Dear Dr. DiTolla,

I just got off the phone with a doctor who has a patient who is allergic to metal. In 2006, he had a zirconia crown made: Lava™ (3M™ ESPE™; St. Paul, Minn.). But the crown keeps falling off. He used Variolink^® (Ivoclar Vivadent; Amherst, N.Y.) to reseat it in 2008. I don’t think Variolink works with zirconia. What should I recommend he use to reseat the crown? Should he prepare the crown in any special way?

– Scott Bigler, CDT, MDT
Tustin, Calif.

Dear Scott,

A couple of things: No need for him to prepare it in any special way, except, of course: The shorter the prep, the more parallel the walls need to be. Some parallel retention boxes and/or grooves are helpful as well, especially on the mesial and distal to resist dislodgement in patients who are bruxers.

Second, I would not use Variolink for this case. Instead, I would use a straight self-curing resin cement, such as PANAVIA™ (Kuraray Co. Ltd.; New York, N.Y.) for this indication.

Lastly, have him coat the inside of the crown with Z-PRIME™ Plus from Bisco (Schaumburg, Ill.). Our initial testing and my personal experience is showing this material to be a good zirconia silanating agent.

Hope that helps!

– Mike

Dear Dr. DiTolla,

WHERE do you get the “six feet, the recommended distance to keep your toothbrush from your toilet…” statistic used in “By the Numbers” (Chairside^®, Winter 2011)? This kind of stupid, non-science fact gets repeated in silly consumer magazines, but to find it in your magazine is just plain irresponsible. Just because you heard it or read it does not make it a fact. And you are continuing the illusion.

If toilet flushing was spreading bacteria in a 6-foot radius, don’t you think there would be other issues? Airborne illnesses, since you have to stand there to activate the flush. Countertops would be thick with fecal bacteria, but they AREN’T!

Show me some literature to back up what you’re printing, or you lose credibility.

– James C. Alder, DMD
Portland, Ore.

Dear James,

I applaud your inner skeptic, and your logic is persuasive. However, microbiologist Dr. Charles Gerba, member of the Department of Virology and Epidemiology at Baylor College of Medicine from 1974 to 1981, does make a strong, science-based appeal to reason concerning the transmission of pathogens through the environment. “Large numbers of bacteria and viruses when seeded into household toilets were shown to remain in the bowl after flushing,” Gerba’s research shows, “due to the adsorption of the organisms to the porcelain surfaces of the bowl, with gradual elution occurring after each flush.”

The “MythBusters” TV show tried and was unable to disprove that particles from a flushed toilet could travel to a toothbrush and, based on the research of Gerba and others, you may wish to reconsider leaving your toothbrush exposed. “The detection of bacteria and viruses falling out onto surfaces in bathrooms after flushing,” according to Gerba, “indicated that they remain airborne long enough to settle on surfaces throughout the bathroom. Thus, there is a possibility that a person may acquire an infection from an aerosol produced by a toilet.” (Emphasis added.) Source: Gerba CP, et al. Microbiological hazards of household toilets: droplet production and the fate of residual organisms. Appl Microbiol. 1975 Aug;30(2):229-37.

Researchers at Aston University, Department of Pharmaceutical and Biological Sciences, in the UK found that “large numbers of micro-organisms persisted on the toilet bowl surface and in the bowl water which were disseminated into the air by further flushes.” According to Dr. John Barker, the study’s lead author, “individuals may be unaware of the risk of air-borne dissemination of microbes when flushing the toilet and the consequent surface contamination that may spread infection within the household, via direct surface-to-hand-to-mouth contact. Some enteric viruses could persist in the air after toilet flushing and infection may be acquired after inhalation and swallowing.” Source: Barker J, et al. The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet. J Appl Microbiol. 2005;99(2):339-47.

In another study, Barker found that, “Salmonella bacteria persisted in the biofilm material found under the recess of the toilet bowl rim, which was difficult to remove with household toilet cleaners. In two homes Salmonella bacteria became incorporated in the scaly biofilm adhering to the toilet bowl surface below the water line. Salmonella enteritidis persisted in one toilet for four weeks after the diarrhoea had stopped, despite the use of cleaning fluids…. The results suggest that during diarrhoeal illness, there is considerable risk of spread of Salmonella infection to other family members via the environment, including contaminated hands and surfaces in the toilet area.” Source: Barker J, et al. Survival of Salmonella in bathrooms and toilets in domestic homes following salmonellosis. J Appl Microbiol. 2000 Jul;89(1):137-44.

– Mike

Dear Dr. DiTolla,

I know IPS e.max^® (Ivoclar Vivadent) is one of your favorite restorations, and it is mine as well. I have been using it in full contour for posteriors for many years now with great success. Glidewell does some of my crowns, and another lab does some of my high-end stuff. I have been getting more into IPS e.max for anteriors as of late and was wondering if, for anterior cases, you do the cutback technique, and/or has Glidewell seen any issues, like chipping, with those? The reason I ask is my other lab likes to do the cutback technique for anterior cases to make them look more lifelike — in fact, I just had mine redone. But I did a case the other day and I saw some chipping at the edge not too long afterward and got concerned; however, the guy was fairly tough on his teeth. Maybe the answer is just case selection. Thanks.

– Jeff Schultz, DDS
Bellaire, Texas

Dear Jeff,

Great question! We cut back and layer all of our anterior IPS e.max here at Glidewell, as well. We try not to wrap the incisal edge with this layer, so that the patient’s lower teeth are in contact with the monolithic portion of the crown during protrusive movements.

That being said, there is still more of a chance that bilayered IPS e.max (80 MPa flexural strength) could chip as opposed to monolithic IPS e.max (400 MPa flexural strength). We do make monolithic IPS e.max in the anterior for dentists who request it.

I agree with you that it comes down to case selection. If I am doing some anterior crowns on a patient without much anterior wear, I will typically select cut-back and layered IPS e.max. If the patient shows a fair amount of wear, or has broken an existing restoration, I am now using BruxZir^® Solid Zirconia as my restoration of choice. The esthetics of BruxZir haven’t quite caught up with IPS e.max yet, but at three times the strength of IPS e.max, it’s nice to know that with BruxZir you’re placing the strongest restoration available.

Hope that helps!

– Mike