Distalizing maxillary molars – how do you do it?

Limitations and contra-indications

The indications for, and contra-indications of, maxillary molar distalization are summarized in Table 1. Most distalization techniques result in loss of anchorage in the form of incisor proclination and are therefore contra-indicated where the incisors are already proclined, where the overjet is increased, or for patients with a protrusive profile. Molar distalization should be avoided in cases with thin labial bone and gingival problems due to the risk of gingival recession and bone dehiscence associated with any resultant incisor proclination.^3,10,11,12 Additionally, distalization of the maxillary molars is not advised in patients with a high Frankfort mandibular plane angle or an anterior open bite. This is because the majority of molar distalization methods are extrusive in nature, resulting in a wedging effect that may open the occlusion.^11,13,14 Buccally flared maxillary molars are a further limitation to molar distalization since a force applied buccally to the centre of rotation may cause further buccal tipping. This is due to the cortical bone of these teeth being less resistant than palatal bone which favours buccal tipping. This, in turn, may compromise the overbite and cause a backwards rotation of the mandible.¹⁵

Maxillary molar distalization is not a solution to significant crowding (more than 6 mm) since the actual maximum amount of space gained with a headgear appliance is somewhat disappointing at between 2 mm–2.5 mm.¹⁶ Maxillary molar distalization should be used with caution in cases with posterior crossbites since the distalized molars tend to occlude more palatally to the wider part of the opposing mandibular dental arch. This can be counteracted by incorporating a midpalatal screw in the distalization appliance (see ‘pendulum appliance’ and ‘nudger appliance’ sections below), activated twice per week to create expansion in the molar region.¹⁷ Moreover, as the maxillary molar is tipped distally, it has a tendency to rotate around the palatal roots, depending on the site of applied force, buccal or palatal. If the distalization technique includes a palatally applied force, as in a pendulum appliance, placing approximately 30 degrees of rotation in the terminal legs of the pendulum/pend-X springs can compensate for this.¹⁸ One important fact to consider is the depth of the palatal vault, as intra-oral molar distalization appliances that rely on palatal bone anchorage are not effective in cases with a shallow palatal vault.¹⁹

Molar distalization techniques

Contemporary maxillary molar distalization techniques are shown in Figure 1.

Mini-distalization techniques

These include the use of brass wire ligatures, elastomeric separators and steel spring clip separators which all act by disimpacting molars that are mesially impacted against an adjacent tooth. Mini-distalizing has been shown to assist partially erupted, tipped and impacted molars to erupt normally.²⁰ Other methods include the Halterman appliance (Figure 2)²¹ and the Humphrey appliance, the latter consisting of a Nance appliance attached to the deciduous molars and a welded ‘S’-shaped wire spring bonded to the mesial ridge of the ectopic molar using composite (Figure 3).

Macro-distalization techniques

Macro-distalization methods have been investigated in a number of studies (Table 2). In general, the macro-distalization techniques can be subdivided into:

Table 2. Effectiveness of maxillary molar distalization with different methods (adapted from Atherton et al16).

Distalization Method	Type of Study	Results (Amount of Molar Distal Movement)
Bass v Frankel/Harvold/Bionator	RCT	Bass appliance achieved 1.6 mm while others achieved no detectable changes
Ni-Ti coil springs v Acrylic splint Herbst	CCT	Ni-Ti coil springs achieved 3.8 mm compared to 0.5 mm with Acrylic splint Herbst
Herbst	Cohort studies	2.7 mm
Enmasse + headgear	A case series	5.7 mm
Herbst v combination headgear with edgewise appliance	Case series	Headgear achieved the least distal movement

Compliance appliances; and

Non-compliance Class II appliances.

Compliance appliances

One of the most well-known methods of maxillary molar distalization is headgear. It is attached via a facebow to molar bands on the maxillary first permanent molars in a high or low pull direction, depending on the overbite (Figure 4). The force level used is 300–350 gm per side and if the appliance is worn 14 hours/day around 2–3 mm of molar distalization can be achieved.¹⁶

Removable functional appliances can be considered as a compliance-dependent maxillary molar distalization technique. One of the effects of functional appliances is correction of the molar relationship. This is achieved by a combination of skeletal changes (19% in the maxillary base and 22% in the mandibular base), as well as dento-alveolar changes (26% in the maxillary dentition and 33% in the mandibular dentition).²²

A removable appliance (nudger appliance) can be used for maxillary molar distalization. Either palatal finger springs (0.6 mm wire) or screws can be used as the active component (Figure 5). A Southend clasp on the incisors and Adams clasps for the molars and premolars aid with appliance fixation. An anterior or posterior biteplate may be required to disengage the occlusion and permit uprighting of the tilted permanent molar (as well as reduction of an increased overbite). Anchorage loss normally manifests as an increase in the overjet.²³

A nudger appliance and headgear in combination can be used for maxillary molar distalization to achieve bodily tooth movement. The combination system consists of an upper removable appliance (URA) with palatal finger springs (activation of 2–3 mm) that act to tip the crown of the molar distally. High-pull headgear worn at night, directed above the centre of rotation of the molar, acts to distalize the root and hold the crown movement achieved during the day-time wear of the URA.²⁴ In addition, the headgear provides a method of reinforcing the anchorage during subsequent retraction of the anterior teeth. Ferro et al²⁵ showed an average of 3.6 mm of molar distal movement and 0.7 mm of anchorage loss when a nudger appliance was used in conjunction with cervical headgear.

Additionally, a removable appliance can also be used for en masse maxillary molar distalization. The standard design of an en masse removable appliance described by McCallin consisted of Adams clasps for the maxillary first permanent molars and first premolars, L-shaped rests over the first molars and headgear tubes soldered to the bridges of the Adams clasps on the first permanent molars. A coffin spring to provide expansion is embedded in the heat-cured acrylic baseplate.²⁶ Other modifications of the en masse appliance, as described by Orton, include replacement of the coffin spring by a midline expansion screw to provide symmetrical bilateral expansion, double clasps for the upper first permanent molars and second premolars, T-shaped occlusal rests and headgear tubes soldered to the molar clasps. Headgear delivering 300–350 gm per side should be used for 14 hours per day. Extraction of the upper second permanent molars may be required. This method has been claimed to achieve 6 mm distal movement of the molars.²⁷

Another compliance method for maxillary molar distalization is the ‘molar distalizing bow’. It consists of two components. First, a 0.8–1.5 mm thick thermoplastic splint is placed over the maxillary model covering the dentition except the teeth to be moved and is extended into the buccal sulcus for better support and retention. A distalizing bow with open coil springs to apply a force to the permanent molars is then fitted into the anterior slot that is embedded in the splint.²⁸

Class II elastics with sliding jigs to distalize the buccal segments are the last in the list of the most commonly used compliance-based maxillary molar distalization techniques (Figure 6). Unlike other inter-maxillary compliance-dependent methods, elastics produce a pulling force rather than a pushing force. Class II elastics are a mainstay of the original Tweed technique in which the pulling forces from the Class II elastics are transmitted to a pushing force via the sliding jigs to distalize the maxillary molars. A force level of 300–350 gm per side is required. One of the side-effects of the Class II elastics is the clockwise rotation of the occlusal plane. It is possible to compensate for this in a growing patient but sliding jigs and Class II elastics are not recommended for more than a period of 6 months in adult patients due to unwanted occlusal effects.^28,29

Non-compliance appliances

These have been subdivided by McSherry and Bradley³⁰ into

Inter-maxillary; and

Intra-maxillary appliances.

Inter-maxillary appliances can be sub classified into:

Appliances producing pulling forces The Severable Adjustable Intermaxillary Force (SAIF) springs (www.truforce.com) were developed by Jasper in 1995.³¹ They consist of long nickel-titanium closed coil springs that are used to apply Class II inter-maxillary traction when fully bonded fixed appliances are in place. The springs are available in two lengths; 7 mm and 10 mm.³⁰ No long-term studies have been published on the use of SAIF springs and they are not used widely because of difficulties encountered in appliance management, including breakage, oral hygiene difficulties and problems with patient comfort.

Appliances producing pushing forces These include appliances that deliver a ‘pushing’ force vector, forcing the attachment points of the appliance away from one another.³¹ In this category are the Class II bite correctors which can be considered as a method of molar distalization since there is thought to be a ‘headgear effect’ with these appliances.³² Class II bite correctors include:

The Herbst appliance (www.americanortho.com): a fixed functional appliance popularized by Pancherz.³³ It consists of a bilateral telescopic mechanism that protrudes the mandible with compensatory maxillary molar distalization. The sagittal correction of the molar relationship results from a combination of skeletal changes (43%) and dento-alveolar changes (57%).³² Its action is similar to that of the Forsus springs (3M, Monrovia, California, USA) and AdvanSync bite correctors (Ormco, California, USA) that are used in conjunction with a transpalatal arch (Figure 7a and b).

The Jasper Jumper (www.americanortho.com) consists of two vinyl coated auxiliary springs attached to the maxillary first permanent molars and to the mandibular archwire anteriorly, with the springs resting in the buccal sulcus. The springs hold the mandible in a protruded position. The majority of the action is reported to be dental, rather than skeletal, change.³⁴

The adjustable bite corrector is similar to the Herbst appliance and to the Jasper Jumper. The advantages are the adjustable length, stretchable springs, and easy adjustment of the attachment parts.³⁵ No long-term studies have been published on this appliance to date.³⁰

The Mandibular Anterior Repositioning Appliance (MARA)³⁰ (www.ortho-concept.com/mara) consists of heavy ‘elbow-shaped’ wires attached to tubes on the maxillary first permanent molar bands or stainless steel crowns. A mandibular first permanent molar crown has an arm projection which engages the elbow of the maxillary molar. The appliance is adjusted so that, when the mandible elevates, the elbow wire guides the lower first permanent molars and repositions the mandible forwards into a Class I relationship. The results of treatment with the MARA are very similar to those produced by the Herbst appliance but with less ‘headgear’ effect on the maxilla and less mandibular incisor proclination than with the Herbst appliance³⁶ (Figure 8).

Intra-maxillary appliances include:

Lip bumper: this consists of a thick round stainless steel wire that fits into the headgear tube of the molar band and is held away from the labial surface of the incisor by loops mesial to the entrance of the molar tubes. The anterior part of the wire is embedded in an acrylic shield which actively displaces the lip forward. The reciprocal force of the displaced lip is transferred to the molars via the heavy wire and results in molar uprighting and distalization. Changes in the soft tissue equilibrium due to the lip bumper can lead to proclination of the incisors, an increase in intercanine width, as well as buccal rolling of the molars.^24,37

Pendulum appliance: this consists of a large Nance button supported and retained by premolar bands and 0.032” titanium-molybdenum alloy (TMA) springs inserted into lingual sheaths on the palatal surface of the bands to distalize the maxillary molars. For additional retention, bonded occlusal rests on the primary molars or second premolars can be included. If a midline screw is added to counteract a potential crossbite, or to correct an actual crossbite, then the appliance is called a Pend-X appliance (Figure 9).¹⁸ Generally, the amount of net distalization ranges from 1/3–2/3 of the created space.^38,39 However, the presence of the maxillary second molars change the ratio so, if the appliance is used after eruption of the second molars, the ratio will be 2/3.¹⁸ This is a similar to the result found by Karlsson and Bondemark,⁴⁰ who showed that the most opportune time to distalize maxillary first permanent molars is before eruption of the second molars. Although an inclusion of an uprighting bend in the distalizing spring of the pendulum appliance could reduce molar tipping, it is associated with mild anchorage loss and increased treatment duration.⁴¹

Jones jig and Lokar distalizing appliance: the Jones jig (www.americanortho.com) uses open-coil nickel-titanium springs attached to the maxillary first permanent molars, and a Nance button attached to the maxillary first or second premolars or the primary molars.⁴² A similar mechanism, called the Lokar distalizing appliance (www.ormco.com) has reported advantages of ease of insertion and ligation.³⁰ Interestingly, Paul et al⁴³ found no difference between the effectiveness of the nudger URA and the Jones jig for maxillary molar distalization.

Distal jet (www.americanortho.com): this uses bilateral tubes of 0.036” internal diameter attached to an acrylic Nance button with a coil, and screw clamps that slide over the tube. The wire from the acrylic ends in a bayonet bend and inserts into a palatal sheath on the maxillary molar band. The Nance button is also attached to a premolar band via a connecting wire. It is claimed that this appliance overcomes the disadvantages of other appliances used for distalizing maxillary molars by reducing the tendency for the teeth to tip, because the force acts through the centre of resistance of the molar and thus produces true bodily tooth movement.¹⁵ (Figure 10).

Nance palatal arch and coil springs: several authors have described the use of a modified Nance palatal arch with coils to distalize maxillary molars.¹⁹ One of these studies compared the effect of headgear (HG) and Nance palatal arch with coil spring (NAC) and found that the NAC was more effective than HG in distalizing molars; however, the anchorage loss was greater.⁴⁴ Another study by the same research team compared the effect of NAC and the repelling rare earth magnet (RRRM group) in molar distalization. The authors showed that the amount of molar distalization was greater in the NAC group than the RRRM group, with improved patient perception in the former group.⁴⁵

Repelling magnets: it has been shown that it is possible to achieve distal movement of the molars using repelling magnets with faster results when the second permanent molars are unerupted.⁴⁵ However, one of the difficulties of using repelling magnets is the force decay over time with the need for frequent reactivation (on a weekly basis), in addition to the difficulty of using them with other metallic appliances such as headgear.⁴⁶

Goshgarian appliance: the Goshgarian appliance can be used to distalize the maxillary molars unilaterally or bilaterally to correct a mild Class II molar relationship by activating the V-shape bend of the TPA, as described by Rebellato in 1995.⁴⁷ In a unilateral maxillary molar distalization case, it is better to reinforce the stable side with headgear, place torque in the archwire to take advantage of cortical anchorage, or use temporary anchorage devices.^{48,49,50,51,52}

Mini-implants: Ismail and Johal⁵³ used mini-implants for anchorage to allow for distalization of the maxillary molars. They showed that suitable sites for the implants are the palatal vault and the retromolar region. If extractions of the maxillary second permanent molars are carried out, then 4–5 mm of distalization is achievable.⁵³ Other uses of the miniscrew implant in the distalization of the maxillary molars is by supporting anchorage, in addition to placing a distal jet appliance⁵⁴ or pendulum appliance.¹⁴

Evidence for the effectiveness of molar distalizaton

Both retrospective and prospective studies using headgear appliances have shown slightly disappointing findings. In one retrospective study, distal movement of the maxillary molars in patients who wore cervical headgear for an 8-month period did not differ from that of an untreated group when they were re-evaluated 7 years later.⁵⁵ Benson et al² compared headgear and a midpalatal implant in a randomized clinical trial as a method of maxillary molar distalization in a group of 51 patients. They found that the molar movement was greater in the implant group than in the headgear group and point ‘A’ in the cephalometric tracings moved in the opposite direction in the headgear group. They concluded that there is no difference between these methods for maximizing anchorage.²

Systematic reviews have shown similarly modest amounts of maxillary molar distal movement can be achieved. Atherton et al undertook a systematic review to investigate various distalization methods and detected the amount of maxillary molar distalization that could be achieved is in the range of 2 mm–2.5 mm (Table 2).¹⁶ Another recent systematic review was undertaken by Antonarakis and Kiliaridis in 2008.⁵⁶ They found that intra-oral appliances for maxillary molar distalization are more effective than extra-oral appliances. However, they recorded moderate but acceptable anchorage loss with intra-oral appliances, causing an increase in the overjet, whereas the extra-oral appliances resulted in a decrease in the overjet. Neither appliance had any significant skeletal effects. They concluded that the optimum time to move maxillary first permanent molars distally is before eruption of the second permanent molars. These findings have been confirmed by the latest Cochrane review with regards to the effectiveness of different molar distalization techniques.⁵⁷

Transition from molar distalization to fixed appliances

The techniques for transition (or retention) following maxillary molar distalization are similar to that of the transition from functional appliances to fixed appliances. These include:^58,59

The method selected will depend on the clinician preference and patient-related factors such as cost, compliance and type of malocclusion, which should be taken into account.

Conclusion

Distal movement of the maxillary molars to produce space for relief of crowding, correction of a Class II molar relationship and reduction of an increased overjet can be undertaken with a range of appliances. Clinicians should be aware that the amount of tooth movement achieved with these appliances is modest.