In Fahrenheit 451, Part 2, "The Sieve and the Sand," what is the importance of the dentifrice commercial?
Assuming that "importance" refers to literary importance—or the importance of the scene to literary elements and development—rather than referring to social criticism importance, then the literary importance of the Denham's Dentifrice commercial is that it quite intensely reveals the violent inner struggle Montag is going through. He is trying to extricate himself from one false society and embed himself in a true society because he has learned "of a time when books were legal and people did not live in fear" (Jepsen and Johnston, spaceagecity.com).
"Shut up, shut up, shut up!" [His] was a plea, a cry so terrible that Montag found himself on his feet, ... this man with the insane, gorged face, the gibbering, dry mouth, the flapping book in his fist.
Montag has been reading his stolen books to Mildred, whose only response is, "Books aren't people. You read and I look around, but there isn't anybody!" when an electronic dog comes sniffing at their front door, exhaling "the smell of blue electricity blowing under the locked door." Montag—the fireman—knows full well what the sniffing dog means. Beatty knows Montag has stolen and expects the return of the book ("If I pick a substitute and Beatty does know which book I stole, he'll guess we've an entire library here!") that very night. He is, as he says himself, "numb" ("I'm numb, he thought") as he slams the house door and goes to board the subway. He has decided to go to Faber and ask to have a duplicate of the stolen book made so he can safely—safely for himself and Mildred and safely for the book—return the stolen book to Beatty.
"There's only one thing to do," he said. "Some time before tonight when I give the book to Beatty, I've got to have a duplicate made."
Riding on the subway amongst so many people, Montag is both scared of what he is doing and earnestly determined to memorize a portion of the New Testament that he holds open (foolhardy action) in his hands. The Denham's Dentifrice jingle has all the passengers tapping their feet and quietly singing along with the jingly words. The jingle acts as a literary counterpoint as it lauds "Denham's Dentifrice. Denham's. Spelled D-E-N-" while Montag struggles to retain the sentence "Consider the lilies of the field. ... Consider the lilies, the lilies, the lilies ...." The old, meaningless society fights against Montag's mind, as detergent would against impurities, "Denham's dental detergent," until he breaks down, shouting "Shut up, shut up, shut up!" to the "rhythm of Denham's Dentifrice, Denham's Dandy Dental Detergent, Denham's Dentifrice Dentifrice Dentifrice, one two, one two three,...."
"'Denham's. Spelled : D-E-N-'
They toil not, neither do they...
A fierce whisper of hot sand through empty sieve.
'Denham's does it!'
Consider the lilies, the lilies, the lilies...
'Denham's dental detergent.'"
So, while "importance" relating to the Denham Dentifrice scene in "The Sieve and the Sand" is a significant factor of the novel as social criticism, the social importance is quite different from the literary importance. Reflecting on Bradbury's opinion of television and on the "detergent" characteristics of Denham's Dentifrice, we might arguably say that the social importance of this scene is that electronic entertainments, like television entertainment, including the jingles of advertisements (so popular on television and other modes of entertainment), scrub away the productive, intelligent and independent thoughts in a person's mind as though they were impurities, even as the detergent dentifrice, "Denham's Dandy Dental Detergent," scrubs away impurities on teeth.
One propaganda technique of advertising is to use repetition and a clever jingle to “imprint” the advertisement’s message on the consumer. We have all had trouble getting a catchy jingle out of our mind or have repeated a clever line of advertising in our everyday conversations (for example, "Wuz up?"). It’s a powerful technique that can overtake the thoughts of a potential buyer, supposedly causing them to run to the nearest store and purchase the product. As Montag is trying to remember a line from the Bible, the dentifrice toothpaste ad is blaring in the background and drowning out his thoughts. It’s so catchy that other people on the bus are tapping their feet and humming along with the ad. The advertiser has done their job. By repeating the unforgettable message, people will buy the product. Bradbury’s purpose in including this episode is to show how media, ads, and technology can take over our lives and become subconsciously ingrained in our psyches. Because Montag can’t concentrate on memorizing the Bible, it shows how distracting technology has become in our lives.
In Part 2 of Fahrenheit 451, as Montag struggles to induce free thought in himself and memorize what he has read, the Denham's Dentifrice jingle plays on the subway sound system. It greatly interferes with Montag's efforts to concentrate, and Bradbury uses this scene to demonstrate how Montag is struggling between two social views and how easily humans can be distracted, prevented from thinking and, essentially, conditioned not to think.
Similarly, the Biblical passage that Montag is trying to memorize--"consider the lilies of the field"--clashes sharply with the "detergent" element of the dentifrice commercial: the contrast is that they want him to scrub something away while he wants to catch and hold on to something.
if you read fast and read all, maybe some of the sand will stay in the sieve. But he read and the words fell through....
By the time Montag leaves Faber's house, his mind is running together the Bible's words with the advertisement's words, illustrating how hard the struggle to have a free mind is.