I have been doing this for 4+ years. I have worked regularly in 4 offices and temped in over 30 additional offices during that time. In every one of them the hygiene column is booked from open to close the same as the doctors column.
(but RDHs dont work 5 to 6 days a week at one office, so they dont use as much of the utilities or staff as a dentist does)
The front office staff answers the phone, books the schedule, bills insurance, etc. for all patients in the office whether they are seeing the dentist or the hygienist for their appt.
(see above; if you have less hygiene appointments than dental appts, then by % allocation, it would still be a 70% dentist to 30% rdh allocation.)
The assistants do a variety of tasks depending on the office but they almost always are the only ones to run instruments (dr. or hyg) through sterilization, they maintain the equipment for every operatory, they sometimes develop xrays for hygiene, they record the numbers for perio charts (done by hygiene), they order and stock supplies for the entire office, they do much more than sit chairside for the dentist.
(again assuming an office has less hours for a rdh; offices where i've shadowed did not have a hygientist at from open to close, and def not every day.)
The equipment in every operatory is essentially identical: patient chair, provider chair, assistant chair, unit, computer, software for computer, shared xray head, digital sensors, intraoral camera, etc. All instruments need to be sterilized so every piece of equipment in the sterilization room is a shared expense.
(correct but a dentist uses certain equipment that rdh's don't and the equipment + procedures done by a dentist are progressively more expensive than a rdh, correct?)
As for the instruments that are used for a hygiene procedure vs one for a dentists procedure they are comparable. The hygienist uses the Cavitron (dr does not) which costs $2300 or so. Each Cavitron tip costs about $150 and I need a minimum of three to make sure that there is a sterile one for each patient. Both dr and hyg use a slow speed hand piece. Each instrument (mirror, explorer, scaler, etc.) can be estimated at about $20-40. My prophy setup is 10 instruments whereas my perio setup is about 14. A composite instrument setup is about 10. Disposables are a larger expense on the hygiene side if you include giving out toothbrushes and floss. Restorative materials are a slight cost but if hygiene is also placing sealants then that can balance out as well in the expense of etch, bond, etc.
That is why Blatchford removes the lab bill prior to dividing the overhead. Once you remove that, everything else is about even. And yeah, hygiene is expensive.
(removing the lab work or not, you still have the same general overhead, but i don't believe that a hygienist gets 50% of that overhead cost for a few days of work; a hygienist thats in 3 days a week or even 4 cannot be allocated the same % as a dentist whos there 6 days a week. In addition, if the office has more than 1 dentist (lets say 2 dentists and 1 specialist) the general allocation expense % would shrink, because the dds + specialists would use way more utilities, lights, staff, and hardware.) At the end of the day, all offices work differently and have different policies. Yes I do agree collections matter more than anything because expenses are variable as based on production (except rent, staff, and a few others) But all in all, depending on how you want to "slice the pizza pie" you can have a RDH look slightly profitable vs. moderately profitable. Again I dont believe its fair to allocate the same expense % because the RDH works less hours a week and therefore incurs less of the expenses.
To do a true analysis where you can really see your profitability its best to properly split everything out. That includes a proper hourly analysis (i.e. RDH works 24 hours a week at an office, whereas the dentist is logging in 50 or 55 hrs, plus his associate is clocking in another 50, can you really say that the hygienist is utilized the staff and utilities just as much as the dentists?)
One thing that plays a big role in our office is the fact that we are a PPO provider for several insurance companies. We therefore write off a large percentage of hygiene appts due to our agreement with them. So we might charge $110 for a prophy but plan A might reimburse at $93 and plan B might reimburse at $78! So as SLOBrule said above, it's all about collections.