Inlay Adhesive Bridges


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 are better than conventional Maryland bridges: there is no darkening of the abutment,when an opaque cement is used, and 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. There has been no clinical maintenance required on any of these placements.

In the prototype stage, only 7 failures occurred: 2 were debonds, 2 were carious failures, and three teeth were lost to terminal periodontal collapse.

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. So one can proceed with confidence if one is willing to learn how to do them, and to maintain the necessary discipline in design and placement.

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 ration of 3 to 1.Her main 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 12 years. Her presenting diastemas were filled with composite resin at the time of placement. Clearly, her plaque scores remain high but when the syndrome of mobility/widened PDM/osteoclasia is broken by stabilization, osteoclasia ceases or at least greatly attenuates.Bone level on radiographs has scarcely declined in this patient's case.

Is mobility a contraindication?
In conventional Maryland method, mobility of the abutments contraindicates placement. In this method, quite to the contrary, periodontal mobility is an indication for placement. This opens a whole new stream of treatment and practice income, and satisfaction and rescue for patients facing conventional 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 and instability.

At much the same cost as the latter,and usually, as an insured service,this is an equally effective treatment to implants that does not entail the emotionally traumatic loss of the teeth.

Variations based on this method
Using this retainer design, many variations have been explored: pontics fabricated in porcelain by laboratory; composite resin pontics fabricated chairside; long spans, from 3-unit to 10-units; metal-to-metal joints over pre-existing and periodontally-failing ceramco crowns; single tooth cantilever pontics; 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 sequelae, collateral to an estimated 10% of all mandibular advancement apnea treatment.

Laboratory aspects
Splints are fabricated on a refractory model, primarily in in non-precious cast-chrome alloy; these are not electrolytic-etched but rather sandblasted chairside immediately prior to placement. A typical laboratory fee of $200 (2016 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" When the soft tissue line heals after extraction, the pontic underside is restored as an ovate pontic chairside using flowable composite resin.

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 abundant area for high-performance adhesive retention, using a luting sequence that delivers over 25MPA with a very long degradation cycle measured in decades. Enamel provides the most adhesive and most durable bonding substrate we have in dentistry.

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. Should work, shouldn't it?

Luting Agents
What luting agent is used? The specific luting agent used in this method is Panavia F2.0, Opaque. A dentin bonding protocol is followed which bypasses the proprietary Panavia S/E DBA which unfortunately only deliver under 10 MPa. (See lab tests performed by Reality Research)

The dentin is instead bonded witht he following sequence: 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 and bonded with Kuraray Photobond, a thin-film Generation V dueal-cure bonding agent.
The literature reports about 20MPa for this protocol. This has proven to be durable,versatile, stain-free,and without sensitivity as a bonding method. Photobond, being Panavia without fillers, and based on the the monomer MDP, has proven very durable clinically in this writer's practice and in the hands of many study club members. An important feature is the effect of benzethonium primers in resisting degradation of the hybridized layer by MMPs. (Metallic Proteases).

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 insertion, a small H-shaped incision is made in tissue to the depth of bone, leaving at least 1mm of the gingival collar remaining oround the abutment and the adjacent tooth. The flap is raised where the pontic inserts subgingivally. Sufficient bone is removed using an irrigated dentate oral surgery bur (FG 1158),initially to allow seating of the inlay.Once seating is confirmed, more bone is taken if needed to create this "biological clearance" from bone. Retraction cord containing epinephrine 8% and aluminum potassium sulpate 7%, Gingibraid 0e,of 1e. is placed.

Once field isolation is recovered,following the formation of a platelet plug, which takes about 6 or 7 minutes, the retainer is cemented. 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.

Compared to an implant; cost,hygiene, difficulty
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 labial ridge volume. 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. At a 15% annual failure rate,with conventional Maryland retainers, this penetration into dentin can lead to unacceptable clinical morbidity in terms of secondary caries. In other words, when your Maryland bridge is going to fall off,and you know it at the outset, it is better that it be placed solely in enamel.

However, with this retainer design, with virtually no 12-year failure rate, the penetration into dentin with this retainer is quite different, and acceptable, in this clinician's eyes. If the retainer is not going to fall off, the what is the problem with dentin penetration? If you don't agree, ask yourself, do we not accept full crown reduction which removes enamel wholesale into dentin every day, around the globe? There is a significant un-luting record with full coverage crowns, lest we forget.
Periodontally, this supra-gingival retainer design is innocuous.As well, endododntic co-morbidity is absent, unles 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, which gave the necessary 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.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.

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 fa=bricated for the flange.

Three Week Appearance

Three month Appearance

Five Year Appearance