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PubMed2006

Film thickness and rheological properties of luting agents for crown cementation.

The film thickness and rheological properties [viscosity and tan sigma], of different resin based crown and bridge luting agents, including Panavia 21, Superbond, All Bond C&B Cement, Variolink were compared with zinc phosphate cement. A modification of the method in ISO 9917 (1991) and a controlled stress rheometer were used to monitor the changes in the film thickness and rheological properties respectively. For each material, the film thickness and rheological characteristics were determined at 60s after start of mixing and then made at regular intervals until immediately before the material was set. For the initial film thickness, the difference among the values for Varionk, Superbond and zinc phosphate cement was not significant (P>0.05), and less than 25microm. The values for All Bond C&B Cement and Panavia 21 were at least twice that of the other materials tested. All Bond C&B Cement produced the highest film thickness value at both the initial period and at 240s. Regarding viscosity, Superbond had the lowest initial value but the highest value at 240s. Variolink gave the highest initial value of viscosity, but the differences in the initial values among the other materials were small. During the whole period of testing, zinc phosphate cement gave the highest values of tan sigma, and Panavia 21 showed no significant change in any of the measured properties. The methods were able to distinguish the behaviour of different cement materials. Some resin cements produce larger than optimal values of film thickness and in some cases this is related to a rapid increase in viscosity after mixing. It is expected that differences in the ability of cements to form thin films will affect the seating of cemented restorations.

Analysis of Variance↗
PubMedDate not supplied

Marginal fit of restorations before and after cementation in vivo.

Triturated luting cements provide convenient clinical handling. This study clinically evaluated the influence of two trituration capsule cement systems on the marginal fit of inner copings for telescoping crowns. Using a randomized parallel design, one coping was cemented using zinc phosphate cement (Phosphacap) and one using a glass-ionomer cement (Ketac-Cem Maxicap) for each of 12 patients. A blind examination of the marginal fit of the restorations was made before and after cementation using the replica technique and a scanning electron microscope. The mean marginal discrepancies for all cast copings were approximately 30 microns (median 23 microns) before cementation. They increased significantly after cementation to 86 microns (median 63 microns) in the zinc phosphate cement copings but to only to 47 microns (median 44 microns) in the glass-ionomer cement copings.

Crowns↗
PubMed1997

Effect of gap size and cement type on gingival microleakage in Class V resin composite inlays.

Microleakage along the gingival interface was measured in 52 teeth that had received standardized preparations at a fixed depth of 2.0 mm and were restored with Class V composite inlays. Two fabrication techniques and two types of luting cement were compared. Twenty-six teeth were cemented with a resin-modified glass-ionomer cement, and 26 were cemented with a conventional resin cement. Half of the inlay patterns in each cementation group were fabricated directly on the tooth, and half were fabricated indirectly on stone dies. The resin cement was more significantly effective in preventing leakage than the resin-modified glass-ionomer cement. There was no statistically significant difference between inlay fabrication techniques. For those inlays cemented with the resin cement, the mean leakage was substantially lower for the indirect patterns than for the direct group. Although this difference was not statistically significant, it suggests that the slightly larger interfacial gap resulting from the fabrication of indirect patterns is effective in creating a better seal.

Cementation↗
PubMed2000

Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations.

STATEMENT OF PROBLEM: Past research has not controlled preparation surface area when examining the influence of dentin desensitizers on the retentive strength of cemented cast crowns, leading to inconsistent results. PURPOSE: This research controlled crown preparation surface area and evaluated the effect of various dentin desensitizers and conventional cementing agents on the in vitro retentive strength of cast crowns. METHODS AND MATERIAL: Freshly extracted human molars were prepared for a standardized crown preparation (26 degrees total convergence, 4 mm axial height) with a custom-made pantograph. Dentin desensitizers included none (control), a polymerizable material (All-Bond 2), and a nonpolymerizable desensitizer (Gluma Desensitizer). Cementing agents included zinc phosphate (Fleck's), glass ionomer (Ketac-Cem), resin-modified glass ionomer (Fuji II), and resin cement (Panavia 21). Twelve teeth were prepared for each test condition (144 teeth total). Individual castings were made from a base metal alloy (Rexillium III). Crowns were removed after storage at 26 degrees C for 48 hours at 100% relative humidity using a universal testing machine at a crosshead speed of 1.27 mm/min. The proportion of cement retained on the tooth and casting after debonding was quantified according to treatment. Statistical treatment included 1- and 2-way ANOVAs, followed by the Tukey-Kramer post hoc test at a preset alpha of 0.05.Results. Resin cement exhibited the highest retentive strength and all dentin treatments resulted in significantly different retentive values (All-Bond 2 (5.68 +/- 0.70 MPa) > control (4.67 +/- 0.48 MPa) > Gluma (4.12 +/- 0.37 MPa)). Retention of resin-modified glass ionomer was between the resin cement and glass ionomer groups: All-Bond 2 (3.46 +/- 0.26 MPa) > Gluma (2.81 +/- 0.15 MPa) = control (2.96 +/- 0.18 MPa). Conventional glass ionomer values were between those of Fuji Plus and zinc phosphate groups: All Bond 2 (2.23 +/- 0. 20 MPa) = control (2.36 +/- 0.20 MPa) > Gluma (1.98 +/- 0.23 MPa). Zinc phosphate had the lowest retention values: control (1.68 +/- 0. 08 MPa) > Gluma (0.81 +/- 0.11 MPa) > All-Bond 2 (0.67 +/- 0.14 MPa). The majority of cement was retained on the debonded tooth surface versus the casting, with the exception of zinc phosphate when used with dentin pretreatments. CONCLUSION: Controlled crown surface areas reduced the variation in strength values permitting high discrimination among retention values of desensitizer/cement combinations. In all but 1 combination, Gluma desensitizer significantly decreased crown retention. With resin cement and resin-modified glass ionomer, use of All-Bond 2 desensitizer significantly increased crown retention values.

Analysis of Variance↗
PubMed2000

Selection of materials for post cementation.

Many types of cement are available for post cementation, each with advantages and disadvantages. For posts with adequate mechanical retention, zinc phosphate is a good choice for patients for whom fluoride release is not considered essential. Posts with compromised mechanical retention benefit from use of a resin-modified glass-ionomer cement, which also releases fluoride. Composite resin cements should be reserved for rare cases where mechanical retention is so compromised that use of a resin-modified glass-ionomer cement provides inadequate retention. Great care is required when using composite resin cements to ensure optimum performance and avoid the creation of difficult-to-remove excess cement. Clinicians should be aware that posts cemented with resin-modified glass ionomer or composite resin cements may be difficult or impossible to remove if access to the root canal system is subsequently required.

Cementation↗
PubMed1996

An experimental study of damage accumulation in cemented hip prostheses.

OBJECTIVE: To develop a methodology to characterize the pattern of crack initiation and damage accumulation in intramedullary fixated cemented prostheses. DESIGN: An experimental physical model of intramedullary fixation was developed which both represents the implant structure and permits monitoring of fatigue crack growth. BACKGROUND: Many joint replacement prostheses are fixed into the medullary cavity of bones using a poly(methylmethacrylate) 'bone cement', which forms a mantle around the prosthesis and locks it to the bone. The endurance of the replacement is, to a great extent, determined by the mechanical durability of the cement and the implant interfaces under cyclic stresses generated by dynamic loading. The cement mantle is subjected to complex multiaxial stresses which vary in particular distribution depending on the prosthesis design. METHODS: Damage accumulation is reported in terms of the number of cracks, the location of cracks, and the rate of crack growth. RESULTS: The results clearly show the nature of damage accumulation in the cement mantle, and that many of the cracks which propagate within the cement mantle are related to cement porosity. CONCLUSION: This study gives experimental evidence to support the hypothesis of a damage accumulation failure scenario in cemented hip reconstructions. RELEVANCE: Cementing is the most popular technique for the fixation of joint replacement prosthesis. However, the sequence of events leading to the failure of cemented fixation is not fully understood. In this paper it is shown that damage accumulation can be directly monitored in an experimental model of cemented intramedullary fixation.

Journal Article↗
PubMed2006

Stabilization/solidification of hazardous and radioactive wastes with alkali-activated cements.

This paper reviews progresses on the use of alkali-activated cements for stabilization/solidification of hazardous and radioactive wastes. Alkali-activated cements consist of an alkaline activator and cementing components, such as blast furnace slag, coal fly ash, phosphorus slag, steel slag, metakaolin, etc., or a combination of two or more of them. Properly designed alkali-activated cements can exhibit both higher early and later strengths than conventional portland cement. The main hydration product of alkali-activated cements is calcium silicate hydrate (CSH) with low Ca/Si ratios or aluminosilicate gel at room temperature; CSH, tobmorite, xonotlite and/or zeolites under hydrothermal condition, no metastable crystalline compounds such as Ca(OH)(2) and calcium sulphoaluminates exist. Alkali-activated cements also exhibit excellent resistance to corrosive environments. The leachability of contaminants from alkali-activated cement stabilized hazardous and radioactive wastes is lower than that from hardened portland cement stabilized wastes. From all these aspects, it is concluded that alkali-activated cements are better matrix for solidification/stabilization of hazardous and radioactive wastes than Portland cement.

Alkalies↗
PubMed2000

Coincidence of otx2 and BMP4 signaling correlates with Xenopus cement gland formation.

We previously showed that otx2 activates ectopic formation of the Xenopus cement gland only in ventrolateral ectoderm, defining a region of the embryo permissive for cement gland formation. In this paper, we explore the molecular identity of this permissive area. One candidate permissive factor is BMP4, whose putative graded inhibition by factors such as noggin has been proposed to activate both cement gland and neural fates. Several lines of evidence are presented to suggest that BMP signaling and otx2 work together to activate cement gland formation. First, BMP4 is highly expressed in the cement gland primordium together with otx2. Second, cement gland formation in isolated ectoderm is always accompanied by coexpression of otx2 and BMP4 RNA, whether cement gland is induced by otx2 or by the BMP protein inhibitor noggin. Third, BMP signaling can modulate otx2 activity, such that increasing BMP signaling preferentially inhibits neural induction by otx2, while decreasing BMP signaling prevents cement gland formation. In addition, we show that a hormone-inducible otx2 activates both ectopic neural and cement gland formation within the cement gland permissive region, in a pattern reminiscent of that found in the embryo. We discuss this observation in view of a model that BMP4 and otx2 work together to promote cement gland formation.

Animals↗
PubMed1998

In vivo skeletal response and biomechanical assessment of two novel polyalkenoate cements following femoral implantation in the female New Zealand White rabbit.

Glass-ionomer cements (GIC) offer several advantages over the conventional acrylic-based bone cements. The formation of an adhesive bond with bone and metals, a low setting exotherm and no systemic or local toxicity are some of the advantages cited. This study examines the in vivo biological and biomechanical behavior of two polyalkenoate cements (LG26 and LG30) implanted for 6 wk into the submetaphyseal spongiosa of the rabbit femur. Cements were implanted as both set cement rods and unset cement dough. Implantation of set rods resulted in the formation of variably mineralized osteoid/woven bone at the bone-cement interface. Mechanical (push-out) testing revealed the strength of this bone-cement interface was of similar magnitude to control (PMMA-rod implanted) animals. The bone of LG cement-dough implanted animals exhibited demineralization of pre-existing bone local to the site of implantation, accumulation of aluminum both locally and at a distance from the site of implantation, and defective mineralization of newly formed osteoid. The histological picture following LG implantation was strikingly similar to human renal osteodystrophy, in which skeletal accumulation of aluminum is a noted feature. The development of a GIC with low/no aluminum release from the unset cement dough is a priority in the further development of these cements for possible orthopaedic applications.

Journal Article↗
PubMed2002

Influence of pressurization on flexural strength distributions of PMMA-based bone cements.

Flexural strength distributions of standard viscosity and low viscosity bone cements based on Polymethylmethacrylate were obtained by testing the materials in four-point bending according to the ISO 5833 protocol. The cement dough was poured into a mold and was allowed to cure at atmospheric pressure. An additional set of specimens of the standard viscosity cement was prepared under pressure while the cement dough was polymerizing in the mold. Following preparation, test specimens were stored in a 37 degrees C water bath for 48 h. The two-parameter Weibull model, which was used to analyze the data, gave a good representation of the fracture loads distribution. Low viscosity cement displayed a higher mean flexural strength and a slightly lower data scatter than standard viscosity cement. The mean flexural strength of the cement increased about 60% when pressure was applied compared with the same material cured at atmospheric pressure. The Weibull modulus, m, characterizes the scattering in the measured values of strength. For the cement prepared at atmospheric pressure the m value was 8.6 while for the cement cured under pressure it was 12.3, which reveals a reduction in the data scatter. The cement tested in four-point bending displayed lower mean flexural strength compared with the cement tested in three-point bending. The influence of the load type upon the mean flexural strength was satisfactory predicted by Weibull model.

Journal Article↗
PubMed2004

Hydration properties of eco-cement pastes from waste sludge ash clinkers.

Three types of hydraulic cements have been developed by incorporating sludge ash from a primary sewage treatment plant and a water purification plant, as well as slag from steelworks (ferrate), as a partial replacement for clay, silica, alumina, and iron oxide in raw cement meal. The raw meal for the pre-determined recipes was prepared by heating it to 1400 degrees C for 6 hr in a clinkerization process, using a simulated incinerator and smelter. The major components of ordinary Portland cement, C3S, C2S, C3A, and C4AF, were all found in the clinkers. Of the three types of eco-cements, the eco-cement A paste was most similar to ordinary Portland cement in terms of composition and compressive strength development, while the eco-cement B paste showed early strength development. The differential thermal analysis species analyses indicated that the hydrates in the eco-cement pastes were mainly calcium hydroxide and CSH gels, like those found in ordinary Portland cement paste. Moreover, the degree of hydration, as determined by nuclear magnetic resonance, increased in all eco-cement pastes with an increasing curing age. The results indicate that it indeed is feasible to use sludge ash and ferrate to replace up to 20% of the mineral components of raw materials for cement.

Compressive Strength↗
PubMed2000

Removal of porcelain veneers aided by a fluorescing luting cement.

PURPOSE: Porcelain veneers are a safe and effective treatment modality for selected teeth that have poor esthetics. However, removal of porcelain veneers that have failed may be time-consuming and involve considerable removal of sound tooth structure adjacent to the veneer. The aim of this study was to evaluate a novel method of porcelain laminate veneer removal by incorporating a fluorescent dye into the luting cement that allows the practitioner to visualize the cement on the tooth and remove the veneer without causing residual damage to the adjacent tooth substance. MATERIALS AND METHODS: Porcelain veneers were luted on extracted teeth with a luting cement modified with a fluorescing agent. Faculty teaching staff and final year dental undergraduates were asked to remove the veneers with the aid of a curing light to render the luting cement visible by fluorescing. They were then asked to compare the removal of comparable veneers without this visual aid and to complete a standard questionnaire. The depth of cure of the conventional and modified cements was measured using a penetrometer. RESULTS: Results of the questionnaire indicated that the operators found removing the veneer cemented with the modified (fluorescing) cement considerably easier than removing the veneer cemented with the conventional cement. Microscopy indicated that more damage was caused to the underlying tooth during removal of conventionally cemented veneers. The incorporation of the dye into the cement reduced the depth of cure from 4.238 mm (SD = 0.025) to 3.761 mm (SD = 0.096).

Dental Debonding↗
PubMed1998

Mortality from lung cancer and population risk attributable to asbestos in an asbestos cement manufacturing town in Italy.

OBJECTIVE: To estimate mortality from lung cancer and the risk attributable to asbestos separately for asbestos cement workers and for the general (non-occupationally exposed) population in the town of Casale Monferrato, where the largest Italian asbestos cement factory had been in operation in 1907-86. According to cancer registry data, in the same town the incidence of malignant mesothelioma in the general population is about 10 times higher than in comparable Italian provinces. METHOD: Decedents from lung cancer in 1989-95 were nominally identified in the list of decedents kept at the Local Health Authority of Casale Monferrato. Workers in the asbestos cement factory have been identified with a search in the nominal list of workers and the same was done for the wives of asbestos cement workers. These lists have already been used in cohort studies. Sensitivity and specificity of the linkage procedure with occupational activity in asbestos cement production have been evaluated in a previous study. Population at risk was estimated on the basis of official figures and on the results of the cohort study of asbestos cement workers. RESULTS: 227 deaths from lung cancer were included (184 men and 43 women). Among the asbestos cement workers mortalities were 234.0 x 100,000 person-years among men and 35.5 among women. Corresponding figures in the general (non-occupationally exposed) population in Casale Monferrato were 80.6 and 18.7. The rates in the general population were not higher than in the rest of the region. Attributable risk (AR) among the asbestos cement workers (and wives) is 67.5% (95% confidence interval (95% CI) 56.8 to 78.2) for men and 51.3% (95% CI 14.9 to 87.8) among women. Population AR to occupational or paraoccupational exposure in the asbestos cement production is 18.3% (95% CI 11.1 to 25.6) among men and 10.1% (95% CI 0 to 24.6) among women. CONCLUSION: This work did not show an increase in mortality from lung cancer for the population not exposed occupationally, but a large excess was found among men and women occupationally exposed in asbestos cement production. The total burden of lung cancer due to occupational exposure to asbestos may be underestimated, as only occupational exposure in asbestos cement production was taken into consideration. Nevertheless even a single factory can be responsible for a considerable proportion of deaths from lung cancer in a population.

Adolescent↗
PubMed1996

[Peculiar cemental lesion of the jaws--its pathological entity and natural history].

Two hundred fifty-five solitary and 42 multiple cases of fibro-osseous lesions of the jaws, and 74 cases of sclerosing osteomyelitis were studied clinico-pathologically, in order to discuss the entity of peculiar cemental lesion with sequester-like appearance, which occurs mainly in the mandibular molar area of over middle-aged females. Four allied lesions, including the sequester-like cemental lesion, were revealed. They were provisionally designated sequestrated cemental masses, cemental masses, focal cemento-osseous dysplasia, and periapical cemental masses respectively, because no entities that were consistent with them could be found in the classifications of World Health Organization (WHO). The above- mentioned peculiar cemental lesion was equivalent to sequestrated cemental masses, which consist of sclerotic cementum and/or osteocementum with inflammation. Cemental masses and periapical cemental masses were related to sequestrated cemental masses. Focal cemento- osseous dysplasia was considered to be a counterpart of lesion which had been recently reported by Summerlin et al. In consideration of similarity and continuity of the histological and clinical findings, the four allied lesions were thought to be arranged in a continuous spectrum of fibro-cemento-osseous dysplasia of the jaws, along with periapical cemental dysplasia and florid cemento-osseous dysplasia that are mentioned in the WHO classification.

Dental Cementum↗
PubMed2005

[Effect of femoral cementing technique on results. Comparison between retrograde technique and vacuum application].

METHODS: To evaluate the penetration depth of cement into trabecular femoral bone, femora of 14 sheep were subjected to simultaneous bilateral cementing. After femoral neck osteotomy, preparation of the bone cavities and jet lavage, cement was applied simultaneously using the conventional retrograde method for one side and vacuum application for the contralateral limb. Bilateral simultaneous pressurisation was then applied. All femoral specimens were X-rayed, sawed into standardised, horizontal, stereometric, identical slices and microradiographed. Cement penetration was assessed using a morphometric software system. RESULTS: No significant differences in depth of cement penetration between sheep femora cemented with the vacuum application method and the standard retrograde method could be found or between the ratio of cement-consolidated and non-cement-consolidated cancellous bone. CONCLUSION: The more complicated and technically challenging method of cement application under vacuum had no advantage in terms of cement interdigitation over the standard retrograde method.

Animals↗
PubMed1983

Acid resistance of enamel exposed to fluoride-containing orthodontic cements.

In a previous study enamel fluoride uptake from fluoride-containing orthodontic cements was evaluated after a 21-day period. The enamel fluoride uptake from a zinc phosphate cement (A), a zinc phosphate cement containing 5 per cent stannous fluoride by weight (B), and a silicophosphate cement (C) was compared. The results indicated that there was a net loss of fluoride from enamel beneath the orthodontic bands cemented with A while the enamel beneath B and C acquired significant amounts of fluoride. The purpose of the present study was to evaluate enamel fluoride uptake after 12 weeks and the effect of the fluoride uptake or loss by the enamel on acid resistance. Five teeth each had bands cemented with cements A, B and C, respectively, and were individually suspended in synthetic saliva for 12 weeks at 37 degrees C. Following this period the bands were removed, the cements were carefully cleaned off the teeth, and the crowns of the teeth were individually suspended in a lactic acid buffer at pH 4 for 4 weeks. Each tooth crown was then sectioned longitudinally and examined microradiographically to study the degree of enamel demineralization. Characteristic subsurface enamel carieslike lesions were noted on all the specimens studied. The carieslike lesions in the enamel exposed to the fluoride-containing cements were considerably reduced. The enamel which had acquired fluoride from the fluoride-containing cements was apparently more resistant to artificial caries attack.

Acids↗
PubMed2000

Pilot study of conditioner/primer effects on resin-dentin bonding after provisional cement contamination using SEM, energy dispersive x-ray spectroscopy, and bond strength evaluation measures.

STATEMENT OF PROBLEM: Previous studies have shown that provisional cement cannot be completely removed from the dentin surface and the remnants inhibit adhesion of resin cement to dentin. PURPOSE: This study investigated the effects of dentin conditioners on resin-dentin bonding after provisional cement contamination. MATERIAL AND METHODS: A total of 216 bovine dentin specimens were divided into 2 groups with and without provisional cement coating on the dentin surface. Each group was further divided into 3 subgroups with 2 conditioning methods and without dentin conditioning (36 specimens per subgroup). The 2 methods applied were (1) phosphoric acid etching and (2) phosphoric acid etching, followed by sodium hypochlorite gel. Provisional cement was completely removed with a curette before dentin conditioning. Stainless steel rods were luted to dentin surfaces with Panavia 21 resin cement. Tensile bond strengths were measured before and after thermocycling. The dentin surface was analyzed by SEM and energy dispersive x-ray spectroscopy. Three-way ANOVA and Scheffe's comparison test were performed (P =. 05). RESULTS: Bond strength was significantly influenced by provisional cement application, type of dentin conditioning, and thermocycling. Bond strength decreased when treated with provisional cement, but the decreased strengths were restored to their original values or higher by both dentin conditioners used. Specimens treated with sodium hypochlorite gel applied after phosphoric acid etching demonstrated the highest bond strengths with good stability after thermocycling. CONCLUSION: Application of sodium hypochlorite gel after phosphoric acid etching was more effective than etching with phosphoric acid alone to eliminate the inhibitory effect of provisional cement remnants on adhesion between resin cement and dentin.

Acid Etching, Dental↗
PubMed1998

Comparative study of the marginal microleakage of six cements in fixed provisional crowns.

STATEMENT OF PROBLEM: In many situations, provisional restorations require a long-term permanence in the oral cavity. During this period, the abutments need the best possible biologic and mechanical protection. In this way, the vitality of the pulp and the integrity of mineralized tissues can be preserved. The luting cement used to fix interim restorations should have good mechanical properties, low solubility, and good adhesion to resist bacterial and molecular penetration. However, because of its provisional nature, the prosthesis should be easy to remove from the abutments. These contrasting requirements may lead to a compromise in cement behavior, particularly in its mechanical properties. PURPOSE: This in vitro study evaluated the marginal microleakage of 4 provisional cements, a cavity base compound and a zinc-phosphate luting cement in provisional acrylic resin crowns fixed on extracted human teeth. MATERIAL AND METHODS: Thirty acrylic resin crowns were made and fitted on intact human premolars with the 6 cements. All restorations were applied in a standardized manner by means of an axial load of 10 kg. Specimens were thermocycled then submerged in a 5% basic fuchsin solution, then sectioned and observed under a light stereomicroscope. A 5-level scale was used to score dye penetration in the tooth/cement interface. RESULTS: A high dye penetration in the tooth/cement interface was present in all 4 provisional cements. Microleakage existed in specimens where zinc-phosphate and cavity base compounds were used; however, it was lower than the other materials. A significant difference (P < .05) was found between zinc-phosphate and one eugenol-free cement and between cavity base and the same eugenol-free cement. CONCLUSIONS: All materials tested demonstrated different degrees of microleakage. Zinc-phosphate and cavity base compound cements had the best sealing properties. This latter, even if conceived as a cavity base, may be considered a good provisional cement as far as microleakage is concerned.

Acrylic Resins↗