Ask Dr. Christensen

In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers. If you would like to submit a question to Dr. Christensen, please send an e-mail to [email protected].

For more on this topic, go to www.dentaleconomics.com and search using the following key words: restorative dentists, flowable resins, composites, Dr. Gordon Christensen.

Q I see advertisements for many flowable resins. The ads contain optimistic claims from their manufacturers. However, I have also seen articles stressing the numerous negative characteristics attributed to these materials. What are their main uses and advantages, and are some brands better than others? A In spite of some significant proven negative characteristics for flowable resin-based composites, they are used by most restorative dentists. The “flowable” characteristic that these materials possess is their obvious positive characteristic. Dentists have welcomed the ease of use of these materials. The ability to place a small canula into a tooth preparation and merely express the material into any location is a highly positive characteristic.

However, although flow and ease of use are desirable flowable characteristics, there are some well-known negative characteristics that should be recognized and dealt with when using these materials. The positive and negative characteristics of the current generation of flowables are:

Desirable characteristics

▲ Flow is the main desirable characteristic.

▲ Flowables are easier to use than putty forms of resin-based composite, which can be difficult to place in some limited access preparations. Resins with more viscosity often have air bubbles when placed in areas of difficult access, and flowables help to reduce this challenge.

Fig. 1 — The two premolar teeth have minimal carious lesions on their proximal surfaces. Many dentists use flowable resin in the depth of the box forms before placing conventional fully-filled resin-based composite. The flowable resin helps to ensure that the line and point angles are filled.

▲ Finishing of flowable resins can be easier than putty resin-based composites. If flowable resin is placed carefully and precisely where it is needed, flowables can require minimal effort and time when finishing.

Fig. 2 — The minimally carious premolars shown in Fig. 1 were bleached and tooth preparations were made. They received a self-etching primer and bond, followed by a slight amount of flowable in the depth of the box form. This was followed by a conventional restorative resin.

Undesirable characteristics

▼ Flowables have higher wear than more fully filled composites. Because of minimal filler content,

Fig. 3 — A deeply carious molar with a loose amalgam on the distal surface.practitioners should expect to see flowables exhibiting much higher wear when compared to conventional fully-filled restorative resins.

▼ The lower filler content of flowables causes lower overall strength when compared to conventional restorative resins.

▼ Flowables have higher expansion and contraction with heat and cold than conventional restorative resins.

▼ Polymerization shrinkage and the resultant polymerization stress in tooth preparations caused by most flowables are two to three times more than values for conventional restorative resins.

▼ Flowable resins have the same potential to cause postoperative tooth sensitivity as fully-filled resin-based composites, and they must have a bonding agent placed between them and the dentin, thus sealing the dentin surface to reduce or eliminate postoperative tooth sensitivity.

Clinical situations where flowables are indicated

A “liner” or “wetting agent” in tooth preparations that is planned to receive conventional restorative resin — This is one of the more popular uses of flowables. In surveys done by CLINICIANS REPORT, more than half of the respondents reported they use flowables in the box-forms of Class II resins and in other tooth preparations before placing the conventional restorative resin (see Figs. 1-6).

Repairing provisional restorations — When a bisacryl provisional restoration has a broken margin or a hole or other defect, flowable resin makes adequate repairs. Flowables are easy to place in these situations, can be light-cured rapidly, and have moderate strength, which is sufficient to provide adequate service potential for a few days or weeks.

Enamel hypoplasia — Occasionally, “white spots” on tooth surfaces are unsightly, and patients want to eliminate them or have them blend better with surrounding tooth structure. It is easy to remove the superficial white spots with a rough diamond, then acid-etch the surface of the tooth preparation, which is usually enamel only, and place some flowable resin into the location. The restorations need only minimal finishing and serve well for several years. The most appropriate brands of flowable in this situation will be discussed later in this article.

Unsightly, stained age cracks on anterior teeth — Mature patients often have cracks in their teeth that

Fig. 4 — The depth of the caries is evident. A cariostatic liner is highly desirable instead of flowable resin.have accumulated stains over a lifetime of eating and drinking pigmented foods and liquids. After bleaching the stains and waiting a few days for the oxygen to dissipate out of the enamel, a slot can be cut in the tooth to remove the crack and stain with a pointed diamond. The correct color of flowable resin is then placed on the acid-etched enamel. Although the restoration does not provide long-term service because of marginal staining and wear, it will serve well for a few years.

Repair of defective restoration margins in esthetic areas — Large Class III or IV restorations accumulate stains on margins after a few years. If the stained margins are in esthetically critical areas, patients want them repaired. When these situations occur, dentists may prefer not to remove the entire restoration. The stains can be removed by cutting a slot in the discolored margin, and placing an appropriate color of flowable resin in the margin. Again, the repair is only an interim restoration, but patients often prefer this more conservative approach to extensive removal and replacement of the old restoration.

Sealants — The physical composition of flowable resins is similar to that of sealants and resin

Fig. 5 — Resin-modified glass ionomer is a better choice than flowable in this tooth because of the deep carious involvement. Fuji Lining Cement LC from GC America or Vitrebond from 3M ESPE are indicated directly on the dentin surface in such situations.

cements. Some dentists use flowable resins as sealants or resin cements, thus eliminating the need to purchase another brand of resin for sealants.

Small tooth preparations in areas of low-wear potential — Frequently, small tooth defects are encountered in areas of expected low-wear potential. Although more wear is expected to occur on the flowable materials during service than if conventional resins were used, the ease of placement of flowables may outweigh their undesirable characteristics in these situations. However, placement of flowables in areas of known high wear, such as worn incisal edges of anterior teeth, is not a logical use of these high-wear materials.

Brands of flowables compared

The same characteristics that are present in fully-filled restorative resins are important in flowable resins. They include:

Filler particle size — If the flowable is being used internally in a restoration (which is the most common use of flowables), the potential smoothness of the material during service is not an important factor, and any brand of flowable can be used in thin increments. Thick layers of flowable resin increase polymerization shrinkage. For such situations, clinicians should use the flowable brand that they are

Fig. 6 — The large finished restoration was not sensitive after placement, and the resin-modified glass ionomer will continue to re-lease fluoride into the tooth.

using for other flowable restoration needs.

Potential retention of smoothness after a period of service in the mouth — As with conventional resins, some brands remain smooth during service but most do not because of their large filler-particle size. Some of the flowables that remain smooth during service are: Venus Diamond Flow from Heraeus; Estelite® Sigma Quick Flowable from Tokuyama; Filtek® Supreme Plus Flowable from 3M ESPE; Heliomolar flow from Ivoclar Vivadent;and Renamel Microfill from Cosmedent®. These brands are desirable for those situations where superficial smoothness and stain resistance during service are desirable.

Radiopacity — When flowable is placed in the box form of Class II restorations, high radiopacity is mandatory. Placing a radiolucent flowable in a box form mimics dental caries in subsequent radiographs. Most flowables have moderate radiopacity. Among the most radiopaque is Tetric Flow from Ivoclar Vivadent.

Shrinkage on polymerization — One of the most undesirable characteristics of flowables is the extreme polymerization shrinkage of some brands. This characteristic should motivate dentists to place flowables in very thin increments (0.5 mm or less). Placement in such thin layers minimizes the resultant stress in the restoration when compared to using flowable resin in thick layers. In recent CLINICIANS REPORT research, SureFil® SDR® Flow from DENTSPLY Caulk had the lowest polymerization shrinkage and shrinkage stress of all brands tested.

A summary of flowable resins

Flowable resin-based composites are good because they flow, but they are bad when considering almost all of their other characteristics. Some remain smooth and can be used when longer-term smoothness is a requirement. Some are highly radiopaque and should be used when liners are placed under some conventional resin restorations. Some have lower polymerization shrinkage and are best when using the resin in larger increments. In other words, selection of flowables should be based on your primary uses for the materials, and it is likely that you will need to use more than one brand. The specific brands suggested in my answer to your question will satisfy specific needs.

Flowable resins are very similar to commercially available sealants. Recently, I produced a DVD that will change most of your previous beliefs and techniques concerning sealants and preventive restorations. Viewing this presentation will improve the longevity of your sealants and help prevent the ongoing dental caries observed under most sealants. Call PCC at (800) 223-6569 or go to www.pccdental.com for more details about V5143, “Sealants and Preventive Resin Restorations — When & How?”

Dr. Christensen is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization initiated in 1981 for dental professionals. Dr. Christensen is a cofounder (with his wife, Rella) and senior consultant of CLINICIANS REPORT (formerly Clinical Research Associates), which since 1976 has conducted research in all areas of dentistry.