Time-related root resorption after application of a controlled continuous orthodontic force

The aim of this investigation was to study root resorption after application of a weekly controlled, continuous orthodontic force of 50 cN (approximately 50 gm). Fifty-six maxillary premolars in 18 boys and 38 girls (mean age 13.8 years) were moved buccally with a fixed orthodontic appliance. The contralateral premolar served as a control. The experimental periods varied from 1 to 7 weeks with eight children in each group. Root resorption was registered after 1 week and occurred in all test teeth but four. The surface extension as well as the depth of the resorption showed a marked increase after 2 weeks. Starting from the third week, eight test teeth exhibited apical root resorption that had reached half way to the pulp, or more. After 7 weeks, the test teeth showed on average more than 20 times larger mean resorbed root contour than the control teeth. Individual variations were considerable regarding both extension and depth of root resorption within each test group and were not correlated to the magnitude of tooth movement achieved. The radiographs failed to reveal any adverse tissue reactions. The great individual variations in root resorption without association to the amount of tooth displacement indicate that so far unknown individual factors are influential in these adverse tissue reactions.

Direct cancer tissue proteomics: a method to identify candidate cancer biomarkers from formalin-fixed paraffin-embedded archival tissues

Successful treatment of multiple cancer types requires early detection and identification of reliable biomarkers present in specific cancer tissues. To test the feasibility of identifying proteins from archival cancer tissues, we have developed a methodology, termed direct tissue proteomics (DTP), which can be used to identify proteins directly from formalin-fixed paraffin-embedded prostate cancer tissue samples. Using minute prostate biopsy sections, we demonstrate the identification of 428 prostate-expressed proteins using the shotgun method. Because the DTP method is not quantitative, we employed the absolute quantification method and demonstrate picogram level quantification of prostate-specific antigen. In depth bioinformatics analysis of these expressed proteins affords the categorization of metabolic pathways that may be important for distinct stages of prostate carcinogenesis. Furthermore, we validate Wnt-3 as an upregulated protein in cancerous prostate cells by immunohistochemistry. We propose that this general strategy provides a roadmap for successful identification of critical molecular targets of multiple cancer types.

Augmentation of intramembraneous bone beyond the skeletal envelope using an occlusive titanium barrier. An experimental study in the rabbit

The aim of this investigation was to evaluate whether augmentation of intramembraneous bone beyond the skeletal envelope can be predictably achieved by placing a completely occlusive barrier on the skull bone of rabbits, hereby creating a secluded space with bone tissue being the only adjoining tissue. The experiment was carried out in 3 New Zealand white rabbits. In each animal, a midline incision was made down to the bone surface of the skull and a skin-periosteal flap was raised to expose the skull bone on both sides of the midline. Two prefabricated titanium domes with an inner diameter of 4.5 mm and an inner height of 3.0 mm were installed on each side. The domes were supplied with a horizontal, peripheral flange and a vertical edge, fitting tightly into a circular slit, prepared by a trephine into the skull bone. This arrangement ensured a stable anchorage of the dome and a reliable peripheral sealing of the space. The skin-periosteal flaps were relocated to cover the domes and sutured. After a healing period of 3 months, the animals were killed and the experimental areas excised and prepared for histological transversal ground sections with each dome in situ. The results demonstrated complete bone fill of all domes, with no signs of ingrowth of other types of tissues, indicating that the use of a barrier with total occlusiveness, sufficient stiffness and stability and reliable peripheral sealing will result in predictable bone augmentation of spaces also beyond the skeletal envelope.

The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue support

The present investigation reports how occlusion may be utilized to establish and maintain stability of fixed bridges in patients with markedly reduced periodontal tissue support. The material consisted of 20 adult patients, aged 27-69, with advanced periodontal breakdown, often in combination with extensive loss of teeth. After periodontal treatment, the patients were rehabilitated with fixed bridges, whose stability was evaluated once a year for 2 to 6 years. The results show that permanent stability of bridgework can be obtained in patients where there is a minimum of remaining periodontal tissue support, even in combination with marked hypermobility of individual abutment teeth. The stability was achieved by proper treatment of the diseased periodontal tissues, and by establishment of stable occlusion in the intercuspal position. When there was a risk of bridge mobility on excursive movements of the mandible, balancing contacts were established for the prevention of migration, tilting and increasing mobility. The study also shows that cantilever pontics can be used to achieve and maintain the stability of fixed bridgework.

Guided bone regeneration of cranial defects, using biodegradable barriers: an experimental pilot study in the rabbit

The aim of this study was to test if a biodegradable barrier could be used to achieve proper bone healing of full-thickness trephine skull defects, applying the biological principle of guided tissue regeneration (GTR). Two New Zealand white rabbits were used. In each animal, 2 circular through-and-through bone defects with a diameter of 8 mm were created in the midline of the frontal and parietal bones of the calvarium. One defect was covered with the mucoperiosteal flaps without placement of an intervening membrane barrier (control). One test defect (test 1) was covered by a biodegradable, non-porous polylactic acid membrane on the outer (supra-calvarial) side of the defect, and 2 test defects (tests 2 and 3) were covered by similar membranes on both the outer and the inner aspects of the defects, prior to flap closure. 6 weeks postsurgically, the animals were sacrificed and the defect areas including surrounding tissues were harvested for histological preparation. The control defect was essentially occupied by supra-calvarial soft tissue, located in direct contact with the dural tissue. In the test cavities, there was a continuous bridge of regenerated bone extending from one edge of the defect to the other, although in test 1 not attaining the same thickness as the bone bordering the defect. In the 2 other test defects, the regenerated bone had reached a thickness almost corresponding to that of the surrounding bone. The bone regeneration was achieved without recourse to adjunctive bone graft materials.(ABSTRACT TRUNCATED AT 250 WORDS)

Occlusal force pattern during chewing and biting in dentitions restored with fixed bridges of cross-arch extension. I. Bilateral end abutments

The pattern of axially directed occlusal forces, i.e. magnitude, distribution, duration and frequency of occlusal forces perpendicular to the occlusal plane, was studied during chewing, swallowing and biting in twelve subjects whose dentitions were periodontally treated and prosthetically restored with fixed, cross-arch bridges whose periodontal support included bilateral end abutments. The measuring devices consisted of four strain gauge transducers bilaterally mounted into pontics of maxillary bridges to represent the posterior and anterior regions. The forces could thus be studied in various parts of as well as over the entire dentition simultaneously. All subjects exhibited a rhythmic chewing pattern with preference of one side as chewing side. Local chewing and biting forces were always larger in the posterior than in the anterior regions and largest in the posterior region of the preferred chewing side. The total chewing and swallowing forces were about 100 Newtons (N) whereas the total maximal bite force in habitual occlusion amounted to 320 N. On average 37% of the total maximal bite force in habitual occlusion was utilized during chewing (and swallowing). The capacity of the periodontal tissues on the preferred chewing side to withstand transient occlusal forces was utilized to an average of 25% during chewing and swallowing and to an average of 57% during biting with maximal strength in habitual occlusion. The mean duration of that part of the chewing cycle during which the teeth were subjected to occlusal forces was 240 ms. The duration of the occlusal forces during swallowing was about three times longer. It is concluded that the periodontal tissues can withstand transient occlusal forces which are much larger than those generally operating during chewing, swallowing and biting with maximal strength in habitual occlusion. However, when the bite force is concentrated to a limited area of the tooth-arch, its magnitude seems to be limited by feedback mechanisms evoked in the periodontal tissues of that region.

The use of a new bioresorbable barrier for guided bone regeneration in connection with implant installation. Case reports

This report presents 4 cases with 6 implant exposures after the installation of Brånemark System implants which called for treatment applying the guided bone regeneration technique. A bioresorbable barrier (GUIDOR Matrix Barrier) was used to cover the defects, 4 defects with and 2 without the support of autologous bone chips. Complete bone filling was found in 4 (2 without and 2 with bone chips) and partial filling in 2 (with bone chips) of the treated defects, as registered at the abutment connection 6-7 months after surgery. Besides its ability to serve as a barrier for guided bone regeneration, it was found that the matrix barrier had the following properties; biocompatibility observed as uneventful tissue healing, malleability facilitating the clinical handling and ability to be resorbed within 6 to 7 months, as evaluated by clinical inspection. The observations of the present case reports indicate that the tested barrier may be used for guided bone regeneration in connection with implant installation. It is advisable, however, to use a supporting material to prevent barrier collapse, although bone regeneration can be achieved in certain situations without such material if the defect morphology is favourable.

Healing-in of root analogue titanium implants placed in extraction sockets. An experimental study in the beagle dog

The aim of these animal experiments was to characterize and evaluate the healing-in of root analogue titanium implants fitting with high precision to the alveolar wall. Four beagle dogs were used in the study. The roots of the 3rd and 4th mandibular premolars in both quadrants of 3 dogs and in 1 quadrant of 1 dog (dog 4) were extracted after hemisection. Each root was machine-copied to 1 titanium analogue. In dog 4, however, 2 titanium analogues were fabricated from each of the 4 extracted roots. This enabled insertion of analogues also into the contralateral sockets obtained by extraction of the corresponding roots immediately before implant installation, which was undertaken 2 weeks after the first extractions. Thus, in all, 32 analogues were implanted in their respective (or contralateral) sockets following ridge incision and elevation of mucoperiosteal flaps. The analogues were carefully covered by the repositioned flaps. In dog 4, 2 analogues from the immediate sockets and 2 from the 2-week sockets were surgically exposed and supplied with titanium crowns after a healing period of 2 months. The healing after implantation was evaluated by clinical, radiographic and histological measures after 2, 12 or 36 months. Two analogues (6%) were lost due to early (during the 1st week) exposure to the oral cavity. Another 2 analogues (6%) were, although not exposed, encapsulated by soft tissue and were easily removed with a surgical forceps. Twenty-eight analogues (88%) were healed-in by contact between bone and implant (osseointegration).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of barrier occlusiveness on guided bone augmentation. An experimental study in the rat

The present study was designed to test perforated and non-perforated barriers for their ability to promote augmentation of bone tissue. More specifically, 1 totally occlusive barrier and 6 barriers with perforation sizes of about 10, 25, 50, 75, 100, and 300 microns and 1 group with no barriers placed (open test chambers) were used to test the effect of a barrier's occlusiveness on the amount and composition of augmented tissue over time. The skull of the rat was used as the experimental area. Prefabricated, flexible silicone frames with an inferior flange for peripheral sealing to the bone surface and a central vertical through hole with a diameter of 3.6 mm and a height of 2 mm were used as test chambers. The barriers were inserted to cover the superior opening of the through hole. The healing periods were 4, 8, and 12 weeks. All test chambers exhibited newly formed skull bone which was augmented over time. The placement of totally occlusive barriers resulted in the slowest rate of bone tissue augmentation but in a highly predictable manner, i.e., there were only small individual variations. Placement of barriers with perforations exceeding 10 microns, on the other hand, resulted in a faster rate of bone augmentation with larger individual variations and a totally different augmentation pattern. A pronounced augmentation of calvarial soft tissue from the sagittal suture of the skull as well as ingrowth of suprabony connective tissue through the barriers were also observed. After 12 weeks of healing, no differences in the amount of augmented mineralized bone related to perforation sizes > 10 microns were found. The open test chambers also showed bone augmentation, although most of their volume was occupied by suprabony connective tissue.

Long-term prognosis of extensive polyunit cantilevered fixed partial dentures

The aim of this retrospective study was to elucidate the long-term prognoses of extensive fixed partial dentures including unilateral or bilateral polyunit cantilevers in patients with healthy but reduced periodontal support. Following periodontal therapy 36 cross-arch fixed partial dentures with two or more cantilever units unilaterally or bilaterally were fitted in 34 patients. In the prosthodontic design, special attention was given to the retention to long parallel preparations, to the dimensions of the framework, and to the occlusal design. After completion of therapy, the patients were enrolled in a regular maintenance care program and followed up for a period of 5 to 12 years. During this follow-up period one abutment tooth was fractured in one patient. One fixed partial denture with extremely reduced periodontal support was lost as a result of complete periodontal breakdown from occlusal trauma. For 33 fixed partial dentures, neither periodontal nor technical complications occurred.

Augmentation of calvarial tissue using non-permeable silicone domes and bovine bone mineral. An experimental study in the rat

The aim of the present study was to evaluate the effect of bovine bone mineral placement as an adjunct to a guided bone regeneration (GBR)-barrier in experimental bone augmentation. Some 18 Sprague-Dawley rats underwent flap surgery in which non-permeable silicone domes were placed on the calvaria. A test group of 9 animals received domes filled with cancellous deproteinized bovine bone mineral (Bio-Oss). The domes of 9 control animals were left empty. The experiment was terminated after 8 weeks of healing. Inspection after histologic preparation found no signs of any foreign body reaction to the implanted bovine bone mineral, which seemed to be well integrated with the augmented tissue. The control specimens healed uniformly with new bone inside the domes at the base of the calvaria. The tissue inside the domes of the test specimens had a completely different architecture with new bone both at the base of the calvaria and at a distance from the base, surrounded by and in close contact with non-mineralized tissue and remaining bovine bone mineral. Some ingrowth of soft connective tissue, most likely from the sagittal skull suture could be seen in most test and control specimens. Histomorphometric analysis revealed that the total amount of augmented tissue was significantly greater in the test group (x = 1.93 +/- 0.21 mm2) than in the control group (x = 0.99 +/- 0.22 mm2), P < 0.001). The control domes contained 0.73 +/- 0.28 mm2 augmented bone, while the corresponding value for the test specimens was 0.35 +/- 0.13 mm2, significantly less than the controls (P < 0.01). The test domes contained 0.83 +/- 0.15 mm2 newly-formed non-mineralized calvarial tissue, significantly more than the controls (x = 0.26 +/- 0.16 mm2), P < 0.001). Remaining particles of bovine bone mineral constituted 0.76 +/- 0.14 mm2, or 39%, of the total amount of augmented tissue in the test group. A considerable shrinkage to about 69% of the height of the initial fill of bovine bone mineral at surgery appeared in the test domes after 8 weeks of healing. The reason for this was probably more due to a denser packing of the bovine bone mineral during healing than to resorptive activity. It was concluded that implantation of bovine bone mineral combined with GBR technique significantly enhances augmentation of calvarial tissue. Early mineralization, however, seems to be retarded compared to non-filled control specimens. Further studies should be made to determine the long-term maturation of augmented tissue including resorption pattern of the bovine bone mineral.

Frequency distribution of individuals aged 20-70 years according to severity of periodontal disease experience in 1973 and 1983

The aim of this study was to compare changes in periodontal status of a Swedish population over a 10-year period expressed as frequency distributions of individuals according to severity of periodontal disease experience. The study involved 600 randomly selected individuals evenly distributed into age groups 20, 30, 40, 50, 60 and 70 years, examined in 1973 and another randomly selected group of 597 individuals similarly age distributed and examined in 1983. Based on clinical data and full mouth intraoral radiographs all individuals were classified into 5 groups according to severity of periodontal disease experience. In 1983, 23% of the individuals were classified as having healthy periodontal tissues, group 1, compared to 8% in 1973. The changes were most pronounced in the age groups 20 and 30 years, among whom 58% and 35%, respectively, were registered as having healthy periodontium in 1983. The prevalence of individuals with gingivitis without signs of lowered periodontal bone level, group 2, was 22% in 1983 compared to 41% in 1973. In all, 49% of the dentate population in 1973 and 45% in 1983 showed no marginal alveolar bone loss. Moderate periodontal bone loss, group 3, was found in 41% of the population in 1983 compared to 47% in 1973. Among 30-, 40-, and 50-year-olds, there were more, and among 60- and 70-year-olds, fewer individuals in this group in 1983 compared to 1973. 96% of the dentate population were classified as belonging to groups 1, 2 or 3 in 1973 compared to 86% in 1983.(ABSTRACT TRUNCATED AT 250 WORDS)

Guided jaw-bone regeneration using an experimental rabbit model

The aims of this study were to evaluate the space-maintaining capacity of two biocompatible barrier materials and to assess the effect of barrier occlusiveness on the amount of regenerated bone. Defects were prepared in the edentulous area on both sides of the maxillas in 22 rabbits. The rabbits were divided into three groups. Gore-Tex augmentation material (GTAM) (ePTFE)-barriers were placed to cover the experimental defects and compared with totally occlusive or perforated titanium foils and uncovered control defects respectively. After four weeks of healing, histological analyses and morphometrical measurements demonstrated that the amount of regenerated bone tissue was about the same underneath the collapsed GTAM-barriers as in the controls. The highest degree of regeneration was obtained in defects underneath the titanium foils, particularly if they were perforated, whether or not they were covered by GTAM-barriers. It was concluded that the space-maintaining properties of a barrier may be at least as important as barrier occlusiveness when regenerating bone defects.

Occlusal force pattern during chewing and biting in dentitions restored with fixed bridges of cross-arch extension. II. Unilateral posterior two-unit cantilevers

The pattern of axially (perpendicular to the occlusal plane) directed occlusal forces developed during light tooth tapping in habitual occlusion, chewing, swallowing and maximal biting was studied in twelve subjects whose dentitions were periodontally treated and prosthetically restored with cross-arch bridges with unilateral posterior two-unit cantilevers. The measuring devices consisted of four strain-gauge transducers uniformly and bilaterally mounted in pontics of maxillary bridges to represent the posterior (end abutment and distal cantilever respectively) and anterior regions. Thus, the forces could be studied locally in various parts of the dentition simultaneously as well as totally over the entire dentition. The results demonstrated that the distal cantilever unit, on average, was subjected to forces about or less than half of those over the contralateral end abutment unit irrespective of the activity studied. Furthermore, the cantilever forces either equalled or were even significantly smaller than those of the anterior regions. All subjects preferred the end abutment side as the chewing side. When the cantilever side was used as the chewing side, which occurred most infrequently, the bolus was usually located in the anterior region. The mean total chewing force (about 50 N) was only about half of that found in a previous study of subjects supplied with cross-arch bridges with bilateral end abutments (Lundgren & Laurell, 1985). Furthermore, on average only 26% of the voluntary muscular capacity was used during chewing, compared with 37% in the 'bilateral end abutment group' referred to. The reasons for the comparably small forces over the distal cantilever unit and the lower muscular utilization during chewing in cross-bridges with unilateral posterior two-unit cantilevers as well as the implications of the findings for the dimension of such bridge constructions are discussed.

Functional analysis of fixed bridges on abutment teeth with reduced periodontal support

The present study examines the function of fixed bridges on abutment teeth with reduced but non-inflamed periodontal tissues. Eighteen patients with advanced periodontal breakdown and indication for oral rehabilitation received periodontol treatment and their dentitions were restored with fixed bridgework. The analysis of function performed 2-5 years after insertion of the reconstructions was made by (1) evaluation of the patients' opinion on chewing ability and function of the masticatory system; (2) clinical examination of the border movements of the mandible, the status of the temporomandivular joints and the chewing muscles, and (3) measurements of the bite force indifferent areas of the dentition. The results of the study show that the functional capacity of the type of extensive bridgework discussed is good and that the patients--in spite of severe loss of periodontal tissue--achieve bite force values that are almost comparable to those in individuals with natural teeth. Comparison of the function of fixed bridges and that of removable dentures is also discussed.

A standardized programme for studying the occlusal force pattern during chewing and biting in prosthetically restored dentitions

A recently described method for studying occlusal forces in prosthetically restored dentitions (Lundgren & Laurell, 1984) was applied in a standardized programme to elucidate the occlusal force pattern and the functional capability of a dentition during chewing and biting. The method is based on the use of strain gauge transducers mounted into preformed matrices evenly distributed over the tooth-arch. The programme was tested in a subject prosthetically restored with a fixed bridge of cross-arch design in the upper jaw, and with unsplinted teeth in the lower jaw. It involved chewing of (a) peanuts, (b) roast beef with potato salad, biting with maximal strength in habitual occlusion and biting over one limited contact area at a time. The magnitude of the occlusal forces developed during chewing and swallowing was well below all biting forces. The magnitude of the total force acting over the entire dentition when biting at maximal strength in habitual occlusion did not seem to be limited by reactions from the teeth or the periodontal tissues but, seemingly, by the capability of the jaw-closing muscles themselves. The magnitude of the local bite force over one limited contact area at a time was much smaller than that which the jaw-closing muscles were able to develop. This indicated that feedback mechanisms in the periodontal tissues and/or the temporo-mandibular joints were limiting factors for these forces. The programme will be applied to studies of dentitions supplied with prosthetic constructions of various design and with different distribution of periodontal support.

Membrane-guided bone regeneration. Segmental radius defects studied in the rabbit

We tested the principle of guided tissue regeneration (GTR) for healing segmental long-bone defects. 7 mm (3 animals) or 10 mm (5 animals) long segmental defects were created in the diaphyses of both radii in 8 rabbits. The defect on one side was covered with a barrier membrane of expanded polytetrafluoroethylene membrane shaped as a tube, while the contralateral side with no membrane served as the control. Healing was followed with radiographs obtained repeatedly during a 13- (n 3) or 27- (n 5) week period. Thereafter, the animals were killed and ground sections of the defect sites were prepared for histologic examination. Radiographically, the control sites showed some early subperiosteal callus formation and nonunion of the defects after 6 weeks. The bone ends were rounded off and sealed with cortical bone. No major changes were noted after 6 weeks. At the test sites, subperiosteal bone formation at the bone ends was first observed radiographically at 2 weeks. At 9 weeks, a thin cortical bone bridged the defect along the inner surface of the membrane. Histologically, an interrupted line of thin, cortical bone was observed along the inner surface of the barrier membrane. Fatty bone marrow occupied the central and largest volume of the defect. We conclude that it seems possible to use the principle of GTR to accomplish bone union of segmental long-bone defects.

Occlusal forces in prosthetically restored dentitions: a methodological study

The present paper describes a method developed to study occlusal forces in prosthetically restored dentitions. Using this method the magnitude, duration and frequency of the forces can be measured in various parts of the dentition simultaneously. The measurements are based on the use of strain gauge transducers of such dimensions that they can be mounted into artificial crowns, bridge-pontics or removable dentures, without interfering with the occlusion. The output signal of each transducer is linear for forces up to 300 N which corresponds to an amplitude (elastic deformation) of 20 microns. At least four transducers are used distributed over the tooth-arch to create bilateral and simultaneous contacts. They are mounted in a supraoccluding position of 20 microns in relation to non-transducer areas. This means that on jaw closure each transducer registers all the force transmitted to that part of the prosthetic construction represented by the transducer, provided there is no force leakage to non-transducer areas. The sum of these local forces constitutes the total force acting on the entire dentition at any given moment.

The influence of the design of two different bioresorbable barriers on the results of guided tissue regeneration therapy. An intra-individual comparative study in the monkey

The aim of the present study was to compare two bioresorbable barriers to evaluate whether differences in design influence the result of guided tissue regeneration (GTR) therapy. Twenty-four (24) plaque exposed, recession type defects in 4 monkeys were treated. Contralateral defects were randomized for test or control treatment. During a healing period of 6 weeks, gingival recession resulting in device exposure occurred at 3 test and 10 control sites. One control barrier was exfoliated. Histologically, 9 of the 12 test barriers were completely integrated with the surrounding tissues. At 3 test sites, epithelium had migrated apically outside the barrier to a level not exceeding one-third of the height of the device. Seven of the 11 control barriers were enclosed by dentogingival epithelium. The adjacent connective tissue exhibited local inflammatory cell infiltrates (ICT). At the remaining 4 control sites, the epithelial downgrowth as well as the adjacent ICT areas were limited to the coronal 1/3 of the device. New attachment; i.e., new cementum with inserting collagen fibers, averaged 2.2 mm and 0.8 mm at the test and control sites respectively (P < 0.01). Based on the results of the present study, it was concluded that a bioresorbable GTR device, designed to prevent epithelial downgrowth along the barrier surface, has a higher potential to promote new attachment formation than a device which does not have this property.

Effects of a doubled orthodontic force magnitude on tooth movement and root resorptions. An inter-individual study in adolescents

The aim of this clinical and histological study was to compare the effects of two controlled, continuous forces of 50 cN (approximately 50 g) and 100 cN (approximately 100 g) on tooth movement and root resorptions. The patients, consisting of 32 individuals, 14 boys and 18 girls (mean age 13.1 years), were divided into four groups of eight individuals. The experimental periods were 4 and 7 weeks. In this investigation, designed as an inter-individual study, only the maxillary first premolar on the right side was utilized. The test tooth was buccally moved by means of a fixed orthodontic appliance. A continuous, weekly controlled force of 50 cN was applied to 16 premolars and a force of 100 cN to the remaining 16 test teeth. The force declined on average 22 per cent during the first week when 50 cN was applied and 27 per cent when 100 cN was applied. Tooth movements were studied on dental casts using a coordinate measuring machine. After 4 and 7 weeks, the tooth movements ranged between 0.5 and 3.4 mm (4 weeks) and 2.7 and 7.1 mm (7 weeks) for 50 cN and between 1.0 and 2.9 mm (4 weeks) and 2.2 and 8.3 mm (7 weeks) for 100 cN, with no significant difference when the force magnitude was doubled. Root resorptions were registered in histological sections in all experimental teeth, more frequently after application of 50 cN compared with 100 cN after 7 weeks. However, the severity of root resorption (extension and depth of resorbed root contour and size of root area on histological sections) did not differ significantly when the applied force was doubled to 100 cN. Great individual variations were noted regarding both the magnitude of tooth movement and amount of root resorption.

The effects of a four-fold increased orthodontic force magnitude on tooth movement and root resorptions. An intra-individual study in adolescents

This clinical and histological study was designed as an intra-individual study to investigate the effect on tooth movements and adverse tissue reactions (root resorption) when a fixed orthodontic appliance was activated with a controlled, continuous force of 50 cN (approximately equal to 50 g) or with a four-fold larger force (200 cN approximately equal to 200 g). The first premolar on both sides of the maxilla in eight individuals, six boys and two girls (mean age 13.0 years), was moved buccally during 7 weeks with 50 cN and 200 cN alternately on the right or left size. During the first week a force reduction of 18 and 28 per cent (on average) was registered in the 50 cN and 200 cN group respectively. Tooth movements were studied by means of dental casts using a coordinate measuring machine. The magnitude of the mean horizontal crown movement increased 50 per cent when a force of 200 cN was applied compared with a 50 cN force (3.4-5.1 mm on average) and the difference was significant. Root resorptions were registered in histological sections of the extracted test teeth with no significant difference in frequency or severity between the two forces used. Individual variations were large regarding both tooth movement and root resorption. Possible reasons to explain the results as well as the clinical implications of the findings are discussed.

Characterization of reaerosolization from impingers in an effort to improve airborne virus sampling

AIMS

To assess the impact of reaerosolization from liquid impingement methods on airborne virus sampling.

METHODS AND RESULTS

An AGI-30 impinger containing particles [MS2 bacteriophage or 30-nm polystyrene latex (PSL)] of known concentration was operated with sterile air. Reaerosolized particles as a function of sampling flow rate and particle concentration in the impinger collection liquid were characterized using a scanning mobility particle sizer. Reaerosolization from the impinger was also compared to that from a BioSampler. Results show that reaerosolization increases as flow rate increases. While the increased particle concentration in the impinger collection liquid leads to an increase in the reaerosolization of PSL particles, it does not necessarily lead to an increase in the reaerosolization of virus particles. Reaerosolization of virus particles begins to decrease as the particle concentration in the impinger collection liquid rises above 10(6) PFU ml(-1). This phenomenon results from aggregation of viral particles at high concentrations. Compared with micron-sized particles, nanosized virus particles are easier to aerosolize because of reduced inertia. Reaerosolization from the BioSampler is demonstrated to be significantly less than that from the impinger.

CONCLUSIONS

Reaerosolization from impingement sampling methods is a mode of loss in airborne virus sampling, although it is not as significant a limitation as the primary particle size of the aerosol. Utilizing a BioSampler coupled with short sampling periods to prevent high accumulative concentrations can minimize the impact of reaerosolization.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study confirms reaerosolization of virus particles to be a mode of loss in impingement sampling and identifies methods to minimize the loss.

Bone augmentation at titanium implants using autologous bone grafts and a bioresorbable barrier. An experimental study in the rabbit tibia

The aim of the present investigation was to compare the effect of using autologous bone particles covered with a bioresorbable matrix barrier with the use of bone particles alone on bone augmentation at titanium implants installed in the rabbit tibia. Two Brånemark System implants, one in each tibia, were inserted in each of 9 rabbits in such a way that 5 threads were not covered with bone. Autologous bone particles were harvested from the skull and placed over the exposed implant surfaces on each tibia. The bone graft on one tibia was covered with a Guidor Matrix Barrier, while the bone graft on the other tibia served as a control. After a healing period of 12 weeks, the animals were sacrificed and specimens taken for histomorphometrical analyses. The analyses showed that a significantly larger volume of augmented bone tissue had formed at the test sites. There were, however, no differences in the amount of mineralized bone. In fact, the difference in tissue volume was due to an increased amount of bone marrow at the test sites. The degree of mineralized bone to implant contact as well as the degree of mineralized bone within the threads at the test implants were similar to that at the controls. In conclusion, it was found that the coverage of particulate autologous bone grafts with a bioresorbable barrier resulted in a larger volume of augmented bone than the use of bone grafts not covered with a barrier.

Occlusal force pattern during mastication in dentitions with mandibular fixed partial dentures supported on osseointegrated implants

The occlusal force pattern during chewing and biting was studied in eight edentulous patients whose dentitions had been restored with mandibular bilateral posterior two-unit cantilever fixed prostheses supported on osseointegrated titanium fixtures and occluding with complete maxillary dentures. The chewing pattern was comparable to that reported for subjects with complete healthy dentitions or with tooth-supported cross-arch fixed partial dentures. However, during chewing and swallowing the voluntary capacity of the jaw-closing muscles was used to a much greater extent. Contrary to reports for cantilevers in tooth-supported cross-arch unilateral posterior two-unit cantilever fixed partial dentures occluding with natural teeth, the posterior cantilever segments in the present fixture-supported cantilever prostheses occluding with complete dentures regularly exhibited the largest local forces. Despite this, material failures of this type of fixed prostheses are rare, as demonstrated in long-term follow-up studies.