R. M. Browne

Odontoblast stimulation in ferrets by dentine matrix components

The possible effects of isolated dentine matrix components on odontoblast secretory activity were investigated in vivo by implantation of lyophilized fractions of these components into cavities prepared in ferret canine teeth. After implantations as short as 14 days there was significant deposition of reactionary dentine by the odontoblasts beneath the cavity and this response increased in a non-linear manner with time of implantation. In contrast, control cavities lacking the dentine matrix components showed no evidence of reactionary dentine deposition. Examination of teeth at early periods of implantation (2 and 5 days) indicated that odontoblast death had not occurred as a result of the operative procedures and that the response was one of stimulation of existing odontoblasts rather than that of induction of a new generation of odontoblast-like cells. The mechanisms of odontoblast stimulation by the dentine matrix components remain to be elucidated, but could be mediated by growth factors within the dentine matrix preparations.

Subperiosteal behaviour of alginate and cellulose wound dressing materials

A histological comparison was undertaken of the tissue response to a new sodium calcium alginate material (Kaltostat) and an oxidized regenerated cellulose wound dressing (Surgicel) when implanted between bone and periosteum in the jaws at intervals of up to 24 wk. Both biomaterials caused a foreign body reaction, persisting up to 12 wk after surgery. New bone formation occurred along the surface of the mandible in some specimens, but was not apparently related to the implants. It was concluded that the implantation of Kaltostat or Surgicel between bone and periosteum in the jaws caused a delay in wound healing, and had no effect on bone induction.

Expression of proliferating cell nuclear antigen (PCNA) and Ki-67 in unicystic ameloblastoma

The expression of proliferating cell nuclear antigen (PCNA) and Ki‐67 was studied in unicystic and solid ameloblastoma (follicular and plexiform types) using a biotin‐streptavidin method on routinely processed paraffin sections. To determine percentage PCNA and Ki‐67 labelling indices, positive tumour cells and total tumour cells were counted in areas of each unicystic ameloblastoma corresponding to cystic linings, intraluminal nodules and invading tumour islands, and in solid ameloblastomas. Positive cells in basal and suprabasal layers of cystic tumour lining were also counted with respect to the length of basement membrane determined by image analysis. In unicystic ameloblastoma the invading islands exhibited a significantly higher PCNA labelling index (29.2 ± 16.4%) than intraluminal nodules (13.6 ± 5.4%; P < 0.05). Cystic tumour lining had relatively few PCNA positive cells and a labelling index (5.5 ± 3.3%) significantly lower than invading islands (P < 0.001) or intraluminal nodules (P < 0.003). The labelling indices of solid ameloblastomas of follicular type (48.1 ± 12.9%) were significantly higher than those of cystic tumour lining (P < 0.0001), intraluminal nodules (P < 0.001) and invading islands (P < 0.04) in unicystic ameloblastoma. Similar relationships were found for Ki‐67 expression except that comparisons involving invading islands and intraluminal nodules were not significant, a finding probably due to the smaller number of specimens available for quantitative analysis. These results indicate differences in proliferative potential between different areas of unicystic ameloblastoma and between unicystic and solid lesions. The fact that invading tumour islands within the fibrous tissue wall showed high labelling indices is in agreement with the clinical observation that their presence may be related to recurrence after conservative surgery. This provides a biological basis for indicating more radical surgical excision as the treatment of choice for this subgroup of lesions.

Expression of epidermal growth factor receptors by odontogenic jaw cysts

The expression of epidermal growth factor receptor (EGFr) by odontogenic epithelium was studied in odontogenic cysts (n=35), ameloblastoma (n=6), and periapical granulomas containing proliferating epithelial rests of Malassez (n=7) using a panel of monoclonal antibodies to EGFr (clone E30, F4 and C11) known to react with formalin-fixed, paraffin-embedded sections. Odontogenic epithelium in all specimens demonstrated immunoreactivity with all three antibodies. Clone E30 consistently gave the most intense, membrane located staining pattern of the three antibodies tested. Generally, staining of epithelial cells progressively diminished with movement away from the basal cell layers toward the most superficial layers of cystic lining or centre of epithelial rests and tumour islands. Developmental odontogenic cysts (odontogenic keratocysts,n= 13; dentigerous cysts,n=11) and ameloblastoma (follicular type,n=5; unicystic type,n=1) expressed a higher level of EGFr staining than inflammatory cysts (radicular cysts,n=11) and the proliferating epithelial rests in periapical granulomas. However, foci of weak EGFr staining of odontogenic keratocyst lining, similar to that seen in radicular cysts, were found in areas associated with inflammation. In addition, epithelial rests not associated with inflammatory cell infiltrates exhibited stronger reactivity for EGFr than proliferating rests within periapical granulomas. These results indicate that the level of EGFr expression by odontogenic cysts and rests is related to the presence of inflammation within adjacent connective tissue and that there is no detectable difference in receptor expression between developmental cysts and ameloblastoma.

Ridge augmentation using solid and porous hydroxylapatite particles with and without autogenous bone or plaster

Edentulous areas of dog jaws were augmented with solid or porous particles of hydroxylapatite (HA) alone, or combined with either finely crushed autogenous bone or plaster of paris. At the end of the experiment (24 weeks), the augmented ridges were firm and stable and covered with healthy mucosa. The ridges augmented with only porous particles of HA demonstrated a greater amount of bone ingrowth compared with the solid, dense particles. The new bone formation occurred in those parts of the implants adjacent to the underlying alveolar bone. The addition of autogenous bone to the HA particles did not enhance bony deposition, and none of the autogenous bone chips survived for 24 weeks. The amount of new bone in the ridges augmented with plaster of paris and HA was similar to the other groups, and the plaster did not interfere with healing. There was evidence of resorption of the underlying cortical bone in many of the specimens.

Tissue response to a haemostatic alginate wound dressing in tooth extraction sockets

Kaltostat is a new haemostatic wound dressing composed of non-woven sodium calcium alginate fibres, and was originally developed to cover exposed wounds of the skin. A histopathological study was undertaken to determine the tissue response to Kaltostat in healing tooth sockets, to obtain a comparison with oxidised regenerated cellulose (Surgicel). Tooth sockets filled with blood clot acted as controls. The results showed that both biomaterials delayed wound healing in the early phase (1-4 weeks), giving rise to foreign body reactions. At 12 weeks there was little difference between the control sockets and the sockets containing the test materials, although remnants of retained dressing materials were identified. Healing of the tooth sockets was complete at 24 weeks.

Biologic basis for interpositional autogenous bone grafts to the mandible

Interpositional autogenous bone grafting procedures were performed in the mandibles of 12 beagle dogs to assess cell survival within the graft and the superiorly repositioned alveolus, and to monitor the remodeling process. Histologic and radiologic results indicated that the grafts were well accepted and that new bone was rapidly laid down on their trabeculae. However, the osteocytes within the autografts generally did not survive. There was no evidence of necrosis of the superiorly displaced alveolus, nor any resorption of its surface cortex, and it rapidly united with the autograft and the mandible to produce a stable structure. This study confirms that the lingual pedicle of soft tissue is adequate to maintain the viability of the superiorly repositioned alveolus or segment and to allow rapid remodeling of the autogenous bone graft.

In vivo surface analysis of titanium and stainless steel miniplates and screws

This study was undertaken to characterize the surfaces of Champy titanium and stainless steel miniplates and screws that had been used to stabilize fractures of the mandible in an animal model. Miniplates and screws were retrieved at 4, 12, and 24 weeks after surgery. Low-vacuum scanning electron microscopy (SEM) of autoclaved unused (control) and test miniplates from the same production batches was undertaken. Energy-dispersive X-ray (EDX) analysis was used to identify compositional variations of the miniplate surface, and Vickers hardness testing was performed. At autopsy, clinical healing of all fractures was noted. SEM analysis indicated no perceptible difference in the surface characteristics of the miniplates at all time intervals. Aluminium and silicon deposits were identified by EDX analysis over the flat surfaces. There was extensive damage to some screw heads. It is concluded that there were no significant changes in the surface characteristics of miniplates retrieved up to 24 weeks after implantation in comparison with controls. Damage to the screws during insertion due to softness of the materials may render their removal difficult. There was no evidence to support the routine removal of titanium or stainless steel miniplates because of surface corrosion up to 6 months after implantation.

A histological study of stainless steel and titanium screws in bone

This study compared histologically the tissue response of stainless steel and titanium screws when inserted into the calvaria of eight beagle dogs for periods of 1, 4, 12, and 24 weeks. There was minimal fibrous reaction around both screw types with excellent long-term bone healing. After 24 weeks there was no discernable difference in the tissue reaction between the two types of screw.

Immunocytochemical expression of parathyroid hormone related protein (PTHrP) in odontogenic jaw cysts

OBJECTIVE To investigate the immunocytochemical expression of parathyroid-hormone-related protein (PTHrP) in odontogenic jaw cysts. DESIGN Retrospective study of archival tissue. SETTING University department, UK. MATERIAL Odontogenic keratocysts (n=27), and dentigerous and radicular cysts (n=10 each). INTERVENTION Immunocytochemistry by biotin streptavidin technique. MAIN OUTCOME MEASURE Intensity of staining of PTHrP determined by TV image analysis. RESULTS The epithelial linings of all the odontogenic keratocysts, 9/10 dentigerous, and 8/10 radicular cysts showed reactivity for PTHrP mainly localised to the basal and suprabasal layers. Odontogenic keratocyst linings expressed significantly higher levels of PTHrP than those of dentigerous and radicular cysts (P<0.003 in each case). There were no differences in epithelial expression of PTHrP between solitary, recurrent and naevoid basal cell carcinoma syndrome-associated odontogenic keratocysts. The fibrous tissue walls of all types of cyst reacted strongly for PTHrP with a trend towards decreasing intensity from odontogenic keratocysts, to dentigerous and then radicular cysts. CONCLUSION It is possible that PTHrP modulates growth and bone resorption in odontogenic cysts. PTHrP may act synergistically with interleukin-1 to increase bone resorption or stimulate osteoblasts and inhibit osteoclasts (resulting in reduced resorption) via its transforming growth factor beta-like activity.