Resin-bonded bridges in North America were developed in the 70s as the “Maryland Bridge”, and were intended to replace single missing anterior teeth. The honeymoon phase of this new method soon passed, as simple enamel bonded flanges, utilizing two anterior abutments, de-bonded with alarming frequency. Today it generally has been abandoned by the profession.
A better Maryland Retainer!!
More than 20 years ago I developed a retainer design which I call the Inlay Maryland Retainer. Since 2003 I have placed over 600 retainers with it. Retention has been 99%.
While outwardly resembling traditional Maryland Retainers, this design has a precision inlay placed mid-lingual., to marry mechanical and adhesive into a hybrid of old-school to new school dentistry.
The multiple unit splint featured in the header photo above is 15 years old. It was placed in a negligent periodontal patient. The teeth were so mobile that the patient could not eat an apple. This 6-unit splint was fabricated with non-precious alloy, cast on a refractory model. This was a very low cost framework. It took an hour to prepare and impress the teeth, and temporize. Insertion required another hour of chair time. 
Splinting the teeth was the first stage in this patients rehabilitation. Once unified in an arch, they could no longer move. Non-surgical periodontal care, SRP, curettage, and home care instruction turned the case around. Inflammation reduced, probing ceased to bleed or was no longer painful. Crevicular depths became shallower, PDL width became narrower. As evident in this slide, her hygiene was never ideal. Nonetheless the patient retained her teeth. The prosthesis defied the odds of early failure seen with outwardly identical flanges in the “Maryland Bridge” design.
The secret is six precision guitar-shaped inlays, similar to this framework below. They positively engage with tooth structure to guarantee full seating at cementation. The flange covers maximum enamel area for adhesion, but no finish lines were placed- asking the lab to cover as much enamel area as possible. The inlay provides anti-rotation features. The design mates 1990s adhesion to 1950s gold casting expertise. The best of two worlds. The slightly proud gingival margin became a second CEJ discontinuity of form and the patient quickly adapted to it.
I have placed 600 units of this design over 20 years. Maxillary cases, of course, require lingual reduction and finish lines.
There are no adhesive failures. Gross neglect can still wreak havoc, in the case of high caries patients developing caries around the abutments. But this amounted to less than 10 units in this time span.
This is a typical laboratory cast.
More historical inprovements in adhesive anterior bridges – the era of proximal grooves
in the 80s and 90s, design improvements from Dr. Yamashita in Japan were popularized by Dr. Ray Bertolotti. These were still enamel-bonded metal flanges, but with parallel proximal grooves, much like 3/4 anterior gold crown designs of the 1950s and 1960s. Retention improved. Cantilever anterior designs proved to be superior to two-abutment bridges. The luting choice was opaque Panavia, which reduced shine-through of the metal to the facial, although greying of the proximal margins in abutments and metal show were still a paramount limitation.
What we learned from the Porcelain Laminate Veneers parallel-groove Maryland Retainers
Proximal grooves illustrated an emerging axiom of the adhesive world; that mechanically sound preparations with resistance and retentive form, once combined with robust resin-enamel adhesion, were the new playing field. But, as outlined above they were cosmetically compromised.
The Inlay method brings the mechanical retention into the middle of the lingual surface. That is the thickest part of the tooth. There is no cosmetic impairment. The proximal surfaces are full thickness. When a suitably opaque luting agent is used, there is no greying, darkening, and only very slight loss of translucency. An inlay depth of 1.2 mm is all that is required to achieve very satisfactory retention, and keys the retainer into the tooth structure to resist dislodgement when the occlusion delivers twisting forces to the retainer-to- tooth interface.
During this period, Porcelain Veneers were the new kid on the block, bonding to labial enamel. When little mechanical forces developed in function, success was high. If the veneer lapped onto the facial surface, displacement forces at the incisal edges in protrusion emerged and retention dropped.
The lesson learned there was that enamel bonding of a prosthesis can be twisted off if there are no mechanical features to accept these loads and thereby protect enamel adhesion from these loads.
Ceramic adhesive anterior prosthetics in the early 2000s
In the early 20002 a German researcher, Professor Dr. Mattias Kern, pioneered the use of milled In-Ceram as the flange and pontic material. A meticulous operator, he was able to achieve highly esthetic and reliable prosthetic results despite the fracture-prone nature and lower flexural strength of this porcelain. Case selection was mandatory. HOwever, the big gain was that Interproximal greying and shine-through became history.
The next step Dr. Kern’s work
in 2010 Dr. Kern took the next step forward in materials, milled 3Y zirconium, with fused labial porcelain. With chairside air-abrasion he was able to exceed 35 mPa bond strengths to zirconium equaling that of a well-executed enamel bond. The extremely high flexural strength of correctly-selected Zirconium permits smaller connectives and hence more realistic embrasures than Inceram.
This approach is now proven. It has a limitation: only use where occlusal loads are lower and highest-quality lab work is guaranteed. It is easier today to persuade patients to accept a white material in a cosmetic setting, rather than metal A seen from the lingual, it is less intrusive than metal. But, from the above analysis it can be seen that the bonding interface is more fallible than an inlay-protected design.
Dr. Kern’s text can be found on Amazon at https://www.amazon.com/RBFDPs-Resin-Bonded-Fixed-Dental-Prostheses/dp/1786980207
As well, he presents a very organized review of his method through Dentaltown by subscription at https://www.dentaltown.com/blog/post/16372/dentaltown-learning-onlineresin-bonded-fixed-dental-prostheses-minimally-invasive-esthetic-and-reliable-by-dr-matthias-kern?st=matthias%20kern
This Handbook’s alternative-Resin bonded bridges developed by Dr. Peter Walford
What is missing in Dr. Kern’s wonderful method is the possibility of wider application. Larger span adhesive prosthodontics beckon, and more demanding occlusal function. Pure adhesion is not sufficient. These require a hybrid retainer with mechanical and adhesive features.
The periodontal Inlay-Maryland splint case in the above discussion has proven bombproof.
Conventional pushback
Some prosthodontists object to entering dentin with an adhesive design. Really. These are the same specialty that strip a whole mouth of enamel without hesitation for full crown coverage. Perhaps their reasoning is based on the historical expectation that de-bond is inevitable with adhesive flanges and hence caries may develop.
But if you know it is not going to de-bond, that fear is moot.
My experience has been, in over 600 insertions, less than 1% de-bonds over 20 years. Essentially, everything I placed is still there. if the support teeth suffered wholesale periodontal collapse, they came out as a unit.
Be objective. As a failure rate, 99% is better than implants. It is also a better than convention full coverage prosthodontics.
Application to the field of Implantology
This retainer dovetails nicely to Implant therapy. It can enable you to bypass common problems with implant placement.
Such as where bony architecture is not suitable for implants, due to alveolar concavity, risking dehiscence. Also where periodontal disease has robbed the alveolus of bone height and bone quantity, and created architecture issues.
Also, as we are learning, peri-implantitis risks subsequent implant loss due to the same microbes and host factors that generate periodontal disease.
The Inlay Maryland is far more economical, and much quicker to complete.
So, to my mind, professional resistance to this design is an attitude born out of unfamiliarity. The goal of this handbook is to familiarize the reader with the design and develop the reader’s skill in applying the method. Then you can fly with it. Airplane travel once seemed risky, even impossible, you know!
Why this retainer is a breakthrough
If you do this procedure right, it proves to be a breakthrough in versatility and reliability.
Changing the path of insertion from vertical to lingual or linguo-incisal is a game-changer. Splints of up to 10 units, including first bicuspids as well as anterior abutments have succeeded for decades. Multiple tooth prosthodontics have become possible. The facial enamel is retained, and all stages of the prosthesis from prep to insertion become faster, easier and less invasive than any other laboratory procedure. Patients prefer them over full coverage and can afford them more readily.
Splinting with dubious abutments
A whole new class of periodontal splints with or without pontics results. A photo of a six unit splint placed in 2004 is found at the header of this page. This latter method provides a transition for future loss of dubious abutments without scrapping the whole prosthesis. If a root fails periodontally, a simple root amputation can eliminate the failed and hopeless root ,but allow the clinical crown and the remaining teeth in their prosthesis carry on. Two months after amputation the clinical crown is returned to full length by adding composite to the amputated natural tooth as an apical extension, a procedure that requires no anesthetic.
For patients facing one or more dubious abutments, a splint will stabilize weak teeth. Once united into an arch form, sextants gain stability. Free of mobility, regenerative periodontal therapies improve osseus quality and soft tissue attachment. The prognosis is vastly improved. Teeth once routinely doomed to extraction can be retained for decades longer. Do you suppose patients appreciate this?
Do you suppose people in this category are just dying to have you extract their incisors and place a 6-on-2 implant prosthesis and part with $10,000. Do you think that is an viable expense for the majority of your patients.
This is a reliable opportunity for you as a practitioner to assert that you care about keeping 5th decade and older patients dentate at a fee roughly 20% of conventional options.
Advantages in lower arch reconstruction
In lower arch rehabilitation, an anterior fixed splint/bridge separates the anterior sextant from the posterior arches. This eliminates the never-satisfactory option of a Kennedy Class IV RPLD, i.e., the Teeter-Totter Partial.
Also, if the teeth are caries-free, the seldom satisfactory six-unit full-coverage lower fixed bridge is bypassed. Endodontic morbidity of heavily-reduced mandibular incisors is bypassed.
This method accomplishes the same end at less than half the fee. It is profitable for the practice because it is so easy and quick. An hour is more than enough time to prepare six inlays, capture an impression, desensitize the dentin on the abutments, and temporize the inlays with a soft LC temp material.
Finally, a lingual path of insertion permits sound engagement with crowded and malposed teeth around an arch; sufficient enamel bonding area becomes the dominant restriction, limited by having the necessary skill to find a retentive inlay variant if the lingual guitar shapes cannot be placed in all the abutments.
My handbooks describe these methods, applications with case examples, precautions, lab instructions, and suggested fees.
Digital design evolution
The evolution is not over. The next stage could be in-office zirconium milling and same-day placement. Improved esthetics in 3Y milling blocks is required and could be very attractive to mainstream dental offices provided they have capable adhesion protocols.
Handbook of Adhesive Bridges
- Adhesive Bridges- Anterior- Inlay Maryland
- Excellent applications for periodontal splinting, which is so poorly-accomplished in today’s dental office, has reached maturity. The lousy alternatives- bulky fiber-reinforced splints, or fragile and short-lived splinting with un-reinforced composite are superseded by a laboratory framework that is compact, strong, durable, retentive, and versatile. This treatment carries the patient forward with minimal tooth loss and maximum versatility when heavily diseased anterior sextants contain several teeth with uncertain periodontal prognosis.
- Adhesive Bridges- Posterior
- This section covers Posterior Adhesive Bridges (Yamashita -design Resin-Bonded Fixed Partial Dentures) and describes how to fabricate adhesion bridges, usually with less or no anesthesia, mo retraction cord nor pulpal involvement long -term.
WHY CONSIDER LEARNING THIS MODALITY?
- 99% retention over a 20 year period with over 600 retainer placements.
- Simplicity in concept and execution: a lingual inlay is mated to a flange of metal covering lingual enamel. Normal burs are used, little time is taken to prepare, impression is simple and conventional, temporization is quick and straightforward, lab prescription is simple, insertion follows conventional approaches, and there is an fee guide for dental plans. See the photos below for a typical impression of the inlay/flange abutment. In this case the lateral incisor was being lost due to external root resorption.
- Note below the attractive 18-year result of replacement of the upper right lateral incisor, mimicking the labioversion of the contralateral upper left incisor.
- No interproximal greying is seen on the right cuspid because the enamel is full-thickness in the interproximal, not thinned by a proximal groove. The abutment looks untouched.
- Application is almost without restriction: The Maryland bridge was contraindicated if teeth were mobile, were recently treated orthodontically, or were rotated and malposed. Deep overbite would also contraindicate a Maryland Bridge. These restrictions are absent in the inlay-flange design.
- The prosthesis can be extended to longer spans, to include first bicuspids in addition to 6 anterior teeth, for spans of 10 teeth, when the path of insertion and integrity of abutments allows. The only insurmountable contraindication is insufficient lingual bonding enamel area. This may be because of restorations on the abutments or because of malpositions of the teeth.
CATEGORIES OF INLAY FLANGE BRIDGES: See Categories of Inlay Flange Bridges
A BEAUTIFUL CLINICAL CASE TO ILLUSTRATE:
Look at the before and after photos of this case below replacing missing lateral incisors. The patient was referred to me for treatment by a study club member. The patient refused full coverage. Previous Maryland bridges were placed 20 years prior in another dental practice and had de-bonded and been re-luted numerous times. There was advanced caries under the de-bonded flanges.
The cuspids were destroyed: they presented with advanced lingual decay under the double-abutment bridges. No lingual enamel was present. Their use as abutments was contraindicated. The centrals were intact and had above average root volume and minimal overbite.
- If the patient wished to retain his natural facial surfaces and be treated with Inlay-Flange retainers, cantilever pontics from the central incisors would be necessary due to the destruction of the cuspids.
- The patient refused full coverage restoration
- There were size dissimilarities in the edentulous spaces visible in the post op photos
- From radiographs, implants were clearly not possible due to root convergence on the left lateral edentulous space .
- The prognosis for the patient was favorable
- shallow overbite
- large root volume of the central incisors
- no signs of periodontal disease in the mouth at age 40
- robust physique and health
- This rendered the choice of central incisors feasible where ordinarily one might shy away from the use of central incisors as abutments.
- We would follow a cantilever design to avoid the higher failure rate of 3-unit flange bridges, because the cuspid and centrals move in differing vectors, leading, according to retrospective studies, to earlier failure than single abutment cantilever pontics. This was well-established in the literature review by Wyatt et al of 7,900 conventional Maryland retainers.Resin-Bonded Fixed Partial Dentures: What’s New? JCDA December 2007, January 2008. Dr. Chris Wyatt, Chair, Prosthodontics, UBC School of Dentistry http://www.cda-adc.ca/jcda/vol-73/issue-10/933.html
- His dental plan would cover the bulk of the treatment costs, a deciding factor for a father of two children building a new house.
TREATMENT RENDERED
The decay on the cuspids was treated with composite resin. The centrals were prepared with inlays into the lingual surfaces, and an anti-rotation dimple was placed into the resin restorations on the cuspids. Convincing pontics were fabricated in low noble alloy, with an ovate undersurface. It was fabricated following the instruction to the lab to fabricate it to 1 mm below the edentuous ridge.
At the time of insertion , a mini-flap raised to allow the pontic to insert sub-tissue . A small amount of crestal bone was removed through the mini-flap to create biological width for healing, which requires differentiation to bone, connective tissue and epithelium under the pontic. The pontic thus emerged realistically from the alveolus. This approach increasing bulk of the interproximal papilla, to fill in black triangles in a way that is not possible with a ridgelap design.
Hemostasis in the insertion into a fresh surgical field was achieved using Hemostatic Etch and Retraction Cord . Cementation with the very durable Panavia F2.0 opaque cement took place under proper conditions of isolation
- The patient suffered no pain from these procedures and was very pleased with the result, despite the built-in compromise of pontic size discrepancy between 12 and 22 due to the orthodontic malposition. His pontics are flossable because floss passes under the rounded anti-rotation dimple set against the cuspids.
- He reports that his friends could not believe the teeth were not real.
- The lack of inflammation around the pontic emergence, the bulk to the pontics at the cervix, healthy response of the tissues to the adjacent porcelain, and the almost normal tissue line combine to form a convincing end result.
- Of course there is a lot of innovation to consider;
- The preparation itself, outline form, inlay form
- Capturing the prep with precision in the impression.
- Making a suitable temporary
- Ensuring the lab gives you what you asked for
- Raising a mini-flap, bone sounding, and removing subjacent bone
- Achieving hemostasis sufficient to prevent contamination of adhesive field in placement
- Ensuring that cuspid disclusion relieves the prostheses of occlusal loads that might de-bond them
- This is the meat of the Handbook, to learn how to do these steps with confidence and without errors.
- BEFORE
- AFTER
