Newer isn’t always better

Nov. 1, 2005
Since technology generally improves in a field, it is quite reasonable to assume that newer is generally better.

Since technology generally improves in a field, it is quite reasonable to assume that newer is generally better. With cosmetic dental products, “better” frequently means easier to use. This is particularly true for dentists who want to enter the booming cosmetic market without investing much time and money learning specialized skills. But easier is not always better when the gain in convenience is offset by a sacrifice in the quality of the outcome. With regard to the newest generations of dental adhesives, quality has been the price of simplicity, and newer is not better, according to current research. The surprisingly good news is that the best of the older adhesives, known as fourth-generation systems, are very effective and unproblematic if one follows some simple procedures.

Introduced in the early ’90s, fourth-generation adhesives are considered the first “universal” systems because they bond to tooth surfaces regardless of how the composite resins are cured (e.g., light-cured, dual-cured, or by means of a chemical reaction). Dentists who use the products must follow a series of steps: they clean the teeth, etch with phosphoric acid, apply primer, and apply adhesive. After the direct composites or lab-fabricated restorations are placed, dentists clean, adjust the bite, finish, and polish.

Although universal adhesives were a breakthrough when introduced, dentists often find the multistage process cumbersome and intimidating - particularly the etching step since over-etching can result in patients having extremely sensitive teeth. Until recently, many dentists avoided the hassle by not offering complicated restorative services. Manufacturers responded by developing overly simplified products, such as the new self-etching systems that consolidate the etching agent, primer, adhesive, and sometimes even the resin into a single bottle or syringe. Self-etching systems have become popular, not only because of the reduced number of steps, but because the systems are specifically designed to prevent over-etching. Therefore, dentists need not take special care to avoid patient sensitivity.

Although self-etching systems are easier to use and do help prevent over-etching, does this make them better? Not from the standpoint of patient results.

First, dentists using fourth-generation systems can easily prevent patient sensitivity. Etching creates a sponge-like scaffolding in the tooth surface that the primer and adhesive should penetrate and reinforce. When the etch goes too deep, it leaves a level of scaffolding that the primer and adhesive cannot reach. Sensitivity arises due to a pressure discrepancy between reinforced and unreinforced levels of scaffolding. If one follows a few simple guidelines, uses the proper concentration of phosphoric acid, and leaves the acid on enamel no more than 15 seconds and on dentin no more than 10 seconds, the etch will produce the right depth of scaffolding, and sensitivity will not occur.

More importantly, current research indicates that self-etching systems fall short of fourth-generation adhesives in terms of the quality of patient outcomes. Reality ( recently published the results of relevant tests conducted by its research laboratory. The lab compared the immediate and 24-hour bond strengths and microleakage scores of self-etchers with OptiBond FL, the popular fourth-generation standby. Across the board, OptiBond FL performed significantly better.

Preliminary studies indicate a general consensus about self-etching systems. Several colleagues I have talked with suggest that self-etchers are necessarily more hydrophilic than the older hydrophobic adhesives. Thus, they are less resistant to bond-degrading hydrolysis. Others note that older systems allow for rinsing after the separate etching step, which facilitates a stronger bond. Self-etchers do not entirely remove smear plugs. This could weaken the bond. I suspect that both of these explanations play a role in possible performance issues and concerns about self-etching.

If future studies support the preliminary research, then the only apparent advantage of self-etching systems is convenience. But what sort of convenience? The new adhesives are less complicated and easier to apply than the multibottle systems. That is an indisputable benefit. But does this short-term benefit really outweigh the inconvenience for both the dentist and patient of having to redo premature failing restorations? When a restoration breaks or pops off because of a poor bond, or turns dark because of microleakage, everyone suffers. In my view, this type of inconvenience is far more severe than having to follow a multistep bonding procedure. The procedure is not terribly difficult; it works well if properly executed. And the more one practices, the easier it gets.

Dr. Christopher Pescatore lectures worldwide on topics such as state-of-the-art esthetic procedures, techniques, and materials. He holds a U.S. patent for a nonmetallic post system to restore endodontically treated teeth. He is the former clinical co-director and current featured speaker at the Las Vegas Institute for Advanced Dental Studies. He has a full time practice in Danville, Calif., dedicated exclusively to esthetic dentistry, and also serves as Clinical Director of MicroDental Laboratories. Contact him at (925) 362-9330, or at [email protected].