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Written by Randy Weiner, DMD Saturday, 01 March 2008 00:00
Dentists make numerous decisions every day that involve their practices. For restorative dentists, one such decision involves which dental material to use. For each indirect restoration that is placed, clinicians must decide which cement to use.
Dental cements serve two purposes. One is to retain restorations or appliances in a fixed position in the mouth.1 These materials hold the tooth and restoration together via some form of attachment, either mechanical or chemical, or a combination of the 2.2 Additionally, cements act as a barrier against microleakage by sealing the interface between the tooth and the restoration.
A number of factors influence the dentist’s decision regarding which cement to use. Cost of the product, ease of use, the number of shades that are available, and whether it will cause the patient discomfort are just a few of the factors.
In 1998, The Dental Advisor, in an issue about temporary cements, concluded among other things that ideally, material kits should be compact and provide for minimal waste, and the material should not continue to flow after the desired amount is expressed.3
To make matters more difficult for us, we have numerous products to choose from. In fact, it has been written that more than 25 manufacturers market cement, some of whom have more than one product.4
The newest category of cements, which are resin based, offer a number of advantages: they are available in self-cured (chemical), light-cured, and dual-cured versions, and they are also found in numerous shades. We have been taught that the longer the crown preparation, the greater the resistance to dislodgment of the casting, and ultimately the greater the retention of the casting. However, there are times when the perfect preparation is not possible. Resin cements are ideal for non-ideal preparations, since they bond to tooth structure and therefore can aid in retention of the prosthesis.
The self- or chemical-cured variety is best suited for use under opaque or metallic restorations where the curing light will not reach. These products will start to set at the end of mixing. In contrast, the light-cured versions have a greater working time, as they begin to set when the operator wants them to set. However, clinicians must ensure that the material is protected from ambient light, as that light source will cause the cement to set. Additionally, light-cured cements do not have the tendency to darken over time, as do the self-cured ones.
The last kind of resin cement, the dual-cured variety, is ideal to use under thick or opaque restorations. The light-cured characteristic helps the clinician initiate the setting process, which allows the casting to be held in place while the remainder of the mix hardens.
Resin cements, due to their ability to bond to tooth structure, have been shown to exhibit less microleakage than other cements.5 In 2003, Attar, et al concluded that dual-cure cements demonstrated the best mechanical and physical properties.6
One clinical aspect of resin cements the dentist should note is that post-cementation removal of excess cement can be difficult, as the cement closely matches the tooth shade and some of it may be left on the tooth. Therefore, it is incumbent upon the operator to be vigilant when removing excess; we have several instruments available to help us. The gingival retractor (available in 2 sizes from Danville Engineering) and the Zekrya Gingival Protector (Zenith/DMG) are examples of such instruments.
Along with the recent introduction of self-etch bonding agents, we now have self-etch resin cements, such as G-Cem (GC America). This material is available in a premeasured capsule, and, as with other self-etch cements, is designed to be used with all indirect restorations (all-metallic, porcelain, and composite-based restorations, including posts). Additionally, this formulation gives a superior bond in faster time.
With G-Cem, there is no risk of postoperative sensitivity, and, since it can be applied to both moist and dry preparations, it is less technique sensitive. It combines seventh-generation resin adhesive technology with the biocompatible properties of glass ionomer cements. Researchers at GC America have developed this cement with water and functional monomers (4-meta and phosphoric ester) rather than polyalkenoate acid to obtain the self-adhesive properties. This allows the material to better infiltrate the dentinal tubules. Additional characteristics are its high aesthetic qualities (better color stability and stain resistance) and fluoride release.
The package that contains the capsules has instructions printed on it, which makes directions for use readily accessible. In fact, it has been written that the easier it is for the clinician to understand the product’s instructions, the greater likelihood that the dentist will use the product.7 The desired ease of use is accomplished with the capsule: Activate the capsule by pressing it down on the countertop. After trituration (10 seconds), the capsule is placed in the dispensing instrument. From here the material can be placed easily into the restoration or the tooth. Cleanup consists of throwing away the capsule and disinfecting the dispensing instrument, which can be used for all other capsules that GC America manufactures, thereby reducing the cost.
The working time for G-Cem is 2 minutes and 15 seconds. After the restoration is seated, the cement at the margin can be light-cured for 2 to 4 seconds and the excess cement or flash can be removed. The material is fully set in 6 minutes and 30 seconds, is “creamy” in texture, and will flow easily. It also possesses high tensile strength.
Figures 1a and 1b. Preoperative photographs.
Figure 2. Shade selection.
Figure 3. Crown preparation.
Figure 4. Margin etched with Tooth Conditioner 34% (DENTSPLY Caulk).
Figure 5. Excess cement prior to curing and removal.
Figure 6. Both crowns after cementation, finishing, and polishing.
Figure 7. Six months post cementation.
A 58-year-old woman wanted her yellow central incisors to be whiter like her other crowns (Figures 1a and 1b). She stated that she knew that her 2 existing crowns on the lateral incisors were not ideal (exposed margins), but at this time she only had the financial means to treat the front teeth, giving her a whiter smile. She also expressed concerns that any new crowns should not have “metal showing at the gums” like one of her crowns did.
There were no medical contraindications to dental treatment; the options given to her were either porcelain veneers or all-ceramic crowns. Due to the size of the existing composites and the stained margins around them (meaning a deep preparation for veneers), the patient chose to have crowns placed. She understood that her crown on tooth No. 10 would still be longer than the new ones. It was also explained to her that the shade of the new crowns might not exactly match her proximal crowns. The chosen shade was A1 (Figure 2). Digital photographs were taken and sent to the lab along with the rest of the case materials.
At the preparation visit she again confirmed that only the 2 front teeth would be treated at this time, and she would replace the other crowns in the future. Anesthesia was placed, and the teeth were prepared with a margin located at the crest of the gingiva (Figure 3). Master impressions were made using Exafast Putty and Exafast NDS Regular (GC America). Bite registration (Jet Blue Bite [Coltène/Whaledent]) and an alginate impression of the lower teeth were made. Temporary crowns were made (Jet [Lang Dental]) and cemented with TempBond Clear (Kerr).
At the delivery appointment, the patient requested that anesthesia be given. Nobel Biocare Procera crowns were tried in, and the patient approved both the shade and the shape. These crowns were to be cemented using G-Cem Shade A2. To ensure a good seal, the enamel at the margin was etched using phosphoric acid for 15 seconds and washed off (Figure 4). To make finishing the margins easier, one crown was cemented at a time. Figure 5 shows the excess material as the crown was seated. The cement was cured for 10 seconds, and the excess was removed. The cement was allowed to cure for 6 minutes, and the margins were finished and polished. Next, the other crown was cemented in place (Figure 6). Figure 7 shows the crowns 6 months after cementation. Notice that the gingival tissue is pink, not red and inflamed. The patient also stated that she was happy with the shade, as it blended in with her other crowns.
- Craig RG, Powers JM. Restorative Dental Materials. 11th ed. St Louis, MO: Mosby; 2002:594.
- Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed prosthodontics. J Prosthet Dent. 1999;81:135-141.
- Farah J. Temporary cements. Dental Advisor. 1998;15(9):2.
- Weisman G, ed. Cements. Dental Products Report. 2005;39(11):114-124.
- Piemjai M, Miyasaka K, Iwasaki Y, et al. Comparison of microleakage of three acid-base luting cements versus one resin-bonded cement for Class V direct composite inlays. J Prosthet Dent. 2002;88:598-603.
- Attar N, Tam LE, McComb D. Mechanical and physical properties of contemporary dental luting agents. J Prosthet Dent. 2003;89:127-134.
- Peutzfeldt A, Vigild M. A survey of the use of dentin-bonding systems in Denmark. Dent Mater. 2001;17:211-216.
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