Final answer:
Alginate is the irreversible hydrocolloid material most widely used for preliminary dental impressions, favored for its detail reproduction, rapid setting, and cost-effectiveness.
Step-by-step explanation:
The irreversible hydrocolloid material used most widely for preliminary impressions in dentistry is alginate. Alginate is prized for its ease of use, affordability, and ability to capture detailed impressions, making it ideal for a variety of dental applications including the creation of study models, orthodontic appliances and preliminary impressions for prosthodontic work.
Although other materials like polyether silicone and polysulfide are also used in dentistry for impressions alginate remains the most popular choice for preliminary impressions due to its rapid setting time and adequate detail reproduction.