Grinding substances between your teeth can be a joy, especially when it is something sweet. And the sweeter the foodstuff, the more chances of the person eating forgetting that our mouths are full of bacteria.  Dr Sandeep Goyal, a dental surgeon at king Faisal Hospital, Rwanda, says different types of bacteria live in our teeth, gums, tongue and other places in the mouth, some are helpful but some can be harmful like those that play a role in tooth decay hence cavity."Tooth cavity is a hole in tooth which is created by the acids produced in our mouth by bacteria. That acid dissolves the tooth structure over a period of time and creates discontinuity in the tooth surface. Initially it is small, but with time it increases in size,” Dr Goyal says.He says cavity is caused by the food we ate which sticks to the teeth for example chocolates, biscuits, bread among others and not cleaned properly, then acid is produced on tooth surfaces, leading to demineralisation and cavity is produced. Brushing every after eating, and at least twice per day is the first remedy to fight tooth cavity.To identify the symptoms of cavity, doctors say initially, there is white patch on tooth surface, which turns black with time. Patient may start feeling sensitivity with air, cold and sweet things.If cavity starts touching the nerves of the tooth, then patient feels sensitivity with hot things, and pain too.Dr Goyal said to diagnose cavity, they use dental probe to check the cavity on tooth. "For depth of cavity, we take x-rays. There are computerised equipment that can help in finding the cavity depth and even at the start of cavity, but these are not available in the country,” he said.The doctor advises to brush at least twice each day using a soft brush and the strokes should be up to down or vertical rather than horizontal.