Optimizing tooth form with direct posterior composite restorations.

Advances in material sciences and technology have provided today's clinicians the strategies to transform the mechanistic approach of operative dentistry into a biologic philosophy. In the last three decades, composite resins have gone from being just an esthetically pleasing way of restoring Class III and Class IV cavities to become the universal material for both anterior and posterior situations as they closely mimic the natural esthetics while restoring the form of the human dentition. In order to enhance their success, clinicians have to rethink their protocol instead of applying the same restorative concepts and principles practiced with metallic restorations. Paralleling the evolution of posterior composite resin materials, cavity designs, restorative techniques and armamentarium have also developed rapidly to successfully employ composite resins in Class II situations. Most of the earlier problems with posterior composites such as poor wear resistance, polymerization shrinkage, postoperative sensitivity, predictable bonding to dentin, etc., have been overcome to a major extent. However, the clinically relevant aspect of achieving tight contacts in Class II situations has challenged clinicians the most. This paper reviews the evolution of techniques and recent developments in achieving predictable contacts with posterior composites. A Medline search was performed for articles on "direct posterior composite contacts." The keywords used were "contacts and contours of posterior composites." The reference list of each article was manually checked for additional articles of relevance.

INTRODUCTION

Optimizing tooth form has always been the “Holy Grail” of operative dentistry. Recreating the missing tooth anatomy is important to not only replace lost structure but also to re-establish ideal form and function. Until recently, this was achieved with traditional materials such as cast gold or amalgam. They provided durable restorations with excellent contacts and contours which lasted for several decades. However, since they were nonadhesive, they required mechanistic cavity preparations with macro retentive features and the results could hardly be called esthetic.

With increasing public demand for esthetic restorations and the advent of adhesive cavity designs, composite resins are gaining popularity as posterior restorative materials.[1] In the last three decades, there has been a continuous evolution of composite resin materials and techniques. Due to this, it is now possible to predictably restore ideal tooth form, while at the same time being minimally invasive and enhancing the esthetics of the patient's dentition.[2]

It can therefore be stated that:

Optimizing tooth form

Minimal intervention and

Enhanced esthetics is the triad of modern conservative dentistry [Figure 1]

Figure 1

Triad of modern conservative dentistry

Presently, composites are challenging the position of amalgam as the material of choice for posterior restorations.[3] While many problems related to the clinical handling of composites have been addressed, obtaining ideal contacts in Class II situations still remains problematic.[4]

This paper reviews the evolution of techniques and recent developments in achieving predictable contacts with posterior composites.

Ideal contacts

The proximal contact or “contact area” refers to the surface area where the proximal faces of neighboring teeth come in contact.[5] Initially, when teeth erupt and meet each other at a point, it is known as a “point contact.” With time, due to proximal attrition, this becomes a “contact area.” The contact area is usually located in the upper middle 1/3rd of the crown of most teeth, providing natural embrasures and an opportunity for good maintenance of the interproximal area.

Ideal contacts serve by

Maintaining the dental arch stability by transmitting forces along the long axis of teeth,

Protecting the interdental papilla by preventing food impaction and,

Influencing speech and cosmetics, especially in the anterior region.[6]

Improper restoration of contact areas causes displacement of the teeth, lifting forces on the teeth, rotation of teeth, deflective occlusal contacts and food impaction.[7] This leads to trauma to the periodontium resulting in pain, inflammation and bleeding.

Can composites replace amalgam as the material of choice for Class II situations?

An ideal composite resin for restoring posterior teeth should fulfill the following criteria:[8]

Wear similar to natural tooth structure or amalgam

Have no plastic deformation in function

Have a simple placement technique

Have minimum polymerization shrinkage

Have excellent marginal adaptation and sealing

Have a radiopacity similar to or greater than tooth structure for ease of radiographic evaluation

Be easy to finish and polish

Be esthetically pleasing

If composite resins are to replace amalgam as the material of choice for restoring contacts in posterior teeth, two issues need to be addressed:

Longevity

Predictability and ease of establishing contacts.

It is difficult to directly compare the longevity of direct restorations for various reasons. This may be due to variables in study design, differences in clinical procedures and materials used and variations in study characteristics. Longitudinal studies on posterior composite restorations over a period of 8 years or more reveal an annual failure rate of 1%--6% compared to 0%--7% for amalgam.[910] Opdam et al,[11] concluded that when operators who are skilled in both amalgam and composite techniques placed restorations, the annual failure rates of both materials were comparable.

Key aspects of direct posterior composite contacts

A review of the relevant literature[1213] reveals that there are certain key aspects to be considered while discussing posterior composite contacts. They are

Proximal contour

Location of the contact area

Contact tightness

Gingival adaptation

Proximal contour

This includes the occlusogingival and the buccolingual contour of the restoration on the proximal aspect. This should be adequate to maintain contact with the adjacent tooth, not overly convex, concave, or flat.

Location of the contact area

Recreation of the contact area in its ideal location will help to develop ideal embrasure form, thereby preserving the health of the gingival col and enabling food deflection during mastication. It is usually located in the upper middle third of the crown of most teeth on both proximal ends of the tooth equator and beneath the marginal ridges.

Contact tightness

Once the restoration is in place, the contacting teeth must be in close approximation. The contact must be neither open nor too tight. This can be checked by using dental floss.

Gingival adaptation

This is very important for long-term success as microleakage at this critical site is a leading cause for secondary caries.

Evolution of clinical techniques in achieving proper contacts and contours with posterior composites

Adapting yesterday's techniques for today's materials does not lead to success. Initially, clinicians continued to use circumferential matrices in a Tofflemire retainer along with a wooden wedge. This resulted in a number of problems:

Circumferential bands created a flat interproximal contour.

During band tightening they also tended to flatten out buccolingually resulting in open contacts.

Additionally, the contact area was shifted more occlusally, closer to the marginal ridge. Not only did this make the restoration more susceptible to fracture, but it also created a larger gingival embrasure with associated food impaction and gingival inflammation.[13]

As an alternative, researchers have recommended the use of circumferential transparent matrices along with light-reflective wedges, the rationale being that light polymerization of the composite would be more effective with this combination.[14] However, in reality, clear matrices were not flexible enough to adapt properly in the posterior region. They are almost twice as thick as metal matrices. Wedge placement was also difficult creating overhangs.[15]

All these problems led to the development of several strategies to develop ideal contacts and contours with direct posterior composite restorations. Relevant among these are

Contact forming instruments

Ceramic inserts

Light tips

Contact forming instruments

These are special instruments designed to create good contacts with posterior composites. They push the matrix toward the contact area during light curing.

For example, Contact Pro (CEJ Dental, San Juan, Capistrano)

Optra contact (Ivoclar, Vivadent) [Figure 2a]

Figure 2

(a) Optra contact–contact-forming instrument. (b) Cerana inserts with size-matched diamond abrasive. (c) Light tip fi tted over light wand.

Contact former (American eagle instruments)

After preliminary steps and placing some composite material in the proximal box area, the instrument is pushed into the composite and pressed against the contact area during light curing. Subsequently additional increments are added. In vitro studies have reported improved contacts with these instruments.[4] However, in clinical use they are too wide for most cavities. It was also observed that the contacts produced by them were closer to the marginal ridge while proximal contour was found to be lacking.[16]

Ceramic inserts

Prefabricated ceramic inserts like Beta Quartz (Lee Pharmaceuticals Co., California), Cerana (Nordiska) etc., are formed from a silica-based glass composite which when heated crystallize to form a ceramic. These inserts are available in various sizes with size-matched diamond abrasives for the cavity preparation [Figure 2b]. The insert is treated with a silane-coupling agent to improve the bonding with composite. Use of these inserts displaces most of the composite from the volume of the restoration thereby improving the properties of the restoration.

Their major benefits are the excellent gingival margin adaptation and the creation of tight contacts.[4]

However, inserts did not gain much popularity in practice because of certain drawbacks, such as:

They created unnatural proximal contour.

It was difficult to optimize the occlusal anatomy.

The dissimilar coefficient of thermal expansion between the ceramic inserts and the composite resin created clinical problems.[413]

Light tips

Unlike with silver amalgam restorations, the gingival margin adaptation has been problematic with direct posterior composites. This aspect is considered to be the “Achilles Heel” of most posterior composite restorations. It has been reported that compared to Class II amalgams, Class II composites leak significantly more at the gingival margins.[17]

The reasons attributed to this are

Polymerization shrinkage of composites.

Difficulty in achieving intimate adaptation of the composite to the gingival margin resulting in voids.

Greater distance of the light guide from the gingival margin.[18]

To enhance gingival adaptation of posterior composites, the use of light tips was recommended. These are special plastic tips that fit over most light wands. They help to focus the light closer to the gingival margin thereby improving the curing and adaptation of the composite material [Figure 2c].

Researchers have shown that for direct composites, use of light wands fitted with light tips significantly lowers the gingival margin leakage.[19] But, these tips may be too large for conservative preparations. Also, the contact is not formed at the right location. Another practical problem was that the tips are prone to breakage.[1316]

In spite of all these strategies, it was not possible to consistently achieve predictable contacts with posterior composites. This is because amalgam and composites are totally different materials. Amalgam is plastic and condensable while composites are viscoelastic and not amenable to condensation. They also undergo polymerization shrinkage upon curing. The cross-linking of resin monomers into polymers is associated with unconstrained volume shrinkage of 2%--5%.[20] This will create shrinkage at the contact area, decreasing the adaptation and contact pressure to the adjacent tooth.[21] Thus, while a simple Tofflemire matrix and wooden wedge are enough for creating good contacts with amalgam, the same does not work for composites.

From the above discussion, it is clear that for achieving anatomically correct contacts with posterior composites, it is necessary to provide sufficient separation between the contacting teeth to compensate for both the matrix band thickness as well as the polymerization shrinkage of the composite resin.[13]

The first real solution to posterior composite contacts came with the introduction of “sectional matrices and contact rings.” Contact rings are based on the principle of the McKean orthodontic separator ring developed 50 years ago. The first contoured sectional matrix was introduced by Meyer in 1985.[13]

Basic principle of contact rings

These rings work by providing slight separation of the contacting teeth. When the ring is expanded and its tines are placed over the contact area between teeth, its spring action applies equal and opposite forces against the teeth thus providing optimum separation. This is what is required to achieve tight contacts with posterior composites. The teeth have to be separated slightly following which the composite must be incrementally built and cured in a passive manner. Finally, the ring is removed and the teeth are brought back into contact. Then the role of the wedge is to only provide optimum gingival adaptation of the matrix band.[1322] Presently, there are several ring systems with varying designs. According to their evolution, they can be categorized as

First generation systems and

Second-generation systems.

First-generation contact ring systems were introduced in the late 1990s and include the Palodent Bitine (Dentsply) [Figure 3a], Contact matrix (Danville Materials) and the Composi-Tight (Garrison Dental) [Figure 3b].

Figure 3

(a) Palodent BiTine rings. (b) Composi-tight rings. (c) Precontoured sectional matrix bands

Palodent BiTine I and BiTine II

This was the first system that was available. The rings have rectangular tines which are parallel. They provide optimum separation (0.55 kg/mm). They lack retentive design because of the parallel tines but are easy to place on wide preparations. BiTine II is an elongated ring to allow stacking over the main ring in case of MOD preparations.

Contact matrix

These rings have rectangular tines which are converging and hence are more retentive. They provide optimum separation (0.38 kg/mm). In this system, a reverse ring is available for MOD preparations.

Composi-Tight matrix

In this system, two separate rings are available for premolar and molar teeth. The rings have converging tines with retentive balls at the end for firmer grip on the teeth. They are omnidirectional. The main problem with this system is that the contacts produced are not so tight (0.27 kg/mm). Also, the large diameter of the rings can lead to their collapse if used in wide cavities.[13]

Precontoured sectional matrix bands

All these systems rely on precontoured sectional dead soft metal matrices that are available in various shapes, thicknesses and sizes depending on the manufacturer.

Overall benefits with the sectional matrices and contact rings[1322–25]

Ease of use and good visibility

Anatomic contour of the bands ensures optimal contact areas and embrasures

Smaller tension on the teeth and greater comfort for the patient

No need for prewedging

Contact dimensions are adequate and in the correct anatomic location

Gingival adaptation of the restoration is good.

Problems with early contact rings

The first generation contact rings were promising but they had their own share of problems as well.[13] Significant among these were

Ring collapse or displacement in case of wide proximal boxes.

Ring stacking that is, placing one ring over the other in case of MOD restoration is a problem.

Most importantly, since the contact rings are made of stainless steel, repeated usage and sterilization effects make them lose their springiness over time.

To address these deficiencies, second-generation rings have been recently introduced.[16] For example, Composi-Tight 3D soft face ring system (Garrison Dental Solutions) and V3 ring system (Triodent). In the present stage of development, they appear to solve the shortcomings of the earlier rings, but hard clinical evidence is lacking.

Composi-Tight 3D soft face ring (Garrison dental solutions)

This has two styles of rings to create the required tooth separation and band adaptation for a tight, natural contact. An assortment of precontoured sectional bands and different sizes of wedges are also available [Figure 4a–b].

Figure 4

(a) Composi-Tight 3D rings. (b) Precontoured bands

The 3D soft face ring is useful in most circumstances. The tines of the ring are covered with silicone to provide good support and contour for the band in wide proximal preparations. The soft face is shaped to mimic the interproximal space between teeth, thus it adapts the band precisely to the tooth contour, eliminating flash [Figure 5]. The slotted bottom fits directly over the wedge.

Figure 5

The 3D soft face ring showing precise band adaptation to tooth contour

V3 Rings (Triodent)

This is the most advanced ring system currently available. It was developed by Dr. Simon McDonald in 2008 [Figure 6a and b]. This system has two types of rings for bicuspid and molar teeth, a selection of precontoured matrix bands and a special wedge called the “wave wedge” to provide optimum gingival adaptation of the matrix band.[26]

Figure 6

(a) V3 ring system. (b) Adaptation of V3 ring on model

It has two major innovations

The ring is fully made of Nickel-Titanium which imparts more springiness and longevity than stainless steel.

V-shaped plastic tines to accommodate the wedge. The tines have also extra width that enables the ring to contact more tooth structure buccally and lingually providing good contour for the restoration.

CONCLUSIONS

From being the material of choice for anterior esthetic restorations, composites are now widely accepted as universal restorative materials for both anterior and posterior situations. Developments in composite technology and clinical techniques have facilitated this. While most difficulties encountered with posterior composite restorations have been solved, achieving tight, anatomically correct interproximal contact has been elusive. Understanding the key aspects for proximal integrity is critical to achieve ideal contacts and contours with Class II composite restorations. At present, most criteria for achieving ideal contacts and contours are well met by the use of pre-contoured sectional matrices and contact rings.