to the proper length depending on the amount of mandibular advancement. The activation is achieved by crimping 2–4 mm crimping bushes onto the rods, whereas when coil springs are used, no activation is required [11]. 

 Figure 7: Universal Bite Jumper 

Open-Bite Intrusion Herbst Appliance: The Open-Bite Intrusion Herbst (Figure 8) for mixed dentition consists of a maxillary and a mandibular part. The maxillary part consists of crowns cemented on the maxillary second deciduous molars and permanent first molars, stops which extend from the deciduous second molars to the deciduous first molars, 0.036′′ stainless steel intrusion wires with helix loops soldered to the deciduous second molars to intrude the maxillary permanent first molars, cantilever extensions with 0.022′′ archwire tubes soldered to the deciduous second molar crowns, and positioning axles distal to the deciduous second molar crowns and just mesial to the permanent first molar crowns. The telescopic axles are initially soldered to the axles to maintain the position of the primary second molars while intruding the permanent first molars, while axles positioned to the first molar crowns are used to connect the Herbst mechanism and maintain the intruded molars during Class II correction [12].

Conclusion

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