Upper expansion orthodontic retainer

A method of forming an orthodontic retainer, comprising:

• creating a cast based on an impression of a patient's maxillary teeth;
• vacuum forming a first material over said cast;
• trimming excess first material such that only first material configured to cover facial, lingual, and occlusal surfaces of the patient's maxillary teeth remains on the cast;
• removing the first material remaining on the cast to obtain a first portion of the retainer;
• trimming said first portion of the retainer along a path following gingival contours of the first portion of the retainer;
• drilling a plurality of holes bi-laterally in the lingual surface of the first material of the first portion of the retainer;
• applying a second material covering a free palatal portion and the plurality of holes drilled in the first portion of the retainer;
• curing said second material to obtain a second portion of the retainer bonded to said first portion of the retainer;
• and
• obtaining the orthodontic retainer comprising the first portion of the retainer and the second portion of the retainer,
• wherein the second portion of the retainer includes a plurality of bulges extending buccally towards the plurality of holes drilled bi-laterally in the lingual surface of the first portion of the retainer in a hole to bulge mating arrangement for facilitating a permanent bonding of the second portion of the retainer to the first portion of the retainer during the curing step.