None, as the consecutive 'o' and 'e' are pronounced separately, and neither affects the pronunciation of the other.
Gastr requires the o, however if enteritis was the root word (leave off itis) the root term of enter would need an o also.
There are four vowels in the term "teacher pet" - e, a, e, and e.
3
Put them in alphabetic order and add combining vowels, regardless of whether the initial letter is a consonant or a vowel.
The word 'stomach' is within anatomical terminology. However, when discussing conditions of the stomach, medical terminology uses the root 'gastr' in addition to prefixes, suffixes and any additional roots plus combining vowels to put them all together smoothly. An example would be 'gastroenteritis' referring to inflammation (itis) of the stomach (gastr) and intestines (enter).
Gastroenteritis is usually resolved within two to three days and there are no long-term effects. If dehydration occurs, recovery is extended by a few days.
The combining term for breastbone is stern(o).
The rule for the order of joining word roots at the beginning of a term is to generally place the more specific root before the more general root. This allows for clearer understanding and interpretation of the term.
Gastritis is the inflammation of the lining of the stomach.
The combining form is that the prefix osteo- is added.
This is because while combining two medical root words one should keep in mind the anatomical arrangement of those root words. Whichever organ comes first anatomically, should be used first. In the above case the gastro i.e. the stomach comes before entero i.e. intestine so only the work gastroenteritis is valid.
The term for combining two or more rhythms simultaneously in music is called polyrhythm.