Proper Clean-up: Removing Excess/Residual Resin-based Dental Cement
Categories:
,
Author(s):
Date: 08-03-2017 03:39:33 am
The primary functions of dental cements are to enhance resistance to displacement and to seal the interface of the restoration to the remaining tooth structure. Available options include but are not limited to composite resin cements and resin modified glass ionomers. Proper selection of dental cements is a key factor that increases the success of restorations. Several factors determine which type of dental cement, restorative material, and restoration a clinician chooses, including the ability to maintain a dry field, esthetic demands, tooth structure, the location of margins and chewing forces.
Resin cements were introduced in the 1970s as an alternative to acid-based reaction cements such as zinc phosphate. These cements vary in their setting mechanisms, which consists of polymerization either by chemical curing, dual curing, or light curing. Resin cements offer good adhesion (and therefore retention) as well as low solubility once set and good compressive strength. They are, however, technique-sensitive, require careful clean-up, and excess cement is generally difficult to remove once set.
Resin-modified glass ionomer cements contain resin filler particles consisting of polymerized functional methacrylate monomers. These monomers modify glass ionomer cements which consist of powder containing fluoroaluminosilicate with a liquid that is composed of polyacrylic acid and tartaric acid. When mixed, the polyacrylic acid reacts with particles and releases aluminum, calcium, and fluoride ions. Resin modified glass ionomers offer improved adhesion, strength, and low solubility. In addition, they are easier to manipulate than glass ionomer cement. The working time is affected by temperature: high temperatures shorten the working time while low temperatures prolong it.
Proper use and clean-up of dental cement
Proper use and clean-up of dental cements ensures the success of restorations and aids in preventing postoperative complications associated with residual cement. Effective removal of excess cement is important in the prevention of gingival bleeding, soft-tissue inflammation, crestal bone loss, and peri-implant disease. The presence of dental cement is a direct result of poor clean-up and use, as well as lack of assessment of residue after cementation. Residual cement can be extremely difficult to remove from subgingival areas, making proper handling at the time of cementation crucial. To reduce the possibility of problems caused by the use of dental cements, several aspects need to be considered.
Appropriate amount of cement and placement
Proper preparation and resistance form help avoid overuse of cement. A thin layer of cement, which for crowns amounts to about 3% of the volume of the crown, should be all that is required (Fig. 1). Application of the cement near but not on restoration margins helps prevent excess cement from building up. When the crown is seated, the cement will flow toward the occlusal table of the preparation and then move to the preparation margins where the excess cement is then readily extruded. Another approach is the placement of a cement vent that helps to minimize hydraulic pressure that could otherwise push the cement subgingivally. Retraction cord also can aid in easy clean-up of excess cement.
Using silicone as a “cementation device” also has been described in the literature. Silicone is first injected into the crown to create an analog. Cement is then placed in the restoration, first seated over the analog to displace most of the excess, and then removed and seated over the preparation. Care must be taken if using this technique to work quickly to avoid the onset of initial setting before the restoration is fully seated over the preparation.
Working and setting times
Working times and setting (or curing) times are important to understand when handling a cement:
- The working time is the time available for the manipulation of unset cement
- The setting time refers to the time that is required for the cement to set or harden from its plastic or fluid stage to a rigid one.
The working and setting times are different for each cement manufacturer, it critical to read the instructions. Long-term success is heavily dependent not only on appropriate selection but also on proper handling and use of dental cements. It is extremely important that all excess cement be removed. This requires a careful technique and an understanding of when during the setting reaction excess cement may be initially removed. Various approaches can be taken to remove excess cement and minimize the risk of residual cement.
Excess cement removal at the restorative margins
Clean-up of resin-modified glass ionomer and glass ionomer cements is easy, as the excess cement can be removed with a plastic instrument or scaler while in the waxy stage. With a dual cure composite resin–based cement, in the case of ceramic restorations that transmit light, using a curing light for 1 to 2 seconds tack cures the cement, making it possible to peel away the excess with an anterior or posterior scaler while the cement is still waxy/ rubber (Fig. 2), and then following this up by using an explorer.
For cementation of opaque metal and zirconia based restorations, however, there is a risk with removing excess dual-cured cement using the tack curing method as the excess cement at the margin will be cured, but not the cement under the restoration since light cannot penetrate through the opaque restoration. Mechanical forces involved during cleanup can weaken or cause failure of the bond if the cement is not sufficiently cured. Therefore, it is recommended for these restorations that the cement be self-cured to reach the gel phase at which point excess can then be conveniently and safely removed.
Timing is important - if cleanup begins before cement reaches a gel state then premature failure of the restoration can occur, and conversely if cleanup is late the cement will already have set making removal of excess cement difficult without rotary instrumentation. For optimal cleanup results, it is important to check the excess cement closely to determine when it reaches the gel phase during which excess cement can be safely and efficiently removed. It is also important to follow the directions for use which should indicate when the gel phase will commence.
Floss also can be used at this stage to remove excess cement, as well as afterwards to remove loose excess in the gingival sulcus, help remove adhered excess, and to check that no residual cement remains. Methods for removing residual cement, beyond the use of floss and scalers for hard set cement, include cleaning with a water and pumice paste and prophylaxis cup, and using an intraoral sand blaster. Of all three, the sand blaster has been the most effective and manual removal the least effective. All surfaces of the tooth should be cleaned, especially the margins.
Removal of residual dental cement around implants
Floss is also used around implant restorations to detect and help remove residual cement. After inserting the floss on both sides of the implant, it is wrapped in a circle and crisscrossed and then moved in a shoeshine motion in the peri-implant crevice. Great care should be taken during removal of residual cement to minimize trauma to the peri-implant tissues, and to avoid roughening the neck of the implant (if exposed) and implant complex– restorative interface (Figs. 3, 4). Titanium implant scalers can be used to debride the area and dislodge excess cement. These are preferred over graphite and plastic scalers that may leave traces of graphite or plastic embedded in the rough surfaces of implants, which may increase the risk of peri-implantitis. Titanium implant scalers are strong enough to remove hard cements, yet have a low Rockwell hardness to avoid scratching implant surfaces.
Clinical and radiographic visualization
Good visualization and moisture control is essential when placing indirect restorations. Good visualization also aids with removal of excess cement. Proper visualization can only be achieved through the use of magnification. Loupes are invaluable in providing this for dentists, dental hygienists, and assistants. Using a dental mirror defogging solution also helps, and systems such as the Isolite system allow for improved visualization with an intraoral light incorporated into the device, in addition to providing for isolation.
There are various method for identifying excess cement. A common method is to use dental tape floss; if the floss is roughened or frayed after being used around the indirect restoration, this can be indicative of residual cement. (Note, however, that adjacent overhangs and calculus also can result in frayed or roughened floss.) It is important to use a radiograph to check for residual cement. It is therefore important to select a cement with radiopaque properties so that it can be detected radiographically. In some cases, the removal of excess cement may require use of a local or topical anesthetic so that the cement can be effectively removed.
Surgical removal of old residual cement is only recommended if nonsurgical removal is unsuccessful. This involves flap surgery to help identify, access and remove residual cement that is located 3 mm to 5 mm subgingivally. While it may be successful, it is invasive and traumatic and represents a failure at the time of treatment planning and restoration.
Conclusion
The risk of residual cement can be avoided and minimized by understanding the properties of different cements, through proper selection and handling. Practitioners should be aware of the point at which excess cement may easily be removed for a given cement, and a thorough check should be made to identify any residual cement and remove it before the patient leaves the office. By using modern technology and tools available in dentistry, it is possible to eliminate the threat posed by residual cement.
References
Bonsor SJ, Pearson GJ. A clinical guide to applied dental materials. 2013. Amsterdam: Elsevier/Churchill Livingstone.
Carson J. The pros and cons of bonding or cement restoration. Available at: http://www.speareducation.com/ spear-review/tag/cementation/ Accessed 15 October, 2014.
Chun Z, White S. Mechanical properties of dental luting cements. Journal of Prosthetic Dentistry. 1999;81(5): 597–609.
Farah J Powers J. Resin Cements. The Dental Advisor. 2003.
Leevailoj C, Platt JA, Cochran MA, Moore BK. In vitro study of fracture incidence and compressive fracture load of all-ceramic crowns cemented with resin-modified glass ionomer and other luting agents. Journal of Prosthetic Dentistry. 1998;80(6):699-707.
Lohbauer U. Dental Glass Ionomer Cements as Permanent Filling Materials: Properties, Limitations and Future Trends. Materials. 2012;3:76-96.
Lowe R.A. Dental cements: an Overview. International Dentistry. 2011;2(2):6-17.
Pameijer CH. A Review of Luting Agents. International Journal of Dentistry. 2012;10:1-7.
Ramaraju SD, Krishna SA, Ramaraju VA, Raju M. A Review of Conventional and Contemporary Luting Agents Used in Dentistry. American Journal of Materials Science and Engineering. 2014; 2(3):28-35.
Wingrove S. Peri-implant therapy for the dental hygienist: Clinical guide to maintenance and disease complications. 2013. Ames, Iowa: Wiley-Blackwell.
Yu H, Zheng M, Cheng H. Proper selection of contemporary dental cements. Oral Health Dental Management. 2014;13(1):54-49.
