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Biomedical subjects

D Buser

Publications and source records attributed to D Buser.

105 records · Page 6Linked to original sources
PubMedDate not supplied

Hypothetical mortality risk associated with spiral computed tomography of the maxilla and mandible.

In the present study, dose measurements have been conducted following examination of the maxilla and mandible with spiral computed tomography (CT). The measurements were carried out with 2 phantoms, a head and neck phantom and a full body phantom. The analysis of applied thermoluminescent dosimeters yielded radiation doses for organs and tissues in the head and neck region between 0.6 and 16.7 mGy when 40 axial slices and 120 kV/165 mAs were used as exposure parameters. The effective dose was calculated as 0.58 and 0.48 mSv in the maxilla and mandible, respectively. Tested methods for dose reduction showed a significant decrease of radiation dose from 40 to 65%. Based on these results, the mortality risk was estimated according to calculation models recommended by the Committee on the Biological Effects of Ionizing Radiations and by the International Commission on Radiological Protection. Both models resulted in similar values. The mortality risk ranges from 46.2 x 10.6 for 20-year-old men to 11.2 x 10(-6) for 65-year-old women. Using 2 methods of dose reduction, the mortality risk decreased by approximately 50 to 60% to 19.1 x 10(-6) for 20-year-old men and 5.5 x 10(-6) for 65-year-old women. It can be concluded that a CT scan of the maxillofacial complex causes a considerable radiation dose when compared with conventional radiographic examinations. Therefore, a careful indication for this imaging technique and dose reduction methods should be considered in daily practice.

Adult↗
PubMedDate not supplied

The radiographic assessment of implant patients: decision-making criteria.

Indications for the most frequently used imaging modalities in implant dentistry are proposed based on clinical need and biologic risk for the patient. To calculate the biologic risk, the authors carried out dose measurements. They demonstrated that the risk from a periapical radiograph is 20% of that from a panoramic radiograph. A panoramic radiograph and a series of 4 conventional tomographs of a single-tooth gap in the molar region carry 5% and 13% of the risk from computed tomography of the maxilla, respectively. Panoramic radiography is considered the standard radiographic examination for treatment planning of implant patients, because it imparts a low dose while giving the best radiographic survey. Periapical radiographs are used to elucidate details or to complete the findings obtained from the panoramic radiograph. Other radiographic methods, such as conventional film tomography or computed tomography, are applied only in special circumstances, film tomography being preferred for smaller regions of interest and computed tomography being justified for the complete maxilla or mandible when methods for dose reduction are followed. During follow-up, intraoral radiography is considered the standard radiographic examination, particularly for implants in the anterior region of the maxilla or for scientific studies. In patients requiring more than 5 periapical images, panoramic radiography is preferred.

Decision Making↗
PubMedDate not supplied

Lateral ridge augmentation and implant placement: an experimental study evaluating implant osseointegration in different augmentation materials in the canine mandible.

The present study investigated the osseointegration of dental implants with a titanium plasma-sprayed surface (TPS) in regenerated and native bone in an experimental dog study. Initially, lateral bone defects were created in the alveolar ridge on both sides of the mandible. Two months later, lateral ridge augmentation was performed with (1) autogenous corticocancellous block grafts, (2) autogenous corticocancellous block grafts and e-PTFE membrane, (3) tricalcium phosphate particles and e-PTFE membrane, or (4) canine-derived demineralized freeze-dried bone allograft particles and e-PTFE membrane. After 4 months, membranes were removed, and non-submerged titanium implants were placed in regenerated bone (test implants) and in native bone (control implants). Two months later, the animals were sacrificed and non-decalcified orofacial sections were evaluated histometrically. All implants demonstrated high percentages (59% to 75%) of bone-to-implant contact, with no significant differences across the various treatment groups. The different grafting techniques did not significantly influence the location of first bone-to-implant contact and the horizontal bone width at the most coronal bone level.

Alveolar Ridge Augmentation↗
PubMedDate not supplied

Crestal bone changes around titanium implants: a methodologic study comparing linear radiographic with histometric measurements.

Generally, endosseous implants can be placed according to a nonsubmerged or a submerged technique and in 1-piece or 2-piece configurations. Recently, it has been shown that peri-implant crestal bone reactions differ significantly radiographically as well as histometrically under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of a microgap (interface) between the implant and the abutment/restoration in 2-piece configurations. The purpose of this study was to evaluate whether standardized radiography as a noninvasive clinical diagnostic method correlates with peri-implant crestal bone levels as determined by histometric analysis. Fifty-nine implants were placed in edentulous mandibular areas of 5 foxhounds in a side-by-side comparison in both submerged and nonsubmerged techniques. Three months after implant placement, abutment connection was performed in the submerged implant sites. At 6 months, all animals were sacrificed, and evaluations of the first bone-to-implant contact (fBIC), determined on standardized periapical radiographs, were compared to similar analyses made from nondecalcified histology. It was shown that both techniques provide the same information (Pearson correlation coefficient = 0.993; P < .001). The precision of the radiographs was within 0.1 mm of the histometry in 73.4% of the evaluations, while the level of agreement fell to between 0.1 and 0.2 mm in 15.9% of the cases. These data demonstrate in an experimental study that standardized periapical radiography can evaluate crestal bone levels around implants clinically accurately (within 0.2 mm) in a high percentage (89%) of cases. These findings are significant because crestal bone levels can be determined using a noninvasive technique, and block sectioning or sacrifice of the animal subject is not required. In addition, longitudinal evaluations can be made accurately such that bone changes over various time periods can be assessed. Such analyses may prove beneficial when trying to distinguish physiologic changes from pathologic changes or when trying to determine causes and effects of bone changes around dental implants.

Alveolar Process↗
PubMedDate not supplied

Healing pattern of bone regeneration in membrane-protected defects: a histologic study in the canine mandible.

In this study, standard and prototype reinforced e-PTFE membranes were used to evaluate the pattern of bone regeneration in membrane-protected defects in the mandibles of four dogs. Following a healing period of 2 and 4 months, control sites without membranes exhibited incomplete osseous healing with a persisting defect. Test sites with membranes demonstrated significantly better bone healing, although bone regeneration was not yet completed at 4 months. The histologic evaluation showed that bone regeneration, once activated, progresses in a programmed sequence through a series of maturation steps, which closely resemble the pattern of bone development and growth.

Alveolar Process↗
PubMedDate not supplied

Osseointegration of titanium implants in bone regenerated in membrane-protected defects: a histologic study in the canine mandible.

In the present histologic study of the mandibles of five foxhounds, 15 nonsubmerged titanium implants were placed in bone regenerated in extended membrane-protected defects during a 6-month healing period. The clinical and radiographic evaluation demonstrated that all 15 implants achieved functional ankylosis within 3 months following implant placement. Subsequently, eight implants were restored with fixed partial dentures and were functionally loaded for 6 months, and seven implants were left unrestored. At the completion of the study, the histologic analysis demonstrated osseointegration with direct bone-to-implant contact for all 15 implants. Therefore, it can be concluded that bone regenerated in membrane-protected defects responds to implant placement like nonregenerated bone, and that this bone is capable of bearing and sustaining functional load. The histologic comparison of restored and unrestored sites demonstrated no apparent differences concerning bone remodeling activities. Furthermore, control sites without implant placement demonstrated bone atrophy underneath the membranes with a thin cortical layer and sparse bone trabeculae. Thus, it can also be concluded that the placement of an implant into regenerated bone stimulated bone maturation and bone remodeling, whereas implant loading did not influence bone remodeling in the present study model.

Alveolar Bone Loss↗
PubMedDate not supplied

Implant-supported restorations in the anterior region: prosthetic considerations.

Achieving functional and aesthetic implant-supported restorations in the partially edentulous patient can be particularly challenging when the implant sites are in the anterior region and not in harmony with the adjacent dentition. The learning objective of this article is to focus on presurgical evaluation of anterior implant sites and systematic development of related therapeutic modalities. Utilization of guided bone regeneration and connective tissue grafting predictably facilitates implant positioning that is compatible with required aesthetic restoration and soft tissue contours. Other aspects, such as abutment protection caps with variable emergence profiles, provisional restorations for the development of optimal periimplant soft tissue contours, and fabrication guidelines for different types of prosthetic restorations, are also discussed.

Alveolar Ridge Augmentation↗
PubMedDate not supplied

Radiographic analysis of regenerated bone around endosseous implants in the canine using recombinant human bone morphogenetic protein-2.

Ideal endosseous implant placement involves a congruent bony housing in close apposition to the implant surface. Clinical situations are encountered, however, in which the entire implant surface cannot be in close apposition to bone. In these instances, bone grafting materials are generally used to regenerate bone around the implant. In this study, a biologically active bone differentiation factor, recombinant human bone morphogenetic protein-2 (rhBMP-2), was used with two different carriers to regenerate bone around implants in standardized critical-sized defects in the canine mandible. Half of the sites had a nonresorbable membrane placed over the defect. Longitudinal standardized radiographs were obtained to assess the amount of bone regeneration on the mesial and distal of the implants after 4 and 12 weeks of healing. Ninety-six implants were placed in 12 fox-hounds. Bone fill was determined by linear measurement of bone on the radiographs, and changes in bone density were evaluated by computer-assisted densitometric image analysis of discrete areas adjacent to the implant. After 4 weeks of healing, nonmembrane sites had significantly greater bone height than membrane-protected sites. Following 12 weeks of healing, sites treated with rhBMP-2 had significantly greater bone formation than untreated sites. Sites treated with rhBMP-2 and a membrane had the greatest bone fill, followed by sites treated with rhBMP-2 but no membrane. Sites without rhBMP-2, whether with or without a membrane, had less bone fill than sites with rhBMP-2. At 12 weeks, sites with a membrane resulted in significantly more gain in bone density than sites without a membrane. Furthermore, sites treated with a collagen carrier resulted in greater gains in bone density than sites treated with a polylactide/glycolide carrier. The results from this study demonstrate by radiographic evidence that new bone formation in critical-sized defects around implants is dependent on time after defect treatment, the type of carrier used, the use of a barrier membrane, and the presence of rhBMP-2. In addition, these findings suggest that rhBMP-2, a bone differentiation factor, can significantly stimulate bone formation around endosseous dental implants.

Analysis of Variance↗
PubMedDate not supplied

Implants placed in immediate extraction sites: a report of histologic and histometric analyses of human biopsies.

Five titanium plasma-sprayed implants were biopsied from a human volunteer 6 months after placement. Four test implants had been placed in immediate extraction sockets, while one implant was placed in a mature site and served as a control. The histologic analysis demonstrated that all five implants achieved osseointegration as demonstrated by light microscopy, whereas a varying degree of bone-implant contact was observed. The non-loaded control implant had the highest percentage of bone-implant contact, 72%, followed by the two implants placed in the canine sites presenting with a horizontal defect dimension of 1.5 nm or less. These implants were placed without a barrier membrane, but in a submerged fashion. The histometric analysis showed a mean bone-implant contact of 50% for these two implants. The lowest mean bone-implant contact (17%) was observed for the two molar implants, which had horizontal defect dimensions of 4 mm; these implants were placed in a non-submerged fashion with the implants perforating an expanded polytetrafluoroethylene membrane. The authors concluded that osseointegration may occur in immediate extraction sites in humans using titanium implants with a plasma-sprayed surface. The horizontal component of the peri-implant defect was apparently the most critical factor relating to the final amount of bone-implant contact.

Alveolar Process↗
PubMedDate not supplied

Removal torque values of titanium implants in the maxilla of miniature pigs.

The purpose of this study was to compare side-by-side two different titanium screw-type implants in the maxillae of miniature pigs. The test implants had a machined and acid-etched surface (Osseotite) whereas the control implants were sandblasted and acid-etched (SLA). After 4, 8, and 12 weeks of healing, removal torque testing was performed to evaluate the shear strength of the bone-implant interface for both implant types. The results demonstrated significant differences between both implant types (P < .01). Osseotite implants revealed mean removal torque values (RTV) of 62.5 Ncm at 4 weeks, 87.6 Ncm at 8 weeks, and 95.7 Ncm at 12 weeks of healing. In contrast, the SLA implants demonstrated mean RTV of 109.6 Ncm, 196.7 Ncm, and 186.8 Ncm at corresponding healing periods. The mean RTV for SLA implants was 75% to 125% higher than for Osseotite implants up to 3 months of healing.

Analysis of Variance↗