Different bone loading patterns due to fixation of three-unit and five-unit implant prostheses.

BACKGROUND: It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs). METHODS: Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress. RESULTS: The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load. CONCLUSIONS: Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development.

Stress and inflammation as a detrimental combination for peri-implant bone loss.

The causes of peri-implant bone loss continue to be controversial. To determine the impact of biomechanical stress and inflammation, we investigated a total of 80 interforaminal implants in situ for more than 10 years. Two stress groups, with 14 patients each, were established: a low-stress situation with single-standing implants, and an increased-stress situation with splinted implants. To categorize inflammation, we introduced a Composite Inflammation Score using 4 inflammatory parameters. Peri-implant bone loss was calculated from digital panoramic radiographs. To differentiate between the effects of stress and inflammation, we compared bone loss in both stress groups at equivalent levels of inflammation. With greater Composite Inflammation Score values, a clear discrepancy between single-standing and splinted implants was evident (p = 0.117/0.000, regression analysis; p = 0.135/0.000, analysis of variance; p = 0.002, t tests). While stress and inflammation alone may not necessarily be detrimental factors, the presence of stress heightens peri-implant bone loss significantly as inflammation increases.

Overdenture attachment selection and the loading of implant and denture-bearing area. Part 1: In vivo verification of stereolithographic model.

Preliminary to a study investigating the force transfer from osseointegrated dental implants to the surrounding bone via various types of overdenture attachment, a stereolithographic model (SL-model) was constructed and compared to an in vivo situation in order to confirm the validity of the modeling technique for the planned measurements of implant strain and denture-bearing area loading. The SL-model was generated using the patient's computer tomographic data and duplicated in a material of known elastic properties. The model was fitted with sensors to measure strains in the peri-implant bone and loading forces within the posterior mandibular bone, i.e. the denture-bearing area of the mandible. Special telescopic copings were constructed to measure implant strain in this model as well as in vivo. Using these copings under identical overdenture loading conditions, the strains measured at the implants in vivo and in vitro were the same and never exceeded a tolerance of two standard deviations or a mean difference of -8.5% of the in vitro value. This indicates that the model was reliable for the measurement of implant strain. Denture-bearing area loading within the alveolar ridge cannot be measured in vivo. Instead, a method of extrapolating in vivo denture-bearing area loading figures from implant strain readings was developed and tested (better than 90% accuracy). These in vivo extrapolated figures were then compared to in vitro readings under otherwise identical loading conditions. The result indicated that the SL-model is reliable for measurements of denture-bearing area loading with an error of 10 to 20%.

Overdenture attachment selection and the loading of implant and denture-bearing area. Part 2: A methodical study using five types of attachment.

In general, an implant is loaded via axial and horizontal forces. Besides this, moment loading can also occur. The aim of this study was to investigate how different prosthetic connectors with overdentures develop force transfer to implant and bone as well as to the denture-bearing alveolar ridge. Five connectors were investigated on a stereolithographic model fabricated according to a real patient situation. The model was fitted with strain gauges on the "bone" distal and medial to the implants and with vertical force transducers in the alveolar "bone" under the denture-bearing area. The parallel-sided rigid telescopic connector developed the highest moment loading of the implant (P<0.001), which would suggest restraint in the use of this connector. The bar construction also showed somewhat high moments but these may have been at least partly exaggerated by the individual patient situation. Loading results through the non-rigid telescopic copings, single spherical attachments and magnet overdentures demonstrated a low level of implant moment loading which would in part result from horizontal forces caused by denture forward shift during force application. The denture-bearing area loading was different with all attachments (P<0.001) and was related to the rigidity of the connector and reached the highest values with the non-rigid telescopic coping. The clinical implications of the various findings are discussed.

High incidence of maternal HLA A, B and C antibodies associated with a mild course of haemolytic disease of the newborn. Group for the Study of Protective Maternal HLA Antibodies in the Clinical Course of HDN.

Mild courses of haemolytic disease of the foetus or newborn (HDN) due to Rh (D) blood group antibodies are associated with and may therefore be ameliorated by maternal antibodies reacting with human leucocyte antigens (HLA) of the child, an observation drawn from our own earlier data (Neppert J, Kissel K. Lancet 1992;339:1481). This study (i) corroborates this association; (ii) reveals shortcomings in the published data; and (iii) examines the characteristics of HDN cases when these shortcomings have been rectified. Samples from 51 women with antibodies against their child's blood group antigens of the Rh system were analysed for HLA A, B, C and DR antibodies during parturition. The mothers were divided into two groups, either severe or mild, dependent upon the clinical course of the HDN, and the incidence of HLA antibody production was determined for each group. HLA A, B, C and/or DR antibodies were detected in 85.2% of those women whose children had a mild course of HDN prenatally or perinatally (n=27). This is statistically greater than the incidence of 50.0% (Fisher's exact test: p=0.014) found in the group of women whose children had a severe HDN either pre- or perinatally (n=24) and is greater than the 35% (n=20; p=0.0001) found in women without Rh or other irregular antibodies. HLA DR antibodies were detected in three cases. The findings support our hypothesis that maternal anti HLA A, B and C antibodies may protect against a potential severe HDN. We therefore assume that those women will benefit who have already had a child with a severe HDN and in whom HLA antibodies were not previously detected, if HLA antibody production is provoked by subcutaneously inoculating with the father's leucocytes before or at the beginning of the new pregnancy.

Use of the direct magnification technique in dental radiology.

OBJECTIVE: To investigate the potential use of the direct magnification (DIMA) technique in dental radiology. METHODS: Radiographs of anatomical specimens and extracted teeth were prepared under clinical conditions using a microfocus (8 and 16 microns focal diameter) X-ray tube. Entrance dose was measured using an ionization chamber. Image quality was assessed in a single-blind test of pairs of images of extracted teeth with and without caries by ten observers. RESULTS: At 7.3 x magnification the values for exposure time and entrance dose were comparable with those for conventional intraoral radiography, 0.1 and 0.25 s and 1.5 and 2.9 mSv respectively. Diagnostic accuracy using the DIMA images was significantly (P < 0.0001) better compared with dental radiographs. CONCLUSION: DIMA images with significantly enhanced diagnostic accuracy can be obtained at comparable exposure times and entrance doses to conventional intraoral radiographs.

Wear behavior of precision attachments.

PURPOSE: The purpose of this article was to compare the wear behavior of precision attachments with plastic inserts to conventional metal-alloy precision attachments. MATERIALS AND METHODS: In a comparative study attachments of various designs were subjected to alternating load cycles in a wear simulator. In addition to conventional adjustable attachments with metal-alloy matrix and patrix elements, attachments with female elements that are lined with plastic inserts were investigated for the first time. In each wear test 10,000 separating and joining movements were performed in an axial direction under a continuous spray of artificial saliva at 37 degrees C. RESULTS: The attachments with metal surfaces showed a rapid loss of approximately 60% of the required separating/joining forces during the first 1,000 cycles; after a further 9,000 cycles these forces fell to 25% and 35%, respectively, of the initial value. The attachments with plastic inserts, by contrast, showed only a 4% and 8% loss, respectively, of the required separating/joining forces even after 10,000 wear cycles. With one attachment type a reproducible 20% increase of retention occurred during the testings. CONCLUSION: The precision attachments with plastic female inserts showed only negligible amounts of wear and the most consistent retentive force in comparison with conventional precision attachments consisting of metal-alloy matrix and patrix components.

Can blood group O red cells of donor origin acquire weak group A reactivity through serum A transferase of the recipient after bone marrow transplantation?

BACKGROUND: Blood group A substance was detected on red cells of a patient who received a bone marrow transplant from a blood group O donor 3.5 years ago. MATERIALS AND METHODS: Peripheral blood was investigated by conventional serological techniques, fluorescence in situ hybridisation, and polymerase chain reaction. RESULTS: All peripheral blood cells are of donor origin. Anti-A and not anti-A, B of blood group O individuals can be absorbed to the group O red cells of the patient. CONCLUSION: We suppose that the patient's residual serum A transferase attaches the appropriate sugar to substance H on the red cell membrane to form substance A.

Can blood group O red cells of donor origin acquire weak group A reactivity through serum A transferase of the recipient after bone marrow transplantation?

Blood group A substance was detected on red cells of a patient who had received a bone marrow transplant from a blood group 0 donor 3 1/2 years ago. All peripheral blood cells are of donor origin. Anti-A but not anti-A,B of blood group 0 individuals can be absorbed to the group 0 red cells of the patient. We suppose that the patient's residual serum A transferase attaches the appropriate sugar to H substance on the red cell membrane to form A substance.