A number of studies about the effects of nonnutritive sucking habits have been carried out in Scandinavia. For example, Kohler and Holst⁴ reported that 4-year-old Swedish children with pacifier- or finger-sucking habits were significantly more likely to develop mal-occlusions (anterior open bite, overjet of 3 millimeters or more, posterior cross-bite) than were children with no history of a habit. A Finnish study found that finger-sucking was significantly associated with excessive overjet and Class II malocclusions, as was pacifier use, but that children with a pacifier habit had "less serious" malocclusions.⁵ A study of 310 Danish 3-year-old children found that anterior open bite was associated with persistent sucking habits, and that Class II canine relationship was associated with continued pacifier use.⁶ Svedmyr⁷ reported on a study of 462 Swedish children aged 1 to 10 years (mostly 3- to 5-year-olds), which found that 60 percent of those with a history of a sucking habit (thumb, finger or pacifier) exhibited malocclusion, whereas only 16 percent of those with no habit had malocclusion (P < .001). In this study, malocclusion was considered to be one or more of the following conditions: maxillary protrusion of 4 mm or more, anterior open bite and unilateral or bilateral crossbites.⁷ A study of Swedish 4-year-olds also found sucking habits to be significantly associated with crossbite and, in their sample, crossbite occurred only among those with a history of a sucking habit.⁸ Another Swedish study, also of 4-year-olds, found retrospectively reported sucking habits also to be significantly associated with crossbites.⁹ Lastly, Ogaard and colleagues¹⁰ examined posterior crossbite in 445 Swedish and Norwegian 3-year-old children with and without previous or continued finger- or pacifier-sucking habits. Logistic regression techniques revealed that pacifier use was associated with decreased maxillary intercanine arch width and increased mandibular intercanine arch width, resulting in crossbite.¹⁰

Other international studies found similar relationships. A study of 2- to 6-year-old children in India found that thumb-suckers were significantly more likely to develop Class II canine and molar relationships and were more likely to have anterior open bite and greater overjet than those with no habits.¹¹ Fukata and colleagues¹² retrospectively reviewed dental records of 930 Japanese children aged 3 to 5 years, and found "maxillary protrusion" and anterior open bite more common among children with digit-sucking habits. A cross-sectional study of 583 3- to 5-year-old Saudi Arabian children found sucking habit history to be associated with anterior open bite, increased overjet and Class II molar and canine relationships.¹³

There have been limited studies of these relationships in the United States. Infante¹⁴ found finger-sucking habits to be significantly associated with posterior crossbite and Class II molar relationships among 821 2- to 6-year-old children. A study of 218 2- to 4-year-olds reported that those with a history of pacifier use had significantly greater mean overjet and significantly higher prevalence of Class II primary canine and molar relationships, open bite and posterior cross-bite than did those with no habit history.^15,16

In summary, nonnutritive sucking habits are associated with a higher prevalence of malocclusion in the primary dentition—including conditions such as Class II canine and molar relationships, anterior open bite, increased overjet, decreased maxillary arch width and increased lower arch width—thus resulting in increased likelihood of posterior crossbite.

While these studies clearly indicate that prolonged nonnutritive sucking habits have deleterious effects on occlusion in the primary dentition, they have provided little information to describe the relationship between duration of these sucking habits and malocclusion (owing to their mostly cross-sectional designs). These limited data suggest that crossbite may persist after a sucking habit is stopped, while open bite and maxillary protrusion occur only with sustained habits⁷; that "persistent" habits were associated with Class II molar and canine relationships¹³; and that pacifier-sucking habits of two years or longer are associated with decreased maxillary arch width and pacifier-sucking habits of three years are associated with increased mandibular arch width. ¹⁰ While these findings offer some information, they have not indicated when nonnutritive sucking habits should be stopped to avoid malocclusions, or what effect cessation of such habits at different times has on dental arch characteristics.

We undertook a study to assess the effects of different durations of nonnutritive sucking habits on the occlusal relationships and the dental arch characteristics in the primary dentition, using a study design that collected nonnutritive sucking data longitudinally from birth through age 5 on a large cohort of healthy children.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Subjects evaluated. Our study was part of The Iowa Fluoride Study, a prospective cohort study of fluoride exposures, dental fluorosis and dental caries.^17–21 The authors were part of a large research team involved in that study. The sample was drawn from nearly 700 children who were participants in The Iowa Fluoride Study; they were enrolled at birth between March 1992 and January 1995, when researchers recruited their mothers to participate while the mothers were at eight postpartum hospital wards in Iowa. These children then were followed prospectively from birth, using a series of mailed questionnaires directed at their mothers, which included questions regarding nonnutritive sucking behaviors at three, six, nine, 12, 16, 20 and 24 months and yearly thereafter. The questions posed to parents at each point asked whether their children had regularly sucked on any objects during the previous period and, if so, asked the parents to identify the object as pacifier, thumb, finger or other object. We did not collect information about the type of pacifier (conventional or "orthodontic").

Members of the research team examined the children at 4 to 5 years of age for dental fluorosis and caries; a large proportion of the mothers also consented to have alginate impressions made of their children’s teeth. Of the 547 subjects whose mothers had consented to the impressions, we were able to obtain usable study models of 526 children. Because the purpose of the study was to relate dental arch characteristics in the primary dentition to longitudinal nonnutritive sucking behaviors, we excluded children who had one or more permanent teeth present or in eruption (n = 98), as well as children whose parents did not provide sufficient data to categorize their sucking behavior (n = 56). As a result, we included in these analyses 372 children with both longitudinal sucking behavior data and dental arch data in the late primary dentition.

Protocol. For each participating child, members of the research team obtained alginate impressions of the maxillary and mandibular arches and poured them in yellow stone. Wax bite registrations were made with children guided into centric occlusion, and the articulated casts were trimmed. Landmarks for the measurements were identified and marked on each model by the same examiner (S.E.B.). Measurements of specific dental arch parameters were made directly from the casts using calipers accurate to 0.05 mm. Measurements were made in millimeters and read directly from the calipers. All models were assessed for occlusal relationships by one examiner (J.J.W.), and arch parameters were measured a minimum of two times by two different examiners (K.L.S. and T.Y.). Individual measurements that differed by more than 0.5 mm were measured a third time to resolve the discrepancies.

Occlusal relationships assessed. We assessed the occlusal relationships of articulated casts. The assessments included classification of primary canine relationship (Angle’s classification), presence or absence of anterior crossbite, posterior crossbite and anterior open bite.

Parameters measured. We recorded measurements (in millimeters) of a variety of parameters for each child.

Arch width. We measured arch widths in the following manner (Figure 1):

View larger version (55K): [in this window] [in a new window]   Figure 1. Arch widths. Intercanine arch widths in the maxillary and mandibular arches were measured from cusp tip to cusp tip of the primary canines, and inter-molar arch widths were measured between the mesiobuccal cusp tips of the right and left second primary molars.

– intercanine arch widths in the maxillary and mandibular arches, from cusp tip to cusp tip;

– intermolar arch widths, between the mesiobuccal cusp tips of the right and left second primary molars.

Arch length. We measured total maxillary and mandibular arch lengths as segments on the right and left sides as follows:

– anterior segment, from the contact area of the central incisors to the contact area between the canine and primary first molar;

– posterior segment, from the contact between the canine and primary first molar to the most distal point of the second primary molar.

We summed the segment lengths for the right and left sides for each arch to determine the total length of each arch (Figure 2).

View larger version (54K): [in this window] [in a new window]   Figure 2. Arch lengths were measured in segments. The anterior segment was measured from the contact area of the central incisors to the contact area between the canine and primary first molar on the right and left sides (A and C). The posterior segment was measured from the contact between the canine and primary first molar to the most distal point of the primary second molar on the right and left sides (B and D). The segment lengths for the right and left sides for each arch were summed to determine each arch’s total length.

View larger version (30K): [in this window] [in a new window]   Figure 3. Arch depths. Canine arch depth was defined as the length of a line running perpendicularly from the midpoint between the central incisors to a line connecting the distal contact points of the right and left canines for both the maxillary and mandibular arches. Molar arch depth was defined as the length of a line running perpendicular from the midpoint between the two central incisors to a line connecting the most distal points of the right and left second primary molars for both the maxillary and mandibular arches.

– anterior arch depth, defined as the length of a line running perpendicularly from the midpoint between the central incisors to a line connecting the distal contact points of the right and left canines;

– posterior arch depth, defined as the length of a line running perpendicular from the midpoint between the two central incisors to a line connecting the most distal points of the right and left primary second molars.

Palatal depth. We measured palatal depth as the length of a line from the deepest point in the palate to a line connecting the cusp tips of the primary second molars (Figure 4).

View larger version (48K): [in this window] [in a new window]   Figure 4. Palatal depth was measured as the length of a line from the deepest point in the palate to a line connecting the buccal cusp tips of the primary second molars.

View larger version (31K): [in this window] [in a new window]   Figure 5. Overjet and overbite. Overjet was measured as the distance along a horizontal plane between the incisal edge of the labial surface of the mandibular central incisor and the incisal edge of the labial surface of the most labially positioned maxillary central incisor. Over-bite was measured as the vertical distance (in millimeters) between the incisal edge of the maxillary central incisor and the incisal edge of the mandibular central incisor.

Nonnutritive sucking habit duration. Comparisons were made between the different levels of nonnutritive sucking exposures. Specifically, children were placed into five groups based on the presence of a nonnutritive sucking habit (of digit or of pacifier) at 12, 24, 36 and 48 months. These five groups were Group 1, habit ceased before 12 months of age; Group 2, habit continued at 12 months but ceased by 24 months; Group 3, habit continued to 24 months, but ceased by 36 months; Group 4, habit continued at 12, 24 and 36 months but ceased by 48 months; and Group 5, habit continued to at least 48 months.

Statistical analysis. We entered data using SPSS Data Entry Builder²² and analyzed them using the SPSS statistical program.²³ We compared the five sucking-habit–duration groups using a one-way analysis of variance; we also performed separate comparisons for boys and girls in this manner. In addition, duration-specific comparisons between those with pacifier-sucking habits and those with digit-sucking habits were made using t tests. Significance was predetermined at P < .05.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Nonnutritive sucking was almost universal among those included in the study, as only eight of the 372 subjects (2.2 percent) were reported as having had no nonnutritive sucking habit at any time during the study. As described previously, subjects were categorized by the duration of their sucking habit based on whether they had a habit at each birthday. In this way, 119 subjects (31.9 percent) were included in Group 1, as they had ceased all sucking habits by 12 months of age; 93 (25.0 percent) were included in Group 2, as they had a habit at 12 months but ceased their habit by 24 months; 69 (18.5 percent) were included in Group 3, as they had a habit at 24 months but had ceased their habit by 36 months; 32 (8.6 percent) were included in Group 4, as they had a habit at 36 months but had ceased their habit by 48 months; and 59 (15.9 percent) were included in Group 5 as they continued to have a nonnutritive sucking habit at 48 months of age.

Type of habit. Table 1 presents data on type of habit (digit-sucking—thumb or finger—or pacifier-sucking) at the last time the child was reported to have had a habit. Digit-sucking habits were more common than pacifier-sucking habits for those whose habits ceased by 12 months of age. However, pacifier-sucking habits predominated for those who ceased their habit between 12 and 48 months of age, but thumb-and finger-sucking habits predominated among those whose habits continued at 48 months of age.

Duration of habit, arch measurements and occlusal characteristics. As shown in Table 2, continued nonnutritive sucking habits to 48 months of age or older resulted in significantly smaller maxillary canine and maxillary molar arch widths; greater maxillary canine and maxillary molar arch depths; greater overjet; smaller overbite; and less palatal depth. Boys and girls did not demonstrate these effects uniformly. For example, maxillary canine arch widths were smaller among those with sucking habits at 48 months of age or older than those with habits of other durations in both sexes combined and among boys and girls separately. In contrast, while maxillary molar arch widths were smaller among those with sucking habits at 48 months of age compared with those of habits of other durations in both sexes combined, when we compared this group to the others separately by sex, only the boys in the group demonstrated a significant difference from the children in the other duration groups.

Table 3 presents the prevalence of selected occlusal conditions by sucking duration group. All of these parameters—anterior open bite, posterior crossbite, excessive overjet and any Class II canine relationship—were significantly more prevalent among those with continued sucking habits at 48 months of age or older than for the other four groups. These parameters also showed a tendency towards increasing prevalence with increased sucking duration. As Table 3 indicates, children with sucking habits at 24 months of age or older had an increased prevalence of these mal-occlusions, but children with continued habits at 48 months had by far the highest prevalence.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

The results of the study are consistent with numerous previous studies in the literature, in that prolonged nonnutritive sucking habits were associated with changes in several dental arch measurements, such as decreased maxillary arch widths, increased overjet and decreased overbite. In addition, those with prolonged habits were more likely to have anterior open bites and posterior crossbites. More importantly, however, the unique design of the present study allowed assessment of the effects of different sucking-habit durations on dental arch measurements and occlusal characteristics. Notably, even when habits were ceased between 24 and 36 months of age, there was increased risk of developing posterior crossbite and increased mandibular canine arch width, compared with those who ceased sucking habits by 12 months of age. In addition to these differences, those who ceased habits between 36 and 48 months also had greater prevalence of excessive overjet, greater maxillary canine arch depth, greater mean overjet and slightly increased prevalence of open bite in comparison with those who ceased sucking habits at a younger age.

Thus, while continuous or long-term nonnutritive sucking habits at or beyond 48 months of age produce rather predictable changes in dental arch measurements and occlusal relationships, children with shorter sucking-habit durations also evidence detectable differences from those who had no habits or ceased habits by 12 months of age. In particular, it appears that sucking habits beyond 24 months of age may result in increased risk of developing posterior crossbite (and a correspondingly increased mandibular canine arch width), and greater overjet. As Table 3 demonstrates, posterior crossbite prevalence steadily increased from 5.8 percent among those who ceased habits by 12 months of age to 13.0 percent among those who ceased habits between 24 and 36 months of age to more than 20 percent for those with a continued habit at 48 months. The study also demonstrated similar trends in prevalence of excessive overjet, anterior open bite and one or more of these malocclusions (Table 3). In addition, the study demonstrated that with longer sucking duration mean overjet, mean palatal depth, mean mandibular canine arch width and mean maxillary canine arch depth were statistically significantly increased (Table 2); however, the magnitude of these differences—generally 1 mm or less—may not be of much clinical significance.

If a child’s sucking habits persist by the time he or she is 36 to 48 months of age, professional assistance in habit discontinuation may be warranted to minimize the risk of developing malocclusion.

Clearly, a key question is whether any of these changes brought about by nonnutritive sucking habits observed in the primary dentition persist into the mixed or permanent dentitions, or whether they resolve. The limited literature in this area suggests that some of the changes resulting from nonnutritive sucking do persist to some extent. In an early longitudinal study of 116 Australian children from age 2 to 8 years, Bowden^24,25 found that increased overjet, decreased overbite and decreased arch widths persisted for two to five years after the habit was stopped.²⁵ Larsson³ investigated the effects of different patterns of pacifier-sucking habits on a number of dental arch and cephalometric variables in 9-year-olds. He found slight effects on the occlusion when pacifier-sucking habits were discontinued before they reached 3 years of age, with more pronounced effects in children with pacifier-sucking habits of four years or longer.³

	CONCLUSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
We will attempt to follow children in this study cohort into the age of mixed dentition and assess the effects of different durations of nonnutritive sucking on dental arch measurements and occlusal characteristics. Given the paucity of longitudinal data reported in the literature and the limitation of the results of this study to the primary dentition, it may be premature to make wholesale changes in recommendations regarding cessation of nonnutritive sucking habits. However, given that some changes that occur because of sucking habits seem to persist past cessation of the habits, it may be prudent to revisit suggestions made by several organizations that habits discontinued by as late as 5 to 8 years of age are of little concern.^26–29 Infants and very young children have an inherent biological drive to suck, and nonnutritive sucking often provides them (and their parents) comfort.^30,31 Thus, recommendations to cease nonnutritive sucking habits before 24 months of age would be unrealistic, potentially detrimental and unnecessary from a dental standpoint. The results of the study suggest some potential harm in continuing habits beyond 24 months of age, with greater risk of developing occlusal problems with longer sucking-habit duration, particularly habits persisting to 48 months of age or beyond.

Therefore, to satisfy infants’ need for sucking while minimizing their risk of developing occlusal abnormalities, the ideal age for discontinuation of nonnutritive sucking habits may be around 24 months. Relatively little harm occurs if such habits are continued to 36 months, so that early dental visits should provide parents with anticipatory guidance to help their children cease such habits by 36 months of age or younger. However, if the child’s habits persist by the time he or she is 36 to 48 months of age, professional assistance in habit discontinuation may be warranted to minimize the risk of developing malocclusion.