KIGALI HEALTH INSTITUTE (KHI) DENTAL DEPARTMENT WORK PRESENTATION GROUP N º 2

WOUND HEALING

DEFINITION A wound is an interruption of the continuity of the skin surface or of any epithelial surface of the body. CLASSIFICATION Wounds may be classified in a number of ways. The following four classification methods may be used.

Classification according to the continuity of the skin: Closed wounds: These are wounds in which there is no interruption of the continuity of the skin or epithelial surface, however the underlying tissues are damaged. Open wounds:In these cases the continuity of the skin is interrupted and the underlying tissues are damaged.

Classification according to the cause: Intentional wounds: These are surgical wounds that are generally inflicted under sterile or surgically clean conditions. Tissues damage is limited as far as possible. Accidental wounds: These are generally result of some form of trauma.

Classification according to the presence or absence of pathogens Clean wounds: These are inflicted under aseptic conditions and therefore a minimum of pathogens are present. Contaminated wounds: Occur in circumstances under which pathogens will probably penetrate the wound and underlying tissues. Infected wounds: Are those in which infection is present due to the successful penetration of pathogens.

Classification according to type or nature of the wound Incision wounds Abrasion wounds Contusion wounds Laceration wound Puncture wounds Penetrating wounds Perforating wounds Pressure sore wounds Hyperthermic wounds Chemical burns Electrical burns Hypothermic burns Radiation Malignant wounds Arterial ulcers Venous ulcers

REACTION TO INJURY-THE PHYSIOLOGY OF WOUND HEALING The healing commences with an inflammatory reaction and ends with the formation of scar tissue. During the healing process changes occur in the cell types of the wound. These process may be described in four stages as follow:

The INFRAMMATORY PHASE This is the commencing stage and displays all the features of inflammation usually associated with infection. In these case however there is no infection because the inflammatory reaction is part of normal healing. It has three important functions namely to dilute toxins, to flood the area with nutrients and to destroy bacteria by phagocytosis. These processes are brought about as follows:

Vasoconstriction of the small blood vessels takes place at the site of the injury. The platelets adhere to the walls of the blood vessels and to the edges of the cut or injured blood vessels. The platelets react with subendothelial substances resulting in the further platelets activity and clotting. Other blood cells are incorporated in the clot, which is then stabilised by fibrin. The clot or thrombus now seals the blood vessel.

The damaged tissues release enzymes, especially histamine. These cause further vasoconstriction which give the area a pale appearance. After the initial vasoconstriction, histamine and other enzymes cause vasodilatation of the surrounding capillaries, giving the area a red appearance. The capillaries become more permeable and serum and white blood corpuscles(leucocytes and macrophages) infiltrate the area surrounding the injury, with consequent swelling.

DESTRUCTIVE PHASE This is another very important stage in the process of healing. The most important feature of this stage is the removal of attenuated tissue and bacteria to make room for new tissue formation. This happens as follows:

The white blood cells especially neutrophils and macrophages, play a key role by engulfing tissue and bacteria. The macrophages lure fibroblast to the area.(Fibroblasts are the cells that manufacture new tissue). New blood vessels grow from the periphery of the wound towards the middle.

PROLIFERATION PHASE The most important characteristic of this stage is enhanced cellular activity, reading to the formation of granulation tissue. Granulation tissue consists of new capillaries supported in a matrix of collagen fibres. This happens as follow:

Endothelial cells grow into the area cleared by macrophages. Fibroblasts enter the area and produce collagen which is the most important structural protein in the body. The fibroblast must be stimulated to produce collagen and the best stimulant is a slightly acid environment. The most important stimulators of fibroblast are vitamin C and lactate ions. These substances collect in the areas with a low oxygen concentration, as in the middle of the wound.

As the proliferation phase continues, the number of capillaries and fibroblasts are reduced to normal revels. The tensile strenght (the strenght required to tear the wound edges) of the wound edges gradually increases. To protect the new fibres, it is important to ensure that the wound edges move as little as possible.

MATURATION PHASE In this phase the deep pink granulation tissue Changes to the pale, avascular tissues known as scar tissue.  The vascularity of the area diminishes.  The number of fibroblast is reduced.  The collagen fibres become enlarged and are rearranged along the tension line of the wound (at right angles to the wound edges)

The scar tissue gradually flattens and become softer Scar tissue never regains structure of the original tissue. It remains weaker than normal tissue and has a thinner epithelial layer.

Ctn… The four stages described above are the physiological stages of wound healing. Two other very important processes, namely contraction and epithelisation, also take place, especially in the presence of tissue loss or destruction, for instance in the case of burns.

CONTRACTION This is the process by which the size of any open wound is diminished without being closed by sutures of skin grafting. This happen as follow:  Collagen is not required.

The stimulating force for contraction is obtained from a cell, and any thing that interferes with cellar viability in the wound edges will inhibit the process. The surrounding skin grows inwards. The growth of new blood vessels at the wound edges is essential.

EPITHELISATION The skin surface consist of pavement epithelial cells. This layer is continually discarded and replaced from below. When an injury takes place, epithelial cells at the edges of the wound proliferate and begin to migrate over the wound. Due to the fact that epithelial cells can only migrate over living or viable tissue, they move to layers under the scab, tissue debris or blood clot.

A dressing is indicated for optimum result because moist condition promote the process.

SUMMARY OF WOUND HEALING STAGENATUREEXPLANATION Stage 1 Stage 2 Stage 3 Stage 4 Inflammatory Destructive Proliferation Maturation Vasoconstriction, platelet activity, clot formation. Removal of attenuated tissue. Neutrophils and macrophages are active. New blood vessels grow from wound edges. Active fibroblasts. Formation of granulation tissue. Reduced vascularity. Scar formation

TYPES OF WOUND HEALING It is generally accepted that three types of wound healing occur:  First intention (Primary closure)  Second intention (Secondary closure)  Third intention (Tertiary closure)

First intention This is desirable for all wounds, but takes place only when there has been no loss of tissue and in cases where the wound edges can easily be approximated by sutures or other material, for instance strips of adhesive tape. Healing takes place with a minimum of granulation tissue and is rapid if no complication, such as infection or gaping of the wound edges, set in.

Second intention This type of healing generally occurs in large, open wounds, where there has been damage to or loss of tissue. Healing takes place by granulation from the base of the wound. The process is slow and produces more scar tissue. Burns and pressure sores are examples of wounds in which this type of wound healing takes place

Third intention This term is used to describe a wound that is surgically closed a few days after injury. It is also known as retarded primary closure. This method is used for wounds that can not be closed immediately after injury due to severe contamination.

Cells of Wound Healing Platelets – Aggregate to form clot – Release growth factors and cytokines – Activate coagulation pathway – Chemoattractant for neutrophils and fibroblasts

Neutrophils – Role in phagocytosis and wound debridement Macrophages – Complete phagocytosis and wound debridement – Major secretor of cytokines and growth factors – Involved in angiogenesis, fibroplasia, matrix synthesis Monocytes

Fibroblasts – Release cytokines and growth factors – Chemoattractant – Synthesizes proteogylcans and fibronectin to create matrix – Transforms to myofibroblasts to contract and close wound

Keratinocytes – Directed by fibroblast release of KGF-1 and -2 – Proliferate, migrate and differentiate into epidermis Endothelial cells – Involved in angiogenesis Lymphocytes

Factors Affecting Wound Healing Local factor  Ischemia  Infection  Foreign bodies  Edema General factors  Age  Obesity  Smoking  Alcohol intake Systemic factors  Cardiovascular disease  Respiratory disease  Adequate blood oxygenation  Metabolic disease  Endocrine disease  Renal failure  Hepatic failure

Nutrition and Wound Healing Factors affecting healing  Changes in energy, CHO, protein, fat, and vitamin mineral metabolism Ex. Loss of protein Decreases wound tensile strength Injury increases  Metabolic rates  Catecholamine levels  Loss of total body water  Cellular protein turnover

Nutrition and Wound Healing  Wounds require energy for collagen synthesis  Protein deprivation  Impairs healing  Impaired collagen synthesis/degradation  Increased rates of infection  Micronutrients  Essential to cellular function Ex. Magnesium  cofactor to enzymatic activity in protein and Collagen synthesis Ex. Zinc  cofactor to RNA/DNA polymerase  Involved in DNA, protein synthesis  Involved in cell proliferation

Nutrition and Wound Healing  Vitamins  Vitamin C Deficiency leads to:  Decreased collagen deposition, angiogenesis  Hemorrhage  Increased infection

Nutrition and Wound Healing  Vitamin A  Enhances inflammatory response  Vitamin E  Stabilizes cell membrane  Antioxidant  Anti-inflammatory agent

COMPLICATIONS OF WOUNDS Some complications of wounds are summarised in the table below: COMPLICATIONEXPLANATION Pain Haemorrhage Pain should diminish as the wound heals. If this does not happen it may be an indication of infection. Primary – at the time of the injury is normal. Secondary- usually due to infections. Occurs 7 to 10 days after injury or surgery.Haematoma (a blood clot in the wound) may retard healing.

COMPLICATIONEXPLANATION Infection Contractures Inability to heal Keloid formation The inflammatory response is normal. Infection may, however, occur. The wound will be red, swollen and tender, and there may be a purulent discharge. The temperature and pulse will be elevated. May occur in injuries over joints. The scar tissue contracts and the joint remains immobile in flexion. Local causes- infection, haematoma, poor blood supply, tension in the wound. Systematic factors- for instance diabetes, anaemia, mal nutrition and carcinoma. Excessive thickening of a scar.