Fleeting Glory

When a patient comes in with a hole in their tooth the size of Montana, it’s a pretty good bet that a restorative prosthesis, such as a crown, bridge or implant, is in his or her future. The catch is that unless the office has a chairside computeraided design/computer-automated manufacturing (CAD/CAM) setup that can mill prosthetics while the patient waits, it could take up to a couple of weeks for the final restoration to arrive from the lab. Rather than let the patient navigate life in the interim with a gap in his or her smile, the dentist is likely to place a provisional (or temporary) restoration.

Temporary restorations not only fill the gap to remedy any esthetic or chewing issues, but they also provide stability to the prepped tooth, while protecting it from thermal shocks, infection and chemical irritants. Of course, these stand-ins — often metal or acrylic — don’t stay put through wishful thinking. They must be luted with a cement material that offers many of the same properties as permanent cement, but with some special characteristics.

Like their permanent counterparts, temporary cements must create good marginal seals and keep provisional restorations in place, but without causing sensitivity. And they serve other functions, too. They are also used in seating implants, as temporary fillings in endodontic procedures, and in provisional placement of final indirect restorations to confirm correct fit. But while permanent cements are expected to stick around, well, permanently, temporary cements are expected to let go without a fuss. “Obviously, we want a cement that will provide adequate retention, but one that’s also easily removed on the day of definitive cementation,” says David Hornbrook, DDS, FAACD, who operates an esthetic dental practice in La Mesa, Calif. But what kinds of cements can meet such seemingly conflicting demands?

IMPLANT CEMENTATION

Because they provide what many see as a preferable solution to prostheses such as dentures or bridges, the use of implants has been gaining traction in dental offices across the country. Nevertheless, many clinicians are more comfortable placing restorative crowns on implant abutments with temporary rather than permanent cement. By using temporary cement, should there ever be an issue (such as an abutment or a screw coming loose), the clinician can easily access the problem without destroying the restorative prosthesis.

Cements used with implants do not necessarily need to follow the same parameters as those used with natural dentition, since sensitivity is not a factor. As with conventional restorations, however, cleanup is critical to avoid periimplantitis. Consequently, cement visibility is paramount. According to William C. Martin, DMD, MS, a diplomate of the American Board of Prosthodontists, and an associate professor and director of the Center for Implant Dentistry in the Department of Oral and Maxillofacial Surgery at the University of Florida, College of Dentistry in Gainesville, “When working with dental implants, we prefer to use cements that contain zinc oxide (noneugenol or eugenol), as these have been shown to exhibit radiopacity, which allows for detection of residual excess cement.”

WITH OR WITHOUT CLOVES?

There are two main categories of cements used in provisional applications: zinc-oxide eugenol, and noneugenol-containing resin cements. Zinc-oxide eugenol (perhaps better known by the acronym ZOE) has been around for years. It is easily mixed and emanates the scent of cloves — which is no surprise as eugenol is clove oil. Eugenol-based cements offer some protection against sensitivity, though, ironically, they also sometimes cause inflammation. In addition, a number of clinicians worry about using them if the ultimate intent is to place the final restoration with a resin-based cement. “Since every restoration I place is ‘bonded’ into place,” notes Hornbrook, “eugenol-containing provisional cements would be a compromise for me.”

But while there is evidence that eugenol can interfere with the polymerization of composite resin cements, some experts assert this may only be the case if the permanent restoration is placed prior to the typical two weeks that the temporary is being worn. “It seems as though eugenol is quickly tied up as the provisional cement hardens,” explains John O. Burgess, DDS, MS, assistant dean at the University of Alabama in Birmingham School of Dentistry. “As long as the residue of provisional cement is thoroughly removed from the prepped tooth after the temporary prosthesis is removed, there is no interference in the polymerization of the permanent resin cement — and no effect on the bond of the resin cement.”

Nonetheless, Burgess notes several benefits of noneugenol-containing resin cements. These agents were developed to correspond with innovations in restorative materials. “Provisional cements,” he says, “have evolved from zinc oxide and eugenol two-paste systems to resin cements that adhere to acrylic or bis-acryl composite provisionals. And when most of the cement stays with the provisional rather than on the prepped tooth, it speeds cleanup. Retention of the provisional restoration has also increased with resin cements — and this decreases the number of recementation procedures needed. Finally, some materials contain desensitizing agents, which may reduce issues with post-operative sensitivity.”

William C. Martin, DMD, MS, a diplomate of the American Board of Prosthodontists, and an associate professor and director of the Center for Implant Dentistry in the Department of Oral and Maxillofacial Surgery at the University of Florida, College of Dentistry in Gainesville, agrees. “Noneugenol cements have served our clinical purposes well,” he says. “This approach reduces the chances of experiencing situations in which bonding the definitive restorations could be compromised. In cases in which sensitivity becomes an issue, we utilize noneugenol or resin temporary cements that contain potassium nitrate.”

Aside from its uses in fireworks and rocket propulsion, potassium nitrate is also a desensitizing agent that, when added to noneugenol luting materials, can help calm post-operative sensitivity. Noneugenol compounds may be zinc oxide, dual-curing composite resin materials, or, if more rigidity is required for enhanced retention, polycarboxylates are another viable choice. Glass ionomers are also a favorite among some clinicians due to their fluoride-releasing ability.

Although reported to have more of a tendency toward microleakage, higher film thickness and less flowability than ZOE, non – eugenol formulas are said to be stronger than ZOE. They are also more retentive, while offering longer working times and a degree of translucency. But, mixing quality and product ratio can play a significant role in cementation success. To this end, the dispensing method is another important element to consider for both reps and clinicians.

TERMS TO LEARN

  • Bis-acryl: Also known as bis-acrylic, this is a type of provisional composite resin that demonstrates high esthetics and low shrinkage
  • Luting Cement: A material designed to retain a restoration through mechanical gap filling, rather than through adhesive bonding
  • Microleakage: If marginal seals are inadequate, tiny amounts of bacteria, fluids and debris can infiltrate to wreak havoc between the restoration and tooth, often leading to restoration failure
  • Polycarboxylate: A dental cement that is a combination of zinc oxide powder and a liquid polycarboxylic acid

DELIVERY SYSTEMS

Most dental cements are two-part affairs that involve the mixing of a base with a catalyst. Whereas cements used to be squeezed out of two tubes and triturated or mixed together with a spatula on a pad or glass slab, the more current delivery systems help ensure better consistency and cut down on wasted material through more precise measuring of compounds.

“Paste-paste” is manufacturer lingo for a system involving two tubes joined into one double-barreled cartridge with two syringe tips. Upon depression of the plunger, precise amounts of compound are expressed from both tubes simultaneously, though they must still be mixed by hand.

The paste-paste automix systems go one better, expressing both base and catalyst through a single mixing tip. “Mixing is important to provide consistent mixes with uniform setting times,” reports Burgess. “A delivery system with self-mixing tips allows the cement to be mixed and injected directly into the provisional crown or fixed partial denture, and speeds the cementing process.”

In fact, all of those with whom we spoke were enthusiastic about automix systems. Hornbrook reports that when placing a provisional cement that needs to be mixed, he prefers one that is mixed in the delivery system (rather than expressed onto a pad and mixed manually). “Most of the better provisional cements on the market today,” he says, “utilize dual-barrel catalyst/base syringes with mixing tips. Some even offer small-orifice intraoral tips so I can inject the cement into the preparation if desired, rather than place it on the provisional itself. The more options I have, the more likely I am to use that particular cement.”

But of all the requirements that the ideal provisional cement must fulfill, easy cleanup ranks high on the list.

PRIMARY CONSIDERATIONS

According to the key opinion leaders we interviewed, cleanup is a huge factor when choosing provisional cements. Because resin-based provisional cements stick to the restoration rather than the tooth upon removal, clinicians view these materials as a tremendous boon. “Remnants of provisional cement can lead to a contaminated surface that is very difficult to clean off,” explains Hornbrook. “With more dentists using self-etching resin cements when placing definitive restorations, any surface contamination is going to be a huge negative factor.”

Leftover residue of provisional cement can adversely affect bond and polymerization of resin-based permanent cements, and may cause the final restoration to fall off. Cleanup of excess cement from the margins is also critical to prevent biofilm buildup and gingival irritation that can result from residual cement.

Aside from cleanup, however, a host of other considerations come into play when choosing provisional cements. Burgess says that among other top considerations he weighs are cost; ease of excess removal immediately after cementation; setting time; enduring retention; adequate seal; and easy removal of the temporary.

And there is usually more than one type of cement that can address the various cases that land in the dentist’s chair. Burgess, for example, says he likes two cements: one that provides high retention when needed for short or tapered preparations; and one that offers low retention for long, parallel-sided preparations.

“When selecting an ideal temporary cement,” notes Martin, “one should first consider its intended use (natural tooth versus dental implant) and the resulting definitive restoration, such as metal-ceramic versus all ceramic, and what type of ceramic (feldspathic, lithium disilicate or zirconia). An ideal temporary cement for natural teeth would be biocompatible and offer mechanical advantages for retention (including low film thickness, and high tensile and compressive strengths). It would likewise deliver esthetic advantages and have working and setting times that allow for seating of the restoration and removal of residual material in a timely fashion.”

POINT of SALE

  • PROVISIONAL CEMENTS

  • Temporary cements allow provisional restorations to be placed and worn while the patient waits for permanent restorations to arrive from the lab.
  • Many clinicians favor the use of provisional cement when placing restorative crowns on implant abutments because if something goes wrong, it will be easy to access the implant underneath.
  • Temporary cements are often used with initial placement of permanent restorations to help ensure correct fit.
  • Even though clinicians are bound to have favorite provisional materials, because every case is different, it’s beneficial for them to have a number of temporary cement choices at their disposal.

PROVISIONAL FUTURE

When asked what influences chairside CAD/CAM systems will have on the use of provisional restorations and temporary cements, our experts all share the observation that, at this point, offices equipped with CAD/CAM technology are in the minority. As Burgess points out, “These systems have been available for more than 20 years, but are found in approximately 12% of dental offices, so they are not being rapidly adopted as of yet.” He feels that as buy-in of CAD/CAM systems increases, the use of provisional restorations — as well as provisional cements — will decline.

Hornbrook, on the other hand, notes, “Since the number of clinicians using chairside CAD/CAM units is still small, I don’t think that this will affect the research and development of better provisional cements. Even many of the CAD/CAM users are still prepping and provisionalizing, and having their patients back for a second visit — so they will still need good provisional cements.”

Martin believes that CAD/CAM technology has limited impact on the full scope of restorative dentistry. “In my opinion,” he says, “the need for interim restorations that require the use of temporary cements will be common in our practices for many years to come.”

Considering the number of variables involved in choosing temporary cements — and because this is likely to remain the case for some time — this is precisely the type of scenario that begs for the expertise of a well-informed sales executive. After all, the selection of the right type of provisional cement can play a huge role in whether or not the temporary stays put or falls into the patient’s spaghetti.

At least one thing is certain: When it comes to provisional cements, one size does not fit all. The wise practitioner will have a number of formulations on hand to tackle whatever a restorative case calls for. And the wise sales professional will ensure that his or her customers are equipped with everything they need to place successful provisional restorations — however fleeting they may be.

BONUS WEB CONTENT : VARIABLES AFFECTING CEMENT CHOICE

  • How long the temporary is expected to remain in place
  • Area of restoration
  • Solubility and reaction to moisture
  • Mechanical and retentive properties
  • Whether retentive features have been created in the preparation
  • How the material is dispensed
  • Ease of handling
  • Mixing time
  • Working time
  • Setting time
  • Curing time
  • How it’s cured
  • Ambient temperature and humidity
  • Radiopacity
  • Desensitizing capabilities
  • Biocompatibility
  • Compatibility with intended permanent cement or restoration in the case of implants
  • Composition of the permanent cement
  • Esthetic considerations
  • Ease of cleanup
MENTOR August 2013, 4(8): 24–27, 29.

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