Porosity plagues composites

June 1, 2005
A few months ago, I cemented anterior Procera crowns with Bistite II DC on two separate cases.

By Michael Miller, DDS

A few months ago, I cemented anterior Procera crowns with Bistite II DC on two separate cases. Recently, the patients returned with debonded crowns. I did not use the ceramic primer on the crowns as recommended by the manufacturer. Previously, I used Panavia 21 without incident for many years. I used the clear shade. I light-cured all margins, placed the air barrier, waited three minutes, then removed cement, and finished. It was difficult to tell if cement remained on the tooth or crown, although it seemed to fail between cement and crown.

Our tests found that three minutes is not enough time to allow this cement to set completely before removing the excess. We found the clear shade requires about 4.5 minutes. This may be one reason for the failures. Another factor could be the lack of aggressive sandblasting inside the crowns. Since silane does not seem to help with alumina and zirconia-based ceramics, very aggressive sandblasting and/or using Rocatec may have helped if the failures were between the ceramic and the cement.

I just realized that bubbles are occurring in the proximal wall of some posterior composites. While preparing a crown next to a previously placed two-surface composite, I noted several bubbles in the composite. One bubble was adjacent to the enamel wall and decay had begun in that wall. Since we can’t see these surfaces, how do I know more of these restorations aren’t a problem? Is there a way to stop this? Do I need to switch composites?

Unfortunately, all composites are plagued with porosity. We have developed a new test to quantify this porosity, with the scores of all REALITY’S CHOICES in the various composite sections of the 2005 Annual Edition. After comparing the porosity scores of composites, you can then make an informed decision on which one you wish to use. The real answer, however, is for manufacturers to improve their quality control, and design better methods to produce these materials with less porosity.

Your evaluation of radiometers seems to conclude that, apart from the fact the LED Radiometer measures values greater than 1,000, you may also use the Optilux Radiometer across the board. Does this mean that if you have the Optilux Radiometer, and you are satisfied knowing that the light is 1,000+, then you don’t have to buy the LED Radiometer?

In addition, 3M ESPE claims that the Elipar FreeLight 2 can’t be used with the LED Radiometer because “they are not compatible.” This sounds strange. Demetron says its radiometer can be used for all LEDs. The FreeLight 2 has a built-in radiometer, but many dentists prefer a more exact comparable measurement. What is your opinion? Did you measure the Elipar FreeLight 2 with both radiometers? Is there any correlation between the reading on the radiometer and the indicator lights on the FreeLight 2?

Our comparison between the Optilux Radiometer and the LED Radiometer showed virtually the same readings, regardless of whether the light was a halogen or LED type. This means there is no compelling reason to buy the LED Radiometer if you have the Optilux Radiometer, assuming that you are not interested in a power reading greater than 1,000mW/cm2.

To answer the second question, we checked with a 3M ESPE spokesperson who does not know who said that the FreeLight 2 cannot be tested with the LED Radiometer. But, as far as its technical services department is concerned, there is no incompatibility between the two. Our tests of the FreeLight 2, using the LED Radiometer, shows a power output ranging from about 750mW/cm2 to 1,000mW/cm2 (as claimed by 3M ESPE). This is dependent on the individual unit. Regardless of the radiometer reading, all units illuminated the five lights of the built-in meter; however, the original FreeLight illuminates three lights of the built-in radiometer, thereby indicating 60 percent power. If 1,000mW/cm2 is 100 percent, then 60 percent should mean the original FreeLight has 600mW/cm2 of power. But testing on the LED Radiometer shows that it produces only 400mW/cm2 of power. Therefore, the built-in radiometer is probably not as accurate as the LED Radiometer.

How long do you recommend etching porcelain intraorally with HF acid? I have read etching time ranges from 90 seconds to 10 minutes. We use Ultradent’s 9 percent Buffered HF acid. Is it just as effective to microetch the margins, and totally skip the HF acid? Finally, does the addition of silane really do anything? I know there have been controversies regarding its use as well.

As indicated in the etchants section of the 2005 Annual Edition of REALITY, etching sandblasted porcelain can be done in one minute. If you don’t sandblast, then you probably want to etch three to four minutes. Ten minutes is definitely an overkill, and a waste of time. Sandblasting only also is effective. But our tests confirm a combination of the two procedures is best. Be aware that different ceramics may etch at different rates. We feel reasonably confident that our protocol should work for most porcelains. Our tests also confirm the efficacy of silane, and we continue to recommend its use.

I recently purchased an Air Techniques ScanX digital X-ray system. It is integrated with Eaglesoft software. I am very disappointed with the images. I have tried many solutions without success. Any suggestions would be appreciated.

ScanX has not participated in our evaluations for the last two years, so we can’t comment on its decline in image clarity. The best resolution that we have found is with Dexis.

How do you feel about using Maxcem for cementing CEREC restorations? Are there any long-term studies on bond strength?

Maxcem should be fine for full coverage, although we have not yet put it through full testing. We have concerns about partial coverage, and believe a more conventional resin cement would serve you better. To answer your second question, we are not aware of any long-term, bond-strength studies.

I have a patient who bleached a year ago. At that time, the incisal one-third of the upper incisors hyper-bleached. We presumed this was because she was using DayWhite for an hour without thoroughly removing the gel immediately before inserting her nightguard. The nightguard is approximately the boundary for the excessive bleaching. We resolved the dilemma by briefly etching the gingival two-thirds of these teeth, and applying DayWhite to these areas alone in-office for a few sessions. She has attempted to touch up without using the splint, and the same phenomenon is happening. Upon close examination, she has normal horizontal perichymata in the gingival two-thirds, and a glossy surface in the incisal one-third. One might think that the opposite effect would be happening - that the “rougher” surface would accept bleach more readily than the hard glossy surface. Do you have any insight into this phenomenon?

We have not seen any studies showing “rougher” areas bleaching more readily than hard glossy areas. While there is conflicting evidence concerning etching before bleaching, we do not endorse it due to the fact that etched enamel does not remineralize as quickly as once thought - it can take months for this to happen. Did you make the bleaching tray with a reservoir? If yes, then we advise making a new tray without a reservoir. If no, then you may want to switch bleaches to see if that helps. There is also a remineralizing paste from GC called Prospec MI Paste, which has recently come on the market. This paste is previewed in the FirstLook section of the 2005 Annual Edition of REALITY. You may want to try having the patient apply it after bleaching, but before inserting the splint.

Dr. Michael Miller is the publisher of REALITY and REALITY Now, the information source for esthetic dentistry. He is an international lecturer and a fellow of the American Academy of Cosmetic Dentistry, as well as a founding member. He maintains a private practice in Houston. For more information on REALITY and to receive a complimentary issue of his monthly update, REALITY Now, call (800) 544-4999 or visit www.realityesthetics.com.