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Risk Indicators and Interceptive Treatment Alternatives for Palatally Displaced Canines
Risk Indicators and Interceptive Treatment Alternatives for Palatally Displaced Canines Tiziano Baccetti The present article reviews diagnostic, prognostic, and therapeutic aspects related to palatal displaced canines (PDCs) and their possible evolution to palatally impacted canines (PICs). Through the analysis of the relevant literature, a series of dental anomalies can be identified that present with a significant clinical association with PDC. Because these tooth disturbances may appear before PDC, they represent risk indicators for the occurrence of the eruption anomaly of the maxillary permanent canine. The second part of this work describes comparatively the effectiveness of several interceptive treatment approaches to PDC to avoid the evolution from PDC to PIC. In particular, the extraction of the deciduous canine, alone or in combination with orthodontic forces aimed to prevent the physiological mesial movement of the upper permanent molar, appears to be able to increase by 2 to 3 times the rate of eruption of PDCs (diagnosed on a panoramic radiograph) with respect to that which occurs in untreated subjects with PDC (spontaneous eruption in about one third of the cases). Rapid maxillary expansion in the early developmental stages may represent a valid alternative for the interceptive treatment of PDCs (diagnosed on a posteroanterior cephalogram). Although genetic factors are known to play a fundamental role in the etiology of PDC (and subsequent PIC), it appears that environmental local factors can be affected by orthodontic/orthopedic approaches during the pathogenetic evolution process leading from PDC to final PIC. (Semin Orthod 2010;16: 186-192.) © 2010 Elsevier Inc. All rights reserved.
alatal impaction of maxillary permanent canines (palatally impacted canines or PICs) is the final outcome of a developmental anomaly that has been defined palatal displacement of the canine (PDC), ie, the intraosseous malposition of the upper permanent canine before the expected time for eruption.1 Although in the
P
Department of Orthodontics, The University of Florence, Florence, Italy. Thomas M. Graber Visiting Scholar, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, the University of Michigan, Ann Arbor. Address correspondence to Tiziano Baccetti, DDS, PhD, Department of Orthodontics, Università degli Studi di Firenze, Via del Ponte di Mezzo, 46 – 48, 50127, Florence, Italy. Phone: 01139-055354265; Fax: 01139-055-609536; E-mail: [email protected] © 2010 Elsevier Inc. All rights reserved. 1073-8746/10/1603-0$30.00/0 doi:10.1053/j.sodo.2010.05.004
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past the expected time for canine eruption was correlated to chronologic age2 (12 years, 3 months in girls and 13 years, 1 month in boys), attention has been given recently to the skeletal maturation of the patient. The upper permanent canine can erupt at any prepubertal or pubertal stage of skeletal development until cervical stage (CS) 5 in cervical vertebral maturation (Fig 1).3 Beyond this stage, which occurs on average 1 year after the end of the adolescent growth spurt, a PDC can be defined as PIC. When the developmental stages of the dentition are used to determine the time of emergence of the maxillary permanent canine delayed dental age is found in association with PDCs.4 The early diagnosis of dental abnormalities that share a common genetic origin with PDC (and PIC) can lead to the identification of risk indicators for PDC. Once PDC is recognized in
Seminars in Orthodontics, Vol 16, No 3 (September), 2010: pp 186-192
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Figure 1. (A) Male subject, 12 years, 3 months old. Tooth is impacted. Diagnosis of impaction is corroborated by the presence of CS 5 in the assessment of skeletal maturation by the cervical vertebral maturation method (B).
the individual patient (in most instances during the late mixed dentition phase), interceptive measures can be implemented to avoid the final establishment of a PIC. These interceptive measures classically tend to facilitate eruption of the canine by acting on local/mechanical factors that may affect the evolution from PDC to PIC. The aim of this work is to review the factors that can be used as early risk indicators for the occurrence of the eruption disorder of maxillary canines and to describe the effectiveness of alternative interceptive therapies to avoid canine impaction in presence of PDC.
Risk Indicators for PDC and PIC The etiology of PDC, and subsequent PIC, has been associated with a multifactorial genetic complex that controls the expression of other, possibly concurrent, tooth anomalies.1 Peck et al1 have also indicated multiple evidential categories for the genetic origin of PDC, ie, familial occurrence,5 bilateral occurrence (17%-45%), sex differences, differences in prevalence rates among different populations, and increased occurrence of other concomitant dental anomalies.6
Gender PDC is significantly more frequent in female subjects, thus indicating involvement of the sexual chromosomes in the etiology of the disorder. In a previous investigation7 the authors analyzed the prevalence and distribution of PDC in a large orthodontic population of 5000 subjects.
The prevalence rate of PDC was 2.4%, with a male-to-female ratio of 1:3.
Associated Dental Anomalies The search for associated dental anomalies is one of the most relevant methods to investigate the genetic determinants of PDC.1,6 The spectrum of possible associations among tooth anomalies was studied by Hoffmeister between 1975 and 1985.8 The following manifestations were found over 3 generations of a family: multiple missing teeth (aplasia of upper lateral incisors), peg-shaped incisors, ectopic eruption of maxillary first permanent molars, and intraosseous displacement of maxillary canines. In 1992, Bjerklin et al9 investigated the associations among 4 tooth and eruption disturbances (ectopic eruption of first molars and of maxillary canines, infraocclusion of primary molars, and aplasia of premolars). The findings indicated the presence of significant reciprocal associations. These results were interpreted supporting the hypothesis of a common, presumably hereditary, etiology for the studied tooth disturbances, each disturbance having incomplete penetrance. A very high prevalence of associated tooth anomalies (70%) was calculated in 1993 in a sample of 169 inherited syndromes presenting with tooth disturbances, strongly suggesting the possibility of genetic relationships among tooth number, size, shape, and structure characteristics.10 These relationships have been confirmed further in the studies by Baccetti6 in 1998 and by Leifert and Jonas11 in 2003. By contrast, the study by Baccetti6 indicated that supernumerary
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teeth and ectopic eruption of first molars are not significantly associated with PDC. In a study by Sacerdoti and Baccetti in 20047 PDC showed reciprocal significant associations with bilateral small-sized upper lateral incisors. Shalish et al12 have demonstrated that the distal angulations of unerupted mandibular premolar is significantly greater in children with PDC. The existence of associations between different tooth anomalies is not only important from an etiologic point of view but also relevant clinically because the early diagnosis of 1 anomaly may indicate an increased risk for later appearance of others. Table 1 illustrates the list of dental anomalies that present with a significant association with PDC and that can be used as risk indicators for the eruption anomaly of the maxillary canine. Figures 2 and 3 illustrate clinical examples of the associations among different dental anomalies.
Interceptive Treatment Alternatives As mentioned previously, although the etiology of PDC (and subsequent PIC) has been linked to a genetic component, the evolution from PDC to PIC can be affected by local/mechanical factors that have become the targets of “interceptive treatment” of PDC to prevent the final occurrence of PIC, as well as to allow the canine to erupt physiologically.
Extraction of the Deciduous Canine The procedure of reducing the prevalence of impacted PDCs by extracting the corresponding deciduous canine has been reported in the dental literature since 1936.13 The outcomes in several individual cases during the subsequent 50 years corroborated the clinical recommendation
Figure 2. Female subject, 11 years, 6 months old. The panoramic radiograph reveals several dental anomalies associated with palatally displaced maxillary left permanent canine: aplasia of upper right second premolar, aplasia of lower left second premolar, and distally angulated unerupted lower right second premolar.
for this interceptive measure, as reviewed by Jacobs.14 The prospective study by Ericson and Kurol in 198815 analyzed the effects of the extraction of the deciduous canine on PDC in rate and time of “spontaneous” eruption. A total of 36 of 46 PDC canines (78%) presented with an improvement in the eruption pathway after removal of the deciduous canines, after a time interval of 6 to 12 months. In a longitudinal 2-year investigation in 1993, Power and Short16 described the achievement of a normal eruptive position of PDC in 62% of the cases after the extraction of the deciduous canines. It should be emphasized that both the studies by Ericson and Kurol and by Power and Short were conducted before the establishment of a genetic basis for PDC. Both studies calculated prevalence rates of canine eruption by use of the number of erupting individual teeth, which is not recommended
Table 1. Relationship Between PDC and Other Dental Anomalies Dental anomalies that are significantly associated with PDC Small size of upper permanent incisors (also bilateral) Aplasia of second premolars Infraocclusion of primary molars Distal angulation of lower second premolars (before their eruption) Enamel hypoplasia Dental anomalies that are not significantly associated with PDC Supernumerary teeth Ectopic eruption of first permanent molars
Figure 3. Female subject, 11 years, 2 months old. The palatally displaced maxillary right permanent canine is associated with the bilateral presence of small-sized upper lateral permanent incisors.
Risk Indicators and Interceptive Treatment of PDC
because of the genetic etiology of the tooth developmental disorder. In fact, cases with bilateral PDCs should not count for 2 independent statistical units because the same etiologic factors act on both sides of the maxillary arch. Therefore, when analyzing data pertaining to PDCs or PICs it is indicated to use individual subjects, and not individual teeth, as statistical units to avoid “inflated” prevalence rates. A study by Leonardi and associates17 failed to find significant effectiveness of deciduous canine extraction for treatment of PDC. However, the power of this study was limited, as stated by the authors in a more recent study that was represented by a randomized prospective approach to interceptive treatment of PDC with the incorporation of untreated controls and a statistically appropriate number of subjects enrolled in the study.18 In this recent investigation, the removal of the deciduous canine as an isolated measure to intercept palatal displacement of maxillary canines showed 65.2% prevalence rate of success, which was significantly greater (almost double) than the success rate in untreated controls (36%). The prevalence rate of canine eruption here was calculated on individual subjects, and eruption of the tooth was defined when a bracket could be placed on the crown of the canine.
Interceptive Therapies, Including the Use of Other Devices: Randomized Clinical Trials Recently, 2 randomized clinical trials have evaluated the role of alternative interceptive approaches to PDC that consisted of either extraction of the deciduous canine in association using either a headgear appliance18 or a rapid maxillary expander.19 The randomized clinical trial by Baccetti et al in 200818 evaluated the effectiveness of deciduous canine extraction in combination with the use of a cervical pull headgear (patients wore the headgear only at night). The randomized prospective design of the investigation comprised 75 subjects with PDCs (92 maxillary canines) who were randomly assigned to 3 groups, for example, extraction of the deciduous canine only; extraction of the deciduous canine and cervical pull headgear; and untreated control group. Panoramic radiographs were evaluated at the time of initial observation, at an average
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age of 11.7 years (T1), and after an average period of 18 months (T2). At T2, an evaluation of the relative success of canine eruption was performed, with a statistical comparison between the groups. A superimposition study on lateral cephalograms at T1 and T2 evaluated the changes in the sagittal position of the upper molars in the 3 groups. As mentioned before, the extraction of the deciduous canine as an isolated measure to intercept palatal displacement of maxillary canines showed 65.2% prevalence rate of success, which was significantly greater than the success rate in untreated control patients (36%). The night-time use of a headgear in addition to the extraction of the deciduous canine was able to induce successful eruption in 87.5% of the cases, with a significant improvement in the measures for intraosseous canine position. There was no significant difference between the 2 interceptive approaches as to time for canine eruption. The cephalometric superimposition study showed a significant mesial movement of the upper first molars in the control group and of the deciduous canine only group when compared with the extraction of the deciduous canine and cervical pull headgear group. It appears therefore that the main effect of the headgear is to prevent the mesial movement of the posterior segments of the upper arch, thus facilitating the maintenance of an eruption pathway for the canine. It should be remembered that in a nonrandomized retrospective study in 2002, Olive20 already reported the significantly favorable effects of a clinical protocol, including the extraction of the deciduous canine followed by fixed appliance therapy to increase the maxillary arch perimeter. A second prospective randomized clinical study was aimed to assess the prevalence rate of eruption of PDCs when diagnosed at an early developmental stage by posteroanterior head films and consequently treated by rapid maxillary expansion (RME). A sample of 60 subjects in the early mixed dentition with PDC diagnosed on posteroanterior cephalogram radiographs according to the method by Sambataro et al21 was enrolled in the trial. The age range of the subjects at first observation (T1) was 7.6 to 9.6 years, with a prepubertal stage of skeletal maturity (CS 1 or 2). The diagnosis of PDC was performed on
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posteroanterior cephalograms because the assessment of PDC on panoramic films is not reliable at these early ages. The 60 subjects were randomly allocated to the treatment group (35 cases) or the no-treatment group (25 cases). The treatment group was treated with a banded rapid maxillary expander; at the end of expansion all patients were retained with the expander in place for 6 month; thereafter, the expander was removed, and patients wore a retention plate at night for 1 year. The no-treatment group did not receive any treatment. At T2 (early permanent dentition, postpubertal, CS 5) all cases were reevaluated. No statistically significant differences were found for any variable at T1. It should be noted that subjects with PDCs in the early mixed dentition did not exhibit transverse deficiency of the maxillary arch. Therefore, the transverse features of the upper maxilla were not related to the etiology of the eruption disorder of the canine, as indicated previously by Langberg and Peck.22 In fact, the indication for RME in the cases enrolled in the clinical study was the presence of mild-tomoderate tooth-size/arch-size discrepancy and/or Class II or Class III tendency, and not transverse maxillary deficiency. The use of the orthopedic device RME assisted in preventing final impaction of PDC, during the developmental stages from PDC to PIC. Once again, although a genetic etiology has been postulated for initial palatal displacement of upper canines, the pathogenesis of the displacement and of final impaction is related especially to the anatomical complexity of the eruption pathway of this tooth,23 that can be affected by environmental alterations. The prevalence rate of successful eruption of the maxillary canines was 65.7% in the group treated with RME, whereas it was only 13.6% in the untreated control group. The comparison was obviously statistically significant and led to the conclusion that the use of a rapid maxillary expander as an early interceptive approach is an effective procedure to increase the rate of eruption of palatally displaced canines. The low prevalence rate for spontaneous eruption of canines in the control patients is caused by methodological aspects of the study that included subjects not only with a diagnosis of PDC but also with a prognosis of PIC, as derived by the analysis of posteroanterior cephalogram films according to the method by Sambataro et al.21
The comparison of the prevalence rate for successful outcomes of RME as an interceptive procedure in PDC subjects with those reported by previous studies on alternative treatment approaches to potentially impacted canines reveals that RME treatment shows a rate of effectiveness (65.7%) similar to the one described for extraction of the deciduous canines alone (78% according to Ericson and Kurol, including improvement of eruption path;15 62% according to Power and Short;16 65.2% according to Baccetti et al18), or in combination with fixed appliances (75% according to Olive20), and smaller than the prevalence rate for eruption of the canines following the use of a cervical-pull headgear (87.5% according Baccetti et al;18 Table 2). Several factors need to be considered when evaluating the outcomes of the alternative interceptive treatment approaches to PDC. Although the extraction of the deciduous canine alone is less effective than when carried out in combination with a headgear appliance, does allow a significantly smaller “burden of treatment” for the patient. Obviously, patients who require the use of orthodontic forces to distalize upper molars (Class II or end-to-end patients, or patients with a tendency to crowding of the upper arch) will benefit from the combined treatment of extraction of the deciduous canine and headgear, both in correction of their malocclusions and of improvement in the probability of canine eruption. In addition, the RME approach (which is independent from the extraction of the deciduous canine) has been evaluated at an early developmental age (7-9 years), when diagnosis of PDC on panoramic films is unreliable and a posteroanterior cephalogram is required. Moreover, the diagnosis of PDC on posteroantrerior cephalograms can be effectively performed only in cases with severe displacement of the canine towards the midfacial structures. A further study is currently evaluating the role of maxillary expansion therapy (in combination with the extraction of the deciduous canine) in more mature patients in the late mixed dentition, with diagnosis of PDC performed classically on a panoramic film.
Conclusions In conclusion, PDC is the developmental antecedent of PIC. If not intercepted with early treatment modalities, PDCs become PICs in 2
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Risk Indicators and Interceptive Treatment of PDC
Table 2. Comparative Tabulation of the Outcomes of Studies on Interceptive Treatment of PDCs
Study
Interceptive Treatment
Age at Time of Interceptive Treatment
Ericson and Kurol, Extraction of deciduous canine alone 198815
10-13 yrs
Power and Short, 199316
Extraction of deciduous canine
11.2 yrs ⫾ 1.43 yrs
Olive, 200220
Extraction of deciduous canine and fixed appliances to gain arch perimeter Extraction of deciduous canine alone
11.4-16.1vyrs
Extraction of deciduous canine and headgear on maxillary molars (at night) Rapid maxillary expansion
11.9 yrs ⫾ 0.9 yrs
Baccetti et al, 200818 Baccetti et al, 200818 Baccetti et al, 200919
11.7 yrs ⫾ 0.8 yrs
7-9 yrs
of 3 cases. Skeletal maturation (by the cervical vertebral maturation method)3 can assist in the determination of the evolution from PDC to PIC: the canine is impacted when it is still in an intraosseous position at CS 5 or beyond (2 or more years after the adolescent growth spurt). Several dental anomalies that are significantly associated with the occurrence of PDC and that become clinically manifest before PDC can represent risk indicators for the eruption anomaly of the maxillary permanent canine. Finally, different interceptive approaches to PDC are able to promote eruption of the displaced canine with a success rate that ranges from 2 to 3 times the rate shown by untreated controls, as assessed in several evidence-based literature reports. Interceptive treatment of PDC to avoid PIC would seem to be clinically recommended.
References 1. Peck S, Peck L, Kataja M: The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 64:249-256, 1994 2. Hurme V: Range of normalcy in the eruption of permanent teeth. J Dent Child 16:11-15, 1949 3. Baccetti T, Franchi L, De Lisa S, et al: Eruption of the maxillary canines in relation to skeletal maturity. Am J Orthod Dentofac Orthop 133:748-751, 2008
Prevalence Rate of Successful Canine Eruption in Treated Subjects
Prevalence Rate of Successful Canine Eruption in Untreated Control Subjects
78% (includes eruption and No controls improvement in eruption pathway; percentage calculated on number of teeth) 62% (Eruption; percentage No controls calculated on number of teeth) 75% (Eruption; percentage No controls calculated on number of teeth) 65.2% (Eruption; percentage calculated on number of subjects) 87.5% (Eruption; percentage calculated on number of subjects)
36%
65.7% (Eruption; percentage calculated on number of subjects)
13.6% (severe PDCs with prediction of impaction)
36%
4. Becker A, Chaushu S: Dental age in maxillary canine ectopia. Am J Orthod Dentofac Orthop 117:657-662, 2000 5. Pirinen S, Arte S, Apajalahti S: Palatal displacement of canine is genetic and related to congenital absence of teeth. J Dent Res 75:1742-1746, 1996 6. Baccetti T: A controlled study of associated dental anomalies. Angle Orthod 68:267-274, 1998 7. Sacerdoti R, Baccetti T: Dentoskeletal features associated with unilateral or bilateral palatal displacement of maxillary canines. Angle Orthod 74:725-732, 2004 8. Hoffmeister H: The ectopic eruption of permanent first molars as a microsymptom of occlusal developmental defects. Schweiz Mschr Zahnmed 95:151-154, 1985 9. Bjerklin K, Kurol J, Valentin J: Ectopic eruption of maxillary first permanent molars and association with other tooth and developmental disturbances. Eur J Orthod 14:369-375, 1992 10. Baccetti T, Della A: Prevalence of dental anomalies in inherited syndromes. A model for the analysis of genetic control on dental development. Minerva Stomatol 42:281-294, 1993 11. Leifert S, Jonas IE: Dental anomalies as a microsymptom of palatal canine displacement. J Orofac Orthop 64:108-120, 2003 12. Shalish M, Chaushu S, Wasserstein A: Malposition of unerupted mandibular second premolar in children with palatally displaced canines. Angle Orthod 79:796-799, 2009 13. Buchner HJ: Root resorption caused by ectopic eruption of maxillary cuspid. Int J Orthod 22:1236-1237, 1936 14. Jacobs SG: Reducing the incidence of unerupted palatally displaced canines by extraction of primary canines. The history and application of this procedure with some case reports. Aust Dent J 43:20-27, 1998
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15. Ericson S, Kurol J: Early treatment of palatally erupting maxillary canines by extraction of the primary canines. Eur J Orthod 10:283-295, 1988 16. Power SM, Short MB: An investigation into the response of palatally displaced canines to the removal of primary canines and an assessment of factors contributing to favourable eruption. Br J Orthod 20:215-223, 1993 17. Leonardi M, Armi P, Franchi L, et al: Two interceptive approaches to palatally displaced canines: A prospective longitudinal study. Angle Orthod 75:581-586, 2004 18. Baccetti T, Leonardi M, Armi P: A randomized clinical study of two interceptive approaches to palatally displaced canines. Eur J Orthod 30:381-385, 2008
19. Baccetti T, Mucedero M, Leonardi M, et al: Interceptive treatment of palatal impaction of maxillary canines with rapid maxillary expansion: A randomized clinical trial. Am J Orthod Dentofac Orthoped 136:657-662, 2009 20. Olive RJ: Orthodontic treatment of palatally impacted maxillary canines. Aust Orthod J 18:64-70, 2002 21. Sambataro S, Baccetti T, Franchi L, et al: Early predictive variables for upper canine impaction as derived from posteroanterior cephalograms. Angle Orthod 75:28-34, 2005 22. Langberg BJ, Peck S: Adequacy of maxillary dental arch width in patients with palatally displaced canines. Am J Orthod Dentofac Orthop 118:220-223, 2000 23. Peck S, Peck L, Kataja M: Site-specificity of tooth maxillary agenesis in subjects with canine malpositions. Angle Orthod 66:473-476, 1996
alatal impaction of maxillary permanent canines (palatally impacted canines or PICs) is the final outcome of a developmental anomaly that has been defined palatal displacement of the canine (PDC), ie, the intraosseous malposition of the upper permanent canine before the expected time for eruption.1 Although in the
P
Department of Orthodontics, The University of Florence, Florence, Italy. Thomas M. Graber Visiting Scholar, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, the University of Michigan, Ann Arbor. Address correspondence to Tiziano Baccetti, DDS, PhD, Department of Orthodontics, Università degli Studi di Firenze, Via del Ponte di Mezzo, 46 – 48, 50127, Florence, Italy. Phone: 01139-055354265; Fax: 01139-055-609536; E-mail: [email protected] © 2010 Elsevier Inc. All rights reserved. 1073-8746/10/1603-0$30.00/0 doi:10.1053/j.sodo.2010.05.004
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past the expected time for canine eruption was correlated to chronologic age2 (12 years, 3 months in girls and 13 years, 1 month in boys), attention has been given recently to the skeletal maturation of the patient. The upper permanent canine can erupt at any prepubertal or pubertal stage of skeletal development until cervical stage (CS) 5 in cervical vertebral maturation (Fig 1).3 Beyond this stage, which occurs on average 1 year after the end of the adolescent growth spurt, a PDC can be defined as PIC. When the developmental stages of the dentition are used to determine the time of emergence of the maxillary permanent canine delayed dental age is found in association with PDCs.4 The early diagnosis of dental abnormalities that share a common genetic origin with PDC (and PIC) can lead to the identification of risk indicators for PDC. Once PDC is recognized in
Seminars in Orthodontics, Vol 16, No 3 (September), 2010: pp 186-192
Risk Indicators and Interceptive Treatment of PDC
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Figure 1. (A) Male subject, 12 years, 3 months old. Tooth is impacted. Diagnosis of impaction is corroborated by the presence of CS 5 in the assessment of skeletal maturation by the cervical vertebral maturation method (B).
the individual patient (in most instances during the late mixed dentition phase), interceptive measures can be implemented to avoid the final establishment of a PIC. These interceptive measures classically tend to facilitate eruption of the canine by acting on local/mechanical factors that may affect the evolution from PDC to PIC. The aim of this work is to review the factors that can be used as early risk indicators for the occurrence of the eruption disorder of maxillary canines and to describe the effectiveness of alternative interceptive therapies to avoid canine impaction in presence of PDC.
Risk Indicators for PDC and PIC The etiology of PDC, and subsequent PIC, has been associated with a multifactorial genetic complex that controls the expression of other, possibly concurrent, tooth anomalies.1 Peck et al1 have also indicated multiple evidential categories for the genetic origin of PDC, ie, familial occurrence,5 bilateral occurrence (17%-45%), sex differences, differences in prevalence rates among different populations, and increased occurrence of other concomitant dental anomalies.6
Gender PDC is significantly more frequent in female subjects, thus indicating involvement of the sexual chromosomes in the etiology of the disorder. In a previous investigation7 the authors analyzed the prevalence and distribution of PDC in a large orthodontic population of 5000 subjects.
The prevalence rate of PDC was 2.4%, with a male-to-female ratio of 1:3.
Associated Dental Anomalies The search for associated dental anomalies is one of the most relevant methods to investigate the genetic determinants of PDC.1,6 The spectrum of possible associations among tooth anomalies was studied by Hoffmeister between 1975 and 1985.8 The following manifestations were found over 3 generations of a family: multiple missing teeth (aplasia of upper lateral incisors), peg-shaped incisors, ectopic eruption of maxillary first permanent molars, and intraosseous displacement of maxillary canines. In 1992, Bjerklin et al9 investigated the associations among 4 tooth and eruption disturbances (ectopic eruption of first molars and of maxillary canines, infraocclusion of primary molars, and aplasia of premolars). The findings indicated the presence of significant reciprocal associations. These results were interpreted supporting the hypothesis of a common, presumably hereditary, etiology for the studied tooth disturbances, each disturbance having incomplete penetrance. A very high prevalence of associated tooth anomalies (70%) was calculated in 1993 in a sample of 169 inherited syndromes presenting with tooth disturbances, strongly suggesting the possibility of genetic relationships among tooth number, size, shape, and structure characteristics.10 These relationships have been confirmed further in the studies by Baccetti6 in 1998 and by Leifert and Jonas11 in 2003. By contrast, the study by Baccetti6 indicated that supernumerary
188
Baccetti
teeth and ectopic eruption of first molars are not significantly associated with PDC. In a study by Sacerdoti and Baccetti in 20047 PDC showed reciprocal significant associations with bilateral small-sized upper lateral incisors. Shalish et al12 have demonstrated that the distal angulations of unerupted mandibular premolar is significantly greater in children with PDC. The existence of associations between different tooth anomalies is not only important from an etiologic point of view but also relevant clinically because the early diagnosis of 1 anomaly may indicate an increased risk for later appearance of others. Table 1 illustrates the list of dental anomalies that present with a significant association with PDC and that can be used as risk indicators for the eruption anomaly of the maxillary canine. Figures 2 and 3 illustrate clinical examples of the associations among different dental anomalies.
Interceptive Treatment Alternatives As mentioned previously, although the etiology of PDC (and subsequent PIC) has been linked to a genetic component, the evolution from PDC to PIC can be affected by local/mechanical factors that have become the targets of “interceptive treatment” of PDC to prevent the final occurrence of PIC, as well as to allow the canine to erupt physiologically.
Extraction of the Deciduous Canine The procedure of reducing the prevalence of impacted PDCs by extracting the corresponding deciduous canine has been reported in the dental literature since 1936.13 The outcomes in several individual cases during the subsequent 50 years corroborated the clinical recommendation
Figure 2. Female subject, 11 years, 6 months old. The panoramic radiograph reveals several dental anomalies associated with palatally displaced maxillary left permanent canine: aplasia of upper right second premolar, aplasia of lower left second premolar, and distally angulated unerupted lower right second premolar.
for this interceptive measure, as reviewed by Jacobs.14 The prospective study by Ericson and Kurol in 198815 analyzed the effects of the extraction of the deciduous canine on PDC in rate and time of “spontaneous” eruption. A total of 36 of 46 PDC canines (78%) presented with an improvement in the eruption pathway after removal of the deciduous canines, after a time interval of 6 to 12 months. In a longitudinal 2-year investigation in 1993, Power and Short16 described the achievement of a normal eruptive position of PDC in 62% of the cases after the extraction of the deciduous canines. It should be emphasized that both the studies by Ericson and Kurol and by Power and Short were conducted before the establishment of a genetic basis for PDC. Both studies calculated prevalence rates of canine eruption by use of the number of erupting individual teeth, which is not recommended
Table 1. Relationship Between PDC and Other Dental Anomalies Dental anomalies that are significantly associated with PDC Small size of upper permanent incisors (also bilateral) Aplasia of second premolars Infraocclusion of primary molars Distal angulation of lower second premolars (before their eruption) Enamel hypoplasia Dental anomalies that are not significantly associated with PDC Supernumerary teeth Ectopic eruption of first permanent molars
Figure 3. Female subject, 11 years, 2 months old. The palatally displaced maxillary right permanent canine is associated with the bilateral presence of small-sized upper lateral permanent incisors.
Risk Indicators and Interceptive Treatment of PDC
because of the genetic etiology of the tooth developmental disorder. In fact, cases with bilateral PDCs should not count for 2 independent statistical units because the same etiologic factors act on both sides of the maxillary arch. Therefore, when analyzing data pertaining to PDCs or PICs it is indicated to use individual subjects, and not individual teeth, as statistical units to avoid “inflated” prevalence rates. A study by Leonardi and associates17 failed to find significant effectiveness of deciduous canine extraction for treatment of PDC. However, the power of this study was limited, as stated by the authors in a more recent study that was represented by a randomized prospective approach to interceptive treatment of PDC with the incorporation of untreated controls and a statistically appropriate number of subjects enrolled in the study.18 In this recent investigation, the removal of the deciduous canine as an isolated measure to intercept palatal displacement of maxillary canines showed 65.2% prevalence rate of success, which was significantly greater (almost double) than the success rate in untreated controls (36%). The prevalence rate of canine eruption here was calculated on individual subjects, and eruption of the tooth was defined when a bracket could be placed on the crown of the canine.
Interceptive Therapies, Including the Use of Other Devices: Randomized Clinical Trials Recently, 2 randomized clinical trials have evaluated the role of alternative interceptive approaches to PDC that consisted of either extraction of the deciduous canine in association using either a headgear appliance18 or a rapid maxillary expander.19 The randomized clinical trial by Baccetti et al in 200818 evaluated the effectiveness of deciduous canine extraction in combination with the use of a cervical pull headgear (patients wore the headgear only at night). The randomized prospective design of the investigation comprised 75 subjects with PDCs (92 maxillary canines) who were randomly assigned to 3 groups, for example, extraction of the deciduous canine only; extraction of the deciduous canine and cervical pull headgear; and untreated control group. Panoramic radiographs were evaluated at the time of initial observation, at an average
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age of 11.7 years (T1), and after an average period of 18 months (T2). At T2, an evaluation of the relative success of canine eruption was performed, with a statistical comparison between the groups. A superimposition study on lateral cephalograms at T1 and T2 evaluated the changes in the sagittal position of the upper molars in the 3 groups. As mentioned before, the extraction of the deciduous canine as an isolated measure to intercept palatal displacement of maxillary canines showed 65.2% prevalence rate of success, which was significantly greater than the success rate in untreated control patients (36%). The night-time use of a headgear in addition to the extraction of the deciduous canine was able to induce successful eruption in 87.5% of the cases, with a significant improvement in the measures for intraosseous canine position. There was no significant difference between the 2 interceptive approaches as to time for canine eruption. The cephalometric superimposition study showed a significant mesial movement of the upper first molars in the control group and of the deciduous canine only group when compared with the extraction of the deciduous canine and cervical pull headgear group. It appears therefore that the main effect of the headgear is to prevent the mesial movement of the posterior segments of the upper arch, thus facilitating the maintenance of an eruption pathway for the canine. It should be remembered that in a nonrandomized retrospective study in 2002, Olive20 already reported the significantly favorable effects of a clinical protocol, including the extraction of the deciduous canine followed by fixed appliance therapy to increase the maxillary arch perimeter. A second prospective randomized clinical study was aimed to assess the prevalence rate of eruption of PDCs when diagnosed at an early developmental stage by posteroanterior head films and consequently treated by rapid maxillary expansion (RME). A sample of 60 subjects in the early mixed dentition with PDC diagnosed on posteroanterior cephalogram radiographs according to the method by Sambataro et al21 was enrolled in the trial. The age range of the subjects at first observation (T1) was 7.6 to 9.6 years, with a prepubertal stage of skeletal maturity (CS 1 or 2). The diagnosis of PDC was performed on
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Baccetti
posteroanterior cephalograms because the assessment of PDC on panoramic films is not reliable at these early ages. The 60 subjects were randomly allocated to the treatment group (35 cases) or the no-treatment group (25 cases). The treatment group was treated with a banded rapid maxillary expander; at the end of expansion all patients were retained with the expander in place for 6 month; thereafter, the expander was removed, and patients wore a retention plate at night for 1 year. The no-treatment group did not receive any treatment. At T2 (early permanent dentition, postpubertal, CS 5) all cases were reevaluated. No statistically significant differences were found for any variable at T1. It should be noted that subjects with PDCs in the early mixed dentition did not exhibit transverse deficiency of the maxillary arch. Therefore, the transverse features of the upper maxilla were not related to the etiology of the eruption disorder of the canine, as indicated previously by Langberg and Peck.22 In fact, the indication for RME in the cases enrolled in the clinical study was the presence of mild-tomoderate tooth-size/arch-size discrepancy and/or Class II or Class III tendency, and not transverse maxillary deficiency. The use of the orthopedic device RME assisted in preventing final impaction of PDC, during the developmental stages from PDC to PIC. Once again, although a genetic etiology has been postulated for initial palatal displacement of upper canines, the pathogenesis of the displacement and of final impaction is related especially to the anatomical complexity of the eruption pathway of this tooth,23 that can be affected by environmental alterations. The prevalence rate of successful eruption of the maxillary canines was 65.7% in the group treated with RME, whereas it was only 13.6% in the untreated control group. The comparison was obviously statistically significant and led to the conclusion that the use of a rapid maxillary expander as an early interceptive approach is an effective procedure to increase the rate of eruption of palatally displaced canines. The low prevalence rate for spontaneous eruption of canines in the control patients is caused by methodological aspects of the study that included subjects not only with a diagnosis of PDC but also with a prognosis of PIC, as derived by the analysis of posteroanterior cephalogram films according to the method by Sambataro et al.21
The comparison of the prevalence rate for successful outcomes of RME as an interceptive procedure in PDC subjects with those reported by previous studies on alternative treatment approaches to potentially impacted canines reveals that RME treatment shows a rate of effectiveness (65.7%) similar to the one described for extraction of the deciduous canines alone (78% according to Ericson and Kurol, including improvement of eruption path;15 62% according to Power and Short;16 65.2% according to Baccetti et al18), or in combination with fixed appliances (75% according to Olive20), and smaller than the prevalence rate for eruption of the canines following the use of a cervical-pull headgear (87.5% according Baccetti et al;18 Table 2). Several factors need to be considered when evaluating the outcomes of the alternative interceptive treatment approaches to PDC. Although the extraction of the deciduous canine alone is less effective than when carried out in combination with a headgear appliance, does allow a significantly smaller “burden of treatment” for the patient. Obviously, patients who require the use of orthodontic forces to distalize upper molars (Class II or end-to-end patients, or patients with a tendency to crowding of the upper arch) will benefit from the combined treatment of extraction of the deciduous canine and headgear, both in correction of their malocclusions and of improvement in the probability of canine eruption. In addition, the RME approach (which is independent from the extraction of the deciduous canine) has been evaluated at an early developmental age (7-9 years), when diagnosis of PDC on panoramic films is unreliable and a posteroanterior cephalogram is required. Moreover, the diagnosis of PDC on posteroantrerior cephalograms can be effectively performed only in cases with severe displacement of the canine towards the midfacial structures. A further study is currently evaluating the role of maxillary expansion therapy (in combination with the extraction of the deciduous canine) in more mature patients in the late mixed dentition, with diagnosis of PDC performed classically on a panoramic film.
Conclusions In conclusion, PDC is the developmental antecedent of PIC. If not intercepted with early treatment modalities, PDCs become PICs in 2
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Risk Indicators and Interceptive Treatment of PDC
Table 2. Comparative Tabulation of the Outcomes of Studies on Interceptive Treatment of PDCs
Study
Interceptive Treatment
Age at Time of Interceptive Treatment
Ericson and Kurol, Extraction of deciduous canine alone 198815
10-13 yrs
Power and Short, 199316
Extraction of deciduous canine
11.2 yrs ⫾ 1.43 yrs
Olive, 200220
Extraction of deciduous canine and fixed appliances to gain arch perimeter Extraction of deciduous canine alone
11.4-16.1vyrs
Extraction of deciduous canine and headgear on maxillary molars (at night) Rapid maxillary expansion
11.9 yrs ⫾ 0.9 yrs
Baccetti et al, 200818 Baccetti et al, 200818 Baccetti et al, 200919
11.7 yrs ⫾ 0.8 yrs
7-9 yrs
of 3 cases. Skeletal maturation (by the cervical vertebral maturation method)3 can assist in the determination of the evolution from PDC to PIC: the canine is impacted when it is still in an intraosseous position at CS 5 or beyond (2 or more years after the adolescent growth spurt). Several dental anomalies that are significantly associated with the occurrence of PDC and that become clinically manifest before PDC can represent risk indicators for the eruption anomaly of the maxillary permanent canine. Finally, different interceptive approaches to PDC are able to promote eruption of the displaced canine with a success rate that ranges from 2 to 3 times the rate shown by untreated controls, as assessed in several evidence-based literature reports. Interceptive treatment of PDC to avoid PIC would seem to be clinically recommended.
References 1. Peck S, Peck L, Kataja M: The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 64:249-256, 1994 2. Hurme V: Range of normalcy in the eruption of permanent teeth. J Dent Child 16:11-15, 1949 3. Baccetti T, Franchi L, De Lisa S, et al: Eruption of the maxillary canines in relation to skeletal maturity. Am J Orthod Dentofac Orthop 133:748-751, 2008
Prevalence Rate of Successful Canine Eruption in Treated Subjects
Prevalence Rate of Successful Canine Eruption in Untreated Control Subjects
78% (includes eruption and No controls improvement in eruption pathway; percentage calculated on number of teeth) 62% (Eruption; percentage No controls calculated on number of teeth) 75% (Eruption; percentage No controls calculated on number of teeth) 65.2% (Eruption; percentage calculated on number of subjects) 87.5% (Eruption; percentage calculated on number of subjects)
36%
65.7% (Eruption; percentage calculated on number of subjects)
13.6% (severe PDCs with prediction of impaction)
36%
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19. Baccetti T, Mucedero M, Leonardi M, et al: Interceptive treatment of palatal impaction of maxillary canines with rapid maxillary expansion: A randomized clinical trial. Am J Orthod Dentofac Orthoped 136:657-662, 2009 20. Olive RJ: Orthodontic treatment of palatally impacted maxillary canines. Aust Orthod J 18:64-70, 2002 21. Sambataro S, Baccetti T, Franchi L, et al: Early predictive variables for upper canine impaction as derived from posteroanterior cephalograms. Angle Orthod 75:28-34, 2005 22. Langberg BJ, Peck S: Adequacy of maxillary dental arch width in patients with palatally displaced canines. Am J Orthod Dentofac Orthop 118:220-223, 2000 23. Peck S, Peck L, Kataja M: Site-specificity of tooth maxillary agenesis in subjects with canine malpositions. Angle Orthod 66:473-476, 1996