The picture shows a hamster's teeth clearly. The bottom teeth in the picture should not be allowed to grow any longer.
Hamsters are rodents and therefore their teeth grow continuously. This means that a hamster needs to grind its teeth down regularly to stop them from overgrowing and the hamster does this by gnawing on something hard. Many hamsters will use the bars of the cage to gnaw on or there are wood chews available from pet shops. Apple wood and hard dog biscuits will also help the hamster to keep its teeth trim. If a hamster had nothing to gnaw on to keep its teeth in trim the teeth may overgrow and could puncture the mouth or jaw. Abnormal conformation of the teeth can sometimes occur for congenital reasons, affected family lines should not be bred from. Hamsters are one of the few animals born with fully developed teeth.
Occasionally a hamster may break a tooth and when this happens the opposite tooth may overgrow because it has nothing to press upon. In the same way if one tooth grows crooked or becomes curved the opposite tooth may overgrow. Older hamsters are prone to teeth that may break easily and teeth that grow crooked so it is important that you check your hamster's teeth when they are older to see that they are growing correctly and it is a good idea to check a younger hamster's teeth from time to time also. This can be done by simply gently pulling the skin around the back of the neck, forcing your hamster to 'smile' by pulling the skin back away from the mouth, revealing its teeth.
If a hamster's teeth become overgrown they can be clipped using a pair of nail clippers but care must be taken to avoid cutting the tongue or cheek. To cut the hamster's teeth, hold the hamster by a good scruff of neck forcing the hamster to 'smile' and ensuring that the hamster remains still. Place the nail clippers around the tooth to be cut, ensuring that the blade behind the tooth is pressed firmly against the tooth to ensure the tongue is out of the way and clip. Many owners will not want to risk cutting the teeth themselves and a vet will be able to clip a hamster's teeth. However, if you have an older hamster whose teeth are growing crooked or curved regular clipping of the teeth may be needed and so you may wish to get the vet to show you how to do it yourself and watch you do it for the first time, before attempting it on your own.
Some hamsters may have real problems with their teeth as they grow older - some have been known to have teeth break continually making it difficult to eat. Older hamsters who have trouble eating because of their teeth can be fed soft foods such as bread, scrambled egg, porridge and hamster mix softened in water or milk.
It is thought by some that a hamsters teeth may break more easily if the diet is low in calcium, this may happen when there are too many sunflower seeds fed as part of the diet. Dog biscuits are a good source of calcium as well as an object to gnaw on, other good sources of calcium would be cheese and milk.
Tooth decay [ Dental Caries ] is becoming more common in the hamster, this is probably related to the sweet hamster snacks which are increasingly becoming available. Signs that this is occurring would include difficulty in eating, salivation and facial swelling. It is possible to extract affected teeth under a general anaesthetic.
Another cause of head tilt and loss of balance may be an ear infection and therefore if the hamster shows no improvement within a day or two veterinary advice should be sought as it may be a curable ear infection.