Custom trays are individual impression trays made from a cast covered from primary impression. The custom impression trays, also made from resin particularly useful in dentistry, is used in creating the final impression of the patient’s mouth. Custom trays can result in a more dimensional accurate reproduction and stability by providing a uniform thickness of material all round the tray. Custom-made impression trays are made from either acrylic or VLC resins in final impressions for crown and bridge restorations and for denture construction. 

Advantages of custom tray:

• More accurate impressions. 
• The operator can better control the thickness of the material minimizing tissue displacement and dimensional changes of impression. 
• Custom trays are less bulky and more stable than stock trays. 
• Custom trays provide anatomically correct extension of denture impression. 
• Custom tray adapts more accurately to the oral vestibules helping in better retention of denture. 

Types of custom tray 

There are two types of custom tray: 

• Close-fit tray 
• Tray with spacer and stop 

Materials used for construction of custom trays

Metallic 

• Cast or swaged metal 

Non-metallic 

• Thermoplastic material 
• ○ Shellac base plate 
• ○ Impression compound 
• Resin 
• ○ Cold cure resin 
• ○ Hot cure resin 
• ○ Light cure resin 

Requirements of a custom tray

• In a moist environment and stability in air 
• Volume stability over time 
• Moisture resistance 
• Rigidity 
• Adhesion of the impression in the tray
• Even thickness of impression material 

Criteria for custom tray construction

• The impression tray must not affect movable structures. 
• The borders should be under extended (2 mm). 
• The rear limits of the impression tray should be slightly over-extended to ensure inclusion of the posterior detail for development of the post-dam area in the upper tray. 
• The tray should have sufficient thickness (2-3 mm) and should be rigid so that it will not fracture during its use. 
• The tray must have a handle for manipulation and the L- shape handle must not interfere with functional movement of the oral structures. 
• The tray must be smooth on its exposed surfaces, and must not have sharp edges which would injure the patient. 

Fabrication of custom tray

• The cast must be soaked in water. 
• The borders of the custom tray should be marked on the cast and are grooved deeper using a carver, acting as a guide to trim the tray later. 
• Severe undercuts must be blocked out using wax. 
• The relief areas are then covered with wax spacers ( step same for close fit and spaced special tray)
• Application of separating medium on a study cast. 
• Using the cold cure acrylic tray material by either sprinkle or dough on technique (for close fit special tray)