October 8, 2021
by Nathaniel C. Lawson, DMD PhD; Bushra Nizami, BDS, Krisha Shah BDS
Cleaning excess cement after cementation of a crown is a tedious but important clinical procedure. Failure to remove excess cement can lead to plaque accumulation, gingival inflammation and possibly even bone loss.1 Removal of cement is even more difficult when using resin cement. A recent Practice Based Research Network study reported that almost 40 percent of single unit crowns were bonded with resin cement.2
Cleaning resin cement can occur either before curing, after tack curing or after complete curing. An American Dental Association Clinical Evaluator Panel survey reported that 21 percent of dentists clean some uncured cement, 85 percent of dentists clean some tack cured cement, and 28 percent of dentists clean some fully cured cement.3 These results suggest that most dentist undergo the challenging procedure of cleaning tack or fully cured resin cement.
The methods used to perform this task can vary. A dental scaler or surgical blade can be used to scrape excess cement, however, these tools have limited access to interproximal areas where crown margins are often the most subgingivally located. Rotary instruments can also be used to remove excess cement, however, these instruments must be carefully oriented so as not to gouge the root surface during use and also have limited access to interproximal areas. Perhaps the easiest, safest and most cost-efficient method to remove excess cement is with the use of floss.
Dental floss is available in several different varieties. Perhaps the most common type of floss is nylon floss. This floss is composed of strands of nylon fibers. A disadvantage of nylon floss is that it can shred during use. Shredding of the floss is inconvenient due to the need to obtain a new piece of floss and also need to retrieve remnant pieces of nylon fibers from between the teeth.
Thicker nylon floss is often referred to as dental tape. Dental tape has additional nylon fibers which makes it stronger and provides additional surface area for cleaning. But the thickness of dental tape makes it more difficult to slide between the contact point.
Another common type of floss is polytetrafluoroethylene (PTFE) floss. This floss is manufactured as a thin, flat sheet. The thinness of the floss allows it to more easily slide in between contacts. A clinical trial confirmed that it requires less force to place PTFE floss interproximally than nylon floss.4 The disadvantage of PTFE floss is that it will often snap during use.
A new type of ultra-high molecular-weight polyethylene (UHMWPE) is available with the commercial name Gorilla Floss (Dental Savings Club). The fibers which are used to fabricate this floss are fabricated in a gel spinning process in which the fibers are drawn, heated, elongated, and cooled. This fabrication process allows molecular alignment, high crystallization, and low density of the polymer used in the fibers. The long molecular chains are responsible for the strength of the UHMWPE fibers. The same fibers used for this floss are also used for other industrial applications, such as body armor, anchor ropes, and paragliding lines.
In order to compare the properties of several different varieties of floss, representative brands were chosen from each category: nylon floss, dental tape, PTFE tape, and UHMWPE floss. The floss samples were obtained from commercial vendors and evaluated at the UAB School of Dentistry.
A custom test was designed to measure the strength of floss. A metal loop was affixed to the base of a universal testing machine. A second loop was affixed to the crosshead of the universal testing machine at a distance of 300mm from the base loop. The crosshead was attached to a load sensor. A length of floss was tied snugly to both the lower and upper loop using four square knots to minimize slippage. The floss was then loaded in tension at a rate of 10mm/min until it broke. The maximum force prior to failure was recorded. Three pieces of floss were used for each type of floss. The average and standard deviation for each type of floss is listed in Table 1.
The thickness of each type of floss was then measured. A representative piece of floss was placed on the stage of a digital light microscope. It was pulled taught with finger pressure and secured with tape. A section of floss was observed with 100x magnification and the thickness of the floss at five different points was measured with image analysis software. The average thickness is listed in Table 1.
Evaluation of the strength of different floss reveals that the UHMWPE floss fractured at over 2x the strength of dental tape, over 3x the strength of nylon tape and over 6x the strength of PTFE tape. The clinical advantage for a floss with this strength would be its ability to remove tenacious pieces of cured resin cement without breaking. Additionally, the strength of the floss would allow insertion of the floss into interproximal areas without snapping the floss. This evaluation also confirmed that nylon floss is stronger than PTFE floss and that dental tape is stronger than nylon floss.
The thickness of the UHMWPE floss (Gorilla Floss-Dental Savings Club) is slightly less than nylon floss and half as thick as dental tape. The PTFE floss is flat and thin. When flossing through contacts. The thin edge will likely orient itself to pass through the contact first. The thickness of the floss is relevant for its ability to pass through a contact. The UHWMPE (Gorilla Floss-Dental
Savings Club) floss is advantageous as it is both thin and strong which should allow it to pass through contacts without snapping.
Aside from the strength and thinness of the UHMWPE floss, another advantage of the floss is its ability to remain rigid when straightened. Most floss will go limp once straightened as there is no resistance to the force of gravity. The UHMWPE floss can remain relatively sturdy when pulled straight such that it can be threaded through the gingival embrasure without the use of a floss threader. This technique will not work if the embrasure is significantly occluded with cured cement or soft tissue. However, often a path can be cleared for the floss such that it can be passed through the contact.
In summary, clean-up of excess cement is a vital but tedious clinical procedure performed in most dental offices. The simplest and most cost-effective method to remove cement, particularly in interproximal spaces, is using dental floss. There are a variety of floss types including nylon, dental tape, PTFE and UHMWPE floss. Nylon floss has a tendency to shred, dental tape may be too thick to slide interproximally, and PTFE floss often snaps due to lack of strength. UHMWPE floss UHWMPE (Gorilla Floss-Dental Savings Club) is strong, relatively thin, and can remain rigid when straightened. For those reasons, it is a very useful tool when cleaning excess resin cement.
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