CREATING PROPER INTERPROXIMAL CONTACTS 

     AND CONTOURS ON POSTERIOR TEETH

INTRODUCTION

Restoration of interproximal defects between posterior teeth is troublesome.  It is difficult to create interproximal convex contours fitting tightly to adjacent convex surfaces, contain material within a preparation and compensate for matrix thickness.   There are many techniques available to restore interproximal areas on posterior teeth, but each technique creates limitations dependant on the situation.  Restoration is easy if various techniques and their limitations, restorative situations, and the appropriate technique for each situation are defined.

TECHNIQUES

Restoration of interproximal areas between posterior teeth requires placement of a matrix to contain material within a tooth preparation.  Matrix bands are contoured or straight, stiff or soft, of different thickness, of different circumferential diameters at various occlusial-gingival heights, and circumferential or segmented to one interproximal side.  Each of these characteristics contributes to matrix ease of placement, production of convex surfaces, and the need to compensate for matrix thickness to obtain tight contacts.  In addition, these factors contribute to matrix fit, ability to contain material within a preparation at various heights, contact location, manipulation of matrix shape by burnishing, formation of embrasures, and matrix deformation by wedge placement.

RESTORATIVE SITUATIONS

Restorative situations are characterized by defect depth, degree of gingival, lingual and facial extension, tooth and defect dimensions and shape, tooth position including tilt, rotation, super eruption, and partial impaction, and tightness of original contacts.  Situations are further defined by interproximal shape, position, and restorative needs of adjacent teeth and opposing teeth, occlusion, and gingival and osseous shape and health.   Final consideration is given to the distance between remaining tooth structure and adjacent tooth structure after tooth preparation and the desired interproximal shape.

MASTERING POSTERIOR INTERPROXIMAL RESTORATION

It is critical to understand techniques used to restore posterior teeth have limitations in specific situations and these limitations can vary from dentist to dentist.  Dentists change their present technique to a new technique and discard the original one when a problem occurs.  The new technique has limitations in specific situations and another technique is tried until no single technique is satisfactory.  Successful restoration comes from matching the best technique to each situation.

Many techniques and situations exist when restoring interproximal areas on posterior teeth.  It is beyond the scope of this article to describe every technique and there are many excellent techniques.  It is important to approach restoration by analyzing restorative situations and how each factor effects a technique.

DEFECT – PROPORTION AND EXTENSION

Proportion of gingival, facial and lingual extension of an interproximal tooth preparation defines how much guidance is provided to a matrix.  A minimal preparation maintains facial and/or lingual contact.  A flat matrix is rounded by remaining tooth structure surrounding a small preparation after tightening the matrix.  In addition, when the contact is left partially intact placement of a matrix separates teeth and creates a tight restoration.  However, when partial contact remains, placement of the matrix is difficult because the tightness of a remaining contact is intensified as there is less contact.  A dead soft matrix is impossible to place with remaining tight contact so a firmer matrix is required.  Often, tooth separation is required to place any matrix.  Tooth separation is accomplished by use of wedges or tooth separators.  

Deep gingival extension creates problems of maintaining composite material within a preparation and/or placement of a matrix.  A shallow preparation does not create problems unless the gingival contact is not broken in which case placement of a matrix past the gingival floor can be difficult.  A deep gingival extension creates restorative problems because a matrix must fit tight at the gingival aspect and resist compressive force of composite placement.  Circumferential bands create horizontal diameters different than those of teeth and therefore, a band which fits tight against a gingival floor may leave an open contact above the band or may be tight in the mid section and loose at the gingival floor.  Placement of a wedge can create reverse contouring of a matrix and concave surfaces.

Deep gingival extension is difficult to restore with a one sided matrix because these matrix do not exert force against the tooth.  Placement of a wedge, especially with enough force to cause tooth separation, reverse curves a matrix. 

CONTACT – TIGHTNESS, POSITION AND SIZE

The tightness of original contacts determines how easy matrix placement will be when the contact area is not broken in the facial, lingual or gingival extensions.  A loose contact allows for easy matrix placement, while a tight contact may negate matrix placement.  Tooth separation or overpreparation is required for tight contacts unless preplanning is done.  In addition, tight contacts on mesial and distal aspects of a tooth is compounded by placement of a matrix into the opposing interproximal space because of tooth shifting.

Tooth structure surrounding small defects can shape a flat matrix to acceptable interproximal contours when the matrix is tight.  Large defects require a contoured matrix to create convex surfaces.  Contoured matrix are precontoured or contoured by burnishing.  Several techniques burnish a matrix while on a tooth and result in a concavity around the convex contact area of an adjacent tooth.  Consequently, direct burnishing, especially of dead soft matrix material, is a nice technique but over burnishing creates problems.  

ADJACENT TEETH

Interproximal contours of an adjacent tooth, combined with matrix shape, locate a contact area in the facial-lingual and occlusion-gingival directions.  Location of a contact area and interproximal contours further defines occlusial, gingival, facial and lingual embrasures.  Interproximal contours of an adjacent tooth are often modified to create proper contact location.  Most commonly an existing restoration which was poorly done or worn with time is modified.  A very common mistake is placement of a restoration against a tooth allowing contact right at the occlusial surface with no occlusial embrasure.  When an occlusial embrasure is created after occlusial adjustment, the contact is lost.

OPPOSING TEETH

Opposing teeth create a physical barrier to restoration size especially in an occlusial dimension.  Opposing cusps that limit marginal ridge height usually caused by supereruption of teeth influences interproximal restoration.  The resulting plunging cusp requires enamelplasty or restoration to allow proper occlusial embrasure and marginal ridge formation.

CLINICAL APPLICATIONS

Restoration of interproximal areas on posterior teeth requires preoperative evaluation of tooth size and position; defect size and location; contact tightness, location and size; adjacent tooth position, size, contours, contact location, size and position, and need for restoration; opposing tooth position, shape, size, contours and need for restoration; and gingival location, size, shape and health.  There are many clinical situations as each restorative characteristic is matched to other characteristics, but key characteristics such as contact tightness and defect extensions determine the technique used.

SLIDING BAND TECHNIQUE

The sliding band technique is used to restore an interproximal area with a tight contact when a portion of the contact will be maintained.  Maintaining a contact ensures tight contact after restoration and minimizes tooth destruction.  A .0015 inch tofflemire matrix band is placed into the interproximal space.  Tooth preparation is accomplished by entering the marginal ridge with a 330 pear shaped carbide bur and drilled apically.  Extension in a buccal and lingual direction is dictated by cavity and decalcification size.  The tofflemire band is moved to the lingual or buccal as tooth preparation is done and the band is damaged from drilling.  The matrix is moved after final preparation followed by placement of a wedge and matrix ring.

The preparation is etched with 37% phosphoric acid for 15 seconds and washed for 10 seconds.  Resin is placed with a microbrush.  The solvent is evaporated by light air application and the remaining filled resin is light cured for 10 seconds.  One to two millimeters of composite is placed into the bottom of the preparation and light cured.  The preparation is filled using a layering technique.  The matrix is removed and the restoration is finished and polished.

PROGRESSIVE WEDGING TECHNIQUE

Wedging is often required to hold a matrix tight to tooth structure at the gingival margin during composite placement.  Extensive tooth preparation to remove caries or old restorations leaves little tooth structure to control matrix band contours.  Wedge placement deforms matrix band shape often resulting in concave interproximal contours.  The progressive wedging technique limits interproximal concave surfaces.

A precontoured matrix band is placed which will allow proper contours.  A wedge is placed from the lingual or facial depending on which provides improved access.  The wedge is placed with enough force to be in physical contact with the band but not exerting force to cause tooth separation.  A G-Ring is placed to hold the matrix band tight to the facial and lingual tooth surfaces.  A G-Ring might cause tooth separation, however, if tooth shape is not accommodating, teeth do not separate.   The matrix band is burnished to further shape it against the adjacent tooth. The preparation is bonded.  Dentin areas are lined with a flowable resin and light cured for 10 seconds.  One to two millimeters of composite is placed at the bottom of the preparation and light cured.  Composite should avoid band displacement and composite excess.  The wedge is tightened to cause tooth separation but the initial composite layers are built to a height which will stop matrix band distortion. The preparation is filled using a layering technique.  The matrix is removed and the restoration is finished and polished.

ROUTINE RESTORATIVE TECHNIQUES

Restoration of interproximal areas between posterior teeth is often successfully accomplished with tofflemire systems used for amalgam.  The static position and shape of the matrix should be analyzed for band thickness, tightness to the gingival floor, proximity to the adjacent contact areas, tightness to mesial and distal walls and final contours.  Adjustment is often required to meet ideal requirements.  Placement of a wooden wedge is used for tooth separation that compensates for band thickness and to hold a matrix tight to the gingival floor.  Mechanical pressure on a band from an instrument presses a band against an adjacent tooth.  Pressure is accomplished by placing a light tip or an instrument firmly against the inside of a band and light curing composite or by placement of firm condensable composite.  Loosening a band may be required so a band can reach an adjacent tooth.

COMPLEX RESTORATIVE SITUATIONS

Complex restorations require creative thinking and evaluation of a restorative situation.  Matrix techniques must allow proper replication of original tooth structure. Creating ideal contours and contacts is potentially compromised by many factors such as adjacent and opposing teeth, little remaining tooth structure, tooth wear, tooth shifting, etc.  Correction of these factors is often required prior to restoration to achieve excellence.

Restoration of adjacent interproximal areas is difficult and gets more difficult as more tooth structure is lost on each tooth.  Restoration of one tooth at a time alleviates most problems.  The technique requires compensation for only one band thickness and the interproximal area of the first restoration is contoured to an ideal shape prior to placement of the second restoration.  

The case above shows a complex case of multiple interproximal restorations on rotated teeth .  The second maxillary left bicuspid has a distal occlusial restoration with facial extension that breaks the contact, has moderate lingual extension with a large lingual embrasure from the first molar rotation, and average gingival extension.  The first molar has a mesial occlusion restoration with facial extension that does not break the contact, has moderate lingual extension with a large lingual embrasure from the first molar rotation, and deep gingival extension.  The second molar has a mesial occlusial distal restoration.  The mesial interproximal area has minimal lingual, facial and gingival extension with tight contact.

Tooth preparation is done after rubber dam isolation and placement of a tofflemire band on the mesial of the second molar for the sliding band technique.  After tooth preparation, a .0015 tofflemire matrix is placed on the mesial of the first molar.  The matrix is burnished prior to placement to precontour the matrix to self-wrap against the tooth.  Two wooden wedges are placed from the lingual and facial to compensate for a large lingual and gingival embrasure.  Composite is place on the lingual outside to maintain matrix position.  Bonding is completed  The preparation is filled using a layering technique.  The matrix is removed and new matrix systems placed to restore the second bicuspid and the distal occlusial of the second molar.  A tofflemire band is easily placed on the second molar with guidance of an occlusial embrasure formed by the mesial restoration.  Prior to placement of the mesial restoration the contact is too tight for easy matrix placement.  The preparations are filled using a layering technique and restorations are completed.

SUMMARY

There are many excellent techniques used for restoration of interproximal areas on posterior teeth.  All techniques have limitations in various situations that must be identified and alternate techniques used in those situations.