Toshio Hosoi

Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers

STATEMENT OF PROBLEM Poor chemical bonding of a denture base resin to cast titanium frameworks often introduces adhesive failure and increases microleakage. PURPOSE This study examined the shear bond strengths of a denture base resin to cast pure titanium, Ti-6Al-4V, and a cobalt-chromium alloy using various adhesive primers. MATERIAL AND METHODS Disks (6.0 mm diameter, 2.5 mm thick) were cast of the 3 alloys. The disk surfaces were grit-blasted with 50 microm alumina and treated with 5 different metal primers (Metal Primer II ¿MP]; Cesead Opaque primer ¿OP]; Meta Base ¿MB]; experimental primer ¿EP]; Siloc bonding system ¿SI]). A denture base resin (Palapress Vario) was then applied on the disks with hole-punched sticky tape (bonding area of 5.0 mm) and a Teflon (PTFE, New Age Industries Inc, Willow Grove, Pa.) ring (6.0 mm diameter x 2.0 mm thick). Specimens without primer were also prepared as controls. All specimens were immersed in 37 degrees C water and thermocycled up to 2,000 cycles. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data were statistically analyzed using 3-way ANOVA, followed by 1-way ANOVA and the Scheffé multiple range test. RESULTS Primers significantly (P <.05) improved shear bond strengths of denture base resin to all metals, among which no significant differences were found. Specimens primed with OP, MP, and EP showed higher bond strengths than did those primed with MB. After thermocycling, the bond strengths of MB and SI decreased substantially; MB showed the least durability (22.8% to 35.5% decrease) among the primers. CONCLUSION The application of 5 primers significantly improved the shear bond strengths of a denture base resin to cast CP titanium, Ti-6Al-4V, and Co-Cr alloy. OP and MP primers exhibited greater bond strength and durability than did MB and SI.

The machinability of cast titanium and Ti-6Al-4V.

This study investigated the machinability (ease of metal removal) of commercially pure (CP) titanium and Ti-6Al-4V alloy. Both CP Ti and Ti-6Al-4V were cast into magnesia molds. Two types of specimens (with alpha-case and without alpha-case) were made for CP Ti and Ti-6Al-4V. Machinability (n = 5) was evaluated as volume loss (mm3) by cutting/grinding the 3.0 mm surface using fissure burs and silicon carbide (SiC) under two machining conditions: (1) two machining forces (100 or 300 gf) at two rotational speeds (15000 or 30000 rpm) for 1 min, and (2) constant machining force of 100 gf and rotational speed of 15000 rpm for 1, 2, 5, 10, and 30 min. As controls, conventionally cast Co-Cr and Type IV gold alloys were evaluated in the same manner as the titanium. When fissure burs were used, there was a significant difference in the machinability between CP titanium with alpha-case and without alpha-case. On the other hand, there was no appreciable difference in the amount of metal removed for each tested metal when using the SiC points.

Wear resistance of experimental Ti-Cu alloys.

After using cast titanium prostheses in clinical dental practice, severe wear of titanium teeth has been observed. This in vitro study evaluated the wear behavior of teeth made with several cast titanium alloys containing copper (CP Ti+3.0 wt% Cu; CP Ti+5.0 wt% Cu; Ti-6Al-4V +1.0 wt% Cu; Ti-6Al-4V+4.0 wt% Cu) and compared the results with those for commercially pure (CP) titanium, Ti-6Al-4V, and gold alloy. Wear testing was performed by repeatedly grinding upper and lower teeth under flowing water in an experimental testing apparatus. Wear resistance was assessed as volume loss (mm(3)) at 5kgf (grinding force) after 50,000 strokes. Greater wear was found for the six types of titanium than for the gold alloy. The wear resistance of the experimental CP Ti+Cu and Ti-6Al-4V+Cu alloys was better than that of CP titanium and Ti-6Al-4V, respectively. Although the gold alloy had the best wear property, the 4% Cu in Ti-6Al-4V alloy exhibited the best results among the titanium metals. Alloying with copper, which introduced the alpha Ti/Ti(2)Cu eutectoid, seemed to improve the wear resistance.

Present status of titanium removable dentures--a review of the literature.

Although porcelain and zirconium oxide might be used for fixed partial dental prostheses instead of conventional dental metals in the near future, removable partial denture (RPD) frameworks will probably continue to be cast with biocompatible metals. Commercially pure (CP) titanium has appropriate mechanical properties, it is lightweight (low density) compared with conventional dental alloys, and has outstanding biocompatibility that prevents metal allergic reactions. This literature review describes the laboratory conditions needed for fabricating titanium frameworks and the present status of titanium removable prostheses. The use of titanium for the production of cast RPD frameworks has gradually increased. There are no reports about metallic allergy apparently caused by CP titanium dentures. The laboratory drawbacks still remain, such as the lengthy burn-out, inferior castability and machinability, reaction layer formed on the cast surface, difficulty of polishing, and high initial costs. However, the clinical problems, such as discoloration of the titanium surfaces, unpleasant metal taste, decrease of clasp retention, tendency for plaque to adhere to the surface, detachment of the denture base resin, and severe wear of titanium teeth, have gradually been resolved. Titanium RPD frameworks have never been reported to fail catastrophically. Thus, titanium is recommended as protection against metal allergy, particularly for large-sized prostheses such as RPDs or complete dentures.

Application of cast iron-platinum keeper to a collapsible denture for a patient with constricted oral opening: a clinical report.

Insertion of a denture is especially difficult for patents with a constricted oral opening. This report describes the fabrication of a collapsible removable partial denture with a cast iron-platinum attachment for a partially edentulous woman with a constricted oral opening resulting from rheumatoid arthritis and a craniotomy for a subarachnoid hemorrhage.

A sectional stock tray system for making impressions

This article describes a sectional stock tray system developed by the authors for making preliminary impressions. It may be used not only for individual dental arches but also for patients with microstomia or constricted oral openings. This system allows many combinations of right and left tray sizes and forms to be assembled into a well-fitted anatomically-conforming tray in spite of individual anatomic discrepancies.

Survey on use of titanium dentures in Tsurumi University Dental Hospital for 11 years

PURPOSE The purpose of this study was to survey the production of titanium dentures in Tsurumi University Dental Hospital and to study the actual use of titanium dentures in our university. METHODS The survey was based on the metal base dentures produced at Tsurumi University Dental Hospital during an 11-year period between April 1995 and March 2006, with relation to the types of metals used in the dentures, types of dentures, dental condition, and the number of artificial teeth. RESULTS 1871 metal base dentures were produced in the study period. The dentures consisted of 1290 cobalt-chromium alloy dentures (68.9%), 350 titanium dentures (18.7%) and 231 platinum-added gold alloy dentures (12.3%). Within the titanium denture groups, 132 were complete dentures (37.7%), 55 were complete overdentures (15.7%) and 163 were removable partial dentures (46.6%). JIS type 3 pure titanium was used in the titanium base of 252 dentures (72.0%). The average number of artificial teeth was 10.9, which was the highest among the three types of metal bases, exhibiting significant differences (P<0.01). CONCLUSION Approximately 32 titanium dentures per year on average were delivered at our university and they were applied to almost edentulous arch compared with the other metal base dentures.

Effect of weight change of mandibular complete dentures on chewing and stability: A pilot study.

STATEMENT OF PROBLEM Little is known as to whether denture weight contributes to the retention and stability of mandibular complete denture. PURPOSE This study compared the jaw movements and denture retention, stability, and comfort of heavy and light weight mandibular complete dentures. MATERIAL AND METHODS Mandibular complete dentures of 12 subjects were duplicated using an autopolymerized polymethyl methacrylate (PMMA) resin. The heavy weight denture was set with weights (20 or 60 g) and the lightweight denture was packed with wax instead of weights. Masticatory movements (3 times each) and denture stability (5 times each) were measured. The subjects expressed their denture preference for comfort and chewing. Results were analyzed using ANOVA and Wilcoxon tests at significance level of alpha=.10. RESULTS Masticatory movements and denture retention were not significantly (P >.10) affected by increasing the weight. Five subjects preferred the heavy denture and 4 subjects preferred light denture for comfort; 3 subjects had no preference. CONCLUSION The weight of a well-fitting mandibular complete denture did not affect jaw movements, denture stability, or patient preference.

Influence of Occlusal Force on Electroencephalograms in Edentulous Patients.

PURPOSE This study explored the effect of improved occlusal force resulting from complete denture treatment on electroencephalogram (EEG) findings to determine if such an outcome is a factor contributing to activation of synaptic/neuronal dysfunction in the brain. MATERIALS AND METHODS Twenty-three individuals with complete upper and lower dentures who visited the Department of Removable Prosthodontics at Tsurumi University Dental Hospital were included in this study. The Dental Prescale Occluzer FPD-705 system was used to perform an objective measurement of occlusal force before and after denture treatment. EEGs were recorded for 3 minutes in patients receiving complete dentures before and after denture treatment. Then, Dα values were calculated using a diagnosis method of neuronal dysfunction analysis to evaluate changes in synaptic/neuronal dysfunction of the brain. To investigate whether occlusal force affects Dα, Spearmans rank correlation coefficient (α = 0.05) was used to test the association between occlusal force (N) and Dα based on the rates of change in occlusal force and Dα calculated by dividing the measurement values after denture treatment by the measurement values before denture treatment. RESULTS Medial occlusal force increased from 184.9 N before treatment to 277.2 N after treatment. A statistically significant increase in occlusal force (p < 0.05) was observed, with a total of 22 participants exhibiting increased occlusal force after denture treatment. The medial Dα value increased from 0.943 before treatment to 0.957 after treatment. A statistically significant increase in Dα (p < 0.05) was observed, and a total of 19 participants exhibited increased Dα values after denture treatment. The regression line was calculated as Y = 14.049X - 12.450. As occlusal force increased, Dα values increased as well. A significant positive correlation was observed between occlusal force and Dα (r = 0.498, p < 0.05). CONCLUSIONS A positive correlation was observed between improved occlusal force attained via complete denture treatment and the activation of Dα. This finding reveals occlusal force as a denture treatment outcome that contributes to the activation of synaptic/neuronal dysfunction in the brain.

Investigation of trends and characteristics in patients with obstructive sleep apnea

BackgroundOral appliance (OA) therapy for obstructive sleep apnea (OSA) has only been part of Japan’s National Health care coverage plan since 2004. Subsequently, not enough time has passed to establish the medical trends and characteristics of OSA patients in Japanese Dental Hospitals.AimThe aim of this study was to investigate the medical trends and the characteristics in patients with OSA who visited our clinic, and to compare our findings with previous studies.Setting and designEpidemiological survey (retrospective study).Materials and methodsTwo hundred and one patients were recruited at the Internal Medicine Division in the Tsurumi University Dental Hospital from February 2006 to December 2008, consecutively. Patients received a medical interview, and a detailed sleep analysis that included a polysomnography (PSG) to verify the exact nature of their condition. The efficacy of OA was assessed in 49 patients who wore an OA and underwent PSG.ResultsOf all subjects, 141 patients visited the Prosthodontic Division to receive OA therapy, 38 patients were treated or received a follow up examination in the Internal Medicine Division. The dropout rate was 10.4% in the all subjects, 17.0% in patients who visited the Prosthodontic Division. The male-to-female ratio was 3.3:1, 3.0:1 in patients who visited the Prosthodontic Division. In addition, females had a lower rate of OAS severity than males. In our patients, the major complication was hypertension and cardiac disease. The success rate of OA was 75.5%.ConclusionThis approach allowed us to reveal some of the trends and characteristics in our patients.