Abstract
Objective
This study aimed to investigate the factors related to the survival of retained deciduous teeth (RDTs).
Materials and methods
RDTs were identified in panoramic X-ray images in 13,516 patients at Nagasaki University Hospital from 2014 to 2018. The survival status of the RDTs was tracked using medical records; survival rates were calculated. The RDTs were divided into two groups: before and after the completion of stable permanent dentition. A shared frailty analysis was performed in each group, estimating hazard ratios and 95% confidence intervals for variables related to survival.
Results
A total of 138 patients (50 male and 88 female participants, 1.02%) had RDTs. The total number of RDTs was 274, with survival rates of 62.48% at 10 years and 53.30% at 20 years. Before the completion of permanent dentition, the longevity of RDTs was associated with two variables: tooth type (anterior/molar) and presence or absence of successive permanent teeth. No variables were associated with RDT survival after permanent dentition was stabilized.
Conclusion
Multiple congenital factors affect the longevity of RDTs before the stabilization of permanent dentition. However, no significant influence was observed based on factors identified retrospectively after the permanent dentition was stabilized.
1
Introduction
Retained deciduous teeth (RDTs) are primary teeth that do not shed naturally at the expected time and remain in the mouth beyond the typical shedding age. The most common cause of late retention is the congenital absence of successive permanent teeth [ , ]. The incidence of the congenital absence of permanent teeth has been reported to be approximately 10% in Japan [ , ], 3.9% in North America, 5.5% in Europe, and 6.3% in Australia [ , ]. These figures include molars, but the incidence of congenital absence of permanent teeth from the incisors to the second premolars, which are directly associated with deciduous teeth, is presumed to be lower.
Deciduous teeth can remain stable if there are no successive permanent teeth. RDTs in good condition can serve as a replacement for permanent teeth, even if successors are congenitally absent [ , ]. A systematic review of treatments in adults with partial edentulism found that the survival rate of primary teeth lacking successive permanent teeth ranged from 83% to 93% at follow-ups of 5–15 years [ ]. Second deciduous molars without successors can survive for a long time [ ].
Factors other than the congenital absence of successive permanent teeth may also influence survival status. The survival rates of deciduous canines and second deciduous molars differ, even when both are considered RDTs [ ]. This suggests that the survival rate of RDTs might be related to the tooth type.
RDTs are prone to ankylosis and infraocclusion, which can lead to functional and aesthetic abnormalities, such as the inclination of adjacent teeth and extrusion of opposing teeth [ ]. Some reports suggest that RDTs should not be preserved and that implant treatment should be performed instead [ ]. However, a treatment approach that aims to preserve the function of the RDTs as much as possible is widely accepted clinically [ , ]. A systematic review of treatment methods for cases of missing permanent teeth also reported that retaining primary teeth is ideal in children and adolescents, wherein the success rate of implant treatment is low [ ]. The treatment method for RDTs should consider both the condition of the RDT itself and patient’s age. When the longevity of a patient’s RDTs can be predicted, the appropriate timing and method of surgical or prosthetic treatment can be determined. However, little information is available on the factors useful for planning RDT treatment [ ].
Different treatment measures may be required depending on the growth stage [ ]. Most previous reports [ , , , , , ] on RDTs were follow-up studies from childhood to adulthood; long-term survival rates into adulthood have not been thoroughly investigated. In this study, we examined radiographs of patients who visited a hospital dentistry clinic over a certain period to investigate factors related to RDT survival.
2
Materials and Methods
2.1
Study design, setting, and participants
This hospital-based cohort study targeted electronic medical records of patients aged 7 years or older at the time of their first visit who underwent panoramic X-ray examinations at Nagasaki University Hospital from July 1, 2014, to December 31, 2018. The age of the target participants was set based on a previous report [ ], revealing that data from children younger than 7 years might lead to misdiagnosis when confirming the congenital absence of permanent teeth. All procedures involving human participants were performed according to the principles of the Declaration of Helsinki. Informed consent was obtained from the participants or their guardians through an opt-out procedure. This study was approved by the Clinical Research Ethics Committee of Nagasaki University Hospital (approval no.: 21062118).
The medical records of single-visit patients whose prognosis was difficult to follow and edentulous patients unlikely to have deciduous teeth were excluded. Seven pediatric dentists selected the deciduous teeth. From the remaining records, patients whose deciduous teeth had remained beyond the average age of eruption were included. The eligibility criterion for RDTs was tooth present in the dentition beyond the average age of eruption of successive permanent tooth [ ] plus two standard deviations.
2.2
Variables
Information on variables presumed to be related to the survival of RDTs was collected from panoramic X-ray images and medical records. Ultimately, data on 17 variables were collected if there were successive permanent teeth, and 14 variables were collected when there were no successors.
2.2.1
Participant information
Information collected included sex, presence or absence of oral cavity-related disease/syndrome/cleft lip and palate, and the number of remaining teeth in the oral cavity at the time of final confirmation of RDTs. The total number of teeth was transformed into three categorical variables after continuity analysis.
2.2.2
RDT information
Data collected included tooth type (anterior/posterior, upper/mandibular, and left/right side), fusion, malposition, morphological abnormalities, presence or absence of successive permanent teeth, history of restorative treatment, history of root canal treatment, history of trauma, and presence of occlusion with opposing teeth.
2.2.3
Successive permanent tooth information
Information on fusion, malposition, and morphological abnormalities was collected from patients with successive permanent teeth.
2.3
Data source
Data of patients with RDT were extracted, and their medical records were followed-up until March 31, 2022. Data were managed using Microsoft® ️ Excel for Mac version 16.78.3 (Microsoft Corp., Redmond, WA), and checked multiple times to avoid duplication and errors. Extraction or spontaneous loss of RDT was defined as an event, and the time until the event occurred was considered survival time. If no events occurred, the survival time was defined at the last observed day.
2.4
Statistical method
Given that the survival of RDTs could be affected by the developmental stage of the dentition, all RDTs were divided into two groups: those whose age at the event or truncation date was younger than the time when the stable permanent dentition was completed (average age in Japanese people: 21 years and 5 months [ ]) (group 1), and those older than this age (group 2).
Fisher’s exact test was first performed to avoid multicollinearity between variables. The survival time and rate of RDTs were calculated using Kaplan–Meier survival analysis; survival curves were drawn.
Shared frailty analysis, a mixed-effects model assuming the same frailty among participants, was selected for analysis. By incorporating a frailty term, these variables can be adjusted, and more precise hazard ratios can be obtained. This method enhances the robustness of the findings and ensures that the potential biases due to clustering are appropriately mitigated. After analyzing the selected variables using the stepwise method, hazard ratios and their respective 95% confidence intervals (CIs) were estimated for the variables assumed to affect RDT survival. The significance level was set at 5%.
JMP Pro 17 version 17.0.0 (SAS Institute Inc., Cary, NC, USA) was used for Fisher’s exact test and Kaplan–Meier survival analysis, and R Studio version 2023.06.2 + 561 (Posit Software, PBC) was used for continuity tests, stepwise methods, and shared frailty analyses.
3
Results
3.1
Participant and descriptive data
Of the 17,980 patients who met the criteria, 4229 patients who had a single visit and whose prognosis was difficult to follow were excluded, as were 235 edentulous patients. Using the images of the remaining 13,516 patients, 138 patients with RDTs (minimum age: 8 years 8 months; maximum age: 68 years 2 months) and 274 RDTs were identified. Table 1 presents the overall patient and RDT data. Patients with trauma history and RDT morphological abnormalities were excluded. Laterality was used only for discrimination purposes and excluded from the variables. All medical records were properly documented; there were no missing data.
| Variables | All | Group 1 | Group 2 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| n | % | 95%CI | n | % | 95%CI | n | % | 95%CI | |
| Participant information | |||||||||
| Sex | |||||||||
| Male | 50.0 | 36.2 | 28.7; 44.5 | 26.0 | 32.1 | 22.9; 42.9 | 24.0 | 42.1 | 30.2; 69.8 |
| Female | 88.0 | 63.8 | 55.5; 71.3 | 55.0 | 67.9 | 57.1; 77.1 | 33.0 | 57.9 | 45.0; 55.0 |
| Oral cavity-related disease/syndrome/cleft lip and palate | |||||||||
| Presence | 17.0 | 12.3 | 7.8; 18.8 | 12.0 | 8.7 | 8.7; 24.1 | 5.0 | 8.8 | 3.8; 18.9 |
| Absence | 121.0 | 87.7 | 81.2; 92.2 | 69.0 | 75.9 | 75.9; 91.3 | 52.0 | 91.2 | 81.1; 96.2 |
| Number of remaining teeth | |||||||||
| 1-24 | 85.0 | 31.0 | 25.8; 36.7 | 74.0 | 42.0 | 35.9; 49.4 | 11.0 | 11.2 | 6.4; 19.0 |
| 25-27 | 98.0 | 35.8 | 30.3; 41.6 | 57.0 | 32.4 | 25.9; 39.6 | 41.0 | 41.8 | 32.7; 51.7 |
| 28-32 | 91.0 | 33.2 | 27.9; 39.0 | 45.0 | 25.6 | 19.7; 32.5 | 46.0 | 46.9 | 37.4; 56.7 |
| RDT information | |||||||||
| Anterior/posterior | |||||||||
| Anterior | 93.0 | 33.9 | 28.6; 39.7 | 70.0 | 39.8 | 32.8; 47.1 | 23.0 | 23.5 | 16.2; 32.8 |
| Posterior | 181.0 | 66.1 | 60.3; 71.4 | 106.0 | 60.2 | 52.9; 67.2 | 75.0 | 76.5 | 67.2; 83.8 |
| Upper/mandibular | |||||||||
| Upper | 112.0 | 40.9 | 35.2; 46.8 | 77.0 | 43.8 | 36.6; 51.1 | 35.0 | 35.7 | 26.9; 45.6 |
| Mandibular | 162.0 | 59.1 | 53.2; 64.8 | 99.0 | 56.3 | 48.9: 63.4 | 63.0 | 64.3 | 54.4; 73.1 |
| Fusion | |||||||||
| Presence | 2.0 | 0.7 | 0.2; 2.6 | 2.0 | 1.1 | 0.3; 4.0 | 0.0 | 0.0 | – |
| Absence | 272.0 | 99.3 | 97.4; 99.8 | 174.0 | 98.9 | 96.0; 99.7 | 98.0 | 100.0 | – |
| Malposition | |||||||||
| Presence | 98.0 | 35.8 | 30.3; 41.6 | 57.0 | 32.4 | 25.9; 39.6 | 41.0 | 41.8 | 32.6; 51.7 |
| Absence | 176.0 | 64.2 | 58.4; 69.7 | 119.0 | 67.6 | 60.4; 74.1 | 57.0 | 58.2 | 48.3; 67.4 |
| Successive permanent teeth | |||||||||
| Presence | 84.0 | 30.7 | 25.5; 36.4 | 66.0 | 37.5 | 30.7; 44.8 | 18.0 | 18.4 | 11.9; 27.2 |
| Absence | 190.0 | 69.3 | 63.6; 74.5 | 110.0 | 62.5 | 55.2; 69.3 | 80.0 | 81.6 | 72.8; 88.1 |
| History of restorative treatment | |||||||||
| Presence | 85.0 | 31.0 | 25.8; 36.7 | 38.0 | 21.6 | 16.2; 28.2 | 47.0 | 48.0 | 38.3; 57.7 |
| Absence | 189.0 | 69.0 | 63.3; 74.2 | 138.0 | 78.4 | 71.8; 83.8 | 51.0 | 52.0 | 42.3; 61.7 |
| History of root canal treatment | |||||||||
| Presence | 12.0 | 4.4 | 2.5; 7.5 | 7.0 | 4.0 | 1.9; 8.0 | 5.0 | 5.1 | 22.0; 11.4 |
| Absence | 262.0 | 95.6 | 92.5; 97.5 | 169.0 | 96.0 | 92.0; 98.1 | 93.0 | 94.9 | 88.6; 97.8 |
| Occlusion with opposing teeth | |||||||||
| Presence | 201.0 | 73.4 | 67.8; 78.2 | 130.0 | 73.9 | 66.9; 79.8 | 71.0 | 72.4 | 62.9; 80.3 |
| Absence | 73.0 | 26.6 | 21.8; 32.2 | 46.0 | 26.1 | 20.2; 33.1 | 27.0 | 27.6 | 19.7; 37.1 |
| Successive permanent tooth information | |||||||||
| Fusion | |||||||||
| Presence | 2.0 | 2.4 | 0.7; 8.3 | 2.0 | 3.0 | 8.4; 10.4 | 0.0 | 0.0 | – |
| Absence | 82.0 | 97.6 | 91.7; 99.3 | 64.0 | 97.0 | 89.6; 99.2 | 18.0 | 100.0 | 82.4; 100.0 |
| Malposition | |||||||||
| Presence | 64.0 | 76.2 | 66.1; 84.0 | 51.0 | 77.3 | 27.1; 49.9 | 13.0 | 72.2 | 49.1; 82.5 |
| Absence | 20.0 | 23.8 | 16.0; 33.9 | 15.0 | 22.7 | 50.1; 72.9 | 5.0 | 27.8 | 12.5; 50.9 |
| Morphological abnormality | |||||||||
| Presence | 7.0 | 8.3 | 4.1; 16.2 | 5.0 | 7.6 | 3.3; 16.5 | 2.0 | 11.1 | 3.1; 32.8 |
| Absence | 77.0 | 91.7 | 83.8; 95.9 | 61.0 | 92.4 | 83.5; 96.7 | 16.0 | 88.9 | 67.2; 96.9 |
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