A method for assessing the clinical solubility and disintegration of luting cements

Time-depending solubility of different fixed prosthetic permanent luting cements

The solubility of dental cements is important property due to their prolonged exposure to oral fluids. Тhe recommended standard is 0.2% mass loss for 24 hours. The aim of the study is to measure and compare the values of the solubility in different types of permanent cements as a function of time of exposure to the solvent. Four types of cements were selected: zinc phosphate (ZP), glass-ionomer (GI), resin-modified glass-ionomer (RG) and polycarboxylate (PC) cement. Totally 120 samples, equally divided in 4 series, were fabricated according to the experimental method recommended for in vitro laboratory measuring of the mass loss of the cement due to solubility. Distilled water was used as a solvent. The measuring of every sample weight was performed before and after immersing in solvent for 1, 7, 14 and 21 days and mass loss was calculated as a percent of initial weight of the sample. According to the results, the mass loss of selected cements after immersion in distilled water for the initial 24hours period was 0.28% for ZP cement, 0.32% for RG, 0.51% for PC and 0.57% for GI cement. After this period, the mass loss decreased and was minimal at the end of the third week. The precise evaluation of this basic characteristic is necessary for predicting clinical behavior of the permanent cement and the exact cement selection in every single case. Keywords: permanent cementation, dental cement, solubility, dissolution

In vivo disintegration of four different luting agents

The purpose of this study was to evaluate the disintegration of luting agents. An intraoral sample holder was made having four holes of 1.4 mm diameter and 2 mm depth. The holder was soldered onto the buccal surface of an orthodontic band, which was cemented to the first upper molar in 12 patients, average age 26 years. The holes were filled with a zinc phosphate (Phosphate Kulzer), a glass ionomer (Ketac Cem), a resin-modified-glass ionomer (Fuji Plus), and a resin cement (Calibra). Impressions were made at baseline, and 6, 12, and 18 months from which epoxy replicas were made, which were scanned with an optical scanner. Total volume loss was calculated. The rank order of mean volume loss was as follows: Phosphate cement > Ketac Cem = Fuji Plus = Calibra. Cement type and time had statistically significant effects on volume loss of cements (P < 0.001). Under in vivo conditions, zinc phosphate cement disintegrated the most, whereas no significant difference was observed for glass ionomer and resin-based cements. As intraoral conditions are considerably less aggressive than experimental laboratory conditions, the erosion behavior of glass ionomer cement was found to be similar to the resin-based cements in contradiction to previous laboratory results.

Seal capability of interim post and core crown with temporary cements

The purpose of the present study was to evaluate the in vitro seal capability of interim post and core crown restorations. Eighty teeth were selected and divided into 8 groups. Four experimental groups received interim posts and core crowns. Half of each group was decoronated at the cementum-enamel junction, groups PCCH and PCZO. The other half was sectioned 2 mm coronal to the cementum-enamel junction, groups PCrZO and PCrCH. The interim post and core crowns were luted with Rely X Temp NE, groups PCrZO and PCZO; Hydro C was used for Groups PCrCH and PCCH. The control groups, PC and PCr, received uncoated post and core crowns; groups OTg and OT were left without interim post and core crowns and were totally open. Infiltration was accessed by dye exposure followed by demineralization of the teeth. The length of the infiltration was measured using digital images taken from the specimens. The images were inserted into the Image Tool 3.0 software. Kruskal-Wallis analysis of variance and Dunn's multiple comparison method were used to test for significant differences among test groups (P < .05). Groups PCrZO and PCrCH showed the least dye penetration, followed by groups PCZO and PCCH. Teeth restored with interim post and core crowns will be subject to leakage. Ethics Committee: 095/2008.

The effect of preparation height and luting agent on the resistance form of cemented cast crowns under load fatigue

STATEMENT OF PROBLEM

The minimum amount of resistance form required for the success of a clinical crown is unknown.There is little information on the fatigue performance of complete coverage restorations on natural tooth preparations cemented with different luting cements.

PURPOSE

The purpose of this study was to evaluate the effect of tooth preparation height and luting agent on resistance form using unidirectional load fatigue testing. For a given tooth preparation with a clinically relevant total occlusal convergence (TOC), the adequacy of resistance form was investigated.

MATERIAL AND METHODS

Sixty-four human maxillary premolars were prepared with occlusal-cervical dimensions of 2, 3,4, or 5 mm and a TOC of 20 degrees. Complete metal crowns were cemented using either zinc phosphate cement (HY Bond;ZP groups) or resin cement (Panavia F; PF groups). Cyclic load fatigue testing was done with an applied load of 6.0 kg at 2.6 Hz. Load cycles to preliminary failure were detected with a strain gauge at the palatal crown-tooth interface. Results were subjected to the Kruskal-Wallis test and the Wilcoxon post-hoc rank sum test (alpha=.05).

RESULTS

Groups ZP4, ZP5, PF2, PF3, PF4, and PF5 had the highest mean number of cycles to preliminary failure,while group ZP2 had the lowest mean number of cycles to failure. Group ZP2 was significantly different (P<.001) from all other test groups for the number of cycles to failure.

CONCLUSIONS

For the 2- and 3-mm preparation height groups, zinc phosphate cement exhibited a poorer fatigue performance compared to Panavia F. There was no significant difference in the number of cycles to failure for groups ZP4,ZP5, PF2, PF3, PF4, and PF5. For both cements, the number of cycles to failure increased with increasing resistance length. (J Prosthet Dent 2009;102:155-164)

Surface roughness average and scanning electron microscopic observations of resin luting agents

The objective of this work was to evaluate the surface roughness changes of three current resin cements after tooth brushing simulation, as well as discuss its relation with scanning electron microscopic observations. The materials employed were Enforce Sure Cure (Dentsply), Rely X (3M-ESPE) and Variolink II (Vivadent). They were subjected to brushing abrasion (100,000 strokes for each specimen) and the surface roughness alterations (before and after strokes) were detected. For each roughness test condition, specimens were coated with gold-palladium and observed on a DSM 900 Zeiss scanning electron microscope. Roughness changes values (Ra) were statistically increased after brushing strokes. Based on the microscopic observations and roughness changes analysis, all cements studied became rougher after brushing strokes.

Crowns and other extra-coronal restorations: try-in and cementation of crowns

Having successfully negotiated the planning, preparation, impression and prescription of your crown, the cementation stage represents the culmination of all your efforts. This stage is not difficult, but a successful outcome needs as much care as the preceding stages. Once a restoration is cemented there is no scope for modification or repeat You have to get it right first time. Decemented crowns often have thick layers of residual cement suggesting problems with either initial seating or cement handling. When the fate of restorations costing hundreds of pounds depends on correct proportioning of cements and the quality of the mix, the value of a well-trained and experienced dental nurse is easy to see. Both dentist and nurse need a working knowledge of the materials they are handling.

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.

In vitro enamel demineralization and the marginal gap of simulated cast restorations with three different cements

PURPOSE

This study investigated 1) the relationship between marginal gap sizes and enamel demineralization, and 2) the influence of three cements on this enamel demineralization.

MATERIALS AND METHODS

Horizontal sections of 60 noncarious, freshly extracted human third molars were randomly assigned to one of four groups. Simulated cast restorations were attached to the specimens with 1) zinc phosphate cement, 2) glass ionomer cement, 3) composite resin cement, or 4) no cement (control). The tooth/restoration gaps were controlled at 51, 102, and 204 microns. The specimens were incubated for 16 weeks in buffered lactic acid gelatin to induce demineralization. Photomicrographs were obtained from sections of each sample using a polarized light microscope. Three evaluators measured wall and primary enamel lesion depths allowing for the determination of a demineralization ratio (DR). Data were analyzed by repeated-measures ANOVA (alpha = 0.05).

RESULTS

The between-evaluator effects were not significant. All evaluators agreed that DR was significantly related to cement (p = .0001) but not to marginal gap size. The resin cement had the smallest DR (0.7 +/- 0.3), and the control group had the greatest (4.4 +/- 2.0).

CONCLUSIONS

The presence of any one of the three investigated cements resulted in decreased demineralization. The amount of demineralization was unaffected by marginal gap size.

Leakage of various types of luting agents

Freshly extracted molar teeth were prepared for complete cast gold crowns cemented with either zinc phosphate cement, polycarboxylate cement, glass ionomer cement, a resin luting agent, or a zinc oxide-eugenol temporary cement. The specimens were tested at 1-, 6-, and 12-month intervals with radioactive 45Ca. The specimens were sectioned, autoradiographs were made, and the marginal leakage was evaluated on a scale of 0 to 3. The results showed that zinc phosphate, polycarboxylate, and glass ionomer cements are equally suited for permanent cementation of restorations. The resin luting agent showed high initial leakage, indicating that it is not as desirable for permanent cementation purposes. The zinc oxide-eugenol cement showed increased leakage with time but is well suited for its indicated purpose, temporary cementation.

An investigation of dental luting cement solubility as a function of the marginal gap

The purpose of this study was to investigate the rate of type I zinc phosphate cement solubility as it relates to the degree of marginal opening. Standardized test samples were constructed that would simulate clinically relevant marginal gaps of 25, 50, 75, and 150 microns and their subsequent cement lines. The study was divided into two phases. Phase 1 evaluated the effects of simple diffusion on cement solubility in a static environment, whereas phase 2 investigated the effects of convective forces on cement dissolution in a dynamic environment. Both the phase 1 and phase 2 studies demonstrated no significant difference in the rate of cement dissolution for the 25-, 50-, and 75-micron test groups. The 150-micron test groups for both studies, however, demonstrated an increase in the rate of cement dissolution. The results of the phase 1 and phase 2 studies should not be compared because different methodologies were used.

A 5-year study comparing a posterior composite resin and an amalgam

Eighty class I and class II light-cured posterior composite resin restorations were compared with 43 class I and class II amalgam restorations during a 5-year period after placement. The results of this clinical study showed that both materials were satisfactory during the time period and that the only significant statistical differences are a poorer marginal integrity for the amalgam and a greater wear rate for the composite resin.

Dissolution mechanism of zinc phosphate dental cement in acetic and lactic acid buffers

When zinc phosphate cement was immersed in 0.1 M acetic and lactic acid buffer solutions adjusted to pH 4.1, its dissolution rate was determined by chemical analysis. The eroded surface of the cement was examined by X-ray diffraction and SEM observation. The dissolution process of the cement immersed in the acetic acid buffer solution was mainly controlled by the diffusion of releasing species through the cement matrix and that of the cement immersed in the lactic acid buffer solution by the decomposition of the cement matrix at the surface.

A laboratory and clinical evaluation of three dental luting cements

The loss of material from specimens of three luting cements was measured after continuous erosion cycling in the laboratory. The glass ionomer luting cement showed significantly less material loss than the zinc polycarboxylate and zinc phosphate luting cements. Two hundred and fifty restorations cemented with one of the three materials were studied clinically for marginal integrity and retention over 3.5 years. The data were tested using survival analysis. Zinc phosphate cement gave the best clinical performance. Possible explanations for the poor correlation between the findings in the laboratory and clinical study are discussed.

In vitro degradation of cements: a comparison of three test methods

Three in vitro tests were evaluated on the basis of their ability to predict the relative resistance of various types of luting cements to disintegration in the oral cavity. The tests were (1) weight loss, (2) reduction in size of cement films held between glass optical flats, and (3) reduction in transverse strength. Storage media evaluated were H2O and 0.1, 0.01, and 0.001 M HAc. These data were compared with previously obtained measurements on the in vivo disintegration rates of the same cements. The best correlation with in vivo disintegration was obtained by test No. 2 when the specimens were subjected to 0.01 M HAc.

A comparison between zinc phosphate and glass ionomer cement in orthodontics

In the past orthodontic band cementation has relied heavily on mechanically retentive cements such as zinc phosphate luting agents. The clinical performance of a glass ionomer cement (GIC), a chemically retentive cement, was evaluated against a conventional zinc phosphate cement (ZP). The recementation values for ZP were significantly higher over a 2-year treatment period than those of GIC. Failures between cement and enamel, and cement and stainless steel were noted for the ZP. Glass ionomer cement had significantly better retentive strength to enamel than to band material. Moisture contamination does not appear to be a problem in orthodontic band cementation with glass ionomer cement.

An evaluation of the significance of the impinging jet method for measuring the acid erosion of dental cements

An extensive review has been made of the impinging jet method for evaluating the durability of dental cements. A comprehensive range of 28 dental cements was examined. The initial rate of erosion was found to be essentially constant. Zinc oxide cements were found to be markedly less durable than alumino-silicate cements. Results broadly correlate with those found in clinical studies.

An erosion test for dental cements

A new method for the in vitro measurement of the erosion of dental cements is described which allows repeated, gentle removal of loose surface debris and provides a direct quantitative measurement of material lost. A linear relationship for erosion against time is demonstrated for a glass polyalkenoate material under mildly acidic conditions. This test method is applicable to all acid/base-type cements and gives results comparable to those from in vivo tests.

Quantitative cement solubility experiments in vivo

The dissolution and dissolution rate of dental luting cements was measured longitudinally. Cement samples in enamel were placed in a full prosthesis and worn in the mouth for up to 6 months. At given intervals, replicas of the cement surfaces were made and quantified by means of SEM stereographic photographs. With a stereometer the distance between cement surface and original enamel surface can be determined quantitatively. The results show in vivo solubility rates for zinc-phosphate and glass-ionomer cement of about 80 microns week-1 and 2 microns week-1 respectively.

Degradation of luting cements measured in vitro and in vivo

The degradation of luting cements was quantified when these cements were held as a 20-micron cement layer. The degradation process, which is mostly a sequence of absorption, disintegration, and solution, was expressed by a time-constant (tau). By using the same test specimens in vitro as well as in vivo, we determined the correlation of both situations.

A new laboratory method for evaluating the relative solubility and erosion of dental cements

A method for accelerating the dissolution and erosion of 'acidic' dental cements has been developed which gave relative solubilities in accordance with in vivo observations, in contrast to the conventional test. It involves subjecting 24-h-old specimens to a jet of dilute acid (lactic or citric) and determining weight loss. The relative ranking for 'acidic' cements in the apparatus and in vivo was: glass ionomer less than silicophosphate less than zinc phosphate less than polycarboxylate. The method was not valid for reinforced zinc oxide/eugenol/EBA cements. Of the two polycarboxylate cements studied, a brand which has the acid in the powder was found to be more soluble than the conventional material. It is proposed that the method be the basis of a new solubility/erosion test in national and international standards for 'acidic' dental cements.

Degradation of luting cements measured in vitro

The described method of measuring degradation of luting cements in vitro, by which various media, including bacteriological, can be used, gives results indicating that degradation is a more complex process than could previously be measured. Degradation appears to be a process following a sequence of absorption, disintegration, and solution. Factors, such as cement, thickness of the cement layer, molarity, and pH of the medium, affect, mostly by interaction, the degradation speed. Though the clinical predictability of this test method is not yet determined, it gives the opportunity to measure the various stages of degradation and to appoint the different factors affecting this process. Clinical tests based on the same principle are in progress.