Excluding the example wherein Ignaz Semmelweis noticed that handwashing between procedures greatly reduces the risk of infections occurring, and evidenced the existence of microorganisms... An example of an important intellectual revolution in the field of Medical Technology is when Antoine-Laurent de Lavoisier first made the phlogiston theory.
Before the phlogiston theory, in 5th century BCE there was the four-element theory, concerning Earth, Water, Air and Fire. In the 9th century, sulfur and mercury were added to the four elements. Not as elements, but principles that could explain the attributes of the seven metals. Then in the 16th century, salt was added to form a tria prima (the three elements of alchemy), between it, sulfur, and mercury. In the 17th century, scientists followed a 5 element theory consisting of earth, water, sulfur, mercury and salt. Robert Boyle (who you may know from his work in the physical properties of gas) rejected these theories in his book The Sceptical Chymist (1661). His studies inched closer to the modern concept of elements we have today.
The phlogiston theory dealt with the quantification of elements in isolation, and examined well their qualitative attributes. While the phlogiston theory turned out to be false, it led to the discovery of hydrogen (thought to be phlogiston) and oxygen (thought to be dephlogisticated air), and eventually the discovery of the composition of water. Through this, it gave Lavoisier the tools to craft the foundations of nomenclature and modern chemistry (even stuff like the Law of Conservation of Mass)!