Radiographs, even digital can miss large carious lesions when decay is present on the buccal surface. A careful intra-oral exam is necessary ( on a regular basis ). Fortunately this lesion had not penetrated the pulp chamber and therefore root canal therapy was not necessary.

Thankfully, regarding anesthesia, we have septocaine. When utilized with a ligmaject ( Intraligamental Anesthesia Syringe ) device  proper anesthesia is achieved without the need for a mandibular block injection.

A ligmaject is not always necessary but in areas with thick bone such as with this first molar it does enhance anesthesia. In other areas a simple infiltration is adequate.

It is also probably wise to use carbocaine 3% on the maxilla rather than septocaine because septocaine seems to last a lot longer and patients don’t really need that. Of course, if more profound anesthesia becomes necessary, septiciane seems to work well.