Oct 25 (Reuters) - Align Technology lowered its full-year revenue forecast on Wednesday, hurt by weak demand for its clear teeth aligners, sending its shares down 21% in extended trading.

The dental company now expects revenue in the range of $3.83 billion to $3.85 billion for 2023, compared with its previous forecast of $3.97 billion to $3.99 billion.

"Our third quarter results reflect lower than expected demand and a more difficult macro environment than we experienced in the first half of 2023," Chief Executive Officer Joe Hogan said in a statement.

Hogan corroborated deteriorating trends in the industry, including decreased patient visits and increased appointment cancellations, as the sector comes under pressure from slowing consumer spending in an uncertain economy.

Those concerns have weighed heavily on shares of companies such as Dentsply Sirona, Envista Holdings Corp , Swiss-based Straumann Holding AG and Align over the last month.

Align's lead product segment, which sells a series of custom-made aligners and other consumables used for straightening teeth, reported revenue of $794.9 million, below estimates of $821.9 million.

Going forward, the company expects overall revenue in both segments to be down sequentially with the strengthening of the dollar against key currencies and longer sales cycles for capital equipment purchases contributing to the decline.

Sales for the company's systems and services segment, which include its intraoral scanners used for diagnosis and recommendation of treatment plans, came in at $165.3 million, compared with estimates of $163.66 million.

On an adjusted basis, Align earned $2.14 per share for the three months ended Sept. 30, below analysts' average estimate of $2.26 per share, according to LSEG data. (Reporting by Pratik Jain in Bengaluru; Editing by Anil D'Silva)