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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↗
PubMed1992

Alternative crown systems. Is the metal-ceramic crown always the restoration of choice?

The metal-ceramic crown system still is selected the most frequently because of its strength and versatility. The ability to select metals for color or strength for single units or fixed partial dentures gives great flexibility, but when esthetics of the anterior region are a prime concern, the all-ceramic crown is still an excellent choice. Choice of which all-ceramic system to use is dependent on the strength demands, esthetic needs, amount of tooth structure that can be preserved, and laboratory support available. Where good tooth structure remains but some color, contour, or incisal length changes are desired, the porcelain laminate veneer is an outstanding esthetic and restorative choice. When good labial tooth structure remains but lingual structure is inadequate, a partial veneer gold crown can be an excellent esthetic choice. If moderate tooth structure is lost or moderate staining is present, the Dicor crown is a superb choice. In those instances in which heavy staining is present, a foil or core system should be considered to completely block out the background colors. As the occlusal forces become more of a factor, selection of a restorative system will depend more on strength than esthetic demands. The aluminous porcelain jacket crown still offers great strength and esthetics at a reasonable price. When most of the color is on the surface of the teeth, or when there is a high translucency to the teeth, Dicor can provide very esthetic results, and the Dicor Plus crown offers the opportunity to develop intrinsic shading. When greater strength is required, selection of a foil and core system is suggested, as might be a system that provides a stronger core material, like Alceram or Inceram. These stronger core materials will render improved flexural and compressive strengths, but some increases in brightness may occur with the increased alumina content of the cores. The future in ceramic restorative dentistry may be in the computer-generated crown if ways to develop internal coloring and layered building can be developed and cost can be controlled. Ceramic crowns are best limited to the anterior region of the mouth where occlusal forces normally are less than those found in the posterior region. In selected cases, in which there is no evidence of parafunctional habits, and when the dentist and technician are well versed in functional occlusion and have maximum restorative control of the occlusion, posterior ceramic restorations will be successful. It is important to remember in these cases that porcelain is harder than enamel and very strong in compression.(ABSTRACT TRUNCATED AT 400 WORDS)

Aluminum Oxide↗
PubMed2001

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory.

Journal Article↗
PubMed1977

[Comparison of the three-dimensional behaviour of the relief of the enamel crown and dentine crown in the permanent dentition in the mole (author's trnasl)].

1. As an example for the dentition of the insectivores, the teeth from 20 wholly conserved skulls of moles were investigated and measured before and after electrolytic decalcification. Every crown was described and photographically registered in the calcified and decalcified states. 2. The relief of the enamel crown was compared to that of the dentine crown. Almost without exceptions, the form of the dentine crown narrowly corresponded to that of the enamel crown. 3. The 3rd lower premolar can be an exception: in one case, its dentine crown showed two cusps while its enamel crown demonstrated only one of them. 4. The form of the crown is determined by genetically fixed and not by functionally induced growth-factors.

Animals↗
PubMed2003

[Clinical value of cast post-core porcelain fused to metal crown in restorating residual root and crown of molars].

OBJECTIVE: To investigate the effect of cast post-core porcelain fused to metal crown on the restoration of residual root and crown of molars. METHODS: One hundred and sixty-four residual roots and crowns of molars were treated with root canal therapy and restored by cast core porcelain fused to metal crown. The restoration effect was assessed at the 3rd, 6th, 12th and 24th month. RESULTS: The strength of dental prosthesis retention, marginal fitness, and strength of crowns were satisfactory. The effective rate reached 95.12% during the 2 year follow-up. CONCLUSION: The cast post-core porcelain fused to metal crown is a better method in treating the residual root and crown of molars.

Adult↗
PubMed2004

Functional relationships between crown morphology and within-crown characteristics of understory saplings of three codominant conifers in a subalpine forest in central Japan.

Light-related plasticity of crown morphology and within-crown characteristics were investigated in understory sun and shade saplings of three codominant subalpine conifers, Abies mariesii M.T. Mast., Abies veitchii Lindl. and Picea jezoensis var. hondoensis (Mayr) Rehd. Compared with those of sun saplings, current-year shoots of shade saplings allocated less biomass to needles, resulting in less dense needle packing and hence less mutual needle shading. The proportion of lateral branch biomass in foliage was either similar in sun and shade saplings or greater in shade saplings, depending on the species, suggesting that, over the lifetime of a branch, greater needle longevity in shade compensates for reduced biomass investment in needles of current-year shoots of shade saplings. Saplings with slower-growing branches tended to have greater needle life spans, suggesting that plasticity of branch growth rate and plasticity of needle life span are interdependent. Both Abies species showed greater light-related plasticity of needle life span and branch growth than P. jezoensis. The greater shade tolerance of the Abies species derives from their broad flattened crowns with slow-growing branches. This type of crown development incurs substantial support costs, but the long needle life span of shade saplings of the Abies species compensates, at least in part, for their low annual investment in foliage, especially in the case of A. mariesii, which has a longer needle life span and slower-growing and stouter branches than A. veitchii. Compared with the Abies species, P. jezoensis had a less plastic crown morphology, and less variability of needle life span and branch growth in response to light, resulting in lower shade tolerance. However, compared with the flattened crown of Abies shade saplings, the conical crown of P. jezoensis saplings imposes a smaller support cost, making this species better adapted to rapid height growth than to survival in shade.

Abies↗
PubMed2001

Assessment of vital pulp therapy for nine complicated crown fractures and fifty-four crown reductions in dogs and cats.

Subjective owner assessment of the success of vital pulp therapy was performed for complicated crown fracture (n = 9) and crown reduction (n = 54) of canine teeth in dogs and cats. Our results documented that owners are not able to accurately determine the outcome of vital pulp therapy. Objective assessment of vital pulp therapy for teeth receiving crown reduction indicated maintenance of vitality in 28 of 28 (100%) teeth. Subjective and objective assessments of vital pulp therapy performed > 7-days following complicated crown fracture indicated 9 of 9 (100%) teeth were non-vital. A poor prognosis for maintenance of tooth vitality is warranted for vital pulp therapy of complicated crown fractures with prolonged pulp exposure regardless of the age of the patient. Whereas, an excellent prognosis can be provided for vital pulp therapy following crown reduction. Semiannual, postoperative oral and radiographic examinations are recommended for a minimum of 2-years to assess vitality in all teeth receiving vital pulp therapy.

Animals↗
PubMed2002

The unusually high proton affinity of aza-18-crown-6 ether: implications for the molecular recognition of lysine in peptides by lariat crown ethers.

Recent studies have shown that 18-crown-6 ether (18C6) will selectively form adducts in the gas phase with small, lysine containing peptides. The present study extends this work by investigating the ability of aza-18-crown-6 ether (A18C6) and L1 (a simple lariat crown ether derivative of A18C6) to form similar noncovalent adducts with the side chain of lysine in model peptides in the gas phase. The substitution of nitrogen for oxygen greatly increases the proton affinity of A18C6 relative to 18C6 and inhibits the formation of noncovalent adducts with small lysine containing peptides. The proton affinity of A18C6 is determined by the kinetic method to be 250 +/- 1 kcal/mol. This value is much higher than that for diethanolamine (228 kcal/mol) or for 18C6 (231 kcal/mol). This unusually high basicity is rationalized by semi-empirical calculations that suggest a highly symmetrical structure for protonated A18C6 in which the three most distant oxygens are able to fold back and hydrogen bond with the protonated nitrogen. In the case of L1, the lariat side chain is attached by an amide bond, lowering the proton affinity of LI relative to that of A18C6. This allows L1 to form noncovalent adducts with lysine despite the fact that steric repulsion within the cavity of the crown is increased to some extent. The relative ammonium ion affinities of these various crown ethers are shown to serve as qualitative predictors for the molecular recognition of lysine. The order of the relative ammonium ion affinities is 18C6>>L1>A18C6 as determined by the kinetic method. These results suggest that the substitution of nitrogen for oxygen in the crown ether is not beneficial for the molecular recognition of lysine.

Ammonia↗
PubMed2004

Crowns cemented on crown preparations lacking geometric resistance form. Part II: effect of cement.

PURPOSE: This study evaluated the effect of different cements on resistance to dislodgment of crowns cemented on preparations lacking geometric resistance form. MATERIALS AND METHODS: A preparation that offered no geometric resistance form, with 20 degrees total occlusal convergence (TOC), 0.9 mm wide shoulder finish line, and a 2.5 mm axial wall height was created on an ivorine tooth using a milling machine. Ten metal test specimen die replicas and 10 standardized metal crowns with recipient sites for the application of external forces through a universal testing machine were fabricated. The crowns were cemented on the dies under 5 and 10 kg external loads, the marginal openings measured, loaded to dislodgment, and cleaned of cement. The process was repeated using zinc oxide and eugenol (ZOE), zinc phosphate (ZPh), resin modified glass ionomer (RMGI), and composite resin (CR) cements. RESULTS: Marginal openings under 5 kg cementation loads were 74.63 (+/-15.04) for ZOE, 75.98 (+/-18.20) microm for ZPh, 98.58 (+/-22.62) microm for RMGI, and 105.82 (+/-20.07) microm for CR cements respectively; under 10 kg cementation loads they were 57.62 (+/-15.86) microm, 59.55 (+/-15.41) microm, 95.00 (+/-19.52) microm, 101.30 (+/-12.52) microm respectively. Oblique dislodgment forces, measured with a Universal testing machine, were 40.18 (+/- 6.76) N for ZOE, 215.65 (+/-45.79) N for ZPh, 165.43 (+/-19.53) N for RMGI, and 181.54 (+/-30.75) N for CR respectively when crowns were cemented under 5 kg loads. The corresponding values for 10 kg loads were 38.62 (+/-4.19), 274.86 (+/-54.22), 139.70 (+/-21.71), and 160.40 (+/-21.21) respectively. Only zinc phosphate cement produced statistically enhanced resistance when crowns were cemented under 10 kg force (p value = 0.035). CONCLUSIONS: Under the conditions of the present study only crowns cemented with zinc phosphate displayed increased resistance to dislodgment on preparations lacking resistance form.

Cementation↗
PubMed2000

Composite crown-form crowns for severely decayed primary molars: a technique for restoring function and esthetics.

Current developments in esthetic dentistry center around new techniques and materials that improve the ability of the clinician to provide esthetic services. This article describes a step-by-step method of placing composite crown-form crowns on severely decayed primary mandibular molars. The described technique allows for restoring, as close as possible, form and function lost to caries in an esthetic mode in cases of severely decayed primary molars that would have required stainless steel crowns had they been treated traditionally. Disadvantages of this treatment mode are that dryness may not be prevented in the proximal margins, especially where subgingival carious involvement is encountered and the margin areas may be contaminated with gingival fluid or blood. Although no long-term follow-up has been reported for the technique, when strong opposition by the parent or child to the stainless steel crown is encountered, and a desire for esthetic restoration is strongly expressed, the composite crown-form crowns may be considered as an alternative.

Child↗
PubMedDate not supplied

Comparative evaluation of effect of auxiliary retentive features on retention of complete cast crowns in teeth with adequate and inadequate crown height. An invitro study.

This study was done to evaluate the retention of complete cast crowns in teeth with adequate and inadequate crown height and to evaluate the effects of auxiliary retentive features on retention from of complete cast crowns. Thirty-six extracted human maxillary first premolars were obtained. In one group teeth were prepared to a constant height of 3.5 mm and in the second group teeth were prepared to a constant height of 2.5 mm. Each group was further subgrouped into three. In the first subgroup teeth were prepared conventionally, second subgroup proximal grooves were incorporated and in the third subgroup proximal boxes were incorporated. Tensional forces required to dislodge each cemented casting from its preparation was used for comparison of retention quality. These results were then subjected to an analysis of variance (ANOVA). The retention of crown in tooth with adequate crown height were statistically highly significant (P < 0001), compared to inadequate crown height and in boxes compared to grooves and conventional preparation.

Analysis of Variance↗
PubMedDate not supplied

Clinical longevity of removable partial dentures retained by telescopic crowns: outcome of the double crown with clearance fit.

PURPOSE: It was the aim of this study to investigate the long-term success of a telescopic crown system that can be used for both rigid and resilient support and to evaluate by means of a literature review whether the use of resilient support may be advantageous compared to other double crown systems when the restoration is placed on only a few remaining teeth. MATERIALS AND METHODS: Patient records were used to evaluate 125 dentures (with 460 abutment teeth) based on the Marburg double crown system. The loss of abutment teeth, endodontic treatment, and fracture of the metallic framework were investigated with regard to the different types of denture support. RESULTS: The probability that a patient would have kept all abutment teeth was 84% after 5 years and 66% after 10 years. No significant differences were found for the two groups "resilient support" (< or = three abutment teeth) and "rigid support" (> or = four abutment teeth). For abutment teeth with a double crown with clearance fit, the risk of loss was 4% after 5 years and 15% after 10 years for rigid support, and 10% and 24%, respectively, for resilient support. The risk of endodontic treatment was 7% after 5 years and 9% after 10 years for rigid support, and 3% and 7%, respectively, for resilient support. None of the denture frameworks showed a fracture during the observation period. CONCLUSION: Removable partial dentures retained by double crowns with clearance fit and constructed without major or minor connectors provide good clinical longevity. The survival rates of abutment teeth were comparable to those reported in the literature for other double crown systems. There was no significant increase of the risk of abutment loss when the restoration was placed on three or fewer remaining teeth and the concept of resilient support was applied.

Adolescent↗
PubMedDate not supplied

The effect of crown length on the fracture resistance of posterior porcelain and glass-ceramic crowns.

This in vitro study measured the changes in the fracture resistance of posterior crowns as a function of crown length. The crowns, 10 for each group, were made of a feldspathic porcelain (Ceramco), a glass-ceramic material (Dicor), and an alumina-reinforced glass (In-Ceram). Three different crown lengths were tested on acrylic resin dies. The restorations were fractured in a testing machine using a steel ball, 12.7 mm in diameter, that contacted the occlusal surface at three distinct points. Statistical analysis was performed using the Weibull distribution. The fracture resistance increased significantly with increasing crown length for all crown materials.

Aluminum Oxide↗
PubMed1991

[Rehabilitation of partially edentulous cases with telescope crowns: modified, fully veneered tapered crowns].

Telescope crowns are well established as prosthodontic retainers for removable partial dentures. After a short review of the advantages and disadvantages of telescope crowns, the specifies of tapered crowns are described. By the use of appropriate tooth preparation and the fabrication of modified, fully resin-veneered tapered crowns, it is possible to improve on the crown contours and the aesthetics provided by conventional tapered crowns. Periodontal prophylactic conditions are also considered.

Aged↗
PubMed2001

Complexation of triorganotin derivatives of [18]crown-6- and [15]crown-5-(benzo-4-carboxylate) with alkali thiocyanates.

Investigations of the simultaneous complexation of tri-n-butyltin and triphenyltin derivatives of [18]crown-6- or [15]crown-5-(benzo-4-carboxylate) by the anion and cation from NaSCN or KSCN are reported. The crystal structure of [Na+ is included in [15]crown-5-C6H3-4-COOSn(C6H5)3NCS]-], 4 NaSCN, displays an unusual zwitterionic nature with one intramolecular charge separation characterized by an Na-Sn distance of 9.29(1) A, and several intermolecular charge separations, the shortest being 5.48(1) A. Similar distances (9.70(2), 9.28(2), intramolecular; 5.40(2) and 5.41(2) A, shortest intermolecular) are observed in the more complicated structure of the corresponding [18]crown-6-(benzo-4-carboxylate) derivative, 3 NaSCN, with two independent molecules in the asymmetric unit. For the tri-n-butyltin analogues 1 and 2, complex equilibria were observed in acetone and unraveled by variable temperature 13C, 117Sn. and 23Na NMR studies. Their complexes with KSCN and NaSCN undergo decomposition in acetone solution, as evidenced by the transformation of [K+ is included in [18]crown-6-[C6H3-4-COOSn(nBu)3NCS]-], into tri-n-butyltin isothiocyanate and a novel dimeric potassium [18]crown-6-(benzo-4-carboxylate), the structure of which was elucidated by X-ray diffraction analysis.

Journal Article↗
PubMed2001

Comparative supramolecular chemistry of coronene, hexahelicene, and [18]crown-6: hydrated and solvated molecular complexes of [18]crown-6 with 5-hydroxyisophthalic acid and related di- and tricarboxylic acids.

The outer rim of C-H bonds of coronene (COR) and hexahelicene (HEL) is similar to that of the crown conformation of [18]crown-6 (CRO), which is exploited for crystal engineering of molecular complexes of CRO. However, although CRO does form the adduct (TMA)2 x CRO x (H2O)2 (TMA = trimesic acid = 1,3,5-benzenetricarboxylic acid), its structure does not correspond to the H-bonded, three-connected honeycomb sheet architectures of (TMA)2 x COR and (TMA)2 x HEL. Instead, porous, but noninterpenetrating, H-bonded four-connected sheets are observed, with the dihydrated, crown-shaped CRO molecules functioning as spacers rather than molecular guests. In the adduct (CHTA)2 x CRO x (H2O)5 (CHTA = cis,cis-1,3,5-cyclohexanetricarboxylic acid), the tetrahydrated CRO molecules again take up the crown conformation and act as spacers, this time within porous, noninterpenetrating H-bonded three-connected sheets. The engineering goal of CRO-filled H-bonded, hexagonal honeycomb cavities similar to the COR- and HEL-filled TMA honeycomb pores in (TMA)2 x COR and (TMA)2 x HEL was met in the adduct (HIPA)6 x CRO x (H2O)10 (HIPA = 5-hydroxyisophthalic acid), crystallized from aqueous EtOH. The crystal structure of this complex is on the one hand built up of isolated hexagonal honeycomb cavities established by six HIPA molecules cyclically linked through pairwise intercarboxylic H bonds. These cavities accommodate the crown-shaped CRO molecules, oriented such that maximally straight C-H...O contacts are enabled between its 12 equatorial H atoms and the surrounding 12 carboxylic groups of HIPA, in complete analogy to the situation prevailing in (TMA)2 x HEL and (probably) (TMA)2 xCOR. The second building block of (HIPA)6 x CRO x (H2O)10 is represented by a centrosymmetric decameric water cluster, which has the connectivity of the carbon skeleton of a bishomocubane with opposite methylene bridges, in agreement with vibrational spectroscopic evidence on gaseous (H2O)10. The crystal architecture of the adduct as a whole may either be likened to a severely distorted NaCl-type lattice, with the (HIPA)6 x CRO units replacing, for example, the Na+ ions, and the water clusters substituting the Cl- ions, or else to a system of stacked host sheets set up by C-H...O bonded (HIPA)6 macrorings, which give rise to perpendicular channels taking up guest columns of alternating, H-bonded CRO and (H2O)10 units. Crystals of another, solvated HIPA-CRO adduct of the composition (HIPA)4 x CRO x (EtOH)2 were obtained from aqueous EtOH. Their crystal structure is related to those of (TMA)2 x HEL and (TMA)2 x COR inasmuch distorted HIPA honeycomb sheets are adopted, which may be developed from the hexagonal TMA sheets by replacing one third of the pairwise intercarboxylic linkages by single interphenolic H bonds. The cavities in the HIPA sheets are thus smaller than those of the TMA honeycomb sheets and elliptically shaped. The HIPA sheets associate in pairs yielding twin cavities which take up one CRO and two EtOH molecules. The CRO molecules are suspended in the twin HIPA cages through H bonds extended from the phenolic OH groups and relayed by interposed EtOH "bridges". In keeping with the elliptic shape of the pores in (HIPA)4 x CRO x (EtOH)2, the CRO molecules are not crown-shaped, but rather adopt the more rectangular form as observed in crystalline CRO itself. The crystal structure of a dihydrate of HIPA itself was analysed, too, which assembles in a complex three-dimensional H-bonded network. It is finally concluded that hydrated CRO appears to be an avid H-bond acceptor, in particular towards carboxylic acids functioning as H-bond donors.

Journal Article↗