P.A. van Damme
Subperiosteal palatal soft tissue expansion. An experimental study in growing domestic cats.
A scientific essay in Medical Sciences
DOCTORAL THESIS defended in public on 6th of December 1996
In this thesis an animal study is described on the feasibility and the effects of palatal mucoperiosteal soft tissue expansion (TE) in growing cats. This application and its results are related to clinical human cleft palate repair. The main idea was to develop a technique to close palatal defects and oronasal communications in an easier or better fashion than the wellestablished ones, by gaining tissue from the direct surroundings, without creation of a donor site defect, and with less negative effects on growth and development of the dento-maxillofacial complex. The effects of TE in scarred and non-scarred tissues were compared.
Chapter 1 is an introduction which reviews the problems of cleft lip, alveolus and palate deformity. The cleft related oronasal communications are to be closed to improve nutrition, respiration, speech and hearing, and dental arch development. The necessary operations are phased in time and modified several times, but nevertheless, they are still known to induce retardation and restriction of dento-maxillofacial growth. Denudation of palatal bone with healing by secondary intention and the inherent scarring, are detrimental in this respect. TE was thought to be a potential improvement of the present cleft closure techniques. Because there were hardly any scientific data available to support this assumption, it was deemed necessary to carry out a study in growing animals. The most important questions to be answered are: 'what is the effect of palatal submucoperiosteal TE on scarred and non-scarred soft tissues ('is there a real gain of tissue?')?' and 'what is the effect on the surrounding hard tissues ('is there marked retardation in their growth and development?')?'.
Chapter 2 presents a review of the literature (from 1981 to 1992) dealing with cranio-maxillofacial TE. TE in skin has been extensively investigated and is an established technique. The application of (sub)mucosal and (sub)mucoperiosteal TE appears to be mainly based on empirical data and lacks support of experimental studies. The deficiencies in scientific knowledge and points of attention for future research are indicated. A survey of more recent literature (1991 to 1996) is provided in Chapter 10.
Chapter 3 deals with the cephalometric analysis of the effects of palatal submucoperiosteal TE in scarred and non-scarred tissues. Seventy-five growing domestic tom cats, assigned to five groups, were used. Tracings of series standardized lateral cephalograms were digitized. The soft tissue gain and the effect on the adjacent and distant bony structures were quantified for the period of active expansion and the period after removal of the tissue expander and part of the gained tissue. A statistically significant soft tissue gain can be achieved. Palatal sagittal growth was significantly retarded and anterior nasomaxillary height increase was accelerated during expansion. There were no significant differences between scarred and non-scarred tissues. After removal of the tissue expander initial correction of abnormal growth was noticed, in particular in the scarred tissue group.
In chapter 4 the results of the three-dimensional morphornetric analysis of the effects of palatal submucoperiosteal TE in scarred and non-scarred tissues are described. Series of dental casts of 75 young growing domestic tom cats, assigned to five groups, were studied and digitized, using a Reflex Microscope. The soft tissue gain and the effects on the surrounding bony and dental structures were quantified. After eight weeks of active expansion a soft tissue area gain of 85% of the base surface of the expander could be realized. The soft tissue gain in sagittal direction was 32%, whereas the soft tissue increase in transversal direction was 36% of the base diameter. During expansion significant deceleration of (anterior) transverse and sagittal growth was evident. There were no significant differences between scarred and non-scarred tissues. After removal of the tissue expander acceleration of growth was noticed, in particular in the scarred tissue group.
In chapter 5 the results of the histological analysis are described. From the 75 young growing cats used in this study, 67 biopsy specimens were taken and 38 cats were sacrificed for more extensive histological evaluation. Mucoperiosteal expansion led to thinning of the epithelium and the original connective tissues layers overlying the expander. A fibrous capsule developed. Its benefits can be questioned as elastic fibres and contractile myofibroblasts were present and no increase in vascularity could be established. A depression of the palatal bone directly under the expander base, caused by osteoclastic bone resorption, was another debatable finding. This seems to be the main explanation for the deceleration of palatal growth during active expansion. All these phenomena seem to be reversible and they normalize in time after removal of the tissue expander.
Chapter 6 describes a case report of clinical application of the palatal mucoperiosteal expansion technique as an adjunct to cleft palate repair in a 37-years old patient. Conventional TE with a standard tissue expander was performed and proved to be a feasible and realistic technique. However, the final outcome seemed to be dependent on the quality and the vascularity of the adjacent tissues. The technique could be an alternative to a lingual flap in the closure of persistent oronasal fistulae in adult patients.
In chapter 7 the data from the previous chapters are mutually compared and related to each other. A critical evaluation of their value for application in the clinical setting of cleft palate repair in the growing individual is presented. It is concluded that palatal mucoperiosteal TE is a feasible technique in growing domestic cats and adults. However, good tissue quality and vascularity seem to be prerequisites for a successful use. In the animal study hemispherical expanders with a diameter of 12 mm were used. After eight weeks of active expansion a mean soft tissue area gain of 85 % of the expander base surface was reached. The gain in the sagittal direction was 32%, whereas in the transversal direction 36% increase was noted. At histological level, thinning of the epithelium and the original connective tissue layers was evidenced. The orientation of the collagenous fibres in the reticular layer had changed to a direction more parallel to the surface of the expander. Also, a fibrous capsule had developed, however without increased vascularity of the capsular tissue. A statistically significant retardation of both sagittal and transverse growth of the bony palate was observed during expansion. On the other hand, the vertical growth of the anterior nasomaxillary height was accelerated. These phenomena disappeared and normalized in the time span after removal of the tissue expander and part of the gained tissue. In the previously scarred tissue animals acceleration of sagittal and transverse growth was recorded. Whether this accelerated growth has to be interpreted as 'catch-up' growth, which would lead to the normal size and measures of unoperated controls, is open to question. Further research is indicated to decide whether or not extrapolation of these animal data to the clinical setting of cleft palate repair in growing individuals is allowed. In adult patients this TE technique can be used as an alternative to a pedicled tongue flap.