Ⅰ. Introduction

Among the various prosthetic treatment methods for restoring the esthetic and functional aspects of missing teeth in the oral cavity, implant-based treatment has become the most widely used and highly regarded approach.^1,2 Success criteria for dental implantation have been explored in several studies, with Albrektsson et al. introducing the widely accepted criteria for assessing implant success.^3,4,5 The most frequently reported success criterion in clinical studies is the survival rate, which indicates whether the implant remains in the mouth or has been removed. Similar to the quality of health scale used to evaluate natural teeth, implant status can be categorized into success, failure, and different levels of success.^5,6 Implant success is defined as an implant being in a clinically optimal condition within the oral cavity, without necessitating removal. Conversely, implant failure is defined as an implant that has either been removed or requires removal from the oral cavity due to clinical or pathological reasons.^3,4,5

Periodontal indices are frequently employed to assess the condition of dental implants.⁷ Although bone quality and quantity have long been considered crucial factors in determining the clinical success of implants, recent focus has shifted to the health of the peri-implant periodontal tissues.⁸ Unlike the tissues surrounding natural teeth, peri-implant tissues do not directly contact the implant surface; instead, they align parallel to the fixture, exhibiting a denser arrangement of collagen fibers.⁹ This unique structure and arrangement of the peri-implant periodontal ligaments makes the implant fixture more susceptible to bacterial infection and physical instability.⁹

This study aimed to systematically review and organize existing research on the criteria for dental implant success, assess the related success rates, and discuss the most up-to-date standards for defining dental implant success. Based on the widely recognized implant success criteria established by Albrektsson, Buser, and Misch, 50 studies were selected for the examination of implant survival rates. From these, 13 studies were meticulously chosen using objective standards, and survival rates were analyzed according to each researcher’s criteria. Furthermore, this study sought to outline the common elements and distinctions among the criteria proposed by these researchers, with the goal of guiding future implant success assessments.

Ⅱ. Materials and Methods

1. Search strategy

PubMed/Medline, Web of Science, and Scopus were searched for literatures published up to 2024. The search utilized the keywords “implant success,” “success criteria of implant,” “success rates,” “survival rates,” and “dental implant,” either alone or in combination using “OR” and “AND.” Of the 50 reviewed studies, 13 were selected^{10,11,12,13,14,15,16,17,18,19,20,21,22} based on the following criteria:

- Retrospective randomized controlled clinical trials with at least a 1-year of follow-up

- Studies with a minimum of 30 patients

- The success and survival criteria used in these studies were based on those of Albrektsson, Misch, or Buser.

- Studies reported from the year 2000 onward

Many of the reviewed studies did not meet the selection criteria due to one or more of the following reasons: they lacked a minimum follow-up period of 1 year as implant fixture needs to be assessed for at least 1year; were published before the 2000s, as advancements in fixture types and implant surface treatment technologies only occurred after this period; included less than 30 patients; or provided insufficient detail regarding implant survival and success rates and treatment outcomes.

2. Peri-implant health, peri-implant mucositis, and peri-implantitis

Healthy peri-implant tissues are characterized by the absence of bleeding on probing, swelling, or suppuration.^23,24 Bleeding on probing indicates inflammation, and the depth of the peri-implant pocket helps assess the extent to which tissues encase the implant. Pocket depths can vary among patients, with the interproximal sites of implants often appearing shorter than the papillae at the interproximal tooth sites.²⁴ Typically, 3–4 mm of keratinized or non-keratinized mucosa covers the implant.²³

Peri-implant mucositis and peri-implantitis share similar clinical features, such as bleeding on probing, swelling, suppuration, and erythema.^25,26 Although both conditions involve inflammation, mucositis does not lead to bone loss, which is present in peri-implantitis. Peri-implantitis refers to an inflammatory process that occurs in the tissues surrounding a functional implant, causing the loss of the supporting bone.²⁷ Probing depths around implants are generally deeper than those around natural teeth, likely due to inflammation-induced swelling or the lack of resistance in implant tissues, which lack cementum, periodontal ligament, and connective tissue fibers.^23,26

Although implants with stable fixation may exhibit pocket depths between 2 and 6 mm, the lack of a standardized probing pressure and the potential for tissue damage make probing depth a less reliable criterion for assessing implant survival.²⁸ Current evidence does not support probing depth as a critical survival metric for implants.²⁹ Although deep pockets (over 5–6 mm) are associated with anaerobic bacterial presence, probing primarily serves to evaluate tissue consistency and signs of inflammation.^27,30 Although not a definitive criterion for implant survival, probing depth can still be a valuable tool for monitoring implants during follow-up.⁵

3. Marginal bone loss

Many studies have reported that the environment surrounding dental implants is unsuitable for maintaining the periodontal ligament.³ The response often misinterpreted as ligament attachment is typically due to fibrous connective tissue, which frequently results in implant failure.^3,31 Recent research has highlighted that osseointegration between the bone and the implant is a critical determinant of the clinical success or failure of an implant.^3,31 However, osseointegration can only be partially assessed through clinical and radiographic evaluations. As post-implantation state changes may develop gradually and are not immediately visible radiographically, long-term observation is necessary to accurately assess osseointegration.^3,32 The key criteria for evaluation include clinical mobility and bone response, while traditional gingival indices are excluded, as they do not directly correlate with implant success, despite being affected by factors such as implant placement and prosthesis design.³²

The marginal bone in the crestal region is an important marker of implant health. It is often measured from the implant’s crestal level during the initial surgery and monitored using radiographic methods. Bone loss is commonly evaluated using periapical radiographs, with studies showing an annual loss of 0–0.2 mm after the first year.³³ This bone loss may result from bacterial infections, particularly anaerobic bacteria in deep pockets, from stress at the bone-implant interface. Stress-related bone loss can create an environment conducive to bacterial growth, further exacerbating bone degradation.^34,35 Given the osseointegration response surrounding implant placement, the extent of bone loss emerges as a significant factor in assessing implant success. Pathological factors that contribute to bone loss around an implant underscore the importance of monitoring this aspect to evaluate the overall success of the implant. According to the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Conditions, as outlined by Berhlundh et al., implant success can be assessed based on radiographic evidence of bone levels.²³ If pre-surgical radiographic records of bone height are available, success is indicated by the absence of bone loss beyond crestal bone level changes due to initial bone remodeling. In cases where pre-surgical records are unavailable, implant success is defined as bone levels at least 3 mm apical to the most coronal portion of the intraosseous part of the implant.²³

4. Pain

Although pain is a highly subjective experience for patients, it serves as a critical indicator when an implant, acting as a foreign body, invades key anatomical structures, such as the infraorbital nerve in the maxilla or the inferior alveolar nerve in the mandible.³⁶ This makes pain a critical factor in determining implant success. When approximately 500 g of force is applied to an implant fixture, pain may indicate nerve encroachment, inflammation, or mobility, emphasizing the importance of monitoring pain during follow-up.⁵

5. Mobility

Previous research has defined implant stability as the absence of vertical or horizontal movement when subjected to 500 g of force.⁵ This stability, known histologically as “osseointegration“ and clinically as “rigid fixation,” is now commonly referred to as the “lack of mobility.” Although microscopic examination may detect minor movements under 75 micrometers, any clinical detection of movement indicates the presence of connective tissue, suggesting implant failure.³⁷ Therefore, assessing implant mobility remains a key factor in evaluating implant success.

Ⅲ. Results

1. Implant success criteria of Albrektsson et al. (1986)

A common shortcoming in implant studies is neglecting the complexity of introducing a foreign device into the body, with the expectation that it will remain functional throughout the patient’s life.³ Successful implant outcomes depend on several factors, including the biocompatibility of the material, the implant surface characteristics, the health and morphology of the implant bed, precise in surgical technique, an undisturbed healing phase, and the long-term design and loading of the prosthesis.^{31,32,38,39,40}

In contrast to the earlier concepts of “fibro-integration“ and ”fibrous osseointegration” as key factors in implant stability, recent arguments emphasized that osseointegration plays a critical role in implant success.⁴¹ Earlier assertions of ligament formation around implants were deemed unpersuasive.^41,42 This led to the establishment of the following success criteria: the implant remains clinically immobile, radiographs show no peri-implant radiolucency, annual bone loss is under 0.2 mm after the first year, and persistent issues like pain or infection are absent.³

2. Implant success criteria of Buser et al. (1990)

Dental implants provide a predictable solution for tooth replacement in edentulous patients. Titanium implants, initially introduced by Brånemark, are favored for their close bone-implant contact.⁴³ Although Brånemark’s method involves submerging implants to avoid infection, the International Team for Oral Implantology (ITI) developed a successful one-stage approach without submersion, utilizing a rough titanium surface.^4,43,44,45

Based on a systematic study of the prognosis of ITI dental implants, Buser established his implant success criteria.⁴ The success criteria for dental implants include the following key factors: the absence of ongoing subjective complaints such as pain, foreign body sensation, or dysesthesia; no recurrent peri-implant infection with suppuration; the lack of implant mobility; the absence of continuous radiolucency around the implant on radiographs; and the feasibility of successful restoration.⁴ These criteria are essential for determining the long-term success and stability of a dental implant. The measurement of alveolar bone crest levels and their temporal changes is a significant factor in evaluating implant success.³ Ensuring that the implant remains immobile is equally important, as any movement indicates implant failure following the osseointegration concept.⁴⁴

3. Implant success criteria of Misch et al. (2007)

To classify an implant as successful, it should exhibit the absence of pain or discomfort during function, maintain stability without any signs of mobility, show minimal radiographic bone loss (< 2 mm from the initial surgery), and have no history of uncontrolled exudate.⁵ Clinical implant failure is indicated by symptoms such as functional pain, implant mobility, radiographic bone loss exceeding half the implant’s length, persistent exudate, or loss of retention in the mouth.⁵ Implants can exist in states other than optimal health, such as satisfactory survival or compromised survival. Satisfactory survival is characterized by the absence of mobility, pain during function, radiographic bone loss of 2–4 mm, and a history of exudate.⁵ By contrast, compromised survival is marked by the presence of functional sensitivity, bone loss over 4 mm but less than half the implant length, a history of exudate, and a probing depth of 7 mm or more.⁵

These criteria are summarized in Table 1. As outlined in the table, the implant success criteria proposed by the three researchers share common factors as well as differences.

Pain, mobility, and bone loss were deemed important by all three researchers. However, Buser excluded bone loss in his criteria due to the minimal bone loss observed with ITI implants. Hence, these factors should be carefully considered when establishing future guidelines.

Ⅳ. Discussion

Defining implant success poses challenges similar to those encountered in establishing the success criteria for natural teeth as both exist on a spectrum from health to disease. Evaluating peri-implant health, mucositis, and peri-implantitis necessitates the consideration of a wide range of implant designs, surface characteristics, and protocols that can influence outcomes. The fundamental criteria for determining implant health are the absence of pain and implant stability, indicated by the lack of mobility. Crestal bone levels are determined by physiological bone remodeling, influenced by local and systemic factors. Traditional implant success criteria, such as marginal bone levels measured via radiographs, need re-evaluation owing to advancements such as roughened implant surfaces, platform switching, and the development of internal connection type of implant. These innovations have resulted in improved outcomes, raising questions about the reliability of previous benchmarks for peri-implant bone remodeling as indicators of success.

In this study, we analyzed and organized the implant success criteria proposed by three prominent figures in the field: Albrektsson, Buser, and Misch. The implant success criteria of these three researchers are summarized in Table 2. The common criteria include the absence of pain and implant mobility as well as the evaluation of infection and peri-implant radiolucency through radiographic images, which serve as indicators for differentiating peri-implant health, mucositis, and implantitis. Bone loss is a critical factor for establishing these success criteria. For example, the success criteria for implants stipulate that no bone loss should occur beyond crestal remodeling changes when presurgical radiographic data are available. In the absence of these records, success is defined as bone levels that are 3 mm or more apical to the coronal portion of the intra-osseous implant.

Albrektsson’s criteria include the absence of paresthesia and neuropathy, while Buser emphasizes the absence of dysesthesia and foreign body sensation, which indicate potential anatomical structural invasion. This study assumes that implants are placed without invading anatomical structures; therefore, such symptoms were excluded from our criteria. Additionally, Buser’s criteria regarding the possibility of restoration were excluded due to the need for further explanation and research.

Misch et al. highlighted the importance of probing depth in assessing bleeding during probing and monitoring changes. However, owing to the differences between peri-implant tissues and natural periodontal tissues, along with the lack of a clear standard for probing force, we did not include probing depth in our criteria. The potential for probing to cause damage and the insufficient research on its relevance to implant survival also contributed to its exclusion.

Defining implant failure is more straightforward than defining success or survival because it can be attributed to various factors. Pain, paresthesia, vertical mobility, and significant and uncontrolled bone loss generally require implant removal. Table 3 presents more concise indicators for determining the success or failure of dental implants. However, further studies are needed to establish specific clinical criteria.

Ⅴ. Conclusion

In this study, we analyzed and synthesized the implant success criteria proposed by Albrektsson et al., which have been widely used in previous and recent studies. The criteria for implant success included the absence of pain, paresthesia, implant mobility, healthy peri-implant tissues, and stabilization of marginal bone loss after the first year. Although this study involved a systematic review of numerous studies, further research, particularly clinical trials, is required. Additionally, although these criteria have been discussed, more specific guidelines should be developed based on the type of implant and prosthesis used.