Thumb sucking is a behavior that can be grouped under a list of habits known as non–nutritive sucking habits. Within this group, we can also find the use of pacifiers, blankets, or sucking on other fingers as a comforting behavior. Thumb-sucking has been considered an activity that serves as an adaptive function by providing stimulation or self-soothing.
Non-nutritive sucking habits are common in young children, and as they grow older, they tend to stop them. In most cases, this habit ceases spontaneously between 2 and 4 years of age.
Nevertheless, if thumb sucking continues, negative consequences can occur, such as a deformity of the nail or paronychia. If the habit persists while the permanent dentition is erupting, malocclusion can occur. This condition can be managed with different approaches, from parental and patient advice, fitting a dental appliance, or behavior modification techniques such as positive reinforcement, calendar with rewards, and counseling, among others.
Clinicians must be aware of the non-nutritive sucking habits, including thumb-sucking and their negative impact on oral health, as well as the complications that can arise with them. Referral to a pediatric dentist for evaluation of dental complications can be considered when the non-nutritive sucking habits persist beyond the 4 years of age despite appropriate behavioral interventions.
The development of sucking by itself is a primitive reflex that appears early in infants. Sucking behavior in children is associated with self-comfort and security feeling. Caregivers commonly introduce pacifiers to help the infants calm down when agitated. A study done in Italy by Ferrante et al. reported that thumb sucking behavior in their study was initiated to stimulate the nasopalatal receptors and receive muscular balance for a release of psychological and physical tension. Therefore, it seems that finger sucking is closely related to the psycho-emotional maturity of a child. Most of the children discontinue this habit spontaneously by the age of 4 years when more developed self-management skills arise.
Non–nutritive sucking habits such as thumb sucking and finger sucking are prevalent among children all over the world, including all socioeconomic classes. The incidence of thumb sucking can be very variable depending on the geographic area. A Swedish study showed an 82% incidence of non–nutritive sucking behaviors during the first five months of life. Another study done in the U.S. showed a 73% incidence of non–nutritive sucking habits in children between 2 and 5 years. As children grow older, the behavior tends to stop. Studies have shown the presence of a digit or pacifier sucking habit in about 48% of children at 4 years of age and 12.1% in children older than 7 years. The habit persists in 1.9% of 12-year-old children.
Thumb sucking can be characterized by the frequency, intensity, and duration of the habit. The duration of the force in thumb/digit is more critical than its magnitude, and the resting pressure has the greatest impact on the position of the tooth. Thumb sucking can lead to dentoalveolar and skeletal malformations.
A thorough history is essential to characterize the frequency, duration, and intensity of the thumb sucking. Physical exam in these patients can be remarkable for blisters located in the affected thumb since vigorous sucking can induce this. Sucking pads or calluses can appear as well, being the result of hyperkeratosis. Findings on the oral exam include upper incisors with proclination and retroclination of the lower incisors due to the placement of the thumb behind the upper incisors. The thumb can also prevent the eruption of the upper and lower incisor leading to the development of anterior open bite and increased overjet.
An oral examination is crucial to evaluate for possible complications of thumb sucking. The first oral evaluation for all children is recommended when the first tooth erupts, no longer than 12 months of age. Examining of the oral soft tissues, palate, alveolar ridges, and any erupted/ erupting teeth is essential. Once dental care is established, monitor of the developing primary dentition and occlusion should be done at regular clinic visits.
Several treatment options have been proposed for thumb sucking. Treatment options can range from counseling to the patient and parent, use of different mouth appliances, implementation of behavior-modification techniques such as advice and incentives for changing behavior, applying a nasty tasting substance to the children's thumbs, myofunctional therapy or combinations of these treatments. A Cochrane review done in 2015, showed that the use of an orthodontic brace or a psychological intervention (such as the use of positive or negative reinforcement) or both, was more likely to lead to cessation of the habit than no treatment.
Within the orthodontic appliances, there are several options available, including palatal cribs, spurs, palatal bars, hay rakes, and cage-type appliances. In severe cases, there can be a need for orthognathic surgery. Once treatment is completed, there is still the possibility of relapse and reestablishment of malocclusion.
Nonsurgical and non-orthodontic interventions that have been studied for treatment in cases of an anterior open bite originated from thumb sucking include orofacial myofunctional therapy and stomahesive wafers. Orofacial myofunctional therapy involves a set of exercises that reeducate muscles involved in swallowing, speech, and resting posture. A study done by Huang et al. included patients from 4 to 12 years that presented with dental habits utilized stomahesive wafers as therapy: these were placed on the incisive papilla so it could guide the tongue to rest in that position. Other interventions in this study included orthodontic devices that used a magnetic device to correct an anterior open bite. The use of this device with the bite block has demonstrated to be an effective treatment for anterior open bite.
With the technology arising, there are new interventions proposed. Krishnappa et al. published a case of an 8-year-old male with persistent thumb sucking habit. They used a device with an alarm that was activated when the child placed the finger into the mouth. The alarm was placed in a wristwatch, making it attractive to the child to wear. The child was followed for 15 months and was found to have decreased frequency of thumb sucking and discontinued the habit totally by 5 months. He was instructed to continue wearing the device for six more months to avoid relapse.
Thumb sucking is characterized as a behavior where a child sucks their thumb, there are no different entities that could be mistaken with it.
Thumb sucking ceases spontaneously between 2 and 4 years of age in most of the cases. Overall the prognosis is benign. If dental malocclusion appears as a consequence of thumb sucking, it can correct by itself if the habit stops and if the skeletal deformity is mild. If the habit persists beyond four years of age, management can be instituted. The risk for relapse of the habit after adequate treatment is always a possibility.
Non-nutritive sucking habits such as thumb sucking can be a risk factor for the development of malocclusion or specifically anterior open bite. Finger sucking has been known to cause an asymmetrical anterior open bite, worst the side where digit sucking happens, and also to be dependant on the duration and frequency of the habit. The etiology of malocclusion due to thumb sucking is due to the presence of the thumb in the mouth and the pressure elicited by it, especially against the teeth, interfering with the eruption path. In a study done by Lopez Freire et al., children with a history of finger sucking had malocclusion 4.25 times higher than kids without a history of it.
There is also a positive association between severe malocclusion and prolonged duration of thumb sucking. The thumb can also be affected and develop complications such as deformities requiring, in some occasions, surgical correction.
Some other of the proposed negative associations with thumb sucking include delayed development of oral functionality. Regarding speech disorders, there is limited research, and the association with this behavior is uncertain. There have been several studies, like the one done by Baker et al., where it was reported that of the 15% of Australian preschoolers that engaged in thumb or finger sucking, there was no association noted with the presence or severity of phonological impairment. Another study done by Barbosa et al. reported that of 128 participants with speech disorders, 18.3% had engaged in finger sucking.
Dental and orofacial consultations are key parts of the team management of thumb sucking.
Parent and caregiver education must include positive reinforcement techniques, including praising the child when he or she doesn't suck the thumb. Parents can try to find alternative ways that are soothing and comforting for children, give reminders for thumb sucking, and involve older kids or family members in ways they can support the affected child to stop sucking their thumb.
Thumb-sucking has been considered as an activity that serves as an adaptive function by providing stimulation or self-soothing. As children grow older, they tend to stop this habit, with most of the cases ceasing spontaneously between 2 and 4 years of age. Referral to a pediatric dentist for evaluation of dental complications of thumb sucking can be considered when the habit persists beyond the four years of age despite appropriate behavioral interventions.
An interprofessional team constituted by pediatricians, dentists, and psychologists provides an integrated approach to persistent thumb sucking along with communication to achieve the best possible outcomes.
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