Poster 749, Sprache: Englisch
Introduction: Since the development of orthodontic fixed appliances, bracket design has undergone many modifications in order to improve treatment efficiency. In the last decades, the popularity of self-ligating brackets has grown based on manufacturers claims of lower friction, faster ligation, less chair time, fewer appointments, shorter treatment time, increased comfort and less pain. The resistance to bracket sliding is a main factor influencing treatment time and eventually the outcome of the orthodontic treatment, therefore is important to ascertain how different bracket prescriptions respond to friction. The aim of this study was to evaluate, in vitro, the resistance in sliding mechanics of conventional ligated brackets and of both active and passive self-ligating brackets when using stainless steel and nickel-titanium archwires; and the effect of tipping on the resistance to such sliding mechanics.
Material and Methods: The 0.022-inch slot brackets Damon® Q™; Prodigy SL™; Smart-Clip™SL3; Victory Series™; Morelli® Roth Standard and Morelli® Roth SLI were tested. The brackets were ligated to 0.016x0.022 inch stainless steel and nickel-titanium archwires. A tipping of 0° or 5° was added to the wires. For each combination of bracket/archwire, 10 sliding tests were performed with the Shimadzu AG-1 5kN testing instrument.
Results: A higher resistance to the sliding was observed with the conventional ligated brackets when compared with the self-ligating brackets, passive or active. There were no statistical differences either between the resistance of active and passive self-ligating brackets or between the resistance of both types of orthodontic archwires for an angulation of 0°. The stainless steel archwires demonstrated a higher resistance for an angulation of 5°. There were no statistical differences between 0° and 5° of tipping.
Conclusion: The self-ligating brackets are an useful tool in orthodontic mechanics, when low levels of friction are needed. When used with small diameter archwires, the resistance to sliding is not affected by small angulations and small degrees tipping. Nevertheless, different metallic alloys present dissimilar behaviour when angulations are present.
Schlagwörter: Sliding Mechanics, Self-ligating brackets, Friction, Resistance
Poster 750, Sprache: Englisch
Purpose: The aim of this in vitro study was to investigate possible morphological and chemical changes induced by the use of glycine powder or sodium bicarbonate powder air polishing on machined and acid-etched titanium surfaces.
Materials and methods: The glycine powder (granulometry
Schlagwörter: dental implants, SEM (scanning elctron microscopy), in vitro test, surface analysis, titanium, metal surface treatment
Poster 751, Sprache: Englisch
Introduction: Surface roughness of zirconia implants is an essential requirement for osseointegration. In order to avoid surface damage and phase transformation one strategy to generate a rough zirconia surface is sandblasting prior to sintering. The aim of the study was to investigate the effect of sandblasting before sintering on the flexural strength.
Material & Methods: Ninty zirconia discs (Zenotec, Wieland) were investigated. Prior to sintering 30 samples were used in the as machined condition, 30 sandblasted with 120 µm and 250 µm Al2O3respectively (distance: 10 mm, 2 bar). Sintering was done according to manufacturer's instruction using the Vita Zyrcomat. The mechanical properties of the resulting sintered zirconia discs were analyzed by biaxial test with additional Weibull statistics according to ISO 6872. From 10 discs of each group Ra values were measured before and after sintering process (surface topography with 121 profiles over an area of 3x3 mm; Perthometer S6P, Mahr, Göttingen).
Results: The biaxial flexural strength depending on the sandblasted particle size was 584 ± 81 MPa for 120 µm, 476 ± 61 MPa for 250 µm and 1298 ± 267 MPa for the machined control group. The Ra values before and after sintering were 3.17 ± 0.39 and 2.95 ± 0.06 µm for 120 µm, 4.01 ± 0.15 and 3.86 ± 0.11 µm for 250 µm sandblasted samples, 0.31 ± 0.1 and 0.27 ± 0.08 µm for the as machined samples.
Conclusion: Similar to sandblasting after sintering sandblasting prior to sintering revealed decreasedbiaxial flexural strength to 45% (120 µm) and 37% (250 µm).
Acknowledgement: This study was supported by Wieland Dental &Technik, Pforzheim.
Schlagwörter: zirconia, biaxial flexural strength, sandblasting, surface roughness
Poster 752, Sprache: Englisch
Background: Reducing the risk of overloading is mandatory to achieve a predictable osseointegration in immediate loading protocols.
Purpose: The aim of this study was to analyse through a three-dimensional Finite Element Analysis (3D-FEA) stress distribution on four implants supporting a full-arch implant-supported fixed bridge (FFB) using different prosthesis design.
Materials and Methods: A 3-D edentulous maxillary model was created using a customized computer software. Four implants were virtually placed into the maxilla and splinted with a FFB of 12 masticatory units. 3 different configurations were evaluated: (1) full acrylic resin prosthesis without framework, (2) acrylic resin veneering material with cast metal framework, (3) acrylic resin veneering material with a carbon fibre framework.
An occlusal load of 150 N was applied on the left most distal portion of the bridge and stresses transmitted into peri-implant bone, to the implants and to the prosthodontic components were recorded.
Results: 3D-FEA revealed higher stresses on the implants (up to +58,27%), on peri-implant bone (up to +56,93%) and in the prosthesis (up to +91,43%) when the full-acrylic denture was simulated.
Conclusions: FEA simulating a maxillary rehabilitation revealed that FFBs endowed with a stiff framework decrease stresses on implants, prosthesis and on the peri-implant bone providing a better load distribution compared with all-acrylic prostheses.
Schlagwörter: Dental implants, Framework, Dental materials, Finite Element Analysis, In vitro study, Prosthodontics
Poster 753, Sprache: Englisch
Introduction: In implant prosthodontics, 50% of the errors generally encountered relate to the techniques used in implant impression and cast contruction. The remaining 50% of errors are generated by inaccurate laboratory procedures. The current dental literature reports conflicting results regarding the best material and the best technique to obtain a faithful reproduction of the position of the implants in an edentulous arch.
Objectives: The aim of this in vitro study was to evaluate by an optical microscope the accuracy of the dental impressions made with 7 different techniques in full-arch rehabilitation dental implant rehabilitations.
Materials and methods: A cast metal framework was realized using a master cast representing a superior jaw in which 4 implants were inserted at th elevel of the canines and of the first molars. Then implant nalogues were screwed to the metal framework and a simplified master cast was realized. This master cast was used for all the tests subsequently described. Impressios of the master cast have een taken using different materials and techniques:
Impregum (polyether) + open tray technique (OTI);
Impregum (polyether) + closed tray technique (CTI);
Impregum (polyether) + open tray splintied technique (OTIS);
Ramitec (polyether) + open tray technique (OTR);
Ramitec (polyether) + closed tray technique (CTR);
Ramitec (polyether) + open tray splinted technique (OTSR);
BF plaster (plaster dental impression) + open tray technique (PLASTER).
For each of these techniques 5 impressions of the master cast have been taken. Standard plastic impression trays provided with rimming were used. A special device was used to standardaze the force exerted during the impression and the direction of the impression tray. Casts have been realized connecting abutment analogues into the impressions. The accuracy of the framework was evaluated by the "one screw test" or Sheffield's test, screwing the metal framework previously realized on the 35 casts. An optical microscope (Smartscope MVP) with a 120x magnification was used to measure the accuracy of the interface between the abutment analogs incorporated in the casts and the metal framework. For each cast 8 measurements were taken: 4 screwing the framework at the level of the implant 26 and 4 screwing the framework at the level of the implant 16.
Statistical analysis: For each of the 35 models acerage values of deviation compared to the master cast were obtained when screwing the stiff framework according to the Sheffield's test. This information was subsequently compared with the respective average values of the master model using a T-test to a sample (one sample T-test).
Results: The casts made with the techniwues PLASTER (0.077±0.033μm, p=0.221), OTI (0.095±0.042μm, p=0.111) and OTSR (0.140±0.080μm, p=0.078) did not show a significant difference compared to the master model (0.056±0.047μm). Considering both the mean values compared to the master cast and the standard deviation of these three techniques, respectively V=0.43, V=0.44, V=0.57 the models obtained with plaster resulted the most similar to the master cast.
Conclusion: 1) Closed tray techniques were the least reliable;
2) The splinting of impression copings with acrylic resin did not improve accuracy;
3) The association of an open tray technique with a stiff material (PLASTER) exhibited the best accuracy.
Schlagwörter: impression materials, impression techniques, implant rehabilitations
Poster 754, Sprache: Englisch
Maxillofacial silicone elastomers are being extensively used for the fabrication of artificial external body parts such as ears, nose and eyes. Some of their properties of clinical advantage are their inertness, softness, flexibility and ability to be coloured artistically. However the most common problem associated with their use is the degradation of their colour and physical properties over time. These changes are mainly attributed to their exposure to Ultra-violet radiation, humidity, cleansing agents, body fluids, adhesives and sometimes, cosmetics. Silicone prostheses therefore need to be re-made periodically.
It is, therefore important to enhance the life of silicone prostheses by preventing/minimising their degradation. This can be achieved by stabilization of the elastomers.
This study evaluates the effect of different UV absorbers on the color change of silicone elastomers.
Schlagwörter: Color, maxillofacial prosthesis, UV absorbers
Poster 755, Sprache: Englisch
A missing anterior tooth can be psychologically as well as socially traumatic to the patient. Conservative solution for the restoration of a single edentulous space in anterior maxilla presents an aesthetic challenge to the clinician.
The objective of this presentation is to describe a simple, economical and fast method to replace a single anterior tooth utilizing an indirectly fabricated composite resin framework reinforced with polyethylene fiber and existing tooth as pontic. This particular design allows for exact repositioning of the coronal part of the extracted tooth in its original intra-oral 3-dimensional position, justifying the name 'NATURAL TOOTH PONTIC'.
Schlagwörter: Natural tooth pontic, ribbond, immediate, esthetics, phonetics, temporary
Poster 756, Sprache: Englisch
Dentinogenesis imperfecta (Hereditary Opalescent Dentin) is a genetic disorder of tooth development. Teeth are discolored (most often a blue-gray or yellow-brown color) and translucent. Teeth are weaker than normal, making them prone to rapid wear, breakage, and loss. In cases where clinical crown structure is severely attrited in dentinogenesis imperfecta, surgical crown lengthening is required prior to prosthetic rehabilitation. Crown lengthening procedures provide adequate tooth structure necessary for retention form, ferrule effect during tooth preparation and impression procedures. It is important to maintain biological width during crown lengthening. This case report present the management of worn out maxillary and mandibular anterior teeth of a 17 year old boy by crown lengthening procedure who was diagnosed with dentinogenesis imperfecta.
Schlagwörter: dentinogenesis imperfecta, crown lengthening, prosthetic rehabilitation, biologic width, attrition, ferrule effect
Poster 757, Sprache: Englisch
A pre-requisite for placement of dental implants is availability of sufficient vital bone.Literature reports vertical and horizontal ridge reduction following extraction, primarily in the initial 3 months. Post extraction socket grafting is performed to avoid future complex bone augmentations. The search for an ideal socket graft material is ongoing.
Aim: To evaluate and compare (Clinically, Radiographically, Histologically,) the quantity of newly formed bone in naturally healing human extraction sockets to sockets grafted with a combination of Medical-Grade Calcium Sulphate Hemihydrate(MGCSH) and Platelet Rich Fibrin(PRF).
Methods: Five patients (both male and females) in the age group of 20-45, who require to undergo multiple extractions in the mandible were selected based on strict inclusion and exclusion criteria. For each patient, one socket received a combination of MGCSH and PRF combination. The other socket was left to heal naturally.
Radiographic analysis of the extraction sites were performed pre and post extraction and after 8 weeks, using a standardized radiographic technique. Bone cores were trephined out of the socket after 8-10 weeks. They were decalcified and the amount of new osteoid deposition and trabaculae formation was evaluated under an Image analyser for determining percentage of vital bone formation.
Results: 36% new bone formation (mostly lamellar) was seen in the grafted sites and 22% in the control sites. Comparisons between the test and control group was performed using un-paired student-t test.
Conclusions and clinical implications: A combination of Calcium sulphate and PRF is highly osteogenic resulting in faster bone formation in extraction sockets. This can be used as a simple, inexpensive, uncomplicated yet effective socket graft material. Its use can yield tooth extraction healing sites ready to receive dental implants at an earlier stage than conventionally healing sockets.
Schlagwörter: osteogenesis, PRF, calcium sulphate
Poster 758, Sprache: Englisch
Endoscopy: A minimally invasive new diagnostic and treatment modality for obstructive diseases of salivary glands. Obstructions due to sialolith, polyps, stricture, kink and foreign bodies are commonly seen in submandibular, parotid glands and ducts. This prevents the free flow of saliva and stagnation under pressure producing pain and swelling.
Sialolithiasis is often treated by different modalities. Small stones can be removed by manipulation or use of sialogogues. Larger stones always require surgical removal of the obstruction, sometimes necessitating gland removal.
The diagnosis and treatment of obstructions can be problematic because of the limitations of standard imaging technique. With the introduction of salivary gland endoscopy, there has been a major step forward not only in providing an accurate means of diagnosis and locating intraductal obstructions but also in permitting minimally invasive treatment that can successfully manage those blockages not accessible intraorally under local anaesthesia in out patient department.
Schlagwörter: Sialolithiasis, Sialogogues, polyps, Stricture, Kink
Poster 759, Sprache: Englisch
Colors are the smiles of nature. The ultimate objective of esthetics in dentistry is to replicate the natural anatomy of the tooth in order to create a beautiful smile.
There are parameters that ensure the replication of natural tooth morphology of which translucency and opacity have been viewed as the most important properties. They are indicators of the quality and quantity of light reflection.
Light reflected from incisal morphology on the labial surface of anterior teeth adds to vitality, whereas less vitality is evident when the anatomy is worn with age. Changes in the color or translucent pattern of natural teeth with aging are generally attributed to changes in translucency of the enamel and dentin layers.
Therefore, the knowledge of human tooth translucency and distribution in terms of age is critical to replicate in esthetically pleasing anterior restorations.
Thus, the aim of this study is to assess the differences in the incisal patterns between age groups and sex in a convenience sample of the population.
Schlagwörter: Stratification, Smile, Translucency, Color, Aesthetics