Healing of Oral Wounds
The word healing refers to replacement of damaged tissue by living tissue to restore function. Healing of wounds is one of the most interesting phenomenon which characterizes a living organism. Some insects, amphibians and crustaceans possess the remarkable ability to replace lost parts. The ability of damaged tissue to repair itself is a response of life itself. It is said that an unhealed wound will eventually result in the death of an organism. Therefore, wound healing must be considered as one of the primary survival mechanisms from birth onwards. It should be clearly understood that the healing of a wound is not an isolated, solitary phenomenon but actually a very complex series of biological events.
Healing is a process not an incident. It consists of wound contraction ascribed at least in part to myofibroblasts, (altered fibroblasts with characteristics of smooth muscle cells ultrastructurally). This contraction causes reduction in the size of the wound in the first few weeks and replacement of lost tissue, brought about by division and migration of neighboring cells. Replacement of the lost tissue by granulation tissue is known as ‘repair’ which results in scarring, and replacement by similar type tissue is known as ‘regeneration’.
Healing of tissue is generally considered to be a phase of the inflammatory reaction, since it cannot be separated from the preceding vascular and cellular phenomena occurring in response to an injury. Where the edges of the wound are approximated, the healing process is fast and is known as healing by first intention or primary healing. When there is tissue loss, and wound edges cannot be apposed, the wound contracts to reduce the size, granulation tissue fills the wound and epithelialization occurs across the wound surface. This is called healing by secondary intention. Granulation tissue is characteristically bright pink in appearance and is composed chiefly of proliferating capillaries and fibroblasts.
Various growth factors and cytokines play a significant role in healing. The epidermal growth factor, produced by the epithelium around the damaged area, helps in the regeneration of the epithelial tissue. Macrophages liberate fibroblast growth factor, which mediates fibroblast activity along with transforming growth factor-α. Endothelial growth factor triggers the formation of new blood vessels.
Oral wounds are common, some sustained accidentally (e.g. jaw fractures), some inflicted by the dentist for a specific purpose (e.g. extraction wounds, biopsy wounds, etc.) and others caused by disease process (e.g. various oral ulcers). The unusual anatomic situation of the oral cavity—the teeth protruding from the bone, the constant inflammation present in the gingival tissues, the presence of countless microorganisms in a warm, moist medium of saliva — all contribute to modify the healing reaction of the various wounds.
A number of factors influence the healing process of wounds in the oral cavity. Although interference with the normal healing phenomena is not a common occurrence, the dentist must recognize the possible causes.
The particular location of a wound is important, as it may modify the rate of healing. Wounds in an area with a good vascular bed heal considerably more rapidly than wounds in an area which is relatively avascular.
Immobilization of the wound is also important in the healing reaction. If the wound is in an area subjected to constant movement so that formation of the new connective tissue is continuously disrupted (e.g. in the corner of the mouth), it will result in delayed healing. Immobilization is particularly important in the healing of bone fractures, for without it bony union may be delayed or even completely inhibited, resulting in fibrous union.
Severe trauma to tissue is an obvious deterrent to rapid wound healing. Under certain situations, however, mild traumatic injury may actually favor the healing process. For example, it is well recognized that a second wound inflicted in the site of a healing initial wound, heals more rapidly than the initial or single wound.
Local temperature in the area of a wound influences the rate of healing, probably by its effect on local circulation and cell multiplication. Thus, in an environment of hyperthermia, wound healing is accelerated while in hypothermia healing is delayed.
The effect of X-ray radiation on the healing of wounds has been extensively studied, and the data indicates that generally low doses of radiation tend to stimulate healing, while large focal doses of radiation or total body radiation tend to suppress healing.
Protein is one of the most important substances, which may influence the speed of wound healing. Numerous clinical studies have indicated that poorly nourished patients with low protein intake resulting in a protein deficiency, manifested by a hypoproteinemia, exhibit a delay in the appearance of new fibroblasts as well as a decreased rate of multiplication of fibroblasts in wounds. Conversely, it has been shown that feeding high protein diets to animals will increase the rate of fibroblastic proliferation and cause wounds to heal more rapidly. The exact manner in which protein influences the wound is not known, although there is considerable evidence that this effect is related to dietary compounds containing free sulfhydryl groups. Of all the essential amino acids, only methionine furnishes such a group, and studies have shown that administration of methionine to hypoproteinemic animals restores the rate of wound healing to a normal level.
Vitamins are another group of nutritional factors related to wound healing. One of these, which has been known for many years to influence the rate of wound healing, is vitamin C or ascorbic acid. It acts through regulation of collagen formation and formation of normal intercellular ground substance of the connective tissue. It appears that, in scurvy or ascorbic acid deficiency, this inhibitory effect on wound healing is specifically related to interference with the production of mucopolysaccharides, which make up the cement substance. Microscopically, it is recognized that fibroblastic proliferation in a wound of a scorbutic animal continues longer than in control animals. This is interpreted to mean that there is prolonged need for formation of connective tissue, and this is borne out by the fact that scorbutic animals exhibit a decreased tensile strength of the healing wounds.
There have been no extensive studies on the possible role of vitamins A and D in wound healing, but the available reports indicate that a vitamin A deficiency retards healing and that vitamins A and D, as in cod liver oil, may be factors in promoting tissue repair. The available studies indicate that riboflavin and pyridoxine deficiencies result in delayed healing process.
Wounds in younger persons heal considerably more rapidly than in elderly persons, and the rate of healing appears to be in inverse proportion to the age of the patient. The cause for this is unknown, but probably relates to the general reduction in the rate of tissue metabolism as the person ages, which itself may be a manifestation of decreased circulatory efficiency. Also at the molecular level, slowing of protein synthesis and formation of structurally altered protein, affects healing.
Wounds which are completely protected from bacterial infection heal considerably more slowly than wounds which are exposed to bacteria or other mild physical irritation. Furthermore, Lattes and his coworkers showed that bacterial infection of wounds suppressed the cortisone-inhibitory effect on fibroplasias in the experimental animal. Some studies on germ free animals with experimental wounds, primarily incised and closed, have shown a reduction in tensile strength, as compared to control animals, thus indicating that the germ free state is a deterrent to wound healing.
It is obvious, however, that severe bacterial infection slows the healing of wounds. In view of the vast bacterial flora of the oral cavity, one might question whether all wounds of the oral cavity are not heavily infected. Since the antibody titer of a person against his/her own microorganisms is usually extremely high, there is seldom cause to worry about infection from autoinoculation. Occasionally, however, the resistance of the tissue is decreased, either locally or on a systemic basis, and an oral wound becomes massively infected and heals slowly, if at all.
Adrenocorticotropic hormone (ACTH) and cortisone are substances that have been repeatedly shown to interfere with the healing of wounds. Not long after ACTH and cortisone were first used clinically, it was noted that wounds in recipients of these compounds exhibited delayed healing. Since this observation, a number of careful experimental studies were carried out in which it was shown that, in patients receiving ACTH or cortisone, the growth of granulation tissue was inhibited, apparently because of inhibition of proliferation of new fibroblasts and new endothelial sprouts and because of a depression of the inflammatory reaction. There is apparently not an actual suppression of mesenchymal activity, but rather a delay in the mesenchymal reaction. An experimental study by Shafer on the healing of extraction wounds in rats receiving cortisone showed that the healing of such wounds was delayed. This would suggest that patients under long time steroid therapy or with Cushing’s syndrome, should be carefully evaluated by the dentist before he or she carries out oral surgical procedures.
Numerous investigators have also studied the effects of administration of pituitary growth hormone and thyroid hormone (thyroxin) and concluded that these had no significant role in wound healing. The opposite situations, obtained by surgical ablation of the pituitary gland and thyroid gland, have also been reported as having no significant effects on wound repair. There is one interesting experimental study in the literature, which shows that wound healing was delayed during pregnancy, but this has not been confirmed clinically.
Diabetes mellitus (insulin deficiency) is one of the most widely recognized diseases in which there is significant, clinically evident retardation in repair of wounds after surgical procedures, including tooth extraction. Wounds in diabetic patients are notoriously slow to heal and frequently show complications in the repair process. The exact mechanism of this phenomenon is not known, but is probably related to disturbance in carbohydrate metabolism at the cellular level in the local area of the wound. Because of this recognized relation of insulin deficiency to wound healing, a number of investigators have studied the effect of administration of insulin to normal animals (hyperinsulinism), but the reports are indecisive on its influence on wound healing. Nevertheless tissue culture studies have almost invariably shown stimulation of fibroblastic proliferation when insulin was added to the growth medium.
Other factors include enzymes, such as trypsin, streptokinase, alkaline phosphatase, and coenzyme adenosine 5-monophosphate, growth-promoting factors such as cartilage and mucopolysaccharide, N-acetyl-D-glucosamine, tissue extracts and pantothenyl alcohol, hydroxyproline, hydrogen ion concentration, electrolyte balance, therapeutic agents such as dilantin sodium, sulfonamides and antibiotics, anticancerous drugs which inhibit cell cycle or kill the cells involved in active proliferation, immunosuppressive drugs, anticoagulants such as heparin and dicumarol, emollients, sclerosing agents, metals, particularly trace elements such as zinc, copper, and deuterium oxide, antigen-antibody reactions, and lathyrism.
The effects of suture materials on healing of skin wounds also have been studied by many investigators. A large comparative study in dogs was reported by Van Winkle and his coworkers, who concluded that, there were no differences in healing among wounds closed with different suture materials up to a postoperative period of about one month. However, on a more long-term basis, they found that wounds sutured with nonabsorbable sutures were weaker than those sutured with absorbable ones and that, in general, there was a lower incidence of wound infection with monofilament sutures than with multifilament sutures. However, in some findings these investigators noted that, when compared with other similar studies, there were species differences, and they cautioned against direct application of such observations to a human patient.
Use of tissue adhesives such as butyl and isobutyl cyanoacrylate have been studied by many investigators. These may serve as an alternative for sutures in wound closure and are widely utilized in surgical procedures involving numerous organs. These adhesives, have also been applied to a variety of surgical procedures of the oral cavity.
Bhaskar and Frisch have reviewed the use of cyanoacrylate adhesives in dentistry, concluding that butyl cyanoacrylate is not only well tolerated by tissues and permits uncomplicated healing but also generally hastens the healing process. It has been successfully tested as a surface dressing after gingivectomy, on mucoperiosteal flaps, biopsy sites, extraction wounds, aphthous ulcers, leukemic ulcerations, pulp capping, and in the grafting of mucosal tissues from one region of the mouth to another.
It may be concluded that the repair of damaged tissue is a vital dynamic process, which may be influenced by a multitude of exogenous and endogenous factors. That alteration in this process does not occur more frequently than it does is proof of the inherent resistance of the living organism to those factors, which could interfere with perpetuation of life. In certain instances this resistance is diminished, and pathologic alterations in the repair phenomenon occur. The factors that may be responsible for this unfortunate occurrence must be recognized and understood so that proper measures may be taken to correct the problem.
Wounds may provide a portal of entry to microorganisms. Infections of the wound delay the healing process. It is a common phenomenon in maxillofacial trauma cases. Most of the times, the oral wounds heal without this complication, but at times the underlying systemic conditions such as diabetes mellitus, immunosuppressive state, etc. make the individual prone to infections.
Hypertrophic scars occur in wounds where healing is delayed. These hypertrophic scars are more cellular and vascular. The remodeling phase in these scars is prolonged; and the imbalance between collagen production and disintegration leads to excess of collagen in these scars. Clinically they appear red, raised, itchy, and tender. They become pale and flat as they mature. Spontaneous resolution may occur in time and this distinguishes them from keloid.
These are common in healing of wounds on the skin and may appear as hypopigmented or hyperpigmented areas. Though hypopigmented scars are not common in the oral cavity, some lesions leave hyperpigmentations while healing (e.g. lichen planus, lichenoid reactions, etc.).
Inflammation of the pulp does not always result in pulpal necrosis. Resolution occurs in a considerable number of cases. Healing of pulp is the common outcome of pulpal inflammation in clinical conditions. But nevertheless, it depends on the degree of infection, inflammation, amount of the pulpal tissue involved, and the age of the patient. If the carious cavities are thoroughly cleaned and restored with suitable materials, the abscesses heal by reparative dentin formation. Pulpal inflammation might even resolve, in teeth with carious lesions remaining, with the formation of sclerotic dentin, which reduces the permeability to bacteria and bacterial products. In some cases, the healing occurs by localized fibrosis.
Healing of periapical lesions may result in the formation of new bone or fibrosis in the involved area. In periapical lesions treated surgically, there is an outgrowth of fibroblasts and capillaries from the surrounding healthy connective tissue. Slowly this granulation tissue fills the entire defect. Osteoblasts appear in the granulation tissue towards the deeper portion adjacent to the healthy bone, and the granulation tissue is gradually replaced by bone in the course of time.
Biopsy is the removal of tissue from the living organism for the purposes of microscopic examination and diagnosis. Although the diagnosis of many lesions can be made clinically by the dentist with experience, such a diagnosis is generally a provisional one, contingent upon the final report on the tissue specimen by the pathologist. Biopsy not only helps in the diagnosis but also serves as a treatment option for smaller lesions by excising in toto, though few lesions do not present a specific microscopic appearance. Nevertheless, the biopsy procedure helps in the treatment plan. Although the microscope in the hands of a qualified pathologist is an irreplaceable diagnostic tool, its limitations must always be kept in mind. Fortunately, with the rapid advancement occurring in scientific techniques adaptable to microscopic diagnosis, such as histochemical techniques, fluorescent microscopy, microradiography, histoautoradiography, transmission and scanning electron microscopy, and so forth, this sphere of diagnostic limitation is gradually shrinking.
Total excision of a small lesion for microscopic study is called excisional biopsy. The pathologist will usually be able to tell the operator whether the lesion was removed in entirety by observing the appearance of the tissue along the line of excision. Excisional biopsy is preferred, if the size of the lesion is such that it may be removed along with a margin of normal tissue and the wound can be closed primarily.
Some lesions are too large to excise initially without having established a diagnosis, or are of such a nature that excision would be inadvisable. In such instances, a small piece is removed for examination. This is termed an incisional or diagnostic biopsy (Fig. 14-1). It is most useful in dealing with large lesions, in which the operator suspects may be treated by some means other than surgery once the diagnosis is made, or lesions in which the diagnosis will determine whether the treatment should be conservative or radical.
Figure 14-1 Epidermoid carcinoma, diagnostic biopsy.
An adequate border of normal mucosa was obtained with the biopsy of the neoplastic mass, and no attempt was made initially to excise the lesion completely.
Needle biopsy has little value in the diagnosis of oral lesions. The scalpel is the instrument of choice, since it cleanly removes the tissue and does not dehydrate it as cautery or the high-frequency cutting knife may. This latter instrument is of great value, however, in dealing with vascular lesions, where it controls bleeding at the biopsy site.
Biopsy technique is a simple procedure and may be carried out by any dentist as a routine clinical procedure if certain precautions are taken and certain rules are followed. The advantages of a biopsy so far outweigh its disadvantages or potential dangers that the biopsy is seldom, if ever, contraindicated in case of a lesion in which the diagnosis has not been established. To ensure obtaining a proper specimen for the pathologist, the following points must be considered:
The report of a biopsy is usually returned to the operator by the pathologist within a few days unless some special procedures, such as decalcification of tooth, bone or other calcified substance or application of special stains, are necessary.
A negative biopsy report or a histopathological diagnosis not in conformity with the expected diagnosis should never be considered final. It means only that there are no features to suggest the expected diagnosis in that particular piece of tissue, which was removed at that particular time. A repeat biopsy should always be performed when there is any doubt about the adequacy or representative nature of the original specimen.
The healing of a biopsy wound of the oral cavity is identical with the healing of a similar wound in any other part of the body and thus may be classified as either primary healing or secondary healing. The nature of the healing process depends upon whether the edges of the wound can be brought into apposition, often by suturing, or whether the lesion must fill in gradually with granulation tissue.
Primary healing, healing by primary intention or healing by first intention is healing that occurs after the excision of a piece of tissue with the close apposition of the edges of the wound by sutures. This is the form of healing one might expect after the excision of a lesion in an area of the oral cavity where the pliability of the tissues is such that the wound may be drawn together and sutured.
When the edges of the wound are brought into contact and held in place by sutures, the blood clots, and in a matter of hours numerous leukocytes are mobilized to that area. Connective tissue cells in the immediate vicinity undergo transformation into fibroblasts, which in turn undergo mitotic division, and the new fibroblasts begin to migrate into and across the line of incision. In time, these cells form thin, delicate collagen fibrils, which intertwine and coalesce in a general direction parallel to the surface of the wound. At the same time, endothelial cells of the capillaries begin to proliferate, and small capillary buds grow out and across the wound. These buds eventually form new capillaries, which fill with blood, and a rich network of young capillaries and capillary loops are formed.
When there is a close apposition of the edges of the wound, the surface epithelium proliferates rapidly across the line of incision and re-establishes the integrity of the surface. The delicate connective tissue fibrils eventually coalesce into denser bundles and usually contract, so that in time all that is left to indicate the biopsy area is a small linear scar which may be depressed below the surface. Because there is no defect which must be filled with new tissue, this type of wound heals rapidly (Fig. 14-2).
Secondary healing, healing by second intention, healing by granulation or healing of an open wound occurs when there is loss of tissue and the edges of the wound cannot be approximated. Healing of this type is often spoken of as a process in which the wound ‘granulates in’ since the material, which fills the defect during the healing process, is called granulation tissue. This type of wound is a result of biopsy of a lesion in an area of the oral cavity in which the tissues are not pliable and in which the edges cannot be approximated. For example, removal of a lesion of the palate or a large lesion of the alveolar ridge is usually followed by healing by second intention, since the edges of the wound cannot be coapted.
After the removal of the lesion, the blood fills the defect, clots and the repair process begins. It is basically identical with healing by primary intention except that the fibroblasts and capillaries have a greater distance to migrate; more granulation tissue must form, and of necessity the healing is slower. Cellular proliferation begins around the periphery of the wound, and the fibroblasts and endothelial cells grow into the clot along fibrin strands. In addition, polymorphonuclear leukocytes, and later, lymphocytes, and mononuclear phagocytes migrate into the granulation tissue from the adjacent vessels and tissues. Large numbers of leukocytes also accumulate on the surface of the wound. As the granulation tissue matures, it becomes more fibrous through condensation of collagen bundles, and the surface of the granulation tissue becomes epithelialized. As in primary healing, the collagen fibrils coalesce and the lesion becomes somewhat less vascular, and eventually the only evidence of the wound may be a small depressed area of the mucosa.
Exfoliative cytology is the study of cells which exfoliate or abrade from the body surfaces. The rationale for exfoliative cytology lies in epithelial physiology. Normal epithelium undergoes exfoliation of its superficial cells due to physiological turnover. The cells of the deeper layers are adherent to each other normally. When the epithelium becomes seat of any pathological condition, the cells may lose their cohesiveness, and cells in the deeper layer may shed along with the superficial cells. These exfoliated cells as well as cells which are scrapped off by means of specific instruments, can be studied quantitatively or qualitatively. Considerable interest has developed in the use of exfoliative oral cytology for the diagnosis of oral mucosal lesions (Fig. 14-3). Application of cytodiagnosis as a routine procedure in the detection of cervical cancer was introduced by George N Papanicolau in 1941. Its application in oral cancer has been known for a long time. In a review of the historic background of oral cytology, von Hamm cited numerous series of cases of patients with oral cancer in which the diagnostic accuracy of cytologic smears was compared with that of the surgical biopsy and was found to be almost identical. He concluded that:
The preferred technique is a relatively simple one. It consists essentially of cleansing the surface of the oral lesion of debris and mucin, and then vigorously scraping the entire surface of the lesion several times with a metal cement spatula, a moistened tongue blade or a cytobrush. The collected material is then quickly spread evenly over a microscopic slide and fixed immediately before the smear dries. The fixative may be either, a commercial preparation such as Spray-cyte, 95% alcohol, or equal parts of alcohol and ether. After the slide is flooded with the fixative, it should be allowed to air-dry for 30 minutes. Slides are never flame fixed as bacteriologic smears. It is essential that the procedure be repeated and a second smear be prepared for submission to the cytologist. In preparing the duplicate slide, a separate scraping should be utilized. Two smears are always submitted from each lesion, since additional staining techniques are frequently employed.
Though exfoliative cytological study has a significant role in cancer diagnosis, it has its own limitations. The presence or extent of invasion cannot be assessed. It should be remembered that the majority of benign lesions that occur in the oral cavity do not lend themselves to cytologic smear. For example, lesions which have a normal appearance and an intact surface, such as a fibroma, should be excised and never smeared. In addition, most authorities agree that leukoplakia does not lend itself to cytologic diagnosis because of the scarcity of viable surface cells in the smears taken from such lesions. Finally, it should be remembered that a negative cytology report does not rule out cancer and that a repeat smear or biopsy is indicated in all clinically suspicious lesions.