Economy Resin Rehabilitation
Matrix-driven direct resin rehabilitation
Michael J. Bannan, DDS, FAGD, AAACD
In the public health setting and in private practice, patients frequently present after years of neglect and deterioration of their dentition. There may be complex issues that include periodontal disease, caries, and occlusal instability that complicate the treatment-planning process. All too often, financial limitation is a primary obstacle to seeking treatment and limits clinicians’ ability to plan conservative, predictable treatment options.1
Teeth that might be restorable with full-coverage restorations often become default extractions because of cost considerations.2 Unfortunately, patients pay the ultimate price with long-term compromise of function and stability. If some key teeth can be saved and restored, the benefits to the patient in terms of health, function, and self-esteem can be significant. Sometimes, lives are changed and new hope helps people get their lives back on a more positive track. This is where dentistry can really make a difference.
This article describes a relatively low-cost, matrix-driven, direct resin technique3 used to restore two compromised dentitions: one compromised primarily by caries, the other addressing occlusal collapse. These dentitions belong to good people on a limited income who are dependent on government assistance to restore their health, function, and self-esteem.
Restorative Matrix Fabrication
Complex restorative cases require clinical decisions so that the operator can visualize the final positions of the restored teeth. The matrix concept has been used for many years and is based on dentofacial analysis, development of the diagnostic wax-up, fabrication of the matrix, and the subsequent management of the matrix and restorative materials.4-6
After a diagnostic wax-up is developed, it is blocked out with a putty spacer and a vacuum-formed stent is overlaid to develop a clear carrier tray (Figure 1). The tray is trimmed to the desired outline, and the block-out material is completely removed.
The clear tray is filled with clear polyvinyl siloxane (PVS) impression material and seated over the diagnostic wax-up to create an accurate registration that will serve as the restorative matrix.7 The clear tray/clear PVS combination yields a more rigid, accurate, and optically clear matrix than other techniques used by the author, although the result is more accurately described as translucent rather than clear (Figure 2).
The matrix is further modified in the areas of the teeth to be restored by making an entrance and exit hole to accommodate injection and venting of a flowable restorative material. The injection technique takes advantage of the hydraulic principle to ensure minimal flash at the cervical margin with a void-free fill as trapped air escapes the vent hole, allowing the restorative material to completely fill the matrix.
The injection technique has several advantages over seating a preloaded matrix. Preloading creates hydraulic resistance that can result in inaccurate or incomplete seating. It also results in more excess cervical flash as the restorative material seeks to vent itself apically. Additionally, preloading may cause voids where trapped air prevents material flow to completely fill the desired contours.
The injection hole should allow for a snug-fitting syringe tip of the restorative material. The author has found that a #6 round bur in a straight handpiece works well. The injection hole should be oriented toward the mesial aspect of the teeth to be restored for convenient delivery. The second vent hole is placed at a distal aspect of the restored segment. The location of the vent is less critical, but should be visualized when excess restorative material is expressed to signify that the injection process is complete (Figure 3).
Prior to placement of the matrix, blocking out the open cervical embrasure can facilitate the ease of access for initial finishing and separation. Trimmed-to-fit wooden wedges (Figure 4) or a soft-tissue shield or dental dam can be employed.
Because the prepared teeth will be adhesively bonded, they need to be well isolated from blood and saliva. Preliminary treatment is usually indicated to address hopeless teeth, gingival inflammation, and rampant subgingival caries prior to this final bonded restorative procedure. Lip retractors combined with absorbent pads are very helpful along with adept four-handed suctioning.
Restorative Material Selection
The choice of restorative material is less clear. Ideal characteristics include:
• Low enough viscosity to hydraulically flow into small preparation features and completely fill the matrix without voids
• Ability to be adhesively bonded to tooth structure
• Dual-cure capability to reduce the risk of underpolymerized resin
• Good postoperative physical properties for wear and fracture resistance
• Esthetic optical properties to blend a single shade into an existing dentition
• Good surface polishability
• Resistance to recurrent caries
Traditional flowable resins lack the filler content and physical properties for long-term function. Bis-acryls have auto-cure capabilities, but are brittle and prone to fracture. Hybrid and nano-restorative composites have great esthetic and physical properties, but lack flowability. The author has found that using a composite heater improves flow for single teeth, but the composite cools and stiffens before multiple teeth can be injected.