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The clinical significance of keratinized gingiva around dental implants

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24

Volume 32, Number 8

compendium     October 2011    

Continuing Education 2

Learning Objectives

•

differentiate anecdotal 

information versus data with 

respect to the need to augment 

keratinized gingiva around dental 

implants

•

discuss the need for keratinized 

tissue around teeth and describe 

anatomical differences between 

teeth and dental implants

•

list possible scenarios

that suggest the need to augment 

keratinized tissue around implants

Whether or not keratinized tissue is needed around dental 

implants to maintain peri-implant health is a controversial 

subject. To clarify this issue a search was conducted for 

clinical trials that appraised the significance of keratinized 

gingiva (KG) around teeth and dental implants. A critical 

assessment of the data revealed that the literature is re-

plete with studies that contradict one another with respect 

to the need for KG as it relates to survivability of implants, 

gingival response to plaque, inflammation, probing depths, 

recession, and loss of bone. When groups of patients with 

and without KG were compared with respect to various 

clinical parameters, a statistically significant better result 

in the presence of KG could be interpreted to indicate that 

having KG is advantageous. However, quantitative differ-

ences between groups with and without KG were usually 

very small.  Overall, the data was interpreted to indicate 

that some patients may need augmentation of keratin-

ized tissue to maintain peri-implant health. Ultimately, 

the decision to augment KG is a judgment call that needs 

to be made by the treating clinician, because there are not 

enough data to facilitate development of definitive guide-

lines relevant to this subject. Apparently, the need for KG 

is patient specific, and at present there is no method to re-

liably predict who would benefit from tissue augmentation. 

The clinical Significance 

of Keratinized Gingiva 

around dental implants 

gary greenstein, DDs, Ms; and john cavallaro, DDs 

abstract

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25

www.dentalaegis.com/cced 

    October 2011     compendium

F

or many years there has been controversy as 

to whether keratinized gingiva (KG) is neces-

sary to maintain health around teeth,

1,2

 and 

this debate persists with respect to the role 

of keratinized tissue adjacent to dental im-

plants.

3-5

 Historically, an increased zone of 

keratinized tissue was presumed desirable 

for the following reasons: provides a resistant barrier to plaque-

induced inflammation

6

; replaces unkeratinized margins to pre-

vent recession

7

; deepens vestibules to provide better access for 

toothbrushing

8

; dissipates functional and masticatory stress 

placed on the gingival margin of a restoration

9

; and improves 

esthetics, patient comfort, and ease of hygiene.

4,10,11

In response to perceived needs for KG, surgical techniques 

were devised to augment gingiva around teeth and implants.

12

 

These procedures continue to be performed because of the 

persistent disagreement concerning the requirement for ke-

ratinized tissue to maintain health. The objective of this pa-

per is to appraise the data and provide a perspective as to why 

generalized conclusions can or cannot be made regarding the 

need for KG to sustain health around dental implants. First, 

data related to the relationship between keratinized tissue and 

teeth are reviewed. Then anatomic differences in tissues sur-

rounding teeth and implants are addressed. These data serve 

as background information for the discussion concerning the 

relevance of KG in maintaining peri-implant health. To avoid 

confusion about anatomic and histological terminology, defini-

tions of terms used in this review are provided in Table 1. The 

specific type of tissue referred to in studies will be stated. Note 

that the terms keratinized mucosa and ke-

ratinized gingiva  represent the same type 

of tissue and may include attached and 

unattached gingiva. 

KeratinizeD tissue arOunD teeth

Numerous authors suggested that a lack 

of keratinized tissue predisposed the peri-

odontium around teeth to deterioration, be-

cause they believed KG was more resistant 

to periodontal destruction than alveolar 

mucosa.

6-8

 To assess the validity of this as-

sumption, clinical trials were performed to 

evaluate whether a band of KG was neces-

sary to maintain health. In 1972, Lang and 

Löe

13

 published the first controlled clinical 

trial that examined the relationship be-

tween the width of KG and gingival health. 

They reported that 80% of tooth surfaces 

with > 2 mm of KG were healthy. However, 

all surfaces with < 2 mm of KG manifested signs of clinical inflam-

mation. It was concluded that 2 mm of KG was needed to main-

tain gingival health (1 mm attached gingiva and 1 mm unattached). 

Subsequently, numerous investigations were conducted to verify 

if keratinized tissue was needed to maintain periodontal health. 

Clinical trials indicated that sites with a minimal amount of KG

9

 

or attached gingiva

14-17

 could remain healthy and that increasing 

the zone of keratinized tissue did not influence periodontal sta-

tus.

15-17

 Furthermore, investigators demonstrated

17,18

 that reducing 

inflammation was sufficient to maintain clinical attachment levels 

regardless of the keratinized tissue’s width. Histologic confirma-

tion that the size of the attached gingiva was noncontributory to 

maintaining health or avoiding recession was provided in a dog 

model,

19

 a finding that was confirmed in a study among humans.

20

 

Long-term data with respect to the stability of margins with 

a lack of KG has been documented. In a group of students with 

a high degree of oral hygiene, areas with inadequate zones of at-

tached gingiva were maintained (4 to 18 years) without further 

recession.

21-23

 In contrast, Agudio et al

24

 reported 10- to 27-year 

data (means 15.3 years) with respect to two groups of patients 

and noted that sites with a lack of attached gingiva manifested a 

mean recession of 0.7 mm and 1 mm, respectively. 

Concerning restorations with subgingival margins, Stetler and 

Bissada

25

 found that teeth with narrow zones (< 2 mm) of keratin-

ized mucosa demonstrated a significantly higher gingival index 

(GI) than teeth with wide zones of KG (> 2 mm). Similarly, in beagle 

dogs, Ericsson and Lindhe

26

 reported that subgingival crown mar-

gins placed in areas with no KG that were allowed to accumulate 

plaque over months were prone to develop larger cellular infiltrates 

than sites with KG. These data conflict with 

the histological report by Wennström et 

al

19

 that indicated there was no difference 

in the inflammatory response with respect 

to the amount of attached gingiva present. 

In  summary,  the  preponderance  of 

evidence indicates that augmenting KG 

around teeth should be approached cau-

tiously. The patient’s dental history and 

chronicity of problems should be assessed 

before performing gingival augmentation. 

Measurements should periodically be taken 

from the cemento-enamel junction (CEJ) 

to the free gingival margin (FGM) to de-

termine if recession occurred, or from the 

CEJ to the base of the pocket to determine 

if loss of clinical attachment occurred.

27

 

Ultimately,  the  status  of  tissues  should 

be the critical determinant as to whether 

KG should be augmented; this decision 

should not be based upon an assumption 

tabLe 1

definition of Terms

alveolar mucosa: unkeratinized 

oral epithelium

gingiva: oral mucosa that is kera-

tinized, described as attached or 

unattached

attached gingiva: gingiva that is 

tightly bound down around teeth 

or implants and continuous with 

the unattached gingiva

unattached gingiva: gingiva 

that is not bound down (eg, free 

gingival margin, soft-tissue wall 

of the sulcus or pocket)

Width of attached gingiva: 

distance from the mucogingival 

junction to the free gingival mar-

gin minus the probing depth

---

26

Volume 32, Number 8

compendium     October 2011    

continuing education 2

that augmenting KG is essential to maintaining periodontal health. 

These conclusions are in accord with the European Workshop on 

Periodontology.

1

 The participants reached the consensus that treat-

ment for the sole purpose of increasing the apicocoronal width of 

the gingiva to maintain periodontal health and prevent the devel-

opment of soft-tissue recession around teeth cannot be justified.

1

 

Subsequent to this report there have been no data that challenged 

the conclusions of the workshop with respect to teeth.

KeratinizeD tissue arOunD iMpLants

differences in periodontal Tissues 

Surrounding Teeth and implants

Teeth and dental implants have either gingiva or mucosa ad-

jacent to them as they emerge into the oral cavity. Within the 

crevice around these structures the oral sulcular epithelium is 

connected to the junctional epithelium (JE). The JE on average is 

1-mm long

28

 and is attached to teeth and dental implants by hemi-

desmosones.

29

 Subjacent to the JE around teeth is a connective 

tissue layer about 1-mm long. Around teeth, this layer contains 

fibers that are perpendicular to the root surfaces and insert into 

the cementum. Surrounding implants, the connective tissue fi-

bers are parallel or oblique

30

 and do not insert into the implant 

surface. In addition, the blood supply around implants is less 

than around teeth, because the periodontal ligament is absent.

31

 

Animal models: Histological Response to  

plaque Accumulation

Due to anatomical differences, peri-implant and periodontal 

tissues may differ in their response to bacterial infections.

26,32

 

Ericsson et al

26

 reported that after cessation of hygiene in a dog 

model the apical extent of the inflammatory infiltrate was larger 

in peri-implant mucosa. Similarly, in a dog model when ligatures 

were placed to induce destruction, there was greater bone loss 

around implants than teeth.

32

 It was suggested that peri-implant 

mucosa might be more susceptible to destruction than tissues 

around teeth. In this regard, when Warrer et al

33

 placed ligatures 

around implants (in monkeys) at sites with and without adjacent 

keratinized mucosa, they noted that locations without keratinized 

tissue demonstrated more recession and attachment loss than 

sites with keratinized tissue. In contrast, Strub et al

34

, in a dog 

model, failed to find differences in peri-implant soft-tissue reces-

sion or bone loss between sites with and without attached gingiva. 

clinical Trial Results in Humans:  

importance of KG 

Concerning the effect of a dearth of KG, there is conflicting infor-

mation in the literature regarding six issues: implant survivability, 

plaque accumulation, tissue inflammation, recession, probing 

depths, and bone loss. These issues are discussed separately, be-

cause within a given study a lack of KG may negatively affect only 

one parameter listed above and not others. Furthermore, it is 

recognized that numerous variables that have not been accounted 

for in many investigations (eg, biotype, smoking, surgical manage-

ment of implant area, occlusal forces, etc.) can affect study results. 

There are several other issues that should be noted with re-

spect to studies that addressed the role of KG around implants. 

Researchers did not differentiate between attached and unat-

tached gingiva. This is probably due to the fact that probing 

depths are usually deeper around implants than healthy teeth be-

cause of differences in the anatomy. In addition, there is difficulty 

in detecting the coronal level of the biologic width, because the 

probe penetrates into the JE and this results in underestimating 

the amount of attached gingiva present.

35

 

Furthermore, measure-

ments are usually taken on the buccal aspect, and studies have not 

related clinical parameters to interproximal tissues. It should also 

be noted that when all of the gingiva is excised in a dog model, the 

marginal tissue that reforms usually has a keratinized margin that 

is not attached.

19

 Therefore, when there is a lack of KG, the typical 

finding is a keratinized margin with mucosa (Figure 1), and only 

rarely is a pure mucosal margin found (Figure 2). 

Fig 2. 

Fig 1. When there is a lack of attached gingiva, the typical finding is 

a keratinized margin with mucosa (site Nos. 23 and 26). 

Fig 2. Site 

No. 10 has a mucosal margin. 

Fig 1. 

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27

www.dentalaegis.com/cced 

    October 2011     compendium