Restricting facial bone growth with skeletal fixation: a preliminary study.

INTRODUCTION: Conventional orthodontic treatment of vertical or anterior maxillary excess by growth modification can be problematic in children because of the high levels of patient compliance required. The purpose of this preliminary study was to investigate the use of rigid skeletal fixation to modify facial bone growth without compliance. METHODS: Three 30-day old female pigs from the same litter were included in phase I. Pediatric miniplates were rigidly fixated with monocortical screws in the experimental pig to bridge the zygomaticomaxillary suture and both the frontonasal and nasomaxillary sutures, bilaterally. In the sham experimental pig, the same surgical protocol was followed, but miniplates were omitted (ie, screw placement only). In the control pig, surgery was not performed. All 3 pigs were housed and fed a normal diet under identical conditions postoperatively for 63 days; then they were killed, their right hemi-skulls were prepared for and underwent 3-dimensional coordinate landmark analysis, and en-bloc specimens from the zygomaticomaxillary, frontonasal, and nasomaxillary sutures of the left hemi-skulls underwent histologic analysis. Two 50-day-old female pigs from the same litter were used in phase II. The same experimental protocol was followed as before for the experimental pig and the sham experimental pig. Both pigs were fed a normal diet for 105 days; then they were killed, and their skulls were prepared for and underwent 3-dimensional coordinate landmark analysis. RESULTS: Rigid plating restricted zygomaticolacrimal suture length, maxillary bone length, nasal bone length, midfacial breadth, and frontal bone length by an average of -14% to -15% (range, -4% to -36%). No growth differences were noted between the animals in maxillary height, mid-premaxillary length, bregma-lambda length, palatal lengths, or mandibular length. Also, plating the sutures produced a clear depressed concavity in the infraorbital region, altered the alignment of the infraorbital plane lateral to the concavity, inhibited the anterior migration of the maxillary tuberosity, and resulted in raised folding on the bony surface adjacent to the zygomaticomaxillary suture. CONCLUSIONS: Rigidly fixating frontonasomaxillary and zygomaticomaxillary sutures inhibits growth of facial bones and might provide a means of restricting excess growth without having to rely on patient compliance. In addition, these altered growth patterns in the plated pig model produced similar and potentially homologous infraorbital features shared by living humans in comparison with ancestral fossil forms.

Examination of the bone-implant interface in experimentally induced osteoporotic bone.

The objective of this study was to explore the hypothesis that osteoporotic-like (OP) conditions have a negative effect on osseointegration (OI) of dental implants. Using an ovariectomized (OVX) rat model, the extent of OI using histologic and histomorphometric analysis (HMA) under a variety of OVX conditions was assessed. Five experimental groups (n = 7 rats per group) were used: 1) OP control, 2) OI control, () OI followed by OVX treatment to induce OP (OI-->OP), 4) OP induction followed by OI (OP-->OI), and 5) OP induction simultaneously with OI (OI = OP). Using undecalcified plastic-embedded cross-sections of the implant site, HMA was performed to determine the percent of bone contact (BC) at the implant-tissue interface and percent of bone area (BA) immediately (1.5-mm diameter) surrounding the implant site. The presence of Bone Sialoprotein (BSP), an important extracellular matrix component of bone, was evaluated using immunohistochemical staining procedures. The implant control resulted in the highest level of OI (BC = 79%; BA = 87%), whereas all groups in which OVX was performed resulted in a significant reduction in BA (70-75%). High levels of BC were observed in established OP conditions (OP-->OI; BC = 79%); however, following OI, induction of OP conditions (OI-->OP) led to a significant reduction in BC (50%). In each of the OP treatment groups, a diminution of cortical bone, increased trabecularization of the host bone site, and loss of staining of BSP was observed. The results of this work indicate that although OI is possible under a variety of OP-like conditions simulating implant placement, the long-term biomechanical stability of implants under these conditions could be compromised and remains unclear. Further research to understand implant use in the complex bone environment under OP-like conditions is encouraged.

Short-term bone responses to hydroxyapatite cement.

PURPOSE: The purpose of this study was to evaluate the short-term wound healing and repair at the tissue/cement interface with different hydroxyapatite cement formulations. MATERIALS AND METHODS: Three groups of Sprague-Dawley rats were implanted with HAC for 3, 7, or 14 days. The medial femur-tibia sites on each leg of the animals were used to create four separate 1.5-mm defects, which were filled with HAC (Bone-Source, Howmedica-Leibinger, Inc.) mixed with either water (W) as a control, an accelerant (0.1 M sodium phosphate, SP), or a stabilizer (1% hydroxypropylmethyl cellulose, HPMC) as diluents. At the appropriate postimplantation times, the animals were euthanized and tissue-implant blocks were prepared for qualitative histopathologic evaluations. RESULTS: Osseoconduction around and into the HAC was observed with all three cement formulations and the control (unfilled) site by day 7 and continued through day 14. The histologic staining did not reveal resorption lacunae or other cellular activities characteristic of osteoclast degradation of HAC. These results suggests that other processes, perhaps physical-chemical in nature, contributed to the initial degradation of the HAC following surgical placement. Structural stability of HAC was noted when using HPMC as the diluent. However, when either W or SP were employed, dissociation (washout) of the HAC into the surrounding tissue was noted. CONCLUSION: HAC is prone to in situ physical-chemical breakdown before the completion of the setting reaction. Diluents designed to stabilize or accelerate the HAC mixture appeared to improve the handling properties of the HAC without compromising the biological characteristics of the cement.