Make your resume and resume differ from those of other candidates. As such, you should never start your resume with such general salutations as dear sir, or dear sir. Normally, when a company posts publicly a recruitment ad, it will surely address the name, address and contact number so as the resumes may be sent to correct address.
However, not everyone can know how to make his resume and resume become decisive to the employer. It is not about spending more time or providing more information in the resume that make that resume becomes well impressive to the employers.