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Inlay Adhesive Bridges



Overview:


One of the techniques taught in my study groups is an anterior inlay adhesive bridge. While resembling the "Maryland" retainer design, viz., a thin extracoronal flange with accessory external retention and resistance features, this design is utterly different.

The flange component is retained, but an intracoronal inlay is used to index the retainer to the tooth definitively, to confer anti-rotation features, and secure resistance to displacement in the incisal or gingival direction. This has proven a breakthrough in reliability. Over a period of ten years, over 400 retainers have been placed, primarily in un-ideal situations.Following an initial prototype phase of development of the design, every unit placed is still in function after 12 years.

Cosmetics
Cosmetics are better than conventional Maryland bridges: there is no darkening of the abutment,provided the correct opaque cement is used. As well,there is no facial show of metal or greying at the line angles.

All the multi-tooth splints made with this method in my practice over the last 12 years are still functioning.I am speaking of 500 successful abutments. There has been no clinical maintenance required on any of these placements. This is not a sketchy or provisional prosthesis. This is reliability as good or better than implants.

In the prototype stage of the first 20 placements, there were 7 failures: 2 debonds, 2 carious failures, and three teeth lost to terminal periodontal collapse.

How much better is this than conventional Maryland Bridges?
To those familiar with the clinical practice and literature of conventional Maryland bridges, these survival rates utterly defy comparison. Typically, according to an international survey of over 7,000 cases of Maryland Bridges,(Wyatt et al) a 15% annual de-bond rate is normal in conventional Maryland splint method.

A typical periodontal splint
A typical periodontal splint is seen in the following three pictures. This patient presented with mobility, diastemas due to flaring of the lower incisors, and a crown/root ratio of 3:1. Her chief complaint was that the teeth felt loose and painful and she could no longer eat apples. This splint has been unchanging and successful and comfortable for the last 12 years. The main clinical obstacle was that diastemas existed between the teeth. The metal framework would show through to the facial as unsightly black interproximals if something was not done. The clinical solution was to opaque the metal framework after cementation as follows: the metal framework and the adjacent proximal tooth surfaces were sandblasted with 37 grit aluminum oxide for ten seconds. The teeth were acid etched with 37% phosphoric acid, and a bonding agent was placed and cured. (Photobond, a MDP-based adhesive, Kuraray Dental Corp). The metal was opaqued (Kerr Kolor A3 opaque) and the diastemas filled with an opaque flowable (Starfill 2B, Danville Dental).
The result has been cosmetically stable for the past 12 years.

As can be seen by the photos, clearly, her plaque scores remain high. However, the periodontal collapse cycle has been interrupted. The forward feedback loop in the syndrome of mobility/widened PDM/osteoclasia has been broken by stabilization, osteoclasia has ceased or at least greatly attenuates.Bone level on radiographs has stabilized in this patient's case.

This is the typical result seen when periodontally splinting with this method. In some cases, there continues to be a decline, but always at a much slower rate, particularly if the etiological factor has been smoking and the patient has successfully quit.

Is mobility a contraindication?
In conventional Maryland method, mobility of the abutments contraindicates placement. In my method, quite to the contrary, periodontal mobility is an indication for placement. This opens a whole new stream of treatment and practice income. It is hard to qualitatively appreciate the satisfaction for patients otherwise facing options of removal of the lower 6 anterior teeth and replacement with two implants and a fixed bridge,at a cost of half a new car. Or else a Kennedy Class IV RPD with attendant discomfort, aesthetic compromise, and anterior-posterior rocking and instability.

Why would this not be a preferred option? At much the same cost as RPLD,and usually, as an insured service,this is superior treatment. Emotionally, compared to the invasiveness and cost ( 600% higher) of implants and traumatic loss of one's identity, it is a much more agreeable choice for the patient.Also, the range of treatment relative to implants is greater, in that bone quality and quantity do not always allow implant treatment to proceed.







Variations based on this method
Using this retainer design, many variations have been explored: as an alternative to lab-fabricated porcealin pontics, composite resin pontics can be fabricated chairside.Long spans that include the bicuspids when the path of insertion prmits, of up to 10-units. Metal-to-metal joints over pre-existing and periodontally-failing ceramco crowns. Single tooth cantilever pontics. Porcelain pontics placed into grafted immediate extraction sockets. Precision partial denture attachments such as ERA or Preci-Vertix?, fixed to a multiple tooth splint or single tooth retainers to optimize partial denture fabrication.

Treatment for apnea patients
This device has also helped to stabilize mobile lower anterior segments loosened by MADs (sleep apnea Mandibular Advancement Devices), a newly recognized and prevalent sequel to this treatment, which the literature is recording as collateral to as high as 10% of all mandibular advancement apnea treatment.

Laboratory aspects
Splints are fabricated on a refractory model, primarily in non-precious cast-chrome alloy. After casting,these are not electrolytic-etched but rather sandblasted chairside immediately prior to placement. A typical laboratory fee of $200to $300 (2017 lab fees) is commensurate with the lack of difficulty or complexity in fabrication; a partial denture framework is far more complex for the lab to make.

Publications about this method
In terms of clinical ease, a simple protocol has been developed and is described in the CARDP Journal. "A New Prosthetic Retainer for Splinting and Tooth Replacement", Journal of the Canadian Academy of Restorative Dentistry and Prosthodontics, Spring 2012, Vol 5-1, pgs. 24-38. http://cardp.ca/wp-content/blogs.dir/1/files/CARDP_V5N1-Spring12.pdfexternalexternal link link

This article covers the Inlay Maryland concept and technique and various applications for its use, and details a highly cosmetic case replacing a lateral incisor, cantilevering from a cuspid.Preparation,instrumentation, temporization,and cementation are described.

Advantages compared to resin/fiber splints in failing mouths
Compared to direct splinting with wire or fibers, this is a more effective restoration. It is less bulky, has higher strength by several orders of magnitude, and it provides continuity for anterior sextants as a whole even when the root of a vulnerable tooth is lost to endodontic or periodontal disease.The diseased root is amputated in situ and the visible crown retained on the splint, as a "natural tooth pontic". The amputated gingival surface is obviously a cosmetic defect for the patient, so two or three weeks later, or whenever the soft tissue has healed after extraction, the tooth is lengthened to a normal gingival extent as an ovate pontic using cosmetically appropriate flowable composite resin. The protocol involves tapering the enamel, sandblasting, acid etch,adhesive, and flowable resin. The viscosity of the flowable is chosen to naturally form into a teardrop below the amputated tooth. Of course it is shaded correctly and an appropriate opacity is chosen as well. The tooth does not have to reach the gingival tissue; in fact, it is preferable from the hygiene standpoint if it doesn't. The important factor is to close the perception of a black space. This often may require lengthening the proximal contact with the adjacent teeth. The protocol for this is to sandblast, bond and place flowable.

Single-tooth cantilever treatment
In the above picture, tooth #12 is a porcelain pontic, cantilevered from #13. The retainer design is a shallow, guitar-shaped inlay, surrounded by a Maryland-type flange. The inlay portion delivers retention and accuracy in seating without facial show of metal to darken the abutment and spoil the case. The path of insertion is slightly inciso-lingual rather than lingual.



To complement the resistance form of the inlay, the flange delivers huge bonding area; the luting sequence, Panavia F2.0 Opaque, acid-etched, delivers over 25MPA with a degradation cycle measured in decades. Enamel provides the most adhesive and most durable bonding substrate we have in dentistry, does it not?

To provide a parallel context, we have the same bonding area and substrate as porcelain laminate veneers, supplemented with a highly retentive inlay, all in a metal without the fragility of porcelain. The flange adhesion is complemented by the inlay, which mechanically keys the restoration to place regardless of tooth mobility, and provides resistance form against gingival or incisal displacement. As well, the inlay accepts any twisting forces that one might expect in use, and spares the flange from a gradual accumulative fatigue that one would expect form mobile teeth. Should work, shouldn't it?

Luting Agents
What luting protocol is used? The specific luting agent used in this method is Panavia F2.0, Opaque.Do not use the tooth-colored or transparent formulation. A dentin bonding protocol is followed which bypasses the proprietary Panavia S/E DBA which unfortunately only deliver under 10 MPa. (See Reality Research for their bench assessments of adhesive outcomes between S/E and total etch protocols.)

The dentin is instead bonded as follows: after a 15-second etch with liquid 37% phosphoric acid, it is rinsed with distilled water, and lightly air dried until all standing water is gone. Then it is primed with Microprime B,(Danville Dental), air dried thoroughly and bonded with Kuraray Photobond, a thin-film Generation V dual-cure bonding agent, which is also air-dried thoroughly. It can be light-cured or not as desired, as it is DC.
The literature reports about 20MPa for Photobond's dentin bonding.

Why does this make sense? Photobond is Panavia without filler. The adhsive monomer is MDP, by now proven to be one of the best if not the best monomer. In this writer;s experience,this has proven to be durable,versatile, stain-free,and without sensitivity as a bonding method. It also has succeeded in the hands of many study club members.

An important feature is the effect of primers-either benzethonium or gluteraldhedye primers in resisting degradation of the hybridized layer by MMPs. (Metallic Proteases).



Esthetics
The esthetics of the cantilever pontic in this case is enhanced by relieving the tissue surface of the stone model 2mm in the laboratory phase, and fabricating the pontic tissue surface to a bullet-form or fully ovate pontic surface. Bone sounding at the preparation appointment revealed that the bone depth below the tissue surface would require relief at insertion, so some bone was removed to ensure adequate "biological width", meaning adequate width for healthy bone and soft tissue under the pontic.



Surgical Placement of pontics
At try-in, a small H-shaped incision is made in tissue to the depth of bone, respecting and leaving undistrubed at least 1mm of the papilla as a collar remaining around the teeth. The flap is raised where the pontic inserts subgingivally. Sufficient bone is removed using an irrigated dentate oral surgery bur (e.g.OSFG 1558) to allow seating of the inlay.Once seating is confirmed, more bone is taken if needed to create "biological clearance" from bone and to allow the normal tissue apparatus of connective tissue and epithelium to reform in the healing stages.

Optimizing enamel bonding
Obviously the next step is to regain isolation so that impeccable bonding can be achieved. The first step is to place retraction cord in the sulci of the abutment and adjacent teeth. The cord chosen should contain epinephrine. Two products that have been successful are Gingibraid 0e, which contains 8% and aluminum potassium sulphate 7%, and Pascal Siltrax EPI #8 or #9. which contain epinephrine alone.

Enamel sandblasting
The lingual surface of the abutment should have been sandblasted for 10 seconds with 37 grit aluminum Oxide with an intraoral sandblaster such as the Danville Microetcher prior to the surgery.This removes the etch-resistant hyperfluoridated outer 10 microns of amorphous remineralized enamel and exposes the structurally cohesive underlying enamel rod ends for optimum and reliable adhesion. This step must not be overlooked , as enamel bonding is not optimized without it. I feel certain that it accounts for my very high success rate. A tidy and rapid method is to place a dental dam with a single hole over the abutment This contains the dust and makes it more comfortable for the patient.

Etching in a surgically contaminated field
Clotting takes about 7 minutes to develop following the flap and surgical phase. Essentially a platelet plug is forming. The abutment(s) should be isolated under rubber dam and etched with 37% liquid phosphoric acid. In the final seconds of the 15 second etch, the etchant is titrated with Hemodent (Pulpdent) (buffered aluminum chloride) or a unbuffered saturated solution of aluminum chloride, prepared by a local pharmacy at lower cost. The site is then rinsed gently with distilled water delivered with a Monoject 412 15cc plastic syringe. Do not use a triple syringe as not only is the water stream contaminated with waterline disinfectants, but it is difficult to deliver an irrigating stream that is gentle enough to not disturb the platelet plug.

Remove the rubber dam The buccal flap is approximated over the facial surface of the pontic, without suturing, healing by secondary intention and thus allowing an increased bulk of keratinized gingiva to cover the pontic, i.e., acting as a soft tissue augmentation procedure.

The final result

The pontic appears to emerge from beneath the tissue, The papillae are full and correct height, although on close examination one can see that the papilla lack facial bulk.


Comparison to an implant; cost,hygiene, difficulty of execution
This simple but essentially sophisticated restoration provides the patient with a flossable, attractive and conservative tooth replacement at about 10 to 15% of the cost of implant therapy. The pontic is flossed in much the same way as an implant, by forming a crossed loop around it like a tourniquet and sliding it subgingivally down the neck of the pontic.

It would have been difficult to achieve an equivalent result aesthetically in this case with implant therapy, given the proximity of the adjacent roots, rotation of the clinical crown, thin tissues, and deficient volume of the labial ridge. In other lateral incisor replacement cases, where root convergence has not been eliminated by orthodontic treatment,this restoration can treat the edentulous area without compromise or risk.

What's not to like? Exposure of dentin?

Clinicians familiar with the unreliability of the conventional Maryland Bridge might, at first glance, reject the penetration into dentin of this method. Maryland retainers, at a 15% annual debond rate should not be allowed to penetrate into dentin due to the risk of secondary caries. In other words, when your Maryland bridge is going to debond, and you expect that from the outset, it is better that it be placed solely in enamel, which won't decay as readily as dentin.

However, with the Inlay/Flange method, which has virtually no failure rate, the penetration into dentin with this retainer is quite a different proposition. If your retainer is not going to fall off, then what is the problem with dentin penetration? If you don't agree, ask yourself, do we not accept full crown reduction into dentin? Is this not standard practice 24/7 around the globe? If we can strip crowns wholesale of dentin, what's wrong with a little inlay? There is a significant record with full coverage crowns un-luting, my friend,lest we live in illusions.

Periodontal and Endodontic Morbidity?
Periodontally, this supra-gingival retainer design is innocuous.
Endododntic morbidity is absent, unless the preparation is clumsy and incautiously deep.

Course of Healing
The 3 pictures below shows the appearance at one month,at three months and at five years. At one month, healing is not yet complete, as seen from the residual inflammation surrounding the pontic emergence. At 3 months, when granulation tissue has been replaced with keratinized tissue, the problem has corrected itself. Long-term stability is seen in the 5 year photo.

Esthetic Evaluation
Note that in this case the aesthetics of the smile was balanced by mimicking the rotation and coronal inclination of contra-lateral lateral incosor. This enabled the pontic to be its appropriate mesio-distal width, so that the patient's smile has credible left/right symmetry. Initially the lab fabricated a conventional pontic,of too narrow a facial dimension, despite instructions to make the pontic in labioversion. The faulty pontic was corrected by a mock-up in flowable resin an sent back for revision. This provided a blueprint to the lab for an improved final.The shading of the cervical is not quite correct but the patient was satisfied and a low lip line hides this imperfection.

The interplay of tissue emergence, inconspicuous retainer design, opaque cementation,and attention to tooth form create an unobtrusive result in this high cosmetics case. It is top value for the patient,taking less than 1.5 hours of chair time between the two appointments.The lab fee was slightly more than a single PFM crown. Consider how that compares to a single tooth implant with grafting and soft tissue management in cost, value, comfort, and expediency.

Temporization
The dentin in the inlay was treated with Microprime B and a soft resin inlay (Ez-Temp Onlay, Cosmedent)was placed between appointnemts, taking minimum chair time. No temporary was fabricated for the flange.

Three Week Appearance


Three month Appearance

Five Year Appearance