According to Wiktionary, the English word 'tooth' can be pronounced as /tʊθ/ (as opposed to its regular pronunciation in RP of /tuːθ/) in certain areas of Wales and the British Midlands.
Is there any information about where this shift comes from? As a native British English speaker, I can attest to having heard this be used, but this variant seemed highly out of place. Furthermore, I was unable to find any other similar words which had undergone the same shift, e.g. booth (which resembles 'tooth' in both their Modern English and respective Middle English forms) and sooth (which matches 'tooth' in Modern and Old English forms). Neither of these two examples have similar shifts listed as variants.
Is there any literature on when/how this shift came about? I am particularly interested in finding out:
- At what point in time the shift was first introduced/became commonplace;
- Whether this (or similar) shifts are also present in other lesser-known dialects, which simply are not listed on Wiktionary;
- Possible reasons for the shift (e.g. as part of a larger local vowel shift more generally unrounding close-back vowels, which just happened to affect 'tooth' as well);
- Why other words, including those with similar origins to 'tooth' (see examples above) have not experienced the same change;
- Whether other areas/dialects also had this difference at one point, but have now moved to the 'standard' pronunciation (if so, why?);
- Whether the similarity in the variation found in both Wales and the Midlands is a mere coincidence, or there is some reason for the resemblance.
Thanks in advance for any information/literature on the topic!