Still put it in a SMALL (a ml or so) amount of carrier oil. Oregano oil can irritate the mucous mebranes neat and it will be easier to get it around. Particularly between the teeth and into the gumline where the bad guys like to hide.
I woke up last night and remembered one of the actions of the oil (essential or otherwise) is to remove the film that builds up over teeth under which the anaerobic bacteria live and breed. Brushing and polishing ones teeth gets a lot of that off, flossing between the teeth some more but many surfaces and especially nooks and crannies get left to their own devices.
Maybe keep the swishing down to only a minute or so. enough to break the barrier but not enough to allow signficant degradation of your tooth cement.
Try a simple litmus test on your waste from swishing.
Now with respect to crowns and cement, what the 'professionals' know:
Effects of dietary oil contamination and absence of prophylaxis on orthodontic bonding
LS TanA, KK LewA and SL TohA2
A School of Postgraduate Dental Studies and, A2 Faculty of Engineering, National University of Singapore, Singapore
'The effect of contamination by dietary oil on acid etching has not been reported in the literature. If dietary oil adversely affects acid etching, then a decrease in bond strength is expected. ... It can therefore be concluded that the presence of dietary oil on the tooth surface does not adversely affect shear bond strength, even if prophylaxis is not carried out. Bond failures for all three groups occurred mainly at the tooth-adhesive interface. '
'DENTAL UNIT WATERLINE ANTIMICROBIAL AGENTS’ EFFECT ON DENTIN BOND STRENGTH
Conclusion. Dental professionals should be aware of potential interactions between dental unit waterline antimicrobial agents and dentin-bonding agents. Further research in this area is warranted, as the clinical implications are uncertain at this time.
Clinical Implications. Dental unit waterline antimicrobial agents may adversely affect dentin bonding strength'
Other research (I a not sure this is representative of an oral environment) on type of cement. Some were better than others.
'The disinfectants showed no significant influence on the loads required for debonding of Syntac Classic/Tetric Ceram, Clearfil Liner Bond 2V/Luxacore and OptiBond FL/Prodigy as compared to the controls. However, the use of disinfectants in the water supply of a dental unit decreased dentin bond strength in the specimens filled with Prime&Bond NT/Spectrum. Disinfectants in the water of dental unit waterlines may have an influence on dentin bonding, depending on the adhesive system used.'
But, maybe they weren't very good in the first place
'The long-term stability of resin-based composite to dentin bond strengths from single bond adhesives is questionable because after 2 yrs, bond strengths for two of the three tested dentin adhesives, OptiBond Solo and Syntac Single Component, were significantly lower than initial strengths.'
Here's a place to go and look at what they know about dental cement.
(BTW Crowns have a life expectancy of only 5 to 15 Years)