Tooth decay

I have second caries on left upper 1st molar, how come?　Feeling some inconvenience that aches when clench hard at the portion. Though the cavity is small, tooth decay must be more into dentine tissue widely. If the infectious phenomena might be invaded, I would have much more pain leading to jaw bone inflammation in combinations with cheek swelling.
How about injection of antibiotics paste poring from the cavity and sealing with some phosphate cementum after sterilization and drying the infected hard tissue?
I found out some opinion that any digging are not always necessary to restore tooth, just upper treatment would be enough by the newest dental practice?
Anyway the setting of my health condition best is the first, because my ancestors must have overcome this kind of disease while the old time of period without any effective medicines.