An Improved Approach to Bonding in Lingual Orthodontics

Abstract

Since its inception,lingual orthodontics has caught the imagination of orthodontists and patients alike. Inspite of its obvious advantages,lingual orthodontics has not been practiced as widely as traditional labial orthodontics.One of the main reason for this is complicated laboratory procedures associated with lingual orthodontics. Various techniques that have been described for indirect bonding in lingual orthodontics like TARG(Torque and Angulation Reference Guide), CLASS (Custom Lingual Appliance Set-up Service) require specially designed and expensive instruments and machines like Torque And Angulation Device,BIOSTAR,etc. Labs providing specialized back-up for lingual orthodontics are few,the laboratory charges significantly increase the treatment cost for the patient.The purpose of this article is to describe a technique for indirect bonding in lingual orthodontics that is accurate,convenient and can be easily incorporated in routine practice without the use of any expensive instruments,so that advantages of lingual orthodontics can reach more people and at lower cost.

INTRODUCTION

Esthetics has always been one of the primary concern for the patient opting for orthodontic treatment. Improvement in one’s appearance can positively affect social and interpersonal interactions.Along with increased interest in adult orthodontics,the demand for esthetic orthodontic appliance has also increased.Increased demand for esthetic alternative to traditional orthodontic appliance prompted the idea of placing the brackets on the lingual side,with a resultant introduction of lingual orthodontic treatment methodology

Current development of lingual orthodontics began in early 1970s,when it became apparent that bonding of bracket was a viable clinical procedure.1,2 Dr. Craven Kurz developed a true lingual appliance in which he bonded plastic Fischer edge-wise brackets to the lingual aspect of anterior teeth and metal brackets to the lingual aspect of posterior dentition,for many of his esthetically concerned adult patients.3,4

In the early 1970s ,when the lingual appliance debuted sensationally ,the number of lingual cases increased exponentially in United States.However,this rapid increase was followed by a decline within a few years.Some patient related problems like tissue irritation,speech difficulties,gingival impingement and occlusal interferences;and some operator related problems like appliance control,appliance placement,ligation and attaching auxillaries were associated with lingual appliance system.However continuous research in this field over the years has led to several improvements in the original lingual appliance.The current lingual appliances are much more refined to address the above mentioned problems and offer a great promise in clinical practice.5-10

It has been universally recognized that precise bracket placement holds the key to success in lingual treatment. Considering the difficulty in gaining access to the lingual surfaces of maxillary and mandibular teeth,indirect bonding technique is pivotal for the success of lingual orthodontics.

In this article,we have described clinical technique for indirect bonding in lingual orthodontics which is a modification of original Hiro system with the addition of cephalometric evaluation and a new method of archwire indexing. The pictures and models that have been used to describe the procedure are of a patient that came to our department for treatment and opted for lingual orthodontics.

METHOD

Indirect bonding Technique:

CONSTRUCTING THE SET-UP:

Accurate impressions are taken using high quality alginate or silicone impression material and models are poured with hard plaster.The hardened models are reduced to a height of 8mm from the base to gingival margin.Two retention slots are made on the bottom of the cast corresponding to the molar region to allow better repositioning of this section once the teeth are sectioned off.Backs of the models are leveled and a complimentary base is produced.There should be no unevenness between model and the base.The finished models are then articulated.(Fig .1)

Next all teeth ,except for molars are sectioned off from the cast using a fine ribbon saw blade and trimmed proximally,taking care not to damage contact points.Molar segments are repositioned on the models using retention slots.Molar segments are not cut until teeth anterior to them are set in order to maintain their vertical and sagital position.Special care is taken to maintain intercanine width and establish IMPA between 90⁰-100⁰. Extraction of teeth is done according to treatment plan. Desired maxillary incisor angulation and position is set according to treatment objectives.All teeth are set as ideally as possible following Andrews six keys of occlusion11 and an ideal wax set-up is prepared.Finally molar segments are removed and trimmed and positioned in the same way as other teeth.Care is taken to flatten the curve of spee and produce a very slight curve of Wilson.(Fig.2)

To confirm if desired incisor angulation is achieved,a cephalogram of articulated models is taken.Inter-incisor angle and incisor occlusal plane angle are measured. 12 Necessary adjustments can be made in the set-up as required in order to achieve planned incisor position.(Fig.3)

IDEAL ARCHWIRE PREPARATION

Once the setup has been fabricated with wax,an ideal archwire with bicuspid insets is prepared with full-size rectangular wire.Archwire is kept as smooth as possible with minimal adjustment bends. It may be required in some cases to make small insets mesially for first molars (Fig. 4)

BRACKET POSITION

In maxillary arch,the vertical midpoint of the molar clinical crown is taken as a reference and a line is drawn extending to anterior teeth.The line should fall within the lower third of the incisors;also there should be a clearance of 1.5mm to the gingival margin. In mandibular arch,height of clinical crown of 1st bicuspid is critical .The middle of this crown is taken as reference point and when this line is extended along anterior teeth,it should pass through middle of clinical crown at a distance of 1.5mm from gingival margin.The bracket should be centredmesio-distally on each tooth.

INDEXING THE ARCH-WIRE POSITION:

This step allows for easy and accurate repositioning of bracket in case patient comes with a broken bracket requiring re-bonding. Sliding hooks are crimped horizontally on wire between 2nd premolar and 1st molar.Next the archwire along with tied brackets is positioned in desired position on the models. This position is indexed in wax as shown in figure.(Fig 5)

CUSTOMISING THE BRACKET BASE

The next step is to transfer all the information of the setup to the brackets.After applying separating media on the models,the prepared ideal archwire along with tied brackets is placed in indexed position.There are small spaces between the bracket base and the tooth surfaces owing to variation in lingual tooth morphology.Light-cure composite resin is then applied to bracket bases and wire repositioned in its indexed position .After removing the excess material,the composite adhesive is light cured.Thus all the information of the setup including in-out tooth position, rotation correction and torque is transferred to customized bracket bases.

FABRICATION OF TRANSFER TRAYS

Transfer trays are fabricated using provisional light cured composite dental resin and and clear cold-cure acrylic resin material. 13 First provisional dental resin is applied onto occlusal part of brackets upto the slot area and cured.Special care is taken to avoid covering the archwire.Next a transfer tray is prepared covering this composite layer with clear cold cure acrylic resin. Elastomeric rings are inserted into acrylic resin transfer trays for ease of holding the trays.Once the acrylic hardens,the whole archwire-bracket-tray assembly is removed.Archwire is disengaged from the bracket slots and transfer trays are trimmed.Marking the transfer trays with tooth numbers helps in easy identification and placement.(Fig.6)

INTRA-ORAL BONDING

The lingual tooth surfaces are first scaled and polished .Next, the tooth surface is etched,rinsed and dried.A thin layer of primer is then applied on etched surface.A very small amount of adhesive is applied onto the bracket base and transfer tray is positioned on tooth accurately.After curing the material,the transfer trays are removed using scalers .(Fig.7)

REBONDING

Accurate rebonding has always been a problem with all lingual techniques that use a flexible inner tray made from pressure vinyl (bioplast) or silicone material. The disadvantage of using these trays for initial bonding is that they cannot be used for rebonding, since the tray no longer fits the patient’s mouth as a result of tooth movement,and has to be sectioned into single trays.All precise references in three planes of space are hence lost.But accurate rebonding can be conveniently done with this technique.14

In case any bracket gets debonded for any reason during the course of the treatment,accurate rebonding can be easily done as follows. First the bracket is ligated to the prepared ideal arch wire.Next the archwire is placed in its indexed position on the set-up model and the procedure described above is repeated to prepare a new transfer tray. (Fig. 8)

DISCUSSION

The only indirect bonding system in the 1980’s was silicone tray system made with torque angulation reference guide(TARG) or customized lingual set-up service(CLASS)8 .However,it was associated with problems such as bonding inaccuracy,bonding failure and increased cost.In 1998,resin core indirect bonding system was published which later became popular as Hiro system.

I have presented a modification of original Hiro technique to provide a method for indirect bonding in lingual orthodontics that is convenient,accurate and avoids the need to purchase expensive instruments or electronic equipments .

The addition of cephalometric evaluation method improves the accuracy of set-up models and can lead to improved accuracy during treatment planning .Bracket customization described in this technique helps to bring the convenience of pre-adjusted appliance in lingual technique .Also,a simple indexing of archwire proves invaluable for accurate rebonding of brackets

A convenient technique, that doesnot require any specialized lab support and that can give accurate bonding and rebonding and which is very affordable will help to make lingual orthodontics to be accepted by more orthodontists and not remain an option available only in selected major cities.

CONCLUSION

The esthetic demand of orthodontic patients is ever increasing.Many adult do not seek orthodontic treatment because of the perceived embarrassment of wearing braces.Under such circumstances,lingual orthodontics providean excellent treatment alternative.But complicated laboratory procedures and increased cost have prevented widespread use of lingual orthodontics.The technique described above is a step towards simple and affordable lingual treatment.

REFERENCES