In the early 2020s, nearly half of New Zealand adults reported that cost of treatment had prevented them from accessing dental care, with higher rates among Māori, Pasifika and individuals living in the most deprived areas. Unaffordable dental care may be explained by a rise in dental service fees over time relative to personal income, as documented in New Zealand between 1978 and 1993. However, there have been no contemporary estimates in New Zealand of how the affordability of dental care has changed. The aims of this study were to analyse the change in dental treatment fees and the personal income of New Zealanders from 1978 to 2023 and to explore differences in affordability of dental care by ethnicity. Average fees for dental treatments were sourced from surveys completed by practising New Zealand dentists. Earnings (from 1978) and personal income data (full population from 2000 and by ethnicity from 2008) were sourced from Statistics NZ and NZ Official Yearbooks. Inflation-adjusted changes in average fees, weekly personal earnings and income were calculated as a percentage change from 1978 levels for fees and earnings and from 2000 for personal income. For the five dental treatments with data available from 1978 to 2023, fees increased in the range of 75%-236%, while earnings increased by 46% over the same period. Fees for other treatments (with data available from 1981 to 2009) similarly increased and mostly surpassed changes in earnings. From 2008 to 2023 the overall increase in personal income (about 21% across all ethnic groups) kept pace with the rising cost of most treatments. However, due to persistent income inequalities, in 2023, Māori and Pasifika would need to spend a higher proportion of their weekly income (approximately 16% and 23% respectively) to receive the same dental treatments as NZ Europeans. Fees for dental treatments have risen markedly in recent decades, more sharply than the price of other goods and services.