Wound healing

Contents1. Introduction

2. Regeneration & repair

3. Healing by primary and secondary intension

4. Molecular biology of wound healing

5. Factors influencing/ complications of wound healing

6. Healing of oral wounds

7. Role of saliva and GCF in wound healing

8. Wound healing following various periodontal therapies

9. Use of lasers in wound healing

10. conclusion

Introduction

A wound/Injury is a disruption of the anatomic structure and

function in any body part.

Wound healing

Healing on the other hand is a cell response to injury in an attempt to restore the normal

structure and function.

Periodontal wound healing

A more complex situation presents itself when a

mucoperiosteal flap is apposed to an instrumented root surface

deprived of its periodontal attachment.

In this case, the wound margins are not two opposing vascular

gingival margins but comprise the rigid nonvascular

mineralized tooth surface, on the one hand, and the connective

tissue and epithelium of the gingival flap, on the other hand.

Process of healing

It involves 2 distinct processes :

At times, both the processes take place

simultaneously

Regeneration Repair

Regeneration

Natural renewal of a structure, produced by growth &

differentiation of new cells and intercellular substances to

form new tissues or parts which function the same as

original tissues.

Growth from the same type of tissue that has been destroyed

or from its precursors.

Periodontal tissues are limited in their regenerative

capacity.

Essential molecules for regeneration

Regeneration related to periodontal tissues

Manifested by:

Mitotic activity in the epithelium of the gingiva and connective tissue

of PDL

Bone remodelling

Continuous deposition of cementum

Most gingival and periodontal diseases are chronic inflammatory

process and, as such are, healing lesions.

Repair- “healing by scar”

Replacement of one tissue with another tissue,

such as fibrous connective tissue, which may not function the

same as the tissue replaced.

Two processes are involved in the repair:

1. Granulation tissue formation

2. Contraction of wounds

Granulation tissue formation

Each granule histologically corresponds to proliferation of new

small blood vessels which are slightly lifted on the surface by a

thin covering of fibroblasts and young collagen

Granulation tissue formation

Phase of inflammation

Phase of clearance

Phase of ingrowth of

granulation tissue

Angiogenesis (neovascularization)

Formation of fibrous tissue (fibrogenesis)

Angiogenesis necessary to sustain newly formed granulation tissue

proliferation of endothelial cells from the margins of the severed

vessels

fibrogenesis

Emigration and proliferation of the fibroblasts at the site of injury

Deposition of these cells which in turn increases collagen synthesis

As the maturation proceeds: there is an increase in the collagen, and a

decrease in the fibroblasts and blood vessels .

This leads to the formation of scar know as CICATRISATION.

Wound contraction

It starts after 2-3 days and the process is completed by the 14th day.

Wound is reduced by 80% of its original size which helps in rapid

healing since lesser surface area of the injured tissue has to be

replaced.

Mechanisms of wound

contraction

dehydration

myofibrobla

sts

Contraction of collage

n

Repair related to periodontal tissues

Simply restores the continuity of the diseased marginal

gingiva and re-establishes a normal gingival sulcus at the

same level on the roots as the base of the pre-existing

periodontal pocket.

Arrests bone destruction but does not result in gain of

gingival attachment or bone height.

wound strength- extracellular matrix

The wound is strengthened by proliferation of fibroblast and myofibroblast

which get structural support from the extracellular matrix

ECM has five main components:

1. collagen

2. adhesive glycoprotein

fibronectin - plasma/ tissue type

tenascin or cytotactin

thrombospondin

3. basement membrane

4. elastic fibres

5. proteoglycans

Healing by first intention(Primary union)

This is defined as healing of a wound which has the following

characteristics:

Clean and uninfected

Surgically incised

Without much loss of cells and tissue

Edges of wound are approximated by surgical suture

Primary union involves the following sequence of events:

Initial hemorrhage

Acute inflammatory response- within 24 hours

Epithelial changes- completes by 48 hours

Organization of fibroblasts- starts around 3rd day

Wound maturation- starts after 1 week and completes

around 4 weeks

The incised wound as well as suture track on either side are filled with blood clot and there is inflammatory response from the margins

spurs of epidermal cells migrate along the incised margin on either side as well as round the suture track, formation of granulation tissue also begins from below.

removal of sutures at around 7th day result in scar tissue at the sites of incision and suture track

Healing by secondary intention(secondary union)

This is defined as-

Open wound with a large tissue defect, at times infected

Extensive loss of cells and tissues

Not approximated by sutures, but is left open

Secondary union consists of the following events :

Initial hemorrhage

Inflammatory process

Epithelial changes

Granulation tissue formation

Wound contraction

A. The open wound is filled with blood clot and there is inflammatory response at

the junction of viable tissue

B. Epithelial spurs from the margins of wound meet in the middle to cover the gap

and separate the underlying viable tissue from necrotic tissue at the surface forming

scab

C. After contraction of the wound ,a scar smaller than the original wound is left

A B C

Molecular biology of wound healing

1. The fibrin clot and inflammatory cells

The important functions of the clot are:

plugs the cut blood vessels and also serves to protect the

denuded tissues temporarily.

reservoir of growth factors and cytokines that are released by the

degranulation of activated platelets and serving as a provisional

matrix for cell migration and might be providing the start signals

for wound repair.

2. Re-epithelialization of wounds

keratinocytes start moving into the defect about 24 hours after the injury

The keratinocytes use receptors on their surface, known as integrins

to bind to laminin in the basal lamina.

Integrins are a family of cell adhesion receptors that mediate cell

surface interactions with extracellular matrix and in some cases

with other cells

At this edge, the cells will have to dissolve the hemidesmosome

attachment, downregulate the expression of α6β4, and upregulate

integrin receptors α5β1, αVβ6 and αVβ5 that are suitable for adhesion

to provisional matrix components.

epidermal growth factor

transforming growth factor-α

heparin-binding epidermal growth factor and

keratinocyte growth factor are involved in stimulating the

proliferation of the epithelial cells here.

3. Matrix degradation and the wound-cleaning process

creation of a migrating path for keratinocytes is achieved by

the dissolution of the fibrin barrier by the enzyme plasmin

that is derived from the activation of plasminogen in the clot.

The two activators, tissue-type plasminogen activator and

urokinase-type plasminogen activator along with its receptor,

are upregulated in the migrating keratinocytes

MMP-1 degrades native collagens and aids cell migration by

destroying collagens I and III.

MMP-9 (also known as gelatinase B) can cleave the collagen in basal

lamina (type IV) and the collagen that forms the anchoring fibrils

(type VII)

MMP10 (also known as stromelysin-2) is also expressed in wounds

and is thought to have a wide spectrum of substrate specificity for

collagen

Connective tissue repair by:

Activation of fibroblasts by platele granules

Angiogenesis by VEGF and b-FGF

Formation of Granulation tissue by TGF, PDGF, FGF and EGF

contraction of the wound by myofibroblasts.

Wound repair involves phenotypic change of fibroblasts from quiescent to proliferating cells, and subsequently to migratory, and then to stationary matrix producing and contractile cells.

In the connective tissue, fibroblasts are surrounded by a matrix that contains collagen and cellular fibronectin as the major components. Consequently, quiescent fibroblasts express collagen receptors α1β1 and α2β1 and the major fibronectin receptor α5β1 integrin which they use for adhesion to the matrix

Factors influencing healing

Local factors

Movement

Foreign bodies

Poor blood supply

Infection

Exposure to UV light facilitates healing

Exposure to ionizing

radiation

Systemic factors

Age

Nutrition

Systemic infection

glucocorticiods

Uncontrolled diabetes

Hematological abnormalities

Complications of wound healing

complications

Infection

Implantation cyst

Pigmentation

Deficient scar formation

Incisional hernia

Keloid formation

Excessive contraction

Neoplasia

Healing of oral wounds

Oral wounds heals faster and with less scarring

than extra oral wounds

It is mainly due to:

factors in saliva

specific microflora of the oral cavity

resemblance of fetal fibroblast with gingival

fibroblast

Role of saliva & GCF in oral wound healing

Physico-chemical factors favoring healing are: appropriate PH ionic strength calcium and magnesium ions

Saliva has an efficient capacity to reduce redox activity

caused by transitional metal ions and inhibit the

production of free radicals that may be beneficial for the

healing process

Lubrication of oral mucosa is beneficial for wound healing

Advantages of moist environment:

Prevention of tissue dehydration and cell death

accelerated angiogenesis

incremental breakdown of fibrin and tissue debris

Presence of growth factor – produced by saliva

Wound healing following various

periodontal therapies

Healing following scaling & root planing

Numerous polymorphonuclear leucocytes can be seen between

residual epithelial cells & crevicular surface in about 2 hrs

There is dilation of blood vessels, oedema & necrosis in the

lateral wall of the pocket

24 hrs after scaling a widespread infiltration of inflammatory

cells and migration of keratinocytes have been observed, in

all areas of the remaining epithelium& in 2 days the entire

pocket is epithlialized.

In 4-5 days a new epithelial attachment may appear at bottom of

sulcus.

Depending on the severity of inflammation & the depth of

the gingival crevice, complete epithelial healing occurs in 1-2

weeks

connective tissue repair by Immature collagen fibers occur within

21days.

healing occurs with the formation of a long thin junctional

epithelium with no connective tissue attachment.

Healing following curettage

A blood clot forms between the root surface & the lateral wall

of the pocket, soon after the curettage

Large number of polymorphonuclear leucocytes after the procedure

rapid proliferation of granulation tissue

Epithelisation of the inner surface of the lateral wall is completed

in 2-7 days

The junctional epithelium is also formed in about 5 days

Healing after surgical gingivectomy

Initial response- formation of a protective surface clot

Clot is then replaced by granulation tissue

By 24 hours there is an increase in new connective tissue cells,

mainly angioblasts just beneath the surface layer of inflammation and

necrosis

By the 3rd day numerous young fibroblasts are located in

the area which start granulation tissue formation.

The highly vascular granulation tissue grows coronally,

creating a new free gingival margin and sulcus

Capillaries derived from the blood vessels of the

periodontal ligament migrate in to the granulation tissue

and within 2 weeks they connect with gingiva vessels

After 5-14 days: surface epitheliazation is complete

During first 4 weeks: keratinization is less than it was

before surgery

Complete epithelial repair takes 1 month.

Complete repair of the C.T. takes about 7 weeks

Flow of GCF is initially increased after gingivectomy and

diminishes as healing progresses.

Healing following electrosurgical gingivectomy

There appears to be little difference in the results obtained after

shallow gingival resection with electrosurgery and that with

periodontal knives.

when used for deep resection close to bone, electrosurgery can

produce gingival recession, bone necrosis and sequestration, loss of

bone height, furcation exposure, and tooth mobility, which do not

occur with the use of periodontal knives.

Healing following depigmentation of gingiva

Healing after surgical depigmentation:

After surgery it was found necessary to cover the exposed lamina propria

with periodontal packs for 7 to 10 days.

After 6 weeks the attached gingiva regenerated by only a delicate scar

present. The newly formed gingiva was clinically non-pigmented.

Healing following cryosurgical depigmentation:

At 2nd to 3rd day: superficial necrosis becomes apparent and a whitish

slough could be separated from the underlying tissue, leaving a clean

pink surface.

In 1-2 weeks: normal gingiva

In 3-4 weeks: keratinization completed.

No postoperative pain, hemorrhage, infection or scarring seen in patients.

Healing following depigmentation by laser:

During lasing gingiva gets covered with a yellowish layer, that could

be easily removed by a wet gauze.

After 1-2 weeks: completion of re-epithelization.

At 4th week: gingiva is similar to normal untreated gingiva i.e.,

lacking melanin pigmentation completely

Healing following flap surgery

Immediately response- clot formation

At edge of flap numerous capillaries are seen

1-3days after surgery space between flap & tooth surface & bone

appears reduced & the epithelial cells along border of the flap start

migrating

By 1 week after surgery 

epithelial cells have migrated & established an attachment to root

surface by means of hemidesmosomes.

The blood clot is replaced by granulation tissue proliferating from

the gingival connective tissue, alveolar bone and periodontal ligament

By 2nd week collagen fibers begins to appear. Collagen fibers gets

arranged parallel to root surface rather than at right angles. The

attachment between soft tissue & tooth surface is weak

By end of one month following surgery the epithelial attachment is

well formed & the gingival crevice is also well epithealised

There is beginning functional arrangement of supracrestal fibres.

In cases where Mucoperiosteal flap…

superficial bone necrosis have been observed during first 3 days

Osteoclastic Resorption occurs in that area which reaches its peak at

4-6 days

Osteoblastic Remodelling occurs subsequently

Loss of alveolar bone height by about 1 mm may be expected after

healing.

Healing following osseous resection

Elevation of Mucoperiosteal Flap results in

temporary loss of nutrient supply to the bone

In addition, surgical resection of bone also

contributes to necrosis of the alveolar crest & osteoclastic resorption

of the bone takes place initially

The initial loss in bone height is compensated to some extent by the

osteoblastic repair and remodelling.

Thus final loss in bone height is clinically insignificant

Osteoblastic activity is even seen after 1 yr. post-operatively

Healing after implant placement

The interface area consists of bone, marrow tissue, and a hematoma

mixed with bone fragments from the drilling process.

In the early phase of healing, woven bone is formed by osteoblasts at

the surfaces of trabecular and endosteal cortical bone surrounding the

implant.

In the late phases of healing, lamellar bone replaces woven bone in a

process of creeping substitution.

Stages of healing of implants

a. Woven Bone Formation: When bone matrix is exposed to extra-cellular

fluid, non-collagenous proteins & growth factors are  set free & initiate

repair.

Woven bone formation dominates the first4-6 weeks

b. Lamellar Bone Formation: From 2nd month post-operatively the

microscopic structure of bone changes to lamellar bone

c. Bone Remodelling: It begins around 3rd month post-operatively.

Initially rapid remodeling occurs which slows down & continues for

rest of the life

Thus complete healing probably takes longer than 3 to 6 months.

Use of lasers in wound healing

Lasers employing low-level energy have been claimed to produce

a positive effect on the biological and bio-chemical processes of

wound re-constitution.

Dermatologic investigations have demonstrated more rapid

epithelialization, enhanced neovascularization, and increased

production of collagen by fibroblasts in vivo

Ultimately, accelerated wound healing, reduced pain and enhanced

neural regeneration.

conclusion

Current scientific evidence points to the presence of:

1. cells originating from the periodontal ligament,

2. wound stability,

3. space provision

4. primary intention healing, as fundamental biologic and clinical

factors that must be met to obtain periodontal regeneration.

Wound healing is achieved by a series of coordinated efforts by

inflammatory cells, keratinocytes, fibroblasts and endothelial

cells responding to a complex array of signals.

Future research will have to be directed towards understanding

in more detail the molecular mechanisms of differential gene

expression in healing wounds.

References Harshmohan, Textbook of essential pathology for dental students-3rd ed.

Jan lindhe, Textbook of clinical periodontology & implant dentistry -

F.A. Carranza, Textbook of clinical periodontology- 10th ed.

Lariha¨kkinen,Veli-jukka Uitto & Hannularj Av, cell biology of gingival

wound healing, periodontology 2000, vol. 24, 2000, 127–152.

Guy A. Catone, Edward Halusic. Photobiology of lasers in oral and

maxillofacial surgery. In: Guy A. Catone, Charles C. Alling. Lasers

applications in oral and maxillofacial surgery. USA: W.B. Saunders

company, 1997.