Here is an example case that I performed. I treated tooth #31 (the lower right second molar). Another endodontist had treated tooth #30 in front.
I was able to locate, clean, instrument and fill the major canal anatomy in a conservative manner. The front root had two separate canals that joined at the tip of the root while the back root had one main canal that split at the tip of the root and exited from two separate exit points (red arrow).
I sealed/restored the tooth with a silver-mercury amalgam restoration. At the 6-month follow-up appointment, the periodontal pocket had healed and the radiograph suggests complete healing of the bone. At the 4-year follow-up, the patient is still asymptomatic and the radiograph appears normal.
When comparing the two endodontically-treated teeth, what stands out in my mind is that while both procedures achieved the same short-term result, by performing treatment with the conservative removal of healthy, natural tooth structure I expect a higher likelihood of good long-term success. Over time, a tooth that is instrumented more aggressively will be more likely to fracture, and thus lost prematurely, even under normal biting forces.
Conservative preparation of the tooth during root canal treatment in this manner is made possible by the use of the surgical operating microscope.
One of the key determinants of the survivability of a tooth is how much natural tooth structure a given tooth has remaining. Once you cut away tooth structure, you can never regain it.