The wear of a posterior composite in an artificial mouth: a clinical correlation.
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Composite Resins↗
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Characterization of two small-particle composite resins.
The in vitro occlusal wear of two recently introduced, small-particle composite resins was evaluated. Twelve disks of each material were opposed by maxillary third molars and subjected to 300,000 masticatory cycles in a servohydraulic model of the human masticatory apparatus. Before and after profiles of the surfaces of both the disks and the teeth were mapped and digitally recorded on magnetic disks. P-50 disks showed significantly (P less than .05) less volume loss than did Herculite disks. Enamel that opposed P-50 disks showed significantly (P less than .001) more wear than did enamel that opposed Herculite disks.
Composite Resins↗
Photoelastic analysis of bone deformation in the region of the mandibular condyle during mastication.
INTRODUCTION: The purpose of this experimental study was to demonstrate the stress patterns arising in the region of the mandibular condyle during mastication. MATERIAL AND METHOD: Stress analysis was performed using reflection photoelasticity to demonstrate deformation occurring on the surface of the mandible. The rami of three fresh dentate human mandibles were coated with a shell of photoelastic resin. Using a novel loading device, these mandibles were then subjected to external forces (muscular traction, resultant mandibular forces and intra-articular reaction force) reproducing a unilateral biting task between the first right molars. Deformations were measured from the working side. RESULTS: The trace of isostatic lines from the isoclinic fringes revealed major differences in stress distributions between the three mandibles. These differences were attributed to differences in shape between the three mandibles. Conversely, we consistently found compressive stress patterns along the posterior border of the ramus and tensile stress patterns along the anterior border of the ramus and in the zone situated below the siqmoid notch. CONCLUSION: These findings suggest that during this particular task, the mandible is subjected to sagittal forces which tend to straighten the mandibular angle. This implies that new concepts are needed for the positioning of osteosynthesis plates in the condylar region, close to the tensile strain lines, as has been recommended also for other parts of the mandible when applying semi-rigid internal fixation.
Biomechanical Phenomena↗
Fracture strength of teeth restored with all-ceramic posts and cores.
OBJECTIVE: The purpose of this in vitro investigation was to evaluate the fracture strength of endodontically treated teeth restored with different all-ceramic posts and cores. METHOD AND MATERIALS: Seventy-two endodontically treated human maxillary central incisors were divided into 3 groups with 24 teeth each and restored with 1 of the following methods: prefabricated zirconia ceramic posts and resin composite buildups; zirconia ceramic posts and copy-milled alumina ceramic cores (2-piece technique), or copy-milled all-ceramic posts and cores made from a zirconia-reinforced glass-infiltrated alumina ceramic (1-piece technique). Each group was divided into 3 subgroups of 8 samples each, consisting of teeth that did not receive crown restorations and were stored for 60 days, teeth restored with all-ceramic crowns and stored for 60 days, and teeth restored with all-ceramic crowns and subjected to 1.2 million loading cycles with 30 N in a chewing simulator. RESULTS: The mean fracture strengths ranged from 205 to 522 N. Prefabricated zirconia posts and resin composite buildups showed a statistically significantly lower fracture strength after chewing simulation than teeth restored with prefabricated zirconia posts and alumina ceramic cores. CONCLUSION: All-ceramic posts and cores made with the 2-piece technique showed promising fracture strengths under the tested conditions.
Acrylic Resins↗
[Splints for adding height with padding for mastication, placed in the upper jaw].
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Acrylic Resins↗
Clinical study on the reasons for and location of failures of metal-ceramic restorations and survival of repairs.
PURPOSE: A recently introduced technique, the Cojet system, using SiOx (Al2O3 coated with silisic acid), provides ultrafine mechanical retention by sandblasting, as well as a chemicophysical bond between the metal-ceramic and the composite resin. This study determined the reasons for and locations of failures of metal-ceramic restorations and evaluated the survival of the intraoral silica-coating system used for the repair of failed restorations. MATERIALS AND METHODS: A total of 153 patients possessing 289 fractured crowns were involved in this study; 255 of these fractures were on fixed partial dentures, whereas 34 were on single crowns. The mean observation period was 34.6 months. The materials used for the repair process were ESPE-Sil for silane; Visiogem, Sinfony, and Dentacolor as opaquers; and Pertac II Aplitip, Sinfony, and Charisma as repairing composite resins. RESULTS: The majority of the failures (65%) occurred in the anterior region. Sixty percent of the failures were observed at the labial, 27% at the buccal, 5% at the incisal, and 8% at the occlusal regions. The fractures were mainly in the maxilla (75%), predominantly at the labial surface. The overall cumulative survival rates of the repairs (89%) showed that the first failures happened mostly from 1 week to 3 months after the repair, without any difference between the composite resins. CONCLUSION: The original failures happened mainly during chewing function or because of accidents, iatrogenic factors, and surgical operations, whereas secondary failures after repair using intraoral silica coating and composite resin were due to trauma, chewing function, or lack of rubber dam application.
Accidents↗
A longitudinal clinical assessment of spark erosion technology in implant-retained overdenture prostheses: a preliminary report.
STATEMENT OF PROBLEM: As adapted for the dental profession, spark erosion technology permits precise machining of retentive metal overdenture frameworks for use in implant prosthetics. PURPOSE: The resultant prostheses are retentive and provide a number of benefits offered by both conventional overdenture and fixed prosthetic designs. MATERIAL AND METHODS: Preliminary data collected from an ongoing 5-year clinical trial were reviewed to qualitatively assess the clinical results obtained from 25 spark eroded implant-retained overdenture prostheses placed in 24 subjects. RESULTS: Throughout an evaluation period of 13.33 months (range 4 to 19 months), subject responses measured by questionnaire were uniformly good. Few complications were encountered and were limited to resin denture base/tooth fractures or retentive component failures that were easily repaired. CONCLUSION: Overdenture prostheses retained by spark eroded milled frameworks offer an acceptable treatment alternative for patients undergoing dental implant therapy.
Dental Alloys↗
Effect of fatigue testing on core integrity and post microleakage of teeth restored with different post systems.
The purpose of this study was to evaluate a new nondestructive test system, which could test concurrently fatigue and microleakage. Fifty, single-rooted teeth were restored with one of the following posts systems and a composite core: titanium ParaPost cemented with zinc phosphate cement; CosmoPost; C-Post; Esthetic C-Post; and FibreKor post, all cemented with resin cement. Samples were embedded and placed in a positioning jig. They were impacted at 45 degrees to the long axis of the tooth with a force of 55 N at a frequency of 3 Hz for a total of 100,000 impacts. After 60,000 impacts, samples were thermocycled. Core integrity and post microleakage were evaluated periodically throughout the 100,000 impacts. Samples showed no detectable displacement of any of the cores, but the metallic group showed a statistically significant increase in microleakage (p < 0.05) at the conclusion of the study compared with the nonmetallic groups.
Analysis of Variance↗
Studies on the development of a microencapsulated delivery system for norbormide, a species-specific acute rodenticide.
Norbormide, a selective rat toxicant, was microencapsulated to both mask the flavour and delay the release until after a lethal dose has been ingested by the rat. To this end, gelatine microspheres containing norbormide were made and over coated with either shellac resin or an equal mixture of shellac and Eudragit RS in a fluid-bed coating machine. The microcapsules absorb water, swell and burst to release their contents. In rats an 8 h window is available to delay the release of encapsulated material. In initial experiments, a shellac coating of 20% w/w was established as suitable for delaying the release. A capsule size range of 200-400 microm was selected, from capsule mastication experiment, for oral gavaging and feeding studies in rat. Oral gavage study has demonstrated for the first time that a substantial delay in release of a lethal dose of an acute poison has been achieved by microencapsulation. Feeding test has demonstrated that there is a fine balance between the size and density of the capsules in the bait to overcome mastication of the capsules by rats. A combination of shellac and Eudragit RS resins is a viable polymeric wall material to control the rate of penetration of water in to microcapsules.
Animals↗
New acrylic resin composite with improved thermal diffusivity.
STATEMENT OF PROBLEM: Studies have shown that physical characteristics of denture base materials may affect patient acceptance of denture prostheses by altering sensory experience of food during mastication. Thermal diffusivity is one material property that has been cited as being important in determining gustatory response, with denture base acrylic resins having low thermal diffusivity compared with denture base metal alloys. PURPOSE: This study prepared and characterized experimental acrylic resin composite material with increased thermal diffusivity. MATERIAL AND METHODS: Sapphire (Al2O3) whiskers were added to conventional denture base acrylic resin during processing to achieve loadings of 9.35% and 15% by volume. Cylindrical test specimens containing an embedded thermocouple were used to determine thermal diffusivity over a physiologic temperature range (0 degree to 70 degrees C). RESULTS: Thermal diffusivities of the sapphire containing composites were found to be significantly higher than the unmodified acrylic resin. Thermal diffusivity was found to increase in proportion to the volume percentage of sapphire filler, which suggested that the high aspect ratio ceramic particles formed a pathway for heat conduction through the insulating polymer matrix. CONCLUSION: The thermal diffusivity of denture base acrylic resin was increased by the addition of thermally conducting sapphire whiskers.
Acrylic Resins↗
Fracture strength of artificially aged 3-unit adhesive fixed partial dentures made of fiber-reinforced composites and ceramics: an in vitro study.
OBJECTIVE: The aim of this in vitro study was to examine the fracture strength of metal-free 3-unit adhesive fixed partial dentures (AFPDs) bonded to mandibular incisors. METHOD AND MATERIALS: Extracted human incisors were positioned in pairs in polymethyl methacrylate resin simulating a clinical anterior situation. Their lingual sides were prepared for adhesive retainers with surfaces and finishing lines in enamel. Eight 3-unit AFPDs were made on master casts per material system: Connect/belleGlass (Girrbach), StickNet (StickTech)/Sinfony (3M Espe), and Empress 2 (Ivoclar Vivadent). The dentures were bonded adhesively using the dual-curing system ED Primer/ Panavia F (Kuraray Europe) and aged by thermocycling (6,000 x 5 degrees C/55 degrees C H2O; 2 minutes each cycle) and mechanical loading (1.2 x 10(6) x 20 N with 1.66 Hz) in an artificial oral environment representing a wearing period of 5 years. The fracture strength was determined in a universal testing machine (UTM 1446, Zwick) at a speed of 1 mm/min, applying the load buccoincisally on the pontics. The different forms of failure were described optically. Medians (25th/75th percentiles) of the fracture results were calculated. Statistical analysis was performed using Mann-Whitney U and Kruskal-Wallis tests (P < or = .05). RESULTS: Five StickNet/Sinfony AFPDs and 7 Empress 2 restorations failed in the artificial oral environment. The remaining Empress 2 dentures showed the highest medians of fracture forces (339 [200/506] N) compared to Connect/belleGlass (257 [242/310] N) and StickNet/Sinfony (256 [204/347] N). Statistical comparisons showed no significant differences. CONCLUSION: Only Connect/belleGlass and Empress 2 showed sufficient resistance against mastication
Composite Resins↗
Tooth wear: use of overlays with metallic structures.
This work is a clinical case report of a patient presenting with marked tooth wear in all teeth, a reduction in the vertical dimension of occlusion, and fatigue in the muscles of mastication. The treatment proposed and effected used a muscle-relaxing appliance and mandibular and maxillary overlay appliances which were adjusted according to the occlusal contacts, vertical dimension of occlusion, and the mandibular positioning. The results obtained were satisfactory in terms of relaxing the muscles involved, reestablishing the dimensions of the lower third of the face, and the functional activities of deglutition, mastication, and speech.
Adult↗
'Airborne' contact dermatitis due to Leica immersion oil.
BACKGROUND: Contact dermatitis has often been described in healthcare staff, resulting essentially from the use of natural rubber latex gloves, antiseptics, and especially aldehydes. This study reports an unusual cause of contact dermatitis in laboratory technicians. MATERIALS AND METHODS: Four patients working in the bacteriology departments of three different hospitals were seen for airborne contact dermatitis. All were patch tested for specific plastics and glues. RESULTS: For all patients, positive patch reactions were obtained with classic epoxy resins, such as diglycidylether of bisphenol, as well as with new types, such as diglycidylether of bisphenol F and an epoxyacrylate resin. CONCLUSIONS: Although phenols and ether handled by the laboratory technicians and an epoxy mastic applied during floor repair were initially suspected, an immersion oil used in light microscopy proved to be the real cause of the dermatitis. To our knowledge, these are the first reported cases due to this type of contact.
Air Pollutants, Occupational↗
Effect of resin-based material combination on the compressive and the flexural strength.
The mechanical properties, elasticity and compressive strength, of restorative materials play a crucial role during mastication for clinical performance of materials in particular stress bearing areas at posterior regions. This in vitro study was objected to evaluate the changes in the compressive and flexural strength of tooth-coloured resin-based dental restorations placed on flowable composites. Specimens in the control group were produced in cylindrical form for testing compressive strength and in quadrangular prism form for flexural strength test. Tetric Ceram, Charisma, Surefil, Admira and two compomers; Dyract AP and Compoglass F in test group specimens were fabricated by placing the control materials on different flowables. The material combinations were as follows: Tetric Ceram/Tetric Flow Charisma/Flowline, Surefil/Dyract Flow, Admira/Admira Flow, Dyract AP/Dyract Flow, Compoglass F/Compoglass Flow. Compressive strength values were measured at the Instron Testing Machine with a cross-head speed of 10 mm min(-1) while flexural strength were determined in three-point bending with a cross-head speed of 1 mm min(-1). One-way anova and Tukey's multiple comparison tests were performed for the statistical analysis. The flexural strength values of Tetric Ceram/Tetric Flow (135.9 +/- 3.2), Charisma/Flowline (120.4 +/- 5.6) and Compoglass F/Compoglass Flow (108.2 +/- 5.2) combinations were statistically greater than Tetric Ceram (110.8 +/- 10.5), Charisma (95.3 +/- 5.3) and Compoglass F (86.9 +/- 4.9). The results of the present study support the idea that the placement of flowable composite as a liner under the resin-based composite restoratives increase the flexural strength.
Compomers↗
Surface texture changes of a composite brushed with "tooth whitening" dentifrices.
OBJECTIVES: The aim of this investigation was to evaluate the significance of selected surface texture parameters used to describe and quantify the effect of tooth brushing with various "tooth whitening" dentifrices on a resin composite surface in vitro. METHODS: Specimens of a microfil resin composite were brushed with selected dentifrices. Surface texture profiles were acquired and analyzed both pre- and post-brushing using a contact diamond stylus. The selected parameters chosen to describe the surface texture were Ra, Rz, Rpm and the Rpm:Rz ratio. Differences between toothpastes were assessed using an ANOVA and a multiple comparisons test, the Student Newman-Keuls procedure. P and t values were calculated to determine if any of the surface roughness parameters were significantly changed by brushing. RESULTS: The results indicate that there were significant changes in the surface texture of the resin composite following tooth brushing with the selected dentifrices. For example, the use of Clinomyn significantly increased the surface roughness of the resin composite, as measured by the Rz parameter, from 2.19 +/- 1.67 microns to 10.02 +/- 2.57 microns (p < 0.05). In addition, the surface texture parameters chosen to describe the properties of the surface should reflect a knowledge of profile shape such as Rpm:Rz ratio, and care should be taken if measurements of surface texture of dental restorative materials are to be used as predictors of clinical performance. SIGNIFICANCE: All the toothpastes chosen for this investigation left a surface on the resin composite which may be prone to crack propagation during "vertical barrelling" movements generated during mastication. However, this may be more of a function of the rigidity of the restorative material rather than the surface left after tooth brushing.
Analysis of Variance↗
Relative wear of enamel opposing low-fusing dental porcelain.
PURPOSE: This study evaluated the wear of human enamel opposing 5 low-fusing dental porcelains and a traditional feldspathic control. In a second experiment, the repeatability of the test method and the effect of ceramic overfiring on enamel wear were also evaluated. MATERIALS AND METHODS: Five low-fusing dental porcelains--Finesse (FI), Rhapsody (RP), IPS d.Sign (DS), Omega 900 (OM), and Duceram LFC (LFC)--and 1 traditional feldspathic porcelain--VMK 68 (VMK)--were formed into disks (n = 10) and used as substrate for the wear test. Enamel was harvested from extracted human molars and machined into cusps with a 5-mm spherical radius (n = 60). The Oregon Health Sciences University oral wear simulator was used to simulate chewing and the size of the resulting enamel wear facets (in mm(2)) were evaluated after a specified number of chewing cycles. A portion of the experiment was duplicated to assess the repeatability of the data and determine the effects of overfiring on enamel wear. Data were subjected to analysis of variance and post hoc tests to determine significant differences. After wear testing, scanning electron micrographs were made using representative ceramic samples from each group. RESULTS: The results indicate that none of the low-fusing ceramics resulted in significantly less wear than the VMK control. In fact, 3 of the low-fusing porcelains (OM, RP, LFC) resulted in significantly greater enamel wear than VMK. Enamel wear was not significantly affected (p = 0.29) by the increased ceramic firing temperature. Wear data were repeatable, with no significant difference (p = 0.56) between the enamel wear from 2 separate experiments. The results from both experiments indicated that ceramic material significantly affected enamel wear (p <0.001). There was significantly less enamel wear opposite DS than LFC. CONCLUSIONS: This work suggests that variations in ceramic composition and microstructure may affect the opposing enamel wear, but that low-fusing temperatures do not necessarily guarantee low enamel wear. Although the clinical relevance of this testing apparatus may be questioned, the testing method was repeatable.
Aluminum Silicates↗
Influence of shearing action of food on contact stress and subsequent wear of stress-bearing composites.
The influence of sliding action of the antagonist on occlusal three-body wear of composites and an amalgam was investigated in vitro by gradual change in the distance between the opposing substrates. When the distance was decreased from 10 microns to approximately 3 microns, wear increased significantly by a factor of two to three and was exclusively of erosive nature. At a slurry-film thickness of approximately 1 micron, direct contacts between the antagonist and protruding composite filler particles started to occur. This consequently slowed the erosive wear. Ultimately, direct contact phenomena predominated, decreasing the wear rate of the various materials to different degrees. Loss of material due to subsurface fatigue could not be demonstrated with a contact pressure of 45 MPa at which the experiments were performed. From this study, it can be concluded that minor alterations of the food-film thickness at the contact areas result in considerable changes in wear rates and wear-rate ranking of composite materials, which may partly explain inconsistencies among clinical trials.
Composite Resins↗
Survival rate and fracture strength of endodontically treated maxillary incisors with moderate defects restored with different post-and-core systems: an in vitro study.
PURPOSE: This study compares the survival rate and fracture strength of endodontically treated maxillary incisors with moderate coronal defects restored with different post-and-core systems after exposure to an artificial mouth. MATERIALS AND METHODS: Sixty-four caries-free human maxillary central incisors were selected for standardized size and quality, endodontically treated, and decoronated 2 mm coronal to the cementoenamel junction. Group 1 was restored with titanium posts and composite cores, group 2 received zirconia posts and a composite core, and in group 3 zirconia posts with a heat-pressed ceramic core were used. Teeth restored with cast posts and cores served as controls. All teeth were prepared and restored with complete cast crowns. All samples were exposed to 1.2 million cycles in a computer-controlled chewing simulator with simultaneous thermocycling. In addition, the samples were loaded until fracture in a static testing device. RESULTS: The survival rates of the different groups were: 94% for titanium/composite, 63% for zirconia/composite, 100% for the all-ceramic post and core, and 94% for the cast post and core. The following mean fracture strengths were obtained: titanium/composite = 425 +/- 155 N, zirconia/composite = 202 +/- 212 N, zirconia/ceramic = 378 +/- 64 N, cast post and core = 426 +/- 178 N. The lower fracture load in the group with zirconia posts and composite cores was statistically significant. The use of zirconia posts resulted in fewer oblique root fractures. CONCLUSION: Prefabricated titanium posts with composite cores, zirconia posts with heat-pressed ceramic cores, and cast posts and cores yield comparable survival rates and fracture strengths for the restoration of crowned maxillary incisors with moderate coronal defects. Survival rates and fracture strengths for zirconia posts with composite cores are significantly lower, so this combination cannot be recommended for clinical use.
Cementation↗