Introduction to Molar Distalization

Abstract

In recent years, the percentage of patients having extraction as a part of orthodontic treatment has decreased considerably as experiments has shown that that extraction does not necessarily guarantee stability of teeth alignment. Proximal stripping also has its own limitation. So which one to opt? Molar distalization in recent years is evolved as an alternative method of gaining space to conventional methods where ever is indicated. Distalising teeth had always been a challenge to orthodontists, of which molar distalisation is the most difficult. However if a proper diagnosis and case selection criteria is carried out molar distalization will soon become an ideal method of gaining space in future.

Keywords: Molar distalization, Intraoral molar distalizers, Ricketts criterion

INTRODUCTION

Current orthodontic philosophies have been oriented towards conservative treatment modalities - to avoid extractions and , at the same time, to try to eliminate the need for patient cooperation. Whenever there is space deficiency, the methods of gaining space that strikes to our mind first are, extraction, expansion and proximal stripping. Angle[1] proposed expansion of dental arches for nearly every patient and stated that extractions for orthodontic purpose was not necessary for stability of results or for aesthetics. He believed that when teeth could be saved by dental treatment, extraction of teeth for orthodontic purpose seemed particularly inappropriate and unacceptable. In 1930’s, Charles Tweed observed relapse after non- extraction expansion treatment and decided to retreat those cases with extraction. One of the most popular topic of continuing research among the orthodontists nowadays is the molar distalization.

HISTORY

In 1982 William Kingsley[2] was the first dentist to achieve correction of Class II molar relation to Class I by means of headgear. Later Oppenheim advocated the use of occipital anchorage for moving maxillary teeth distally into correct relationship without disturbing mandibular teeth. In 1944, he treated a case with extra-oral anchorage for distalizing maxillary molar. Renfroe[6] (1956) reported that lip bumper primarily devised to hold hypertonic lower lip caused a distal movement of lower molars sufficient to change class I to Class II. Gould [8](1957) was first person to discuss about unilateral distalization of molars with extra-oral force. Graber T-M. (1969) extracted the maxillary II molar and distalize the first molar to correct class II div.1. In 1999, A Modified Hilgers Pendulum appliance was introduced, known as the “M-Pendulum appliance” to remove unwanted tipping of maxillary molars by Hilgers[9]. In 2000 a new non-integrated implant-supported device called the Graz Implant-Supported Pendulum (GISP) was introduced. It distalized maxillary 1st & 2nd molars in adults. It consisted of 2 parts: the anchorage plate, which is fixed to the palatal bone via 4 miniscrews, and the removable part, which is a pendulum-type appliance. In 2005, Kinzinger[10] modified the standard pendulum appliance by integrating a distal screw into its base and by special preactivation of the pendulum springs, called Pendulum K appliance.

INDICATIONS

• Class I skeletal,Class II or end to end molar relationship (due to maxillary protrusion but mandible is of normal length).
• Mild to Moderate crowding ( mild arch length discrepancy.
• Midline discrepancy cases.
• Impacted or highly placed cuspids.
• Gaining space ( loss of arch length )due to premature loss of deciduous teeth.
• Favorable maxillary 2nd molar position.
• Low to moderate mandibular plane angle.
• Deep overbite
• Maxillary first molar mesially inclined.
• Second molar extraction cases where the third molars are well formed and erupting properly.
• Straight profile
• Normal, healthy temperomandibular joint
• Correct maxillomandibular relationship
• Normal, short lower face height

CONTRAINDICATIONS

• High mandibular plane angle. (wedging effect)
• Open bite.
• Excessive lower face height.
• Patients with class I or class III molar relation
• Upper molars should not be placed buccopalatally in such a way so that their roots come in contact with the cortical plates during distalization.
• Severe arch length discrepancy patients

GENERAL CONSIDERATIONS

Proffit described the amount of force for bodily movement of molar is 100-120 gms and approximately 50-60 gms for tipping movement.Continuous forces are preferred than intermittent or interrupted forces.

FORCE DIRECTION

• Should be along the arch form
• Should be as close to the centre of resistance of the molar as possible

ANCHORAGE CONSIDERATIONS

Since perfect bodily movement is almost never achieved, at the end of the distalization, a distally tipped molar results.Loss of space may occur during its uprighting.Hence, maximum control and bodily movement of the molar is desired during distalization. According to some reports 1/3rd of the space created is due to anchor loss which is expressed as an increase in the overjet.Intermolar width increase by 2.9 – 4.4 mm is indicated. Tendency of the molar to return mesially particularly if 2nd molars are present(ANDREASON AND NAESSIG 1968).Molars are not used as anchorage for at least 4-5 months after they have been moved distally(GIANELLY AJO 1998).

CLASSIFICATION

The APPLIANCES used for molar distalization can be divided into

1. Removable appliances and

2. Fixed appliances.

Removable appliances

• Extra oral traction

• Head gear

• Removable appliances
• Sliding jigs with intermaxillary elastics.
• The cetlin appliance
• Acrylic cervical occipital appliance (ACCO)

Fixed appliances

• Intra Oral – Maxillary Molar Distalizer
• K Loop Molar Distalization Appliance
• Hilgers Pendulum Appliance
• Super Elastic Niti Wire
• Niti Coil Springs
• Open Coil Jig
• Distal Jet Applince
• First Class Appliance
• Fixed Piston Appliance
• Magnets
• Space Regainers
• Tma Transpalatal Arch
• Wilson Rapid Molar Distalizer
• Mandibular Molar Distalizer
• Franzulum Appliance
• Lip Bumper
• Mandibular Jones Jig

Intramaxillary appliance:

• Wislons 3D appliance
• Repelling Magnets
• The pendulum appliance
• Niti based appliances : archwires – single loop, double loop; Compressed coil springs
• Jones jig
• Distal Jet
• Fixed piston appliances
• IBMD
• K-loop
• Distalix
• Franzulum appliance
• Lokar appliance
• First class appliance
• Carriere’s Distalizer

Intermaxillary appliance:

• Herbst appliance
• Jasper Jumper
• Eureka Spring
• Klapper superspring
• IMPLANT supported distalization

DIAGNOSIS

The first step is to confirm the diagnosis of a forward maxillary molar position.

And to check the centric relation position (and vertical status) and the TMJ status. All records must be correlated, ie, cephalometrics, functional axiographics, and radiologic exams (MRI, CT scan).Korn has cautioned against using extraoral force in patients with undiagnosed meniscus disorders who are borderline clickers with an "end-on click.

RADIOGRAPHIC ASSESSMENT

SKELETAL CONVEXITY AND GROWTH PREDICTION helps to differentiate bw a forward maxilla and a backward mandible. In growing patients growth prediction has to be done to determine what the positive convexity would be with time and growth. For example, a +4 mm convexity at 8 years of age could be completely different at maturity, according to the facial pattern.This will permit clinician to know if extraoral force, functional therapy and or DISTALIZATION are indicated.

RICKETTS CRITERION

Ricketts stated that the position of the maxillary molar (M1) should be that the distal surface of the molar should be perpendicular to the pterygoid vertical(ptv).The clinical norm is age+3 and clinical deviation is +/-3 mm.( growing patients). In good skeletal and dental class I relationships , the facial axis normally crosses the mesial cusp of M1. In non-growing patients mean value is 18 mm.If the distance M1/PTV is shorter than the normal measurement, the possibility for distalization is low and possible extractions will depend on growth potential and the presence of 3rd molar.

IOPA OPG ASSESSMENT

• Absence of upper 3rd molars offer better prognosis.
• Posterior crowding as indicated by distal angulation of the molars make distalization unsuitable.

TREATMENT PLANNING

The treatment approach is divided into two phases. Objectives of 1st phase/space gaining phase: 1. To distalize the upper molars bodily so that the patients will occlude in Super class – I occlusion (i.e. over corrected). 2. To achieve generalized spacing through dento alveolar widening and growth. 3.To correct molar inclination, rotation and cross bite. Objectives of second phase/consolidation phase are: 1. Andrew’s six keys to normal occlusion. 2. Overbite, overjet and all dental malpositions are corrected.

SUCCESS RATE

There are 3 age related pt groupings and success rate and prognosis differ for each; Mixed dentition age – Procedure is 90%+ successful and molar correction can be completed within 6-8 months.

Adolescent dentition age - cusp to cusp molar relationships are corrected reasonably well. Full class II relatioships are difficult to resolve.( presence of 2nd molars).

Adult dentition age – success rate is highly variable and more failures are noted.

CONCLUSION

In summary a favorable time to move the molars distally appears to be the mixed dentition before the eruption of the second molars. Patient selection is of atmost importance and should not be overlooked. Right appliance should be selected for the right patient at right time. Appliance should be selected for patient not patient for appliance. To fight a borderline case distalization is a important weapon in orthodontists armamentarium.

REFERENCES