Peri-implantitis: A Classification Update

The cases of peri-implantitis are soaring rapidly in the current scenario. It is very important to have adequate knowledge about the etiology, pathogenesis, clinical features, radiological features, and treatment of peri-implantitis. In this context, the classification of the disease is of utmost importance for planning and execution of the treatment. Various classifications have been proposed over the years and with each classification, more information is being added and there is a lack of universal acceptance of a single classification. Clinical errors may be anticipated due to miscommunication and misguidance. Thus, it is important to sensitize the clinicians about different classification systems. This review attempts to compile and critically analyze existing classification systems of peri-implant diseases.


INTRODUCTION
Peri-implantitis is defined as a plaque-associated pathologic condition occurring in the tissue around dental implants, characterized by inflammation in the peri-implant mucosa and subsequent progressive loss of supporting bone. 1 It is the most frequent complication of dental implants and occurs from 1% to 47% at implant level, 2-9 based on various study designs and population sizes. [10][11][12] It presents a public health issue. [13][14][15] Peri-implantitis is associated with a history of chronic periodontitis, poor plaque control skills, and lack of regular maintenance care after implant therapy. 16 The risk factors for peri-implantitis are patient-related, prosthesis-related, clinician-related and implant design, and site-related. 17 Further investigations are necessary for the role of occlusal overload 18 , genetic factors 19 , rheumatoid arthritis with concomitant connective tissue disease 20 , increased time of loading 21 , and alcohol consumption. 22 Peri-implantitis shows signs of inflammation, bleeding on probing and/or suppuration, increased probing depths and/or recession of the mucosal margin and radiographic bone loss compared to previous examinations. 23 Diagnosis of peri-implantitis: 24 • Evidence of visual inflammatory changes in the peri-implant soft tissues combined with bleeding on probing and/or suppuration.
• Increasing probing pocket depths as compared to measurements obtained at the placement of the supra-structure.
• Progressive bone loss in relation to the radiographic bone level assessment at 1 year following the delivery of the implant-supported prosthetics reconstruction.
• In the absence of initial radiographs and probing depths, radiographic evidence of bone level ≥3 mm and/or probing depths ≥6 mm in conjunction with profuse bleeding represents peri-implantitis.
Historically, the periapical implant lesion has been described into 2 types as retrograde peri-implantitis by Sussman in 1998. 28 Type 1: Occurs when the insertion of the implant results in devitalization of the adjacent tooth either by direct contact or overheating of the surrounding bone

Vanden Bogaerde (2004)
This classification considers peri-implant bone defects in the progression of the regenerative process: 31 (1) Closed defects: It is characterized by the maintenance of intact surrounding bone walls.
(2) Open defects: It is the one that lack one or more bone walls.

Lang NP et al. (2004)
The classification has included clinical signs, radiographic features and treatment to describe various stages of peri-implantitis. 32 Pocket depth (PD) <3 mm, no plaque or bleeding: No therapy Stage A PD <3 mm, plaque and/or bleeding on probing: Mechanical cleansing and polishing, oral hygienic maintenance instructions.
Stage B PD 4-5 mm, radiologically no bone loss: Mechanical cleansing and polishing, oral hygienic maintenance instructions plus local anti-infective therapy (e.g Chlorhexidine).
Stage C PD >5 mm, radiologically bone loss <2 mm: Mechanical cleansing and polishing, microbiological test, local and systemic antibiotic therapy.

Schwarz et al. (2008)
The configuration of the bony defect as: 33 Class

Renvert & Claffey (2008)
Classification of peri-implant diseases and advised treatment regimen was given by Renvert and Claffey 34 as shown in Table1.
(Bleeding and/or suppuration noted on two or more aspects of the implant. Bone loss measured on radiographs from time of definitive prosthesis loading to current radiograph. If not available, the earliest available radiograph following loading to be used.)

Kadkhodazadeh and Amid (2013)
The classification system for peri-implant disease in association with natural teeth was termed periimplant soft tissue (PIST). 38 It gave a better view to the clinicians about the etiology of the disease. The classification is shown in Table 3.  Type 5: Slit-like; Bone pocket is narrow and deep, with a width of ≤0.5 mm and a depth equalling twice the width or more, or an undercut >0.5 mm and proportion of undercut <50%.

Kazemi (2015)
Kazemi in 2015 classified peri-implantitis into four classes: 40 Peri-Implantitis Type 1: Inflammation of the gum tissue with no loss of bone or gum tissue. The gum tissue may appear red, is painful to touch, and may bleed during brushing or flossing.
Peri-Implantitis Type 2: Inflammation, along with loss of bone on one side of the implant, with normal gum tissue level. Depending on the amount of the bone loss, it can be further categorized as:

Decker et al. (2015)
They grouped peri-implantitis according to the prognosis 42 as shown in table 4. The prognosis was done by the recommended clinical intervention and probability of achieving implant stability.

Shah et al. (2016)
Shah et al. classified retrograde implantitis into 3 classes. 43 It is defined as a clinically symptomatic periapical lesion that develops within the first few after implant insertion while the coronal portion of the implant sustains a normal bone to the implant interface.

Ramanauskaite and Juodzbalys 2016
The classification was done on the basis of

Sarmiento et al. (2016)
It was proposed by Sarmiento, Norton, and Fiorellini in 2016. 25 It was based on the etiology of periimplantitis which is listed as follows:

Canullo et al. (2016)
They proposed a classification based on the etiology associated with distinguishing predictive profiles. 45 The three subtypes are 1, Plaque-induced 2. Prosthetically triggered 3. Surgically

Suzuki, Hsiao and Misch (2017)
They described implant quality scales based on clinical conditions and management as shown in Table 6. 46

Tallarico et al. (2018)
They categorized diagnostic criteria for the estimation of the implant pathologic bone loss around an implant in function as DC1-6. 48 In DC-4, the progression of pathologic bone loss was described as chronic and acute. Chronic

CRITICAL APPRAISAL OF DIFFERENT CLASSIFICATIONS
The first attempt to classify defects in implant bone was done by Spiekerman in 1984, who described the type of bone loss around implant according to the shape of the defect. 26 The classification failed to give a quantitative value to the amount of bone loss. This was followed by the classification given by Jovanovic, which mainly addressed the horizontal bone loss and a combination pattern was addressed.
Implant periapical lesions were classified as inactive and infected by Reiser and Nevins in 1995. 50 The first attempt to classify retrograde peri-implantitis was done by Sussman. 28 In 2006, Diago et al. described retrograde peri-implantitis as acute nonsuppurated, acute suppurated, or chronic according to its evolution. 51 Shah et al. in 2016 gave a simpler classification of retrograde peri-implantitis. 43 Vanden Bogaerde described the bone defects as closed and open. 31 It is the simplest classification but it lacks important information due to its broad approach. In the same year, Lang et al. gave a complete classification by including clinical, radiographic features and also guiding the treatment. 32 It was the first classification that gave definite values for the definition of the stages and was not objective. Peri-implant pocket depth was included along with radiographic features and treatment. It was the first classification that gave a complete narration of the disease involved. But the radiographic bone loss was only differentiated as <2 mm and >2 mm. The severity of all the cases with radiographic bone loss>2 mm was grouped in one class, which cannot be justified.
In 2008, Schwarz et al. classified peri-implant bone loss as intraosseous and supraalveolar. Special consideration was given to dehiscence on the buccal aspect. 33 Renvert and Claffey in their 2012 classification included implant fracture and mobility in their classification. 34 Implant mobility>1mm horizontal movability was given the treatment of explantation. The degree of mobility was not considered. Koldsland et al. in 2010 grouped periimplantitis under two categories. 35 All the cases with radiographic bone loss ≥3mm were placed in one category. This classification also failed to address the severity of peri-implantitis as in Lang's classification. Moreover, the classification was more primitive compared to Lang's classification which was given half a decade earlier. In 2011, Nogueira F et al. described Peri-implant mucosal inflammation (PIMI) along with prognosis, treatment, and supportive implant treatment. 36 But, the classification lacked the important parameter of diagnosis: the peri-implant pocket depth.
It was only in 2012 that Froum and Rosen addressed another important aspect: the severity of radiographic bone loss. 37 Kadkhodazadeh and Amid in 2013 gave a classification system for peri-implant disease in association with natural teeth. 38 Zhang et al. classified the peri-implant defects according to shape in the orthopantamograms. 39 This system did not provide any quantitative and definite value and was more objective. Classifications were also given by Kazemi; Suzuki, Hsiao, and Misch; Ata-Ali et al. and Decker et al. [40][41][42]46 Decker et al. included prognosis and Ramanauskaite and Juodzbalys evaluated periimplantitis based on only radiographic bone level evaluation (mesial and distal). 44 The most detailed classification was given by Passi et al. in which all the important parameters required for the diagnosis of peri-implantitis were addressed. 26 This was the first time that the grade of implant mobility was considered. Sarmento et al. and Canullo et al. in 2016 gave separate classifications based on the etiology of peri-implantitis. 25,45 Tallarico et al. defined terms such as acute, chronic, localized, focalized, and generalized in terms of peri-implantitis. 48 Most of the classifications proposed have different criteria for the definition of peri-implantitis. According to the AAP classification, 47 periimplantitis is described as radiographic evidence of bone level ≥3 mm and/or probing depths ≥6 mm in conjunction with profuse bleeding (in the absence of initial radiographs and probing depths). Thus, any system which has defined periimplantitis with pocket depth less than 6 mm or radiographic evidence of bone loss less than 3 mm cannot be incorporated as periimplantitis in actual sense by the AAP criteria 47 . This necessitates the need for the introduction of a new classification system of peri-implantitis.

SUMMARY
Various classification systems have been introduced to classify peri-implantitis. Mere diagnosis of peri-implantitis is not enough as the cases of periimplantitis is rapidly increasing. It is the duty of the clinician to be aware of the classification systems and incorporate the most appropriate system in their routine classification.