The average primary care dentist recorded a net profit of £96,135 in 2006-2007, but that sum had fallen to just £74,400 by 2011-12, according to NHS England.
The statistics, which follow the controversial decision to impose a real-terms pay cut on dentists, triggered a war of words between health chiefs and the British Dental Association (BDA).
The BDA said they exposed the 'failure of the Government to support dental practice,' and called for the cuts to be reversed.
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But NHS England, in its pay review for 2014, insisted: 'It is clear that dentists continue to receive a good income.
'This remains a well remunerated profession.
'For dentists holding a contract, earnings were considerably higher at an average of £112,800, down 3.7% from the previous year’s £117,200.
'The data also show some dentists earning considerably more, with 1% earning over £300,000.'
The statistics show profits rising sharply from 2004-05 (£80,032) to peak in 2006-07 (£96,135), only to fall back in four of the five years since.
The BDA suggested part of the decline could be explained by fewer patients opting for private treatment since the pain of the financial crash in 2008.
But it said the primary explanation was the year-on-year failure to properly compensate dentists for the rising costs of their expenses and of expanding regulations.
Dr John Milne, the chairman of the BDA’s general dental practice committee, said: 'The data clearly shows the effect of the failure of the Government to support dental practice.
'The imposition of "efficiencies" by the Department of Health have resulted in successive pay cuts for the profession – rather than the governments intended pay freezes for those working in the public sector.
'The costs involved in providing care have risen inexorably in recent years, both in the costs of regulation and also the costs of compliance with HTM01(05).
'If dentists are to continue their contribution to improving oral health, these funding cuts must be reversed.'
The statistics show the percentage of payments that are intended to cover expenses has also fallen, from 58.6% in 2004-05 to 53.8% in 2011-12.
However, they also show the number of dentists is still on the rise – from 20,160 in 2006-7, to 22,003 in 2009-10 and to 23,201 in 2012-13.
NHS England argued it was 'hard to compare with previous years,' because of a shift towards 'personal and practice incorporation,' which takes profits out of self-employment and into company accounts.
In March, health secretary Jeremy Hunt sparked anger by rejecting an independent review body’s call for an across-the-board 1% rise for salaried and hospital dentists.
Instead, dentists on ‘progression pay’ – an annual increase, linked to length of service and skills – will receive only that salary hike, not the proposed 1%.
And Mr Hunt also hacked back the recommended increase in gross earnings for general dental practitioners (GDPs) from 1.8% to 1.6%.