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Thumb sucking is a behavior found in humans, chimpanzees, captive ring-tailed lemurs, and other primates. It usually involves placing the thumb into the mouth and rhythmically repeating sucking contact for a prolonged duration. It can also be accomplished with any piece of skin within reach (such as the big toe) and is considered to be soothing and therapeutic for the person. As a child develops the habit, it will usually develop a "favorite" finger to suck on.
At birth, a baby will reflexively suck any object placed in its mouth; this is the sucking reflex responsible for breastfeeding. From the very first time they engage in nutritive feeding, infants learn that the habit can not only provide valuable nourishment, but also a great deal of pleasure, comfort, and warmth. Whether from a mother, bottle, or pacifier, this behavior, over time, begins to become associated with a very strong, self-soothing, and pleasurable oral sensation. As the child grows older, and is eventually weaned off the nutritional sucking, they can either develop alternative means for receiving those same feelings of physical and emotional fulfillment, or they can continue experiencing those pleasantly soothing experiences by beginning to suck their thumbs or fingers. This reflex disappears at about 4 months of age; thumb sucking is not purely an instinctive behavior and therefore can last much longer. Moreover, ultrasound scans have revealed that thumb sucking can start before birth, as early as 15 weeks from conception; whether this behavior is voluntary or due to random movements of the fetus in the womb is not conclusively known.
Thumb sucking generally stops by the age of 5 years. Some older children will retain the habit, which can cause severe dental problems. While most dentists would recommend breaking the habit as early as possible, it has been shown that as long as the habit is broken before the onset of permanent teeth, at around 5 years old, the damage is reversible. Thumb sucking is sometimes retained into adulthood and may be due to stereotypic movement disorder, another psychiatric disorder, or simply habit continuation.
Dental problems and prevention
Most children stop sucking on thumbs, pacifiers or other objects on their own between 2 and 4 years of age. No harm is done to their teeth or jaws until permanent teeth start to erupt. The only time it might cause concern is if it goes on beyond 6 to 8 years of age. At this time, it may affect the shape of the oral cavity or dentition. Thumbsucking leads to open bite, a high arched palate because of the pressure created in the mouth by the buccinator muscle. This habit can also cause the maxillary central incisors to tip labially and the mandibilar incisors to tip lingually as the thumb rests on them during the course of sucking. Aside from the damaging physical aspects of thumb sucking, there are also additional risks, which unfortunately, are present at all ages. These include increased risk of infection from communicable diseases, due to the simple fact that non-sterile thumbs are covered with infectious agents, as well as many social implications. Some children experience social difficulties, as often children are taunted by their peers for engaging in what they can consider to be an “immature” habit. This taunting often results the child being rejected by the group or being subjected to ridicule by their peers, which can cause understandable psychological stress.
To prevent their children from sucking their thumbs some parents use bitterants or piquant substances on their child's hands—although this is not a procedure encouraged by the American Dental Association or the Association of Pediatric Dentists. During the 1950s, parents could get a series of sharp prongs known as "hay-rakes" cemented to a child's teeth to discourage sucking.
The American Dental Association recommends:
Clinical studies have shown that appliances such as TGuards can be 90% effective in breaking the thumb or finger sucking habit. Rather than use bitterants or piquants, which are not endorsed by the ADA due to their causing of discomfort or pain, TGuards break the habit simply by removing the suction responsible for generating the feelings of comfort and nurture. Other appliances are available, such as fabric thumb guards from Thumbsie, each having their own benefits and features depending on the child's age, willpower and motivation.