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Biomedical subjects

W H Bell

Publications and source records attributed to W H Bell.

At least 55 records · Page 3Linked to original sources
PubMed1999

Intraoral mandibular distraction osteogenesis.

During recent years, distraction osteogenesis has gained in popularity for the treatment of various bone deficiencies either in the vertical, transverse, or anteroposterior dimension. Distraction osteogenesis has been shown to be an effective technique for mandibular widening and lengthening where traditional orthognathic surgery has important limitations. The intraoral approach to these procedures prevents damage to the inferior alveolar nerve and the developing dental follicles, and eliminates hypertrophic facial scars. Intraoral distraction osteogenesis also avoids donor-site morbidity, and minimizes the need for blood transfusion or prolonged fixation. This intraoral application provides for enhanced patient acceptance and reduces the potentially negative psychosocial effects of wearing an extraoral distraction appliance.

Clinical Protocols↗
PubMed1997

Distraction osteogenesis to widen the mandible.

The purpose of this investigation was to elucidate the biology of distraction osteogenesis during mandibular widening. Midsymphyseal vertical interdental osteotomies were performed in nine Macaca mulatta monkeys. After a latency period a tooth-borne appliance was activated at a rate of 0.5 mm twice a day for 7-10 days. The appliance was then stabilized for a period of 4 or 8 weeks. The distraction gap at the inferior portion of the symphysis was bridged completely by new bony trabeculae. Bone formation in the interdental area was apparently related to the surgical technique. Newly formed bony trabeculae were oriented parallel to the direction of distraction. The location of the osteotomy site with an adequate margin of alveolar bone contiguous with the adjacent teeth was necessary for the induction of the distraction osteogenesis. Disproportional movement between superior and inferior portions of the distracted segments was noted.

Alveolar Process↗
PubMed1997

Reactive changes in the temporomandibular joint after mandibular midline osteodistraction.

The purpose of this study was to evaluate the histologic changes within the condyle in response to mandibular widening using osteodistraction. Mandibular midline osteotomies were made in nine Macaca mulatta monkeys and tooth-borne distraction devices were bonded to the mandibular dentition. Distraction was continued until a 3-5 mm widening was achieved. The appliances were then stabilized for a period of 4 weeks. Non-decalcified sagittal sections of the lateral, middle and medial thirds of the condyles were analyzed. Although three of the seven animals showed no unusual morphology, four others exhibited morphologic differences within the fibrous layer, cartilage layer or bone/cartilage interface. Histologic changes were seen to occur in the fibrous layer, cartilaginous layer and cartilage/bone interface. The severity of these changes were correlated with the likely rotational forces directed at the condyle on the postero-lateral and antero-medial surfaces.

Analysis of Variance↗
PubMed1997

Mandibular widening by intraoral distraction osteogenesis.

Transverse mandibular deficiency with crowding of the mandibular anterior teeth is frequently present in patients with Class I and II malocclusions. The hallmarks of treatment by compensating orthodontics, functional appliances or orthopaedic devices are instability, compromised periodontium and compromised facial aesthetics. A new surgical technique has been developed to widen the mandible. The method is based upon gradual osteodistraction following vertical interdental symphyseal osteotomy. Ten patients with transverse mandibular deficiency and significant dental crowding were treated by symphyseal distraction and subsequent non-extraction decompensating orthodontic treatment. Either an intraoral tooth-borne Hyrax appliance or a new custom-made bone-borne osteodistractor was used to gradually widen the mandible. The surgical procedures were accomplished under local anaesthesia and intravenous sedation in an ambulatory surgical setting using an individualized distraction protocol. The appliances were activated 7 days after symphyseal osteotomies, once each day at a rate of 1 mm per day and stabilized for 30-40 days after distraction. After the segments were distracted, non-extraction orthodontic alignment of the mandibular anterior teeth was accomplished. The symphyseal distraction gaps were bridged by new bony regenerate. Distraction osteogenesis provided an efficient surgical alternative to orthognathic surgery for widening the mandible and treatment of transverse mandibular deficiency without extraction of teeth.

Adolescent↗
PubMed1995

Wound healing after multisegmental Le Fort I osteotomy and transection of the descending palatine vessels.

PURPOSE: Vascular ischemia has been associated with improper soft tissue flap design, stretching of the palatal vascular pedicle, bony segmentation, transection of the descending palatal vessels, or hypotension. This study examined Le Fort I osteotomy wound healing after some of these surgical maneuvers. MATERIALS AND METHODS: Clinically analogous four-segment Le Fort I osteotomies were accomplished through circumvestibular incisions in nine adult rhesus monkeys and the animals were killed at 0, 3, 7, 14, and 28 days after surgery. Revascularization and bone healing were studied by microangiographic and histologic techniques. RESULTS: The findings indicated that the palatal mucosa or labial-buccal gingiva and mucosa provide adequate nutrient pedicles for Le Fort I osteotomies accomplished through a circumvestibular type incision. CONCLUSIONS: It was concluded that segmentalization, stretching of the vascular pedicles, or transection of the descending palatine vessels have only transitory discernible effects on revascularization and bone healing.

Animals↗
PubMed1994

Biomechanical properties of small bone screws.

PURPOSE: To evaluate systematically the biomechanical properties of 13 popular screw designs, ranging from 0.8 to 2.0 mm in diameter. METHODS: Screws were characterized in terms of external, core, and drill diameter; cutting flute and head design; material; pitch, thread depth; and height of shank (unthreaded portion) and shank with plate. They were tested in standardized bone specimens (2 x 2.5cm slabs of fresh bovine femur) 1, 2, 3, and 4-mm thick. For each screw-bone thickness combination, 10 trials were conducted to determine push-out force (POF) and another 10 trials to determine insertion (IT) and maximum torque (MT) yielding a total of 1,040 tests. RESULTS: Among the 13 different screws, in 1-mm thick bone, both the lowest (108.5 N) and highest (294.9 N) POF were created by 2-mm screws (P < .001); that with the lowest POF had a long unthreaded shank and pitch, that with highest POF had a short unthreaded shank and pitch. Screws with 0.8- to 1.5-mm diameters showed no differences in POF. The 2-mm screw with the lowest POF also had the lowest MT in 1-mm thick bone compared with the other 2-mm screws (P < .001). In thicker bones (> 2 mm), two 2-mm screws showed 30% to 50% lower MT than the other same size screws (P < .001) because their head slots stripped easily. When all screws were considered together for a particular bone thickness, torque was strongly predicted by screw diameter (MT: r = .94, P < .001; IT: r = 0.92, P < .001). Screws with the same diameters varied significantly in IT because of differences in self-tapping cutting flute design. CONCLUSION: External diameter, unthreaded shank height, head slot, and self-tapping cutting flute design had the greatest impact on screw strength and efficiency in thin cortical bone. Thread depth, core diameter, and metal type did not affect performance significantly. Under these highly standardized in vitro conditions, the ideal 2-mm screw has an unthreaded shank that is as short as possible, and the pitch is about 0.8 mm. Additional aspects of a clinical situation beside holding strength must, however, be considered when choosing a screw.

Analysis of Variance↗
PubMed1994

Esthetic contour analysis of the submental cervical region: a study based on ideal subjects and surgical patients.

A cephalometric analysis of the submental-cervical region was carried out by examining and comparing 16 white adults who had ideal submental-cervical esthetics with 16 adult orthognathic surgery patients who were treated by submental lipectomy or liposuction and various orthognathic surgical procedures. A normative data base of the submental-cervical region was derived from the ideal subject group. The submental-cervical morphology of the preoperative patients differed significantly from the ideal subjects. The submental-cervical angle (Sm-Ce) and the submental soft tissue thickness at C point (IBM-Sm) presented the greatest disparity between the ideal subjects (118.0 degrees, 28.0 mm) and the preoperative patients (158.3 degrees, 42.1 mm, each P < .001). After surgery, Sm-Ce and IBM-Sm decreased to 132.8 degrees (P < .001) and 28.7 mm (P < .001), respectively. By the end of 6 months postoperative, the mean values of Sm-Ce and IBM-Sm were 131.1 degrees and 28.6 mm. The submental soft tissue thickness of the patients 6 months after surgery was not statistically different from the ideal subjects (each P > .05). Orthognathic surgical procedures with concomitant submental lipectomy or liposuction had a significant effect on the contour of the submental and cervical soft tissues.

Adolescent↗
PubMed1993

Long-term osseous and soft tissue changes after large chin advancements.

When a large chin advancement is performed and a broad musculo-periosteal pedicle is preserved, excessive stretching of the suprahyoid musculature may occur, leading to instability or resorption of the advanced genial segment. The present study was designed to evaluate long-term osseous and soft tissue changes after large advancement genioplasties (greater than 10 mm), achieved by horizontal osteotomy of the inferior border of the mandible, with preservation of a musculo-periosteal pedicle to the advanced genial segment. Bone remodeling and the inherent soft tissue changes were radiographically assessed in a long-term follow-up period (mean = 26.8 months), with attention to observe progressive osseous changes. Despite the observed 17% bone resorption, the enveloping soft tissues of the chin followed the bony movement in a ratio of 1:0.83. Osseous resorption was not progressive, and the soft tissue changes remained unaltered. A broad musculo-periosteal pedicle consistent with the surgical objective should remain attached to the advanced genial segment to minimize osseous resorption and achieve more predictable soft tissue changes. We emphasize the need for a longer follow-up period (25-30 years) to determine the effect of the stabilization devices and osseous remodeling, specially in younger patients.

Adolescent↗
PubMed1992

Location of the nasolacrimal canal in relation to the high Le Fort I osteotomy.

The positional relationship between the high-level Le Fort I osteotomy and the nasolacrimal canal was studied in standard posteroanterior and lateral cephalograms made of 100 adult dry skulls after orienting the Frankfort horizontal of each skull to the natural horizontal plane. The simulated high-level Le Fort I osteotomy in all of the 100 skulls was under the level of the inferior orifice of the nasolacrimal canal by a mean distance of 5.2 mm (range, 0.5 to 11.5 mm). The average distance between the canal orifice and a line which extended from the lacrimal fossa to the anterior attachment of the inferior turbinate was 0.7 mm (range, 2.0 mm medially to 3.5 mm laterally). The maxillary height was strongly correlated to the height of the infraorbital foramen (r = .59, P less than .001) and the simulated osteotomy (r = .57, P less than .001). The results indicate that the osteotomy, when made just beneath the infraorbital foramen and extending into the piriform rim at the level of anterior attachment of the inferior turbinate, will usually not jeopardize the nasolacrimal duct within its bony canal. A line drawn from the lacrimal fossa to the anterior attachment of the inferior turbinate on the anterior aspect of the maxilla is a good approximation of the course of the nasolacrimal canal.

Humans↗
PubMed1992

Temporomandibular joint adaptation following inferior repositioning of the maxilla in adult monkeys.

Treatment of adults with vertical maxillary deficiency (short faces) has continually been an intriguing challenge for surgeons and orthodontists. For this category of patients, the introduction of simultaneous bone grafting and Le Fort I osteotomy has opened the door for improved treatment. However, despite the improved surgical techniques, surgeons have been reluctant to increase the vertical dimension of the maxilla by Le Fort I osteotomy with interpositional bone grafts because of inconsistent and variable stability after surgery. This study examines structural and functional adaptation of the adult temporomandibular joint and stability in a primate model following surgical lengthening of the maxilla in the vertical dimension. Results suggest that maxillary surgery and autorotation can alter condylar stress within physiologic ranges. However, further studies are indicated to clarify the surgery's long-term effect.

Adaptation, Physiological↗
PubMed1991

Bone resorption, stability, and soft-tissue changes following large chin advancements.

Large advancement genioplasties were performed in 10 patients (mean advancement, 11.7 mm) by horizontal osteotomy of the inferior border of the mandible, with preservation of a musculoperiosteal pedicle to the advanced genial segment. Preoperative, immediate postoperative, and long-term follow-up lateral cephalometric radiographs were retrospectively analyzed to evaluate the osseous and soft-tissue changes of the chin. After a mean follow-up period of 15 months, 76% of the initial advancement was preserved, representing 24% osseous resorption. The enveloping soft tissues of the chin followed the bony movement in a ratio of 1:0.88. Horizontal osteotomy of the inferior border of the mandible was a relatively stable procedure when used for large chin advancements. The broadcast possible musculoperiosteal pedicle should remain attached to the advanced genial segment to minimize osseous resorption and to achieve more predictable soft-tissue changes.

Adolescent↗