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MODB


As clinicians, we are seeing a virtual epidemic of cusp fractures in the patient population in the fifth and older decades,subsequent to amalgam restoration. In this present economic recession, it may be difficult for patients to afford crown work as readily as in the past. Clinicians today need a method to do the MODB well.


The MODB procedure essentially represents the marriage of a Class V to a Class II. In our study club we use a device Dr. Walford has invented, the "Bandbender", see Bandbender, to improve the proximal contour of Tofflemire matrix bands as needed. With the "Bandbender" it is easy to generate a restoration with full occlusal contact, proper proximal form and contacts, lifelike gingival and occlusal embrasures, and layering in the enamel that mimics the natural tooth. The MODB in direct composite resin represents a unique opportunity for restorative conservatism. Is it not beneficial to both patient and practitioner alike to be able to place this aesthetic option at 30% of the cost of a ceramic restoration.



Incrementing the resin restoration Incremental Placement

Cost to the patient; revenue to the practice

Above we see two MODBs which were placed for a combined cost to the patient of two-thirds of a single crown. However,if one realistically subtracts the costs for lab work, impression materials, shade photos,temporization, shipping, and second appointment for cementation and cement costs, the actual net profit for the dental office can be very similar to that of conventional crowns, if the direct restoration is placed efficiently. A single crown can sum up to two hours; the comparable direct MODB is easily done in 50 minutes from seating to dismissal, with little materials cost.

One important time-saver is to limit the resin to a single shade, and to focus on correct value as the dominant criterion. Most general-purpose nanofill resins have sufficiently lifelike transparency/opacity to approximate natural teeth. The best have high polishability,and when contour and anatomy are correct the cusp tips are suitably thin and generate a degree of translucency. In direct resins, one cannot hope to approximate the entire spectrum of detailing that is available from modern ceramic labs, at least, not in a normal fee-for-service context. But a very credible and believable restoration can be achieved if one finesses these other important parameters.

In the above picture, the second bicuspid is four years old, and it was restored with a hybrid resin. The first bicuspid was restored with a newer nano-hybrid, and is only one year old. Both have full cusp structure, multiple occlusal stops, and proximal contact. They are surviving well, and,from previous clinical experience, will continue to survive well despite the lack of molar occlusion in that arch.

Lifespan and aesthetics

The clinical questions then become:
  • Can the aesthetic outcome be satisfactory?
  • Will the restorations stand up without maintenance issues such as broken marginal ridges, de-bond, chipping, marginal stain, or discoloration?


The answers to these questions depend greatly upon the resins used, and the care taken to place them. If resins match the functional load, are correct in shade, and are placed with an effective matrix, a trouble-free satisfactory clinical life can be anticipated. If the expertise taught in the study club is applied, and all technique factors optimized- best selected adhesives, curing lights, isolation, matrixing, wedges, resins, and finishing devices- success will not be denied.

And let's not live with illusions; while composite has lower parameters than cast metals, leucite-reinforced porcelain, or zirconium, these materials have a finite lifespan, and may also entrain a cascade of other interventions, such as devitalization of the pulp, periodontal inflammation or recession,and recurrent caries. As well,crowns have their own range of breakdowns over time.

  • they lose lustre...
  • develop shade mismatch as contiguous natural teeth darken over time...
  • unattractive metal margins once buried subgingivally become exposed....
  • porcelain may fracture or chip.

It is rare to see ceramic crowns over 20 years old that would not benefit from replacement.

The salient questions are:
  1. How good is good enough? If functional durability is adequate, including a safety margin for biting accidents such as olive pits or popcorn husks, then the fear of restorative material failure disappears as a clinical issue.
  2. What happens when the restoration fails? What is the exit path? If failures are gradual and do not generate catastrophic sequelae, then the approach is more benign than alternatives. Considering that the consequence of crown failure must be a new crown, then the MODB in composite is even more effective in a lifetime cost/benefit perspective.
  3. Once committed to using composite, how does one make the very best use of the materials and process and thereby gain the most from them?

Against the benchmark of a ceramic restoration, assumed to be a 20-year restoration, a ten year composite MODB looks like an acceptable clinical alternative. A lifespan of ten years, provided at a cost of 30% of an indirect procedure, makes good economic sense, especially if you are the patient! When cosmetic demands are reasonable, restoring three teeth for the price of one crown is the better deal, especially if one is in or near retirement.

The photo below shows two MODBs. They are more than a decade old. Despite being older resins, and a mid- buccal finish line, where it is most obvious, they are not a social disfigurement to the patient. What was the technique for these older restorations?

A 45-degree bevel was placed mid-facially.A small initial increment to restore the buccal bevel was made with Aria, a microfill flowable manufactured by Danville Dental, and it was cured against the matrix. This smooth finishing material effectively hides resin-to-tooth interfaces, when a bevel of 45 degrees or greater is used. Cases done with Aria used this way have proven resistant to staining and/or discoloration over a ten-year period. However, this technique has now been superceded by the Wet-Pack" margin placement method described below, which requires one less material in the armamentarium.


Wet-Pack Margins.


This method ensures a void-free, stain-resistant and invisible margin. A small amount of flowable is placed over the buccal margin,inside a Tofflemire matrix. Without curing, final paste resin is condensed into place, removing any flowable that expresses or "pools" above the paste resin with a brush, and then the increment is cured.

Which Flowable? The flowable resin can be selected from the manufacturer's integrated product line, and be same shade as the final paste resin, or it can be a general-purpose flowable that approximates the chosen shade. Shade is not as critical as one might think,because the volume of remaining flowable at the cavosurface is small. However, one achieves the best result if the shade is at least close in value. Transparency should higher rather than opaque. Bear in mind that the flowable in this case is very thin and is replacing enamel against a tapering beveled finish line, so that the transition from restorative material to tooth is gradual. For more about bevels.,See http://www.peterwalforddentistry.com/tiki/tiki-index.php?page=CompositeResin07&highlight=bevelsexternal link

The purpose of this technique is to eliminate voids at the margin. The majority of flowable is expressed past the margin; whatever remains at the cavosurface fills what would have become marginal voids otherwise. This technique, when mated to appropriately beveled margins, the result is cosmetically outstanding and durable.

The term "Wet-Pack? Margin" has been coined to describe this technique, and to distinguish it from the term "Injection Molded" for a similar technique in the Clark Bioclear Method. It should be reserved for margins that can be subsequently finished without risk of iatrogenic effects. For this reason, in opposition to some writers, this author believes it should never be used interproximally. Typical results from the wet=-pack margin method are shown in the photos below.





Summary

The key elements for success with the MODB restoration are:
  • Proper matrixing for contacts
  • Resins which match the functional loads
  • Proper buccal finish line for invisible tooth/resin transition
  • Layering methods that are simple yet swift.
  • A facial surface with highlights that blend with the surrounding arch
  • Finishing expertise that develops proper contour and preserves cusp arms,
  • Polishing and surfacing that mimic the topography of the natural teeth. In the photo below, note the proper development of the buccal cusp of the second bicuspid, including a slight hollowing of the cusp arms. As well, the highlight seen on the buccal surface approximates that of the adjacent teeth. Also, the value- the degree of lightness or darkness, is close to that of the adjacent teeth, which are bleached from dehydration under the ruber dam in this surface. As well, there is some undulation of the facial surface, rather than a machine- defined surface, such as one sees on an industrial product, like a coffee cup. These are the features that the human eye subliminally perceives when reading a smile for attractiveness. When contour,outline, surface and highlights are correct or very close to correct, then the esthetic senses are not offended. When too many of these features are wrong, the result is jarring and inharmonious, regardless of material. Over time, with practice, these results become progressively more attainable with direct resins.

,,
This writer's experience with this restoration has been extremely positive, ten years lifespan being easily achievable..

Pulpal considerations


The pulp is seldom encroached upon at the gingival margin with this restoration. Conversely, many crown procedures requires heavy buccal reduction - 1.5 to 2mm to create the room necessary for proper aesthetics in porcelain. In many maxillary teeth, especially in smaller teeth, this axial reduction places the crown into deep dentin. Deep dentin is completely different from shallow dentin:
  • It is 40% to 88% tubules
  • These tubules contain more odontoblast cell bodies than superficial dentin. Deep preparation entails histological damage.
  • Superficial dentin contains 4% to 10% tubules, making restorations in this zone relatively innocuous.

The direct MODB is commonly the result of an oblique fracture of the pulpal floor of a previous amalgam restoration to the CEJ, and is therefore intrinsically in the pulpally innocuous zone. Preparation for a composite restoration does not require a great deal of increased axial penetration to establish a clean, restorable finish line. Often, the presenting surfaces are sclerotic, the tubules are closed, and little new cutting is required to prepare the tooth. This allows the direct restoration to be the more comfortable of the two options.

Cutting larger, more open and more cellular tubules invites pulpal injury during crown procedures: dentin dessication, heat from burs, ionic stress from water spray and suction, negative effects from astringents, medications, temporary and permanent cements. As well, microleakage of fluids and organisms occurs demonstrably between prep and cementation appointments.

Against this benchmark, the MODB spares the pulp a heavy workout.

At the very least, with a ten year probable lifespan,a MODB restoration postpones crown placement by this length of time. The patient gains another decade for secondary dentin deposition to move the pulp away from the treatment zone.

Pins are not required for the resin MODB. Clinical experience has shown no de-bond using adhesives alone.

Matrixing Interproximal Furcations


One limitation that many clinicians face is the difficulty in matrixing the concavity of mesial roots of MODBs. Maxillary first bicuspids often have a mesial root that is concave, an awkward situation to matrix and even more problematic to finish if resin overhang develops.

The distal of maxillary first molars also frequently present root concavity, which can be very problematic to restore directly. This consideration alone often pushes treatment towards laboratory-mediated solutions. The "Bandbender" matrix method, see Bandbender,solves this problem, as the Bandbender can create both convex and concave curvatures in the same matrix, and thus can estalish proper interproximal contact at the same time as adapting to a concave gingival margin.

With an anatomical and well adapted matrix, the job of finessing the mesial root concavity becomes relatively straightforward.

To purchase a Bandbender, see Bandbender.