INTRODUCTION

It is generally accepted that a disruption in arch integrity of the primary or mixed dentition without space maintenance will lead to a malocclusion that is dependent upon the type and time of tooth loss. Miyamoto and co-workers1 demonstrated that in a study of 225 school children the premature loss of primary canines and molars resulted in the need for orthodontic treatment when no space maintenance was utilized. In a review of the literature, Owen2 and Bell et al.3 have indicated that in almost all cases of early tooth loss, some decrease of arch length is to be expected, and this loss occurs within the first 6 months after the tooth is lost, at the time of active tooth eruption.

The insertion of space maintainers does not automatically follow the premature loss of deciduous teeth. The decision as to the type and placement of a space maintainer rests with the following criteria: when the tooth was lost, what tooth was lost, from which arch the tooth was lost, whether the permanent successor is present, the occurrence of space loss, the existing arch length requirements for the permanent dentition, and the cooperation and oral health status of the patient.

The premature loss of primary first molars requires space maintenance only under specific circumstances.3 During the active eruption of the permanent first molar from ages 5–7 years, mesially directed forces may result in the loss of first primary molar space. Additionally, when the first permanent molar is in an end-to-end relationship before an early or late mesial shift has occurred, space loss may occur as a result of potential molar occlusal adjustments.

Additional factors often ignored in potential space loss are the morphologic differences of the child's face. Patterns of vertical or horizontal growth that are apparent clinically are usually overlooked in the young child as a result of established criteria for radiation exposure and the lack of necessity for cephalograms at a young age. Therefore, whether the patient exhibits a hypodivergent or hyperdivergent facial appearance, the diagnosis must be made during the clinical examination. The purpose of this investigation was to determine how much, if any, space loss occurred when the maxillary or mandibular first primary molar was lost prematurely in patients with end-on, Class I, and Class II molar occlusions and horizontal or vertical facial growth patterns.

MATERIALS AND METHODS

The patients examined in this study were obtained from the University Clinics at Stony Brook University and gave consent as private patients to participate. Approval was also granted by the Internal Review Board of Stony Brook University on the Use of Human Subjects. The total patient sample of consecutively treated patients of the age group specified consisted of 226 children, 135 females and 91 males ranging in age from 7 years 8 months to 8 years 2 months.

Inclusion criteria consisted of the following:

• Signed consent form;

• Age group of patients between 7 years and 8.5 years;

• A mixed dentition with the permanent molar relationship in an end-on molar occlusion, Class I or Class II molar occlusion; the presence of four erupting or erupted maxillary incisors and four erupting or erupted mandibular incisors;

• A unilateral missing maxillary or mandibular first primary molar that had been extracted within 1 week of the examination or one that was planned for extraction; the contralateral and opposing arch having an intact occlusion;

• One-half or less root formation of the first premolar in the jaw below the missing first primary molar;

• No other missing teeth resulting from extraction or trauma;

• The absence of interproximal caries;

• The absence of any appliances in the oral cavity; and

• Parents or caretakers who did not want the child to receive a space maintainer.

Direct intraoral measurements were made twice by the first author and twice by the third author with a digital caliper set to the accuracy of 0.1 mm after the extraction of the first primary molar or of the space previously created as a result of the extraction. A second measurement was repeated 1 minute after the initial measurement, and the four measurements from both examiners were averaged to obtain a final number. All extraction sites were measured at the initial examination and at 9 months after the extraction procedure. The intact side served as a control. Space change was defined as the distance between the mesial midpoint of the first permanent molar and the distal midpoint of the primary canine. Of the 226 patients examined, only 12 displayed a full Class II molar occlusion (5%) and were therefore placed into the end-on category.

RESULTS

The intraclass correlation coefficient revealed good repeatability for all intraoral and extraoral measurements. The mean value for all intraoral measurements was .966 (range, .875–.995) for intraobserver repeatability and .944 (range, .845–.990) for interobserver repeatability, respectively. The mean value for all extraoral (facial) measurements was .975 (range, .915–.995) for intraobserver repeatability and .950 (range, .880–.980) for interobserver repeatability, respectively.

Table 1 represents the overall composition of the patients in the study. All patients who displayed a leptoprosopic facial form appeared clinically to be hyperdivergent, while the combined mesoprosopic/euryprosopic group was normodivergent. The majority of patients had end-on molar occlusions in the early mixed dentition. These individuals comprised 60% of the patients, while Class I molar occlusions occurred in 40% of the patients examined. Of the total population examined, 39% were leptoprosopic, while the majority (61%) displayed mesoprosopic/euryprosopic facial forms.

Table 1. The Total Number of Missing Maxillary and Mandibular First Primary Molars Displaying Either an End-On Molar Occlusion, Class II Occlusion, or Class I Occlusion and their Associated Facial Forms

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The Leptoprosopic Facial Form and End-On Molar Occlusion (Table 2)

Table 2. Comparison of Space Changes (mm) Between the Initial Examination and 9-Month-Follow-Up Examination in Both the Control and Extraction Sides for Patients with End-On Molar Occlusions and Leptoprosopic or Mesoprosopic/Euryprosopic Facial Forms

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Patients displaying a leptoprosopic facial form and end-on molar occlusion showed no change in either the maxillary or mandibular control sides. However, both maxillary and mandibular space loss occurred in the first primary molar site that was statistically significant. Average space loss in the maxilla was 1.75 mm, and in the mandible the average space loss was 1.38 mm. The clinical loss of space in the maxilla was due to mesial migration of both the second primary molar and permanent first molar. All space loss in the maxilla (29 extraction sites) displayed this form of lost space. Space loss in the mandible was due to both mesial migration of the teeth distal to the extraction space and distal movement of the primary canine in 21 of the individuals, while the remainder of space loss appeared attributable to mesial migration of the distal segments in four subjects.

The Leptoprosopic Facial Form and Class I Molar Occlusion (Table 3)

Table 3. Comparison of Space Changes (mm) between the Initial Examination and the Follow-Up Examination at 9 Months in Both the Control and Extraction Sides in Patients with Class I Molar Occlusions and Leptoprosopic or Mesoprosopic/Euryprosopic Facial Forms

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The maxillary and mandibular control sides showed no loss of space during the time period examined. After 9 months, space loss occurred in both the maxillary and mandibular extraction sites in the leptoprosopic facial form patients. On average, maxillary space loss was 0.89 mm, and in the mandible, space loss was 1.71 mm. Both values were statistically significant. The pattern of space loss was identical to that of the patients with end-on molar occlusions. All space loss in the maxilla of 18 individuals was due to mesial migration, while the pattern of space loss in the mandible occurred by mesial migration of the distal segments and distal tipping of the primary canine in 15 individuals and by mesial migration only in two subjects.

Mean Space Changes

When an end-on occlusion was evaluated for mean space change that occurred over the 9-month period in patients with a leptoprosopic facial form and the combined facial forms, a statistically significant difference was observed for both the maxillary and mandibular sites, respectively. Average space change for the end-on occlusion patients with a leptoprosopic facial form was −1.75 mm in the maxilla and −1.38 mm in the mandible, while the combined forms showed a +0.07-mm change in the maxilla and a −1.59-mm change in the mandible. A statistically significant difference was also observed when the Class I patients were compared with their respective facial forms. Average space change for the Class I occlusion patients with a leptoprosopic facial form was −0.89 mm in the maxilla and −1.71 in the mandible, while the mesoprosopic/euryprosopic forms resulted in changes of −0.11 mm in the maxilla and −0.08 mm in the mandible, respectively (Table 4).

Table 4. Mean Space Changes (mm) in the Primary First Molar Extraction Sites in Patients with Leptoprosopic vs Mesoprosopic/Euryprosopic Facial Forms and End-On and Class I Molar Occlusions

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Comparison of space change with leptoprosopic facial forms vs mesoprosopic/euryprosopic facial forms with respect to the end-on and Class I occlusions yielded the following results: a statistically significant difference was noted in the maxilla of leptoprosopic individuals when the end-on and Class I occlusion were compared for mean space change; a statistically significant difference was also observed in the mandible of the mesoprosopic/euryprosopic individuals when an end-on and Class I occlusion were compared to each other (Table 4).

DISCUSSION

Conflicting perspectives exist for the clinical management of prematurely lost first primary molars.2–13 Kisling9 have indicated that after the eruption of the first permanent molar, space maintainers need not be inserted, since negligible space is lost at this time, a recommendation also supported by the American Academy of Pediatric Dentistry.12 However, the degree of interdigitation of the permanent molar occlusion may play a vital role in terms of whether space maintenance is or is not required,14 as our results indicate.

We observed that the facial pattern of children after 7 years of age, as well as molar occlusion, may influence the necessity for space maintainers when early recommendations made them unnecessary.11,12 Although the use of appliances is advocated to maintain space for the eruption of the permanent dentition when the primary teeth are lost prematurely, it is not entirely age- or stage-of–first permanent molar eruption–dependent8,9 when facial appraisal is developed at the chairside.

Since the pattern of facial growth has been established at an early age,14–16 very little if any change is anticipated to naturally occur. Leptoprosopic individuals represented 39% of patients examined, while it was more common to observe the combined mesoprosopic/euryprosopic individuals, as we originally suspected, since the lower face elongates as the child matures17,18; however, the growth pattern appeared to influence the degree of space loss when combined with the molar relationship. Leptoprosopic patients with end-on and Class I molar occlusions consistently lost space in the maxillary and mandibular first primary molar site, while space loss in the combined group of patients only occurred in the mandibular extraction site with end-on occlusions. The loss of mandibular space in the combined group is consistent with findings that report a greater loss of space in the mandible than in the maxilla,2,6,7 possibly due to the combination of both mesial and distal movements into the extraction site. This finding is also consistent with studies19–23 that have shown that weaker jaw muscles are associated with hyperdivergent individuals, who also display reduced muscle size, efficiency, and anchorage loss during orthodontic tooth movement. No space loss in the maxilla or mandible was observed in individuals with a Class I molar occlusion and mesoprosopic/euryprosopic facial forms, indicating that space maintenance may not be necessary in patients with these clinical findings.

Interestingly, when mean space changes were evaluated all end-on and Class I occlusions, respectively, were statistically significant, except for mandibular extraction space between the leptoprosopic and combined facial forms. Comparison of mean value differences within a fraction of a millimeter in the maxilla of Class I individuals is clinically insignificant; however, it is important to note the large variation in space loss between the leptoprosopic and combined forms. When the leptoprosopic individuals were compared to mesoprosopic/euryprosopic patients, a statistically significant difference was observed in the maxilla of the leptoprosopic form for end-on vs Class I patients and in the mandible of the mesoprosopic/euryprosopic form for end-on vs Class I individuals. The high mean space change in the extraction site appeared to be due to the end-on occlusions in which space loss was more apparent. Although statistically insignificant, no appreciable space change occurred in the maxilla of the combined facial form group, regardless of whether the occlusion was end-on or Class I. Statistically insignificant, but clinically significant, was the space loss change in the mandible for both the end-on and Class I occlusions with the leptoprosopic facial form. This amount of space loss has treatment implications. These clinical finding may indicate that facial forms as well as occlusal relationships of the permanent first molar indicate the use and need of space maintenance when primary first molars are prematurely lost.

No determination of permanent molar root length completion was evaluated in these patients; therefore, it is also possible that until root formation is completed, permanent first molar movement may result in loss of space in patients with weaker musculatures as well. Although space loss was reported in the study, no change in the overall molar classification (Angle) was observed. The lack of change in the molar occlusal relationship despite space loss was most likely the result of concurrent normal antero-posterior growth of the jaws.

Based upon these findings, it is advised that space maintenance for the premature loss of primary first molars be revisited. The placement of a space maintainer in the maxilla or mandible is recommended when a patient presents with one of the following conditions: (1) a leptoprosopic facial form and end-on molar relationship and missing maxillary or mandibular primary first molars or (2) a mesoprosopic/euryprosopic facial form, end-on molar occlusion, and missing mandibular first primary molars. The occlusal relationship of the permanent first molar or its eruptive status is no longer the sole factor in this treatment planning decision, but should be a component in space management.

CONCLUSIONS

• During a 9-month observation period after the premature loss of the primary first molar, space loss occurs in the maxilla and mandible of patients with a leptoprosopic facial form and Class I or end-on molar occlusion.

• During a 9-month observation period after the loss of the primary first molar in patients with a mesoprosopic/euryprosopic facial form, loss of space occurred only at the mandibular site.

• The reevaluation of the usage of space maintenance for prematurely lost primary first molars should also be based upon facial forms and not exclusively on the eruptive status of the first permanent molar or on molar occlusion alone.