Final answer:
The usually phlegmatic dentist lost his usual calm and self-control after consuming alcohol, leading to out-of-character and distressing situations.
Step-by-step explanation:
After two drinks the usually phlegmatic dentist lost all his inhibition. The calm and imperturbable demeanor typical of the phlegmatic personality, often characterized by a high tolerance for stress and an unemotional response to external stimuli, had been diminished.
The excerpts provided suggest that under the influence of alcohol, the dentist's usual temperament was compromised, leading to events that were out of character, from the distressing episode with the billiard ball to the heated interaction with Marcus.