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Choosing a dental cement
HANDS ON Dental Materials Choosing a dental cement Background.—The plethora of dental cements now available make choosing the right one a complicated event. Dentists cement many materials to teeth, such as temporary crowns, posts, Maryland and non-metallic winged bridges, and crowns and veneers that are fabricated in the laboratory or at chairside. Factors that influence the choice of dental cement include whether the cementing is designed for a permanent or retrievable restoration, the tooth’s pulp status, and esthetics. Temporary Cements.—Zinc oxide and eugenol (ZOE) combinations are the principal ingredients in temporary cements. They are designed to keep the crown in place but permit retrievability. Eugenol-free cements were developed to address problems with lower bond strength in the presence of eugenol. However, the newer bonding agents are often bis-acryl-based, making the bond strength effect of eugenol no longer an issue. When the temporary crown is cemented in the esthetic zone, you must consider shade selection. Traditional ZOE cements tend to be deeply opaque; resin-based options now come in various shades. Demands for cements to minimize bacterial invasion and seal cut dentin have led to the inclusion of agents such as chlorhexidine, fluoride, and potassium. Permanent Cements.—The fit of a restoration is essential in a successful permanent restoration. When you have addressed occlusion and minimized extraneous stress factors, using a resin cement can reliably obtain good adhesion. Today, porcelain restorations can be bonded to teeth with almost no inherent retention of the preparation. Depending on the clinical situation, you can choose among zinc phosphate, carboxylate, glass ionomers, resin-modified glass ionomers, resins, and self-bonding resins. Each offers particular advantages for specific situations. Statistics from tests run by manufacturers and length of time the product has been available are not the best predictors of performance. It is best to consider your clinical needs and choose a cementing agent accordingly. For example, zinc phosphate has essentially no bond strength and tests poorly in laboratory settings, but has been used successfully for over 100 years. No one has yet determined the universal value of bond strength to dentin needed for a successful restoration. Be cautious when using self-curing adhesive
resins in partial coverage porcelain restorations with minimal inherent retention. In these situations, more traditional bonded resins with higher bond strength values are generally more successful. Tooth Preparation.—The surface to which the cement is being adhered must be as clean as possible. Some materials work better if the tooth surface is rewetted; this is a matter to check out with the manufacturer of your chosen material. Choices.—The choice of cement depends on the type of restoration. Posts can be treated like inlays but with less access to the tooth, no light curing, and no enamel to increase bond strength. Post material dictates what surface treatment is needed for the best bond. If the goal is to stabilize the core material and distribute forces evenly in the remaining root, bond the post material to the tooth. The best choice is a resin ionomer or a self-etching adhesive resin cement. Because resin ionomer cements have cracked all-porcelain crowns, it may be best to choose a self-etching, dual-cure adhesive resin cement and carefully follow the manufacturer’s instructions for surface preparation. For metal-based crowns, nearly every cement performs well under most conditions. If you choose a resin cement for the metal crown, make sure it is self- or dual-curing. Permit the dual-cure cement to cure on its own so that you don’t interfere with the bond developing at the microgap of the margin. For gold margins, use a self-curing resin and remove the excess within the time recommended, thereby protecting the marginal seal. Metal-supported bonded bridges require bonding to the adjacent enamel using resins that are not light cured. The more traditional resins give the best results. Ceramic crowns vary in material, thickness, purpose, and esthetics. Partial coverage posterior porcelain restorations often have no significant retention form. Light-cured resins are generally not an option; dual- and self-cure resins are better choices. Prep designs with less retention require more bond strength in the cement chosen. Traditional resin cements with a separate bonding process tend to be stronger than self-etching adhesive resins. In all cases be sure to adhere strictly to the manufacturer’s directions.
Volume 54
Issue 1
2009
9
Full-coverage ceramic crowns are also made of various materials, each with specific requirements for cementing. The inherent weakness of conventional glass-ceramic restorations is compensated for by choosing an adhesive system and resin cement that will bond securely to the underlying tooth structure. The thickness of the restoration dictates whether you should choose a self-, dual-, or light-curing resin cement. Pretreatment of a glass-ceramic crown with hydrofluoric acid and silane is essential. Both resin and resin-modified glass ionomers perform well in cementing alumina-based ceramics. Air abrasion in the laboratory plus silane and cement constitutes the best approach. Zirconia frameworks are similar to metal-based crowns, with no surface treatment needed. In these crowns, tooth status is more important than type of crown. Self- and dual-cure cements are the best choices. Porcelain veneers are often thin enough to cure through. A clear/translucent shade is widely useful, with a white opaque and a medium opacity shade covering most other cases. Have the etching and silane application done in the laboratory, not the office, because the thin feldspathic porcelain has little strength. The air abrasion needed for aluminabased ceramic crowns should also be done in the laboratory, so they are ready for cementation upon delivery. The greatest working time is provided by using a light-cure-only resin cement. Self-cure resins are usually the best choice, since
dual-cure resins contain an activator that can affect the color of the porcelain veneer. If self-adhesive resins are chosen, tooth preparation and placement are vital. These resins are highly sensitive to technique, and bond strength can be a casualty of an imperfect process.
Clinical Significance.—The choice of an appropriate cement is in constant flux. The best approach is to be proficient with each type of cement and know just what the manufacturer recommends for excellent results. Keep cements from each category on hand and practice your technique along with your assistant. Remember, too, that just because the product is the latest, it may not be the greatest—or the most appropriate choice for your clinical situation.
Carstensen S: Dental cement: The essential link. AGD Impact July 2008 Reprints available from the Academy of General Dentistry. Fax your request to Jo Posselt (312/440-4261) or e-mail AGDJournal@ agd.org
Devices Electrosurgery and lasers for cutting soft tissues Background.—All dentists are familiar with cutting soft tissue using a scalpel and understand the negative and positive aspects of this approach. Electrosurgery and lasers are also used to cut oral soft tissues, but dentists may be less conversant with the comparative value of the two methods. Use of the laser was compared with electrosurgery, noting clinical factors associated with each approach. Electrosurgery.—With electrosurgery, heat is applied in a controlled, precise way to the soft tissue site. This creates irreversible thermal changes in the soft tissues. Monopolar and bipolar electrosurgery units are available. Both are effective, but monopolar electrosurgery is used more often. Most dentists use fully rectified current on a medium setting to achieve a cut without dragging. Available currents include fully rectified filtered, fully rectified, or partially rectified. Electrosurgery has proved useful in gingivectomy, gingivoplasty, tissue management with fixed prosthodontics, obtaining access for restorations and crown buildups, crown lengthening procedures, reduction of
10
Dental Abstracts
tuberosities, eliminating excess soft tissues, reducing periodontal pockets, operculectomy, frenectomy, and biopsy when enough healthy tissue is present to provide wide margins. The advantages of electrosurgery include reduced cost for the equipment, the electrode’s ability to cut on the sides as well as the tip, the ability to bend the electrode, ease of cutting, immediate hemostasis, consistency in cutting, minimal pain after the cut, minimal trauma to the soft tissue, and a self-disinfecting tip. However, anesthesia is required, just the name ‘‘electrosurgery’’ can provoke anxiety in patients, the burned flesh has an odor, the operator has little tactile appreciation of what is being cut, the heat of the monopolar unit is too great to be used with implants, bone damage can occur, and explosive environments must be avoided. Some evidence indicates that electrosurgery can interfere with the action of pacemakers, and patients who have had irradiation, who have diabetes, or who have blood dyscrasias may have poor healing after surgery.
resins in partial coverage porcelain restorations with minimal inherent retention. In these situations, more traditional bonded resins with higher bond strength values are generally more successful. Tooth Preparation.—The surface to which the cement is being adhered must be as clean as possible. Some materials work better if the tooth surface is rewetted; this is a matter to check out with the manufacturer of your chosen material. Choices.—The choice of cement depends on the type of restoration. Posts can be treated like inlays but with less access to the tooth, no light curing, and no enamel to increase bond strength. Post material dictates what surface treatment is needed for the best bond. If the goal is to stabilize the core material and distribute forces evenly in the remaining root, bond the post material to the tooth. The best choice is a resin ionomer or a self-etching adhesive resin cement. Because resin ionomer cements have cracked all-porcelain crowns, it may be best to choose a self-etching, dual-cure adhesive resin cement and carefully follow the manufacturer’s instructions for surface preparation. For metal-based crowns, nearly every cement performs well under most conditions. If you choose a resin cement for the metal crown, make sure it is self- or dual-curing. Permit the dual-cure cement to cure on its own so that you don’t interfere with the bond developing at the microgap of the margin. For gold margins, use a self-curing resin and remove the excess within the time recommended, thereby protecting the marginal seal. Metal-supported bonded bridges require bonding to the adjacent enamel using resins that are not light cured. The more traditional resins give the best results. Ceramic crowns vary in material, thickness, purpose, and esthetics. Partial coverage posterior porcelain restorations often have no significant retention form. Light-cured resins are generally not an option; dual- and self-cure resins are better choices. Prep designs with less retention require more bond strength in the cement chosen. Traditional resin cements with a separate bonding process tend to be stronger than self-etching adhesive resins. In all cases be sure to adhere strictly to the manufacturer’s directions.
Volume 54
Issue 1
2009
9
Full-coverage ceramic crowns are also made of various materials, each with specific requirements for cementing. The inherent weakness of conventional glass-ceramic restorations is compensated for by choosing an adhesive system and resin cement that will bond securely to the underlying tooth structure. The thickness of the restoration dictates whether you should choose a self-, dual-, or light-curing resin cement. Pretreatment of a glass-ceramic crown with hydrofluoric acid and silane is essential. Both resin and resin-modified glass ionomers perform well in cementing alumina-based ceramics. Air abrasion in the laboratory plus silane and cement constitutes the best approach. Zirconia frameworks are similar to metal-based crowns, with no surface treatment needed. In these crowns, tooth status is more important than type of crown. Self- and dual-cure cements are the best choices. Porcelain veneers are often thin enough to cure through. A clear/translucent shade is widely useful, with a white opaque and a medium opacity shade covering most other cases. Have the etching and silane application done in the laboratory, not the office, because the thin feldspathic porcelain has little strength. The air abrasion needed for aluminabased ceramic crowns should also be done in the laboratory, so they are ready for cementation upon delivery. The greatest working time is provided by using a light-cure-only resin cement. Self-cure resins are usually the best choice, since
dual-cure resins contain an activator that can affect the color of the porcelain veneer. If self-adhesive resins are chosen, tooth preparation and placement are vital. These resins are highly sensitive to technique, and bond strength can be a casualty of an imperfect process.
Clinical Significance.—The choice of an appropriate cement is in constant flux. The best approach is to be proficient with each type of cement and know just what the manufacturer recommends for excellent results. Keep cements from each category on hand and practice your technique along with your assistant. Remember, too, that just because the product is the latest, it may not be the greatest—or the most appropriate choice for your clinical situation.
Carstensen S: Dental cement: The essential link. AGD Impact July 2008 Reprints available from the Academy of General Dentistry. Fax your request to Jo Posselt (312/440-4261) or e-mail AGDJournal@ agd.org
Devices Electrosurgery and lasers for cutting soft tissues Background.—All dentists are familiar with cutting soft tissue using a scalpel and understand the negative and positive aspects of this approach. Electrosurgery and lasers are also used to cut oral soft tissues, but dentists may be less conversant with the comparative value of the two methods. Use of the laser was compared with electrosurgery, noting clinical factors associated with each approach. Electrosurgery.—With electrosurgery, heat is applied in a controlled, precise way to the soft tissue site. This creates irreversible thermal changes in the soft tissues. Monopolar and bipolar electrosurgery units are available. Both are effective, but monopolar electrosurgery is used more often. Most dentists use fully rectified current on a medium setting to achieve a cut without dragging. Available currents include fully rectified filtered, fully rectified, or partially rectified. Electrosurgery has proved useful in gingivectomy, gingivoplasty, tissue management with fixed prosthodontics, obtaining access for restorations and crown buildups, crown lengthening procedures, reduction of
10
Dental Abstracts
tuberosities, eliminating excess soft tissues, reducing periodontal pockets, operculectomy, frenectomy, and biopsy when enough healthy tissue is present to provide wide margins. The advantages of electrosurgery include reduced cost for the equipment, the electrode’s ability to cut on the sides as well as the tip, the ability to bend the electrode, ease of cutting, immediate hemostasis, consistency in cutting, minimal pain after the cut, minimal trauma to the soft tissue, and a self-disinfecting tip. However, anesthesia is required, just the name ‘‘electrosurgery’’ can provoke anxiety in patients, the burned flesh has an odor, the operator has little tactile appreciation of what is being cut, the heat of the monopolar unit is too great to be used with implants, bone damage can occur, and explosive environments must be avoided. Some evidence indicates that electrosurgery can interfere with the action of pacemakers, and patients who have had irradiation, who have diabetes, or who have blood dyscrasias may have poor healing after surgery.