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.