Scaling does not cause Dentin exposure. Dentin is exposed due to loss of enamel which can be due to physical reasons like vigorous tooth brushing or chemical reasons like acidic beverages or due to Cavitation. In either case the first step would be a proper clinical examination to evaluate the exact cause of your constant dull pain. The right treatment can be suggested after the right diagnosis has been made. The various treatment options can include changing of your toothpaste to a desensitizing one or a filling. But at least one thing is for sure that scaling is not the reason for this Dentin exposure. Root exposure can occur after scaling but that is not caused by scaling it is caused by the deposits which are removed from the root surface during scaling. Regards.