The presence of an oral habit in a 3- to 6-year-old child is an important finding during the clinical examination. An oral habit is not usually present in children near the end of this age group. Preferably, a habit that has resulted in movement of the primary incisors or has inhibited their eruption will have been eliminated before the permanent incisors erupt. If a habit that causes dental changes is not eliminated or spontaneously discontinued before the permanent incisors erupt, they too will be affected. On the other hand, these are not irreversible changes. If the habit is stopped during the mixed-dentition years, the adverse dental changes will begin to reverse naturally. Appliance therapy may be required, but generally the teeth will move toward a more neutral position with the absence of the forces of the habit.
If no dental changes have occurred, no treatment can be advocated on the grounds of dental health, but some patients and parents may want treatment because digit or pacifier habits become less socially acceptable as the child becomes older. One study has shown that school-aged children consider thumb suckers significantly less intelligent, less attractive, and less desirable as friends.8 Efforts to discourage the habit may involve as little as a conversation between the dentist and the child, or they may involve more complex appliance therapy. The most important point to remember about any intervention is that the child must want to discontinue the habit for treatment to be successful.
Thumb and finger habits make up the majority of oral habits. About two thirds of such habits are ended by 5 years of age.14 Dentists are often questioned about the kinds of problems these habits may cause if they are prolonged. The malocclusions caused by nonnutritive sucking may be more of an individual response than a highly specific cause-and-effect relationship.4 The types of dental changes that a digit habit may cause vary with the amount of force applied to the teeth and how long the force is applied (daily and in months or years) as well as the manner in which the digit is positioned in the mouth. Research and clinical experience have shown that as little as 35 grams of force can tip a tooth.26 It is apparent that children vary in the amount of force applied during sucking. Some suck with a great deal of intensity and others essentially rest the digit in their mouth. The amount of time spent sucking a digit will have an impact on tooth movement. The amount of time sucking (in months) probably plays the most critical role in tooth movement caused by a digit habit.24 Clinical experience suggests that 4 to 6 hours of force per day is probably the minimum necessary to cause tooth movement.26 Therefore a child who sucks intermittently with high force may not produce much tooth movement at all, whereas a child who sucks with less force but continuously (for more than 6 hours) can cause significant dental change, which is consistent with the equilibrium theory. The duration of digit sucking habits (months or years) is positively related to an increased prevalence of anterior open bite or reduced overbite, increased overjet, greater maxillary arch depth, and decreased maxillary arch width.24 The most frequently reported dental signs of an active habit are the following:
Anterior open bite, or the lack of vertical overlap of the upper and lower incisors when the posterior teeth are in occlusion, develops because the digit rests directly on the incisors (Figure 26-1). This prevents complete or continued eruption of the incisors, whereas the posterior teeth are free to erupt. Anterior open bite may also be caused by intrusion of the incisors. However, inhibition of eruption is easier to accomplish than true intrusion, which would be the result of a habit of greater duration.
FIGURE 26-1 This patient’s anterior open bite is a direct result of an active thumb sucking habit. An open bite results when the thumb impedes eruption of the anterior teeth, moves them facially, and allows the posterior teeth to erupt passively. Actual intrusion of the anterior teeth is possible but unlikely.
Faciolingual movement of the incisors depends on how the thumb or finger is placed and how many fingers are placed in the mouth. Some consider this positional variable to be a confounding factor related to force and duration of the habit. Usually, the thumb is placed so that it exerts pressure on the lingual surfaces of the maxillary incisors and on the labial surfaces of the mandibular incisors (Figure 26-2). A child who actively sucks can create enough force to tip the upper incisors facially and the lower incisors lingually. The result is an increased overjet and, by virtue of the tipping, decreased overbite.
FIGURE 26-2 With most thumb sucking habits, the thumb exerts pressure on the lingual surface of the maxillary incisors and on the facial surface of the mandibular incisors. This causes the maxillary incisors to tip facially and the mandibular incisors to tip lingually, resulting in increased overjet.
Maxillary arch constriction is probably due to the change in equilibrium balance between the oral musculature and the tongue.27 When the thumb is placed in the mouth, the tongue is forced down and away from the palate. The orbicularis oris and buccinator muscles continue to exert a force on the buccal surfaces of the maxillary dentition, especially when these muscles are contracted during sucking. Because the tongue no longer exerts a counterbalancing force from the lingual surface, the posterior maxillary arch collapses into crossbite (Figure 26-3).
FIGURE 26-3 This patient exhibits a right maxillary posterior crossbite. A posterior crossbite is often the side effect of a thumb or pacifier habit because the tongue is displaced inferiorly and the orbicularis oris and buccinator muscles exert a force on the upper teeth. When there is no counterbalancing force from the tongue, the upper arch falls into crossbite.
Data on the amount of skeletal change are not clear. Some believe the maxilla and its alveolar process are moved anteriorly and superiorly.17 Certainly, if the teeth are moved, some alveolar change occurs. Whether this is translated to the skeletal maxilla is not as well known. In one study a significantly higher percentage of distal step molar relationships in 5-year-olds was noted among digit suckers compared with children with no sucking habit.9
Timing of treatment must be gauged carefully. If parents or the child do not want to engage in treatment, it should not be attempted. The child should be given an opportunity to stop the habit spontaneously before the permanent teeth erupt. If treatment is selected as an alternative, it is generally undertaken between the ages of 4 and 6 years. Delay until the early school-age years allows for spontaneous discontinuation of the habit by many children, often through peer pressure at school. As long as the habit is eliminated before full eruption of the permanent incisors, the eruption process will spontaneously reduce the overjet and open bite as the permanent teeth occupy new positions. It is generally agreed that interception of a digit sucking habit does no harm to the child’s emotional development, nor does it result in habit substitution. However, the dentist should evaluate the child for psychological overtones before embarking on habit elimination. Such procedures might best be postponed for children who have recently undergone stressful changes in their lives, such as a new sibling, separation or divorce of parents, moving to a new community, or changing schools. Four different approaches to treatment have been advocated, depending on the willingness of the child to stop the habit. It is important to select the approach that is age appropriate and acceptable to parents to increase the odds of successful treatment.
The simplest yet least widely applicable approach is counseling with the patient. This involves discussion between the dentist and the patient of the problems created by nonnutritive sucking. These adultlike discussions focus on the changes that have occurred because of the sucking and their impact on aesthetics. Usually an appeal is made to the children on the basis of their maturity and responsibility. Clearly, this approach is best aimed at older children who can conceptually grasp the issue and who may be feeling social pressure to stop the habit. Some children are captured by this approach and successfully eliminate their habit.
The second approach, reminder therapy, is appropriate for those who desire to stop the habit but need some help. The purpose of any treatment should be thoroughly explained to the child. An adhesive bandage secured with waterproof tape on the offending finger can serve as a constant reminder not to place the finger in the mouth (Figure 26-4). The bandage remains in place until the habit is extinguished. There are some parents who are reluctant to use the bandage as a reminder. They are concerned that it may come off during sleep and the child may swallow or aspirate the bandage. Therefore some clinicians use a mitten or a tube sock to cover the fingers of the hand. This is especially useful during sleeping hours. Other commercial products such as shirts that cover the hand or plastic sleeves that cover the thumb are available. Another approach is to paint a commercially available bitter substance on the fingers that are sucked. However, sometimes this type of therapy is perceived as punishment and may not be as effective as a neutral reminder. In conclusion, reminder therapy works by changing the sucking sensation enjoyed by the child.