Source: Align Technology 

Third quarter of 2014 proved to be a positive surprise for Align Technology (NASDAQ:ALGN). The maker of dental medical devices reported earnings that surpassed both analyst expectations and the company's own projections. 

Align announces its fourth-quarter financial results on Jan. 29. Can the company continue the streak? Here are three key things to watch that could make the difference between an average quarter and an impressive one.

1. Spending stability
CEO Tom Prescott attributed last quarter's better-than-expected earnings to improving gross margin and control of operating expenses. Keeping spending at stable levels will be critical for Align to again beat expectations.

Align has shown that it can keep general and administrative expenses under control effectively. During the first nine months of 2014, G&A expense decreased slightly compared to the same period in the prior year.

The bigger question relates to sales and marketing expenses, which made up over 56% of total operating expenses during the first three quarters of 2014. If Align can keep the growth of sales and marketing costs to a manageable level, another nice earnings surprise will be much more likely.

2. Seasonal surprises
Fourth quarter historically contains both good news and bad news for Align Technology. The bad news is that the end of the year is typically slower in North America with fewer teens beginning orthodontic treatment after the school year begins. On the other hand, during the fall North American general practitioners tend to make up somewhat for slower summers due to vacations.

The really good news for Align during fourth quarter should come from its international business. There's usually a summer slump as many people take vacations. The final quarter of the year should mean a rebound in the number of procedures performed.

Align CFO Tom White predicted in October that fourth quarter should shape up nicely for North American and international sales. Any surprises that deviate from this outlook hold the potential to impact Align's stock price.

3. Pricing power
Even if Align controls expenses well and avoids any negative seasonal surprises, the company's pricing power for its Invisalign product is still of paramount importance. Average selling price, or ASP, for Invisalign during the third quarter was up 4.5% year-over-year but slightly lower sequentially.

Source: Align Technology 

There are three significant components to Align's average selling prices. First, currency fluctuations make a big difference. Second, sales promotions can reduce the ASP. Third, the complexity of procedures performed factors into the selling price -- the more complicated a procedure is, the more Align can charge.

For the fourth quarter, Align projects ASP's could decrease a bit. Tom White suggested in October that currency swings made the biggest impact on the company's estimates. Sales promotions in the fourth quarter, especially in international markets, will also be at play. Over the longer term, though, the trend toward more complex procedures in Align's international business should push ASP's higher. 

Analysts expect Align to report fourth-quarter earnings between $0.47 and $0.50 per share, with the consensus estimate of $0.49 per share. The company provided guidance with that same range. 

The market seemed a little disappointed with the company's fourth-quarter guidance in October. It's entirely possible that Align's management might have sandbagged a little. If so, Align might be poised to again deliver a pleasant surprise.