Introduction
Although it has been suggested that orthodontic treatment might lead to changes in the dental pulp, no clinical study has attempted to investigate the incidence of pulp necrosis after orthodontic therapy. The purpose of this clinical trial was to determine whether pulp testing response is altered after rapid palatal expansion (RPE).
Methods
Twenty-five adolescent patients (9 boys, 16 girls; ages, 10-16 years) participated in the study. A hyrax appliance was cemented on the first permanent molars and first premolars (when fully erupted). The appliance was activated twice daily (0.5 mm) for 2 weeks. An electric pulp tester (EPT) was used to test at the buccal cusp tips of the molars and premolars. Teeth that did not respond to the EPT were subsequently tested thermally with Endo Ice (Hygienic Corporation, Akron, Ohio).
Results
All maxillary molars and erupted premolars of the 25 patients responded positively to pulp tests before cementation of the hyrax appliance. Of the 49 molars tested, 46 responded positively to the EPT, and 3 responded positively to the cold testing (CT). Of the 42 first premolars tested, 40 responded positively to the EPT and 2 to the CT. Of the 38 second premolars tested, 35 responded positively to the EPT and 3 to the CT. Two weeks after the initial activation of the hyrax appliance, 93 teeth in 17 subjects were tested. Of the 93 teeth, 73 teeth responded positively to the EPT and 20 to the CT. Three to 6 weeks after hyrax activation was discontinued, 59 teeth were tested; 48 tested positively to the EPT and 10 to the CT. One tooth (maxillary left first molar) did not respond to either EPT or CT. Finally, 3 to 9 months into retention, all molars and premolars of 23 subjects tested positive to pulp tests, 92 teeth to the EPT and 25 to the CT. The maxillary left first molar that had not responded to the tests at the 3-to-6 week check responded positively to the CT at the final check.
Conclusions
After RPE therapy in children and adolescents, the pulp of the posterior permanent teeth examined in this study was vital.
Occasionally, reports suggest that teeth have been devitalized by orthodontic treatment. There is only anecdotal evidence, and no clinical study has attempted to determine the incidence of pulpal necrosis after orthodontic therapy.
Experimental studies have evaluated the effects of orthodontic forces on pulp tissue. Several investigators have suggested that injury from orthodontic forces might be permanent and that the pulp eventually could lose its vitality. According to other researchers, however, orthodontic forces do not have significant long-lasting effects on the dental pulp.
McDonald and Pitt Ford, using laser doppler flowmetry, found decreased blood flow after orthodontic loading of the teeth, with increased blood flow after 32 minutes. This increase in blood flow normalized after 72 hours. Under certain circumstances, such as orthodontic force application, the microcirculatory system can increase pulpal blood flow and generate new blood vessels. Thus, pulp inflammation might elicit a localized circulatory response that is restricted to a particular region and does not necessarily produce general circulatory changes in the pulp.
Although those studies suggest that orthodontic treatment can cause changes, reversible or irreversible, in dental pulp, no clinical study has attempted to investigate the incidence of pulp necrosis after orthodontic therapy. Therefore, the purpose of this clinical trial was to determine whether there are changes in pulp testing response after rapid palatal expansion (RPE) in children and adolescents. Treatment with RPE was selected because heavier forces would more likely affect the pulp vasculature than the lighter forces typically experienced with fixed appliances.
Material and methods
Twenty-five adolescent patients (9 boys, 16 girls; ages, 10-16 years) who were planned to have RPE as a part of their orthodontic therapy were selected to participate in the study. They met the following criteria: (1) no major systemic disease, (2) not using any medications, (3) healthy periodontium (minimal gingival inflammation, probing depths ≤3 mm, no bone loss as determined by radiographs) and dentition (no carious lesions or extensive restorations), and (4) no endodontically treated teeth. All patients were given oral hygiene instructions and closely monitored to prevent inflammation of the gingival tissues.
A hyrax or modified hyrax expander (only the first molars were banded) fabricated by Clear Advantage Laboratory (Nanuet, NY) was cemented on the first permanent molars and the first premolars (when fully erupted) with glass ionomer cement (Ketac, ESPE, Seefeld, Germany). This appliance was activated as follows. At placement, the jackscrew was activated twice. Each turn of the jackscrew equates to 0.25 mm of expansion. Accordingly, total initial activation was 0.5 mm. After initial activation, the patient’s parent was instructed to activate the jackscrew twice daily, once in the morning and once in the evening. The daily activation was 0.5 mm until satisfactory palatal expansion was achieved. The progress of expansion was observed every week during the active phase (2-3 weeks).
An electric pulp tester (EPT) (Analytic Technology, Redmond, Wash) was used in this study. Toothpaste was the conducting medium. The testing site was confined to the buccal cusp tips of the molars and premolars. The probe did not touch any orthodontic band or restoration. Teeth that did not respond to the EPT were then tested thermally with Endo Ice (Hygenic Corporation, Akron, Ohio). Only permanent teeth were subjected to the EPT; the deciduous dentition was excluded. All experimental teeth were isolated with cotton rolls and dried thoroughly before testing. Results for the EPT readings and the thermal testing were recorded as a positive or negative (yes or no) response.
The electric pulp tests were performed at the following treatment intervals:
- 1.
Time point 1 (T1): immediately before placement of the separators. This reading provided a baseline for the study.
- 2.
Time point 2 (T2): approximately 2 weeks into treatment, when the jackscrew was stabilized and locked, and RPE therapy was terminated.
- 3.
Time point 3 (T3): 3 to 6 weeks after activation was discontinued, or 2 to 4 weeks into retention.
- 4.
Time point 4 (T4): 3 to 9 months after the RPE force was stopped.
The study was approved by the Institutional Review Board of Columbia University Medical Center, New York, NY.
Results
The results are summarized in Tables I through III .
| Observation periods | T1 | T2 | T3 | T4 |
|---|---|---|---|---|
| Patients (n) | 25 | 17 | 11 | 23 |
| First molars tested (EPT or CT) (n) | 49 | 33 | 21 | 45 |
| First premolars tested (EPT or CT) (n) | 42 | 32 | 20 | 36 |
| Second premolars tested (EPT or CT) (n) | 38 | 28 | 18 | 36 |
| T1 | T2 | T3 | T4 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EPT | CT | NR | EPT | CT | NR | EPT | CT | NR | EPT | CT | NR | |
| First molars (n) | 46 | 3 | 0 | 26 | 7 | 0 | 17 | 3 | 1 | 34 | 11 | 0 |
| First premolars (n) | 40 | 2 | 0 | 25 | 7 | 0 | 16 | 4 | 0 | 29 | 7 | 0 |
| Second premolars (n) | 35 | 3 | 0 | 22 | 6 | 0 | 15 | 3 | 0 | 29 | 7 | 0 |
| T1 | T2 | T3 | T4 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| EPT | CT | EPT | CT | EPT | CT | EPT | CT | ||
| Subject # 4 | UR 6 | Y | Y | Y | Y | ||||
| UR 5 | Y | Y | Y | Y | |||||
| UR 4 | Y | Y | N | Y | Y | ||||
| Subject # 6 | UL 4 | Y | Y | N | Y | Y | |||
| UL 5 | Y | N | Y | N | Y | Y | |||
| UL 6 | Y | N | Y | Y | Y | ||||
At T1, all maxillary molars and erupted premolars of the 25 patients responded positively to pulp tests before cementation of the hyrax appliance. Of the 49 molars tested at T1, 46 responded positively to the EPT, and 3 responded positively to the cold testing (CT). Of the 42 first premolars tested at T1, 40 responded positively to the EPT, and 2 responded positively to the CT. Of the 38 second premolars tested at T1, 35 responded positively to the EPT, and 3 responded positively to the CT.
At T2, 2 weeks after the activation of the hyrax appliance, 17 subjects were tested. A total of 93 teeth were tested for pulp vitality. Of the 93 teeth, 73 teeth responded positively to the EPT, and 20 responded positively to the CT.
At T3, 3 to 6 weeks after hyrax activation stopped, 59 teeth were tested. Forty-eight teeth tested positive to the EPT, and 10 tested positive to the CT. One tooth (maxillary left first molar) did not respond to either EPT or CT.
At T4, 3 to 9 months in retention, all molars and premolars of 23 subjects tested positive in the pulp tests. A total of 92 teeth tested positive to the EPT, and 25 tested positive to the CT. The maxillary left first molar that had not responded at T3 responded positively to CT at T4. The response of teeth to the EPT or CT varied. Table III shows the longitudinal pulpal responses of the maxillary first molars, first premolars, and second premolars to the EPT and the CT of 2 subjects.
In addition, the numbers of teeth tested at T4, T2, and T3 are not exactly the same as in T1 because a few patients missed at least 1 appointment.
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