Effect of low-temperature degradation on the mechanical and microstructural properties of tooth-colored 3Y-TZP ceramics.

The aim of the present study was to evaluate the effects of low-temperature degradation (LTD) induced by autoclaving on the mechanical and microstructural properties of tooth-colored 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). In total, 162 disc-shaped 3Y-TZP specimens were prepared. Two-thirds of the specimens were shaded by either the infiltration or powder mixing methods while the remaining specimens were used without coloring. The specimens were autoclaved at 134 °C for 0, 10, and 100 h to induce LTD (n=18 for each group). Chemical compositions were analyzed with X-ray fluorescence spectroscopy. Biaxial flexural strength was measured using a piston-on-three-ball test. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy, respectively. The tooth-colored 3Y-TZP specimens contained Fe2O3 and Er2O3 (infiltration technique), and Fe2O3 (powder mixing method) at concentrations of<0.5 wt%. The tooth-colored 3Y-TZP had higher strength than the non-colored material after 100 h of autoclaving. In terms of surface fraction and penetration depth, the generation of monoclinic phase was significantly lower in the tooth-colored 3Y-TZP than in the non-colored material. The tooth-colored 3Y-TZP possessed equivalent biaxial flexural strength to that of the non-colored material and higher resistance to LTD regardless of the coloring technique (infiltration technique or powder mixing method) when the coloring pigments were contained at concentrations used in the present study.

The influence of low-temperature degradation and cyclic loading on the fracture resistance of monolithic zirconia molar crowns.

The present study analyzed the kinetics of low-temperature degradation (LTD) in zirconia, and evaluated the influence of LTD and cyclic loading on the fracture resistance of monolithic zirconia molar crowns. Bar-shaped zirconia specimens were divided into nine groups and autoclaved at 134°C for 0-200h to induce LTD. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy. Monolithic zirconia molar crowns were prepared for crown fracture testing. The crowns were autoclaved for 0-100h (n=6) and cemented to dies. Six crown-die samples that were not autoclaved and six samples that were autoclaved for 100h were subjected to cyclic loading with a load of 300N for 240,000 cycles. All samples were tested in a load-to-failure test. The monoclinic fraction on the surface increased with autoclaving time and reached a plateau after 50h. The depth of the monoclinic phase increased without reaching a plateau. The fracture load of the crowns significantly decreased from 5683N (SD: 342) to 3975N (SD: 194) after 100h of autoclaving. Cyclic loading did not significantly affect the fracture resistance of the crowns in all cases. Kinetic analysis showed no linear correlation between the surface fraction and depth of the monoclinic phase after 50h of autoclaving. Even though LTD increased the monoclinic phase, resulting in lower strength, the fracture resistance of the monolithic zirconia crowns was still sufficient to withstand the loading conditions in the molar regions.

Work-related skin and airway symptoms among Swedish dentists rarely cause sick leave or change of professional career.

Dentistry usually is 'wet work' with risk of damage to the skin barrier, and the hands may be exposed to skin irritants and contact-sensitizing substances used in dental materials or gloves. Airway irritants may also be present. This study assessed the consequences of work-related skin and airway symptoms among dentists in terms of contact with health authorities, sick leave, or changes in the professional career. A questionnaire on these factors was answered by more than 3000 Swedish dentists. Only 6% of the respondents had consulted a physician, although 22% had noted work-related skin symptoms. In 2% the skin symptoms had caused sick leave, and about 2% had reported their skin symptoms as an occupational disease. Two per cent had consulted a physician owing to work-related airway symptoms, which is a minor part of the 13% who had experienced such symptoms when in contact with dental materials. Twenty-five dentists (<1%) had been on sick leave because of work-related airway symptoms. Only 1 dentists reported change of activities or occupation owing to work-related skin or airway symptoms, and in most cases these symptoms only contributed to their decision. In summary, whereas sick leave in dentists because of musculoskeletal problems may be common, the present study shows that this is not the case for work-related skin or airway symptoms, and such symptoms seldom affect the dentists' professional career.

Expander elements in craniofacial surgery: an experimental study in rabbits.

With the inception of craniofacial surgery elaborate surgical procedures were introduced for the treatment of craniosynostosis. Recently the use of implantable springs to aid simple strip craniectomies for these conditions has been described. Having shown the feasibility of using springs for dynamic skull reshaping, several questions remain to be answered, all of them about how to control the spring action clinically. One of the most important questions concerns force. The purpose of this study was to evaluate experimentally the effect of two springs of different strengths on the growth of rabbit calvaria after strip craniectomy. Thirty-two 6-week-old rabbits were randomised into one of four groups: sham-operation where only amalgam markers were inserted after subperiostal dissection; strip craniectomy of the sagittal suture, no expansion; strip craniectomy of the sagittal suture and insertion of an expander element made of titanium molybdenum alloy (TMA); and strip craniectomy sagittal suture and insertion of an expander element made of stainless steel (SS). SS springs delivered a range of forces from 2.42-2.18 N, whereas the TMA expander elements delivered a range from 1.39-1.09 N. The parietal bone marker separation after 12 weeks was 4.9 mm in the TMA group and 7.4 mm in the SS group. This resulted in a significant increase of the calvarian height compared with control groups. Histological examination showed intramembranous bone formation in the bone gap in all groups.

Protective gloves in Swedish dentistry: use and side-effects.

BACKGROUND: During the 1980s routine wearing of gloves in dentistry was recommended by health authorities in several countries. However, prolonged glove use is associated with side-effects of irritant and allergic origin. OBJECTIVES: To investigate the extent of glove use and self-reported glove intolerance reactions among Swedish dentists, and to examine how far IgE-mediated allergy to natural rubber latex (NRL) occurs in subjects who report rapid itching when in contact with protective gloves. SUBJECTS/METHODS: A postal questionnaire was answered by 3083 of 3500 licensed dentists, a response rate of 88%. Of the dentists who reported rapidly occurring itching of the hands from gloves, 131 of 170 attended a clinical examination including a skin prick test (SPT) and a serological examination (RAST) for IgE-mediated allergy. RESULTS: Seventy-three per cent of the dentists reported daily glove use of more than 2 h, 48% more than 6 h a day, and 6% reported no use. NRL gloves were used most frequently (P < 0.001) and were the main material that elicited symptoms (P < 0.001). Female dentists reported more frequent glove use than males, as did young dentists (P < 0.001) compared with older ones. Females also preferred vinyl gloves. Glove intolerance reactions were reported by 723 (23%) dentists, [females 28%, males 21% (P < 0.001)] and were more common in younger dentists. Of the 417 dentists with reported hand eczema during the previous year, 54% reported glove intolerance, compared with 20% of the dentists without hand eczema (P < 0.001). A logistic regression analysis including hand eczema, age, sex and atopy showed that all these factors contributed significantly to the risk of glove intolerance, and that hand eczema was a stronger factor than atopy. In 15 of 131 (11%) dentists examined for reported glove-related itch, latex allergy was verified by SPT and/or RAST. Glove-related conjunctivitis, rhinitis and asthma, in contrast to skin symptoms, showed a significant association with IgE-mediated allergy to NRL. CONCLUSIONS: Swedish dentists show good compliance with the recommendations for routine glove use. Intolerance reactions are frequently reported, especially by dentists with hand eczema, which emphasizes the need for preventive skin care programmes. Glove-related symptoms from mucous membranes showed a higher association with IgE-mediated allergy to NRL than reported itching of the skin, a fact that should be considered when composing screening questionnaires for NRL sensitization

Influence of pH and storage time on the sorption and solubility behaviour of three composite resin materials.

OBJECTIVES: The aim of this study was to determine whether pH and time has any influence on the sorption and solubility behaviour of composite resin materials stored in a buffer solution. METHODS: Three hybrid composite restorative resin materials (Spectrum, Z-100 and ArtGlass) with different matrix structure and filler composition were studied. One hundred and twenty specimens of each material were produced according to ISO 4049. The materials were stored in McIlvain's buffer solution at different pH (4, 6 and 8) at 1, 7, 60 and 180 days. pH measurements were carried out before and after completed storage. RESULTS: Time had a significant influence on the sorption and solubility behaviour of the composite resin materials tested. One of the materials Z-100 showed a significant mass increase and/or decrease depending on the pH of the solution. The material Spectrum was significantly influenced by pH, resulting in different sorption depending on the pH of the solution. CONCLUSIONS: Time of storage was important for the sorption and solubility behaviour of the composite resin materials tested. Comparison of solubility for one of the materials showed twice as high values in the present study as previously reported when distilled water was used as storage medium. pH in the solution seems to have an influence on the sorption and solubility behaviour of composite resin materials. The sensitivity of the sorption and solubility behaviour to time and pH of the materials tested seems to be related to the hydrophilicity of the matrix and the chemical composition of the filler.

Water sorption and solubility of dental composites and identification of monomers released in an aqueous environment.

Water sorption and solubility of six proprietary composite resin materials were assessed, and monomers eluted from the organic matrix during water storage identified. Water sorption and solubility tests were carried out with the following storage times: 4 h, 24 h and 7, 60 and 180 days. After storage, water sorption and solubility were determined. Eluted monomers were analysed by high performance liquid chromatography (HPLC). Correlation between the retention time of the registered peak and the reference peak was observed, and UV-spectra confirmed the identity. The results showed an increase in water sorption until equilibrium for all materials with one exception. The solubility behaviour of the composite resin materials tested revealed variations, with both mass decrease and increase. The resin composition influences the water sorption and solubility behaviour of composite resin materials. The HPLC analysis of eluted components revealed that triethyleneglycol dimethacrylate (TEGDMA) was the main monomer released. Maximal monomer concentration in the eluate was observed after 7 days. During the test period, quantifiable quantities of urethanedimethacrylate (UEDMA) monomer were observed, whereas 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (Bis-GMA) was only found in detectable quantities. No detectable quantities of bisphenol-A were observed during the test period.

Histomorphometric and mechanical evaluation of the bone-tissue response to implants prepared with different orientation of surface topography.

BACKGROUND: Several studies have shown that in soft tissue, the orientation of surface topography affects cell response. However, the response of hard tissue to the orientation is not fully understood. PURPOSE: This study was undertaken to determine how orientation of the microstructure of implant surfaces influences bone healing. MATERIALS AND METHODS: Forty cylindrical implants were prepared with a dominant orientation of the microstructure (20 with a horizontal orientation and 20 with a vertical orientation) and investigated in vivo. Three methods for surface topographic characterization were used to investigate the topography in different resolution levels. RESULTS: Topographic analysis showed that a clear orientation was achieved at the implant surface, and a rougher surface structure was found on the vertically oriented grooves than on the horizontal ones. The implants were inserted in the tibia of 10 New Zealand White rabbits. Pull-out tests and histomorphometric analyses of ground-sections were made after 12 weeks of healing. The pull-out test showed a higher mean value for the vertically grooved implants, but the difference was not significant. Histomorphometric analyses showed no statistically significant differences between the horizontally and the vertically grooved implants when measuring bone-to-implant contact or amount of bone area around the implant. CONCLUSIONS: No advantages could be found for either the horizontal or vertical orientation compared with each other, but further studies are needed in which implant roughness should be similar between the different topographies.

Contact allergy and hand eczema in Swedish dentists.

Hand eczema and contact allergy in Swedish dentists were studied in a multidisciplinary project. The aims of the study were to establish diagnoses, to investigate the occurrence of contact allergy, in particular to (meth)acrylates, and to evaluate certain consequences of hand eczema. A postal questionnaire on skin symptoms, atopy and occupational experience was mailed to 3,500 dentists aged <65 years, and licensed 1965-1995. The response rate was 88%. Among dentists living in 3 major cities, 14.9% (n= 191) reported hand eczema during the previous year. They were invited to a clinical examination, including patch testing with a standard and a dental series. 158/191 (83%) dentists attended, and hand eczema diagnosis was confirmed in 149/158 (94%). Irritant contact dermatitis was diagnosed in 67% and allergic contact dermatitis in 28%. On patch testing, 50% presented at least 1 positive reaction. The most frequent allergens were nickel sulfate, fragrance mix, gold sodium thiosulfate and thiuram mix. 7 (5%) had positive reactions to (meth)acrylates, all to 2-hydroxyethyl methacrylate and 6 also to ethyleneglycol dimethacrylate. 38% had consulted a physician, 4% had been on sick-leave and 1% had changed occupational tasks due to hand eczema. No dentist with allergy to acrylates had been on sick-leave or changed occupation. It is concluded that dentistry is a high-risk occupation for hand eczema, and that irritant contact dermatitis is most common. The prevalence of contact allergy to acrylates was below 1% in the population of responding dentists, and in most cases did not have serious medical, social or occupational consequences.

On composite resin materials. Degradation, erosion and possible adverse effects in dentists.

PURPOSE: The aims of this thesis were: 1. To study the effect of water and pH on composite resin materials in vitro by assessing sorption, solubility, monomers eluted and flexural properties. 2. To study adverse effects on the skin in dentists possibly caused by acrylic resin-based materials. MATERIALS AND METHODS: Proprietary composite resin materials were used for the in vitro experiments. The tests were performed according to the ISO 4049 (1988) with the exception of McIlvaine's solution used in Study II and the storage times. The analysis of eluted monomers was performed using HPLC. The flexural properties were tested in a three-point bending equipment. The secant modulus and deflection at break were calculated for description of the viscoelastic behaviour of the material tested. To study the adverse effects on skin in dentists, a questionnaire was sent to 3500 randomly selected Swedish dentists. A response rate of 88% was achieved and the data were statistically analysed and compared with the results of two studies on skin symptoms among the general Swedish population. Dentists living in the three main cities in Sweden who had experienced hand eczema during the last 12 months were invited to a clinical examination in which a patch test was included. RESULTS: A wide range in sorption and solubility over the test period was found, with low sorption values observed for materials containing hydrophobic matrix monomers. A maximum concentration of monomers eluted was found after 7 days of storage, and TEGDMA was the main monomer released. pH affected the sorption and solubility behaviour for two of the three materials tested. The flexural strength and modulus of the composite resin material were lowered after water storage and the secant modulus and deflection at break could describe the viscoelastic behaviour. The prevalence of dry skin and hand eczema was high in dentists compared to two age-matched general population samples investigated using identical questions. The most important predictor for adult hand eczema was found to be childhood eczema. At the clinical examination, irritant contact dermatitis was the predominant diagnosis. Seven per cent reported skin symptoms when working with acrylic resin-based material but the true prevalence of hand eczema caused by acrylates was below 1%. Contact allergy was diagnosed, however, in 50% of the dentists, mainly due to other allergens such as nickel, perfumes or rubber chemicals. CONCLUSIONS: The matrix composition was shown to be important for the sorption and solubility behaviour of the composite resin materials tested and a maximum release of monomers occurred after 7 days of storage. pH affected the water sorption and solubility behaviour. Calculation of the secant modulus and the deflection at break allowed the plasticising effect of water on composite resin material to be observed. The prevalence of hand eczema was high among dentists, with irritant contact dermatitis as the predominant diagnosis. Childhood eczema was the most important predictor for adult hand eczema. The prevalence of hand eczema owing to acrylates was below 1%.

Water sorption and flexural properties of a composite resin cement.

PURPOSE: The aim of this study was to assess the water sorption and determine the influence of water on flexural properties of a composite resin cement of 2 different viscosities. MATERIALS AND METHODS: A dual-cured composite resin cement of 2 different viscosities was tested according to International Standards Organization standards for dental composite materials. The samples tested for water sorption were stored in distilled water for 7 or 60 days. The samples tested for flexural properties were divided into 2 groups and stored either wet in distilled water or dry for 1, 7, or 60 days. After storage, a flexural test was performed with 3-point bending equipment. RESULTS: A significant increase in water sorption for both viscosities was registered as the storage time increased, but no significant difference between the 2 viscosities was recorded. Significantly lower strength and modulus were found for specimens that were wet stored for 60 days compared with the dry-stored ones, and significant changes in deflection at break were also registered. There were no differences in flexural properties between the 2 viscosities. Because of the lubricant and plasticizing effect of water on composite resin materials, the secant modulus and deflection at break seem to be valid methods to describe the complete deflection behavior. CONCLUSION: Water has an important effect on the flexural properties of composite resin cement after 60 days of storage time. No significant differences in water sorption and flexural properties were found between the high and low viscosities of the composite resin cement studied.

Prevalence of self-reported hand eczema and skin symptoms associated with dental materials among Swedish dentists.

In the present study we investigated the prevalence of self-reported hand eczema as well as subjective associations between skin symptoms and composite/bonding or other dental materials among Swedish dentists. A questionnaire on skin symptoms, atopy, occupational experience, and other background factors was sent to a random sample (n=3,500) of all dentists licensed since 1965. This group corresponds to about half of the country's occupationally active dentists. The response rate was 88%. The questionnaire had previously been validated against clinical dermatological examination of subjects reporting hand eczema. The prevalence of dry and rough skin on the hands was high (45%). Hand eczema during the previous 12 months was reported by 13.5%. Dry skin and hand eczema were more common among dentists than in two age-matched general population samples investigated using identical questions. The difference versus the general population was most pronounced (about two-fold) among male dentists. A history of childhood eczema was the most important predictor for adult hand eczema, with a prevalence ratio of 2.4 compared to dentists without childhood eczema. Seven % reported skin symptoms when working with acrylic resins, and 15% had experienced rapid itching related to protective gloves.

Tolerance test of five different types of crowns on single-tooth implants.

PURPOSE: The main purpose of the present experimental study was to compare five different types of crowns, cemented on implant abutments, regarding their capability to withstand loads. MATERIALS AND METHODS: Three types of all-ceramic crowns, a gold-foil-reinforced porcelain crown, and, as a control, a conventional metal ceramic crown were tested. Each crown was cemented onto an Astra Tech Single-Tooth implant. The five types of crowns, three of each type, and the titanium implants were subjected to loading in Lloyd test equipment until part of them was damaged, at which point the compression value was recorded and the deflection and bending moment were calculated. Comparisons were made on the basis of these data. RESULTS: The results showed that the all-ceramic crowns fitted with a core should be able to withstand normally occurring biting forces without difficulty. The foil crown was also judged to be acceptable, while the bending moment of the cast call-ceramic crown without a core was considered unpredictable. The values for the metal ceramic design were as predicted, ie, they were clearly the highest in the study; the superior strength of metal ceramics should still be taken into account when deciding between all-ceramic solutions and the conventional metal ceramic crown. CONCLUSION: It was concluded that all-ceramic crowns are weaker than conventional metal ceramic crowns: however, based on estimated maximum clinical loading (370 N in the incisor and premolar regions), In-Cream and AllCeram crowns seem to function satisfactorily on implants.

Microhardness and surface topography of a composite resin cement after water storage.

PURPOSE: The aims of this study were to assess changes in the microhardness and surface roughness of a dual-cured composite resin cement after water storage for different periods of time. MATERIALS AND METHODS: Sixty specimens were divided into four groups comprising high- and low-viscosity cement specimens stored either dry or in water for 1 to 60 days. Microhardness and surface roughness measurements were made after 1, 7, and 60 days of storage. RESULTS: It was found that that although interactions complicated the interpretation of the results, the water-stored samples had a significantly lower microhardness compared to the dry-stored specimens for every time interval. In addition, the high-viscosity specimens had a significantly higher microhardness compared to the low-viscosity specimens. An increased microhardness was found for all groups, except for the low-viscosity, water-stored specimens after 60 days of water storage, which was attributed to an effect of the chemical postcuring process. Although difficult to evaluate from a clinical point of view, the laser profilometry analysis revealed that a significantly increased surface roughness was found after water storage and increased storage time that was possibly caused by a deterioration of the resin-matrix surface. CONCLUSION: For the permanency of the interfacial luting material, a high microhardness value seems to be important.

Ceramic inlay systems: some clinical aspects.

Due to their inertness and unsurpassed aesthetic properties, ceramic materials are increasingly used as inlay materials. Based on a questionnaire, the frequency and character of complications related to ceramic inlay therapy were assessed and some important pitfalls and clinical relevant factors discussed. A majority of the dentists performed between 1 and 10 ceramic inlays per month using several different ceramic materials. As many as 85% of the dentists had observed complications in connection with ceramic inlays. Most frequency reported was hypersensitivity of a transient nature (15%). The material revealed an overall inlay fracture frequency of 5%, but the individual variations were high. Tooth fracture, loss of retention and other complications such as secondary caries, endodontic envolvement, colour mismatch and a surface and edge deterioration occurred with a varying but lower frequency. Failure analysis revealed a large number of causative factors among which cavity and inlay design, bonding procedures, selection of luting material and proper case selection were regarded as the most important. Due consideration to the strength of remaining tooth substance was found to be important in reducing the problem of hypersensitivity and the risk of tooth and inlay fracture.