Survival of retained permanent canines after autotransplantation: A retrospective cohort study

Introduction

After third molars, canines are the teeth most commonly affected by displacement and impaction. Although orthodontic surgical treatment represents the standard method for realignment of canines, autotransplantation (autoTX) functions as the second-line therapy if orthodontic alignment does not succeed in treating impaction and severe displacement. This retrospective cohort study aimed to identify clinical predictors for postoperative survival and endodontic treatment needs after autoTX of severely displaced and impacted canines.

Methods

The study cohort comprised patients who received canine autoTX in a single surgical center between 2006 and 2018. Canines with severe displacement and retention were surgically treated using a standardized protocol. Statistical analysis of survival probability was performed with the Kaplan–Meier method, and bivariate data were analyzed using logistic regression and the Pearson chi-square test. Nonparametric continuous variables were analyzed using the Mann-Whitney U test.

Results

Data from 319 patients with 378 canine grafts were available for analysis after a mean follow-up of 54.7 ± 36.5 months on the patient level (range, 0.3-181.8 months). With 25 lost autotransplants, the cumulative survival rate was 93.4%. Patient age at surgery, the state of the apical foramen, endodontic treatment need, and persistence of deciduous teeth at the implantation site had a significant negative impact on autotransplant survival ( P <0.05). Endodontic treatment need was significantly related to the patient’s age at surgery, the state of the apical foramen, and preoperative orthodontic traction ( P <0.05). Thus, these independent variables were identified as clinical predictors for the survival of both the autotransplant and the dental pulp. Gender, ischemia time, postoperative ankylosis, or site of autoTX did not influence any of the outcome variables.

Conclusions

The high survival rates of autotransplanted permanent canines make this treatment a promising option, especially in patients with severe tooth displacement, in which orthodontic treatment alone cannot provide predictable alignment, irrespective of the patient’s age. Interpreting age and preoperative orthodontic traction as delaying the onset of autoTX and state of apex, time-dependent aspects seem to be of great importance for postoperative complications leading to endodontic treatment or graft loss. Therefore, early implementation of autoTX as a treatment modality for impacted, severely displaced, and vain exposed canines in daily surgical practice should be encouraged.

Highlights

1.

Large retrospective cohort study on a total of 378 transplanted canines.
2.

High survival rates (93.4 %) were reported after a mean observation time of 56 months on tooth level.
3.

Pre-OP orthodontics contributes to significant higher post-OP endodontic treatment.

Delayed or impeded eruption of permanent teeth has different anatomic reasons, such as displacement, retention, or impaction. Teeth are designated as displaced or ectopic when their intraosseous position is uncommon and their direction of eruption is radiologically unusual. Tooth retention exists when tooth eruption through the mucosa is delayed for >2 years in normal position and development and without a discernible mechanical obstruction in the eruption path. This phenomenon was also described as “primary retention” for teeth, in which cessation of eruption was observed, without any physical barriers, as well as “normal” development and position of the tooth in the alveolar bone. Teeth are referred to as impacted when they are completely covered by bone, and eruption of the remaining dentition has already been finished. ^, The etiology of impaction can be traced back to common factors like a lack of space because of crowding and premature loss of deciduous teeth. Tooth displacement itself was described as another factor responsible for tooth impaction. After third molars, maxillary canines are the second most frequently impacted teeth, revealing a prevalence ranging from 0.9%-5.0%. ^, According to previous findings, ^, the eruption of maxillary canines should proceed at a mean age of 12.3 years in girls and 13.1 years in boys. Based on the epidemiologic data of studies in 7 different European countries and 2 countries in the Middle East, eruption of permanent maxillary canines is supposed to be completed between 10.5 years and 11.4 years of age in girls and 10.8 years and 12.0 years in boys. Because of the different causes of eruption disturbances and for reasons of simplification, the term retention will be used in this article to describe eruption disturbances of maxillary and mandibular canines.

Possible clinical indicators for retention of permanent canines have been described as persistence of deciduous canines without any signs of mobility in adolescents aged >14 or 15 years, absence or asymmetry of the labial canine bulge, presence of a palatal bulge, and distal tipping or migration of the lateral incisor. Common reasons for canine retention are tooth size-arch length discrepancies, prolonged retention or an early loss of the deciduous canine, ectopic position and eruption of the tooth, alveolar clefts, ankylosis, cysts, and neoplasms as eruption obstacles or root dilacerations. According to epidemiologic findings, canine retention is 2-fold greater in the maxilla. The long path of eruption, lack of guidance during an eruption, or genetic predisposition are supposedly responsible for this unequal distribution. ^, Impaction of the permanent maxillary canine is twice as common in females and 3 times greater at the palatal side of the maxilla. ^, Because of their frequent horizontal/oblique inclination, palatally retained maxillary canines seldom erupt on their own without surgical exposure and subsequent orthodontic traction, whereas bucally retained maxillary canines are more often displaying a favorable inclination in a more vertical angulation.

Because of their high functional and esthetic impact, different treatment modalities have been developed for the alignment of retained canines into the dental arch. Nontreatment of retained canines may result in complications such as displacement and loss of vitality of the adjacent incisors, shortening of the dental arch, formation of follicular cysts, canine ankylosis, recurrent infections and pain, internal and/or external resorption of the canine and adjacent teeth (mostly lateral incisors), or combinations of these findings.

According to the clinical guidelines published in 2012 by the Clinical Standards Committee of the Faculty of Dental Surgery, Royal College of Surgeons of England, autogenous transplantation of retained teeth, also referred to as autotransplantation (autoTX) or transalveolar transplantation, is 1 of 5 potential treatment options for tooth realignment. This surgical treatment modality is primarily suggested in patients in which retained teeth could not be reintegrated successfully into the dental arch by active orthodontic movement because of the severity of malposition or ankylosis or if the patient is unwilling to wear orthodontic appliances. ^, Therefore, for these patients, autoTX of retained canines represents a promising treatment option. Autogenous transplantation of ectopically retained canines is a proven therapeutic method with an average 5-year survival rate of 86.7% (range, 70.0%-100.0%) as derived as the mean value from a number of studies published between 1966 and 2011. Unfortunately, long-term data after autologous transalveolar canine transplantation are scarce today, as stated in a recently published systematic review. Furthermore, the influence of prognostic factors on the survival of autotransplanted teeth should be investigated. Those factors are represented by previous orthodontic treatment and root maturity with their impact on postoperative complications such as root resorption and ankylosis, respectively, and endodontic treatment needs.

Material and methods

Patients with at least 1 retained canine in the maxilla or the mandible were treated between October 2006 and April 2018 in a single surgical center.

Objective parameters for the decision to leave tooth extrusion in favor of autoTX were not extensively described in the relevant literature. The clinical decision to perform autoTX was based on our observations and observations made by other study groups, as Sagne et al, that if after at least 6 months of extrusion, any signs of a tooth movement could be approved, extrusion attempts were stated as not promising. Based on the observation of Andersson et al, as well as on our clinical experience, that extrusion might be impeded by ankylosis of the root of the displaced canine, percussion testing was deployed as an additional diagnostic criterion for treatment decision. The decision for autoTX was made in close coordination with the referring orthodontists.

In summary, decision-making was performed closely following the criteria of Ahlberg et al, and Gonnissen et al, in which a decision for autoTX was made if canines were in a difficult malposition, indicating orthodontic treatment as complicated and time-consuming, or when the patient refused orthodontic realignment, failed after surgical exposure, respectively.

At least 1 of the following decision criteria had to be met for patient inclusion: (1) poor prognosis for realignment of ectopic canines as assessed by interdisciplinary assessment between the treating orthodontist and the maxillofacial surgeon, (2) failure of realignment of ectopic canines by orthodontic exposure and extrusion, (3) refusal of wearing orthodontic appliances by the patient, and (4) formation of the tooth root of at least two-thirds to one-half of the expected root length.

Site preparation was necessary for every patient before autoTX, independently from the insertion protocol ( Table I ). Refusal for orthodontic appliances was present in patients who did not want the canine to be extruded with orthodontic brackets. Thus, it is unclear for the authors if there is a necessity to visualize this as an exclusion criterion in the flow chart. Moreover, wearing or not wearing orthodontic appliances was not explicitly documented in this study. Of course, in patients rejecting orthodontic appliances, if the space for the transplant was too narrow, autoTX could not be performed.

Table I

Distribution of independent variables gender, arch, insertion protocol, orthodontic traction, state of apex and endodontic treatment (tooth level)

Variables	n (%)
Gender
Female	213 (66.8)
Male	106 (33.2)
Arch
Maxilla	320 (84.7)
Mandible	58 (15.3)
Insertion protocol
Site preparation after deciduous tooth extraction	147 (38.9)
Site preparation with deciduous tooth missing	231 (61.1)
Orthodontic traction
Yes	108 (28.6)
No	270 (71.4)
Open apex
Yes	157 (41.5)
No	221 (58.5)
Endodontic treatment
Yes	80 (21.2)
No	298 (78.8)

Written informed consent was obtained from the patients and, in case of being underage, from the children’s custodian. Ethical approval was granted by the ethical committee of the Ludwig-Maximilians-University Munich (project no. 18-538, 2019). Patient records were analyzed retrospectively.

Only available data from the last examination of patients were included in the analysis.

Preoperative diagnostics were performed clinically and by cone-beam computed tomography (3D eXam; KaVo Dental GmbH, Biberach, Germany) or conventional panoramic radiography (Orthophos XG, Dentsply Sirona GmbH, Bensheim, Germany) to evaluate the congruence between the graft and the recipient site, the available space, and the position of the retained canine. If limited space was available at the recipient site, the gap between the neighboring teeth was opened preoperatively by the deployment of orthodontic measures. Based on the observation of Andersson et al, as well as on the author’s own clinical experience, that extrusion might be impeded by ankylosis of the root of the displaced canine, percussion testing was deployed as an additional diagnostic criterion for treatment decision. The occurrence of ankylosis of the root was presumed just in case the percussion sound was estimated as bright and metallic. In addition, intraoral radiography was performed postoperatively for every transplant according to the practice internal protocol to assess the graft’s root length and the condition of the surrounding bone. ^, The stage of root development was determined preoperatively by radiography and intraoperatively by visual inspection of the apex. The degree of root development was designated as complete when the apical foramen was closed and when the root was fully formed, according to the maturation stage V, as proposed by Cvek’s classification in 1992. The formation of the roots was 75% or higher in all patients after surgical removal of the canine and visual inspection.

Transplantation of impacted canines was performed under general anesthesia with nasal intubation in an open flap procedure via a marginal incision as a standard approach at the displacement site. If retained teeth were completely covered by bone, the covering bone was carefully removed by drilling with a rotating steel bur under constant irrigation with sterile saline solution. After the exposure, the impacted canines were mobilized atraumatically, extracted, and stored extraorally for as short a time as possible in a solution of 10.0 mL isotonic saline supplemented by 4.0 mg dexamethasone and 100.0 mg doxycycline. ^,

In case of persistence of the deciduous canine, the primary tooth was removed, and the extraction socket was carefully prepared with a rotating steel bur under constant rinsing with sterile saline solution before the graft was positioned into its designated location. If the patient was missing a deciduous canine, a new transplant bed (neo-alveolus) was prepared using the same preparation protocol in the vacant space between the adjacent teeth. Fixation of the grafts was performed according to the respective situation either by fixation to the adjacent teeth with a flexible titanium trauma splint (Medartis, Basel, Switzerland), or with adhesive resin bonding to an existing orthodontic appliance or with a suture.

Oral intake of doxycycline was administered for 5 days postoperatively for infection prophylaxis with dosage depending on the patient’s age and weight (infants > 11 years: 1 × 50 mg <40 kg; 1 × 100 mg 40-75 kg; 2 × 100 mg >75 kg). Ibuprofen 200, 400, or 600 mg was prescribed according to the manufacturer’s specifications for the age and weight of patients.

According to the practice concept, the suture fixation was removed after a healing period of 2 weeks, whereas the flexible titanium trauma splint or the adhesive fixation to the orthodontic appliance was removed after 3 weeks and replaced by a conventional orthodontic bracket fixation, depending on the clinical situation of the degree of mobility of transplants. ^, Postoperative orthodontic final alignment of the transplants was performed, when applicable, with fixed orthodontic appliances. Clinical and radiologic parameters of the transplants were analyzed at 3, 6, 9, and 12 months during the first year after surgery. After the first year, recalls were planned as annual examinations. The intervals between the different annual check-ups did not always meet the 12-month intervals exactly.

Postoperative endodontic treatment was carried out symptomatically according to a standard practice-specific protocol, ^, regardless of the root’s developmental status, when the autotransplanted teeth displayed radiologic signs of root resorption or apical periodontitis and/or clinical symptoms of irreversible pulpitis or pulp necrosis (referred to as endodontic treatment need). To ensure aseptic conditions, a rubber dam was applied, and root canals were irrigated with 2.5% sodium hypochlorite solution and 17.0% ethylenediaminetetraacetic acid. Calcium hydroxide was applied to the root canals because of its excellent antimicrobial potential and tissue healing capacity. Another rationale for the selection of calcium hydroxide as a resorbable root-filling material was the possible exposition to periradicular tissues in case of unexpected root resorption. ^,

Data for analysis of the survival rate and its clinical parameters were collected retrospectively from the patient’s records. All those patients who could not be reached or who refused participation in the follow-up were not included in the analysis. Exclusion was solely because of missing clinical records of the patients. The influence of the following variables on the survival of autotransplants and endodontic treatment needs were investigated: (1) gender, (2) location (maxillary and mandibular arch), (3) number of transplants per patient, (4) preoperative orthodontics, (5) missing or persisting deciduous canine (insertion protocol), (6) state of foramen, (7) postoperative endodontic treatment, and (8) time of clinical function after surgery. This study was conducted under consideration of the STrengthening the Reporting of OBservational studies in Epidemiology guidelines (STROBE).

Statistical analysis

Statistical analysis was performed with WinSTAT (Robert K. Fitch, version 2012.1.0.96) and BiAS (version 11.10; epsilon-Verlag GbR Hochheim, Darmstadt, Germany). Further statistical analyses were performed with the Mann-Whitney U test, Pearson chi-square test, and logistic regression analysis. Fisher exact test was performed as an alternative to the Pearson chi-square test in the statistical analysis of autotransplant loss in dependency of different influence variables because of the relatively small number of events . For regression analysis of bivariate data, continuous data of the independent variable “age at surgical intervention” on tooth level were transformed into 2 dummy variables. Because of the observation that the mean age at surgery was 17.2 years, a cutoff age of 18.0 years was set for the 2 groups. Analysis of survival probability was performed with the Kaplan–Meier statistics. The level of significance was set at α = 0.05.

Results

In total, 440 retained canines of 370 patients were surgically realigned into the dental arch by means of autoTX between October 2006 and April 2018 in a single surgical center. Postoperative complications like pain and infection were very rarely observed.

All patients were intended to be included in this retrospective analysis. Because of a refusal to participate, unknown place of residence, or lack of contact possibility, 51 patients (14.1%) with 62 grafts (13.8%) had to be excluded in this retrospective study because of missing consent for participation, resulting in a final sample size of n = 319 patients with n = 378 teeth ( Fig 1 ). The mean follow-up period was 56.0 ± 36.9 months at the tooth level and 54.7 months at the patient level for the included participants (range, 0.3-181.5 months). More than half of the patients (n = 213; 56.3%) and autotransplants (n = 174; 54.5%) displayed a clinical follow-up of ≥50 months.

On the patient level, the mean age of patients was 17.2 ± 58.4 years (range, 8.4 ± 58.4 years) at the time of surgical intervention, whereas the mean age of the patients was 21.8 ± 8.1 years at the follow-up examination (range, 9.4-59.8 years). There was no significant difference in patient´s age at the time of follow-up examination between female (21.4 years) and male patients (22.5 years) ( P = 0.602).

Most patients had 1 ectopically retained canine (n = 261; 81.8%), 57 patients had 2 retained canines (17.9%), and 1 patient displayed 3 retained canines (0.3%). Nearly two-thirds of the autoTXs on the tooth level (n = 256, 67.7%) and the patient level (n = 213; 66.8%) were performed in female patients, and most autoTXs were conducted in the maxilla (n = 320; 84.7%) ( Table I ). Less than half of the canines (n = 157; 41.5%) displayed an open apical foramen; a closed apical foramen was observed in 221 canines (58.5%). Most autotransplants that did not receive orthodontic traction preoperatively (n = 270; 71.4%) displayed no postoperative endodontic treatment needs during the follow-up period (n = 298; 78.8%) ( Table I ). Regarding the insertion protocol, more than half of all grafts (n = 231; 61.1%) were transplanted after the preparation of a new bony socket (neo-alveolus) because of a missing deciduous canine in the transplant region. ( Table I ). The mean extraoral storage time of the grafts between surgical removal and reinsertion was 5.4 ± 0.2 minutes (range, 0.0-35.0 minutes) (Transdat database, patent no. 30 2018 107 792).

Of the 378 autotransplants, 80 canines had to be treated endodontically (21.2%) ( Fig 1 ; Table I ). The mean period until the necessity for endodontic treatment was 65.2 ± 33.7 months (range, 1.2-148.2 months) and 5.4 ± 2.8 years (range, 0.1-12.4 years), respectively. During the first 7 years after surgery, 55 of the 80 endodontic-treated autotransplants (68.8%) revealed necessity for endodontic treatment. After this time point, the remaining 25 patients with endodontic treatment needs occurred between >7.0 and 12.4 years after surgical intervention. Therefore, the first 7 years after surgical realignment of retained canines appear to be of higher risk for endodontic complications.

Moreover, 88% of the endodontic-treated canines (n = 71) were located in the maxilla. However, there was no statistically significant influence of location on autotransplant survival, which is attributed to the higher number of autotransplants in the maxilla ( P = 0.252). Neither ankylosis ( P = 0.803) nor extraoral storage time ( P = 0.595) had a significant impact on the endodontic treatment need of the autotransplants ( Table II ).

Table II

Logistic regression analysis: Independent variables for endodontic treatment need

Reference group	Variable	OR	95% CI	P value
Lower age at surgery (age ≤18 y)	Higher age at surgery (age >18 y)	2.2	1.2614-3.9500	0.006 ^∗
No ankylosis	Ankylosis	0.9	0.3940-2.0204	0.784
Female gender	Male gender	1.3	0.8016-2.2517	0.262
Immediate insertion after extraction of persistent deciduous tooth	No persistent deciduous tooth at surgery	0.7	0.8016-2.2517	0.208
Mandible	Maxilla	0.6	0.3012-1.3775	0.256
Open apical foramen	Closed apical foramen	2.9	1.6751-5.2690	<0.001 ^∗
No preoperative orthodontic traction	Preoperative orthodontic traction	2.1	1.2441-3.5033	0.005 ^∗