Tooth decay was low in pre-agricultural societies, but the advent of farming society about 10,000 years ago correlated with an increase in tooth decay (cavities). An infected tooth from Italy partially cleaned with flint tools, between 13,820 and 14,160 years old, represents the oldest known dentistry, although a 2017 study suggests that 130,000 years ago the Neanderthals already used rudimentary dentistry tools. The Indus valley has yielded evidence of dentistry being practised as far back as 7000 BC, during the Stone Age. The Neolithic site of Mehrgarh indicates that this form of dentistry involved curing tooth related disorders with bow drills operated, perhaps, by skilled bead-crafters. The reconstruction of this ancient form of dentistry showed that the methods used were reliable and effective. The earliest dental filling, made of beeswax, was discovered in Slovenia and dates from 6500 years ago. Dentistry was practised in prehistoric Malta, as evidenced by a skull which had an abscess lanced from the root of a tooth dating back to around 2500 BC.