Myofibroblasts in healing laser excision wounds

BACKGROUND AND OBJECTIVE

The lack of myofibroblasts, cells responsible for wound contraction, has been suggested to be the underlying factor to the clinically observed minimal contraction in CO2 laser wounds. However, the histologic background to this phenomenon in laser excisions has not been thoroughly clarified. Therefore, we analyzed the expression of myofibroblasts in healing laser excisions and control excisions made by scalpel.

STUDY DESIGN/MATERIALS AND METHODS

CO2 laser (continuous wave, 5 W) or scalpel excision wounds were created in the dorsal tongue mucosa of 144 rats. Sixteen additional rats were kept as untreated controls. Specimens from the tongues were cut at 16 different healing time points and fixed in 10% formalin. Immunohistochemical stainings with monoclonal antibodies to vimentin and to alpha-smooth muscle actin were done to determine microscopically the contractile type of myofibroblasts.

RESULTS

The maximum amount of myofibroblasts was almost three times higher in scalpel than in laser excisions. The peak value was reached at 4 days in laser and at 3 days in scalpel wounds. The increase reverted to normal levels at 14 days in laser and at 6 days in scalpel wounds, respectively.

CONCLUSION

Myofibroblasts appeared and disappeared slower in laser wounds. There were clearly fewer myofibroblasts in CO2 laser than in corresponding scalpel excisions known to heal by contraction. The lack of contractile myofibroblasts, therefore, is suggested as the reason for the minimal degree of contraction in CO2 laser excision wounds.

Effect of snuff and smoking on tenascin expression in oral mucosa

We have shown, by using two monoclonal antibodies (143DB7 and 100EB2), that the expression of the extracellular matrix protein tenascin (Tn) is increased in the connective tissue of biopsies taken from snuff users' and tobacco smokers' oral mucosa. In normal oral mucosa Tn was seen to underlie the epithelium as a thin delicate band. The most increase in Tn reaction was observed in snuff users' mucosa while the immunoreaction in smokers' mucosa was less conspicuous. Often the most prominent Tn reaction took place in association with round cell inflammatory infiltration, indicating epithelial irritation. Tn has been shown to take part in epithelial-mesenchymal interactions during embryogenesis, wound healing and tumorigenesis. Here, a superficial epithelial irritant has been shown to cause conspicuous alterations not only in the epithelial cell layers but also in the underlying connective tissue by increasing its Tn content. As a result of our findings we suggest a further link for Tn in a dynamic epithelial-mesenchymal interplay by virtue of this marked connective tissue reaction in snuff users' and smokers' oral mucosa.

Effect of snuff on cytokeratin expression in oral vestibular sulcus epithelium

Differences in the expression of cytokeratins (CK) in specimens obtained from snuff-affected oral epithelium of the maxillary vestibular sulcus and clinically normal sulcular epithelium were studied by indirect immunofluorescence staining with a panel of monoclonal antibodies (MAbs). CK 14, a marker of stratified squamous epithelium was not seen expressed in 3/11 of the snuff user's specimens. Terminal differentiation markers, typical of cornified epithelia (CK 1, 9, 10 and 11), were detected suprabasally in the snuff user's keratosis but not in the normal control epithelium. The use of snuff seemed to change the CK staining pattern of the mucosa so that it resembles more that of a cornified type of epithelium. Simple epithelial-type CK were included in the study in order to establish the CK profile of the snuff-induced keratosis, for comparison with normal and dysplastic lesions. MAb to CK 7 and 19 showed reactivity in the basal cells and suprabasally whereas the monospecific MAb anti-CK 7 showed suprabasal staining both in the control and affected epithelia. By using MAbs, we found no immunoreactivity against CK 18 either in normal or affected epithelia, whereas we found suprabasal reaction (5/11) against CK 8 in the snuff user's epithelia. The two MAbs demonstrating the expression of CK 19, normally confined to the basal cells of the stratified squamous epithelium, showed variable patterns of expression both in basal cells and suprabasally in the snuff lesions. The results show that use of oral snuff causes some alterations in the CK expression pattern of the affected epithelium. Whether the alterations are indicative of a premalignant change is, however, uncertain. The results encourage further studies on the subject.

Transformation of hydroxyapatite to fluorapatite by irradiation with high-energy CO2 laser

High-energy laser irradiation has been shown to cause crystalline transformations in apatites, which may lead to the formation of tricalcium phosphates with a resulting decrease in acid resistance. Depending on the nature and energy density of laser irradiation used, however, an increase of acid resistance of dental enamel has also been reported after laser irradiation. The aim of the present study was to investigate the phase transformation of hydroxyapatite (HA) to fluorapatite (FA) in a model system that incorporates sodium fluoride (NaF) into apatite structure by using laser irradiation. A CO2 laser was used at energy densities ranging from 21 to 500 J/cm2. Synthetic HA mixed with NaF (10:1) was the target of laser irradiation. The crystalline structures were then investigated using X-ray diffraction analysis. The results showed that a phase transformation of HA to FA could be realized, and that the threshold energy density needed was 38 J/cm2. Not only is the finding crystallographically important, but it also opens new perspectives for future research regarding the development of laser technology for clinical purposes.

Tenascin expression in mucocutaneous diseases and related lesions of human oral mucosa

The expression of tenascin was assessed immunohistochemically. In normal oral mucosa, immunoreactivity for tenascin was seen either as a delicate line underlining the epithelium or in the stromal papillae. In oral lichen planus, a marked enhancement of tenascin immunoreactivity in the lamina propria was associated with focal infiltrates of inflammatory cells and seemed to reflect the intensity of inflammation. In lichenoid reactions in which only a sparse inflammatory infiltrate was present a band-like tenascin reactivity was seen. Oral psoriform reactions and chronic hyperplastic candidosis showed a prominent tenascin reaction in the connective tissue papillae among infiltrates of inflammatory cells. The results show that tenascin content is increased in oral mucocutaneous diseases and related lesions and that the abundance of tenascin reflects the intensity of the inflammatory reaction.

Lack of effect of hormonal treatment and smoking on cytokeratin expression in buccal mucosa

Differences in cytokeratin expression of clinically normal buccal mucosa were studied in 50 healthy women by indirect immunofluorescence staining with monoclonal antibodies. The subjects were divided into four groups: control group (N = 18), smokers (N = 8), oral contraceptive users (N = 8) and smokers receiving oral contraceptives (N = 16). Our findings indicate that cytokeratin expression in noncornified stratified epithelium is not influenced by smoking or oestradiol/progesterone treatment. Only cytokeratin No. 19 showed variable patterns of expression but the differences could not be ascribed to smoking or contraceptives. Cytokeratin No. 19 gave a positive reaction in the basal and suprabasal layers in 34 subjects (68%). In 9 (18%) specimens, the staining was positive in the basal cells and showed a positive heterogeneous cytoplasmic reaction in the suprabasal cells. Interestingly, cytokeratin No. 7 was recognized in all epithelial cells except the basal cells. Our results suggest that changes in the serum oestradiol levels do not affect the cytokeratin pattern in buccal mucosa.

Distribution of tenascin in oral premalignant lesions and squamous cell carcinoma

The distribution of the extracellular matrix (ECM) protein tenascin (Tn) was studied in oral premalignant lesions and squamous cell carcinoma by using the monoclonal antibody (Mab) 143DB7. In normal buccal and palatal mucosa, in ventral tongue, in floor of mouth and in gingiva, immunoreaction for Tn was seen to be distributed as a continuous thin, delicate line merely in the basement membrane region. Hyperkeratosis without dysplasia showed a distinct zone of enhanced Tn immunoreactivity immediately beneath the epithelium. In dysplasias of various degree, enhancement of the stromal Tn content could be observed, being most conspicuous in carcinoma in situ lesions. In most invasive carcinoma cases the Tn immunoreactivity was intense, extending deeply into the underlying stroma. In such lesions Tn-reaction often covered the total stroma. Notably, the strongest immunoreaction was seen at the advancing edges of the tumor. The triggering factor for stromal Tn enhancement seems to be of epithelial origin. The enhanced expression of Tn suggests that Tn plays a role in organizing and remodelling the stroma to support active epithelial proliferation and migration. However, it also seems that inflammation is associated with Tn expressions.

Healing of rat mouth mucosa after irradiation with CO2, Nd:YAG, and CO2-Nd:YAG combination lasers

The healing process of wounds made by a combination laser was studied in 90 rats. The laser system enabled both separate and combined use of CO2 and Nd:YAG laser irradiations. The laser wounds and the control excision wounds made by alligator forceps appeared on both sides of the tongue. Specimens from the wound sites were taken immediately, 6 h, and 1, 2, 4, 7, 11, 21, 28, and 42 days after surgery. The wound-healing process was studied by macroscopic evaluation before preparing the specimens for light microscopy. Some differences were noted in the wound-healing process among the three groups into which the experimental animals were divided. Tissue coagulation damage was most extensive in the Nd:YAG laser sites, where it was observed in its full extent 4 days after surgery. Epithelial cells were seen to begin to proliferate in all the wounds 6 h after surgery. Re-epithelialization was completed by between 7 (CO2) and 21 days (Nd:YAG) at all the wound sites. The inflammatory cell infiltration was more prominent in the Nd:YAG and the CO2-Nd:YAG combination laser wounds than in the CO2 and excision wounds during healing. Tissue regeneration occurred faster with less contraction in the combination CO2-Nd:YAG wounds than in Nd:YAG wounds. The best macroscopic healing result was seen in the CO2 wound sites. The combination laser was effective both at cutting and at coagulating tissue. Combining the CO2 and Nd:YAG laser irradiation into one beam resulted in a greater incision depth than what could have been expected from using the two lasers separately.

Distribution of tenascin in healing incision, excision and laser wounds

The distribution of the extracellular matrix glycoprotein, tenascin, was studied in normal mucosa and during healing of scalpel incised or excised and CO2 laser-wounded rat tongue dorsal mucosa in 51 male Sprague-Dawley rats over a period of 21 days. A polyclonal antibody specific for tenascin was applied in indirect immunofluorescence microscopy. In normal mucosa tenascin was sparsely distributed in a discontinuous manner at the tips of the connective tissue papillae in association with the basement membrane (BM) and in the walls of the capillaries. In all the healing wounds there was a marked increase in the distribution of tenascin, particularly close to the BMs at the wound edges beneath the proliferating and migrating epithelium, and later on during healing in the regenerating connective tissue (CT) area. This expression subsided later on during healing. Laser surgery did not alter the ability of fibroblasts to synthesize tenascin. The transient expression of tenascin in the BMs and CT of the healing wounds suggests that this protein could play an important role in providing ideal conditions for cell movement, and in the deposition and organization of other extracellular matrix (ECM) glycoproteins during tissue repair.

Effects of carbon dioxide, Nd:YAG and carbon dioxide-Nd:YAG combination lasers at high energy densities on synthetic hydroxyaptite

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J.cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 A and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. alpha-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of TCP.

Irradiation of human dental tissues with CO2-, Nd:YAG-, and CO2-Nd:YAG combination laser

Extracted third molars were used to study the effect of Nd:YAG laser irradiation combined with CO2 laser beam on dental hard tissues. The specimens were studied with SEM after lasing and the size of the impact areas and beam penetration into enamel and dentin were planimetrically analyzed. High-energy CO2 laser (e.g. 10 s irradiation with 10 W output energy) penetrated all enamel and dentin. The simultaneous addition of Nd:YAG irradiation to the CO2 beam was found to increase the effect of CO2 laser, while Nd:YAG irradiation alone, used with equivalent energy densities, did not cause any effect on enamel surface. Thus, Nd:YAG laser was found to potentiate statistically significantly the effect of CO2 irradiation, but the morphologic alterations on dental hard tissues, such as crater formation at the beam focus site, appeared to be due to CO2 irradiation alone.

Fibronectins in healing incision, excision and laser wounds

The distribution of extracellular matrix (ECM) glycoproteins, fibronectins (FNs), was studied in healing scalpel incision, excision and laser wounds of rat tongue dorsal mucosa over a healing period of 42 days by indirect immunofluorescence microscopy using mono- and polyclonal antibodies. A monoclonal antibody (Mab) DH1 was used to detect extradomain-A containing cellular fibronectin (ED-AcFN), and a polyclonal antiserum was utilized to recognize all forms of FNs. In normal tissue ED-AcFN was confined only to the endothelia of larger blood vessels whereas in healing wounds abundant immunoreactive deposits were found in regenerating connective tissue and endothelia of capillaries. The increased content of FNs revealed with both antibodies subsided later on during healing. The results suggest that the locally produced ED-AcFN is essential for tissue regeneration and plays a distinct functional role during wound healing. Laser treatment did not affect the ability of wound fibroblasts to synthesize and deposit cFN. The results provide further evidence that certain embryonic characteristics are seen in regenerating tissue.

Oral focal epithelial hyperplasia removed with CO2 laser

A case of oral focal epithelial hyperplasia (FEH) treated with CO2 laser surgery is presented. Histological diagnosis is discussed. The association of human papillomavirus (HPV) type 32 with the lesions is demonstrated with DNA in situ hybridization technique. Laser surgery is suggested as a treatment of choice.

Myofibroblasts in healing laser wounds of rat tongue mucosa

The distribution of myofibroblasts was studied in healing laser incisions compared with scalpel-incision and excision wounds in dorsal tongue mucosa and excision wounds in back skin. Myofibroblasts (m-f-b) were visualized by staining with NBD-phallacidin, a fluorescent probe specific for F-actin, and by electron microscopy. Few, randomly-orientated m-f-b were found in laser wounds over 28 days. Neither m-f-b nor contraction were seen in the scalpel-incisions. No contraction was observed in the laser wounds whereas an organized network of m-f-b with substantial contraction occurred in excision wounds. It is suggested that lack of contraction in laser wounds is partially due to the fewness of m-f-b. The residual connective tissue matrix resisting the laser treatment also seems to play a role in preventing the wound contraction.

Extracellular matrix in healing CO2 laser incision wound

Extracellular matrix components laminin, Type IV collagen, Type III collagen, and fibronectin, of laser-treated rat tongue mucosa were studied over a healing period of 28 days by using immunohistochemical and electron microscopic techniques. Their distribution and amount in laser wounds was compared with that in scalpel incisions and normal tongue mucosa. Laser treatment caused an extensive destruction of both epithelial and stromal cells but left much of the connective tissue matrix intact. Basement membranes, in particular, appeared to resist laser irradiation. During the study period the laser-induced lesions healed through reparative synthesis of matrix proteins which led to filling of the tissue defects. The regenerative processes with concomitant re-epithelialization took place more slowly in laser-treated than in scalpel incision wounds. The relative resistance of the matrix proteins against laser irradiation and the slow removal and replacement of the residual matrix is suggested to account at least partially for the lack of scarring and contraction frequently observed in laser-treated areas.

Healing of laser and scalpel incision wounds of rat tongue mucosa as studied with cytokeratin antibodies

The healing process of laser- and scalpel-incision wounds of rat tongue mucosa was investigated by the indirect immunofluorescence technique using a monoclonal cytokeratin antibody (PKK2) binding to low molecular weight keratins of basal keratinocytes, two antibodies reacting with suprabasal keratins and a monoclonal antibody reacting with desmosomes. The wounds were made parallel on both sides of the tongue in thirty animals. In normal tongue only the basal cell layer and the cells at the base of the rete ridges showed PKK2-positivity. In both types of wounds at the same healing phase the whole proliferative cell layer showed a bright PKK2-positivity. The cell proliferation appeared to be confined to all cells of the mucosa. The disturbance in the keratin expression of the healing mucosa could also be revealed with another monoclonal (58CH8) antibody, which reacted only with the suprabasal cells in normal tongue mucosa but lacked reactivity with the healing keratinocytes, whereas polyclonal antibodies to callus keratins showed a bright reactivity also in the healing keratinocytes. Monoclonal antibodies to desmoplakins indicated that the keratinocytes in both types of wounds had normal desmosomal cell-to-cell junctions. As the healing process advanced, the PKK2-positivity regressed to that seen in normal tongue mucosa.

A comparative study of healing of laser and scalpel incision wounds in rat oral mucosa

Capillary proliferation and inflammatory cell infiltration were evaluated in healing laser and scalpel incision wounds in rat tongue mucosa in 22 Sprague-Dawley rats for a period of 28 days. The incisions were made in parallel on both sides of the midline of the tongue. Specimens for immunohistochemical and histologic examination were taken immediately, 6 h, 2, 11, and 28 days after the surgery. The microscopic inspection of the sections stained immunohistologically for factor VIII-related antigen, a marker for endothelial cells, suggested a smaller amount of capillaries immediately and during the early healing phase in the vicinity of the laser incisions when compared with the scalpel incisions. The proliferation of capillaries during healing was also retarded at the lasered sites. The microscopic inspection of the histologic specimens showed that the inflammatory cell infiltration appeared slower but was more prominent in the healing laser wounds than in the healing scalpel incision wounds.

Laser-induced alterations in rat oral mucosa

The alterations during healing in laser and scalpel incised palate and tongue mucosa were studied in 37 Spraque-Dawley rats by taking specimens for light and electron microscopic inspection immediately and 4, 7, 11 and 21 days after the treatments. The laser incision differed from the conventional incision: it was horizontally broader, more superficial, not bleeding and contained some charred and necrotic tissue particles; there were more inflammatory cells during healing, and the healing was slightly retarded. The damaged area around the laser incision was very narrow. In EM, the lasered areas showed total cell disruption with no morphologic details seen at the treated site. Adjacent to those sites, charred-appearing particles were seen scattered and embedded also in the connective tissue. The most resistant cell organelles against laser-caused disruption were desmosomes and nuclear membranes. After 21 days' observation the ultrastructural study still revealed cell damage even though the reepithelialization as such seemed to be complete.

Study of titanium screws as retrograde fillings using bacteria and dye

The tightness of retrograde titanium screw fillings and retrograde amalgam fillings was compared in 17 human, single-rooted teeth using Serratia marcescens bacteria in vitro. The root canals were subjected to instrumentation and irrigation, after which 2 mm was cut off from the apical end. Eight of the teeth were sealed using retrograde titanium screw fillings and nine using retrograde amalgam fillings. The teeth were suspended by means of wires in test tubes, with the crowns upwards and the roots immersed in trypticase soy broth. Suspensions of Serratia marcescens bacteria were placed in the root canals, and samples from the broth were plated daily. The bacteria penetrated the apical titanium screw seals in 2 to 7 days, and the retrograde amalgam fillings readily on the first day. Thus, the titanium screws seemed to provide a tighter seal. Staining with India ink showed that penetration had occurred at the tooth-filling margin and that the instrumentation had not caused any fractures to the roots.