Morbidity after midline mandibulotomy and radiation therapy

PURPOSE

To assess the morbidity of mandibulotomy in patients treated for neoplasms of the oropharynx and oral cavity, and to determine if postoperative radiation therapy to the mandibulotomy site carries an increased risk of complications.

PATIENTS AND METHODS

The medical charts of 30 patients treated between 1992 and 1996 undergoing midline mandibulotomy for tumors of the oral cavity (7 patients) and oropharynx (23 patients) were retrospectively reviewed. Three patients presented with recurrent disease, 1 of whom was previously irradiated. Twenty-five patients received postoperative radiation after mandibulotomy to a median dose of 60 Gy to the primary tumor bed, whereas 5 patients were treated with surgery alone. The patients were separated into those whose mandibulotomy site was within the radiation treatment field (n = 9), and those whose site was shielded (n = 10). Median follow-up was 27.8 months (range 5-81 months). End points included significant pain involving the mandibulotomy site, trismus, malocclusion, wound infection, osteoradionecrosis, and time to oral intake.

RESULTS

There were no postoperative deaths. Minor wound infection or breakdown occurred in 4/30 patients (13%). All of these resolved with local care and parenteral antibiotics. More serious complications involving the mandibulotomy occurred in 2 patients (7%). One patient had chronic wound drainage at the mandibular osteotomy site, which healed after plate removal. Another patient developed osteoradionecrosis. No patient developed trismus or malocclusion. With a median follow-up of 27.8 months, 4 patients have recurred locally. The complication rate was 11% for patients whose mandibulotomy site was irradiated, and 30% for those whose site was shielded.

CONCLUSION

Mandibulotomy can be safely performed in patients who are likely to require postoperative external radiation.

[Effect of bFGF on regeneration of distracted mandibles after radiation]

The potential of distraction osteogenesis in mandibular reconstruction has been limited by its questionable efficacy in previously irradiated bone. The possible osteogenetic effect of recombinant human basic fibroblast growth factor (bFGF) on lengthening of irradiated mandibles was investigated in beagle dogs. We studied nine adult dogs which underwent a full course of external beam radiation therapy (60 Gy/30 fractions). Six months after completion of radiotherapy, the molars were extracted bilaterally followed by bone lengthening of the mandible using an intraoral device. On postoperative day 3 and 7 we injected 10 micrograms bFGF into the osteotomy site of each right hemimandible. The left sides were used as controls. The time course in ossification of the distracted area was evaluated at 2, 4, and 6 weeks after completion of bone lengthening. The radiographs of the newly formed bone tissue were measured by digital image analysis. Corresponding to the radiographic findings, the histological examination of the removed jaws showed an earlier and more intensive bone formation in the treated side after 2, 4, and 6 weeks compared to the control side. We conclude that bFGF promotes the ossification of distracted mandibles after radiation therapy in dogs.

[Retrospective analysis of the prognostic significance of the manner of mandibular resection and adjuvant radiotherapy in para-mandibular carcinomas]

The prognostic effect of bone resection (continuous vs non-continuous) was analysed in a retrospective study of 100 patients who were treated for squamous cell carcinoma located close to the lower jaw, between 1983 and 1994. Tumour stage, type of bone resection, extent of lymphatic node resection, dose of radiotherapy and chemotherapy were documented. Prognosis was characterised by the statistical end points "death", "metastasis" and "relapse". Thirty-two stage pT2 carcinomas, half of which were treated by continuous and half by non-continuous resection of the lower jaw, showed the same occurrence of the statistical end points death, metastasis or relapse. There was a trend towards a significantly longer survival time and metastasis-free interval in the group of continuous resection. The hazard ratios, however, showed no effect depending on the type of resection. However, both tumour stage (pTNM) and dose of radiation independently influenced prognosis in multivariate analysis. Consequently, three groups were defined. Univariate analysis of 62 patients without radiotherapy vs 19 with low-dose radiotherapy (36 Gy) and 19 with high-dose (62 Gy) showed a positive effect on the rate and time of survival in the group treated with high-dose radiotherapy. This was confirmed by multivariate analysis showing significantly lower hazard ratios for death and metastasis in the high-dose radiotherapy group after adjusting to cofactors (e.g. tumour stage). The data of this study challenge the current concept of resection of the lower jaw. However, due to the low number of patients and the retrospective character of the study, it is not possible to give suggestions regarding established therapy concepts. The advances of a high-dose radiotherapy in this study should be the subject of further multicentre retrospective and prospective randomised trials.

Implants placed in an irradiated dog mandible: a morphometric analysis

The objective of this research was to evaluate the influence of radiotherapy on the osseointegration of oral implants in a canine model. After the extraction of all mandibular premolars and first and second molars, 11 male beagles were divided into 3 groups. The control group (3 dogs) received no radiation. The second group (4 dogs) was irradiated 4 weeks after implantation. The third group (4 dogs) was irradiated 8 weeks before implantation. Eight implants were placed in each dog, in an alternating pattern: 4 non-submerged ITI Bonefit titanium plasma spray-coated and 4 submerged Steri-Oss hydroxyapatite-coated. The irradiated dogs received 4.3 Gy daily for 10 days. After 6 months of osseointegration, the dogs were sacrificed and each hemimandible was dissected to isolate the implants. Quantification of the extent of the direct bone-implant contact was carried out by scanning electron microscopy backscattered electron images that reproduced each implant in its entirety, using a digitizing table connected to a computer. The results were expressed as a percentage of direct bone-implant contact versus total perimeter accessible to bone. The bone contact percentage for the control group was 87% for Steri-Oss implants and 69% for the ITI Bonefit implants; for the animals irradiated after implantation, the percentages were 82 for Steri-Oss implants and 58 for ITI Bonefit implants; and for the animals irradiated before implantation, the percentages were 62 for Steri-Oss implants and 28 for ITI Bonefit implants. A statistically significant difference appeared between the 2 types of implants (P < .001). A statistically significant difference was also seen between the 3 groups for both types of implants, except between the control group and the group irradiated after implantation (P = .14). This indicates that, overall, the timing of irradiation influences osseointegration. Osseointegration is possible before and after radiotherapy; however, the direct bone-implant contact increased when the implants were placed before irradiation.

Effects of cancer therapy on dental and maxillofacial development in children: report of case

Malignant lymphoma is one of the most common hematological diseases of children. The prognosis is fairly good with multimodal cancer therapy. We reported a boy with Burkitt's lymphoma in the nasal cavity who received chemotherapy and irradiation of the head and neck area at four years of age. During seven years of follow-up, we studied the developmental effects of cancer therapy, including general growth, maxillofacial bones, and dentition. Compared with boys of matching age, the development of his entire body and maxillofacial bones was delayed. In the irradiated areas, the roots of teeth were short or poorly developed and the root apices showed premature closure. After the patient was in remission from the tumor in his early childhood, the long-term effects of cancer therapy on dental and maxillofacial development are worth our further evaluation and follow-up.

Optimisation of patient doses in programmable dental panoramic radiography

OBJECTIVES

To estimate the radiation-related risk associated with twelve imaging programs available on the Orthophos (Siemens, Erlangen, Germany) dental panoramic radiography unit.

METHODS

Organ absorbed doses for each program were measured using a Rando anthropomorphic phantom loaded with thermoluminescent dosemeters. Effective dose (E) was calculated in two ways; first, using the method recommended by the International Commission on Radiological Protection, which excludes the salivary glands (designated Eexc), and second, with its inclusion (designated Einc). Organ and effective doses were both used to compare the various imaging programs.

RESULTS

In 11 of the 12 programs studied the salivary glands received the highest individual organ dose, and Einc was found to be up to double Eexc. When the image was restricted to the dentition (program 2) organ doses were lower than for the complete jaws (program 1) by up to 85%, and Eexc and Einc reduced by about one half. When programs 2 and 6 (to image the temporomandibular joints) are used in place of program 1, the former combination provides more image information at an equivalent risk.

CONCLUSIONS

The value of E in panoramic radiography depends on the inclusion of the salivary glands in the calculation and the magnitude of the dose.

A study on the morphological changes of the rat mandibular bone with TEA CO2 laser

OBJECTIVE

The purpose of this study was to investigate the morphological changes of the bone structure induced by transversely excited, atmospheric TEA pressure CO2 laser irradiation. Moreover, the healing process at 3 weeks was also observed.

SUMMARY BACKGROUND DATA

It has been demonstrated that dental hard tissue can be removed by a long pulse of TEA CO2 laser irradiation with minimal thermal damage. However, there are few studies on the morphological changes of the TEA CO2 laser on bone tissue.

METHODS

The TEA CO2 laser was irradiated on the surface of the rat mandibular bone under the following irradiation conditions: wavelength, 10.6 microns; output, 95 mJ/pulse; pulse repetition rate, 1 Hz; irradiation time, 7.5 microseconds/shot; spot size, 0.8 x 1.5 mm; energy density, 7.9 J/cm2. Histological and scanning electron microscopic examinations were performed.

RESULTS

In the stereoscopic examination, a defect with clean-cut margins was produced. In the light microscopic examination, a basophilic line at the bottom of the defect was noted. Examining the defect with SEM, a smear-like appearance and cone structures were found. In the histological examination, a healing process by formation of new bones at the junction site was recognized.

CONCLUSIONS

These findings suggest that it is possible to remove bone tissues by TEA CO2 laser irradiation. However, a particle-like structure associated with a basophilic line and melted surface indicated that some thermal damage was produced during the laser irradiation.

Osteoradionecrosis of the mandible: a microradiographic study of cortical bone

We undertook a microradiographic study in osteoradionecrotic mandibular bone to estimate the number of vascular channels in the compact bone, number of resorption areas, and number of regeneration areas. Normal mandibles had a similar number of vascular channels/vision field compared with compact bone in other parts of the body. Irradiation itself did not significantly alter this number. After osteoradionecrosis had developed in the mandible, the number of vascular channels increased (p = 0.02). Treatment with hyperbaric oxygen further increased the number of vascular channels/vision field (p < 0.003). The normal mandible had no resorptive or regenerative areas, either before or after radiotherapy. The osteoradionecrotic mandible, however, had an increased number of resorptive as well as regenerative areas/vision field. Fluorescence as an indication of incorporation of tetracycline was seen in the regenerative areas of all osteoradionecrotic specimens treated with doxycycline. The process started from the vascular channels, periosteum, and endosteum. We conclude that the compact bone of mandibular osteoradionecrosis has high metabolic activity with active resorption and regeneration of bone and the limitation of the blood supply through cortical vascular channels, seems to be only one of many important factors.

[Comparative studies of Brånemark implants in the irradiated and not irradiated mandible]

A comparative study was carried out of 276 Brånemark fixtures in the irradiated and nonirradiated anterior mandible with a mean follow-up period of 58.2 months. Postoperative radiotherapy with 60 Gy and 100% isodose for the anterior mandible using a 6-MV linear accelerator, conventional fractioning, and a split-course technique was administered in the irradiated patient group. HBO therapy was not applied. A statistical difference in the 5-year success rate between the irradiated and nonirradiated group was not found. Nevertheless, a significantly higher rate of perioperative soft tissue complications at implant insertion was seen in the irradiated group. The statistical analysis showed no significance for sex, interval between radiation and implant insertion (with a minimum of 10 months), or type of periimplant soft tissue (regional vs. flap). The prognosis for implants in the irradiated mandible was, however, statistically improved (n = 0.0035) when the healing period was longer than 4 months. Mobile periimplant soft tissue proved to be the main problem regardless of radiation load. Late complications have not been observed so far. The available results and clinical studies support a positive assessment of the regenerative potential of the irradiated mandible with regard to osteointegration of endosseous implants. A preceding radiotherapy up to 60 Gy should therefore not be considered as a contraindication for an implant/prosthetic rehabilitation.

The cranial-spinal junction in medulloblastoma: does it matter?

PURPOSE

Late effects of treatment in children and young adults with medulloblastoma can be influenced by the technique employed in radiating the craniospinal axis. The purpose of this study is to determine whether the placement of the cranial-spinal junction has an impact on dose to the cervical spinal cord and surrounding organs.

METHODS AND MATERIALS

Five patients underwent computed tomography (CT) simulation in the prone position for craniospinal irradiation. A dose of 36 Gy was prescribed to the entire neuraxis. The doses to the cervical spinal cord and surrounding organs were calculated using a cranial-spinal junction at the C1-C2 vertebral interspace (high junction) or at the lowest point in the neck, with exclusion of the shoulders in the lateral cranial fields (low junction). The volume of critical organs at risk, as well as dose to these structures using the cranial and spinal field(s) were outlined and calculated using the CMS FOCUS 3-dimensional treatment planning system.

RESULTS

The average dose to the cervical spinal cord was 11.9% higher than the prescribed dose with the low junction, and 6.7% higher with the high junction. However, doses to the thyroid gland, mandible, pharynx, and larynx were increased by an average of 29.6%, 75.8%, 70.6%, and 227.7%, respectively, by the use of the high junction compared to the low junction.

CONCLUSION

A higher dose to the cervical spinal cord can be minimized by using a high junction. However, this would be at the cost of substantially increased doses to surrounding organs such as the thyroid gland, mandible, pharynx, and larynx. This can be critical in children and young adults, where hypothyroidism, mandibular hypoplasia, and development of second malignancies may be a late sequela of radiation therapy.

Clinical delivery of intensity modulated conformal radiotherapy for relapsed or second-primary head and neck cancer using a multileaf collimator with dynamic control

BACKGROUND AND PURPOSE

Concave dose distributions generated by intensity modulated radiotherapy (IMRT) were applied to re-irradiate three patients with pharyngeal cancer.

PATIENTS, MATERIALS AND METHODS

Conventional radiotherapy for oropharyngeal (patients 1 and 3) or nasopharyngeal (patient 2) cancers was followed by relapsing or new tumors in the nasopharynx (patients 1 and 2) and hypopharynx (patient 3). Six non-opposed coplanar intensity modulated beams were generated by combining non-modulated beamparts with intensities (weights) obtained by minimizing a biophysical objective function. Beamparts were delivered by a dynamic MLC (Elekta Oncology Systems, Crawley, UK) forced in step and shoot mode.

RESULTS AND CONCLUSIONS

Median PTV-doses (and ranges) for the three patients were 73 (65-78), 67 (59-72) and 63 (48-68) Gy. Maximum point doses to brain stem and spinal cord were, respectively, 67 Gy (60% of volume below 30 Gy) and 32 Gy (97% below 10 Gy) for patient 1; 60 Gy (69% below 30 Gy) and 34 Gy (92% below 10 Gy) for patient 2 and 21 Gy (96% below 10 Gy) at spinal cord for patient 3. Maximum point doses to the mandible were 69 Gy for patient 1 and 64 Gy for patient 2 with, respectively, 66 and 92% of the volume below 20 Gy. A treatment session, using the dynamic MLC, was finished within a 15-min time slot.

Rehabilitation with dental implants of oral cancer patients

The aim of this study was to evaluate the risks and complications of rehabilitation with dental implants after tumour surgery and radiotherapy. After a disease-free survival of 18 months, 29 patients who had undergone oral cancer treatment were rehabilitated with dental implants. The complication rate of implants in irradiated, non-irradiated and grafted bone was analyzed at least 3 years after implant placement. In the healing period, 28.6% of the implants in irradiated bone and 8.4% in non-irradiated bone showed soft tissue complications. Of the implants, 26.7% in the irradiated and 14.7% in the non-irradiated mandibular bone were lost in the first 36 months after placement. Thirty-one point two percent of implants inserted in non-irradiated bone grafts were affected and did not osseointegrate. Of 109 inserted implants, 70 were suitable for prosthetic rehabilitation. There are high complication rates after implant placement in oral cancer patients. Irradiation adversely affects soft tissue healing. Osseointegration is frequently disturbed, especially when implants were placed in non-vascularized bone grafts.

Histologic evidence of osseointegration in the irradiated and reconstructed mandible: a case report

Osseointegrated implants are widely used in dental rehabilitation. They are particularly valuable if the structures supporting a denture had to be removed because of oral cancer. Additionally, many of these patients undergo radiotherapy, but cancer and radiotherapy are seen as relative contraindications for implant therapy. In the literature, there are few clinical studies documenting successful oral rehabilitation using implants in such patients. The authors report a clinical case in which histologic evidence of osseointegration can be demonstrated in an irradiated and reconstructed mandible. This observation should encourage the extended application of implants in rehabilitation following oral cancer surgery.

Effect of biphosphonates on abnormal mandibular growth of rats intoxicated with uranium

Intoxication with uranium induces severe alterations in kidneys and in acute intoxications inhibits bone formation and bone growth. Administered at high doses, uranium leads to death, an event that can be prevented by the administration of ethane-1-hydroxy-1,1 biphosphonate (EHBP), which would presumably exert its effect via its chelating properties. Based on this information, the aim of the present study was to determine the best therapeutic method for treatment using biphosphonates to prevent mandibular growth alterations in animals that survive uranyl nitrate poisoning. Seven groups of Wistar rats weighing 14 g were used as follows: I, untreated control; II, one intraperitoneal injection (IPI) of 2 mg Kg(-1) of body weight of uranyl nitrate (238U). In groups III to VII animals were intoxicated as in Group II and in addition were given a single injection of 10 mg Kg(-1) of ethane-1-hydroxy-1, 1-biphosphonate (EHBP), or 3-amine-1, 1-hydroxypropylene-1, 1 biphosphonate (APD) as follows; Group III, IPI of EHBP given immediately after poisoning (0 h); IV, IPI of EHBP given at 24 h; V, subcutaneous injection (SCI) of EHBP at 0 h; VI, SCI of EHBP at 48 h; VII SCI of APD at 0 h. Survivors were killed on the sixtieth day. Body weight increase, survival rate, and biometric parameters of mandibular growth (Eratalay's method) were studied. Student's "t" test was used for statistical analysis. On day 60 there was only one survivor in Group II and none in Group IV. All animals in the other groups survived. Mandibular growth parameters showed the worst results in Group VII and the best in Group V for which no difference with the controls was observed. These results show that a single subcutaneous injection of EHBP given immediately after uranium poisoning, apart from preventing death, is capable of preventing undesirable alterations in mandibular growth.

Craniofacial growth in children treated for malignant diseases

With the improving cure rate in childhood malignancies, increasing interest has been focused on the long-term survivors of childhood cancer and the quality of their life. The severity of long-term disturbances in dental and craniofacial development is dependent on the age of the child at diagnosis, if chemotherapy is combined with radiation or not. With regard to craniofacial development combination chemotherapy has no effects compared with healthy controls, whereas children treated cranial irradiation before 5 years of age exhibit a reduced growth of the mandible. Conditioning before bone marrow transplantation with total body irradiation results in a significantly reduced growth of the craniofacial skeleton. The mandible was four times more radiosensitive compared with the maxilla. With attention to the dental and craniofacial development, occlusion and craniomandibular function, children in risk groups should be followed, and given prophylactic treatment and intervention at appropriate times to reduce the consequences of the disease itself and the therapy given.

Endosseous implant and autogenous bone graft reconstruction of mandibular discontinuity: a 12-year longitudinal study of 31 patients

Surgical, medical, and prosthodontic records of 61 consecutively treated patients with mandibular discontinuity were reviewed retrospectively. All 61 patients had undergone discontinuity reconstruction with autogenous bone grafts; 31 of 61 had also received endosseous dental implants and a dental osseoprosthesis. Of these 31 implant-reconstructed patients, 23 had free autogenous nonvascularized and 8 had vascularized bone grafts. The surgical-prosthetic protocol consisted primarily of secondary, free autogenous nonvascularized bone graft reconstruction and secondary root-form endosseous implant and fixed prosthesis dental reconstruction. Vascularized bone (8 patients) or soft tissue (4 patients) grafts were utilized selectively for severely compromised patients after extensive oncologic resection, avulsive trauma, or after previous radiation treatment. Endosseous implant survival (95.5% in 31 patients), autogenous bone graft success (98.4% in 61 patients), and dental osseoprosthesis success (100% in 31 patients) were favorable. A high incidence (9.1%) of nonfunctioning (sleeping) implants was recorded for this patient population. The need to remove the titanium mesh tray for various reasons (17.6%) and the need to reconstruct soft tissue in the irradiated patient (12%) were noteworthy.

A review of the Marx protocols: prevention and management of osteoradionecrosis by combining surgery and hyperbaric oxygen therapy

The 30/10 protocol is employed in the treatment of established osteoradionecrosis. No surgery should be attempted before the first 30 HBO treatments have provided sufficient angiogenesis to support surgical wounding. After 30 treatments surgical management can be staged according to the extent of improvement achieved after HBO and the size of sequestrum or area of osteolysis. If the ORN extends to the inferior border of the mandible or if it manifests as an orocutaneous fistula or pathological fracture, discontinuity resection of the necrotic bone and soft tissue will be required to resolve the disease. Unless HBO and surgery are combined in the management of ORN, the results are not long lasting or satisfactory. Even though resection of stage three ORN seems unduly aggressive, it has stood the test of time. By using the Marx protocols in the treatment of ORN, more than 95 per cent of patients can be successfully cured of their disease with predictable, functional and aesthetically acceptable outcomes.

Experimental study of radiation effect on the mandibular microvasculature of the guinea pig

OBJECTIVE

This experimental study was performed to explore the intraosseous microvascular alterations in the irradiated mandible and to increase understanding of the pathogenesis of osteoradionecrosis.

METHODS

One hundred twenty-eight guinea pigs were grouped according to different radiation sources and dosages. Fractioned radiation was delivered to the right mandibles. Dental extractions were conducted at 1, 3, and 5 months respectively, after radiation. One month later, the animals were examined by means of gross observation, histopathology, and microvascular corrosion castings.

RESULTS

Histologic evaluation showed bone absorption within 2 months following radiation. Four months later, the number of osteocytes decreased and pyknosis and empty lacunae were commonly seen. The casting specimens revealed under scanning electron microscopy that capillary disconnection and obliteration with subsequent vein shrinkage aggravated over time. In the nonhealing dental extraction site, a large-scale vascular network defect presented with focal capillary proliferation around.

CONCLUSIONS

The capillary is the part most vulnerable to the damage caused by radiation in the vascular system of the mandible. On the basis of "hypovascular, hypoxic, hypocellular" structure, local microcirculation failure induced by the trauma-repairing process leads to occurrence of osteoradionecrosis of jaws.

An evaluation of root canal treatment in patients who have received irradiation to the mandible and maxilla

OBJECTIVE

The purpose of this study was to evaluate the success and failure of root canal treatment performed in areas of previous irradiation and to examine any cases of osteoradionecrosis associated with such treatment.

STUDY DESIGN

A retrospective analysis was done on 22 teeth that had root canal treatment after radiation therapy. Strict radiographic and clinical criteria were used to determine success and failure.

RESULTS

There was a mean follow-up period of 19 months. Of 22 cases, 20 (91%) were considered successful. Both failures occurred with a diagnosis of pulpal necrosis. There were no occurrences of osteoradionecrosis.

CONCLUSIONS

Our study showed that root canal treatment in previously irradiated patients may be successful. In addition, treatment approaches, as well as the criteria for success and failure, should be the same for irradiated patients as for those who have not received radiation treatment.

Dental prosthetic reconstruction of osseointegrated implants placed in irradiated bone

Nineteen patients who were treated for oncologic pathology by surgery and radiotherapy (average dose = 57 Gy) received prosthetic reconstruction with 53 implants placed in the residual mandible or maxilla and/or replacement bone graft. Implants were placed within a minimum period of 5 months after radiotherapy. The healing period before placement of the prosthesis also was at least 5 months. Two to six implants were placed as a function of tooth loss and required prosthetic design. Prostheses included both removable and fixed restorations. Two implants were lost as a result of osseointegration failure. Fifteen implants in six patients could not be followed throughout the study because of patient expiration. Patients were followed up to 68 months and for an average of 38 months. No osteoradionecrosis phenomenon was seen in this study. However, caution is urged in placing implants in irradiated bone because of the potential for osteoradionecrosis. Patients should be carefully selected and a strict therapeutic protocol should be followed.

[Secondary repair of oro-pharyngectomy with mandibular resection and radionecrosis]

There are two pitfalls to be avoided in transmandibular buccopharyngectomy: mandibular amputation and inversely a contemplative wait-and-see attitude. Preservative measures require a precise evaluation of bone invasion, surgical approaches respecting the lip and cutaneo-muscular flaps, and an early assessment of the secondary effects of radiotherapy. Reasonable use of bone periosteal free flaps and striving for immediate reconstruction of each defect certainly leads to an interventionist behavior, but which can be conducted under better conditions and more attainable objectives than after mandibular deformation, a pharyngostomia or recent radionecrosis. Microsurgical procedures are nothing more than technical mastery and can lead to arrogant behavior. Fifty cases illustrate this position.

Effects of irradiation and methyl-triazene on craniofacial development in mouse embryos: a semiautomated morphometric analysis

OBJECTIVE

The purpose of the present study was a 2D-semiautomated morphometric analysis of craniofacial growth in nuclear magnetic resonance imaged (NMRI) mouse embryos.

METHODS

The NMRI mouse embryos were exposed in utero to either a single dose of 2 Gy X-irradiation on day 9 of gestation (113 embryos) or to 1.5 mg methyl-triazene administered orally to their pregnant mothers on gestational day 10.5 (124 embryos). An additional group of 108 embryos was used as controls. Digitized pictures of embryos from gestational days 14 to 17 were taken in lateral right view using a video system. Landmarks were located and digitized for computerized analysis of growth changes in relation to developmental stages of the face.

RESULTS

The results revealed that the snout of control embryos lengthens during the developmental period considered. The snout of embryos previously submitted to methyl-triazene displayed micrognathia, and all treated fetuses exhibited macroscopic signs of microcephaly with a reduced mandible. The snouts of irradiated embryos appeared shortened at the 14-day stage and continued to shorten as development proceeded. A shortening of the midface was detected macroscopically in 83% of the cases.

CONCLUSION

The results of this morphometric analysis enabled us to trace the developmental progression of the induced dysmorphosis and to assess the differences compared with normal development.

Dosimetric measurement of scattered radiation from dental implants in simulated head and neck radiotherapy

The purpose of this study was to examine the dose enhancement at bone-implant interfaces from scattered radiation during simulated head and neck radiotherapy. Three cylindric implant systems with different compositions (pure titanium, titanium-aluminum-vanadium alloy, titanium coated with hydroxyapatite) and a high gold content transmandibular implant system (gold-copper-silver alloy) were studied. Extruded lithium fluoride single crystal chips were used as thermoluminescent material to measure radiation dose enhancement at 0, 1, and 2 mm from the bone-implant interface. The relative doses in buccal, lingual, mesial, and distal directions were also recorded and compared. The results indicated that the highest dose enhancement occurred at a distance of 0 mm from the bone-implant interface for all the implant systems studied. The transmandibular implants had higher scattered radiation than other groups at 0 mm and at 1 mm from the bone-implant interface. There was no significant difference of dose enhancement between buccal, lingual, mesial, and distal directions. Titanium implants coated with hydroxyapatite demonstrated the best results under the simulated irradiation.

Osseointegration of dental implants in bone irradiated with 40, 50 or 60 gy doses. An experimental study with beagle dogs

Construction of different kinds of prostheses on irradiated bone tissues after tumour surgery is a complicated part of modern implantology. In irradiated regions of the jaws where the bone layers are thin and the blood supply also is minimal, knowledge of the impact of each dose of radiation is very important. The aim of this study was to compare the bone response around titanium implants loaded with fixed bridges in dog mandibles irradiated with total doses of 40, 50 or 60 Gy. The results suggest that after irradiation with 40-50 Gy, when the dose is fractioned in order to achieve higher tolerance of the tissues compared with single dose irradiation, titanium implants may become osseointegrated in the mandibles. For high success rates, however, careful planning of radiotherapy and selection of implantation site with an adequate blood supply are essential.