This varies from individual to individual. Factors affecting the development of dental disease include diet, chewing habits, the degree of dental care provided at home, genetics and the presence of other illnesses. If your pet will allow you to check its mouth, you can look at its teeth and gums weekly for obvious signs of problems (red or bleeding gums, broken or mobile teeth, swellings etc).
Most vets recommend that all dogs and cats be given a thorough physical examination at least once a year, and this is the perfect opportunity to discuss any dental issues your pet may have. Older animals, those with chronic health problems and those that have an increased susceptibility to dental problems will generally need to be seen more frequently. Your vet is the best person to advise you on this.
Of course, if you suspect your pet has a dental problem, it is best to arrange a dental check without delay.
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