New designs for cavity preparations in posterior composites

Twenty-five years after their inception, posterior composites remain unpredictable. In comparison to amalgam restorations, posterior composites show significantly higher failure rates, are more costly, take longer to place, have more postoperative symptoms leak, stain, chip and cause food impaction

What's wrong with posterior composites

Endodontists joke that posterior composites are the number one killer of pulps, that leaking composites are their "number one" referral source. Most studies have shown that Class I and Class II composites have a significantly higher failure rate than amalgam restorations. The AMA, ADA, FDA, US Public Health service, CDC, NIH and WHO have all declared amalgam safe. In light of this evidence and overwhelming opinion, how can we in good conscience continue to place posterior composites? So let's ask one more time, what's wrong with posterior composites Why are we content to provide a posterior composite restoration that essentially cripples the tooth in the name of esthetics, knowing that there is no proven systemic health benefit compared to amalgam

The G. V. Black Era

G. V. Black was a consummate dentist/scientist and his exquisite designs for cavity preparation were a huge step forward for dentistry. Unfortunately, we are discovering today that those cavity shapes weaken the posterior dentition and lead to fracturing in even the most conservative applications
A two-year study -planned for future publishing- utilized 16 X magnifications to evaluate each posterior tooth that was treated for replacement of an amalgam or posterior composite, Found

Sharp internal line angles are only a small part of the problem

Joining the occlusal to the interproximal is the worst possible design for crack avoidance and the most common area for crack initiation

Most fractures initiate in dentin at the line angles

Interrupted cavities were more crack resistant than connected cavity preparations

One of dentistry's myths is that amalgam expansion causes tooth fracture. Expansion failures have never been proven. The fracture problem does not originate with amalgam, per se. It originates in iatrogenic GV Black cavity preparations. And just as many of us feared, we are seeing the same pattern of fracturing in teeth with posterior composites now that enough time has elapsed to assess their longevity

The Simonson Transition

Dr. Richard Simonson is widely recognized as a pioneer in new cavity preparation shapes for minimally invasive, bonded, resin-based posterior composites. In spite of his innovations, the GV Black preparations that taught in school twenty years ago have been only slightly modified for posterior composites in the typical dental practice and in most dental schools

A flat metal matrix, traditional wedge, boxy cavity shapes, biofilm that is difficult to remove just past the margins and incremental composite loading combine to give the common result. The Clark Class II shape, aggressive "sanding" of the interproximal with a lightning strip prior to placing the matrix, an anatomic, translucent matrix that allows the composite to form an ideal feather edge, and injection molded single phase composite placement combine for a superior result

Problems associated with current posterior composite

Composite is a poor biological space filler. A biological space filler such as amalgam or gold foil does not require any adhesion to the tooth surface. Composite on the other hand must be sealed 360 degrees and from inside to out

Unlike amalgam and gold foil techniques, "packing composite into a hole" is not a predictable method. Excellent clinicians have been dealt an unfair hand when it comes to Class II composites. Most of the features of the traditional cavity preparations such as parallel walls, resistance and retention form work against posterior composites What we have observed at CRA and under the microscope is that polymerization shrinkage cannot be eliminated, only mitigated. The best margin is no margin, and when composite extends slightly past the cavo-surface margin, it is generally well sealed with no white line. When we polish back to the margin, the white line often appears. "Composite sealing" with thin resins applied after filling the cavity may reduce wear. However, trying to seal an imperfect margin after the fact is futile. As explored these white lines, they generally extend completely to the pulpal floor, far beyond the reach of a sealer.

C factor has been oversimplified and remains a significant problem.

Posterior composites should go "on" not "in" the tooth.

Minimally Traumatic dentistry should be considered as an upgrade of "Minimally Invasive" dentistry. Well meaning dentists are promoting minimally invasive dentistry The best long term outcomes are more important than the race to minimize the micrograms of tooth structure that are removed. For example, the tunnel preparation preserves the enamel of the marginal ridge but unnecessarily weakens the tooth and impedes clinical visualization. Incomplete caries removal combined with excessive tooth weakening are unacceptable casualties of the noble mission to save marginal ridge enamel.

The Fissurotomy and "Cala Lilly" Class I; The Clark Class II

The fissurotomy class I, Cala Lilly Class I and the Clark Class II are fairly radical departures from GB Black's system of preparing and restoring posterior teeth. These new cavity designs are based on adhesive composite restorative materials and engineered to resists tooth fracturing. The new primary goal of first-time interproximal caries restoration is to avoid connecting the occusal to the interproximal a concept that Simonson first advocated
The different sizes of the occlusal portion of the new Clark Class II cavity preparation are summarized as follow

Small defects; Fissurotomy shaped

Moderate lesion; Cala Lilly shape

Large sized lesion or amalgam replacement; cusp tip to cusp tip splinting Cala Lilly shape

A New Fissurotomy Technique (Occlusal Portion

This new technique has five important components

First, the concept of "sealing over" caries and grossly contaminated pits and fissures is questioned, and replaced by exacting micromechanical instrumentation

Second, the size and shape of fissure preparation burs is completely modernized with the development of the Fissurotomy Bur System (SS White, Lakewood, NJ). The #556 is unfortunately the most utilized operative bur in dentistry and is largely responsible for the current "epidemic" of cracked teeth. Today this protocol involves the use of both the Fissurotomy Original Bur as well as the narrower Fissurotomy NTF Bur. Fissurotomy Burs are scientifically developed instruments for the diagnosis and treatment of hidden caries and should be utilized to create proper preparation form and function for the placement of composite restorations. The Fissurotomy NTF Bur is ideal for ultraconservative micro preparations of pit and fissure defects. The thin carbide tip of the Fissurotomy Burs will not "strip" quickly like thin diamonds

Third, each occlusal defect is addressed separately, wherein the clinician should avoid the temptation to "connect the dots

Fourth, the restorative material of choice is a robust, filled composite such as a flowable composite and/or heated paste composite

Fifth, the use of advanced clinical magnification ranging from 3.5X to 16X is imperative

The Calla Lilly (occlusal portion): The Cala Lilly, a beautiful trumpet shaped flower Its name was used to describe the new cavity shape for medium to large sized Class I composites. Traditional parallel walled cavity preparations have not been shown to provide the adequate volume of enamel rod engagement. Compounding the problem is parallel cavity walls that do not afford proper angle of intersection of enamel rods to provide long term splinting of posterior tooth

The Clark Class II (Interproximal portion

The goal of first-time interproximal caries restoration is to avoid connecting the occlusal to the interproximal, which is a concept that Simonson first advocated. The next evolution of this design is the saucer shape with serpentine/disappearing margins The final change is discarding and replacing old filling techniques, matrixing systems and curing techniques

Can These Things Last

Early posterior composites showed unacceptable wear. Microfills like Heliomolar had excellent wear resistance but mediocre strength. Marginal ridge fracture was common Many modern composites now exhibit excellent strength and wear resistance. In several studies, composite/enamel bonding has exhibited very lengthy in vitro success that does not deteriorate over time. The key is that the initial bond must be exquisite and engage large areas of enamel, such as seen in enamel-based porcelain and composite veneers