There are many publications and websites that try to accurately compare effective radiation dose but it's not that simple.  For example there are two ways to quantify effective radiation, the ICRP 1990 recommendations and the ICRP 2007 recommendations.  The 2007 recommendations give more weight to the salivary glands, skin, and other organs than before which result in effective doses being higher when measured using the 2007 recommendations.  Most publications though use the 1990 recommendations since they were written before the release of the 2007 recommendations.  Comparing 1990 to 2007 based doses is like comparing apples to oranges so you should double check which method is being used.

Secondly, the absorbed dose of a CBCT system varies widely within the system itself based on the FOV, scan time, kVp, and mA settings used in the scan.  CBCT manufacturers will sometimes report their scan with the lowest radiation dose and then the scans of their competition with the largest radiation doses.

Finally, the radiation dose measurement depends on the phantom used by the company or researcher to measure the dose.  There are a number of different phantoms available which can have a varied number of sensors placed in them to measure the dose.  Thus far there is no standard phantom for use in measuring radiation.

It's for the above reasons that I do not report radiation doses on my website since I believe with all these variables it is like comparing apples to oranges and somewhat deceptive.

Currently the best sources for comparing radiation doses are the publications of Dr. Ludlow of UNC.  I would start with J Am Dent Assoc. 2008 Sep;139(9):1237-43. "Patient risk related to common dental radiographic examinations: the impact of 2007 International Commission on Radiological Protection recommendations regarding dose calculation." Ludlow JB, Davies-Ludlow LE, White SC. which gives a great overview of standard 2D dental imaging doses in 1990 and 2007 measurements.  Secondly I would review Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008 Jul;106(1):106-14. Epub 2008 May 27."Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology." Ludlow JB, Ivanovic M. which takes the same approach to reviewing CBCT and Medical CT systems.

I hope this clears up any confusion.