Comparison of denture base adaptation between additive and conventional fabrication techniques.

PURPOSE: This in vitro study compared the adaptation of denture bases fabricated by injection molding (IM), compression molding (CM), liquid crystal display (LCD), and digital light processing (DLP) techniques. MATERIAL AND METHODS: A definitive maxillary cast was duplicated using a silicone mold to create 40 gypsum casts that were laser scanned before any fabrication procedures were initiated. For the DLP and LCD groups, 20 denture bases (10 in each group) were virtually designed and manufactured referring to the digitalized data. For the CM and IM groups, 20 denture bases (10 in each group) were molded using gypsum models. A total of 40 gypsum models and their corresponding denture bases were scanned. The scanned intaglio surface of each denture base was superimposed on the scanned reference cast to compare the degree of tissue surface adaptation. The three-dimensional surface deviations of the total intaglio surface, denture border apex, palatal vault, and crest of the ridge were evaluated on the basis of the best fit algorithm technique using inspection software. The data were statistically analyzed using one-way ANOVA and Tukey's multiple comparison test (α = 0.05). RESULTS: According to the superimposing results, for the total intaglio surface, the lowest deviation was present on the injection-molded group and the highest deviation occurred on the LCD group. For the palatal vault, the lowest deviation was present on the DLP group and the highest deviation occurred in the compression molded group. For the crest of the ridge, the lowest deviation was present in the injection-molded group and the highest deviation occurred in the LCD group. For the denture border apex, the lowest deviation was present in the DLP group and the highest deviation occurred in the LCD group. CONCLUSIONS: Maxillary denture bases fabricated using DLP and IM techniques showed higher surface adaptation than the bases fabricated using LCD and CM techniques. Among the conventional techniques, higher compatible dentures can be produced with IM; among the additive techniques, higher compatible dentures can be produced with DLP.

Effects of boron on the mechanical properties of polymethylmethacrylate denture base material.

PURPOSE: The objective of this study was to determine whether the addition of different types of boron (Borax, Boric Acid and Colemanite) to polymethyl methacrylate denture base resin would improve flexural and impact strengths, and surface hardness of polymethyl methacrylate. MATERIALS AND METHODS: Borax, Boric acid, Colemanite were added to heat polymerized polymethyl methacrylate specimens were prepared for flexural strength (65x10x2.5 mm), impact strength (50x6x4 mm), and hardness (20x6x4 mm) tests according to the manufacturers' instructions (n=10). To determine flexural strength of the specimens, they were loaded until failure on a universal testing machine using a three point bending test. Specimens were subjected to the Charpy impact test machine. Hardness of the specimens was measured with an analog shoremeter Shore D. The data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=0.05). RESULTS: The highest mean flexural strength value was seen in 3% Borax group and followed by 1% Colemanite group. In addition, the highest mean impact strength value was recorded in 1% Colemanite group, and differences between 1% Colemanite group and control group were found to be statistically significant (p=0,001). Furthermore, there was significant difference in hardness between control group and all other groups (p<0.001). CONCLUSION: The addition of 1% Colemanite to polymethyl methacrylate improved the mechanical properties of PMMA.

Bonding Strength of Ceromer with Direct Laser Sintered, Ni-Cr-Based, and ZrO2 Metal Infrastructures After Er:YAG, Nd:YAG, and Ho:YAG Laser Surface Treatments-A Comparative In Vitro Study.

OBJECTIVE: Laser modalities instead of conventional surface treatment techniques have been suggested to obtain an adequate micromechanical bonding between dental super- and infrastructures. The present study was undertaken to assess the effect of surface treatment with Ho:YAG, Er:YAG, and Nd:YAG laser modalities on the shear bond strength (SBS) of ceromer to different types of metal infrastructures in in vitro settings. METHODS: The study specimens consisted of 40 direct laser sintered (DLS), 40 Ni-Cr-based, and 40 zirconium oxide (ZrO2) infrastructures. In each infrastructure group, the specimens were divided randomly into five treatment modalities (n = 8): no treatment (controls), sandblasting, Er:YAG, Nd:YAG, and Ho:YAG lasers. The DLS, Ni-Cr-based, and ZrO2 infrastructures were prepared in the final dimensions of 7 mm in diameter and 3 mm in thickness in line with the ISO 11405 standard. Ceromer as superstructure was applied to all the infrastructures after their surface treatments according to the selected treatment modality. SBS test was performed to test the effectiveness of surface treatments. A stereomicroscope was used to determine the changes in the surface morphology of specimens. RESULTS: Among the laser modalities and sandblasting, Ho:YAG laser caused the most important increase in the DLS and Ni-Cr-based infrastructures but sandblasting caused the most important increase in the ZrO2 infrastructure. In all the infrastructures, Nd:YAG laser has the least effectiveness, and Er:YAG laser makes an intermediate success. The stereomicroscopy images presented that the applications of laser surface treatments altered the surface in all the infrastructures. CONCLUSIONS: Overall, in current experimental settings, Ho:YAG, Nd:YAG, and Er:YAG lasers, in order of strength, are effective in improving the bonding of ceromer to all the infrastructures. Ho:YAG laser is more effective in the DLS and Ni-Cr-based infrastructures, but sandblasting is more effective in the ZrO2 infrastructure. The studied laser modalities need to be subjected for further studies to determine their appropriate settings and the specifications to be used in prosthodontics.

The Effects of Er:YAG, Nd:YAG, and Ho:YAG Laser Surface Treatments to Acrylic Resin Denture Bases on the Tensile Bond Strength of Silicone-Based Resilient Liners.

OBJECTIVE: The present study was to assess the effect of surface treatments of Er:YAG, Nd:YAG, and Ho:YAG lasers on the tensile bond strength of a silicone-based resilient liner to an acrylic denture in an in vitro setting. METHODS: Experimental dumbbell-shaped specimens (75 mm) were produced by combining two acrylate pieces fabricated from heat-polymerized acrylic resin (36 mm) with 3 mm of Molloplast(®)-B filling between them. The specimens (n=200) were randomly divided in half for thermocycling, and each 100 specimen set was randomized into five groups (n=20) with different surface treatments: control (no surface treatment), sandblasting, Er:YAG laser, Nd:YAG laser, and Ho:YAG laser. A tensile bond strength test was performed. The effect of the laser surface treatments was examined with scanning electron microscopy. RESULTS: Only the Er:YAG laser increased the tensile bond strength compared with the other treatments. The other laser groups showed lower bond strengths. The Ho:YAG laser resulted in considerably reduced tensile bond strength. The scanning electron microscopy images showed that applying laser surface treatments modified the surface of the denture base resin. CONCLUSIONS: There was not an overall improvement with the use of the studied laser modalities in the adhesion quality of resilient denture liner to acrylic resin, although Er:YAG laser showed a potential to improve their adhesion. These laser modalities need to be subjected to further studies to determine optimal setup for use in prosthodontics.

Investigation of flexural strength and cytotoxicity of acrylic resin copolymers by using different polymerization methods.

PURPOSE: The aim of this study was to appraise the some mechanical properties of polymethyl methacrylate based denture base resin polymerized by copolymerization mechanism, and to investigate the cytotoxic effect of these copolymer resins. MATERIALS AND METHODS: 2-hydroxyethyl methacrylate (HEMA) and isobutyl methacrylate (IBMA) were added to monomers of conventional heat polymerized and injection-molded poly methyl methacrylate (PMMA) resin contents of 2%, 3%, and 5% by volume and polymerization was carried out. Three-point bending test was performed to detect flexural strength and the elasticity modulus of the resins. To determine the statistical differences between the study groups, the Kruskall-Wallis test was performed. Then pairwise comparisons were performed between significant groups by Mann-Whitney U test. Agar-overlay test was performed to determine cytotoxic effect of copolymer resins. Chemical analysis was determined by FTIR spectrum. RESULTS: Synthesis of the copolymer was approved by FTIR spectroscopy. Within the conventional heat-polymerized group maximum transverse strength had been seen in the HEMA 2% concentration; however, when the concentration ratio increased, the strength decreased. In the injection-molded group, maximum transverse strength had been seen in the IBMA 2% concentration; also as the concentration ratio increased, the strength decreased. Only IBMA showed no cytotoxic effect at low concentrations when both two polymerization methods applied while HEMA showed cytotoxic effect in the injection-molded resins. CONCLUSION: Within the limitations of this study, it may be concluded that IBMA and HEMA may be used in low concentration and at high temperature to obtain non-cytotoxic and durable copolymer structure.

A longitudinal study on lung disease in dental technicians: what has changed after seven years?

OBJECTIVES: The aim of this 7-year follow-up study was to determine respiratory changes in dental technicians. MATERIAL AND METHODS: In our region, in the year 2005, 36 dental technicians were evaluated with a cross-sectional study on respiratory occupational diseases, and in 2012 we evaluated them again. Inclusion of information on respiratory symptoms and demographic features questionnaires was applied. Pulmonary function tests (PFT) were performed. Chest X-rays (CXR) were evaluated according to the ILO-2000 classification. For the comparisons of the technicians' findings in 2005 and 2012, data analyses were performed with the Wilcoxon test in addition to descriptive statistical procedures. RESULTS: In 2012, 19 out of the 36 technicians continued to work in the same place, so we were able to evaluate their findings. The prevalence of respiratory symptoms in dental technician was as follows: dyspnea 7 (37%), cough 6 (32%), and phlegm 5 (26%). According to ILO classifications in 2005, among the 36 technicians, 5 (13.8%) had pneumoconiosis. At the end of 7 years, there were 9 pneumoconiosis cases among the 19 remaining technicians (47%). Thus, there was a statistically significant progression on the profusion of the radiologic findings (p < 0.005). Also there was a significant worsening on spirometric findings (p < 0.05). CONCLUSION: In dental technicians, a determination of both radiologic and functional progressions at the end of 7 years demonstrate that the primary and secondary preventive measures are necessary for these workplaces. Workplaces must be regularly controlled for worker health and hygiene.

Shear bond strength of veneering ceramic to zirconia core after different surface treatments.

OBJECTIVE: The aim of this study was to evaluate the effect of different surface treatments: sandblasting, liners, and different laser irradiations on shear bond strength (SBS) of pre-sintered zirconia to veneer ceramic. BACKGROUND DATA: The SBS between veneering porcelain and zirconium oxide (ZrO2) substructure was weak. Various surface treatment methods have been suggested for zirconia to obtain high bond strength to veneering porcelain. There is no study that evaluated the bond strength between veneering porcelain and the different surface treatments on pre-sintered ZrO2 substructure. METHODS: Two hundred specimens with 7 mm diameter and 3 mm height pre-sintered zirconia blocks were fabricated. Specimens were randomly divided into 10 groups (n=20) according to surface treatments applied. Group C, untreated (Control); Group E, erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiated; Group N, neodymium:yttrium-aluminum-garnet (Nd:YAG) laser irradiated; Group SB, sandblasted; Group L, liner applied; Group NL, Nd:YAG laser irradiated+liner applied; Group EL, Er:YAG laser irradiated+liner applied; Group SN, sandblasted+Nd:YAG laser irradiated; Group SE, sandblasted+Er:YAG laser irradiated; and Group SL, sandblasted+liner applied. The disks were then veneered with veneering porcelain. Before the experiment, specimens were steeped in 37°C distilled water for 24 h. All specimens were thermocycled for 5000 cycles between 5°C and 55°C with a 30 sec dwell time. Shear bond strength test was performed at a crosshead speed of 1 mm/min. The fractured specimens were examined under a stereomicroscope to evaluate the fracture pattern. RESULTS: Surface treatments significantly changing the topography of the yttrium-stabilized tetragonal zirconia (Y-TZP) ceramic according to scanning electron microscopic (SEM) images. The highest mean bond strength value was obtained in Group SE, and the lowest bond strength value was observed in NL group. Bond strength values of the other groups were similar to each other. CONCLUSIONS: This study shows that sandblasting+Er:YAG, sandblasting, Er:YAG+liner, sandblasting+Nd:YAG, and Er:YAG laser treatment on pre-sintered ZrO2 substructure increased the bond strength to veneering porcelain, compared with other surface treatments. After different surface treatments, there was no difference in surface roughness of pre-sintered zirconia to compare after sintering; sintering enhanced the bond strength within the limitations of present study.

Histopathological evaluation of the effects of fiber reinforced acrylic resins on living tissues.

OBJECTIVE: The aim of this study was the histopathological evaluation of the effects of the fiber reinforced acrylic resins on living tissues. MATERIALS AND METHODS: The study was performed on 21 rabbits. Three groups, each including seven subjects, were formed. There was no applied plate in the control group. For the second group, heat-polymerized acrylic resin plates were inserted. For the third group, heat-polymerized acrylic resin plates containing proportionally 5% chopped silanated E type glass fiber were inserted. Plates were fixed to the palatine bone of the rabbits with titanium screws. Before the implementation of the plates and 1 month after the plates were applied, soft tissue samples were taken from the buccal mucosa of the rabbits. Also, tissue samples were taken from the control group. All samples were evaluated histopathologically. RESULTS: In the control group, only a focal atrophy was observed. In the acrylic group, large decomposition containing erythrocytes under the parahyperkeratotic region and micro-vesicle like spongiotic tissue reactions were observed. In the fiber reinforced acrylic group, widespread focal atrophy, bulgy look of the epithelium cells similar to apoptosis, over-distension and sub-corneal decomposition had been observed. In terms of atrophy and hyperkeratosis there were no statistically significant differences among groups. However, in respect to sub-corneal decomposition, there was a statistically significant difference in the fiber reinforced group (p < 0.01). CONCLUSIONS: The statistically significant difference in the sub-corneal decomposition of the fiber reinforced group had made us think that fiber edges had a traumatic effect on the reaction.

Strength of the bond between a silicone lining material and denture resin after Er:YAG laser treatments with different pulse durations and levels of energy.

The purpose of this study was to investigate the tensile strength of the bond between a silicone lining material and heat-cured polymethyl methacrylate (PMMA) denture base resin after Er:YAG laser treatment with different pulse durations and energy levels. PMMA test specimens were fabricated and each received one of six surface treatments: no treatment (control), and five Er:YAG laser treatments comprising (1) 100 mJ, 1 W, long pulse duration, (2) 200 mJ, 2 W, long pulse duration, (3) 200 mJ, 2 W, very short pulse duration, (4) 300 mJ, 3 W, long pulse duration, and (5) 400 mJ, 4 W, long pulse duration. The resilient liner specimens (n = 15) were processed between two PMMA blocks. The tensile strengths of the bonds between the liners and PMMA were determined using a universal testing machine at a crosshead speed of 5 mm/min. The mode of failure was characterized as cohesive, adhesive, or mixed modes. One-way ANOVA and the post hoc Tukey-Kramer multiple comparisons test were used to analyze the data (α = 0.05). There was a statistically significantly difference in tensile bond strength between laser-treated and untreated specimens (P < 0.05). The 300-mJ, 3 W, long pulse duration laser treatment produced the highest mean tensile bond strength. In addition, the long pulse duration treatments resulted in greater bond strength than very short pulse duration treatment (P < 0.05). Laser irradiation produced significant surface texture changes of the denture base material and improved the adhesion between denture base and soft lining material. In addition, different pulse durations and energy levels were found to effectively increase the strength of the bond.

Multidisciplinary approach for esthetic, functional, and quality-of-life outcome in soft palate cleft patient.

The fabrication of a Suersen obturator prosthesis with titanium framework is described in the case of a 43-year-old man with congenital absence of the soft palate. The patient revealed an open soft palate, bilateral cleft lip and palate, Angle Class III dental malocclusion, and anterior and posterior crossbite. He was treated with a multidisciplinary approach. A Dolder bar was fabricated between the maxillary canines, and telescopic crowns were prepared for maxillary premolars. Angle Class III tooth relation was readjusted to tooth-tooth relation; closure of the nasopharynx and oropharynx was performed by Suersen method, which improves speech.

Shear bond strength of resin cement to zirconia ceramic after aluminum oxide sandblasting and various laser treatments.

OBJECTIVE: The aim of this study was to evaluate the effect of different surface treatments; sandblasting, Er:YAG, Nd:YAG, or CO(2) laser irradiation on the shear bond strength (SBS) of zirconia ceramic to dentin. BACKGROUND DATA: Zirconia is not properly luted with resin cements. Various surface treatment methods have been suggested for zirconia to obtain high bond strength to resin cements. There is no study that compared the effect of different laser types (Er:YAG, Nd:YAG, CO(2)) with sandblasting on SBS between zirconia and dentin. METHODS: One hundred and twenty human maxillary third molar teeth were sectioned 3 mm below the occlusal surfaces, embedded in a metal ring with autopolymerizing acrylic resin, and stored in distilled water at 37(0)C. One hundred and twenty disc-shaped zirconia specimens were fabricated (6 mm in diameter and 4 mm in thickness), and randomly assigned to six groups (n=20): Group 1, untreated (control); Group 2, sandblasted; Group 3, Er:YAG laser irradiated; Group 4, Nd:YAG laser irradiated with contact; Group 5, Nd:YAG laser irradiated with non-contact; Group 6, CO(2) laser irradiated. They were cemented onto the dentin with dual-cured resin cement (Variolink(®)). After they were stored in distilled water at 37(0)C for 24 h, the SBS test was performed at a crosshead speed of 1 mm/min. The fractured specimens were examined under a stereomicroscope to evaluate the fracture pattern. RESULTS: Results of this study did not show statistically significant differences between Groups 1 and 2, or among Groups 3, 4 and 5. The lowest SBS was recorded in Group 6 (CO(2) laser), and the highest SBS was recorded in Group 4 (Nd:YAG laser with contact), followed by Group 3 (Er:YAG laser). The adhesive failure mode was predominantly observed in Groups 2, 3, 5, and 6. Group 1 showed 45% mixed failure and Group 4 showed 50% mixed failure. CONCLUSIONS: This study shows that Er:YAG and Nd:YAG laser treatment increased the bond strength of zirconia compared to sandbasting and CO(2) laser treatment.

Prevalence of respiratory abnormalities and pneumoconiosis in dental laboratory technicians.

A preventable occupational disease, pneumoconiosis that is often widespread on to a very kind of quartz, carbon and metal dust exposed work place.The data for the prevalence of pneumoconiosis and respiratory findings among dental laboratory technician is insufficient. The aim of this study is to determine the prevalence of pneumoconiosis and respiratory findings among dental laboratory technicians, working in province of Sivas. For this reason all the dental technicians (except 2, totally 36) participated in the study. A questionnaire which contains demographic characteristics, work conditions and symptoms were applied to all participants. Also spirometric measurements and chest x-rays were performed. The x-rays of dental technicians were evaluated by a radiologist and a chest disease specialist according to the ILO-2000 classification of pneumoconiosis. Almost half of the all participants have dyspnea and phlegm expectoration. The prevalence of pneumoconiosis was 5 (13.8%) among 36 dental technicians. There were no statistically significant differences between two groups with regard to respiratory symptoms. Values of lung function parameters of the dental technician group were not significantly different from those of control group except FEV(1). In conclusion, dental laboratory technicians are at significant risks for occupational respiratory diseases so the primary prevention rules are essential for these work places.

Cytotoxicity evaluation of two different composites with/without fibers and one nanohybrid composite.

In this study, cytotoxicity of two different composites with/without fibers (Adoro/Vectris and SculpturePlus/FiberKor) and one nanohybrid composite (Artglass) were investigated and compared. Composites used in the study were prepared as cylindrical discs of 2 mm depth and 8 mm diameter according to ISO 10993 recommendation. Adoro/Vectris and SculpturePlus/ FiberKor groups were divided into composite, fiber, and composite+fiber groups. Agar diffusion method was employed, and cytotoxicity rankings were determined using lysis index scores. For statistical analysis, Kruskal-Wallis and Mann-Whitney U tests were used. Amongst the composites, Adoro was found to be less cytotoxic than Sculpture Plus and Artglass materials--which were of the same cytotoxicity ranking. Between the fiber and composite materials, the former were found to be more cytotoxic than the latter; in particular, Vectris was found to be more cytotoxic than FiberKor. It was observed that upon combining with the fibers, the cytotoxic effect of the composites increased. This cytotoxicity enhancement was manifested as an additional effect in Adoro/Vectris group but as a synergistic effect in SculpturePlus/FiberKor group.

The effect of personality type on denture satisfaction.

PURPOSE: The aim of this study was to determine the correlation between personality type and denture satisfaction of totally and partially edentulous patients. MATERIALS AND METHODS: Two hundred thirty-nine patients (107 women and 132 men) aged 31 to 78 years (mean, 51.87) using removable dentures (165 maxillary and mandibular partial, 51 maxillary and mandibular complete, and 23 maxillary complete and mandibular partial) were asked to fill out a questionnaire on their satisfaction with their dentures with regard to esthetics, speaking ability, and masticatory function. Personality types were evaluated using both the responses to this questionnaire and the Type A Behavior Pattern Test. Chi-square test and logistic regression analysis were used to compare the denture satisfaction scores of the groups (Type A, Type B, and Type AB). The level of statistical significance was set at P = .05. RESULTS: Denture satisfaction of the patients with regard to esthetics, speaking ability, and masticatory function was affected by personality type. Statistically significant differences were found between Type A and types B and AB, as well as between types B and AB. CONCLUSION: The personality type of the patients had an effect on their satisfaction with dentures. The lowest denture satisfaction values were observed in the Type A patients.

Surface roughness of new microhybrid resin-based composites.

BACKGROUND: Rough, poorly polished resin-based composite (RBC) surfaces contribute to staining, plaque accumulation, gingival irritation and recurrent caries. Proper finishing and polishing enhance both the esthetics and the longevity of restored teeth. METHODS: The authors evaluated the influence of various finishing and polishing techniques on the surface roughness of four microhybrid RBCs. Thirty samples of each material were cured under Mylar matrix strips (Yates and Bird/Motloid, Chicago). All microhybrid RBC specimens were finished with multifluted carbide burs, except for the Mylar matrix strip samples, and then were polished using one of four finishing systems: Sof-Lex contouring and polishing disks (3M ESPE, St. Paul, Minn.); Enhance Finishing System (Dentsply-Caulk, Milford, Del.) followed by Prisma Gloss (Dentsply-Caulk) polishing paste application; Astropol finishing, polishing and high-gloss polishing system (Ivoclar Vivadent, Schaan, Liechtenstein); and Astrobrush polishing system (Ivoclar Vivadent). The authors tested the samples to obtain average surface roughness and analyzed the values. RESULTS: The use of the Astrobrush technique caused the greatest roughness on all RBC specimens. The smoothest surface was produced with a carbide bur followed by aluminum oxide disks, Astropol technique and Enhance technique. Overall, there were differences in surface quality among the materials. InTen-S (Ivoclar Vivadent) had statistically lower surface roughness values after finishing and polishing with the Astrobrush technique, compared with the other RBCs. CONCLUSION: The highest surface roughness values were achieved after the Astrobrush technique was used. The Sof-Lex aluminum oxide disks, and Enhance and Astropol techniques provided the smoothest surface. CLINICAL IMPLICATIONS: The Sof-Lex, Enhance and Astropol techniques produced a smooth surface after the finishing and polishing of materials, while the Astrobrush technique yielded the least favorable results.

The effect of glass fiber distribution on the transverse strength and surface smoothness of two denture resins.

The aim of this study was to evaluate the effect of glass fiber distribution on the transverse strength and surface smoothness of conventional heat cured acrylic and autopolymerizing acrylic of an injection-molding system. Forty rectangular (65x10x2.5 mm) acrylic test specimens were prepared from both acrylic types: 10 with 5% (w/w) 6 mm length fiber and 10 without fiber for both groups. Transverse strength test was applied to these specimens. Surface samples were taken from the broken and polished surfaces of these specimens and evaluated using SEM. The addition of fiber was found to cause a statistically significant increase in the transverse strength of the injection system's acrylic. In SEM observation it was revealed that there was good adhesion between glass fiber and both acrylic resins. The glass fibers distribution was more even in the injection system's acrylic. It is suggested that injection system's acrylic be fiber-reinforced to reduce denture fractures.