Workshops of The Conference

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Intra-Radicular Rehabilitation

The increasing predictability of endodontic treatment has made these procedures far more popular with both patients and professionals in recent decades. In particular, patient acceptance has increased as the discomfort associated with endodontic procedures has decreased; thus patients are encouraged to treat and maintain their teeth rather than having them extracted. The dental profession's very successful, long-term public education campaign focused on keeping the dentition for a lifetime has significantly affected patient attitudes.

After endodontic treatment is successfully completed, the dentist faces the task of restoring the remaining radicular structure to full form and function. In most cases, the remaining root structure is relatively intact, and the post-endodontic treatment (post-and-core followed by a full crown) is routine. A number of established techniques and materials are available for restoring the endodontically treated tooth. Typically, if the post-and-core is to succeed, the dentinal structure must be sufficiently strong to support the post/core/crown complex.

Post-endodontic restorative challenges

Not all clinical situations are ideal, however. When the remaining post-endodontic tooth structure is a flared, open, or very wide canal, the restoration to function and esthetics often requires intra-radicular rehabilitation of the tooth. These situations, some within the dentist's control and some without, present the practitioner with specific technical challenges in the clinical restoration of endodontically treated teeth. Non-ideal restorative situations may be due to a number of causes:

Young children have large canals which tend to shrink with age. When a child fractures an anterior tooth at an early age, the endodontically treated canal is typically a very large space with relatively thin dentinal walls surrounding it.

In some teeth, large canals persist to adulthood. After endodontic treatment, they present similar problems to the restoring dentist. (In both cases, the size and shape of the canal are totally outside of the dentist's control. They are simply conditions which must be treated.)

Extensive decay may have destroyed a large part of the coronal (and possibly the radicular) structure prior to endodontic treatment. In these cases, it is likely that the very little remaining dentin is a thin circumference of tooth structure surrounding the endodontic filling.

Where the operator is not conservative of tooth structure, over-instrumentation or aggressive filing can inadvertently result in a very flared canal quite similar to a young canal or one with extensive decay.

All of the above post-endodontic clinical conditions present restorative management problems.

Intra-radicular rehabilitation (IRR), prior to post insertion and cementation increases the likelihood of restorative success.

Treatment planning

The first decision is to evaluate whether the remaining dentinal structure is in fact strong enough to support the post/core/crown complex for masticatory and esthetic function.

Contraindications to intra-radicular rehabilitation include

There is inadequate remaining dentinal structure.
The remaining tooth structure is compromised.
The remaining root structure is located too far subgingivally to be practically restored.
The remaining root structure cannot be adequately isolated for effective moisture control.
In these situations, implant therapy should be considered, preferably prior to endodontics

Cementation

It is important to recognize that an ill-fitting post, whether due to the canal's shape or its condition, is less likely to be successful in retaining the prosthetic restoration. It may, in fact, fracture the remaining tooth structure when subjected to functional loads and parafunctional forces.

The post cement has often been used as a displacement material to substitute for a good fit to the remaining tooth structure. This practice is particularly prevalent with pre-fabricated posts that approximate the actual canal shape. Pre-fabricated post systems function best in situations where significant root structure, suitable for luting, remains.

Non-adhesive cements, however, are intended as luting materials, not to be used in great thickness or bulk. Non-resin cements do not contribute to the strength or the integrity of the tooth/post/core/crown monobloc complex, and as such, increasing the cement thickness may proportionally limit the longevity of the restoration.

The compromised root structure can be reinforced with intra-radicular rehabilitation, a technique that has been developed along with adhesive and composite dentistry. Utilizing the more recent advances in dentinal and enamel adhesion, it is possible to reline the internal anatomy of the remaining post-endodontic root structure in order to develop an ideal post space

Intra-radicular rehabilitation provides greatly improved post retention and pre-dictability in cases where the restorative prognosis would otherwise be very limited.

The rationale for intra-radicular rehabilitation

It has been generally accepted that posts in endodontically treated teeth do not actually strengthen the remaining radicular structure. In fact, the data indicates that placing a post actually weakens the remaining tooth structure. It is important to realize, however, that none of these studies reported on adhesive and composite techniques; they all involved traditional cast or pre-fabricated posts cemented with zinc phosphate.

More recent studies have clearly shown that fiber posts bonded with composite resin cores are less likely to cause root fractures than stainless steel posts. This indicates that the bonded post-and-core monobloc contributes to the continuing strength and integrity of the remaining tooth structure.

Practitioners agree that the ideal post should provide retention for the core and protection for the remaining radicular struture, without transmitting severe masticatory or parafunctional stresses. Current research indicates that the best design is a passive, parallel-sided post that is intimately adapted into a custom-prepared channel of sufficient length relative to the crestal height of the supporting bone. Where the prepared channel is wide and cannot be composed of natural tooth material, adhesive composite rehabilitation can serve to provide similar function and stability.

Adhesive resin can replace (non-adhesive) luting cement in post cementation; resin adhesively restores lost tooth structure. Resin cement eliminates the flaring internal anatomy of the wide canal, optimizing the post channel preparation procedure. Cementation of pre-fabricated posts with composite resin has been described. However, using the composite strictly as a cement does not capitalize on the full restorative capacities of the various resins that are available. Stronger, more highly-filled composite resin restorative materials can be utilized to increase the diametric dimension of the remaining radicular structure, increasing the thick ness of the root walls, while simultaneously developing an ideally-shaped and sized post space.

The bonding, tensile, and shear strengths of composite resin to dentin and enamel are well-established, and indicate the potential of its clinical performance in the root/ post/core/crown complex.

The basic principle for intra-radicular rehabilitation is that the polymerization contraction of composite resin is less strong than the currently available bonding strengths of adhesives to dentin and enamel. This property causes the composite resin inside the canal, as it is curing, to shrink towards the bonded radicular walls and slightly away from the light transmitting post (LTP) that guides the light down the length of the canal.

Once the curing process is completed, the composite is securely bonded to the surrounding dentinal walls while the non-adhesive LTP is somewhat loose in the central space created by the polymerization contraction of the composite. The LTP can be gently disengaged from the surrounding composite, and eased out of the tooth. This leaves an intentionally formed space that accommodates the bondable post perfectly.

Needless to say, the light transmitting post must be made of a material that is non-bondable to BIS GMA or polyurethane dental adhesive and restorative materials. If the LTP were to adhere to the rehabilitating resin, the forces of polymerization contraction over the post/cement/radicular dentin complex would concentrate on the weakest component. In many cases, these forces would be strong enough to fracture the remaining radicular dentin.

Materials

The Luminex Light Transmitting Post Kit consists of three components: a reamer, a light transmitting post (LTP), and a bondable post
All the instruments are size-mated
• The reamer creates a space that is just somewhat larger than the light transmitting post.
• The LTP, in turn, is just fractionally larger in diameter than the bonded post.
Thus, each succeeding component fits into the space created by the previous one. The sizes are noted on the instruments by a series of parallel rings.
The post bonds adhesively to composites; the single-use LTP does NOT.

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

Composites Are Being Warmed Up

As the dental profession has turned increasingly to composite restorations, there has been a demand for improved clinical properties. A significant part of recent dental research has been focused specifically on eliminating practitioner concerns in the areas of material quality, ease-of-use, and finishing. The goal of both dentists and manufacturers is a restorative material that is relatively easy to place (not technique sensitive), convenient to polymerize (rapid and effective), long lasting and aesthetic

The major objectives in composite restoration include

Reduction of required light curing or polymerization time - many practitioners rush this step

Increased depth of cure - not every layer of composite is the suggested 2mm or less

Enhanced conversion (polymerization) ratio

These past three decades, research has focused on parameters such as various light sources, curing light intensity, curing time, clinical positioning, and the effect of moisture in the restorative field. Evaluating direct composite placement under varying thermal conditions has not been a common direction for research. This is rather surprising, considering that the physical property advantages of heat-curing composites in the manufacture of extra-orally fabricated inlays and onlays have been long been established

Instructions typically call on dentists to store their composites in a refrigerator until immediately prior to use. This is to ostensibly increase the materials' shelf-life and clinical properties. According to the latest research, this is probably the worst possible course of action

In fact, the warming of composites to body temperature or somewhat higher immediately prior to placement, has been shown to improve composite properties and to reduce curing times significantly. While any practical means may be used to heat the composite syringe or compule to the desired temperature, the Calset Composite Heater (shown in the picture) has been specifically designed to warm the materials to one of two scientifically predetermined levels. In evaluating the bottom hardness of composites that were cured with different light sources, varying only the composite's Temperature at the Moment of Polymerization (TMP), Bortolotto and Krejci1 found that the insertion temperature had a significant influence on the hardness of a composite. The restorations that were inserted pre-warmed to 40°C (only 3°C warmer than body temperature and therefore quite comfortable even for unanaesthetized teeth) were significantly harder (Vickers scale) than the composite restorations that were inserted at room temperature (22°C). The hardness values at 40°C were approximately double those where the composite was inserted at 5°C -the approximate temperature of a commercial refrigerator

Another very significant finding was that the curing time for a layer of composite at room temperature could be halved when it was warmed to 40°C, without affecting its hardness properties
Clinical significance: pre-warming restorative composite to slightly above body temperature improves the depth of cure AND reduces curing time by 50%

Stansbury's study of composite conversion values under various thermal conditions provides even more dramatic results. A higher conversion ratio (double bond formation = polymerization) at a greater depth increases the material modulus resulting in less flexure, and less potential for restoration fracture under loading Three esthetic restorative materials (microfill, hybrid, packable) were compared under three different light curing modes (LED, halogen, plasma arc) at two different temperatures (23°C and 54.5°C). An elevated composite temperature during photopolymerization offered substantially higher immediate and final conversion values in all the tested composite materials, and with all the different curing lights Elevating the composite temperature from 23°C to 54.5°C decreased the required curing time by 50-80%

Clinical significance: pre-warming restorative composite improves the conversion rate, with a concomitant improvement in the fracture resistance, of the material AND reduces curing time by 50% or more

Rueggeberg indicates that composite TMP significantly impacts polymerization time Once the restorative is warmed to body temperature, the next 20°C does not significantly reduce the curing time, however. At 58°C, there is a major upward step in the conversion ratio, remaining constant until 68°C, at which point another significant increase is noted. Ideal polymerization temperatures are found at the lower end of each thermal window: body temperature (37°), medium heat (54-58°C), and higher heat (68°C). Warmed composites exhibit no increase in polymerization when halogen curing is adjusted between 20-60 seconds

Clinical significance: ideal restorative composite pre-warming temperature points are scientifically established AND curing times For Pre-Warmed Composite Can Be Significantly Reduced

Littlejohn et al measured composite conversion at various TMP levels. a significant improvement in conversion was observed warming composite from room temperature to body temperature

Clinical significance: composite pre-warmed to at least body temperature offers a better restoration with improved physical properties, both in the short and the long term

Flowable resins help to achieve better marginal adaptation in large posterior restorations. This technique involves a clinical compromise, however. The flowable's decreased filler content provides the low viscosity; this requires a larger resin component, thereby increasing polymerization shrinkage

Visco-elastic composite resins exhibit decreased viscosity and greater flowability at higher temperatures. Rueggeburg5 demonstrated that a composite's film thickness is reduced by 30% as it is heated to 54°C. Thus, a pre-warmed micro-hybrid composite both flowable and highly filled, placed at the gingival margins of a deep restoration eliminates the technical compromise of flowable resins

Overheating the pulp is always a concern (iatrogenic damage can result). Rueggeberg measured the maximum intrapulpal temperature rise from the application of a 57.2°C composite material; the observed 1.6°C increase well within the established pulpal tolerance of more than 10°C

Clinical technique for pre-warming composite

Turn Calset unit on (press control switch once). The amber LED indicates normal function

Green LED flashes to indicate composite warming 10 minutes to reach 54°C

Green LED shines steadily to indicate pre-set temperature

Heated compule is loaded into the syringe gun and applied directly to the tooth preparation

For added convenience, the top portion of the Calset unit is removable from the heater and transportable to a remote location. The top segment acts as a heat sink that keeps the composite warm for several minutes. Neither extended warming (up to eight hours) nor repeated thermocycling of composites has any deleterious effects on the material's properties

Dental technicians have been placing and polymerizing composites under elevated thermal conditions in the fabrication of extra-oral composite restorations for many years

This technique is now available for direct intraoral composite restorations, as well

Pre-warming composites is a practical means predictably improving composite properties in dental restorations