A Radiographic Classication for Retrograde Peri-implantitis
The Journal of Contemporary Dental Practice, April 2016;17(4):313-321 313
Background: Retrograde peri-implantitis (RPI) is an inamma-
tory disease that affects the apical part of an osseointegrated
implant, while the coronal portion of the implant sustains a normal
bone-to-implant interface. It is a diagnostic and therapeutic
dilemma for implantologists. There is lack of a standard classica-
tion system and a denite treatment algorithm for the same. This
article aims to introduce a classication system for RPI based on
the radiographic amount of bone loss around an implant apex.
Materials and methods: A search of PubMed database was
conducted with the keywords “retrograde peri-implantitis” and
“implant periapical lesion.” Preoperative intraoral periapical
(IOPA) radiographs of implants with RPI in case reports/case
series were compiled. A total of 54 IOPAs from 36 articles were
compiled and were assessed.
Results: Three different classes were proposed. The amount
of bone loss from the apex of the implant to the most coronal
part of radiolucency was calculated as a percentage of the total
implant length and classied into one of the three classes: Mild,
moderate, and advanced. Treatment options and prognosis have
been suggested for each class.
Conclusion: The proposed classication may allow for an easy
and reproducible radiographic assessment of the RPI lesion and
may serve as a guideline to prognosis and treatment planning.
Keywords: Implant, Periapical implant bone loss, Periapical
How to cite this article: Shah R, Thomas R, Kumar ABT,
Mehta DS. A Radiographic Classication for Retrograde Peri-
implantitis. J Contemp Dent Pract 2016;17(4):313-321.
Source of support: Nil
Conict of interest: None
A Radiographic Classication for Retrograde
1Rucha Shah, 2Raison Thomas, 3AB Tarun Kumar, 4Dhoom Singh Mehta
1-4Department of Periodontics, Bapuji Dental College and
Hospital, Davangere, Karnataka, India
Corresponding Author: Rucha Shah, Lecturer, Department
of Periodontics, Bapuji Dental College and Hospital, Davangere
Karnataka, India, Phone: +917676279879, e-mail: srucha2k@
Dental implants have revolutionized the ﬁeld of dentistry.
Since the era of Brånemark, vast improvements have been
made in our understanding of dental implant physiology
and biology. Similar to natural teeth, implants are also
susceptible to plaque bioﬁlm formation and subsequent
soft tissue and bone destruction. The most common inﬂam-
matory lesion of dental implant is peri-implantitis. The
term was ﬁrst suggested by Mombelli et al1 and several
classiﬁcations for the same exist.2-4 Another separate entity
“retrograde peri-implantitis (RPI)” was ﬁrst introduced by
McAllister et al in 1992.5 It was described as a “clinically
symptomatic periapical lesion that develops within the
ﬁrst few months after implant insertion while the coronal
portion of the implant sustains a normal bone to implant
interface.” Retrograde peri-implantitis is a relatively rare
clinical entity and there is a paucity of scientiﬁc literature
on this topic.6,7 The etiology is not clear but most of the
cases show bacterial infection. The management of this
lesion is mainly empirical and may include open-ﬂap
debridement, guided bone regeneration, implant apical
resection, or explantation.
Till date, there is no uniformly accepted deﬁnition or
classiﬁcation of RPI. A previous classiﬁcation has been pro-
posed by Reiser and Nevins,8 who classiﬁed RPI as either
inactive or infected lesions. Sussman9 classiﬁed RPI into
two types based on the origin of the lesion: Type 1 – implant
to tooth, which occurs during osteotomy preparation either
by direct trauma or through indirect damage, which causes
the adjacent pulp to undergo devitalization, and type 2 –
tooth to implant, which occurs shortly after the placement
of the implant when an adjacent tooth develops a periapi-
cal pathology, either by operative damage to the pulp or
through reactivation of a prior apical lesion. Peñarrocha-
Diago et al10 classiﬁed the RPI lesion according to the
stages in which it involves into acute nonsuppurated apical
peri-implantitis, acute suppurated apical peri-implantitis,
Rucha Shah et al
or subacute or suppurated ﬁstulized apical peri-implantitis.
They also suggested treatment guidelines for all the stages.
A periodontal, implant, separate, and traumatic (PIST)
classiﬁcation has been proposed by Kadkhodazadeh and
Amid,11 which has combined peri-implant, periodontal,
and periapical lesions. The degree of bone loss around the
implant apex may inﬂuence the choice of treatment and
prognosis of RPI. None of the existing classiﬁcations clas-
sify RPI according to the severity of involvement. Also, no
guidelines are present regarding the prognosis for the same.
A reproducible quantitative classiﬁcation is much
more objective and has several beneﬁts. It aids in the
determination of relatively more accurate and standard-
ized diagnosis and prognosis. A quantitative classiﬁcation
considering the degree of bone destruction around an
implant is not present. Such classiﬁcations already exist
for periodontitis and peri-implantitis.2,12 A standard case
deﬁnition enables the estimation of true prevalence of any
condition. While analyzing different treatment modali-
ties, a baseline standard classiﬁcation system may give a
better guideline so as to assess which treatment modality
is more effective. It can be expected that the severity of
involvement is one of the main factors that can dictate
the type of treatment and prognosis of a case. Thus, this
classiﬁcation was based on the severity of involvement.
The aim of this article is to introduce a classiﬁcation for
RPI quantitatively based on the radiographic amount of
bone destruction seen for mild, moderate, and advanced
grades of RPI.
MATERIALS AND METHODS
An electronic literature search was done in the PubMed
database. The keywords used were “retrograde peri-
implantitis (RPI)” and “implant periapical lesion (IPL).”
The search was performed in December 2015 and all
results thus, obtained were included. The total number of
hits using RPI was 22 and using IPL was 76. After removal
of duplicates (n = 8), 89 results were obtained. The search
hits were then screened for clear relevance by an analysis
of the title and abstract by two reviewers. A total of
56 articles were considered.6-11,13-62 A total of 33 articles
were excluded as being not relevant.63-95 Those articles not
in the English language were excluded (n = 1).40 Full text
of rest of the articles was sought. Seven were not available
as full text, and hence were not included.9,27,28,32,46,59,62
Another article was excluded as it was an animal study
(n = 1).56 The process is demonstrated in Flow Chart 1.
From the articles for which full text was available, images
of high-quality intraoral periapical (IOPA) radiographs of
the implant having RPI immediately after diagnosis were
obtained. Twelve of the articles were excluded as they
had no IOPAs of the lesion.7,11,24,25,33,35,37-39,45,48,53 A total of
54 IOPAs from 36 articles were compiled. One periodon-
tist (SR) and one implantologist (TAB) independently
analyzed the IOPAs. The proposed classiﬁcation was pre-
pared keeping in mind several requirements as previously
described.63 The requirements were for it to be comprehen-
sive enough to include all possible periapical lesions around
the dental implant, to be simple, logical, reasonable, and
reproducible. It should be acceptable, have ease of applica-
tion, should be scientiﬁcally based (by considering all the
recently published literature), and should be helpful to
determine the prognosis and treatment guidelines.11 After
several sessions of discussion, consensus regarding the
radiological classiﬁcation was reached and the following
classiﬁcation was proposed. Also, wherever the treatment
protocol was mentioned, it was recorded against the type
of treatment given in different class.
Radiographic Classication of RPI
To classify the RPI lesions, bone loss was measured in
an apico-coronal direction from the apex of the implant
to the most coronal point of extension of bone loss in
millimeters. The derived value was then calculated as a
percentage of the radiographic implant length (Fig. 1A).
The bone loss around the implant may or may not involve
both the implant surfaces (medial and distal) (Figs 1B to
1D). Depending on this percentage, the observed bone
loss was assigned into one of the three categories:
1. Mild lesion (class I) is characterized by radiographic
bone loss that extends to <25% of the implant length
from the implant apex (Fig. 2A).
2. Moderate lesion (class II) is characterized by radio-
graphic bone loss between 25 and 50% of the implant
length as measured from the implant apex (Fig. 2B).
3. Advanced lesion (class III) is characterized by
radiographic bone loss extending to > 50% of the
implant length from the implant apex (Fig. 2C).
Flow Chart 1: Process for selection of articles for
A Radiographic Classication for Retrograde Peri-implantitis
The Journal of Contemporary Dental Practice, April 2016;17(4):313-321 315
The statistical analysis was done using Statistical Package
for the Social Sciences (SPSS) software version 16.0. The
frequency of observation of each class was also calculated.
Interexaminer variation was assessed using Cohen K
In the classiﬁcation agreement of the evaluators, the K
value was found to be 0.67, which can be considered
as a good agreement. The distribution of the different
classes is demonstrated in Table 1. The most commonly
encountered classiﬁcation is class II.
Figs 1A to D: The method to classify a retrograde peri-implantitis
lesion: (A) Measurement of bone loss (measure the length marked
in arrow and divide by the radiographic total length of implant),
(B and C) Both these lesions would be classied as class I (% bone
loss is < 25% in both scenario), and (D) Even though the apical
extension of lesion is same as in Figure B, this is class III lesion as
percentage of involved implant is more than 50%
Figs 2A to C: Figure demonstrating the various proposed classes
for retrograde peri-implantitis (RPI): (A) Class I mild RPI (bone loss
< 25% of implant length from implant apex), (B) class II moderate
RPI (bone loss 25–50% of implant length from implant apex), and
(C) Class III advanced RPI (bone loss > 50% of implant length from
Table 1: Proposed classication of retrograde periodontitis
Classication Stage Amount of bone loss
Class I Mild Extends <25% of the implant
length from implant apex
Class II Moderate 25–50% of the implant length
from implant apex
Class III Advanced >50% of the implant length from
Implant dentistry is becoming widely accepted as a
routine treatment modality. With the increase in the
number of implants being placed, cases of RPI are not as
rare as they were once. Retrograde peri-implantitis has
been attributed to a large number of etiologies including
bone overheating, poor bone quality, drilling beyond
implant length, contamination during insertion, bone
microfractures secondary to premature loading, and
implant insertion in a site with existing inﬂammation, such
as apical periodontitis. However, the current consensus is
that the etiology for RPI is primarily bacterial in nature
and other factors may act as secondary complicating
factors.30 The diagnosis of RPI is based on clinical signs
and symptoms and radiographic ﬁndings. The clinical
manifestations of RPI include pain, inﬂammation, ﬁstula
formation, and swelling or in advanced cases implant
mobility.31 The clinical features may not clearly indicate/
Rucha Shah et al
corelate with the actual extent of the lesion. Radiographic
features include a radiolucency surrounding or including
the implant apex with relatively normal marginal bone.31
This article introduces a simple and descriptive
classiﬁcation for RPI. The interprofessional commu-
nication can be beneﬁted from such a classiﬁcation
system, which clearly differentiates lesions based on
their severity. A well-accepted classiﬁcation has the
advantages of facilitating communication, improved
understanding of the nature, and response of the treated
cases. The proposed classiﬁcation takes into considera-
tion the radiographic extent of peri-implant bone loss.
The rationale of classiﬁcation was to give a clear clinical
distinction of various stages, treatment suggestions,
Unlike periodontitis and peri-implantitis, the RPI
lesion is not amenable to clinical examination like probing
and even may not show telltale clinical signs. The clinical
features are not deﬁnite or omnipresent and vary greatly.31
Sometimes, the lesion may be asymptomatic. Although
radiographic changes may not be present in the acute
initial stages, the late and symptomatic stages always
demonstrate the presence of an apical radiolucency.31
Hence, radiographic features were taken as the basis of
A standardized periapical radiograph can give
accurate values of the amount of bone loss around the
implant apex; however, owing to the vast variety of
shapes and morphology of implants, absolute values
may be difﬁcult to compare among different implants.
Hence, the present classiﬁcation is proposed based on
the percentage bone loss relative to the length of the
implant. A standardized radiograph immediately after
implant placement may provide details about the baseline
relationship of bone-to-implant apex and facilitate
comparison with the later radiographs to assess the extent
of bone that has been lost during the given time period.
The previous classiﬁcation by Reiser and Nevins8
proposed that the inactive form was actually an apical
scar which could have resulted from a residual bone
cavity created while placing an implant that was shorter
than the osteotomy. The active or infected form was
explained as occurring when an implant apex was placed
in close proximity to an existing infection or placement of
contaminated implant or that resulting from bone necrosis
caused by overheating during preparation. The authors
suggested that the inactive type of RPI should be observed
and monitored whereas the infected type required
surgical intervention, elimination of the infection, and
reception of apical part of implant or implant removal
depending on the extent of the infection and the stability
of the implant. This classiﬁcation is based on the lesion
activity and does give treatment guidelines. However, it
does not differentiate between the treatment modalities
on the basis of extent of bone involvement.
The classiﬁcation of RPI by Sussman9 describes two
types of RPI, i.e., Type 1: Implant to tooth caused due
to a direct or indirect trauma caused to the adjacent
tooth during osteotomy preparation. A type 2 lesion is
described as tooth to implant in which there is spread
of infection from an endodontically involved tooth
to adjacent implant. This classiﬁcation gives an idea
about the etiology of the RPI lesion. It does not give any
information regarding the degree of bone destruction
around the implant. Also it does not provide any
overview of the prognosis or guidelines for the type of
treatment to be rendered in speciﬁc cases.
Peñarrocha-Diago et al classified the RPI lesion
according to the stages of involvement. The ﬁrst stage
was the acute non-suppurated apical peri-implantitis
characterized by redness, swelling, and acute pain but
no radiographic features. The second stage was acute
suppurated apical peri-implantitis, which has similar
clinical features as the ﬁrst stage along with a radiolucent
lesion at the implant apex. The next stage was subacute
or suppurated ﬁstulized apical peri-implantitis, which is
characterized by dull pain and mild swelling and redness
along with deﬁned periapical radiolucency, which may
continue as marginal bone loss. For the ﬁrst two stages,
periapical surgery was suggested, whereas for the third
stage, surgery was suggested in the absence of implant
mobility. In this classiﬁcation, treatment guidelines are
provided, but the extent of involvement of the lesion was
The PIST classification has been proposed by
Kadkhodazadeh and Amid for peri-implant, periodontal,
and periapical lesions. It is an etiology-based classiﬁca-
tion. The classes relating to apical peri-implantitis are
P-1, which is primary periodontitis in adjacent tooth
and secondary involvement of implant. In P-3 there is
primary periodontitis in adjacent tooth and marginal and
periapical implantitis. In class I-1 it is primarily apical
peri-implant lesion, which may involve the apical part
of adjacent tooth secondarily. In the S-1 lesion, apical
lesions are seen on both implant and adjacent tooth but
they occur independently of each other. In S-3 there are
apical and marginal lesions on both implant and natural
tooth, also occurring separately from each other. T-0 is an
asymptomatic periapical lesion involving implant and/or
adjacent tooth, whereas T-1 is a symptomatic periapical
lesion involving implant and/or adjacent tooth. This clas-
siﬁcation is comp rehensive; however, it does not provide
any treatment indications.
In the current classiﬁcations, no quantiﬁcation of bone
loss, prognosis, or case-speciﬁc treatment indications are
outlined clearly. Some cases can occur as an overlap in
A Radiographic Classication for Retrograde Peri-implantitis
The Journal of Contemporary Dental Practice, April 2016;17(4):313-321 317
two stages. To overcome the shortcomings of the present
classifications, this classification is being proposed.
The chances of overlap are minimum and the degree
of bone loss can be clearly assessed. When assessed for
interobserver agreement, the scores were interpreted as
good. Hence, it can be said that it is easy and reproducible
and has good interexaminer reliability. To the best of our
knowledge, this is the ﬁrst attempt at classifying RPI
quantitatively according to the radiographic amount of
bone destruction seen.
On performing literature search, the authors found
56 published reports on RPI. This demonstrates the
relatively low frequency of occurrence of these lesions.
The incidence of this lesion may range from 1.6%
in the maxilla to 2.7% in the mandible.6 To create a
classiﬁcation, sufﬁcient data should be assessed for it to
be comprehensive and universally applicable. Hence, the
authors collected all available high-quality IOPA from the
published literature on which the proposed classiﬁcation
Majority of the IOPAs examined by the authors fell
in class II as per the proposed classiﬁcation. This can
be attributed to the fact that an unchecked lesion
progresses from class I to III over a period of time. A
class I lesion is an early mild lesion and may not be
often diagnosed. A class III lesion is too advanced, may
frequently be associated with implant mobility, and hence
may be explanted. Such cases may not be reported as
frequently as their successfully managed counterparts.
A class II lesion is more successfully managed when
Chan et al15 have proposed a decision tree for the
management of RPI. According to them, a mobile implant
must be explanted; symptomatic immobile implant
should be managed by surgical intervention. For lesions
associated with endodontically involved teeth, the
ﬁrst line of management is to treat the tooth and wait,
and if lesion does not resolve, surgical intervention is
indicated. However, there is no differentiation between
lines of treatment depending on the size of the lesion at
the time of diagnosis. A class III or II lesion may require
comparatively aggressive and extensive management as
compared with a class I lesion. Another excellent decision
tree has been proposed by Park et al55 for the management
of RPI. They have considered bone loss less than half
the length of implant as adequate osseointegration.
For such cases they suggested surgical management
of nonendodontically compromised cases. When the
bone loss involved more than half the length of implant,
osseointegration is considered inadequate and implant
is suggested to be removed and new wider implant
placement is recommended. They have also classiﬁed
the bone defect of less than 5 mm to be managed by
membrane placement only, whereas more than 5 mm to be
managed by bone grafting in conjunction with membrane
placement. Though the basic distinction is presented for
the extent of lesion, the distinction between adequate
and inadequate osseointegration is too sudden. This may
lead to improper management of borderline cases, and
some cases that could be managed surgically can go for
From the selected articles, the type of treatment done
was also recorded. When reviewed in the cases selected,
class I and II lesions are most commonly managed with
open-ﬂap debridement. This may or may not be followed
by placement of bone graft and/or barrier mem-
brane.19,21 Also, most of the lesions in these classes tend
to show complete resolution. Some of the reports also
advocate the apical resection of implant,7 but increas-
ing evidence indicates that guided bone regeneration
is successful in the management of these cases. When
the lesions belonged to class III at the time of diagnosis,
the management is frequently more aggressive includ-
ing open-ﬂap debridement, bone graft, and barrier
membrane placement and/or resection of the apical
part of the implant.7,13,14,18,51 If the lesion does not
resolve or the implant is clinically mobile, the implant
has to be explanted.36,42,54,55 There are also reports of
successful implant placement after explantation at the
The pathogenesis of an endodontic lesion is remark-
ably similar to periodontitis and peri-implantitis in
terms of involved chemical mediators and responses at
the host cellular level.96 However, the healing potential
of an endodontic lesion is quite high as compared with
a periodontitis or conventional peri-implantitis. It has
been observed that following the treatment, resolution of
the apical radiolucency is observed in most of the cases.
This has been attributed to the fact that after completion
of the therapy, a closed environment is obtained and
healing occurs relatively undisturbed.96 Similarly, RPI is
a closed lesion. Once the nidus of infection is removed by
open-ﬂap debridement, a completely closed environment
is achieved. The healing potential of such lesions after
intervention may be similarly higher than in conven-
tional peri-implantitis, where the crestal bone is involved.
This justiﬁes the ﬁnding in the literature that even after
advanced bone involvement such as in proposed class III
there are chances of complete resolution of the lesion.19
Based on the above observations and two previously
published treatment algorithms, a modiﬁed decision tree
has been proposed. Apart from the etiology, it also consid-
ers the extent of the lesion and gives treatment sugges-
tions based on it (Flow Chart 2). Once the diagnosis of RPI
is established, the clinician must differentiate it as either a
primary implant lesion or a lesion arising endodontically
Rucha Shah et al
in adjacent tooth and involving implant secondarily. If
the lesion is primary, it should be classiﬁed into class I,
II, or III. A class I lesion can be managed by open-ﬂap
debridement and it can be followed by implant surface
decontamination. A class II lesion has to be assessed for
accessibility. Open-ﬂap debridement followed by guided
bone regeneration using barrier membranes and/or bone
graft is suggested when accessibility to the lesion is good.
In case of poor accessibility, open-ﬂap debridement fol-
lowed by resection of apical part of implant, followed by
guided bone regeneration using barrier membranes and/
or bone graft, is suggested. A class III lesion demonstrates
advanced bone loss, and hence, the implant mobility must
be assessed. If mobility is absent, the treatment should
be done similar to a class II lesion; however, if implant
mobility is seen, explantation should be performed. After
explantation, if sufﬁcient bone remains to achieve good
implant stability and the decontamination of the site is
thorough, immediate wide diameter implant placement
can be done. However, if sufﬁcient bone is not present,
guided bone regeneration followed by delayed implant
placement has to be followed.
If the lesion is secondary to primary endodontic lesion
from an adjacent tooth, endodontic management of the
offending tooth should be performed. This should be
followed up for up to 1 to 3 months. Closed endodontic
lesions have high healing potential and demonstrate com-
plete resolution of periapical lesion.96 If resolution occurs,
the patient should be kept under monitoring. If the lesion
shows no sign of resolution or shows signs of progressing,
it should now be managed as a primary implant lesion.
Also, from the reviewed articles it was noted that most of
the lesions in classes I and II tend to show complete reso-
lution.13,14,18,19,21 The prognosis can be considered fair to
good. The resolution frequency of class III lesions is lower
than that of class I and II lesions. The prognosis can be from
fair to poor (in case of mobility).36,42,54,55 To the best of our
knowledge, this is the ﬁrst classiﬁcation that comments
on the prognosis based on the extent of the lesion of RPI.
This classiﬁcation can be used in the formulation of
sophisticated standardized treatment algorithms. Such
algorithms guide clinicians, so as to decide which treat-
ment modality to follow when faced by a particular clinical
scenario. It may be helpful to clinicians managing cases of
RPI, the treatment of which still remains highly empirical.
As our knowledge about the pathogenesis of RPI increases,
modiﬁcations of this classiﬁcation may be suggested.
This classiﬁcation quantiﬁes and describes peri-implant
apical bone loss in an objective and reproducible
manner. The proposed classiﬁcation can be applied for
standardization purposes in research methodologies so
as to have a reliable comparison of the initial lesion and
compare the treatment outcomes in different studies with
similar aims. Further research is required to analyze the
validity of this proposed classiﬁcation.
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