Outcome of Single Dental Implants Over 38–40 Years: A Long‐Term Follow‐Up Study

ABSTRACT

Introduction

This is a comprehensive, long‐term follow‐up study of single‐implant treatments. At the Brånemark Clinic in Gothenburg, Sweden, during the period of 1982–1985, 16 patients received single‐tooth implants.

Objective

This study evaluates the survival rate of the implants after nearly four decades, focusing on the biological and technical complications.

Methods

Of the original 16 patients with a total of 23 implants, 13 patients with 18 implants were available for the follow‐up and were included in the study. Clinical and radiographic examinations were performed on these patients.

Results

The cumulative survival rates were 95.6% for the implants and 60.9% for the implant‐supported crowns after 38–40 years in function. The marginal bone level changes were 0.9 ± 1.0 mm (range, −0.5─3.0 mm) over the follow‐up period.

The frequency of biological complications was low; although mucositis was common, no cases of peri‐implantitis were observed. The mean plaque index was 16.9% ± 11.6% (range, 1%─34%) and the mean probing depth around the implants was 3.8 ± 2.2 mm (range, 0.0─7.0 mm). Few technical complications were observed, although many of the original implant‐supported crowns had been replaced for esthetic reasons.

Conclusion

The findings emphasize the importance of long‐term follow‐up in implant dentistry, particularly for younger patients, to improve understanding of potential complications and the longevity of treatment outcomes. Overall, single‐tooth implants have a favorable long‐term prognosis, though crown replacement may eventually be necessary.

1. Introduction

Replacing a missing tooth with an implant is today considered a standard treatment option for single‐tooth gaps. Numerous clinical studies have demonstrated that single‐implant treatment is predictable, with high success rates even after long‐term follow‐up [1, 2].

From the mid‐1960s, dental implants were initially used to support prostheses in fully edentulous patients, and subsequently, also in partially edentulous patients [3, 4, 5]. Almost two decades later, single implants were introduced as a treatment option for patients with single‐tooth gaps [6]. However, single implant treatment posed challenges related to esthetic and mechanical problems, such as rotation of the abutment screw, which needed to be addressed. The prosthetic components of the implant, that is, the abutment and crown, have undergone several stages of development, focusing on both the design and improvements to the materials used [7, 8].

Currently, many patients worldwide receive treatment with single implants. Common causes of single‐tooth gaps include trauma and aplasia, indicating that many of these patients are young. While several studies on single implants have reported 5–10 years of follow‐up, it is crucial to acquire knowledge regarding the complications that may arise over a much longer period. This is particularly relevant for young patients, as they are expected to retain their implants far into the future.

Early on, Per‐Ingvar Brånemark and colleagues recognized the importance of documenting and clinically following up on the initial patients who were treated with implants, to confirm the efficacy of the treatment. Therefore, at the Brånemark Clinic in Gothenburg, a 3‐year prospective study was conducted on the first 16 patients in the world who received treatment with Brånemark single implants [9]. Now, close to 40 years later, almost all of the patients have been re‐evaluated, providing us with long‐term outcome data on these treatments.

The aim of this study was to follow up and report on the dental implant survival rate and frequency of complications for the initial patients who underwent single‐tooth implant treatment 38–40 years ago.

2. Materials and Methods

2.1. Patient Cohort

The present study covers a group of patients who were consecutively treated with implant‐supported single crowns in the maxillae or mandibulae at one clinic (The Brånemark Clinic, Public Dental Health Service, Gothenburg, Sweden). This group of patients has been described in an earlier publication [9]. In brief, the study examined 16 patients (8 females, 8 males) aged between 14 and 48 years, who received single‐tooth implants in the permanent dentition. In total, 23 turned‐surfaced Brånemark System implants (Nobel Biocare AB, Gothenburg, Sweden) were placed, 5 of which had a conical design. The study included patients with partial anodontia, dental trauma, and tooth loss due to periapical or periodontal lesions. The implants were placed between December 1982 and November 1985, with healing abutments connected between June 1983 and May 1986. Different suprastructural designs were employed, including hexagonal interfaces and conical abutment cylinders with telescopic superstructures, with the goal of enhancing stability and esthetics.

In the present study, the same patients were invited to the clinic for a follow‐up visit schedule, excluding those who were deceased. Patients were included if they agreed to participate in the study. The follow‐up examinations were carried out in the same clinic by two prosthodontists. The data recorded during the follow‐up visits included clinical evaluations for technical and biologic complications, radiographic evaluation, intraoral scanning, and clinical photography.

All data collection procedures were conducted in accordance with the 2013 amendment of the Helsinki Declaration of 1964 for biomedical research involving human subjects. This study was approved by the Ethics Review Authority in Sweden (Dnr. 2023‐00888‐01). Informed consent was obtained from each participant in the study. This study was carried out in accordance with the STROBE statement guidelines for observational studies.

The main objective of this study was to assess implant survival, while the secondary objective was to evaluate long‐term implant safety and performance by assessing the frequencies of biological and technical complications, as well as the marginal bone levels (MBLs) and changes in these levels.

2.2. Radiographic Analyses

Baseline x‐radiographs were taken at the time of prosthetic loading and paired radiographs were acquired at the follow‐up visit at 38–40 years after surgery. All of the MBL measurements were conducted by two experienced prosthodontists using the Planmeca Romexis 3D imaging software (Planmeca Oy, Helsinki, Finland). These measurements were defined as the distance from the reference point (implant platform) to the most‐apical level of the bone. The MBLs were recorded on both the mesial and distal sides, and the MBLs are presented as the average values, calculated as (mesial + distal)/2. Negative MBL values indicate bone levels below the reference point, while positive values indicate bone levels above the reference point. Changes in the marginal bone levels (MBLC) were calculated using paired radiographs, with negative values indicating bone loss.

2.3. Clinical Examinations

The clinical examination included data collection for both technical and biological parameters. The stability of the implant‐supported single crown, fractures or chipping of the porcelain layer were noted. Four‐point probing depth measurement around the implant crown was performed, and the biofilm was measured using a disclosing agent. The plaque index according to Quigley and Hein was determined through plaque staining [10]. The presence or absence of plaque was recorded on four surfaces on all teeth and implants: mesial, buccal, distal, and lingual. The plaque index was calculated by summing the measurements and then dividing by the number of sites measured. The value indicates the percentage of tooth surfaces that exhibited plaque.

Biological complications were defined as follows. Peri‐implant mucositis was identified by bleeding and/or suppuration on gentle probing, as determined by the sulcus bleeding index, without any bone loss beyond the initial remodeling. Peri‐implantitis was characterized by spontaneous bleeding and/or suppuration along with probing depths of ≥ 6 mm and marginal bone loss of ≥ 0.5 mm beyond the initial remodeling (in cases with matching radiographs) or an MBL of ≥ 3 mm apical to the implant platform [11].

2.4. Statistical Analysis

A descriptive statistical analysis was conducted to calculate means, standard deviations, and ranges to summarize the collected data. The implant served as the primary unit of analysis, while gender, cause of edentulism, and the number of implants per patient were analyzed at the patient level. The Cumulative Survival Rate (CSR) at the implant level was determined using a Kaplan–Meier Survival Analysis, with withdrawn data considered as censored. All statistical analyses were performed using the IBM SPSS Statistics software ver. 29.0.2.0 (20) (IBM, Armonk, NY, USA).

3. Results

3.1. Baseline Characteristics

All of the 16 patients treated and included in the original study were tracked and examined, except for three patients. One patient with two implants had already been excluded in the 3‐years FUP due to one implant failure 30 months after surgery and the second implant was recovered. Of the remaining 15 patients, one was deceased, and one was excluded because the implants were connected to a full‐mouth implant‐supported prosthesis (Figure 1). The 13 included patients with 18 implants, except one, were examined by two experienced prosthodontists. One female patient was not able to come to the clinic and the clinical examination was carried out by the patient's general dentist. The main evaluated characteristics of the 13 included patients (54% women) provided with 18 implants are shown in Table 1. The mean age at surgery was 23.0 ± 5.35 years (range, 14–34 years) and 61.9 ± 5.51 years (range, 53–73 years) at the follow‐up visit (mean follow‐up time: 38.9 ± 0.8 years; range, 37.9–40.5 years). The causes of edentulism in the patients included in the study were trauma (54%) and aplasia (46%). Out of 18 implants, 16 (89%) were placed in the maxilla, and most of the implants were placed to restore the maxillary incisors (72%). All of the implants were placed following a two‐stage surgery protocol with delayed loading, and no implant received bone grafts prior to implant placement. The second surgery was performed 7.0 ± 2.1 months (range, 5.0–11.2 months) after implant placement, and loading occurred 3.0 ± 2.4 months (range, 0.0–9.7 months) after the second surgery or 10.1 ± 3.1 months (range, 5.2–15.8 months) after the first surgery.

FIGURE 1.

Flow chart of the included patients.

TABLE 1.

Main patient and implant characteristics at baseline (implant surgery) and at the follow‐up (FUP) visit.

Patients	Gender	Age at surgery	Age at FUP	FUP (years)	Cause of edentulism	Number of implants	Implant design	Implant position (FDI notation)	ASA score at FUP	Smoking habit at FUP	Allergies at FUP
1	Male	33	71	38	Trauma	1	Standard	11	2	No	No
2	Male	21	62	40	Aplasia	1	Standard	22	2	Yes	Yes
3	Female	34	73	40	Trauma	1	Standard	21	2	Yes	No
4	Male	29	67	38	Trauma	1	Standard	21	1	No	No
5	Female	20	59	39	Trauma	2	Standard	11, 21	2	No	Yes
6	Female	17	56	39	Aplasia	2	Standard	34, 45	1	No	No
7	Female	20	58	39	Aplasia	1	Conical	23	1	No	Yes
8	Male	26	66	40	Aplasia	2	Standard	13, 23	2	Yes	No
9	Female	28	67	39	Trauma	1	Conical	21	1	No	Yes
10	Male	23	62	38	Aplasia	2	Standard	12, 22	2	No	No
11	Male	19	58	39	Aplasia	2	Conical	12, 22	1	No	Yes
12	Female	14	53	39	Trauma	1	Standard	11	2	No	No
13	Female	24	63	40	Trauma	1	Standard	21	1	No	Yes

Abbreviations: ASA: American Society of Anesthesiologists Classification; FDI: Federal Dentaire Internationale.

3.2. Outcome Measures

At the follow‐up examination 38–40 years after surgery, all 18 implants from the 3‐year follow‐up were still in place, yielding a 95.6% CSR (Table 2). Table 3 shows the different MBLs at baseline and at the follow‐up examination. At the time of prosthetic loading (Baseline), the mean MBL was −1.7 ± 0.9 mm (range, −3.3–0.0 mm), and at 38–40 years of follow‐up it was −0.8 ± 1.5 mm (range, −2.6–3.0 mm). Based on paired measurements, the MBLCs were 0.9 ± 1.0 mm (range, −0.5–3.0 mm). Notably, most of the implants showed a bone gain over the follow‐up period.

TABLE 2.

Lifetime table and cumulative survival rates (CSR) of the original implants and crowns in the followed‐up patients.

Follow‐up period	Implants				Crowns
	Implants	Withdrawn	Fail	CSR	Crown	Withdrawn	Fail	CSR (%)
Implant surgery	23			100
Prosthetic delivery	23			100	23			100
3 years	21	1	1	95.6	19	1	3	86.9
3–39 years	18	3		95.6	10	3	6	60.9

TABLE 3.

Marginal bone levels (MBL) and marginal bone level changes (MBLC) (in mm) at baseline and at follow‐up (FUP). Positive values indicate bone levels above the reference point or bone gain (MBLC).

Patient	Implant position	Baseline			FUP			MBLC
		MBL			MBL
		Mesial	Distal	Mean	Mesial	Distal	Mean	Means
1	11	−1.6	−1.9	−1.8	−2.2	−2.2	−2.2	−0.5
2	22	−1.6	−1.7	−1.7	−1.5	−1.8	−1.7	0.0
3	21	0.0	0.0	0.0	2.5	2.6	2.6	2.6
4	21	−1.6	−1.6	−1.6	−1.6	−1.6	−1.6	0.0
5	11	−1.6	0.0	−0.8	−0.8	−1.3	−1.1	−0.3
	21	−2.0	−1.6	−1.8	−1.5	−1.4	−1.5	0.4
6	34	−1.8	−1.1	−1.5	−1.7	−1.4	−1.6	−0.1
	45	−1.7	−2.0	−1.9	−1.7	−1.5	−1.6	0.3
7	23	−1.5	−2.3	−1.9	0.7	0.0	0.4	2.2
8	13	−1.6	−1.5	−1.6	0.0	0.0	0.0	1.6
	23	−1.5	−1.5	−1.5	−0.5	−0.5	−0.5	1.0
9	21	−5.5	0.0	−2.8	−2.2	−2.0	−2.1	0.7
10	12	−1.9	−1.8	−1.9	−1.7	−1.4	−1.6	0.3
	22	−2.8	−3.2	−3.0	−2.6	−2.6	−2.6	0.4
11	12	−3.4	−2.1	−2.8	−1.3	−1.1	−1.2	1.6
	22	−3.2	−3.4	−3.3	−1.6	−1.5	−1.6	1.8
12	11	−1.6	−1.7	−1.7	0.6	−1.5	−0.5	1.2
13	21	0.0	0.0	0.0	2.8	3.1	3.0	3.0

Note: Bold represents the average at the bone level for the 4 surfaces of each individual implant.

Plaque accumulations were observed on all teeth and implants during the follow‐up visit. The mean plaque index was 16.9% ± 11.6% (range, 1%–34%). The mean probing depth around the implants was 3.8 ± 2.2 mm (range, 0.0–7.0 mm). Noteworthy, a probing depth of up to 11 mm was observed at isolated sites. Bleeding on probing occurred in 12 implants (67%) and suppuration was observed on 2 implants (11%). Mucositis was common, although no peri‐implantitis or fistulas were observed. The data on the biological measurements for each implant are shown in Table 4.

TABLE 4.

Examination data at the follow‐up visit for the individual patients.

Patient	Implant position	PI (%)	Probing depth (mm)				Mean	Bleeding	Suppuration
			Distal	Buccal	Mesial	Lingual
1	11	23	7	6	9	5	6.8	Yes	No
2	22	1	4	4	5	5	4.5	Yes	No
3	21	31	4	4	5	5	4.5	Yes	No
4	21	23	5	4	5	4	4.5	No	No
5	11	7	8	5	8	5	6.5	No	No
	21	7	11	4	7	6	7.0	Yes	No
6	34	2	6	0	5	6	4.3	No	No
	45	2	4	0	4	6	3.5	No	No
7	23	10	5	0	6	4	3.8	Yes	No
8	13	34	0	0	0	4	1.0	No	No
	23	34	0	4	5	5	3.5	Yes	No
9	21	23	4	0	6	6	4.0	Yes	Yes
10	12	13	5	0	6	0	2.8	No	No
	22	13	4	0	7	0	2.8	Yes	Yes
11	12	23	0	0	0	0	0.0	Yes	No
	22	23	0	0	0	0	0.0	Yes	No
12	11	28	0	0	0	8	2.0	Yes	No
13	21	na	7	7	7	7	7.0	Yes	No

Note: Bold represents the average at the bone level for the 4 surfaces of each individual implant.

Abbreviations: na: data not available; PI: plaque index.

The implant‐supported crowns were originally designed using prefabricated titanium abutments veneered with composite resin or metal‐ceramic crowns that were cemented outside the mouth and screw‐retained to the implant. One patient received a screw‐retained full‐ceramic crown which was still in place at the 38–40‐year follow‐up visit. The CSRs after 3 years of functionality were 95.6% and 86.9% for the implants and crowns, respectively (Table 2).

None of the composite resin crowns were still in function at the 38–40‐year follow‐up visit. Six patients with seven implant‐supported crowns had not replaced the original crown, resulting in a 60.9% CSR at the 38–40‐year follow‐up. Five patients replaced seven composite resin crowns for esthetic reasons 6–11 years after delivery of the first crown. For two patients with three crowns, the reason and time for replacement was unclear. One patient with two crowns was undergoing replacement of one of the crowns by the general dentist and had at the time of the 38–40‐year follow‐up examination a temporary crown in place.

Out of 18 crowns, 6 were cement‐retained and the remaining 12 used screw‐retention. All but one of the cement‐retained crowns were placed on Brånemark CeraOne System abutments, while one was cemented on a titanium abutment. All the screw‐retained crowns were placed on titanium abutments.

At the follow‐up visit one crown was found to be loose. This crown was unscrewed for inspection; all the components were undamaged, and the crown was re‐screwed. Another crown had a minor fracture, and one was classified as having porcelain chipping. The temporary crown, which was under replacement, had a fracture. The other crowns had no signs of damage or technical complications.

4. Discussion

This study evaluating the initial cohort of patients treated with single‐tooth implants reveals excellent long‐term functionality over nearly four decades. Although only a small group of patients was included in the study, all the patients from the original study, except for two who were deceased, were examined in the present study.

At the 38–40‐year follow‐up, all of the 18 implants that were examined were in function and the CSR for the implants was 95.6%. These favorable results for the implants are consistent with the results from other studies with similar designs, which reported CSRs of 96.1% for implants after 14–20 years [12], 91.5% after 16–22 years [13], and 96.8% after 18 years [14]. However, the follow‐up times in these studies were significantly shorter, but they included a larger number of participants.

The implant‐supported crowns in the present study had a CSR of only 60.9%, which is considerably lower than the CSR of the implants. In a systematic review, the survival rate for single‐tooth implant crown restorations was reported to be as high as 89.5% following a 10‐year evaluation [1, 2]. In addition, the CSR for the crowns in the present study is significantly lower than those reported by Winistky et al. and Bergenblock et al., that is, CSRs for crowns of 80.4% and 83.8%, respectively [12, 14]. Similarly, Dierens et al. reported a prosthetic survival rate of 73% after 16–22 years, (but with an overall complication rate of 57%), with esthetic issues being the main reason for crown replacement rather than technical problems [15]. Thus, the results of the present study support earlier findings that single‐tooth implants have an excellent long‐term prognosis, even though the probability of needing to replace the implant crown increases over time. One possible explanation for the high number of crown replacements seen in the present study is that the initial crowns in the original cohort were specifically designed to evaluate the crown and abutment design [6]. Consequently, several of these crowns were initially made of resin and were later replaced due to poor esthetics, which was the most‐common reason for making a new crown.

In another systematic review of single implant crowns, common technical complications after 5 years included screw loosening (8.8%), loss of retention (4.1%), and fracture of the veneer (3.5%) [16]. Similarly, in the present study, there were few technical complications observed with the current implant supported crowns and only one crown had a loose screw.

The design of all the abutments involved prefabricated cylinders, whereby the crown was cemented extra‐orally, and these two components were then screwed onto the implant [6]. Interestingly, despite advancements in the design and retention of both abutments and crowns over the years, the prosthetic solutions for single‐tooth implants used today have reverted back to a similar procedure used in the initial treatments [17].

In the present study, the probing depth ranged from 0 to 11 mm, and 22% of the implants had a mean probing depth > 6 mm (Table 4). However, it was not possible to compare any changes in probing depth over time due to the lack of baseline data for these patients. Even though mucositis was common, and several implants had ≥ 6 mm probing depth, no implants were diagnosed with peri‐implantitis, as there were no bone levels ≥ 3 mm apical of the most‐coronal portion of the implant [11]. However, deep probing depth is not necessarily an indication of disease or bone loss but instead is a result of deep placement of the implant or could be a long‐term effect of facial growth [18, 19].

Not only were all of the examined implants in function after 38–40 years, but they also exhibited remarkably stable bone levels over the follow‐up period. The MBLs showed only very small changes over this long period of time, which is in accordance with the results of other follow‐up studies on single‐tooth implants [18, 20]. Interestingly, there was even bone gain in most of the implants, and the bone level was also located above the reference point on these implants (Table 3 and Figure 2). However, while the radiological observations may indicate a favorable bone response, the observed coronal bone growth does not necessarily reflect direct bone‐to‐abutment contact.

FIGURE 2.

Radiographs collected at baseline with an acrylic crown (A) in 1984 and at the 40‐year follow‐up (B) with a cemented ceramic crown placed on a Nobel Brånemark CeraOne abutment. The arrows indicate the marginal bone levels (MBL) at baseline (A) and at the follow‐up visit (B), and show significant bone gain during the follow‐up period.

From this study, despite the limited number of participants, it is evident that single‐tooth implants have a favorable long‐term prognosis. However, it is crucial to identify potential causes of failure and factors that contribute to successful treatments. In a review conducted by Chrcanovic et al., factors contributing to dental implant failures were investigated. The review examined more than 60 possible factors influencing implant survival, illustrating the challenges linked to identifying the reasons for implant losses [21]. Nevertheless, certain situations that correlate with higher implant failures were identified, including both patient‐related and treatment‐related factors. Still, a higher number of implants placed in a patient is associated with an increased risk of solitary implant failure, whereas single‐implant prostheses demonstrate better outcomes compared to multiple‐implant‐supported fixed prostheses in edentulous patients.

In the present study, in addition to patient‐related factors, surgical technique may have been an important factor for implant survival. All of the implants were placed using a two‐stage surgery protocol with delayed loading, and none received bone grafts. The average healing time between the two surgeries was 7 months, with implants being loaded on average 10 months after fixture installation. These are relatively long treatment times, so current praxis of shortened treatment times may come at the cost of more‐frequent implant loss.

Other important factors for implant survival may include the design of the implant (e.g., conical fixtures) and modification of the implant surface. Today, most commercial implants have a moderately rough implant surface to ensure faster and more‐efficient osseointegration. In a 15‐year follow‐up study, moderately rough anodized surfaces supporting single‐tooth restorations demonstrated favorable long‐term outcomes [22]. Nonetheless, all of the implants in the present study had machined surfaces and still showed excellent long‐term results.

It was a challenge to locate all of the patients included in the present study, since they were young at the time for treatment and several of the participants had moved to cities far away from the present clinic. The participants were not only willing to participate and travel long distances for the study but also took pride in being among the earliest single‐tooth implant patients. It has been suggested that patients that are included in small research groups show higher follow‐up compliance compared to other patients [2].

As mentioned in the Introduction (Section 1), single‐tooth implant treatment is currently very common, and millions of patients have undergone this treatment to replace single tooth gaps. In many cases, these patients are young and are expected to retain their implant for many years. To enhance our understanding of treatment outcomes and potential complications, it is crucial to conduct long‐term follow‐up studies such as the present one.

Despite the limited number of participants and the absence of a control group, this study offers valuable insights into the longevity of single‐tooth implants. While the original crown restorations may require eventual replacement, stable bone levels suggest a promising prognosis for the existing single implants, even after 38–40 years of use.

5. Conclusion

Single‐tooth implants show a high survival rate, with good long‐term prognosis for the implant in this small group of patients. However, the probability of having to replace the implant‐supported crown increases with time.

Author Contributions

Sargon Barkarmo contributed to conception, design, data acquisition, drafted, and critically revised the manuscript. Jan Kowar contributed to conception, design, data acquisition, drafted, and critically revised the manuscript. Both authors gave final approval and agree to be accountable for all aspects of the work.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.