Abstract
Osseointegrated dental implants represent a successful treatment modality for partial and complete edentulism. However, concerns persist regarding their impact on adjacent natural teeth. Conflicting literature exists regarding complications such as caries, mobility, and fractures in neighboring teeth, with few studies comparing these effects with those observed in contralateral natural teeth. This retrospective study aimed to assess the impact of single posterior implant-supported rehabilitation on adjacent natural teeth compared to contralateral teeth. We retrospectively screened and analyzed electronic records of all patients who underwent treatment with a single posterior implant-supported restoration (premolar or molar) at a single public dental clinic between August 2010 and August 2020. We evaluated adjacent natural teeth for four potential complications: primary caries, secondary caries, tooth cracks or fractures, and tooth mobility. Chi-square tests compared the occurrence and rates of complications between teeth adjacent to single implants and contralateral teeth. Additionally, we conducted statistical comparisons to analyze the types of complications observed in teeth adjacent to single implants. Among the 1100 patients who received posterior single implants during the study period, 167 patients (15.1%) experienced complications in a tooth adjacent to the implant. The majority of these complications were attributed to either primary (41.3%) or secondary (53.3%) caries. A significant correlation was observed between the type of complication in the adjacent tooth and the status of the control tooth (χ2 = 21.73, p = 0.01). Specifically, in cases of primary caries, the majority (68.1%) of control teeth remained classified as intact. Furthermore, in a comparison between teeth with crack/fracture complications and control teeth, 83.3% of control teeth remained intact (p = 0.01). Mobility complications were significantly associated with diabetic patients (p = 0.041) and a longer duration until implant rehabilitation (p = 0.006). Patients experiencing crack/fracture and mobility complications required a higher number of dental implants compared to other categories (p = 0.043). This study revealed a significant correlation between posterior single implants and the occurrence of complications in adjacent teeth, while most of the contralateral teeth remained intact. Clinical relevance. Meticulous monitoring of implant patients is crucial for assessing the condition of adjacent teeth and effectively manage potential complications, particularly in high-risk patients.
Keywords: Single implant-supported restoration, Adjacent teeth, Contralateral natural tooth, Complications, Caries
Subject terms: Medical research, Risk factors
Introduction
Osseointegrated dental implants have proven to be a successful treatment modality in partial and complete edentulism, with high survival rates of 95% and 86.7% after 5- and 10-years respectively1,2.
Moreover, single implant-supported restorations for posterior missing teeth have demonstrated high success, with survival rates reaching 98.9% over an average follow-up period of 61 months3. Despite their efficacy, concerns persist regarding the potential impact of implant-supported restorations on adjacent natural teeth.
While single-tooth implants offer advantages such as conservation of existing tooth structure compared to traditional fixed partial dentures, questions remain regarding the occurrence of biological and technical complications in adjacent natural teeth. Existing literature presents conflicting findings, with some studies reporting minimal complications in teeth neighboring implants3–5, while others note high rate of complications in teeth adjacent to dental implants [6.7].
Complications observed in teeth adjacent to implants include primary and secondary caries, tooth mobility, root canal treatment, and even vertical root fractures6–8. Potential explanations for these complications include the loss of proximal contact points between implants and adjacent teeth, leading to an increased incidence of caries and periodontal disease9–12. Additionally, alterations in occlusal loads between implants and natural teeth due to differences in mobility over time may contribute to adverse outcomes6.
Most studies investigating the effects of a single implant on adjacent teeth and tissues do not compare these effects with those observed in the natural tooth contralateral to the implant. To the best of our knowledge, only one study has utilized the patient’s contralateral teeth as controls to examine the impact of single-tooth implant restorations on the survival and morbidity of adjacent teeth6. Since the human body typically exhibits symmetrical features, it is reasonable to expect that both sides of the mouth will manifest similar complications around natural teeth. Therefore, by using contralateral teeth as controls in our study, thereby enabling within-patient comparisons, we aimed to minimize potential confounding factors from inter-individual differences and provide a more comprehensive understanding of the effects of single-tooth implants on adjacent oral structures.
Consequently, the present study aims to retrospectively evaluate the impact of single posterior implant-supported rehabilitation on adjacent natural teeth compared to contralateral natural teeth.
Materials and methods
Study sample
Electronic records of all patients treated with single posterior implants and their associated restorations (premolars or molars) at a single public dental clinic, part of ‘Clalit Smile,’ the largest national network of public clinics in the country, were retrospectively screened and analyzed, following institutional review board approval (#COM1-0087-20), for treatments conducted between August 2010 and August 2020. All procedures were conducted in accordance with relevant guidelines and regulations.
Patients were included if they met the following criteria: aged over 18 years; had a single posterior natural tooth adjacent to the site of the single posterior implant-supported restoration, free of periapical pathology; had a contralateral natural tooth with two adjacent natural teeth, free of periapical pathology; and had preoperative and postoperative clinical and radiographic records.
Patients were excluded if they had uncontrolled medical conditions (the distinction between controlled and uncontrolled conditions was determined based on physicians’ notes), untreated periodontal disease, incomplete records, or were unavailable for recall. In addition, implants with periimplantitis were excluded from the study13.
All demographic, clinical patient-related, and postoperative follow-up data were extracted from the patients’ dental records. In the routine of the public clinic, patients underwent checkups every 6 months, which included two bite-wing X-rays. During these follow-up visits, tooth cleaning by an oral hygienist was also conducted. Reviewed information included assessments of oral hygiene, primary and secondary dental caries, tooth mobility, tooth fracture, and periapical status of teeth adjacent to the implant and the contralateral tooth. One examiner (M.K.) assessed all radiographic and clinical records. All implant procedures were carried out by either a periodontist or an oral surgeon. One implant system was used: Alfa-Bio Tec. (Dental Implants Manufacturer, Petah Tikva, Israel).
Patient demographics such as age, gender, systemic medical history (specifically Diabetes Mellitus [DM], hypertension, ischemic heart disease, osteoporosis, and intake of bisphosphonates [bone modulating medications]), tobacco use, periodontal status, DMF index (Decayed, Missing, and Filled teeth), and the total number of dental implants for each patient, were all included in the datasheet. The DMF index was categorized into three groups: Low (DMF 0–4), medium (DMF 5–8), and high (DMF above 9).
The adjacent natural teeth, comprising the study group, were evaluated for four potential complications: primary caries, secondary caries (localized to the proximal surface facing the dental implant), tooth crack or fracture (analyzed collectively), and tooth mobility (classified as yes or no). In contrast, the contralateral natural teeth, comprising the control group, were categorized as reconstructed (with any type of filling), crowned, extracted, or intact. Each implant was independently assessed as a single site (without considering each side of the implant separately).
If a complication occurred, further data extracted included: implant location, implant diameter, distance between the tooth and implant (measured at the cementoenamel junction), number of implants, time until implant restoration, time elapsed from dental implant rehabilitation to onset of adjacent tooth complication, and periodontal classification (according to the latest classification of periodontal disease 201813). Periodontal status was categorized as mild disease (Stage 1), moderate disease (Stage 2), and severe disease (Stages 3–4).
Statistical methods and synthesis of results
Data analysis was performed using SPSS version 27. Descriptive statistics were utilized to present frequencies (N/%) for categorical variables, such as sex, and means with standard deviations for continuous variables, such as age. We tested the distributions of the continuous variables (e.g. distance between tooth and implant) by using Shapiro-Wils tests. Results showed non-normal distribution. Therefore, we employed non-parametric tests. To compare the number and rates of complications between teeth adjacent to single implants and control teeth, Chi-square tests were employed. Additionally, the types of complications for the teeth adjacent to single implants were compared across clinical characteristics using Chi-square tests for categorical variables and Kruskal-Wallis procedures for continuous variables. We also evaluated a multivariate binary logistic regression model that predicts secondary caries (in comparison with primary caries). A significant level of 5% (p < 0.05) was used. However, to avoid increased type 1 error due to multiple comparisons, we adjusted the alpha, with Bonferroni correction.
Results
After reviewing all patient files with single posterior implant-supported restorations between August 2010 and August 2020 at a specific public dental clinic, 1,100 files met the inclusion criteria. The mean follow-up duration was 61.6 (± 30) months. Among these, 167 patients (15.2%), forming the cohort, experienced documented complications in the tooth adjacent to a single posterior implant during the follow-up period.
Table 1 presents the characteristics of the patients in the cohort. The results indicate that approximately half of the cohort comprised males (48.5%), with an average age of participants at 59.17 (± 12.78) years. Among the participants in the cohort, 14.4% were diagnosed with DM, 9.6% with high blood pressure, 13.8% with heart disease, 4.2% with osteoporosis, and another 4.2% with bisphosphonate use.
Table 1.
The characteristics of the patients in the cohort.
| Characteristic | Frequency (Number) | % | Mean | ±SD |
|---|---|---|---|---|
| Sex (male) | 81 | 48.5 | ||
| Age | 59.17 | 12.78 | ||
| Diabetes mellitus (DM) | 24 | 14.4 | ||
| High blood pressure | 16 | 9.6 | ||
| Heart disease | 23 | 13.8 | ||
| Osteoporosis | 7 | 4.2 | ||
| Bisphosphonates | 7 | 4.2 | ||
| Vitamin D | 14 | 8.4 | ||
| Smoking | 26 | 15.6 | ||
| DMF | ||||
| • Low | 9 | 5.4 | ||
| • Medium | 77 | 46.1 | ||
| • High | 81 | 48.5 | ||
| Reason of extraction and placing the single implant | ||||
| • Caries | 95 | 56.9 | ||
| • Tooth crack | 22 | 13.2 | ||
| • Tooth fracture | 18 | 10.8 | ||
| • Tooth mobility | 12 | 7.2 | ||
| • Other | 20 | 12.0 | ||
| Perio diagnosis | ||||
| • Stage 1 | 40 | 24.0 | ||
| • Stage 2 | 83 | 49.7 | ||
| • Stages 3–4 | 44 | 26.3 | ||
Standard deviation-SD.
Table 2 presents the characteristics of the teeth in the cohort. Regarding the type of complications in the adjacent teeth, the majority experienced either primary (41.3%) or secondary (53.3%) caries, with approximately 57% attributing caries as the primary reason for extraction and placement of the single implant.
Table 2.
The characteristics of the teeth in the cohort.
| Characteristic | Frequency (Number) | % | Mean | ±SD |
|---|---|---|---|---|
| Implant location | ||||
| • Molar | 114 | 68.3 | ||
| • Pre-molar | 53 | 31.7 | ||
| Adjacent tooth involved (molar) | 66 | 39.5 | ||
| Jaw | ||||
| • Upper | 51 | 30.5 | ||
| • Lower | 116 | 69.5 | ||
| Type of sinus lift | ||||
| • None | 157 | 94.0 | ||
| • Open | 8 | 4.8 | ||
| • Close | 2 | 1.2 | ||
| Distance between the tooth and the implant | 4.01 | 1.37 | ||
| Implant diameter | 3.73 | 0.12 | ||
| Number of implants | 3.45 | 2.46 | ||
| Time until restoration (months) | 5.25 | 2.46 | ||
| Time until complication (months) | 43.44 | 22.21 | ||
| Type of complication in the adjacent tooth | ||||
| • Primary caries | 69 | 41.3 | ||
| • Secondary caries | 89 | 53.3 | ||
| • Tooth crack/fracture | 6 | 3.6 | ||
| • Tooth mobility | 3 | 1.8 | ||
| Status of control tooth | ||||
| • Reconstruction | 26 | 15.6 | ||
| • Crown | 30 | 18.0 | ||
| • Extraction | 15 | 9.0 | ||
| • Intact | 96 | 57.5 | ||
Standard deviation-SD.
Table 3 illustrates the association between the type of complication in the adjacent tooth (study group) and the status of the contralateral tooth (control group). The findings reveal a significant correlation (χ2 = 21.73, p = 0.01) between the groups.
Table 3.
The association between the type of complication in the study group and the corresponding status of the control group.
| Control group | Study group | ||||
|---|---|---|---|---|---|
| Primary caries (69 teeth) | Secondary caries (89 teeth) | All caries (158 teeth) | Tooth crack/fracture (6 teeth) | Tooth mobility (3 teeth) | |
| Recontruction | 7 | 19 | 26 | 0 | 0 |
| 10.1% | 21.3% | 16.5% | 0.0% | 0.0% | |
| Crown | 10 | 19 | 29 | 1 | 0 |
| 14.5% | 21.3% | 18.4% | 16.7% | 0.0% | |
| Extraction | 5 | 8 | 13 | 0 | 2 |
| 7.2% | 9.0% | 8.2% | 0.0% | 66.7% | |
| Intact | 47 | 43 | 90 | 5 | 1 |
| 68.1% | 48.3% | 57% | 83.3% | 33.3% | |
Standard deviation-SD.
Specifically, among teeth in the study group with primary caries or tooth crack/fracture, most of the control teeth were classified as intact (68.1% and 83.3%, respectively). However, for teeth in the study group exhibiting mobility, a majority of the control teeth were extracted (66.7%). Additionally, among teeth in the study group with secondary caries, 42.63% of the control teeth were either reconstructed (21.3%) or crowned (21.3%).
When combining all cases of caries (primary and secondary) in the study group (Table 2), a significant correlation was also observed (χ2 = 14.12, p = 0.01). Higher rates of caries in the study group were associated with restorations, including reconstructions (16.5%) and crowns (18.4%), compared to only 8.2% of extractions in the control group.
Table 4 presents detailed data specific to the comparison between the different complication groups in the study cohort. Statistical analyses were performed to evaluate differences among the various types of complication groups.
Table 4.
Comparison between different complication groups in the study cohort.
| Primary caries (69 teeth) | Secondary caries (89 teeth) | Tooth crack/fracture (6 teeth) | Tooth mobility (3 teeth) | p -value | |
|---|---|---|---|---|---|
| Sex (Male) | 28 (40.6%) | 49 (55.1%) | 2 (33.3%) | 2 (66.7%) | p= 0.24 |
| Age (Mean ± SD) | 58.33 (±12.95) | 59.10 (±12.69) | 62.50 (±11.39) | 74.00 (±6.55) | p= 0.192 |
| Implant location | p= 0.285 | ||||
| • Molar | 51 (73.9%) | 59 (66.3%) | 3 (50.0%) | 1 (33.3%) | |
| • Pre-molar | 18 (26.1%) | 30 (33.7%) | 3 (50.0%) | 2 (66.7%) | |
| Adjacent tooth involved (molar) | 25 (36.2%) | 39 (43.8%) | 1 (16.7%) | 1 (33.3%) | p= 0.501 |
| Jaw | p= 0.585 | ||||
| • Upper | 21 (30.4%) | 26 (29.2%) | 1 (33.3%) | 18 (29.0%) | |
| • Lower | 48 (69.6%) | 63 (70.8%) | 4 (66.7%) | 1 (33.3%) | |
| Diabetes | 8 (11.6%) | 14 (15.7%) | 0 | 2 (66.7%) | p= 0.041 |
| High blood pressure | 7 (10.1%) | 8 (9.0%) | 0 | 1 (33.3%) | p= 0.449 |
| Heart disease | 7 (10.1%) | 15 (16.9%) | 1 (16.7%) | 0 | p= 0.573 |
| Osteoporosis | 4 (5.8%) | 0 | 0 | 2 (3.2%) | p= 0.963 |
| Bisphosphonates | 4 (5.8%) | 3 (3.4%) | 0 | 0 | p= 0.805 |
| Vitamin D | 6 (8.8%) | 7 (7.9%) | 1 (16.7%) | 0 | p= 0.837 |
| Smoking | 13 (18.8%) | 12 (13.5%) | 1 (16.7%) | 0 | p= 0.702 |
| Time until restoration months (Mean ± SD) | 5.12 (±2.26) | 5.34 (±2.21) | 3.33 (±1.75) | 9.33 (±8.38) | p= 0.006 |
| Time until complication months (Mean ± SD) | 42.33 (±20.66) | 42.27 (±22.54) | 63.83 (±27.45) | 63.00 (±16.00) | p= 0.055 |
| DMF | p= 0.252 | ||||
| • Low | 4 (5.8%) | 4 (4.5%) | 0 | 1 (33.3%) | |
| • Medium | 35 (50.7%) | 40 (44.9%) | 2 (33.3%) | 0 | |
| • High | 30 (43.5%) | 45 (50.6%) | 4 (66.7%) | 2 (66.7%) | |
| Type of sinus lift (open) | 6 (8.7%) | 6 (6.7%) | 0 | 2 (66.7%) | p= 0.003 |
| Distance between tooth and implant mm (Mean ± SD) | 4.05 (±1.45) | 4.00 (±1.31) | 3.66 (±1.69) | 3.73 (±0.75) | p= 0.901 |
| Implant diameter (Mean ± SD) | 3.72 (±0.11) | 3.73 (±0.13) | 3.70 (0) | 3.70 (0) | p= 0.912 |
| Number of implants (Mean ± SD) | 2.96 (±2.04) | 3.65 (±2.66) | 5.17 (±2.04) | 5.33 (±3.51) | p= 0.043 |
| Perio diagnosis | p= 0.104 | ||||
| • Stage 1 | 21 (30.4%) | 19 (21.3%) | 0 | 0 | |
| • Stage 2 | 33 (47.8%) | 47 (52.8%) | 2 (33.3%) | 1 (33.3%) | |
| • Stages 3–4 | 15 (21.7%) | 23 (25.8%) | 4 (66.7%) | 2 (66.7%) |
No statistical significance was observed between any of the four complication groups and various demographic and clinical factors, including age, sex, jaw, implant location, specific tooth involved, systemic diseases (except DM), smoking status, DMF (Decayed, Missing, Filled) index, implant diameter, distance between the tooth and implant, and the time from prosthetic rehabilitation of the implant to the time of complication appearance.
However, statistical significance was observed for DM among the different complication groups, with tooth mobility showing a significantly higher prevalence (66.7%) compared to those with other complications (p = 0.041). It is noteworthy that the number of mobile teeth was only three.
Regarding the periodontal status, no statistical significance was observed with any of the complications. However, it is noteworthy that 66% of the mobile teeth were classified as severe disease. Due to the limited number of mobile teeth, statistical significance could not be determined.
The occurrence of open sinus lift procedures was significantly more frequent in implants associated with tooth mobility (66.7%) compared to those with other complications (p = 0.003).
The time from implant surgery to restoration placement was longer in the tooth mobility group (9.33 ± 8.38months), while shorter in the tooth crack/fracture group (3.33 ± 1.75months) (p = 0.006).
Additionally, a higher number of implants were found in the tooth crack/fracture and tooth mobility groups (5.17 ± 2.04 and 5.33 ± 3.51, respectively) compared to the other two complication groups (p = 0.043).
The multivariate regression analysis indicates that the presence of an adjacent tooth is the sole predictor for an increased risk of secondary caries (Odds Ratio [OR] = 1.07,95% CI [1.00–1.15], p = 0.04) (Table 5).
Table 5.
Odds ratio of multivariate model predicting secondary caries (vs. primary caries).
| OR | 95% CI for OR | P | ||
|---|---|---|---|---|
| Lower | Upper | |||
| Gender (Male Vs. Female) | 0.55 | 0.27 | 1.12 | 0.10 |
| Age | 1.00 | 0.97 | 1.03 | 0.84 |
| Location of implant (Pre-molar vs. molar) | 1.74 | 0.76 | 3.98 | 0.19 |
| Adjacent tooth | 1.74 | 1.00 | 1.15 | 0.04 |
| Jaw (Lower vs. upper) | 0.25 | 0.05 | 1.22 | 0.09 |
| Diabetes | 1.37 | 0.49 | 3.82 | 0.54 |
| High blood pressure | 0.74 | 0.23 | 2.40 | 0.61 |
| Heart disease | 1.74 | 0.59 | 5.17 | 0.32 |
| Bisphosphonates | 1.12 | 0.20 | 6.32 | 0.90 |
| Vitamin D / Calcium | 1.57 | 0.42 | 5.79 | 0.50 |
| Smoking | 1.69 | 0.67 | 4.29 | 0.27 |
| Time till prosthodontics (months) | 1.08 | 0.92 | 1.26 | 0.35 |
| Time till failure (months) | 1.00 | 0.99 | 1.02 | 0.81 |
Furthermore, we conducted a Cox regression analysis to predict the occurrence of secondary caries over time (Table 6). The results indicate that age and implant location (premolar vs. molar) are significant predictors of secondary caries. Specifically, increasing age is associated with a reduced risk of developing secondary caries (HR = 0.63, 95% CI: 0.40–1.00), suggesting that older individuals are less prone to this complication. Additionally, implants placed in the premolar region are associated with a significantly higher risk of secondary caries compared to those in the molar region (HR = 1.77, 95% CI: 1.05–2.97).
Table 6.
Hazard ratio of Cox regression predicting secondary caries.
| HR | 95% CI for OR | P | ||
|---|---|---|---|---|
| Lower | Upper | |||
| Gender (Male Vs. Female) | 0.99 | 0.97 | 1.01 | 0.18 |
| Age | 0.63 | 0.40 | 1.00 | 0.05 |
| Location of implant (Pre-molar vs. molar) | 1.77 | 1.05 | 2.97 | 0.03 |
| Adjacent tooth | 1.05 | 1.00 | 1.10 | 0.06 |
| Jaw (Lower vs. upper) | 0.65 | 0.22 | 1.94 | 0.44 |
| Diabetes | 1.07 | 0.57 | 2.02 | 0.84 |
| High blood pressure | 0.74 | 0.23 | 2.40 | 0.61 |
| Heart disease | 1.18 | 0.52 | 2.67 | 0.69 |
| Bisphosphonates | 1.05 | 0.28 | 3.97 | 0.94 |
| Vitamin D / Calcium | 1.28 | 0.52 | 3.13 | 0.60 |
Discussion
The current study evaluated the influence of single posterior implant-supported rehabilitations on adjacent natural teeth compared to contralateral natural teeth. Among the 1,100 patients meeting the inclusion criteria, 167 (15.2%) experienced documented complications in teeth adjacent to the implant over a follow-up period of up to 10 years. Among these complications, the majority were either primary caries (41.3%) or secondary carries (53.3%). A significant correlation was found between the type of complication in the adjacent tooth and the status of the control tooth (χ² = 21.73, p = 0.01). Notably, in cases of primary caries, most control teeth (68.1%) remained classified as intact.
Unlike previous studies, our study utilized the patient’s contralateral teeth as controls, enabling within-patient comparisons and eliminating inter-individual differences3–5,7.
The current results indicate a significantly higher incidence of complications compared to previous reports. Misch et al. observed that only 5% of adjacent teeth developed interproximal decay over a 10-year period, while Priest reported just one case of tooth replacement and one extraction within the same timeframe3,4. Krennmair et al. found that only 4 adjacent teeth (3%) required intervention during a 3-year follow-up period5. These earlier studies, published over 20 years ago, reported remarkably low incidences of interproximal decay compared to recent findings, including ours and those of others6,7. Notably, these older studies lacked specified inclusion and exclusion criteria, which may have influenced their outcomes.
On the other hand, our complication rate aligns with those reported by Duqum et al., who also used contralateral teeth as controls and reached the same conclusion as our study: the incidence of restorative retreatment was significantly higher for teeth adjacent to implant restorations compared to contralateral controls6. Similarly, Tagger-Green et al., in their recent retrospective case–control study, reported a high incidence of complications in adjacent teeth (16.7%) over a 10-year follow-up period6,7.
Our primary finding was the elevated incidence of primary caries (41.3%) and secondary caries (53.3%) observed in the teeth neighboring the implant during the 10-year follow-up period. In addition, the presence of an adjacent tooth increased the risk of secondary caries, with an odds ratio of 1.07 at a 95% confidence interval. These findings align with findings from previous retrospective studies. Tagger-Green et al. reported a relatively high rate of complications in teeth adjacent to dental implants, with secondary caries emerging as the most prevalent7. Another study indicated that the incidence of caries in teeth adjacent to implants in molar sites ranged from 7.4 to 40%, with variability depending on the distance between the tooth and the implant14. Furthermore, their results suggested that the presence of a previous restoration on the neighboring tooth significantly elevated the risk of secondary caries, with an odds ratio of 2.25 at a 95% confidence level.
Of particular interest was the significant correlation (χ2 = 21.73, p= 0.01) we identified between the type of complication in the adjacent tooth (study group) and the status of the contralateral tooth (control group). Specifically, within the primary caries complication, the majority of control teeth were classified as intact (68.1%). This finding is in line with the retrospective study conducted by Duqum et al., which highlighted a significantly higher incidence of restorative retreatment in teeth adjacent to implant restorations compared to contralateral controls6.
Recent systematic reviews have highlighted that loss of proximal contact between implants and adjacent teeth occurs in a considerable percentage of cases, ranging from 34 to 66%15–17. This phenomenon may be attributed to the anterior component of occlusal force causes tooth movement while the implant functions similarly to an ankylosed tooth. Consequently, open proximal contacts may develop, leading to food impaction and potentially increasing the risk of caries and periodontal disease. In our current study, while 41.3% of adjacent teeth experienced primary caries, most control teeth remained intact, as the arch integrity on the contralateral side was undisturbed. Additionally, the presence of a restoration in the implant adjacent tooth often leads to a gap between the tooth and the restoration, rendering it more susceptible to secondary caries due to food impaction14. This could explain the high incidence of secondary caries (53.3%) observed among the adjacent teeth. To prevent the opening of proximal contact points between implant restorations and teeth, one potential solution could involve the use of an occlusal splint at night18.
An interesting finding was the significantly high incidence of secondary caries (53.3%) in the adjacent teeth, while 42.63% of the control teeth were either reconstructed (21.3%) or crowned (21.3%). Although no statistical significance was found between any of the four complication groups and the DMF index, 50.6% of the adjacent teeth with secondary caries were in the high DMF group. Hence, a notable proportion of the contralateral teeth were not intact.
The Cox regression analysis revealed that increasing age was associated with a reduced risk of developing secondary caries, suggesting that older individuals are less susceptible to this complication. This finding aligns with the retrospective study by Tagger-Green et al., which reported a higher prevalence of younger patients in the primary caries group. Additionally, our analysis showed that implants placed in the premolar region were associated with a significantly higher risk of secondary caries compared to those placed in the molar region. In contrast, Tagger-Green et al. found no statistically significant difference based on implant location7.
The subsequent specific investigation revealed that tooth crack/fracture complications were associated with 83.3% of control teeth classified as normal. These fractures encompass vertical root fractures (VRFs), which originate from the root at any level, and cracked teeth, associated with complete or incomplete fractures originating from the crown and extending subgingivally19,20. Recent reports from case series and systematic reviews suggest a possible association between the presence of an implant and the development of VRFs in adjacent endodontically treated teeth, termed “implant-associated cracked teeth”8,19. Furthermore, it was shown that implant placement was also associated with higher odds of having multiple cracks in non-endodontically adjacent teeth21. The postulated mechanism is that with implant-supported rehabilitations, occlusal loads are intentionally decreased to reduce the risk of implant occlusal overload, resulting in increased occlusal load on adjacent natural teeth.
Mobile teeth in the study group were associated with 66.7% of extracted contralateral teeth. Mobility is significantly higher among patients with severe periodontal disease. While no statistical significance was observed in the current study between the periodontal status and any of the complications, it is notable that 66% of the mobile teeth were classified as severe disease. However, due to the small number of mobile teeth, statistical significance cannot be drawn. Excessive masticatory force on a compromised periodontium can lead to tooth hypermobility. This may be exacerbated by the design of crowns on implant-supported restorations, which often have smaller occlusal tables to reduce occlusal load on the implant. As a result, adjacent teeth experience increased load, potentially contributing to hypermobility in teeth with reduced periodontal support22. In cases of severe periodontal diseases, bone loss often necessitates more extensive bone augmentations and open sinus lifts before implant placement. This finding aligns with our observation that the occurrence of open sinus lift procedures was significantly more frequent in implants associated with tooth mobility (66.7%) compared to those with other complications (p = 0.003).
Additionally, a higher prevalence of Diabetes Mellitus (DM) was found among patients with tooth mobility (66.7%) compared to those with other complications (p= 0.041). DM plays a crucial role in the pathogenesis of periodontitis. Evidence-based literature has depicted an increased incidence and severity of periodontitis in subjects with DM. The mechanism is still not entirely clear, but studies have shown that gingival tissue in periodontitis subjects with DM exhibits an upregulation in the expression of tissue inhibitors of metalloproteinase (TIMP)−3and TIMP-4. This increased expression of TIMP correlates with the severity of periodontal disease activity. The upregulation of TIMP expression is considered a compensatory response to the ongoing process of periodontal destruction23.
The time elapsed from implant surgery to restoration placement showed statistical significance across the complication groups (p= 0.006). Notably, this interval was longer in the tooth mobility group and shorter in the tooth crack/fracture group, with mean durations of 9.33 ± 8.38 months and 3.33 ± 1.75 months, respectively. Given that 66% of the mobile teeth were classified as severe disease, it’s common for severe periodontal patients to require augmentation procedures during implant placement, resulting in longer healing time before restoration placement. In contrast, for non-periodontal patients, the typical healing time ranges between 3 and 4 months24.
Regarding the number of implants per patient, a higher number was found in the tooth crack/fracture and tooth mobility groups (5.17 ± 2.04 and 5.33 ± 3.51, respectively) compared to the other two complication groups (p= 0.043). The presence of many implants in a patient’s mouth may increase the risk of tooth mobility or tooth crack/fracture. This is because implants lack gingival fibers and periodontal ligament (PDL) fibers, leaving the surrounding teeth exposed to higher occlusal loads8.
This study benefits from its extended follow-up period and within-patient comparisons of implant-adjacent natural teeth versus contralateral teeth, which enhance the validity of the findings. Additionally, all radiographic and clinical records were assessed by a single examiner (M.K.), eliminating the need for calibration between multiple examiners. Furthermore, the study was conducted at a single public dental clinic from August 2010 to August 2020, ensuring consistency in implant procedures, all of which were performed by either a periodontist or an oral surgeon using a single implant system.
However, the study’s retrospective design is a primary limitation, leading to non-standardized clinical procedures and reliance on subjective documentation in patient records. Moreover, the study population consisted of patients who were compliant with follow-up and maintenance visits. This may introduce selection bias and limit the generalizability of the findings, as individuals attending regular follow-up appointments often exhibit better oral hygiene than those who do not.
Conclusions
Although using implants as replacements for missing teeth is a viable long-term treatment, this study revealed a significant correlation between posterior single implants and the occurrence of complications in adjacent teeth. Notably, the majority of contralateral teeth remained intact. Most of these complications were attributed to either primary (41.3%) or secondary (53.3%) caries. The clinical implications of our findings have the potential to influence treatment planning for patients at high risk for caries. Meticulous monitoring of implant patients is essential to evaluate the condition of adjacent teeth and manage potential complications. Additionally, placing two implants at molar sites, when possible, is recommended to minimize spaces for food impaction and lower the risk of secondary caries. Furthermore, the use of an occlusal splint is advised to prevent the opening of proximal contacts.
Future research with a larger sample size and extended follow-up period would offer more comprehensive insights into the specific factors contributing to these complications. In addition, further studies are needed to evaluate the effect of occlusal splints to prevent the opening of proximal contacts.
Author contributions
N.F.: Design; data collection; analysis and article writing. N.T.G.: Data analysis; revision and approval. M.K.: Data collection and analysis. S.L.: Concept; data analysis; statistics and article writing.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Data availability
The datasets used and/or analyzed during the current study can be obtained from the corresponding author on reasonable request.
Declarations
Competing interests
The authors declare no competing interests.
Institutional review board statement
Ethical approval for the study was obtained from the Helsinki Committee at Meir Medical Center (Ethics Committee #COM1-0087-20). Meir Medical Center is part of the national ‘Clalit’ network of clinics in Israel, which serves all clinics within the Clalit Fund. Both Dr. Fridenberg and Dr. Tagger-Green are affiliated with a clinic within this network.
Informed consent
Statement: Informed consent was obtained from all subjects.
Conflict of interest
The authors declare no conflict of interest.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Naama Fridenberg and Nirit Tagger-Green contributed equally.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analyzed during the current study can be obtained from the corresponding author on reasonable request.