WORCESTER — The attorney general's office is taking a chomp out of Aspen Dental for its alleged deceptive advertising and marketing prices, as well as its failure to provide refunds to customers.   Attorney General Martha Coakley's office reports Aspen Dental Management and Aspen Dental Associates of New England agreed to a $990,000 settlement. Aspen Dental has offices in Worcester, Auburn and Leominster, among more than a dozen locations across Massachusetts.   "We allege this dental company took advantage of its patients by deceptively marketing its services and unfairly charging in advance for dental treatments," Ms. Coakley said in a statement. "Under this settlement, affected consumers will get the relief they deserve and Aspen will be prevented from continuing these unlawful practices in the commonwealth."   An assurance of discontinuance was filed in Suffolk Superior Court Monday. The document says Aspen staff ran misleading advertisements and unlawfully charged customers for treatments weeks or months before they were rendered. The company also reportedly failed to give refunds for services not provided.   Aspen is to pay at least $770,000 in restitution to thousands of first-time customers in the Bay State and a $220,000 fine to the state. The company advertised "free" dental exams and X-rays, according to the state, but charged for those services instead between September 2009 and December 2013.   Aspen must also refund all prepayments by former Aspen customers for dental services that were not provided. Consumers who are entitled to a refund will be notified directly by the company.   As part of the settlement, Aspen has agreed it won't require consumers to pay in advance, with the exception for custom-made prosthetics and treatments completed within 30 days of payment. Aspen has vowed it will no longer engage in misleading advertising, including advertising services as free without prominently stating exceptions.   Executives have agreed Aspen will provide good-faith estimates of costs prior to rendering services and will fully disclose any third-party financing arrangements offered to its clients. It will also detail and comply with its refund policy. Office employees will be trained on making such accurate disclosures, according to Ms. Coakley's office, and the company will not permit any dentist without a valid license to have final decision-making authority over treatment plans.