Final answer:
Outlining the frenums in a custom tray is crucial for creating a comfortable dental impression that accurately captures the oral structures, ensuring the proper fit of dental prosthetics without impinging on delicate mouth structures.
Step-by-step explanation:
It is important to outline the frenums in a custom tray because the frenums are delicate structures in the mouth, which can affect the fit and comfort of dental prosthetics. When creating a custom tray for dental impressions, it is crucial to ensure that there is appropriate space to accommodate the frenums. If the tray impinges on the frenums, it could cause discomfort or distort the impression, leading to an inaccurate mold of the teeth and soft tissue. Therefore, accounting for frenum location allows for a more accurate and comfortable fit of dental appliances such as dentures. By outlining the frenums on the custom tray, the dentist or dental technician makes sure that the final prosthetic device does not interfere with these structures and provides the best possible fit for the patient.