INTRODUCTION — Oral habits that are acquired during infancy (eg, nonnutritive sucking) can have adverse health consequences, such as early cessation of breastfeeding or increased risk of otitis media. The identification of such habits and assessment of immediate and long-term effects on the teeth and orofacial development should be made as early as possible [1,2]. After infancy, persistent oral habits have little effect on health but can affect facial growth, oral function, the occlusal relationship, and facial esthetics .
The short- and long-term effects of oral habits are reviewed here. Preventive dental care and counseling for infants and young children are discussed separately. (See "Preventive dental care and counseling for infants and young children".)
Epidemiology — Nonnutritive sucking behavior (eg, sucking on a pacifier, thumb, or fingers) is a normal part of early development that may become a learned habit. It is a self-soothing behavior that occurs in 70 to 90 percent of infants in various populations [4-8]. The frequency of sucking on digits or pacifiers decreases with increasing age; by the age of four to five years, nonnutritive sucking usually is replaced by other coping mechanisms, and the prevalence decreases .
Children who use a pacifier are less likely to suck on their thumb or fingers [9,10]. Compared with pacifier sucking, digit sucking is more likely to persist into the fourth or fifth year of life, when it may become problematic [11-13]. If it persists into the period of permanent tooth eruption, nonnutritive sucking may contribute to the development of malocclusion . Pacifier use does not appear to be related to an increased risk of development of early childhood caries unless the bulb is laced with sugar or dipped into a sweet liquid before use .
Dental effects — Nonnutritive sucking habits may be associated with increased prevalence of malocclusion in the primary dentition and mixed dentition and increased risk of trauma to the upper front permanent teeth [16-19].
The types of malocclusion that have been described in the primary or mixed dentition in children with sucking habits include [3,20]:
●Anterior open bite – The upper and lower anterior teeth do not overlap (picture 1).
●Posterior crossbite – The upper posterior teeth bite inside the lower posterior teeth on one or both sides (picture 2).
●Excessive overjet – Excessive horizontal overlap of the upper relative to the lower front teeth (picture 3); in children with digit-sucking habits, excessive overjet may be exacerbated by lower front teeth that are positioned toward the tongue (lingually positioned).
●Class II malocclusion – The upper jaw protrudes too far in front of the lower jaw.
●Effects in primary dentition – Nonnutritive sucking behaviors are associated with malocclusion in the primary dentition. In a systematic review of 15 observational studies, nonnutritive sucking habits were associated with varying risks of malocclusion . Children with digit-sucking habits are more likely than those who use pacifiers to develop excessive overjet, while those who use pacifiers are more likely to develop posterior crossbite [21,22]. The risk of malocclusion increases directly with frequency, duration, and intensity of the sucking habit and is not eliminated by the use of "orthodontic" pacifiers [2,17,21,23].
●Effects in mixed dentition – Prolonged nonnutritive sucking habits have been associated with malocclusion in the mixed dentition.
In longitudinal and cross-sectional studies, there is an association between persistent nonnutritive sucking habits (digits or pacifiers) and Class II malocclusion, excessive overjet, posterior crossbite, and anterior open bite in the permanent dentition [18,24-28]. The effects of pacifier use were more pronounced when pacifier use was continued beyond the age of four years . Associations between nonnutritive sucking and arch changes in children with digital sucking habits are inconsistent [24-26]. Among children with persistent pacifier use, decreased arch width typically resolved two to three years after discontinuation [24,25].
●Effects in permanent dentition – Few studies have evaluated whether habit-related malocclusion of the primary dentition persists into the permanent dentition after discontinuation of the habit.
●Dental trauma – Children with digital sucking habits may be at increased risk for dental trauma because of excessive overjet. In a longitudinal observational study, traumatic injuries to the maxillary anterior teeth were more common in children with a digital sucking habit than in those who used a pacifier or did not have a sucking habit . However, in a separate study of children undergoing orthodontic treatment for excessive overjet, there was no correlation between severity of overjet and the prevalence of trauma to the incisors (approximately 25 percent) .
Other possible effects — Although causality remains unproven, pacifier use has been associated with other health effects.
Increased risk of acute otitis media — Nonnutritive sucking habits have been associated with increased risk of acute otitis media. The association between pacifier use and acute otitis media (AOM) has been reported in a meta-analysis and several prospective studies [30-32]. The meta-analysis evaluating the risk factors for AOM found pacifier use was associated with increased risk of development of otitis media (pooled relative risk 1.24, 95% CI 1.06-1.46) based upon two studies involving 4110 patients [31,33,34]. (See "Acute otitis media in children: Epidemiology, microbiology, and complications", section on 'Risk and protective factors'.)
Early cessation of breastfeeding
●Pacifier use – A cause-and-effect relationship between pacifier use and early cessation of breastfeeding has not been established. (See "Initiation of breastfeeding", section on 'Pacifier use'.)
Although multiple observational studies suggest an association between pacifier use and early cessation of breastfeeding and decreased frequency and duration of breastfeeding events [36-44], a systematic review of randomized and quasirandomized trials concluded that pacifier use in healthy full-term infants does not reduce breastfeeding duration up to four months of age . Pacifier use may contribute to a faulty sucking technique or may be a marker for other breastfeeding problems or reduced motivation to breastfeed [36,46-48].
Decreased risk of sudden infant death syndrome — Use of a pacifier appears to reduce the risk of sudden infant death syndrome (SIDS). The mechanism for this association is unclear and causality has not been established. Nonetheless, the American Academy of Pediatrics (AAP) recommends offering a pacifier at naptime and bedtime to reduce the risk of SIDS . (See "Sudden infant death syndrome: Risk factors and risk reduction strategies", section on 'Protective factors'.)
Miscellaneous effects — Digit sucking is associated with an increased risk of development of chronic infections (eg, paronychia) and/or digital deformities . (See "Paronychia", section on 'Introduction'.)
Pacifier use has been associated with increased frequency of oral yeast infections and levels of Candida organisms in the mouth [51-53] and has been identified as a risk factor for lead poisoning .
Balancing the risks and benefits — Decisions about pacifier use must balance the potential risks and benefits. The AAP suggests that the introduction of a pacifier to breastfed infants be delayed until breastfeeding is well established but that thereafter pacifiers be offered at sleep to reduce the risk of SIDS . Well-established breastfeeding is indicated by adequate milk supply; a latch that is comfortable, consistent, and successfully transfers milk; and appropriate weight gain. The time needed to achieve these milestones varies from infant to infant.
When pacifiers are introduced, the optimal type of pacifier is uncertain. A systematic review found insufficient evidence to conclude that "orthodontic" pacifiers prevent malocclusions compared with conventional pacifiers .
Among toddlers with pacifier-associated malocclusion, discontinuation of pacifier use is preferred. Pending discontinuation, use of thin-neck pacifier may be beneficial. In a randomized trial in toddlers (mean age 20.3 months) with pacifier-associated open bite, the thin-neck pacifier group had greater reduction in overbite and overjet at the 12-month follow-up than the conventional or physiologic pacifier group, but the greatest reduction occurred in the group that was weaned off pacifiers .
Interventions to break the habit — To minimize dental effects, we recommend intervention to address sucking habits at approximately two years of age [13,23]. Consultation with the child's dental health provider should be obtained.
The level of intervention for nonnutritive sucking habits depends upon the severity of the problem (eg, frequency, intensity, and duration of the habit) . As a general rule, the habit may be more difficult to break if it is "meaningful" (maintained by some underlying psychological disturbance), conscious, and generalized across multiple settings and if the child is older, female, and not willing to cooperate in cessation efforts .
Strategies may include :
●Discontinuation of caregiver comments about thumb sucking if caregiver attention appears to have reinforced the behavior
●Management of sources of stress and anxiety in the child's life
●A program consisting of positive reinforcement for avoidance of digit sucking (eg, a sticker chart) and negative reinforcement (the application of an aversive tasting substance to the digit)
●Intra-oral dental appliances that serve as a reminder not to suck and/or that interfere with the seal that is necessary for sucking are effective interventions when necessary
A 2015 systematic review of six randomized or quasirandomized trials (252 participants) of interventions for digit sucking in children 2.5 to 18 years of age found that intra-oral dental appliances and positive and negative reinforcement are beneficial in stopping nonnutritive sucking; however, this evidence was of low quality, and more definitive studies are needed to assess the effectiveness of these methods .
Causes — Chronic mouth-breathing can be caused by chronic nasal obstruction/congestion (eg, from allergies or asthma), adenoidal hypertrophy, or anatomic abnormalities (eg, cleft palate), or it may be a learned habit [59-62]. Chronic mouth-breathing is reported to be associated with a characteristic pattern of facial growth; however, the association is disputed .
Prevalence — The prevalence of chronic mouth-breathing among children depends upon the method of assessment and the age of the child [64-66]. It ranges from 9 percent of four-year-olds (based on caregiver report) to 40 percent of first-graders (based upon a 15-minute observation period), although these methods of ascertainment have not been correlated with clinical significance [63,64,67-69].
Orofacial effects — Limited evidence supports an association between chronic mouth-breathing and orofacial effects. Several, but not all, studies suggest that chronic mouth-breathing produces long, narrow faces and that treatment of nasal obstruction results in improved facial morphology [63,70-72]. These studies are limited by the lack of a consistent, clinically relevant definition of chronic mouth-breathing, leading to possible misclassification of subjects in at least some studies. Nonetheless, there is some evidence of an association between nasal obstruction and malocclusion and undesirable facial morphology. Studies in animals support the association .
The primary orofacial effects of chronic mouth-breathing include narrowing of the maxillary arch and over-eruption of the permanent molars with downward and posterior rotation of the mandible (figure 1). These effects are mediated through the altered tongue position and the open-mouth posture. It is not known what proportion of time must be spent in mouth-breathing to be clinically relevant.
●Narrow upper arch – Maxillary arch width is reduced (resulting in posterior crossbite) in children with chronic mouth-breathing, compared with age- and/or sex-matched controls [66,74-78]. The narrow maxillary arch in children with chronic mouth-breathing is related to the altered position of the tongue in oral compared with nasal breathing. In nasal breathing, the tongue rests against the palate where it exerts lateral pressure and plays an important role in the widening of the maxillary arch. In contrast, in mouth-breathing, the tongue rests lower in the oral cavity and thus exerts less lateral pressure on the maxillary arch .
●Over-eruption of the permanent molars with mandibular rotation – Over-eruption of the permanent molars may result in children with chronic mouth-breathing because of lack of contact between the teeth or tissue of opposing arches. Permanent teeth typically continue to erupt until they make contact with teeth or tissue in the opposing arch. Over-eruption of the permanent molars can lead to downward and posterior rotation of the mandible, resulting in increased height of the lower face and retrusion of the mandible. Studies are conflicting as to whether treatment of nasal obstruction (eg, adenoidectomy, aggressive treatment of asthma or nasal allergies) prevents or ameliorates this process . The available data are limited to small observational studies, many of which lacked a control group.
Management — Early and aggressive treatment, including referral to an otolaryngologist if necessary, is warranted for any respiratory or anatomic problem that predisposes a young child to a mouth-breathing pattern .
BRUXISM — Bruxism, the habitual grinding of teeth, usually occurs during sleep, but it also can occur as an unconscious habit during the waking hours . It is reported to occur in 15 to 24 percent of children [81-83]. The frequency of bruxism peaks between 7 and 10 years of age, and then it decreases; it rarely persists through adolescence [6,81,84]. In children, although bruxism is sometimes linked to stress  or parasomnias , it is typically a self-limited problem and rarely requires intervention. In contrast, bruxism in adults can cause severe damage to the teeth and is associated with muscular headaches . (See "Sleep-related movement disorders in childhood", section on 'Sleep-related bruxism'.)
SUMMARY AND RECOMMENDATIONS
●Nonnutritive sucking – Nonnutritive sucking (eg, sucking on a pacifier, thumb, or fingers) is a self-soothing behavior that is normal in early development but may become a learned habit. (See 'Epidemiology' above.)
Prolonged nonnutritive sucking is associated with increased prevalence of malocclusion in the primary and mixed dentition and increased risk of trauma to the upper permanent front teeth. The prevalence of malocclusion increases with increased frequency, duration, and intensity of the sucking habit. (See 'Dental effects' above.)
Although pacifier use is associated with an increased risk of otitis media, early cessation of breastfeeding, and decreased risk of sudden infant death syndrome, cause-and-effect relationships for these associations have not been established. (See 'Other possible effects' above.)
To minimize the dental effects of nonnutritive sucking, sucking habits should be addressed at approximately two years of age. The level of intervention depends upon the severity of the problem. (See 'Interventions to break the habit' above.)
●Chronic mouth-breathing – Chronic mouth-breathing can be caused by chronic nasal obstruction/congestion, adenoidal hypertrophy, or anatomic abnormalities, or it may be a learned habit. Chronic mouth-breathing may be associated with orofacial effects, including narrowing of the maxillary arch and over-eruption of the permanent molars with downward and posterior rotation of the mandible (figure 1). Early and aggressive treatment of conditions that predispose to chronic-mouth-breathing is warranted. (See 'Chronic mouth-breathing' above.)
●Bruxism – Bruxism is the habitual grinding of teeth, usually during sleep. The frequency of bruxism peaks between 7 and 10 years of age and then declines. In children, bruxism is typically a self-limited problem and rarely requires intervention. (See 'Bruxism' above.)
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