Wear resistance of 3D-printed denture tooth resin opposing zirconia and metal antagonists.

STATEMENT OF PROBLEM: Additive manufacturing technology can be used for denture bases and also denture teeth. Therefore, the mechanical properties of 3D-printed resin denture teeth should be evaluated. PURPOSE: The purpose of this in vitro study was to compare the wear resistance of 3D-printed denture tooth resin with that of conventionally prefabricated denture teeth. MATERIAL AND METHODS: Eighty substrate specimens were prepared with 5 kinds of resin denture teeth: 3D-printed denture tooth resin (DENTCA denture tooth resin; DENTCA, Inc), Artic 6 (Kulzer GmbH), Preference (Candulor AG), Premium 6 (Kulzer GmbH), and Surpass (GC Corp). The 3D-printed denture tooth specimens were made of methacrylate-based photopolymerized resin by stereolithography 3D printing. Antagonistic surfaces were made from zirconia by milling and from cobalt-chromium (Co-Cr) alloy by 3D printing and casting. The specimens were loaded at 49 N for 30 000 cycles under thermocycling conditions in a mastication simulator. Wear resistance was measured by calculating the volume of substance lost. Wear surface characteristics were observed by using a scanning electron microscope (SEM). Two-way ANOVA was used to analyze the data (α=.05). RESULTS: The influence of the resin denture teeth and the type of antagonist were both statistically significant. The wear volume loss of the 3D-printed denture tooth resin was higher than that of Artic 6 and Preference when opposing the zirconia and the metal antagonists (P<.05). The 3D-printed denture tooth resin did not show a significant difference from Premium 6 with the zirconia and the metal antagonists or Surpass with the zirconia antagonist. From the SEM images, the specimens of the 3D-printed denture tooth resin showed a relatively smooth surface with the zirconia antagonist and exhibited cracks when opposed by the metal antagonist. CONCLUSIONS: The results suggest that 3D-printing by using resin materials provides adequate wear resistance for denture tooth use.

Screw loosening and changes in removal torque relative to abutment screw length in a dental implant with external abutment connection after oblique cyclic loading.

PURPOSE: This study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading. MATERIALS AND METHODS: External connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a 30° angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons. RESULTS: All assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P<.001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647). CONCLUSION: Within the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

3D Printing of Resin Material for Denture Artificial Teeth: Chipping and Indirect Tensile Fracture Resistance.

3D printing of denture artificial teeth with resin materials is worthy of study in a novel way. This study evaluated chipping and indirect tensile fracture resistance of 3D printing resin material (Dentca 3D printing denture teeth resin) compared with conventionally prefabricated resin denture teeth (Premium-8, Surpass, SR-Orthosit-PE, and Preference). One hundred tooth specimens were prepared for testing. The 3D printed tooth specimens were printed at a 50 µm layer thickness with methacrylate-based photopolymerized resin by stereolithography 3D printing. Chipping and indirect tensile fracture tests were conducted at a speed of 1 mm/min until fracture. The indirect tensile fracture loads of the 3D printed resin teeth were higher than those of Premium-8, Surpass, and SR-Orthosit-PE, and lower than those of Preference teeth. Regarding chipping resistance, the 3D printed resin teeth were not different from Surpass and SR-Orthosit-PE, and were lower than Premium-8 and Preference teeth. The 3D printed resin teeth exhibited vertical fracture of the loaded cusp without deformation in chipping. The 3D printed resin teeth showed simultaneous fracture of two cusps in indirect tensile fracture, unlike other teeth. The results of this study suggest that 3D printing technology using resin materials provides adequate fracture resistance for denture artificial tooth use.

Wear Resistance of 3D Printing Resin Material Opposing Zirconia and Metal Antagonists.

3D printing offers many advantages in dental prosthesis manufacturing. This study evaluated the wear resistance of 3D printing resin material compared with milling and conventional resin materials. Sixty substrate specimens were prepared with three types of resin materials: 3D printed resin, milled resin, and self-cured resin. The 3D printed specimens were printed at a build angle of 0° and 100 μm layer thickness by digital light processing 3D printing. Two kinds of abraders were made of zirconia and CoCr alloy. The specimens were loaded at 5 kg for 30,000 chewing cycles with vertical and horizontal movements under thermocycling condition. The 3D printed resin did not show significant difference in the maximal depth loss or the volume loss of wear compared to the milled and the self-cured resins. No significant difference was revealed depending on the abraders in the maximal depth loss or the volume loss of wear. In SEM views, the 3D printed resin showed cracks and separation of inter-layer bonds when opposing the metal abrader. The results suggest that the 3D printing using resin materials provides adequate wear resistance for dental use.

Effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement.

PURPOSE: To evaluate the effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement. MATERIALS AND METHODS: The specimens were prepared to evaluate the bond strength of epoxy resin-based fiber posts (D.T. Light-Post) to dual-curing resin cement (RelyX U200). The specimens were divided into four groups (n=18) according to different surface treatments: group 1, no treatment; group 2, silanization; group 3, silanization after hydrogen peroxide etching; group 4, silanization with warm drying at 80℃ after hydrogen peroxide etching. After storage of the specimens in distilled water at 37℃ for 24 hours, the shear bond strength (in MPa) between the fiber post and resin cement was measured using a universal testing machine. The fractured surface of the fiber post was examined using scanning electron microscopy. Data were analyzed using one-way ANOVA and post-hoc analysis with Tukey's HSD test (α=0.05). RESULTS: Silanization of the fiber post (Group 2) significantly increased the bond strength in comparison with the non treated control (Group 1) (P<.05). Heat drying after silanization also significantly increased the bond strength (Group 3 and 4) (P<.05). However, no effect was determined for hydrogen peroxide etching before applying silane agent (Group 2 and 3) (P>.05). CONCLUSION: Fiber post silanization and subsequent heat treatment (80℃) with warm air blower can be beneficial in clinical post cementation. However, hydrogen peroxide etching prior to silanization was not effective in this study.

Frequency of bone graft in implant surgery.

BACKGROUND: Implant surgery has become popular with the advance of surgical techniques such as sinus lifting, guided bone regeneration, and block bone graft. However, there were no data about the frequency of bone graft during implant surgery. The purpose of this study was to report the frequency and types of bone graft depending on dental implant patients' profile to complement the database regarding implant surgery. METHODS: The implant operations had been performed from January 2006 to October 2014. The upper and lower jaws were divided into six sextants. A total of 792 sextants were included in this study. Patient information including sex, age, sites, bone graft, and types of bone were investigated. RESULTS: A total of 1512 implants had been placed. Male and female sextants were 421 and 371, respectively (M:F = 1:0.88). Average age was 54.3 (ranging from 20 to 88 years old). Implants were placed in the posterior maxilla (322 sextants, 40.7 %), posterior mandible (286 sextants, 36.1 %), anterior maxilla (127 sextants, 16.1 %), and anterior mandible (57 sextants, 7.2 %). Bone graft was performed in 50.3 % of the sextants. Among the bone grafted sites, sinus lifting with lateral approach (22.1 %) and guided bone regeneration (22.7 %) were performed most frequently. CONCLUSIONS: Bone graft in implant surgery was necessary to augment defects. More than half of the sextants needed bone graft for implant installation.

Dexamethasone Delivery by an Implant-Mediated Drug Delivery System in the Canine Mandible.

BACKGROUND: A newly introduced implant-mediated drug delivery system (IMDDS) showed promising results in a rabbit tibia model. The aim of the present study is to evaluate whether dexamethasone administered by the IMDDS has sustained effects in the canine mandible - a different anatomic location, in a different species. METHODS: IMDDS was installed at the mesial root of the second premolar site in the mandibles of six beagle dogs. After complete healing, 10 mg dexamethasone was administered through the IMDDS. The same amount of drug was administered to five control animals by intramuscular injection. The release pattern was monitored for 2 weeks by measuring plasma drug concentrations. RESULTS: A sustained plasma dexamethasone concentration was detected after a peak at 6 hours until the end of the observation period, despite individual variations. The concentration was lower than reported in the rabbit tibia model. In contrast, plasma concentration of the control group showed an early peak at 2 hours and decreased rapidly. CONCLUSION: Dexamethasone was effectively released from the IMDDS for a prolonged time in the canine mandible model.

Accidental migration of a dental implant into the ethmoid sinus following a transalveolar sinus elevation procedure.

BACKGROUND: Migration of a dental implant into the paranasal sinuses may be the result of sinus membrane perforation, loss of osseointegration, and lack of initial stability. The majority of displaced implants migrate into the maxillary sinus, which may cause sinusitis. PURPOSE: The purpose of this study is to report an extremely rare ethmoid sinus migration of a dental implant after crestal approach in a resorbed posterior maxilla. MATERIALS AND METHODS: A 60-year old Korean male with a noncontributory medical history was referred from a local clinic to remove the migrated dental implant in the right ethmoid sinus. The patient had symptoms of mild sinusitis. The implant had been placed 6 months earlier through the bone-added transalveolar approach in a severely resorbed maxilla. RESULTS: The displaced implant was removed through the intraoral approach. A lateral window was made and an endoscopic surgery was performed to remove the implant. Healing was uneventful, and sinusitis symptom had ceased. CONCLUSION: The crestal approach for severely resorbed posterior maxillae should be performed when there is a potential for primary stability. If bone quality is poor and initial stability cannot be achieved, lateral window sinus elevation procedure is a better option for successful implant placement. Migrated implant may be removed with antrostomy and endoscopic surgery.

Illuminating light-dependent color shifts in core and veneer layers of dental all-ceramics.

The color of an object is perceived differently depending on the ambient light conditions. Since dental all-ceramic restorations are fabricated by building up several layers to reproduce the tooth shade, the optical properties of each layer should be optimized for successful shade reproduction. This study aimed to determine the separate contributions of the color shifts in each of the core and veneer layers of all-ceramics by switching the illuminating lights on the color shifts of layered ceramics. Specimens of seven kinds of core ceramics and the corresponding veneer ceramics for each core were fabricated with a layered thickness of 1.5 mm. A sintering ceramic was used as a reference core material. The Commission Internationale de l'Eclairage (CIE) color coordinates of core, veneer, and layered specimens were measured with a spectroradiometer under the CIE illuminant D65 (daylight), A (incandescent lamp), and F9 (fluorescent lamp) simulating lights. Color shifts of the layered specimens were primarily determined by the CIE a shifts (D65 to A switch) or by the CIE b shifts (D65 to F9 switch) of the veneer layer. The color coordinates shifts in the constituent layers differentially influenced those of the layered specimens by the kind of switched lights. Therefore, the optical properties of the constituent layers of all-ceramics should be controlled to reflect these findings.

Simultaneous sinus lift and implant installation: prospective study of consecutive two hundred seventeen sinus lift and four hundred sixty-two implants.

PURPOSE: If less than 4 mm of residual bone is remained in posterior maxilla, two-stage operation is recommended for implant installation. However, if primary stability could be obtained using tapered designed implants, one-stage surgery could be performed with reliable success rate in severely resorbed maxilla. The purpose of this prospective study was to evaluate survival and success rates of the implants simultaneously placed into grafted sinus using rough-surfaced implant. MATERIALS AND METHODS: A total of two hundred seventeen consecutive sinus lifting through lateral approach and four hundred sixty-two simultaneous implants were installed from November 2003 for 5.5 years. Xenogenic bone was used solely for bone graft materials. Second surgery was performed around 6 months after operation and porcelain fused metal or gold crown was used for definitive restorations. Cumulative survival and success rates were evaluated according to residual alveolar bone height (RABH), smoking status, and Schneiderian membrane perforation. RESULTS: The mean follow-up was 57.1 ± 15.6 (36-98) months. Of the four hundred sixty-two implants, two hundred sixty-two implants (56.7%: group 1) were installed in posterior maxilla less than 4-mm RABH and two hundred implants (43.3%: group 2) were placed in over 5-mm RABH. The cumulative survival and success rates were 98.91% and 96.54%. There was no statistically significant difference in success rate between group 1 and group 2 (p = .3135). Perforation of the membrane was not related to success (p = .7162), but smoking status is significantly related with implant failure (p = .0003). CONCLUSIONS: Sinus lifting with simultaneous implant placement could be used to treat atrophic maxilla in patients with minimal RABH when initial stability could be obtained by using taper designed implants with surgical techniques. Smoking is a possible factor for implant failure. Membrane perforation did not have an adverse effect on implant success if the membrane was repaired with absorbable membrane and fibrin glue.

Osteonecrosis of the jaw after implant surgery in patients treated with bisphosphonates--a presentation of six consecutive cases.

BACKGROUND: Osteonecrosis of the jaws in patients treated with bisphosphonates is mostly associated with intravenous bisphosphonates while the incidence associated with oral bisphosphonates is not significant. PURPOSE: The purpose of this paper is to describe a series of cases of jaw osteonecrosis that may be associated with dental implant placement in patients who had taken nitrogen containing bisphosphonates via oral and/or intravenous route. PATIENTS: Six female patients were treated for osteonecrosis of the jaw after implant placement. An average age was 71.8 ± 6.5 years old and they had a history of bisphosphonate use. Two patients suffered from cancer and the other patients had osteoporosis. Two osteoporosis patients had taken only oral bisphosphonate and the other patients received intravenous bisphosphonates. RESULTS: Resection of necrotized bone, implant removal, and primary closure were performed in five patients and four patients showed uneventful healing. One patient presented recurrence at the maxilla and underwent further extraction and resection. One patient presented with an exposure of the bone after implant placement was treated with an advanced flap closure, and the implants were preserved. CONCLUSION: Unusual jaw necrosis after dental implant surgery might be related with oral and/or intravenous bisphosphonates. Wide resection of necrotic bone, collagen graft, and primary closure are key factors for successful healing.

Perceived color shift of ceramics according to the change of illuminating light with spectroradiometer.

PURPOSE: Perceived color of ceramics changes by the spectral power distribution of ambient light. This study aimed to quantify the amount of shifts in color and color coordinates of clinically simulated seven all-ceramics due to the switch of three ambient light sources using a human vision simulating spectroradiometer. MATERIALS AND METHODS: CIE color coordinates, such as L*, a* and b*,of ceramic specimens were measured under three light sources, which simulate the CIE standard illuminant D65 (daylight), A (incandescent lamp), and F9 (fluorescent lamp). Shifts in color and color coordinate by the switch of lights were determined. Influence of the switched light (D65 to A, or D65 to F9), shade of veneer ceramics (A2 or A3), and brand of ceramics on the shifts was analyzed by a three-way ANOVA. RESULTS: Shifts in color and color coordinates were influenced by three factors (P<.05). Color shifts by the switch to A were in the range of 5.9 to 7.7 ΔE*ab units, and those by the switch to F9 were 7.7 to 10.2; all of which were unacceptable (ΔE*ab > 5.5). When switched to A, CIE a* increased (Δa*: 5.6 to 7.6), however, CIE b* increased (Δb*: 4.9 to 7.8) when switched to F9. CONCLUSION: Clinically simulated ceramics demonstrated clinically unacceptable color shifts according to the switches in ambient lights based on spectroradiometric readings. Therefore, shade matching and compatibility evaluation should be performed considering ambient lighting conditions and should be done under most relevant lighting condition.

Immediate free iliac bone graft after nonsegmental mandibular resection and delayed implant placement: a case series.

BACKGROUND: Resection of mandibular tumors without proper reconstruction may lead to unfavorable esthetic and function results. The purpose of this case series was to describe clinical results and a technique to prevent tissue loss using nonvascular iliac grafts immediately following tumor resection and long-term stability of the implants. MATERIALS AND METHODS: Three female patients presented with oral neoplasms (2 ameloblastoma and 1 ossifying fibroma). The mandibular reconstruction was performed with nonvascularized iliac grafts simultaneous with tumor removal. Subsequently, 10 dental implants were placed 6 to 9 months after reconstruction and restored. Survival and success of the implants were evaluated. RESULTS: Marginal mandibulectomy in 1 patient and buccal bone resection in 2 patients was performed; the resection sites were reconstructed with an immediate nonvascularized iliac graft. All implants survived and were successful during follow-up periods between 44 and 105 months. Mean marginal bone loss of 10 implants was 0.09 mm. CONCLUSIONS: Immediate reconstruction with nonvascularized iliac grafts following tumor resection may be a viable treatment option for nonsegmental inlay osseous defects. In these case series, the resorption of the iliac bone was minimal after 6 to 9 months consolidation periods.

Effect of silane activation on shear bond strength of fiber-reinforced composite post to resin cement.

PURPOSE: Among the surface treatment methods suggested to enhance the adhesion of resin cement to fiber-reinforced composite posts, conflicting results have been obtained with silanization. In this study, the effects of silanization, heat activation after silanization, on the bond strength between fiber-reinforced composite post and resin cement were determined. MATERIALS AND METHODS: Six groups (n=7) were established to evaluate two types of fiber post (FRC Postec Plus, D.T. Light Post) and three surface treatments (no treatment; air drying; drying at 38℃). Every specimen were bonded with dual-curing resin cement (Variolink N) and stored in distilled water for 24 hours at 37℃. Shear-bond strength (MPa) between the fiber post and the resin cement were measured using universal testing device. The data were analyzed with 1-way ANOVA and by multiple comparisons according to Tukey's HSD (α=0.05). The effect of surface treatment, fiber post type, and the interactions between these two factors were analyzed using 2-way ANOVA and independent sample T-tests. RESULTS: Silanization of the FRC Postec Plus significantly increased bond strength compared with the respective non-treated control, whereas no effect was determined for the D.T. Light Post. Heat drying the silane coupling agent on to the fiber-reinforced post did not significantly improve bond strength compared to air-syringe drying. CONCLUSION: The bond strength between the fiber-reinforced post and the resin cement was significantly increased with silanization in regards to the FRC Postec Plus post. Bond strength was not significantly improved by heat activation of the silane coupling agent.

Three-dimensional finite element analysis of the deformation of the human mandible: a preliminary study from the perspective of orthodontic mini-implant stability.

OBJECTIVE: The aims of this study were to investigate mandibular deformation under clenching and to estimate its effect on the stability of orthodontic mini-implants (OMI). METHODS: Three finite element models were constructed using computed tomography (CT) images of 3 adults with different mandibular plane angles (A, low; B, average; and C, high). An OMI was placed between #45 and #46 in each model. Mandibular deformation under premolar and molar clenching was simulated. Comparisons were made between peri-orthodontic mini-implant compressive strain (POMI-CSTN) under clenching and orthodontic traction forces (150 g and 200 g). RESULTS: Three models with different mandibular plane angles demonstrated different functional deformation characteristics. The compressive strains around the OMI were distributed mesiodistally rather than occlusogingivally. In model A, the maximum POMI-CSTN under clenching was observed at the mesial aspect of #46 (1,401.75 microstrain [µE]), and similar maximum POMI-CSTN was observed under a traction force of 150 g (1,415 µE). CONCLUSIONS: The maximum POMI-CSTN developed by clenching failed to exceed the normally allowed compressive cortical bone strains; however, additional orthodontic traction force to the OMI may increase POMI-CSTN to compromise OMI stability.

Three-dimensional interpretation of intercanine width change in children: a 9-year longitudinal study.

INTRODUCTION: The immutability of intercanine width has long been the subject of discussion. The aims of this study were to describe the longitudinal intercanine width changes of children from 6 to 14 years of age and to interpret them with a 3-dimensional method. METHODS: Complete dental stone casts were annually prepared for 66 subjects (50 girls, 16 boys) from 6 to 14 years of age. By using 3-dimensional laser scanning and reconstruction software, virtual casts were constructed. Intercanine width was measured as well as the related 3-dimensional measurements, such as the area of the intercanine triangle, the intercanine angle, the radius of the inscribed circle, and the angles formed by the virtual axes of the canines and the occlusal plane. The measurement changes over time were analyzed by using mixed-effects analysis for longitudinal data. RESULTS: There were slight decreases in intercanine widths for both sexes and both arches. However, the amounts of change were relatively small when compared with the initial values and individual random variability. The values of area, the angles formed by the virtual axes of the canines and the occlusal plane, and the radius showed decreasing trends, whereas the intercanine angle exhibited increasing trends during the observation period. Although the intercanine width changed over time, it was not clinically significant, showing relative stability. CONCLUSIONS: The intercanine width of an untreated subject after stabilization in the mouth is considered to be quite stable, even though individual variation is great.

Curing efficiency of various resin-based materials polymerized through different ceramic thicknesses and curing time.

PURPOSE: The aim of this in vitro study was to examine the curing efficiency of various resin-based materials polymerized through ceramic restorations with 3 different thicknesses. Curing efficiency was evaluated by determining the surface microhardness (VHN) of the resin specimens. MATERIALS AND METHODS: Four kinds of resin materials were used. Z350 (3M ESPE Filtek™ Z350: A2 Shade), Z250 (3M ESPE Filtek™ Z250: A2 Shade) and Variolink® II (VL: Ivoclar vivadent, base: transparent) either with or without a self-curing catalyst (VLC: Ivoclar vivadent, catalyst: low viscosity/transparent) were filled into the silicone mold (10 mm diameter, 1 mm thick). They were cured through ceramic discs (IPS e.max Press MO-0 ingot ivoclar vivadent, 10 mm diameter, 0.5, 1 and 2 mm thicknesses) by LED light-curing units for 20 and 40 seconds. Vicker's microhardness numbers (VHNs) were measured on the bottom surfaces by a microhardness tester. Data were analyzed using a 3- way analysis of variance (ANOVA) at a significance level of 0.05. RESULTS: The thickness of ceramic disc increased, the VHNs of all four resin types were decreased (P<.05). The mean VHN values of the resins light cured for 40 seconds were significantly higher than that of LED for 20 seconds in all four resin materials (P<.05). VLC showed significantly higher VHN values than VL regardless of other conditions (P<.05). Z350 and Z250 showed higher values than VL or VLC (P<.01). CONCLUSION: Thinner ceramic disc with increased curing time resulted higher VHN values of all resin materials. The use of a catalyst produced a greater hardness with all polymerization methods. Restorative resin materials (Z350, Z250) showed higher VHN values than resin cement materials (VL, VLC).

Full mouth rehabilitation on a bilateral condylar fractured patient using orthognathic surgery and dental implant.

BACKGROUND: Mandibular displacement is a common complication of condylar fracture. In the mandibular displacement due to condylar fracture, it is difficult to restore both esthetics and function without using orthognathic surgery. CASE DESCRIPTION: This clinical report described a full mouth rehabilitation in the patient with bilateral condylar fractures and displaced mandible using bilateral sagittal split ramus osteotomy (BSSRO) and simultaneous dental implant surgery. Mandibular position was determined by model surgery through the diagnostic wax up and restoration of fractured teeth. The precise amount of the mandibular shift can be obtained from the ideal intercuspation of remaining teeth. CLINICAL IMPLICATION: Mandibular displacement by both condylar fractures can be successfully treated by orthognathic surgery. Determination of occlusal plane and visualization from diagnostic wax up are mandatory for mandibular repositioning of model surgery. Stable occlusion and regular recall check up are needed for long-term outcome.

Changes in stress relaxation property and softness of soft denture lining materials after cyclic loading.

OBJECTIVES: Soft denture lining materials show varied and changeable stress relaxation property and softness under cyclic loading conditions. The purpose of this study was to determine the changes in the stress relaxation property and the softness of commercial soft lining materials after cyclic loading. METHODS: One plasticized acrylic-based material (Coe Soft: COS) and two silicone-based materials (Mucosoft: MUS; Sofreliner S: SFL) were investigated. For each material, 10 cylinder-shaped specimens were subjected to 29 days of cyclic loading, 1800 times per day; other 10 unloaded specimens were used as control groups. Stress relaxation ratio and softness were measured after 1, 4, 8, 15, 22 and 29 days of cyclic loading or storage. RESULTS: During 29 day period, the stress relaxation ratios of the cyclic loaded and unloaded COS, MUS and SFL specimens were 28.5-31.6% and 30.9-32.6%, 6.4-15.1% and 1.8-15.4%, 14.0-38.2% and 19.8-40.6%, respectively. The softness values of the cyclic loaded and unloaded COS, MUS and SFL specimens were 42.6-60.6% and 56.4-61.8%, 47.6-52.5% and 46.9-51.5%, 56.6-58.4% and 58.0-65.1%, respectively. Based on repeated-measures, 3-way ANOVA, the stress relaxation ratio was influenced by the loaded or stored period and the type of material (p<0.05), but not by the application of cyclic loading; the softness value was influenced by the loaded or stored period and the application of cyclic loading (p<0.05), but not by the type of material. SIGNIFICANCE: Soft lining materials showed the loaded or stored period and the material type dependent stress relaxation properties regardless of the application of cyclic loading. Softness value was influenced by the loaded or stored period and the application of cyclic loading.

Difference in illuminant-dependent color changes of shade guide tabs by the shade designation relative to three illuminants.

PURPOSE: To determine the difference in illuminant-dependent color changes of shade guide tabs of Vita Lumin (VITA), Chromascop (CHRO) and Vita 3D-Master (3D-M) shade guides by the shade designation in each shade guide. METHODS: Color of 16 tabs of VITA, 20 tabs of CHRO and 29 tabs of 3D-M was measured according to the CIELAB color scale relative to the CIE standard illuminant D65, A and F2. Color differences (deltaE*ab) between the A1 tab and other VITA tabs, between the 110 tab and other CHRO tabs and between the 0M1 tab and other 3D-M tabs relative to the three illuminants were calculated, and the ratios of deltaE*ab values relative to the different illuminants [deltaE*ab(A)/deltaE*ab(D65), deltaE*ab(F2)/deltaE*ab(D65) and deltaE*ab(F2)/deltaE*ab(A)] were calculated. Ratios of the hue angle shifts of each shade tab by the change of illuminant over the corresponding value of the Al, the 110 or the 0M1 tab were also calculated. Differences in the ratios of color difference and hue angle shift were analyzed with a repeated measures, two-way analysis of variance (alpha = 0.05). RESULTS: Ratios of deltaE*ab values by the illuminant were 0.90-1.17, 0.95-1.07 and 0.99-1.06 for the VITA, the CHRO and the 3D-M shade guide, respectively. Ratios of the hue angle shifts by the illuminant were from -1.6 to 1.8 for the VITA, from -7.3 to 1.2 for the CHRO and from -1.2 to 3.1 for the 3D-M. Changes in color and hue angle of shade tabs were significantly different by the shade tab designation when illuminant was changed (P < 0.01).