Occasionally, reports suggest that teeth have

ORIGINAL ARTICLE Pulp vitality after rapid palatal expansion Jamin J. Cho, a Stella Efstratiadis, b and Gunnar Hasselgren c New York, NY 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. (Am J Orthod Dentofacial Orthop 2010;137:254-8) 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. 1-4 According to other researchers, however, orthodontic forces do not have significant longlasting effects on the dental pulp. 5-10 McDonald and Pitt Ford, 11 using laser doppler flowmetry, found decreased blood flow after orthodontic a Private practice, New York, NY. b Professor, Division of Orthodontics, College of Dental Medicine, Columbia University, New York, NY. c Professor, Division of Endodontics, College of Dental Medicine, Columbia University, New York, NY. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Stella Efstratiadis, Columbia University, College of Dental Medicine, Division of Orthodontics, 630 W 168 St, New York, NY 10032; e-mail, sse1@columbia.edu. Submitted, December 2007; revised and accepted, April 2008. 0889-5406/$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2008.04.023 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 12 and generate new blood vessels. 13 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. 14 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) 254

American Journal of Orthodontics and Dentofacial Orthopedics Cho, Efstratiadis, and Hasselgren 255 Volume 137, Number 2 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. Table I. Patients and teeth tested by EPT and CT stimulation 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, Before placement of separators; T2, 2 weeks into RPE treatment; T3, 3-6 weeks into retention; T4, 3-9 months into retention. RESULTS The results are summarized in Tables I through III. 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. DISCUSSION RPE therapy is a common treatment modality used to correct maxillary transverse deficiency. RPE treatment was selected for this study because, theoretically, heavier forces would more likely affect the pulp vasculature than lighter forces typical with fixed appliances. A single activation of the expansion screw produces

256 Cho, Efstratiadis, and Hasselgren American Journal of Orthodontics and Dentofacial Orthopedics February 2010 Table II. Responses of teeth to EPT and CT stimulation 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, Before placement of separators; T2, 2 weeks into RPE treatment; T3, 3-6 weeks into retention; T4, 3-9 months into retention; NR, no response to either test. Table III. Longitudinal pulp responses of 2 patients to EPT and CT stimulation 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 N, No; Y, yes; UR 6, Upper right first molar; UR 5, upper right second premolar; UR 4, upper right first premolar; UL 6, upper left first molar; UL 5, upper left second premolar; UL 4, upper left first premolar; T1, before placement of separators; T2, 2 weeks into RPE treatment; T3, 3-6 weeks into retention; T4, 3-9 months into retention. about 3 to 10 lbs (1360-4545 g) of force. 15 Each subsequent turn produces a cumulative effect. Accordingly, the jackscrew appliance can produce cumulative loads of 20 lbs or more after several daily turns. 16 Patients with an activation schedule of 2 turns of the jackscrew per day can experience a constant expansion force of 1 to 13 lbs. 15 Moreover, if a tooth is subjected to a heavy force, the periodontal ligament might be compressed so that the blood flow is compromised, resulting in hyaline degeneration. 17,18 This can cause undermining resorption. With undermining resorption, tooth movement is delayed until the adjacent bone marrow space is removed. At that point, the tooth jumps to a new position. Conceivably, a large enough jump of the root apex could sever the vascular supply to the pulp and result in devitalization. 19 An EPT was used to test the response of the pulp to orthopedic-orthodontic movement because it is a noninvasive, simple tool used for determining the vitality of teeth. The threshold response to the pulp tester depends on the placement of the probe on the tooth and the tooth type. The teeth tested did not have abrasions or attrition on the enamel. The same probe placement was ensured during testing on the cusp tips of permanent first molars and first premolars. This placement made it possible to avoid the orthodontic bands. CT is considered more reliable than EPT for assessing pulp health. 20,21 For this reason, teeth that did not respond to EPT were subsequently tested thermally with Endo Ice. Results of the EPT and thermal testing were recorded as a positive or negative (yes or no) response only. The response times were not recorded for either mode of testing. Variation from tooth to tooth, condition of the enamel, site of placement on the tooth, and possibility of nerve accommodation for each apparatus can cause widely different response times. 22 For this reason, response times have little value in determining the status of the pulp and even less value when used comparatively among patients. 23 All teeth tested responded positively to the EPT or the CT at all observation points with only 1 exception. One tooth responded negatively to both EPT and CT. The negative reading was recorded 3 1 2 weeks after expansion was completed. However, this tooth later responded positively to the CT at T4 (3-6 months after RPE therapy). The explanation for this could be that there is a period after orthodontic treatment or trauma when the stimulus threshold to pulp testing might be so increased that a response is not registered. 23 Attempts have been made to quantify the response to the EPT performed with the analytic pulp tester that we used in this study. The device has a numeric scale (1-80), and these numbers have been used to register changes in test responses. Cave et al 21 used this method when evaluating pulp test responses in orthodontic patients. They reported that the response threshold increased after the application of force. A recent study could not verify these findings. 24 Changes in test results might not necessarily reflect changes in the pulp tissue. Even minute changes in test probe positioning will give different numerical values in the same tooth, and the condition of the battery might play a role. 25-27 Therefore, it appears prudent to use all pulp tests, electric and thermal, as yes or no tests. Investigations of the effects on the dental pulp from more invasive procedures, such as segment alveolar osteotomy and autotransplantation, indicate that the pulp has a seemingly extraordinary ability to withstand

American Journal of Orthodontics and Dentofacial Orthopedics Cho, Efstratiadis, and Hasselgren 257 Volume 137, Number 2 insults. 28-32 For example, after alveolar segmental osteotomy, 28 of 128 teeth did not respond to electrical stimulation. However, only 5 of the 28 teeth required additional endodontic or extraction therapy. In light of the studies highlighting the resiliency of the pulp after alveolar segmental osteotomy and autotransplantation, it is not surprising that no teeth in this study were necrotic after RPE. All patients in the study were adolescents from 10 to 16 years old. According to Moorrees et al, 33 root formation of molars and premolars is completed between 12 1 2 and 17 years of age. Conclusions from autotransplantation studies imply that immature root formation and pulps with wider apical foramina have a strong ability to recover from injuries that could compromise the nerve and blood supply to the pulp. 30,31,34 In addition, bone density in children and adolescents is not as great as in adults. This explains why traumatic injuries to children s dentition often fall in the luxation or subluxation classification, whereas similar traumatic event in adults often result in root fractures. Studies have evaluated angiogenic changes in dental pulp after orthodontic movement. The pulp microvessel numbers in all patients were significantly greater after orthodontic tooth movement. The authors concluded that there is an increase in angiogenic growth factors in the pulp of orthodontically moved teeth. 13 This repair process could account for the fact that few iatrogenic problems are encountered during fixed orthodontic therapy. 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