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 . 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\".)
NONNUTRITIVE SUCKING — 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 . 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 . Compared with pacifier sucking, digit sucking is more likely to persist into the fourth or fifth year of life, when it may become problematic . 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 .
Overview of 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 teeth .
In addition to the dental effects of nonnutritive sucking, pacifier use has been associated with numerous other health effects, including increased risk of development of otitis media, early cessation of breastfeeding, and possible decreased risk of sudden infant death syndrome (SIDS). These effects are less clearly associated with digit sucking. A cause-and-effect relationship for these associations has not been established, and in some situations reverse causality may play a role .
Dental effects — The association between digit sucking and abnormalities in the primary dentition was reported as early as the 1870s . It is described in several retrospective studies, many of which used questionnaires to assess sucking behaviors . The association is consistent, although its strength varies depending upon the study. The risk of malocclusion increases directly with frequency, duration, and intensity of sucking habit and is not eliminated by the use of \"orthodontic\" pacifiers.
The following types of malocclusion in the primary dentition are associated with sucking habits:
Open bite (the upper and lower anterior teeth do not overlap)
Posterior crossbite (the upper posterior teeth bite inside the lower posterior teeth on one or both sides)
Excessive overjet (excessive horizontal overlap of the upper relative to the lower front teeth); in children with digit habits, it may be exacerbated by lower incisors that are positioned toward the tongue (lingually positioned)
Class II relationship (the upper jaw protrudes too far in front of the lower jaw)
Few studies have evaluated whether habit-related malocclusion of the primary dentition persists into the permanent dentition. In one longitudinal study of 116 Australian children two to eight years of age, persistent finger sucking was related to increased overjet and a proportion of Class II malocclusions; dental arch width was not affected [30,31]. In contrast, pacifier use was associated with decreased arch width that typically resolved within two to three years after pacifier use was discontinued. Increased prevalence of posterior crossbite among children with nonnutritive sucking habits was not noted in this study.
A cross-sectional study of 320 nine-year-old children evaluated the relationship between various patterns of digit and pacifier sucking and facial growth and occlusion . Finger-sucking was associated with greater overjet, decreased maxillary arch width, and increased maxillary arch length. The effects of pacifier use were more pronounced when pacifier use was continued beyond the age of four years . The permanent dentition of a subset of the cohort was examined when they reached 16 years of age . Skeletal changes, including anterior rotation of the nasal and mandibular planes, were found more commonly among those with a previous sucking habit than in those without. In addition, Class II malocclusions and traumatic injuries to the maxillary anterior teeth were found more commonly among those with a history of finger sucking than those who used a pacifier or did not have a sucking habit.
In a 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) . Children with a history of trauma were likely to report additional trauma. Most of the injuries were mild and involved the permanent central incisors.
Another study evaluated the relationship between sucking habits and malocclusion and swallowing habits of 10- to 11-year-old children . Among children with a history of a sucking habit, persistence of a tongue thrust swallowing pattern was found more commonly; this swallowing pattern was associated with Class II malocclusion, extreme maxillary overjet, and open bite. However, the tongue-thrust pattern did not account completely for malocclusion because there was an increased frequency of malocclusion independent of the swallowing pattern.
A study of 444 eight- and nine-year-old children who had extensive longitudinal nonnutritive sucking data collected periodically from birth found that prolonged pacifier habits (to 24 to 47 months of age) were associated with increased occurrence of anterior open bite and Class II malocclusion in the early mixed dentition . Prolonged digit habits were associated with anterior open bite, although any habit (digit and/or pacifier) was associated with posterior crossbite .
Otitis media — The association between pacifier use and acute otitis media (AOM) has been reported in one meta-analysis and several prospective studies . 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 .
The association of digit sucking and otitis media is less clear; it was not found in either of the studies described above , but it has been described in others .
Breastfeeding — The association between pacifier use and early cessation of breastfeeding has been documented in several longitudinal studies . The association remains even after controlling for potential confounding variables including age, sex, birth weight, maternal education, and family income. In these studies, early cessation of breastfeeding is two to three times more likely to occur among pacifier users than non-users. Pacifiers also have been associated with shorter duration of breastfeeding at each feeding event and fewer feeding events per day .
A cause-and-effect relationship between pacifier use and early cessation of breastfeeding has not been established, and it may be that pacifier use is a marker for breastfeeding problems or reduced motivation to breastfeed . An alternative explanation is that such pacifier use contributes to a faulty sucking technique, which in turn leads to breastfeeding problems .
An association between digit sucking and early cessation of breastfeeding is reported in some studies but not in others.
SIDS — An association between pacifier use and decreased incidence of sudden infant death syndrome (SIDS) has been reported in case-control studies (odds ratio 0.38 to 0.44 in various studies) . Although a cause-and-effect relationship has not been established [59,60], a meta-analysis found that pacifiers given for sleep had \"dramatic beneficial results\" in preventing SIDS . The American Academy of Pediatrics recommends that caregivers “consider offering a pacifier at nap time and bedtime” to prevent SIDS .
Miscellaneous effects — Digit sucking is associated with an increased risk of development of chronic infections (eg, paronychia) and/or potential orthopedic problems .
Pacifier use is associated with increased frequency of oral yeast infections and levels of Candida organisms in the mouth and has been identified as a risk factor for lead poisoning. In addition, pacifier use has been associated with increased parent-reported symptoms (wheezing, earache, vomiting, fever, diarrhea, and colic) in four- to six-month-old infants . However, in this questionnaire survey, the cause-and-effect relationship was not established, and the pacifier may have been used as a means of comfort after the illness was established.
Pacifier use — Recommendations for pacifier use must balance the potential risks and benefits. The American Academy of Pediatrics suggests that for breastfed infants the introduction of a pacifier be delayed until breast feeding is well established (one month of age), but that thereafter pacifiers be offered at sleep to reduce the risk of SIDS .
Breaking the habit — To minimize dental effects, we recommend intervention to address sucking habits before three years of age. 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 psychologic 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 parental comments about thumb sucking if parental 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 the application of an aversive tasting substance to the digit
Intraoral 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
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 . 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 . It ranges from 9 percent of four-year-olds (based on parental 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 .
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 . 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, the evidence seems to support 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, over-eruption of the permanent molars, and downward and posterior rotation of the mandible. 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 who are chronic mouth-breathers, compared with age- and/or sex-matched controls. The narrow maxillary arch in chronic mouth-breathers 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 .
Mandibular rotation — Permanent teeth typically continue to erupt until they make contact with teeth or tissue in the opposing arch. Because this contact is missing in chronic mouth-breathers, over-eruption of the permanent molars may result. 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.
The association between mandibular rotation and nasal obstruction is supported by numerous studies in which treatment of nasal obstruction (eg, adenoidectomy, aggressive treatment of asthma or nasal allergies) led to improved mandibular position :
In one study, the mandibular morphology of 26 children who were five years status postadenoidectomy for nasal obstruction was compared with that of age- and sex-matched controls . Surgery resulted in improved facial height and less retrusive mandibles compared with preoperative morphology. However, the morphology of the adenoidectomy group remained different from that of a control group with no history of mouth-breathing or nasal airway obstruction.
In another study, pre- and postoperative dental casts and mandibular radiographs of 22 children who underwent tonsillectomy for sleep apnea were compared with those of children without upper airway obstruction . Two years after surgery, anterior open bites and posterior crossbites had resolved in 16 of 19 children; the best results were obtained in children who underwent surgery before reaching the age of six years.
Management — We recommend early and aggressive treatment, including referral to an otolaryngologist if necessary, 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 . The frequency of bruxism peaks between 7 and 10 years of age, and then it decreases; it rarely persists through adolescence . 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 .
SUMMARY AND RECOMMENDATIONS
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.
Nonnutritive sucking is associated with increased prevalence of malocclusion in the primary and mixed dentition and increased risk of trauma to the upper front teeth. The prevalence of malocclusion increases with increased duration of the sucking habit.
Pacifier use is associated with an increased risk of otitis media, early cessation of breastfeeding, and decreased risk of sudden infant death syndrome (SIDS). However, cause-and-effect relationships for these associations have not been established.
To minimize the dental effects of nonnutritive sucking, we recommend intervention to address sucking habits before three years of age. The level of intervention depends upon the severity of the problem.
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 appears to be associated with orofacial effects, including narrowing of the maxillary arch, over-eruption of the permanent molars, and downward and posterior rotation of the mandible. It is not known what proportion of time must be spent in mouth-breathing to be clinically relevant.
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.