Effect of Thixotropic Agent on the Color Stability of Platinum-Based Silicone Maxillofacial Elastomers after Artificial Aging.

Maxillofacial prostheses are essential for restoring natural appearance and function in individuals with defects in the head and neck regions. Thixotropic agents, as liquid additives, are known to increase the viscosity of silicone elastomers. However, color deterioration remains a challenge in facial prostheses, leading to the need for refabrication. Despite this, there is limited research on the effect of thixotropic agents on the color stability of silicone maxillofacial elastomers. This study aims to investigate the impact of different thixotropic agent amounts on the color degradation of various maxillofacial silicone elastomers. Three elastomers (A-2000, A-2006, and A-2186) were combined with five pigments (no pigment as control, red, yellow, blue, and a mixture of red, yellow, and blue), and mixed with six thixotropic agent quantities (0, 1, 2, 3, 4, and 5 drops). A total of 450 specimens were fabricated (n = 5) and aged in an artificial aging chamber. L*, a*, b* readings were obtained before and after aging using a digital spectrophotometer. Color difference (ΔE*) means and standard deviations for 150 kj/m2, 300 kj/m2, and 450 kj/m2 were calculated. Statistical analyses, including four-way ANOVA and Fisher's PLSD test, were conducted to determine any significant differences (p < 0.05) among the groups. A comprehensive analysis revealed significant four-way interactions among the groups. In the mixed-pigmentation group, adding 4 drops of thixotropic agent resulted in ΔE* above 3 only in A-2186 silicone at 300 and 450 kj/m2 energy levels. However, the color stability of mixed-pigmented A-2000 and A-2006 remained within the acceptable thresholds of 3 ΔE* at all irradiance levels in this study. At each energy level, A-2006 exhibited the highest color stability with an increasing thixotropic agent quantity among all the silicones. Conversely, A-2186 was more affected by the increased number of thixotropic agent drops in each pigmentation group, including the control group at 450 kj/m2. The quantity of thixotropic agent plays a crucial role in determining the color stability of different silicone elastomers pigmented with various intrinsic pigments. The thixotropic agent amount has a more significant impact on color stability than the type of pigment used in the silicone elastomers. A key overarching insight from this investigation is the identification of a safety threshold for the thixotropic agent quantity of 3 drops for each silicone type, pigmentation, and energy level. These findings highlight the importance of considering the proper combination of thixotropic agents, pigments, and silicone materials to achieve optimal color stability in maxillofacial prosthetic applications.

Dynamic and static load performance of dental biomaterial systems with conical implant-abutment connections.

BACKGROUND: The stability of the implant-abutment interface is an important factor that influences load distribution on the marginal bone. OBJECTIVE: In this study, three dental implants with the same connection were subjected to different dynamic loading cycles. The fracture strengths and the horizontal compatibility of implants were assessed. METHODS: Eighty four implant specimens were embedded in a polyacetal cylinder as simulated bone loss of 3 mm from the implant platform. Three of the implants were used to determine the endurance limit. The other specimens were subdivided into four subgroups (n = 6): three for dynamic + static loading, and one for static loading (control group). The tests were performed by applying a compression load. The dynamic loading experiments included three different cycles with endurance upper limit loads at a frequency of 10 Hz. RESULTS: The differences between the fracture strength values of the implant brands were found to be statistically significant. However, there were no meaningful differences between the fracture strength values of implants of the same brand. The specimens of the DTI implant system had the lowest strength (647.9 ± 41.5 N) and the SEM analysis indicated that the Implantium implant system had the shortest horizontal gaps. CONCLUSIONS: There was a negative correlation between the fracture strengths and size of the microgaps. The importance of these in vitro results needs to be validated by clinical trials because the loads in the mouth can be applied from various angles.

Color and translucency of zirconia infrastructures and porcelain-layered systems.

STATEMENT OF PROBLEM: A good color match combined with a proper translucency match results in excellent esthetics for a metal-free restoration, yet basic color and translucency comparisons between available zirconia systems are not well described. PURPOSE: The purpose of this in vitro study was to compare the color and translucency of commercially available zirconia materials. MATERIAL AND METHODS: Eight specimen disks were formed in each of the single-layer (0.5-mm thick) groups and double-layer (0.5-mm zirconia with 1.0-mm porcelain) groups for each of 5 zirconia-based substructure systems. Colors on black, gray, and white backings were used to obtain CIEDE2000 color differences between the zirconia systems in the layering groups and to obtain relative translucency parameter (RTP) values. Color differences were compared with perceptibility and acceptability thresholds, and comparisons in RTP were made using analyses of variance and the Bonferroni corrected Student t tests (α=.05). RESULTS: The Shrout-Fleiss random set reliability for the duplicate L* determinations was 0.9992, 0.9756 for a*, and 0.9959 for b*. Although some mean color differences were below or at the perceptibility threshold, most differences were at or above the acceptability threshold. For the single-layer configuration, 1 material system had higher RTP values than every other material (P<.001), and another material had lower RTP values than every other material (P<.001). CONCLUSIONS: The results of this study present significant differences in both color and translucency among 5 ceramic substrate systems when studied in single layers. Perceivable and often unacceptable differences in color were also found among these materials when layered with porcelain. It is concluded that the esthetics of restorations which use a ceramic substrate is notably affected by the ceramic system used.

Effects of different loading protocols on the secondary stability and peri-implant bone density of the single implants in the posterior maxilla.

BACKGROUND: Immediate or early loading of dental implants becomes a clinically feasible concept. PURPOSE: The aim was to evaluate the effects of different loading protocols (immediate, early, and delayed) on secondary stability and peri-implant bone density of single implants in the posterior maxilla. MATERIALS AND METHODS: Thirty-nine implants (Dentium, South-Korea) were placed in 39 patients. After placement, implant stability values (ISQ) and baseline peri-implant bone density values derived from cone-beam computed tomography were recorded. Thirteen implants were included randomly in each loading groups. The secondary ISQ values were recorded during follow-up visits. Peri-implant bone density values were measured 1 year after placement again. Data was statistically analyzed. RESULTS: Immediate-loaded group showed the lowest ISQ values, 1 month after placement. During the next follow-up visits, delayed-loaded group showed the lowest ISQ values while other groups showed comparable results. Early loading increased the peri-implant bone density greater than the other groups. CONCLUSIONS: The peri-implant bone of early-loaded implants was significantly denser than that of immediate- and delayed-loaded implants, 1 year after placement. Density increment can be judged as the radiological findings of loaded-bone, which may also reduce the need for histomorphometric analysis of human biopsy to evaluate the bone reaction around the implants.

Effects of NSAIDs and hydroxyapatite coating on osseointegration.

PURPOSE: The aim of our study is to investigate the bone ongrowth of two different alternative surfaces and the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on osseointegration. METHODS: Hips of 40 New Zealand white rabbits were operated bilaterally. Hydroxyapatite (HA)-coated titanium rods were implanted into the right femur, and grit-blasted titanium rods were implanted into the left femur. They were divided into three groups. At the end of 8 weeks, both femora of the rabbits were removed and investigated biomechanically and histologically. RESULTS: HA-coated implants had a significantly better failure load and "percentage of bone-implant contact" than grit-blasted implants. There was no significant difference between the medication groups as a result of the biomechanical and histologic investigations. CONCLUSIONS: Our results indicate that NSAIDs did not have any negative effect on the osseointegration. HA-coated implants may provide more tensile strength and greater bone-implant contact rate in comparison with grit-blasted implants.

Does cone beam computed tomography-derived bone density give predictable data about stability changes of immediately loaded implants?: A 1-year resonance frequency follow-up study.

The aim of this clinical study was to evaluate whether preoperative bone density value derived from cone-beam computed tomography (CBCT) gives predictable data about primary and secondary stability characteristics of immediately loaded dental implants under different clinical variables. A total of 77 immediately loaded implants placed in 23 patients were included the study. Bone density values of the implant recipient sites were recorded using CBCT. The maximum insertion torque values (ITVs) of the implants were recorded using a digital torque meter during surgery. Resonance frequency measurements were taken using the Osstell Mentor at 4 time points; immediately after surgery (implant stability quotient [ISQ]0) and after 1 (ISQ1), 3 months (ISQ3), and 12 months (ISQ12) of loading. Data were analyzed statistically. The mean bone density and ITVs of all implants were 565 ± 81 and 36.8 ± 3.8 N · cm, respectively. The mean ISQ values were 73.6 ± 5.8 at baseline, 71.1 ± 6.5 after 1 month, 74.8 ± 5.6 after 3 months, and 76.6 ± 5.1 after 12 months of loading. Statistically significant differences were observed between ISQ0 and ISQ1 (P < 0.001), and ISQ0 and ISQ12 (P < 0.001), but not between ISQ0 and ISQ3 (P > 0.05). In regard to stability changes over time, statistically significant correlations were found between bone density values from CBCT and ISQ follow-up measurements, and between ITV and ISQ follow-up measurements in all examination periods. Thus, it is possible to predict primary and secondary stability characteristics of immediately loaded implants by using preoperative CBCT scan and perioperative ITV.

Evaluation of relationship between preoperative bone density values derived from cone beam computed tomography and implant stability parameters: a clinical study.

OBJECTIVES: The aim of this study was to explore the efficacy of bone density value derived from cone beam computed tomography (CBCT) by evaluating its correlation with implant stability parameters including insertion torque value (ITV) and radiofrequency analysis in relation to different clinical variables including location, gender, age, bone quality, and implant diameter. MATERIAL AND METHODS: A total of 65 implants were placed in 17 patients. The bone densities of implant recipient sites were preoperatively recorded using CBCT. Bone quality was subjectively assessed, which depends on the stiffness of the jawbone according to the Lekholm and Zarb index during drilling procedure. The maximum ITV of each implant was recorded using a digital torque meter during implant placement. Resonance frequency measurements were taken using an Osstell Mentor immediately after implant placement. Data were analyzed statistically. RESULTS: The mean bone density, insertion torque, and implant stability quotient values of all implants were 556 ± 80, 37.4 ± 3.3 Ncm, and 73.8 ± 7.2, respectively. Statistically significant correlations were found between bone density values from CBCT and implant stability parameters in relation to all variables. CONCLUSION: Bone density assessment using CBCT is an efficient method and significantly correlated with implant stability parameters and Lekholm and Zarb index. Thus, it is possible to predict initial implant stability and possibility of immediate or early loading using CBCT scans prior to implant placement.

Metal ceramic bond after multiple castings of base metal alloy.

STATEMENT OF PROBLEM: Remelting previously cast metal can produce a critical change in metal-oxide composition at the dental alloy surface. PURPOSE: The purpose of this study was to evaluate the effect of multiple castings on bonding of a single selected base metal and a dental ceramic, and to compare results from shear bond and 3-point-bending tests. MATERIAL AND METHODS: Three groups of dental alloy (Remanium CSe) were prepared by mixing 50% fresh alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% fresh alloy and served as control (C0). The second group consisted of equal amounts of fresh alloy and alloy remnants cast only once (C1). The third and fourth groups contained 50% fresh alloy and alloy cast twice (C2) and 3 times (C3), respectively. The bond load (N) between alloy and dental porcelain (VMK 95 Metal Ceramic) was evaluated, using shear bond and 3-point bending tests. The fracture surfaces of the specimens subjected to testing were analyzed using a stereomicroscope and scanning electron microscope. One-way ANOVA followed by the Tukey multiple comparison test was used for analysis of bond data (alpha=.01). RESULTS: The mean shear bond load (SD) of C0 (738.0 (77.1) N) was significantly higher than that of C1 (577.8(139.4) N), C2 (494.8 (77.6) N), and C3 (480.5 (60.9) N). Mean peak load for the 3-point-bending test of specimens cast from C0 (39.8 (1.79) N) was significantly higher than for other groups (P<.01). No significant difference was found between C1 (24.4 (5.60) N), C2 (23.2 (4.03) N), and C3 (22.8 (1.79) N) in terms of the shear bond test and the 3-point bending test. CONCLUSIONS: In general, there was agreement between the 2 bond strength tests to indicate that including re cast base alloy with fresh alloy for metal decreases metal-to-ceramic bond strengths. (J Prosthet Dent 2009;102:165-171)

Influence of layer thickness on stress distribution in ceramic-cement-dentin multilayer systems.

The effects of dentin and cement thicknesses on stress level and distribution of crack propagation in ceramic-cement-dentin multilayer complex were analyzed. Custom-designed finite element analysis program based on JL Analyzer was used to analyze the stress distribution and present the maximum principal stress locations. In Zirconia, all the maximum stress values were above 100 MPa. In Empress II, they ranged between 50 and 105 MPa, which were approximately one-third of those of Zirconia. In Feldspathic, the maximum stress values were generally lower than 50 MPa. In all groups with 30 microm cement thickness, the highest values were observed at the bottom surface. For cement thicknesses at 50, 70, and 100 microm, maximum stress was found to occur at the top surface. However, changes in dentin thickness did not bring about significant changes in maximum stress values. Results of this study revealed the roles played by the following variables in the failure of a multilayer structure: cement thickness had a minor influence, dentin thickness exerted no influence, but the thickness and type of ceramic system played a significant role.

Effect of botulinum toxin-A in myofascial pain patients with or without functional disc displacement.

PURPOSE: To evaluate the effects of botulinum toxin-A in the treatment of patients who have myofascial pain with or without functional disc displacement. PATIENTS AND METHODS: Twenty-four participants were randomly assigned to the study by using Research Diagnostic Criteria for Temporomandibular Disorders. All patients were informed about botulinum toxin-A, and were required to give informed consent. Before the injections, patients were asked to fill out a Biobehavioral Questionnaire to evaluate their pain and psychological status, and afterward, electromyography of the right and left masseter and anterior temporal muscles was recorded. Saline was injected into the masseter and anterior temporal muscles in the placebo group, and botulinum toxin-A was used in the study group. On days 14 and 28, patients were asked to fill out a Biobehavioral Questionnaire again, and electromyography of the right and left masseter and anterior temporal muscles was recorded again. RESULTS: The study group showed improvement in pain and psychological status. Although a decrease in the action potentials of the masseter muscles on day 14 was followed by an increase on day 28, the reduction of pain scores and improvement in psychological status continued on day 28. CONCLUSIONS: The injection of botulinum toxin-A decreases the muscle action potential in 14 days. The patients also show improvement in pain and psychological status.

Placement of implants in the mandible reconstructed with free vascularized fibula flap: comparison of 2 cases.

The reconstruction of mandibular continuity defects after tumor resection with free vascularized bone flaps is considered to be a treatment option. Although the fibula flap presents many advantages, it does not offer sufficient bone height to restore the alveolar arch when reconstruction involves a dentate mandible. In this report, 2 patients who were referred to our clinic with reconstructed mandibles with diagnosis of amelablastoma are presented and compared. The mandibles of these patients were reconstructed with free vascularized fibula flaps. Whereas one of the reconstructed mandibles was vertically distracted before implant placement, distraction procedure was not carried out for the other patient. Increasing height of the fibula flap by distraction osteogenesis before implant placement in dentate mandible is desirable from a functional and esthetic point of view.

Effect of tulle on the mechanical properties of a maxillofacial silicone elastomer.

The purpose of this research was to investigate if physical properties could be improved by incorporating a tulle reinforcement material into a maxillofacial silicone elastomer. A-2186 silicone elastomer was used in this study. The study group consisted of 20 elastomer specimens incorporated with tulle and fabricated in dumbbell-shaped silicone patterns using ASTM D412 and D624 standards. The control group consisted of 20 elastomer specimens fabricated without tulle. Tensile strength, ultimate elongation, and tear strength of all specimens were measured and analyzed. Statistical analyses were performed using Mann-Whitney U test with a statistical significance at 95% confidence level. It was found that the tensile and tear strengths of tulle-incorporated maxillofacial silicone elastomer were higher than those without tulle incorporation (p < 0.05). Therefore, findings of this study suggested that tulle successfully reinforced a maxillofacial silicone elastomer by providing it with better mechanical properties and augmented strength--especially for the delicate edges of maxillofacial prostheses.

Histomorphometric evaluation of implants coated with enamel or dentine derived fluoride-substituted apatite.

OBJECTIVES: The aim of this study was to compare osseous healing characteristics of titanium implants coated with enamel-derived fluoride-substituted apatite (EFSA) or dentin-derived fluoride-substituted apatite (DFSA). METHODS: Fluoride-substituted apatite was derived from extracted human teeth with calcination method at 850 degrees C. DFSA and EFSA were separated and carefully ground with a blade grinder. Twenty-four titanium implants were prepared from a 99.99% pure titanium bar. EFSA and DFSA powders were sprayed separately on implants. As control group, unsprayed and sandblasted pure titanium implants were used. Eight adult rams were used in the study. One EFSA coated, 1 DFSA coated and 1 control implants were placed into right tibia of each rams. The rams were sacrificed after 6 months of healing. Undecalcified sections were prepared according to Donath's method and histomorphometric evaluation of implants was made. RESULTS: The mean bone contact percentage of DFSA-coated, EFSA-coated and control implants was 89.88%+/-2.34, 70.19%+/-13.11 and 53.12%+/-5.76 respectively. This study suggests that DFSA-coated implants achieved better bone contact than EFSA-coated implants (P<0.05). Also study groups presented better bone contact than control group (P<0.05). CONCLUSIONS: The results of this study show that although DFSA-coated implants achieved better bone contact, both DFSA and EFSA can be considered as appropriate coating materials.

Structure and mechanical properties of Cresco-Ti laser-welded joints and stress analyses using finite element models of fixed distal extension and fixed partial prosthetic designs.

STATEMENT OF PROBLEM: The Cresco-Ti System uses a laser-welded process that provides an efficient technique to achieve passive fit frameworks. However, mechanical behavior of the laser-welded joint under biomechanical stress factors has not been demonstrated. PURPOSE: This study describes the effect of Cresco-Ti laser-welding conditions on the material properties of the welded specimen and analyzes stresses on the weld joint through 3-dimensional finite element models (3-D FEM) of implant-supported fixed dentures with cantilever extensions and fixed partial denture designs. MATERIAL AND METHODS: Twenty Grade III (ASTM B348) commercially pure titanium specimens were machine-milled to the dimensions described in the EN10002-1 tensile test standard and divided into test (n = 10) and control (n = 10) groups. The test specimens were sectioned and laser-welded. All specimens were subjected to tensile testing to determine yield strength (YS), ultimate tensile strength (UTS), and percent elongation (PE). The Knoop micro-indentation test was performed to determine the hardness of all specimens. On welded specimens, the hardness test was performed at the welded surface. Data were analyzed with the Mann-Whitney U test and Student's t test (alpha=.05). Fracture surfaces were examined by scanning electron microscopy to characterize the mode of fracture and identify defects due to welding. Three-dimensional FEMs were created that simulated a fixed denture with cantilever extensions supported by 5 implants (M1) and a fixed partial denture supported by 2 implants (M2), 1 of which was angled 30 degrees mesio-axially. An oblique load of 400 N with 15 degrees lingual-axial inclinations was applied to both models at various locations. RESULTS: Test specimens fractured between the weld and the parent material. No porosities were observed on the fractured surfaces. Mean values for YS, UTS, PE, and Knoop hardness were 428 +/- 88 MPa, 574 +/- 113 MPa, 11.2 +/- 0.4%, 270 +/- 17 KHN, respectively, for the control group and 642 +/- 2 MPa, 772 +/- 72 MPa, 4.8 +/- 0.7%, 353 +/- 23 KHN, respectively, for the test group. The differences between the groups were significant for all mechanical properties ( P <.05). For both models, the FEA revealed that maximum principal stresses were concentrated at the framework-weld junction but did not exceed the UTS of the weld joint. CONCLUSION: Within the constraints of the finite element models, mechanical failure of the welded joint between the support and the framework may not be expected under biomechanical conditions simulated in this study.