Restorative dentistry (Proceedings)

Restorative dental problems, although not as involved as those in human dentistry, can be very technique-sensitive and difficult to resolve. The resolution of particular problems is usually dependent upon the choice and imagination or inventiveness of the operator. Restorative problems are usually those of a mechanical or iatrogenic nature rather than medical or pathological. The restoration of the coronal aspect of endodontically treated teeth, with carious lesions, coronal defects, and missing teeth constitute the bulk of restorative problems.

Dental materials

Complete texts have been written describing the many materials used in dentistry, their strengths, failings, and applications. Dental materials are constantly evolving in use, effectiveness, and variety. Some basic materials employed over the past two decades are still in use, and quite effective. Dental materials of choice for animal dentistry are composites; chemical and light cured varieties, glass ionomers and silver amalgam.

It must be remembered that there is no strength to be gained from most dental restorative materials. The opposite is quite often true, for sound tooth structure is removed to achieve mechanical retention of some composite restorations and silver amalgam. Glass ionomer cements do not require mechanical retention, however they lack resistance to abrasion, and like all restoratives, they do not lend themselves to sheer strength when lateral force is placed upon them. Therefore, lost tooth structure incisal to the remaining tooth crown cannot be replaced with existing dental materials; they will invariably fracture.

Problems encountered in the use of dental materials are usually the result of poor technique, lack of familiarity with the properties and uses of the various materials, improper instrumentation, and failure to follow the manufactures instructions in a step-by-step manner to completion.

There are many publications available to the veterinarian from the manufacturers detailing in total all the properties of their products, their applications, instrumentation, and an atlas detailing step-by-step procedures.

The most common problem in veterinary dentistry is the use of glass ionomer cements to restore cervical line resorptive lesions in cats. Failure usually is the result of poor visibility, gingival hemorrhage contaminating the area, and poor restorative technique. Cats with resorptive lesions should have a thorough prophylaxis at 10 to 12 day prior to restorative procedures. The removal of dental plaque and inflammatory agents will help to control hemorrhage during restorative procedures.

A fine gauge gingival retraction chord placed in the gingival sulcus prior to restoration retracts the gingiva, providing better visibility while controlling sulcular bleeding.

A glass ionomer restorative material of choice is placed into the lesion as per the manufacturer's instructions, and finished to proper anatomic contour. It is best to complete the restoration with the retraction chord in place until completion. If the retraction chord tends to block visibility to the lesion, it may be removed just before placement of the restorative material. The hemostatic agents in the chord usually will have retracted the gingiva for visibility, while providing sufficient hemostasis to place the restoration before moisture contamination.

Proper attention to finish is essential. The restorative material must not have overhanging ledges, or a roughened surface that can provide plague retentive areas. A smooth, polished finish can be had with the use of fine sanding disks, and special finishing rubber cups and wheels available from all dental supply houses.

Cavity design

Many restorative procedures fail because of poor cavity design. The mechanics of cavity preparation must be adhered to. Cavity design basically is the removal of caries, if present, and any unsupported enamel, while providing mechanical retention for the restorative materials. The use of adhesive materials can eliminate the need for mechanical retention.

There is no stereotypical design of cavity preparation. Each is designed with the specific purpose of the elimination of caries, restriction of resorption, reduction of sensitivity (in the case of feline root resorption and sensitivity), and to restore coronal anatomy.

Each restoration is designed to perform the additional steps necessitated by the limitations of the operator or restorative material. Poor preparation accounts for the majority of restorative failures.

Clinicians are advised to review human restorative dental publications to familiarize themselves with the principals of cavity preparation and design. Cavity marginal integrity, gingival extension of the restoration, unsupported enamel rods, and restoration evaluation all play an important role in achieving success.

The objectives of cavity design

The objectives of cavity preparation are: (1) removal of all caries; (2) removal of defects that predispose to carious activity; (3) extension of margins allowing access for instrumentation; (4) providing retention for the restorative material; and (5) preservation of a maximum amount of tooth structure retaining the inherent strength contained in a tooth.

Smoothness of cavity walls and margins is generally accepted as a desirable quality. Instrumentation of cavity preparation is essential to restorative success. The use of sharp burs and diamond instruments will help to prevent chipping of the enamel at the periphery of the restoration when the bur moves out of the cavity preparation. Smooth margins can be produced with 12-bladed finishing burs (e.g., a 7901 or 7902 12-bladed bur). The cavity margins can be planed or smoothed with hand instruments, such as angle formers or gingival margin trimmers. Hand instruments of these types are effective in the removal of unsupported enamel rods.

Pins do not strengthen dental filling materials. Observations of restorative failures have shown that the restorations are weaker following pin placement. Pins do retain restorative material and will resist dislodgement due to the forces of mastication. Their use in animal dentistry should be used in conjunction with endo posts restorations or to aid in the retention of base build-up materials for fill cast crown coverage.

Reinforcement of endodontically treated teeth

Reinforcement of endodontically treated teeth in animal dentistry is directly related to the degree of tooth destruction, type of restorative materials, the design of the cavity preparation, and the amount of retention created for the restoration. Reinforcement of endodontically treated teeth in animal dentistry most commonly involves slab fractures of upper 4th premolars, and the design, preparation, and construction of cast restorations of canine teeth. Although the same principals apply to all teeth, upper 4th premolars often present with the entire lateral surface of the tooth lost, and the gingiva above the fracture edematous, and inflamed. The natural food deflecting mechanism of the tooth is lost with the fractured segment, allowing for the resultant periodontal problem.

One must take into consideration this phenomenon before considering odontoplasty - a method employed by some clinicians to remove this natural defecting projection of enamel with high speed cutting burs. Their theory is that if this bulge of enamel were removed, plaque would not accumulate. This is a drastic cure with extenuating complications for a simple problem. If plaque collects above the cervical projection of enamel, the client has only to brush the area to remove plaque, and prevent gingivitis while preserving the natural deflecting mechanism of the tooth. This is a logical, less traumatic, and less likely way to create a pulpal response solution to a plaque retentive area.

After conventional endodontic therapy, the endodontically treated root canals - both mesial and distal - are utilized for retention. Both roots are prepared and filled with endodontic posts of proper width and length. Endodontic post systems, such as the Para post system by Coltène/Whaledent provide excellent instructions for the placement of their endodontic posts. These systems provide reinforcement via the root for the restoration material. Caution should be exercised in the preparation and partial root obturation with dowel pins and posts. They increase the fracture potential of the root. Posts are never forced into the root canal. Proper post selection is dependent upon the root canal diameter. Self threaded pins may be utilized with the endodontic post system for added retention, if enough tooth structure is present to retain supplemental pins, and their placement will not weaken tooth structure.

After conventional endodontic therapy, a post diameter is selected that will fit the diameter of the prepared and obturated root canal. The endodontic post system usually contains five different diameters of posts, with a pin or post hole drill for each size. After size selection has been determined, the mesial and distal canals are prepared with the proper size drill in a slow speed hand piece to a depth that will provide a fifty percent root depth to coronal exposure of the post. The post often may need to be shortened to provide this ratio, while not extending beyond the residual crown height. Drilling of the canal is along the same pathway as the endodontic root system. The drill can remove the core gutta percha to the desired depth; however, the chance of total gutta percha removal is present along with the chance of lateral root wall perforation. When the drill is placed into freshly seated gutta percha, total removal of the gutta percha with the post hole drill is likely to occur. This complication can be avoided when slab fracture restoration with retentive posts and endodontics are performed at the same appointment

After selection of the gutta percha point is made and pre-filled into the root canal during endodontic therapy, the apical one-third of the gutta percha point is cut off. The root canal is filled with cement, and the excised tip of gutta percha is inserted into the canal. The tip is guided into place with the use of an endodontic plugger of proper size and seated firmly into position in the apex, perfecting an apical seal. This will leave the coronal ⅔ of the root canal clear to preparation and placement of the endodontic post without fear of removing the entire pulpal contents.

After both canals post hole preparations are complete, the endodontic posts are fitted and seated with a cement of the operators choice, preferably a glass ionomer cement. The cement is placed into the post holes with a spiral filling bur to avoid air entrapment. After cementation, additional treaded pins can be placed into sound enamel if present, to supplement retention. Composite filling material is placed around the posts and pins in 2mm layers and light cured, or in controllable amounts if chemically cured, to restore the proper coronal anatomy.

The restoration is finished with finishing burs and sandpaper disks to contour. A final polish with flexible rubber polishing wheels and cups completes the restoration. Do not place or attempt to place restorative material beyond the remaining coronal length of tooth structure. The added restorative material beyond the existing natural tooth structure will fracture quite easily, often taking part of the needed labial surface composite with it.

Placement of full crown coverage on upper premolars or lower molars is not recommended. This is a very technique -sensitive procedure, and beyond the capabilities of most practitioners. The vast majority, especially the upper 4th premolar, can be treated by the above describe procedure. Problems in occlusion, occlusal disharmonies, contact areas, and temporal mandibular joint considerations, to name a few, are constant.

Post and core build up with crown coverage can be utilized to restore function in the case of guard dogs. Prognosis is only fair if most or all of the clinical crown has been lost. The stress and torque factors upon the retained root by a necessarily large endodontic post usually leads to long axis root fracture in time. If crown coverage is a must, the covering crown length must be one-half or less of the original crown length to reduce torque factors.

The procedure is the same as described for post placement in upper 4th premolars. After the core buildup has been placed, an impression of the canine crown is taken with a dental impression material of choice. Either an alginate impression can be taken, if it can be poured up in dental stone immediately, or one of the many silicone rubber types of impression material. These do not require an immediate pour up in stone. An opposing arch impression is taken and poured up in stone, if an alginate impression is taken. The opposing model is needed for proper articulation and relation of the cast crown to its opposing teeth.

All models or impressions are sent to a qualified dental laboratory for crown construction. The cast crown is best cemented with a glass ionomer cement for proper retention.

Conclusion

Of all the animal dental discipline, the one that comes the closest to human dentistry is operative or restorative dentistry. Total coverage of the many restorative procedures and problems in one chapter is impossible, but many fine human restorative texts are available to the veterinarian to guide them in this vast and rapidly changing discipline of dentistry.

Bibliography

Baraban, D. J.: The Restoration of Pulpless Teeth. Dental Clinics of North America.1967.

Black, G. V.: Black's Operative Dentistry. Vol. 2. 1955.

Kornfield, M.: Mouth Rehabilitation. St. Louis, C.V. Mosby Co. 1975.

Lau, V. M. S.: Dental Clinics of North America. 1975.

Markley, R. L.: Pin Reinforcement and Retention of Amalgam Foundations and Restoration. J.A.D.A. 1958.

Metrick, L.: Canal Obliteration with a Post Crown. J. Canad. Dent. Assoc. 1961.

Neagley, R. L.: The Effect of Dowel Preparation on the Apical Seal of Endodontically Treated Teeth. Oral Surg. 1969.