Molar distalization in orthodontics – a review

Norman William Kingsley¹ described for the first time a headgear apparatus by which Class I relationship of the first molars could be achieved.² Weingberger, in his ‘Historical review of orthodontics’ states that extra-oral anchorage was first described by Gunnell, in 1822, whereas Guilford used headgear for correcting protruding maxillary teeth in 1866.³ Subsequently, extra-oral anchorage was rarely discussed until Kloehn designed headgear as we know it today.⁴ Since then, building on this concept, a number of headgears have been developed. However, more recently the emphasis has been on non-compliance, intra-oral distalizing devices.

Oppenheim advocated that the position of mandibular teeth is usually correct for an individual and occipital anchorage must be used to move maxillary teeth distally into a correct relationship without disturbing mandibular teeth.⁵ In 1944, he treated a case using extra-oral anchorage to distalize the maxillary molars.

Renfroe reported that a lip bumper, primarily devised to control a hypertonic lower lip, causes distal movement of lower molars sufficient to change a Class I molar relationship into a Class II.⁶ Gould was the first person to discuss the unilateral distalization of molars using extra-oral force.⁷

Klein evaluated the effect of cervical traction on the upper permanent first molar.⁸

Guerrero James presented the technique for the posterior movement of maxillary teeth using an ‘Atkinson Buccal Bar’.⁹ The mechanics used produced minimum strain on the mandibular anchorage unit and non-cooperation by the patient will not produce unwanted or lack of movement of the teeth, as may occur with other techniques.

Graber supported the philosophy of second permanent molar extractions in certain Class II malocclusions to allow distalization of upper buccal segments.¹⁰

Leonard described in detail the appliance design and use of the Acrylic Cervical Occipital Appliance (ACCO) to effect en masse distalization of buccal segments in the maxillary as well as mandibular buccal segments.¹¹

‘Tandem Yoke’ was introduced by Hogs in 1970; it consists of bimetric arch modules designed for ease of insertion and removal.¹²

Melson studied the effects of cervical traction by using metallic implants in the maxilla as reference points as suggested by Bjork.¹³ The study also analysed the influence of tilt of the outer bow in the horizontal plane on the maxillary molar distalization. The results from a study sample of 20 patients revealed that maxillary molar distalization, in the shortest time, was achieved by a downward tilt of the extra-oral bow.

Cetline and Tenhoeve emphasized a non-extraction treatment approach and documented 10 cases with various technical procedures.¹⁴ They used molar distalization in both maxillary and mandibular arches as a major source of space and believed that none of the basic principles of orthodontics were violated in doing so.

Tabash et al reported that extra-oral appliances of one type or another have been used for many years for molar distalization.¹⁵ Extra-oral traction may be applied to the upper arch in association with fixed or removable appliances, but the object in all cases is to move the upper posterior teeth distally and thereby provide space anteriorly for the alignment of incisors or reduction of overjet.

When distal molar movement is required, headgear is a very efficient appliance. Its reciprocal force is not transmitted to other teeth and it can be used at earlier stages of the mixed dentition.

Taylor explained the Crozat principle and technique and suggested that it uses molar distalization and rotation as the major source of gaining space.¹⁶

Gianelly et al demonstrated the use of intra-arch repelling magnets to distalize maxillary molars in a Class II malocclusion case.¹⁷ They reported that magnets were reliable, easy to place, well tolerated and do not require patient compliance. The study revealed rapid molar distalization without any significant loss of anchorage.

Valant John demonstrated the use of a modified Herbst appliance to produce a substantial increase in maxillary arch length in a growing patient by extracting second molars and distalizing maxillary first molars into the space made available.¹⁸

Cash Robert described a case of bilateral Class II malocclusion that was treated on non-extraction basis, using a ‘Jasper Jumper’ appliance.¹⁹ The results showed that forces generated by the Jasper Jumper cause significant distalization of upper first molars with no negative treatments effects.

Jeckel and Rakosi described an intra-oral removable appliance that offered controlled distal movement of the molars. The appliance, called ‘Molar Distalizing Bow (MDB)’ is versatile with various modifications possible.² The appliance causes effective first molar distalization before eruption or after extraction of second molars.

Gianelly, Bednar and Dietz demonstrated the use of Japanese NiTi super elastic coils to move maxillary molars distally.²⁰ These coils exerted 100 g of force and moved molars distally 1–1.5 mm per month with little or no patient cooperation. They employed a modified Nance appliance cemented onto the first premolars as the source of anchorage, in conjunction with fixed appliances.

Hilgers made a landmark contribution towards Class II non-compliance treatment by introducing an appliance called the ‘Pendulum Appliance’.²¹ The appliance derives its name from its broad swinging arc motion; like a pendulum in motion; the force is exerted from the midline of the palate to the upper molars. This intra-oral appliance seems to satisfy most of the requirements of an ideal molar distalization appliance, including excellent patient tolerance and the ability to distalize molars.

Snodgrass introduced a ‘Fixed Palatal Expander’ that could incorporate maxillary expansion, molar rotation and distalization at the same time.²² This appliance reduces the treatment time.

A Modified Pendulum appliance was introduced by Scuzzo and Takemoto.²³ The horizontal loops are inverted to allow bodily distalization of molars. The pre-activation given prior to intra-oral placement is in the range of 40–45 degrees rather than 60 degrees, as in a conventional or Hilger's Pendulum appliance.

Reiner similarly proposed a modification of the traditional Nance holding arch for the purpose of unilateral molar distalization.²⁴ The mean molar distalization achieved was 0.19 mm per week (SD 0.05 mm).

Jones and White described the use of a new intra-oral appliance named a ‘Jones Jig’.²⁵ The appliance could be used with any mechanotherapy and produced rapid molar distalization unilaterally or bilaterally in growing or non-growing individuals. The appliance employed the use of nickel titanium open coil springs and is a predictable and painless method of maxillary molar distalization.

Jasper and McNamara discussed the clinical management of the ‘Jasper Jumper’, including anchorage preparation and torque application to produce posterior movement of maxillary buccal segments.²⁶

Kalra²⁷ described an appliance termed a ‘K-Loop Molar Distalizer’ (Figure 1) which achieved bodily molar movement and controlled tipping or uncontrolled tipping, as per the treatment requirements. The appliance consists of a K-loop of TMA wire to produce force and moments and a Nance button to resist anchorage. A significant amount of molar distalization could be achieved with the K-loop without significant loss of anchorage.

The ‘Fixed Piston’ appliance, introduced by Greenfield in 1995, claimed to produce bodily distal movement of maxillary first molars without the need for an extra-oral appliance and with no loss of anterior anchorage.²⁸

Ghosh and Nanda analysed the dental, skeletal and soft tissue effects of the Pendulum appliance as a molar distalizer on 41 subjects.²⁹ Their study revealed the Pendulum appliance to be an effective and reliable intra-oral method for distalizing maxillary molars provided the anchorage is adequately reinforced.

Carano et al developed an intra-oral molar distalizing appliance called the ‘Distal Jet’ to distalize the maxillary molars.³⁰ The rate of molar movement was reportedly comparable with other intra-oral distalization methods, like magnets and Jones Jig.

In 1997, Klapper³¹ introduced the ‘Klapper Super Spring’ for the correction of Class II malocclusion. In 1998, a cable was wrapped with a coil and ‘Klapper Super Spring II’ was the result.

This appliance is an auxiliary which is fitted to fully banded upper and lower fixed appliances. The appliance consists of a bilateral length of multiplex nickel titanium which is bent back on itself attaching to the upper first molar tube and the lower arch wire by means of a helical loop. The springs lie in the buccal vestibule. The effect of the spring is to place a distalizing and intrusive force to the upper first molar. The appliance comes in two sizes, a 27 mm primarily designed for extraction cases and 40 mm for non-extraction cases. The springs are paired for left and right sides.

The latest design of the spring requires a special oval tube to be fitted to the upper first molars. This facilitates bucco-lingual adjustment of the springs in the vestibule and aids patient comfort. The springs can be readily removed for adjustment or activation.

Giancotti and Cozza utilized the super elasticity and shape memory property of nickel titanium wires and introduced what they called a ‘Nickel Titanium Double Loop’ system for simultaneous distalization of first and second molars.³² In their study they presented one case treated by this system and proposed it to be an ideal appliance for simultaneous first and second molar distalization in the permanent dentition when traditional intra-oral forces may prove ineffective.

Starnes introduced long nickel titanium closed coil springs that are used to apply Class II inter-maxillary traction when fully banded fixed appliances are in place.³³ The springs are tied in place with steel ligatures and are worn in place of inter-maxillary elastics.

Fortini, Lupoli and Parri proposed a new intra-oral molar distalizing appliance called the ‘First Class Appliance’.³⁴ Their main aim was to minimize the amount of anchorage loss in the anterior segment, as the molars are distalized.

Chung, Park and Ko Su Jin proposed the use of a newly developed intra-oral removable appliance for effective bodily molar distalization without causing any significant incisor flaring.³⁵ The appliance they developed is termed the ‘C-space Retainer’.

Keles and Sayinsu developed a new intra-oral appliance called the ‘Intra-oral Bodily Molar Distalizer (IBMD)’, with the aim of achieving bodily molar distalization without any patient cooperation.³⁶ The appliance, designed primarily to achieve bodily molar distalization, is composed of two components, the distalizing unit and the anchorage unit. The active part or distalizing unit of the appliance is made of 0.032” x 0.032” TMA springs. The distalizer section of the spring applies a crown tipping force, whereas the uprighting section applies a root uprighting force to the first molars. The springs are activated by pulling from mesial to distal and then seating into the palatal hinge cap attachments welded to the first molar bands. The anchorage unit of the appliance is formed by a wide acrylic Nance button extending to the palatal aspect of incisors and is thick enough to function as an anterior bite plane. The button is stabilized with the 0.045” stainless steel wire soldered to premolar bands. The appliance must produce a total of about 230 g of distalizing force on both sides. The purpose of the appliance is to establish Class I molar relationship in an average period of 7.5 months with an average molar distalization of 3.37 mm with 8 degrees of distal tipping.

Sugawara et al investigated the possibility of predictably moving maxillary molars distally in non-growing patients with the Skeletal Anchorage System (SAS) to improve malocclusions without having to extract premolars on a patient non-compliance basis.³⁷ With the advent of the SAS it is, indeed, now possible to move maxillary molars distally in non-growing patients and to improve malocclusions without having to extract the premolars and regardless of the patient's compliance.

It has overcome the two major drawbacks of other intra-oral and extra-oral appliances used for molar distalization, namely:

Various molar distalization appliances in orthodontics from 1822 to 2006 are listed in Table 1.