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If it has been about 3 years since you've been to the dentist and you have heavy calculus, gumline irritation, some recession and exposed "edge" of your teeth which you can feel with your fingernail, it is likely that a simple cleaning will not be adequate. There is likely calculus below the gumline in certain areas. This requires a "deep cleaning". In addition, the amount of calculus present may simply be more than your dentist feels he can adequately remove & clean in a normal cleaning appointment.
As far as determining if there is bone loss or a "turn for the worse: : A clinical exam plus Xrays generally reveal bone loss - and calculus below the gumline. They can also show bone loss and any deterioration in your periodontal health (gums and supporting bone).
A second opinion is always an option - the choice should be yours. But from what you have described, a deep cleaning makes sense.
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