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Biomedical subjects

W H Steen

Publications and source records attributed to W H Steen.

At least 19 recordsLinked to original sources
PubMed1997

Radiographic evaluation of mandibular augmentation with prefabricated hydroxylapatite/fibrin glue implants.

PURPOSE: This study radiographically evaluated the stability of mandibular height during a 2-year follow-up after augmentation with prefabricated hydroxylapatite/fibrin glue (HA/FG) implants. PATIENTS AND METHODS: Standardized, lateral oblique cephalometric radiographs were made of 22 patients 6, 12, and 24 months postoperatively and analyzed with a newly developed, computerized image analysis technique. RESULTS: The average height of the HA/FG implants after augmentation was 9.45 mm. Average loss of total height of the augmented mandibles was 2.31 mm after 6 months, 2.90 mm after 12 months, and 3.93 mm after 24 months. Reduction of HA/FG implant height alone was 0.62 mm after 6 months, 1.24 mm after 12 months, and 2.03 mm after 24 months. Reduction occurred mainly during the first 6-month evaluation period and was probably primarily caused by adaptation of the implant to the surface of the mandible. An inferior compression of the implant or resorption of the alveolar crest and underlying basilar bone are possible reasons for loss of total mandibular height. CONCLUSION: The results indicate that prefabricated HA/FG implants used for augmentation of edentulous mandibles show little reduction in height, but are not completely stable during a 2-year evaluation period.

Adult↗
PubMed1996

Loading conditions of endosseous implants in an edentulous human mandible: a three-dimensional, finite-element study.

The design of dental superstructures influences the loading on dental implants and the deformation of the anterior interforaminal bone in an edentulous mandible. This deformation causes stress in the bone around the implants and may lead to bone resorption and loss of the implant. The stress distribution around dental implants in an edentulous mandible was calculated by means of a three-dimensional, finite-element model of the anterior part of the jaw. This model was built from data obtained from slices of a single human mandible and was provided with four endosseous implants in the interforaminal region. The implants were either connected with a bar or remained solitary. The solitary implants or the bars were loaded either uniformly or non-uniformly. In case of a non-uniform distribution, either the central bar or the central implants were loaded or the lateral bars or the lateral implants were loaded. The most extreme stresses in the bone were always located around the neck of the implant. In the case of the uniform distribution of the loading there were more or less equal extreme principal stresses around the central and lateral implants. If the load was not uniformly distributed on the superstructure then the implant that was nearest to the place of loading showed the highest stress concentration; with connected implants there was a reduction in the magnitude of the extreme principal stresses compared to solitary implants.

Bite Force↗
PubMed1994

Reductions in size and left-right asymmetry of teeth in human oligodontia.

Tooth size and left-right asymmetry of tooth dimensions in oligodontia were compared with those of a control group. Both early and late developing teeth were severely affected, and almost all teeth had significant reductions, compared to the control group, in mesiodistal and labiolingual dimensions. Left-right asymmetry of tooth dimensions was also found, but for the mesiodistal dimensions these were not significantly different from the control group. The occurrence of reductions in tooth size and left-right asymmetries suggests that oligodontia is not just an isolated phenomenon. The left-right asymmetry indicates a developmental instability in these individuals. More research is needed, to reveal the aetiology and pathogenesis of oligodontia.

Adolescent↗
PubMed1994

Location of implants in the interforaminal region of the mandible and the consequences for the design of the superstructure.

The location and the number of implants to support an overdenture is of major importance for the superstructure design. Sometimes, jaw bone anatomy or posteriorly placed implants enforce the use of an angular bar to achieve a position above the alveolar ridge. Loads on such a bar may introduce a moment on the implants which can result in high bone stresses and eventually the loss of the implants. This study on stress distribution in the bone around the implants in an edentulous mandible was performed using a three-dimensional finite element model. One model with two implants placed just anteriorly of the mental foramen and connected with an anteriorly placed bar, following the curvature of the alveolar ridge, was compared with two other designs. First with a similar model but now without a bar and secondly with a model with four implants connected with straight bars. It is concluded that loading a bar, which is placed anteriorly of the interconnecting line between two implants, causes extremely large compressive and tensile stress concentrations in the bone around the implants. Therefore, in those cases, it is advised not to connect the implants or, in case a bar-clip attachment is preferred, to place additional implants in the frontal region.

Bite Force↗
PubMed1993

A three-dimensional, finite-element analysis of bone around dental implants in an edentulous human mandible.

The design of dental superstructures influences the loading on dental implants and the deformation of the anterior interforaminal bone in an edentulous mandible. This deformation causes stress in the bone around the implants and may lead to bone resorption and loss of the implant. The stress distribution around dental implants in an edentulous mandible was calculated by means of a three-dimensional, finite-element model of an entire lower jaw. This model was built from data obtained from slices of a single human mandible and was provided with two endosseous implants in the interforaminal region. The implants were either connected with a bar or remained solitary, and were loaded with a horizontal bite force of 10 N, a vertical bite force of 35 N, or an oblique bite force of 70 N. The most extreme principal stresses in the bone were always located around the neck of the implant. Stress around the implant was, therefore, not only caused by the local deformation of the bone due to movement of the implant and interface relative to the surrounding bone but also by the bending of the mandible. The most extreme principal stress was found with oblique bite forces. The highest maximum and lowest minimum principal stresses were 7.4 and -16.2 MPa in the model without the bar and 6.5 and -16.5 MPa in the model with the bar. When differences in the amount of bite force were eliminated, the vertical bite force resulted in the lowest stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Bite Force↗
PubMed1993

A comparison of three finite element models of an edentulous mandible provided with implants.

The stress distribution in an edentulous mandible provided with two implants in the interforaminal region was calculated by means of three different finite element models. The implants were connected with a bar or remained solitary. The first model was a three-dimensional representation of the entire mandible, the second model of the interforaminal region of this same mandible, whilst the third model was a two-dimensional representation of the interforaminal region. The differences in stress distribution around the connected implants and the solitary implants between these three models were analysed. It can be concluded that for a parameter study the stress distribution around the dental implants following from a three-dimensional finite element model of only the interforaminal region of an edentulous mandible can be used. For such studies therefore, benefit can be gained from the advantages of reduced modelling and calculation time.

Bite Force↗
PubMed1993

Taurodontism and length of teeth in patients with oligodontia.

Taurodontism and a reduced tooth length are reported to occur in patients with oligondontia. The aim of this study was to evaluate the occurrence of these factors in Dutch patients with oligodontia. Panoramic radiographs of 117 patients with oligodontia and 91 controls were collected. Taurodontism of the mandibular first molars was recorded and the length of cuspids, bicuspids and first molars of the mandible were measured. In patients with oligodontia 28.9% showed taurodontism of one or two mandibular first molars. The prevalence of taurodontism in normal Dutch subjects was 9.9%. No significant differences were found between the two sexes in both groups. Neither was there a significant difference in the unilateral and bilateral occurrence of taurodontism. The present findings supported the hypothesis that taurodontism may be the result of an ectodermal defect and a manifestation of developmental instability in patients with oligodontia. The length of mandibular cuspids and first molars in females were significantly reduced. In males only the lower right first molar was significantly reduced. The reduced length of the teeth may also be the result of a defect in ectodermal cells. Both taurodontism and a reduced length are of importance considering dental therapy.

Adolescent↗
PubMed1993

A comparison of methods to assess marginal bone height around endosseous implants.

3 methods of measurements of marginal bone level on intra-oral radiographs of endosseous implants are described: measurements with a computerized image analysis system, with a magnifying-glass and with a digital sliding gauge. The accuracy of each of these methods was investigated and compared. The intra- and inter-observer error analysis showed that determining the precise bone height on the image is responsible for a large standard deviation for each method. It is concluded that measurements with a digital sliding gauge are preferable because it is easy to put into practice, and in addition, accuracy matches the accuracy of the other methods.

Alveolar Bone Loss↗
PubMed1992

Masticatory ability, denture quality, and oral conditions in edentulous subjects.

This study investigated the relationships between the ability of 38 patients with complete dentures to comminute a tough artificial test food and their answers to questions about the chewing experience. Also, clinical assessments were made of denture quality and oral conditions. Significant but weak relationships were found between the ability to comminute the test food and the subjective chewing experience as well as the degree of resorption of the mandibular residual ridge. Masticatory ability is conceivably determined by many other factors as well. Results indicate that dentists cannot rely on asking denture wearers about chewing problems and clinical responses with respect to oral conditions and denture quality for predicting those patients' masticatory abilities. The ability of wearers of complete dentures to comminute tough foods should be determined individually by a series of chewing tests.

Adult↗
PubMed1992

Standardized radiographs of the alveolar crest around implants in the mandible.

The techniques currently used for standardized longitudinal radiographic evaluation of the supporting bone around dental implants are not suitable for general application. An aiming device is described for intraoral radiography used to evaluate the crestal bone height around dental implants used as retention for overdentures. This aiming device has been tested on four different implant systems by four dentists. Error analysis of serial radiographs indicates small deviations in reproducibility. It is concluded that this method is suitable for routine evaluation of dental implants.

Alveolar Process↗
PubMed1992

Comminution of food by complete-denture wearers.

A method for quantifying the comminution of an artificial test food (Optosil) was evaluated with respect to its suitability for measurements of masticatory performance in complete-denture wearers. Reference was made to subjects with natural dentitions. The description of particle size distributions generated by complete-denture wearers by a Rosin-Rammler equation was subject to limitations, due to the presence of large proportions of almost-intact particles, which had hardly been damaged or broken during chewing. This finding might be explained by: (i) the relatively high fracture strength of Optosil as compared with natural foods; and (ii) the limitations of complete-denture wearers in exerting bite forces. The particle size distributions obtained after repeated measurements and described by linear interpolation of data points were reproducible. In comparison with young adults with natural dentitions, the denture-wearers needed approximately seven times more chewing strokes to achieve an equivalent reduction in particle size.

Adult↗
PubMed1990

[Oligodontia].

In every dental practice patients with oligodontia can be met. Oligodontia can occur solitary or as part of a syndrome. It is important for the dentist to be familiar with the various symptoms, including those of oligodontia as part of a syndrome.

Anodontia↗
PubMed1988

Anticoagulants and cataract surgery.

A series of 49 cataract operations in 42 patients is presented in support of our contention that if anticoagulants are necessary for a patient's well being, they should not be discontinued for cataract surgery.

Aged↗
PubMed1984

Errors in oblique cephalometric radiographic projections of the edentulous mandible. Part I: Geometric errors.

Geometric errors that occur in oblique cephalometric radiographic projections of the edentulous mandible were calculated for different focal-spot-to-object distances (1500, 3000, and 6000 mm). The horizontal errors from tolerance of the porion and nasion fixation in the cephalostat were calculated. The same was done for the vertical errors caused by the variability of the rest position. From the results of this study it can be concluded that the distance between focal spot and object should be as large as possible. It was also found that it is important to minimize the differences in enlargement that may occur on radiograms of different subjects because of changes in the position of the mandible. This position can be standardized by the use of an individual support.

Cephalometry↗
PubMed1984

A study of the radiographic aluminum equivalent values of the mandible.

A longitudinal study of bone changes in the mandible was conducted. Duplicate radiographs were taken at 3-month intervals with the use of a positioning instrument, which included an aluminum calibrating wedge. The in-duplicate values obtained over the investigation period made it possible to assess the precision of the method and to analyze effects that take place with time. Significant bone changes were observed in seven volunteers between various observation periods at intervals of 6 and 9 months.

Absorptiometry, Photon↗