Protection of yttria-stabilized zirconia for dental applications by oxidic PVD coating.

In this study, the application of transparent physical vapor deposition (PVD) coatings on zirconia ceramics was examined as an approach to retard the low-temperature degradation of zirconia for dental applications. Transparent monolayers of titanium oxide (TixOy) and multilayers consisting of titanium oxide-alumina-titanium oxide (TixOy-AlxOy-TixOy) were deposited onto standardized discs of 3Y-TZP using magnetron sputtering. Using X-ray photospectroscopy and time-of-flight secondary-ion mass spectrometry, the compositions of the coatings were verified, and an approximate thickness of 50 nm for each type of coating was ascertained. After aging the coated and uncoated samples in water vapor at 134°C and 3 bar for 4, 8, 16, 32, 64 and 128 h, the monoclinic phase content was determined using X-ray diffraction, and its impact on mechanical properties was assessed in biaxial flexural strength tests. In addition, the depth of the transformation zone was measured from scanning electron microscopy images of the fracture surfaces of hydrothermally aged samples. The results revealed that the tetragonal-to-monoclinic phase transformation of the zirconia ceramic was retarded by the application of PVD coatings. During the first stages of aging, the coated samples exhibited a significantly lower monoclinic phase content than the uncoated samples and, after 128 h of aging, showed a transformation zone which was only ∼12-15 µm thick compared to ∼30 µm in the control group. Biaxial flexural strength decreased by ∼10% during aging and was not influenced by the application of a PVD coating.

Finite element analysis of equine incisor teeth. Part 1: determination of the material parameters of the periodontal ligament.

In equine dentistry, periodontal diseases are frequently found in aged horses. Excessive strains and stresses within the periodontal ligament (PDL) occurring during the masticatory cycle may be predisposing factors especially in old horses with short, worn teeth. The finite element (FE) analysis is a valuable tool to investigate such strains and stresses in biological materials but a precondition for a realistic and reliable FE analysis is accurate knowledge of material parameters. As no data exist concerning the PDL of equine incisor teeth, this study was undertaken to determine the equine specific, age related and load dependent Young's modulus of equine incisors. To determine the biomechanical behaviour of the PDL, the incisor jaw-regions of horses of different ages were sectioned into 5mm thick slice samples and the incisors experimentally intruded (i.e. axially displaced into the alveolus) while recording the load-displacement relationship. Based on high resolution micro-computer tomography (µCT)-datasets, reliable and detailed 3-dimensional models of the slice samples were constructed focusing on precisely modelling the anatomy of the PDL. FE calculations were then performed and set-actual comparisons of the FE results with the experimentally measured displacements enabled the Young's modulus of the PDL to be determined. The results of this study reflect the typical non-linear behaviour of the collagen fibres of the PDL and present a high load dependency of the PDL's Young's modulus. Further investigations calculating the strains and stresses within the periodontal ligament, teeth and surrounding bone of the entire rostral aspect of the jaw are warranted.

Finite element analysis in 3-D models of equine cheek teeth.

Periodontal diseases occur frequently in equine dentistry and excessive strain in biological tissues is assumed to be a predisposing factor in their development. Finite element (FE) analysis enables strains and stresses occurring in the periodontium to be calculated and is a useful tool for testing this hypothesis. The current study aimed to establish reliable 3-D models from equine maxillary and mandibular cheek teeth for use in FE simulations, with particular attention to the detailed construction of the periodontal ligament (PDL). Age-related morphological aspects of the teeth and the periodontium were also considered by constructing different models for three defined age groups. Finally, the biomechanical behaviour of the equine PDL was examined during experimental tooth intrusion (i.e. axial displacement of the tooth into its alveolar socket). The results showed an increase in intrusion with increasing age due to age-related changes in the periodontal elastic properties. The general stress level in PDL and surrounding bone also increased with age. Reliable FE models were established to calculate aetiologically relevant biomechanical effects occurring in the equine periodontium.

Stress analysis of an all-ceramic FDP loaded according to different occlusal concepts.

The aim of this study was to investigate the influence of four different occlusal concepts on stress distribution in a four-unit fixed dental prosthesis (FDP) made of zirconia. A three-dimensional finite element (FE) model was created and four model versions with between 15 and 42 contact points were developed. A force of 300 N was distributed over the chewing surface according to the different occlusal concepts and virtually applied perpendicularly to the occlusal plane in each version. Then, FE analysis was performed and stress distribution evaluated. Generally, highest tensile stresses were located at the point of load application within the veneering layer and ranged from 104 to 204 MPa. The highest tensile stresses within the framework were located at the basal side of the connectors and ranged between 12 and 39 MPa. This study shows that the distribution of occlusal contact points significantly influences the stresses induced by occlusal forces in four-unit all-ceramic fixed dental prostheses and strongly suggests that the number and distribution of occlusal contacts may be important to minimise fatigue effects caused by cycling.

Influence of the veneering process on the marginal fit of zirconia fixed dental prostheses.

Distortions in the marginal region during manufacture are detrimental to the long-term success of fixed dental prostheses (FDPs). The aim of the present in vitro study was to evaluate changes in marginal fit because of the veneering process of four-unit FDPs made from different zirconia materials. Two groups of FDPs with 10 specimens each were machined from white body zirconia blanks (VITA In-Ceram YZ Cubes, KaVo Everest ZS-Blanks) by means of computer-aided design/computer-aided manufacturing systems and subsequently sintered to their final density. The marginal and internal gaps of the frameworks were determined using a replica technique. Afterwards, frameworks were veneered with the recommended ceramics (VITA VM9, GC Initial Zr), and fitting accuracy was evaluated again. Statistical analyses were performed by Student's t-test with the level of significance chosen at 0.05. With one framework/veneering system (Everest ZS-Blanks/Initial Zr), both marginal gap (P = 0.019) and internal gap (P = 0.001) at the premolar retainer were significantly affected by the veneering process. The resulting distortions were directed towards the lumina of the retainers and the mean values of the measured gaps decreased by about 23.8 mum (marginal gap) and 27.3 mum (internal gap). For the other system (In-Ceram YZ Cubes/VM9), no distortions because of the veneering were found. The veneering of zirconia restorations may lead to significant changes in the marginal fit, while the combination of core and veneering material used influences the resulting distortions.

Load-bearing capacity of direct four unit provisional composite bridges with fibre reinforcement.

The aim of the current in vitro study was to evaluate the load-bearing capacity of provisional four-unit bridges with and without two different types of glass-fibre reinforcement produced in a direct technique with a silicon template from the composite materials Protemp, Luxatemp and CronMix. From each composite material, 30 bridges were manufactured, 10 without fibre reinforcement, 10 with Stick/StickNet and 10 with everStick/everStickNet reinforcement. After artificial aging by thermocycling samples were cemented onto a master model and subjected to load testing in a universal testing machine. Mean force at fracture for the groups without fibre reinforcement varied from 486 to 612 N. Depending on the material combination, fibre reinforcement resulted in a slightly increased or a reduced mean load-bearing capacity, varying from 674 N for the combination of Protemp and Stick to 262 N for CronMix and everStick. Position of fibres within the resin pontic was found to have an important influence on load-bearing capacity of reinforced bridges. Scanning electron microscopic investigation showed good adhesion of everStick fibres to the pre-impregnation resin whereas bonding of Stick fibres to the embedding polymer was incomplete. In conclusion, fibre reinforcement with Stick or everStick did not improve the load-bearing capacity of direct provisional bridges made from Protemp, Luxatemp, or CronMix as the position of fibres could not be controlled during the direct manufacturing process. To increase the load-bearing capacity of the provisional bridges, an exact positioning of fibres at the tension side in the dental laboratory is necessary.

Elongated styloid process: when is it really elongated?

OBJECTIVE: The styloid process (SP) is often denoted as elongated when it is longer than 30 mm or 33 mm. These dimensions, based on early reports, do not respect the natural variation of the SP. The aim of this study is to investigate the natural variation of the length of the SP. Knowing this variation is a prerequisite for consistent terminology in anatomy and anthropology; it is essential for the classification of the SP as elongated on panoramic radiographs (PRs). MATERIALS AND METHODS: 1000 consecutive PRs of a normal population were retrieved from inactive files at the Dental School of the Hannover Medical University. Measurements of the length of the SPs were made directly on the radiographs from the caudal margin of the tympanic plate to the tip of the SP. RESULTS: On 521 of the 1000 PRs the length of the SP could be measured at least on one side. As there was no significant difference between distributions on the left and right side, both sides were combined to give a total of 837 measurements. The median was 28.0 mm, the interquartile range was from 23.0 mm to 36.0 mm. The distribution depends significantly on age and gender. The 90th percentile varies between 42 mm for women under 35 years and 49 mm for men aged over 35 years. CONCLUSIONS: The medians in our sample correspond to the thresholds for elongated SP quoted in the literature. Our results show that these thresholds are too low, since they are exceeded in 50% of normal patients. We propose that the SP should be considered to be elongated only if its length exceeds 45 mm, which corresponds to the average of the 90th percentiles for different sex and age groups.

[Styloid process: radiograph and craniomandibular dysfunction (CMD)]. / Processus styloideus: Röntgenbild und cranio-mandibuläre Dysfunktion (CMD).

The aim of the study was to investigate the suitability of orthopantomograms for measuring the length of the styloid process (SP), and to determine the frequency of elongated SP in patients with craniomandibular dysfunction (CMD). For 350 patients, two ortho-pantomograms were available, produced by a SIEMENS Orthophos 5 using programs P1 and P6, respectively, plus a craniomandibular function index. The SP length measurements from the orthopantomograms and the palpation findings were correlated. In 34,7% of the 700 orthopantomograms the SP was measurable. The mean length was determined to be 29.1 mm in OPT1 films on both sides. In the OPT6 films the length values were 30.1 mm on the right, and 30.4 mm on the left side. In CMD patients there was no evidence of the SP causing the complaints. Two conclusions can be made: For epidemiologic studies on the length of the styloid process, the orthopantomogram is of limited use. In CMD patients the elongated styloid process is of negligible importance as a cause of complaints.

Surface quality achieved by polishing and by varnishing of temporary crown and fixed partial denture resins.

STATEMENT OF PROBLEM: Studies have suggested that coating a temporary restoration with varnish material could replace time-consuming polishing procedures needed for achieving an optimally smooth surface. PURPOSE: This study examined the surface roughness of acrylic resins after having been polished or coated with different varnish materials. MATERIAL AND METHODS: A total of 360 cylindrical specimens were fabricated from 9 brands of resin. One surface on each specimen was machined flat and subsequently either polished with rubber polishers or coated with 1 of 9 varnishes. Selected specimens were subjected to thermal cycling (5 degrees C to 55 degrees C, 2000 cycles). Surface quality was assessed by means of a profilometer and by SEM examination. RESULTS: Polished specimens had average surface roughness values (Ra) of 0.8 microm; differences in roughness between materials were small, but statistically significant. Type of coating had a significant influence on surface quality. Depending on the combination of materials used, the coating produced both smoother and rougher surfaces than polishing (0.4 microm < Ra < 4.6 microm). Five coatings were deemed not to be clinically applicable because of poor wetting properties. Thermal cycling did not significantly influence surface quality, but caused minute cracks in the cyanoacrylate coating. CONCLUSION: In regard to surface quality and applicability, the use of varnishes on temporary restorations is not advisable.

An experience in telenursing.

The purpose of this article is to describe how a telemedicine system was used to complete a family and home assessment and to discuss issues facing advanced practice nurses (APNs) when they use such systems in practice. Incorporating discharge care into advanced practice is an increasingly important component of the nursing care given during acute illness. Telemedicine systems offer a mechanism for assessing the ways in which home situations impact on patient recovery. Telemedicine provides a method for early intervention that can ameliorate or prevent developing problems relatively inexpensively. The advantages and disadvantages of one such system, the Picasso, are described.

Reducing readmission rates through discharge interventions.

Readmissions to the hospital account for a significant number of all hospital admissions. Early discharge and inadequate care both during and after hospitalization are among the causes cited. Increasingly complex care and an aging population mandate that clinical nurse specialists (CNSs) in acute care settings assume more pivotal roles in discharge planning and care. Discharge program and intervention models, and ways to incorporate discharge interventions into advanced practice in acute care hospitals, are discussed. In addition, the effectiveness of CNSs and their required qualifications are presented.

Measurement of tooth displacements and mouthpiece forces during brass instrument playing.

In order to assess the actual load on front teeth and tooth supportive tissue during brass instrument playing, a measuring system was developed permitting simultaneous recordings of mouthpiece forces and incisor deflections. By the application of strain gauges, the mouthpiece itself was converted into an extra-oral force transducer, whilst an intra-oral metal appliance similar to a removable partial denture served as the base for strain gauge transducers sensing incisor displacements. The measurements only slightly affected the handling of the instruments under examination (trumpet, french horn, tenor horn, and tuba) and yielded the following average results for three to five players per instrument: peak force values were in the range of 29 N (tuba) to 50 N (trumpet), and the respective peak displacements were 43 microns and 100 microns.

[Measuring the accuracy of various elastomeric impression materials using a CNC coordinate measuring device (Part 1)]. / Bestimmung der Abformgenauigkeit verschiedener Elastomere mit Hilfe einer 3D-Koordinatenmessmaschine. (Teil 1).

This study compares the accuracy of 23 impression materials. With each material seven impressions of a stainless steel master die were taken under standardized conditions. Characteristical dimensions of the master die and of the stone dies as well were determined by means of a CNC coordinate measuring device. Differences in prepared tooth heights ranged between -36 and +19 microns. The occlusal distances between prepared teeth were 2 to 54 microns greater on the stone dies than on the master die. Diameters differed by -89 to +52 microns. The two phase impressions tended to result in stone dies of reduced size, whereas single phase and double mix impression techniques produced larger stone dies than the master die.

[Creep of amalgam fillings under clasp rests]. / Kriechverhalten von Amalgamfüllungen unter Auflageklammern.

A clinically realistic experiment was set up to obtain information on the amount of vertical settling of clasp rests in amalgam restorations under functional loading. Mesioocclusal cavities were prepared in 16 lower molar specimens cast in brass. The cavities were filled with amalgam and provided with a mesial rest seat. A constant load of 100 N was applied via a simplified (experimental) saddle to a cobalt-chromium E-clasp cast to the saddle. The duration of the load corresponded to 160 days of clinical function. The chronological course of vertical displacement was analyzed mathematically. According to this result the process can be divided into three components: settling immediately upon load initiation (mean value 96 microns, transition creep (mean value 25 microns) and creep ata constant rate (mean value 15 microns). The mean overall vertical displacement of the rests was 136 microns, the maximum value 287 microns. These findings suggest that vertical settling of a clasp rest into its seat in an amalgam restoration may eventually result in significant changes in occlusion and may almost completely exhaust gingival resilience.

Three-dimensional stress distribution around a dental implant at different stages of interface development.

An anchor-type ceramic dental implant contained in a section of the mandibular molar region was modeled for finite element stress analysis. The distributions of stresses in the bone around the implant due to axial and transverse loading were calculated for different stages of normal and pathological development of the implant-bone interface. Highest stress concentrations are observed in the crestal region with transverse loading when spongy bone surrounds the implant immediately after surgery. Development of a lamina dura around the implant slightly reduces severe stress peaks, whereas ingrowth of connective tissue almost eliminates them.

[Testing of tissue adhesive strength in bone]. / Klebfestigkeitsuntersuchungen am Knochen.

In a specially designed system the adhesive strength of bone pieces glued with all relevant adhesives was determined. The experiments were performed under dry, moderate moisture and simulated in vivo conditions.

[Adhesives in surgery of the skeleton system, part 2: the adhesive strength from 22 adhesives in bone surgery (author's transl)]. / Klebungen am Skelettsystem, Teil 2: Untersuchung der Klebfestigkeit von 22 Klebstoffen am Knochen.

For the first time all relevant adhesive groups were analyzed for their adhesive strength in bone-surgery. After having glued bone pieces in a special designed system, the tensil- and shearing-strength was determined. All adhesives showed a loss of adhesive strength under in vivo-conditions. Moderate moisture increased the tensile strength in some adhesives. While the fibrin adhesive had only a low adhesive strength under simulated in vivo-conditions, the adhesives containing gelatine, epoxy resin or acrylates reached reasonable results. The relationship between chemical structure and adhesive strength will be further used for the development of a special bone adhesive as a new surgeon's tool.