RIO DE JANEIRO (AP) -- The orthodontist bent intently over Flavia Soares da Costa's open mouth, tightening the glimmering silver brackets that are remaking her smile.
Not long ago, it would have been all but unthinkable for the 33-year-old former secretary and single mother to undergo such pricey dental work.
But Costa's fortunes have recently improved, with a promotion and a raise that brought her disposable income.
In fact, an estimated 40 million people such as Costa have joined the ranks of Brazil's middle class between 2003 and 2011, according to the Fundacao Getulio Vargas economic think tank, providing them with enormous purchasing power and sparking businesses to come up with new marketing techniques to woo them.
For most of its modern history, Brazil has been a nation of the starkest economic divides: Super rich, super poor. Businesses that sold anything but the most basic items trained their sights on the upper strata.
Now, Brazil is a major player in a global economic shift that is seeing formerly "developing" nations morph into "middle income" countries — where a burgeoning middle class is driving a boom in business to capitalize on the sea change.
From gyms to hair salons, travel agencies to home appliance stores, "everyone wants to dance with the new middle class," a recent opinion article in the Folha de S. Paulo daily said.
The metamorphosis is largely the product of a decade of mostly solid economic growth and an array of cash-transfer social programs that pay Brazilians a stipend for meeting social goals, such as keeping their kids in school.
The economic think tank defines the middle class, or Class C as it's known here, as households with monthly incomes of $600 to $2,590. In 1993, just over 45 million people were considered Class C. In 2011, their ranks had swollen to more than 105 million — accounting for 46 percent of the country's buying power.
Similarly, the economy has grown to meet demand.
In 2000, 4.2 million small businesses had less than 100 employees, according to the Brazilian Support Service for Micro and Small Businesses, a private industry group. A decade later, 6.1 million small businesses had such workforces, and the number of larger businesses doubled to 60,000.
"Practically all companies across the board are interested in getting a piece of this market, if only because of the sheer numbers involved," said Renato Meirelles, CEO of Data Popular, a marketing firm specializing in the middle and lower classes. "Tapping into this market can prove extremely lucrative."
Entrepreneur Alex Todres is a case in point. The 30-something Sao Paulo resident founded ViajaNet, an online travel site that posted $100 million in sales in 2011, its second year of operation.
Todres and partner Bob Rossato loosely copied the design and function of the website of their former employer Decolar.com, Brazil's leading online travel portal, tweaking it for middle-class customers, many of whom are first-time flyers.
They replaced jargon that on other Brazilian travel sites would normally be in English, such as "gate" and "boarding card," with plain Portuguese. The pair also made it easier for customers to pay in installments — an ingrained habit in Brazil, where consumers tend to buy even low-ticket products like tennis shoes and irons in ten monthly payments.
"The product that we offer is essentially the same as the competition," Todres said in a telephone interview. "The difference lies in the purchasing experience."
A similar strategy paid off for Luiz Otavio Temido, CEO of the Simetria chain of orthodontic clinics in and around Rio de Janeiro.
In beauty-obsessed Brazil, straight, white teeth are almost as much of a status symbol as fast cars. So braces, along with computers, cell phones and college degrees, often count among the newly minted middle class' first investments, said marketing specialist Meirelles.
"For a long time, braces were seen as something that was reserved for people in Ipanema or Leblon," said Temido, referring to two of Rio's most chic, highest-rent neighborhoods. "Our innovation was to introduce techniques that made it possible to make care both high-quality and affordable."
Temido was able to sharply cut costs by creating multi-chair offices instead of private rooms in his orthodontic clinics, and relying on lower-paid hygienists and dentists.
Passing those savings onto patients allowed Temido to court the lower middle class. Patients at Simetria pay a flat fee of $50 a month, or an average of about $1,200 per treatment. That compares with top clinics in wealthy neighborhoods, where treatments often start at around $10,000, Temido said.
"I always had this complex about the gap in my front teeth, so this is something I've always wanted," said Simetria patient Costa, who got braces as soon as she was promoted from law firm secretary to the head of the firm's administrative service. "Things are getting better, and this is proof."
To woo consumers such as Costa, nationwide gym chain Bio Ritmo launched the lower-cost Smart Fit gyms, which are equipped with high-tech machines but don't offer classes. Exclusive Sao Paulo-based beauty salon Jacques Janine created the low-cost Basic Beauty branches, while pricey chocolate-maker Kopenhagen launched its own more affordable line, Cacau Brasil.
In a mall on Sao Paulo's gilded Avenida Paulista, 24-year-old Natalia Santos paced around the Taita jewelry and gift shop, holding gold-plated rings and precious-stone earrings up to the light, giving them a hard eye.
Four years ago, she never would have shopped in the area's expensive shops. Her work as an office administrator then brought in $400 a month, which when combined with the income of her father, the only other earner in the home where she lives, kept her household under the official middle-class line.
But Brazil's economic expansion and record low levels of unemployment, among other factors, have helped drive up Santos' income, as her employers gave her raises to reward her hard work and keep her from taking jobs elsewhere. She now makes $600 a month.
"Four years ago, I never would have bought like this, on impulse," Santos said shortly after spending $45 on a ring for herself and a violet sachet for a friend's engagement party. "I think it's absurd to buy so often and I always have regrets, but I love to spend."
Even TV Globo, the broadcaster behind the nightly soap operas that dominate ratings with high-drama sagas of the rich and fabulous, is courting the middle class.
"Avenida Brasil," the story of a young woman's vengeance on the nouveau-riche stepmother who abandoned her in a landfill, and "Cheias de Charme," about a trio of maids-turned-pop stars, have become hit soaps by featuring middle-class protagonists. In an unusual move, the show's handful of upperclass characters are relegated to the background.
Marketing specialist Meirelles said catering to the middle class requires first understanding the audience.
"Here in Brazil, there's a real problem in understanding how the lower middle class thinks," he said. "This lower class doesn't hold up the elite as a model. The reference for these people is not the rich, but rather the neighbor who succeeded."
With Brazil's commodity-driven growth slowing over the last year, the government is looking to domestic consumers, particularly the Class C, to spur on the economy. The Central Bank has slashed a benchmark interest rate to a record low, hoping it will spark consumer spending by generally making credit more available.
But skeptics worry that the new consumers are already too indebted to shoulder the lion's share of future growth. Economists estimate 20 percent of Brazilians' household monthly income goes to debt payments, and the Serasa Experian credit rating agency said that in the first half of 2012, consumer defaults in Brazil were 19.1 percent higher than in the same period last year.
Between her braces and the night classes she's taking toward her undergraduate degree, Simetria orthodontic patient Costa says she taps out her disposable income every month.
"It's a big investment in my future," she said.