Treatment Modalities to Achieve Nasal Symmetry in Unilateral Cleft Lip/Nasal Deformity: An Objective and Comparative Evaluation

Introduction

Primary cleft lip repair techniques do not address the nasal deformity adequately resulting in nasal asymmetry. Maneuvers employed to minimize this have varying degrees of success.

Aim

To assess the outcome of different treatment modalities employed to establish nasal symmetry in unilateral cleft lip.

Methods

100 patients with complete unilateral cleft lip/ palate operated for primary cheiloplasty with modified Millard's rotation advancement technique were divided into five groups. Group 1: lip repair alone, Group 2: NAM followed by lip repair, Group 3: lip repair followed by placement of conformers, Group 4: NAM followed by lip repair and placement of conformers, Group 5: lip repair with semi-open rhinoplasty. Objective assessment was done using measurable parameters after 12 months post-operatively on a 1:1 standard photograph.

Results

Group 5 showed statistical significance in all parameters assessed. Progressive improvement in nasal symmetry was noted from Group 1 to Group V.

Conclusion

In our study, group V, i.e., modified Millard's repair with semi-open rhinoplasty improved the results in terms of all the objective parameters assessed. The results of the other groups showed improvement though not consistent in all parameters. Naso-alveolar molding is an effective adjunct. Additionally, nasal conformers proved to be of great value in retaining the results obtained post-surgery.

Human dental pulp stromal cell conditioned medium alters endothelial cell behavior

Background

Angiogenesis is of utmost importance for tissue regeneration and repair. Human dental pulp stromal cells (hDPSCs) possess angiogenic potential, as they secrete paracrine factors that may alter the host microenvironment. However, more insight into how hDPSCs guide endothelial cells (ECs) in a paracrine fashion is yet to be obtained. Therefore, the current study aimed to investigate the effect(s) of conditioned medium derived from hDPSCs (hDPSC-CM) on EC behavior in vitro.

Methods

hDPSCs were harvested from third molars scheduled for surgical removal under informed consent. The angiogenic profile of hDPSC-CM was identified using human angiogenesis antibody array and enzyme-linked immunosorbent assay (ELISA). Using real-time reverse transcription-polymerase chain reaction (RT-PCR) and ELISA, the mRNA and protein expression level of specific angiogenic biomarkers was determined in human umbilical vein endothelial cells (HUVECs) exposed to hDPSC-CM. The effect of hDPSC-CM on HUVEC attachment, proliferation and migration was evaluated by crystal violet staining, MTT, transwell migration along with real-time cell monitoring assays (xCELLigence; ACEA Biosciences, Inc.). A Matrigel assay was included to examine the influence of hDPSC-CM on HUVEC network formation. Endothelial growth medium (EGM-2) and EGM-2 supplemented with hDPSC-CM served as experimental groups, whereas endothelial basal medium (EBM-2) was set as negative control.

Results

A wide range of proangiogenic and antiangiogenic factors, including vascular endothelial growth factor, tissue inhibitor of metalloproteinase protein 1, plasminogen activator inhibitor (serpin E1), urokinase plasminogen activator and stromal cell-derived factor 1, was abundantly detected in hDPSC-CM by protein profiling array and ELISA. hDPSC-CM significantly accelerated the adhesion phases, from sedimentation to attachment and spreading, the proliferation rate and migration of HUVECs as shown in both endpoint assays and real-time cell analysis recordings. Furthermore, Matrigel assay demonstrated that hDPSC-CM stimulated tubulogenesis, affecting angiogenic parameters such as the number of nodes, meshes and total tube length.

Conclusions

The sustained proangiogenic and promaturation effects of hDPSC-CM shown in this in vitro study strongly suggest that the trophic factors released by hDPSCs are able to trigger pronounced angiogenic responses, even beyond EGM-2 considered as an optimal culture condition for ECs.

Assessment of Alar Flare and Efficacy of Alar Cinch Suture in the Management of Alar Flare Following Le Fort 1 Superior Repositioning: A Comparative Study

OBJECTIVES

To prospectively analyze the amount of alar flare, factors contributing to alar flare and efficacy of cinch suture as an adjunctive procedure for alar flare reduction.

STUDY DESIGN

Thirty adult patients with vertical maxillary excess, who underwent Le Fort 1 impaction, were divided into 2 groups of 15 each. Alar cinch was performed as an adjunct procedure in group 2 patients and results were compared to group 1 which was the control group. Measurements were made on the patients and on 1:1 standardized photographs.

RESULTS

Group 2 showed a near pre-operative alar position compared to group 1. The alar flare resulting from every millimeter of impaction was significantly less in group 2 compared to group 1.

CONCLUSION

Alar cinch suture restores the normal alar width by preventing the lateral drift of the naso-labial muscle and thereby reducing the postoperative nasal flare significantly.

Photocatalytically induced hydrophilicity influences bone remodelling at longer healing periods: a rabbit study

OBJECTIVES

Previously, we have reported that photocatalytically active hydrophilicity of the anatase titanium dioxide (TiO₂) nanoparticles coated onto commercially pure titanium discs presented significantly improved hydrophilicity after ultraviolet irradiation. As hydrophilicity has shown enhancement of osseointegration, the in vivo responses were of great interest. The aim of this study was to evaluate whether or not the photo-activated hydrophilicity generated at the time of implant placement has an effect on the longer healing periods for osseointegration.

MATERIALS AND METHODS

Photocatatytically active nanostructured TiO₂ powder (Degussa P-25), which consists of approximately 80% anatase and 20% rutile, was spin-coated onto commercially pure titanium discs and was heat-treated thereafter. These P25-coated discs were irradiated with ultraviolet (UV) light for the test (+UV) group, and non-irradiated discs were prepared for the control (-UV) group. Both groups of discs were placed in the rabbits' tibiae. After 12 weeks of healing period, histological analysis and gene expression analysis using real-time RT-PCR were performed.

RESULTS

From the histological analyses, there were no specific differences between -UV and +UV groups. However, from the gene expression analysis, ALP, RUNX-2 and IL-10 were significantly upregulated for the +UV group compared with the -UV group.

CONCLUSIONS

The biologically enhancing effect to photocatalytically activated surfaces remained even after 12 weeks of healing time in terms of genetic responses.

Integrin-mediated adhesion of human mesenchymal stem cells to extracellular matrix proteins adsorbed to polymer surfaces

In vitro, degradable aliphatic polyesters are widely used as cell carriers for bone tissue engineering, despite their lack of biological cues. Their biological active surface is rather determined by an adsorbed layer of proteins from the surrounding media. Initial cell fate, including adhesion and proliferation, which are key properties for efficient cell carriers, is determined by the adsorbed layer of proteins. Herein we have investigated the ability of human bone marrow derived stem cells (hBMSC) to adhere to extracellular matrix (ECM) proteins, including fibronectin and vitronectin which are present in plasma and serum. hBMSC expressed integrins for collagens, laminins, fibronectin and vitronectin. Accordingly, hBMSC strongly adhered to these purified ECM proteins by using the corresponding integrins. Although purified fibronectin and vitronectin adsorbed to aliphatic polyesters to a lower extent than to cell culture polystyrene, these low levels were sufficient to mediate adhesion of hBMSC. It was found that plasma- and serum-coated polystyrene adsorbed significant levels of both fibronectin and vitronectin, and fibronectin was identified as the major adhesive component of plasma for hBMSC; however, aliphatic polyesters adsorbed minimal levels of fibronectin under similar conditions resulting in impaired cell adhesion. Altogether, the results suggest that the efficiency of aliphatic polyesters cell carriers could be improved by increasing their ability to adsorb fibronectin.

Genetic responses to nanostructured calcium-phosphate-coated implants

Nanostructured calcium phosphate (CaP) has been histologically and biomechanically proven to enhance osseointegration of implants; however, conventional techniques were not sufficiently sensitive to capture its biological effects fully. Here, we compared the conventional removal torque (RTQ) evaluation and gene expression in tissues around nanostructured CaP-coated implants, using real-time RT-PCR, with those of uncoated implants, in a rabbit model. At 2 wks, RTQ values were significantly higher, alkaline phosphatase (ALP) expression was significantly higher, and runt-related transcription factor 2 and tumor necrosis factor-α expressions were significantly lower in the coated than in the uncoated implants. This indicates that inflammatory responses were suppressed and osteoprogenitor activity increased around the CaP-coated surface. At 4 wks, although RTQ values did not significantly differ between the 2 groups, ALP and osteocalcin (OCN) were significantly up-regulated in the coated group, indicating progressive mineralization of the bone around the implant. Moreover, an osteoclast marker, adenosine triphosphatase, which indicates acidification of the resorption lacunae, was significantly higher for the coated implants, suggesting gradual resorption of the CaP coating. This study reveals detailed genetic responses to nanostructured CaP-coated implants and provides evidence that the effect of nanotopography is significant during the osseointegration cascade.

In vitro and in vivo degradation profile of aliphatic polyesters subjected to electron beam sterilization

Degradation characteristics in response to electron beam sterilization of designed and biodegradable aliphatic polyester scaffolds are relevant for clinically successful synthetic graft tissue regeneration. Scaffold degradation in vitro and in vivo were documented and correlated to the macroscopic structure and chemical design of the original polymer. The materials tested were of inherently diverse hydrophobicity and crystallinity: poly(L-lactide) (poly(LLA)) and random copolymers from L-lactide and ε-caprolactone or 1,5-dioxepan-2-one, fabricated into porous and non-porous scaffolds. After sterilization, the samples underwent hydrolysis in vitro for up to a year. In vivo, scaffolds were surgically implanted into rat calvarial defects and retrieved for analysis after 28 and 91days. In vitro, poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) samples degraded most rapidly during hydrolysis, due to the pronounced chain-shortening reaction caused by the sterilization. This was indicated by the rapid decrease in both mass and molecular weight of poly(LLA-co-DXO). Poly(L-lactide-co-ε-caprolactone) (poly(LLA-co-CL)) samples were also strongly affected by sterilization, but mass loss was more gradual; molecular weight decreased rapidly during hydrolysis. Least affected by sterilization were the poly(LLA) samples, which subsequently showed low mass loss rate and molecular weight decrease during hydrolysis. Mechanical stability varied greatly: poly(LLA-co-CL) withstood mechanical testing for up to 182 days, while poly(LLA) and poly(LLA-co-DXO) samples quickly became too brittle. Poly(LLA-co-DXO) samples unexpectedly degraded more rapidly in vitro than in vivo. After sterilization by electron beam irradiation, the three biodegradable polymers present widely diverse degradation profiles, both in vitro and in vivo. Each exhibits the potential to be tailored to meet diverse clinical tissue engineering requirements.

Bone regeneration and stem cells

This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.

A Role for α11β1 Integrin in the Human Periodontal Ligament

We previously demonstrated a role for α11β1 integrin in periodontal ligament (PDL)-driven tooth eruption in the mouse. To explore a possible role for α11β1 in the human periodontium, we have characterized the expression and function of α11 in human PDL tissue, in human PDL fibroblasts (hPDLF), and in human gingival fibroblasts (hGF). α11 expression was detected in PDL tissue, in hPDLF, and in hGF cells. Platelet-derived growth factor-BB and insulin-like growth factor II stimulated contraction of collagen lattices by both types of fibroblasts. α2 integrin blocking antibodies and the use of α11 siRNA demonstrated a role for both α2β1 and α11β1 in collagen lattice remodeling. Analysis of the proximal ITGA11 promoter from persons with chronic periodontal disease failed to reveal any polymorphism. Analysis of our data shows that α11β1 is a major collagen receptor on cultured human PDL cells and implies that it is also functionally important in the PDL in vivo.

Cytotoxicity of new resin-, calcium hydroxide- and silicone-based root canal sealers on fibroblasts derived from human gingiva and L929 cell lines

AIM

To assess ex vivo the cytotoxic effects of five new root canal sealers (RC Sealer, Epiphany, EndoREZ, GuttaFlow and Acroseal) and three existing products (AH Plus, RoekoSeal and Apexit) using primary human gingival fibroblasts (HGF) and a mouse fibroblast cell line, L929.

METHODOLOGY

Eight samples of each sealer were fabricated in sterile cylindrical Teflon blocks, 4.4 mm diameter and 2 mm height and then divided into two groups, fresh and aged specimens. Extraction of fresh specimens was carried out after setting whilst aged specimens were placed in Petri dishes and kept in a humid chamber at 37 degrees C for 7 days before extraction in cell culture medium using the ratio 1.25 cm(2) mL(-1). Undiluted eluates were used for the dimethylthiazol diphenyltetrazolium bromide (MTT) assay with HGF and L-929. Morphology of HGF cells was also examined by an inverted microscope using undiluted eluates of the sealers. The results were analysed using a two-tailed t-test (alpha = 0.05) between groups.

RESULTS

Resin-based (Epiphany and EndoREZ) and calcium hydroxide-based (Apexit and Acroseal) sealers were significantly more cytotoxic than other sealers (P<0.05). However, L929 cells were more sensitive to Apexit and EndoREZ than HGF cells. RC Sealer showed mild cytotoxicity to HGF at both setting times. AH Plus did not exert any cytotoxic effect to HGF and aged specimens appeared to induce cellular proliferation. RoekoSeal and GuttaFlow also demonstrated mild cytotoxicity. GuttaFlow was slightly more cytotoxic to both cultures, especially when tested fresh.

CONCLUSIONS

Toxicity varied but RC Sealer and GuttaFlow were the least toxic new sealers.

Determining optimal surface roughness of TiO(2) blasted titanium implant material for attachment, proliferation and differentiation of cells derived from human mandibular alveolar bone

In the complex process of bone formation at the implant-tissue interface, implant surface roughness is an important factor modulating osteoblastic function. In this study, primary cultures of osteoblast-like cells, derived from human mandibular bone, were used. The aim was to examine the effect of varying surface roughness of titanium implant material on cellular attachment, proliferation and differentiation. A recognized method of increasing surface roughness and enlarging the surface area of titanium implants is by blasting with titanium dioxide particles: the four specimen types in the study comprised surfaces which were machine-turned only, or blasted after turning, with 63-90 microm, 106-180 microm, or 180-300 microm TiO(2) particles, respectively. The specimens were analyzed by scanning electron microscopy and confocal laser scanning. The turned samples had the smoothest surfaces: average height deviation (S(a)) of 0.20 microm. The roughest were those blasted with 180-300 microm particles, S(a) value 1.38 microm. Blasting with intermediate particle sizes yielded S(a) values of 0.72 microm and 1.30 microm, respectively. Cell profile areas were measured using a semiautomatic interactive image analyzer. Figures were expressed as percentage of attachment. DNA synthesis was estimated by measuring the amount of [(3)H]-thymidine incorporation into trichloroacetic acid (TCA) insoluble cell precipitates. The specific activity of alkaline phosphatase was assayed using p-nitrophenylphosphate as a substrate. The ability of the cells to synthesize osteocalcin was investigated in serum-free culture medium using the ELSA-OST-NAT immunoradiometric kit. After 3 h of culture, the percentage of cellular attachment did not differ significantly between specimens blasted with 180-300 micromparticles and the turned specimens. All blasted surfaces showed significantly higher [(3)H]-thymidine incorporation than the turned surfaces (P<0.05), with the highest on the surfaces blasted with 180-300 microm particles. Osteocalcin synthesis by the cells in response to stimulation by 1,25(OH)2D3, was also significantly greater (P<0.05) on the surfaces blasted with TiO(2) particles. However, analysis of alkaline phosphatase activity disclosed no significant differences among the four surface modifications. It is concluded that in this cellular model, the proliferation and differentiation of cells derived from human mandibular bone is enhanced by surface roughness of the titanium implant. However, increasing the size of the blasting particles to 300 microm does not further increase the initial attachment of the cells compared to turned surfaces and those blasted with 63-90 microm particles.

Effects of titanium surfaces blasted with TiO2 particles on the initial attachment of cells derived from human mandibular bone. A scanning electron microscopic and histomorphometric analysis

This study was performed to determine the effect of commercially pure titanium surfaces blasted with TiO2 particles on the biological responses of cells derived from human mandibular bone. The morphology and attachment of those cells were investigated on turned titanium surfaces (control) and surfaces blasted with 45 microns (standard), 45-63 microns, and 63-90 microns TiO2 particles. The surfaces were analyzed in a scanning electron microscope. Based on surface analyses reported elsewhere, the turned samples had the smoothest surfaces and the roughest were those blasted with the largest particles (63-90 microns). The cell profile areas were measured using a semi-automatic interactive image analyzer. The attachment was determined as a ratio of the area of cell profiles and the total micrograph area and was expressed as percentage of attachment. Morphologically, the cells were heterogeneous. In general, the cells had spread well on all titanium surfaces, indicating good attachment to both smooth and rough surfaces. After 1, 3 and 6 h, the percentage of cell attachment did not differ significantly between the surfaces blasted with 63-90 microns and the turned surfaces, but was significantly lower on the surfaces blasted with 45 microns or 45-63 microns particles. After 24 h the surfaces blasted with 63-90 microns particles had a higher rate of cell attachment than all the other surfaces including the controls. It is concluded that attachment and growth of cells originating from human mandibular bone in vitro, are influenced by the micro-texture of the implant surface.

Attachment and proliferation of human oral fibroblasts to titanium surfaces blasted with TiO2 particles. A scanning electron microscopic and histomorphometric analysis

The purpose of this study was to determine the effect of c.p. titanium surfaces blasted with TiO2 particles on the biological responses of human gingival fibroblasts (HGF). Fibroblast morphology and attachment were investigated on turned (control) titanium surfaces and those blasted with 45 microns (standard), 45-63 microns, and 63-90 microns TiO2 particles. The specimens were analyzed using a confocal laser scanner and SEM. The cell profile areas were measured using a semiautomatic interactive image analyser. The figures were expressed as percent of attachment. The turned samples had the smoothest surfaces and the roughest were those blasted with 63-90 microns. All TiO2 blasted specimens had homogeneous surfaces. Cells appeared to flatten, spread and form cellular bridges with the adjacent cells. Fibroblasts on the turned titanium surfaces appeared to follow the direction of the fine irregularities on the surface but tended to spread haphazardly on the blasted surfaces. The attachment assays showed no significant difference in the percentage of fibroblast cell attachment on the standard surfaces compared to the turned surfaces. Both surfaces blasted with 45-63 microns or 63-90 microns had significantly (P < 0.05) lower percentages of cell attachment than the control. The surfaces blasted with 63-90 microns particles had the lowest rate of cell attachment. A significant correlation (P < 0.01) was found between the degree of particle size and attachment of fibroblasts after 1-72 h. It is concluded that surface micro-texture influences the attachment and growth of HGF: surfaces blasted with 45 microns TiO2 do not inhibit fibroblast attachment and smooth or finely grooved surfaces could be conducive to cellular attachment.

Psoriatic spondyloarthropathy with secondary amyloidosis

We report an HLA-B27 positive patient with severe psoriatic spondyloarthropathy who developed secondary reactive amyloidosis. The clinical course was characterized by progressive renal failure with nephrotic syndrome and cardiac dysfunction. He died suddenly and autopsy revealed diffuse amyloid deposits in the heart, kidneys, and many other organs. Amyloid deposits were present in the cardiac conduction system including the sinoatrial and atrioventricular nodes, myocardial interstitium, and intramyocardial small blood vessels. The severe AA amyloid deposit in the heart with involvement of conduction system is unusual, and has not been described in patients with psoriasis or psoriatic arthritis.

[Characteristics of the occurrence of hematotoxic side effects of cytostatic drugs--results of a retrospective 10 year study of a district hospital]

From 1978 to 1988 in 77 patients of a district hospital, 58 females and 19 males, with malignant tumours or haemoblastoses a therapy with cytostatic agents was finished. A retrospective study analyses characteristics of haematotoxic side effects of cytostatic agents, which despite usual dosage according to the valid guide-lines have appeared in this patient population. According to this the granulocytopoiesis is injured most frequently and most severely. In one third of all patients under influence of cytostatic agents the number of the segment-nuclear granulocytes in the peripheral blood decreased deeper than 0.5 Gpt/l (severe neutropenia). In toxic influences on the thrombopoiesis slight and medium degrees of severity are dominating. Lesions of the erythropoiesis are apparently more infrequent, though they are more difficult to be proved. Further characteristics in the occurrence of severe neutropenias (date, dependence on age, pharmacological aspects) are demonstrated and discussed.

The cellular contributions of blastema and stump to 180 degrees supernumerary limbs in the axolotl

By inverting triploid blastemas onto diploid stumps (and vice versa) the cellular contributions to supernumerary limbs so generated have been assessed. The four classes of 180 degrees supernumerary limbs each had a different mixture of stump and blastemal cells. The mesoderm of normal supernumeraries was composed entirely or almost entirely of stump cells and were always of stump handedness. The mesoderm of symmetrical supernumeraries was of variable composition, it could be mostly stump, mostly blastema or half and half. In part normal/part symmetrical supernumeraries the normal part was usually of stump origin and the aberrant symmetrical part of blastemal origin. In part normal/part inverted supernumeraries the normal part came from the stump and the inverted part from the inverted blastema. The handedness of each part of these supernumeraries corresponded with its cellular origin. The epidermis of the supernumeraries was not of the same relative composition as the mesoderm, it tended to have a larger stump component. The black/white marker was also used and this too tended not to conform to the mesodermal contribution patterns. These results are discussed in terms of rules for generating supernumeraries and it is concluded that with the exception of symmetrical supernumeraries the cellular contributions of stump and blastema determine their structure.

The cellular contributions of blastema and stump to 180° supernumerary limbs in the axolotl

By inverting triploid blastemas onto diploid stumps (and vice versa) the cellular contributions to supernumerary limbs so generated have been assessed. The four classes of 180° supernumerary limbs each had a different mixture of stump and blastemal cells. The mesoderm of normal supernumeraries was composed entirely or almost entirely of stump cells and were always of stump handedness. The mesoderm of symmetrical supernumeraries was of variable composition, it could be mostly stump, mostly blastema or half and half. In part normal/part symmetrical supernumeraries the normal part was usually of stump origin and the abberant symmetrical part of blastemal origin. In part normal/part inverted supernumeraries the normal part came from the stump and the inverted part from the inverted blastema. The handedness of each part of these supernumeraries corresponded with its cellular origin. The epidermis of the supernumeraries was not of the same relative composition as the mesoderm, it tended to have a larger stump component. The black/white marker was also used and this too tended not to conform to the mesodermal contribution patterns. These results are discussed in terms of rules for generating supernumeraries and it is concluded that with the exception of symmetrical supernumeraries the cellular contributions of stump and blastema determine their structure.

Axial organization of the regenerating limb: asymmetrical behaviour following skin transplantation

An extensive series of skin grafting operations has been performed to investigate axial organization in the regenerating axolotl limb. Semicircular cuffs of skin from either anterior, posterior, dorsal or ventral surfaces were exchanged between right and left limbs thereby creating limbs with double anterior, double posterior, double dorsal or double ventral skin, all with normal internal tissues. Both fore and hindlimbs were used at both upper and lower limb levels. Following amputation through the grafted region the resulting regenerates were analysed both by whole-mount cartilage staining to observe the pattern of digits and by serial sectioning to observe the pattern of muscles. There were clear asymmetries in ability to produce duplications - posterior to anterior grafts resulted in a consistently high frequency of digital duplications, whereas anterior to posterior grafts produced very few. Similarly, dorsal to ventral grafts resulted in a good frequency of muscle duplications, whereas ventral to dorsal grafts did not. Such asymmetrical behavior is not predicted by most models involving local cell:cell interactions and the significance of the results for theories of pattern formation is discussed.

Axial organization of the regenerating limb: asymmetrical behaviour following skin transplantation

An extensive series of skin grafting operations has been performed to investigate axial organization in the regenerating axolotl limb. Semicircular cuffs of skin from either anterior, posterior, dorsal or ventral surfaces were exchanged between right and left limbs thereby creating limbs with double anterior, double posterior, double dorsal or double ventral skin, all with normal internal tissues. Both fore and hindlimbs were used at both upper and lower limb levels. Following amputation through the grafted region the resulting regenerates were analysed both by whole-mount cartilage staining to observe the pattern of digits and by serial sectioning to observe the pattern of muscles. There were clear asymmetries in ability to produce duplications - posterior to anterior grafts resulted in a consistently high frequency of digital duplications, whereas anterior to posterior grafts produced very few. Similarly, dorsal to ventral grafts resulted in a good frequency of muscle duplications, whereas ventral to dorsal grafts did not. Such asymmetrical behaviour is not predicted by most models involving local cell:cell interactions and the significance of the results for theories of pattern formation is discussed.