Shares of Align Technology Inc. /zigman2/quotes/200300692/composite ALGN +0.10% slumped 6.1% toward a four-month low in afternoon trading Wednesday, enough to pace the S&P 500's /zigman2/quotes/210599714/realtime SPX +0.30% decliners, after Stifel Nicolaus analyst Jonathan Block warned investors that his research suggests volumes deteriorated in recent months. Block's warning comes two weeks before the aesthetic dentistry products company is slated to report third-quarter results, after the Oct. 27 closing bell. Block said his past "quarterly diligence" was bullish, leading him to take aggressive stances heading into the previous four quarterly reports, all which beat both profit and revenue expectations. "However, our 3Q21 checks came back soft, and as a result, we view risk/reward for the upcoming print differently versus the last handful of quarters," Block wrote in a note to clients. Meanwhile, he reiterated the buy rating he's had on the stock for at least the past three years and kept his stock price target at $750. The current FactSet consensus for third-quarter earnings per share of $2.59 is the same as it was at the start of the third quarter, while the revenue consensus of $976.9 million has increased from $956.1 million. The stock has shed 8.4% over the past three months, while share of rival SmileDirectClub Inc. /zigman2/quotes/214109287/composite SDC +2.76% have tumbled 20.0% and the S&P 500 has eased 0.1%.