To compare pre-treatment and post-treatment dental arches in relation to intercanine and intermolar width changes in extraction and non-extraction treatment in class I and class II cases. Materials and methods: This retrospective study was conducted in the department of Orthodontics and Dentofacial Orthopaedics, Yenepoya Dental College, Yenepoya (Deemed to be University), Mangalore. Forty-four study models were selected randomly for this study based on the inclusion and exclusion criteria.Inter canine and intermolar width were measured using digital Vernier Calliper in extraction and non-extraction Class I and Class II groups. Results: The intercanine width was significant only in extraction group of Class II and insignificant in all other groups of class I and Class II. The intermolar width showed significant changes in Class I groups in both extraction and non-extraction while only non-extraction had significant change In Class II groups. Conclusion: There is no significant changes observed in extraction and non-extraction treatment protocol, but there were differences between the class I and class II cases. The increase in the arch width was significantly more whether its ICW or IMW in class II cases than in class I cases.