Effects of cement, cement space, marginal design, seating aid materials, and seating force on crown cementation

An evaluation of the effects of a die spacer, the seating force, the marginal design, seating aid materials, and the cement type during cementation was conducted. Two stainless steel dies were used: one with a 1 mm shoulder and the other with a shoulder and a 65-degree bevel. Ten stone dies were produced from each metal die and half were painted with four layers of die spacer. The crowns were waxed on the dies and cast in a nonprecious alloy, and the seating of crowns was measured with a micrometer before and after cementation. Comparisons were made between zinc phosphate and glass ionomer cements under two seating forces of 5 and 30 lb using an orangewood stick or E-Z-bite seating aid. ANOVA and the Newman-Keuls test revealed that the use of a die spacer, a heavier force of 30 lb, and glass ionomer cement significantly improved crown seating. The beveled preparation led to superior crown seating when the heavier force or glass ionomer cement was used. The orangewood stick and bite device had a similar effect on crown seating.     

Effect of cement types on the tensile strength of metallic crowns submitted to thermocycling

The relationship between metallic cast crowns and tensile strength according to cement types submitted to thermocycling was studied. Seventy-two metallic crowns were cast with Verabond II Ni-Cr alloy and cemented in standardized preparations with 10 masculine tapering. Three types of finishing line (45-degree chamfered, 20-degree bevel shoulder and right shoulder) were made with diamond burs on bovine teeth. Twenty-four metallic crowns in each group were randomly subdivided into three subgroups of 8 samples each according to the cement used: SS White zinc phosphate cement, Vitremer resin-modified glass ionomer cement, and Rely X resin cement and were submitted to thermocycling. Retention was evaluated according to tensile load required to displace the metallic cast crowns from tooth preparations with an Instron testing machine. ANOVA and Tukey's test showed a statistically significant difference among luting materials, with greater results for Rely X resin cement (24.9 kgf) followed by SS White zinc phosphate cement (13.3 kgf) and Vitremer resin-modified glass ionomer cement (10.1 kgf). The finishing line types did not influence the tensile resistance of the crowns fixed with the three cements. Increased tensile resistance of metallic crowns fixed on bovine teeth was obtained with resin cement, independent of the finishing line types.     

Retentive strength, disintegration, and marginal quality of luting cements.

This study evaluated the retention of complete crowns by using five different methods of cementation. Complete crowns were prepared with standardized dimensions on extracted human molars. Metal crowns were cast with a high noble gold ceramic alloy and were cemented with zinc phosphate cement, glass ionomer cement, composite resin cement, composite resin cement with a dentinal bonding agent, and adhesive resin cement. The retention was measured by subjecting the specimens to tensile load until fracture occurred. The disintegration was measured according to American Dental Association Specification No. 8, and the condition of the cements at the margins of crowns was analyzed by use of a scanning electron microscope. Kruskal-Wallis one-way analysis of variance revealed statistically significant differences between the mean retentive strengths. The retention of the zinc phosphate and the glass ionomer groups was significantly different from that of the adhesive resin group. The retention of the adhesive resin cement was 65% greater than the retention of the composite resin and the composite resin/dentinal bonding agent group, but the Mann-Whitney Wilcoxon rank sum test did not depict this difference as significant. The mean +/- SD of the disintegration for the zinc phosphate, the glass ionomer cement, and the composite resin cement was 0.025 +/- 0.013, 0.023 +/- 0.011, and 0.017 +/- 0.001, respectively. The scanning electron microscope analysis of the margins revealed that the composite resin cement was almost intact, the zinc phosphate was subjected to limited disintegration, and the glass ionomer displayed the worst marginal integrity.     

不同制作和粘接方法对铸造金属桩核固位性影响的研究

目的:探索铸造金属桩核制作方法、粘接方法和粘接剂种类对其固位的影响。方法:选择80颗完整的新鲜无龋坏下颌单根管双尖牙,在釉牙骨质界上2 mm处去除临床牙冠,行根管治疗,根管预备和铸造桩核制作及粘接。根据制作方法将80个样本分为两大组(直接法和间接法),每组40个。每组又根据粘接方法(使用螺旋输送器和未使用)和粘接剂(玻璃离子水门汀和磷酸锌水门汀)不同下分4小组,每组10个样本。将样本置于23 ℃室温生理盐水中存放24 h后放置于万能力学测试机上,以0.5mm/min的速度进行拉力试验直到失败,从而得出固位力大小。结果:本实验中影响固位力的最明显因素为粘接方法,使用了螺旋输送器组的固位力明显高于未使用螺旋输送器组(P<0.05);不同制作方法对固位力无明显影响(P>0.05),使用磷酸锌粘接剂组固位力高于使用玻璃离子粘接剂组。然而制作方法,粘接方法和粘接剂种类间是有密切的交互作用的(P<0.05)。结论:制作方法并不影响铸造桩核的固位力,磷酸锌粘接剂性能优于玻璃离子粘接剂,粘接方法对固位力有显著的影响,建议在粘接过程中使用螺旋输送器。     

Comparison of effect of desensitizing agents on the retention of crowns cemented with luting agents: an in vitro study

PURPOSE

Many dentists use desensitizing agents to prevent hypersensitivity. This study compared and evaluated the effect of two desensitizing agents on the retention of cast crowns when cemented with various luting agents.

MATERIALS AND METHODS

Ninety freshly extracted human molars were prepared with flat occlusal surface, 6 degree taper and approximately 4 mm axial length. The prepared specimens were divided into 3 groups and each group is further divided into 3 subgroups. Desensitizing agents used were GC Tooth Mousse and GLUMA® desensitizer. Cementing agents used were zinc phosphate, glass ionomer and resin modified glass ionomer cement. Individual crowns with loop were made from base metal alloy. Desensitizing agents were applied before cementation of crowns except for control group. Under tensional force the crowns were removed using an automated universal testing machine. Statistical analysis included one-way ANOVA followed by Turkey-Kramer post hoc test at a preset alpha of 0.05.

RESULTS

Resin modified glass ionomer cement exhibited the highest retentive strength and all dentin treatments resulted in significantly different retentive values (In Kg.): GLUMA (49.02 ± 3.32) > Control (48.61 ± 3.54) > Tooth mousse (48.34 ± 2.94). Retentive strength for glass ionomer cement were GLUMA (41.14 ± 2.42) > Tooth mousse (40.32 ± 3.89) > Control (39.09 ± 2.80). For zinc phosphate cement the retentive strength were lowest GLUMA (27.92 ± 3.20) > Control (27.69 ± 3.39) > Tooth mousse (25.27 ± 4.60).

CONCLUSION

The use of GLUMA® desensitizer has no effect on crown retention. GC Tooth Mousse does not affect the retentive ability of glass ionomer and resin modified glass ionomer cement, but it decreases the retentive ability of zinc phosphate cement.     

The degree of zinc phosphate cement coverage of complete crown preparations and its effect on crown retention.

This investigation examined the amount of retentive area covered by cement under complete coverage crowns and its effect on retention. Sixty crowns of self-cured acrylic resin were prepared on 60 identical brass dies and were divided into six groups of 10 crowns each according to different cement applications. The results showed that retention was dependent on the amount of retentive area covered by the cement. The amount of cement in the occlusal part of the cementation space did not affect retention.     

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.     

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.     

Comparative Evaluation of Bond Strengths of Different Core Materials with Various Luting Agents Used for Cast Crown Restorations

The coronal cast restoration continues to be used commonly to restore mutilated, endodontically treated teeth. The tensile bond strength of luting cements is of critical importance as many of failures are at the core and the crown interface. An invitro study with aim to evaluate and compare bond strengths of luting cements between different core materials and cast crowns. A total of 45 extracted identical mandibular second premolars were endodontically treated and divided into 3 groups of 15 each. Specimens in first group were restored with cast post and core (Group C), and specimens in second group were restored with stainless steel parapost and composite core material (Group B) and specimens in third group were restored with stainless steel parapost and glass ionomer core build (Group G). Standardized crown preparation was done for all the specimens to receive cast crowns. Each group was further divided into 3 subgroups and were cemented using 3 different luting cements namely, resin cement, polycarboxylate cement, glass ionomer cement (Type I). The samples of each subgroup (n = 5) were subjected to tensile testing using Universal Testing Machine at a crosshead speed of 2 mm/min till the dislodgement of crown from the core surface was observed. The bond strengths were significantly different according one way ANOVA (F-150.76 and p < 0.0000). The results of the study showed that the specimens cemented with resin cement in cast core, composite core and glass ionomer core exhibited significantly higher bond strengths as compared to specimens cemented with glass ionomer and polycarboxylate cement. Composite resin core and resin cement combinations were superior to all other cement and core combinations tested.     

A comparative study of retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements with stainless steel crowns - an in vitro study

An in vitro study was conducted to compare the retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements using Instron universal testing machine. Thirty preformed and pretrimmed stainless steel crowns were used for cementation on 30 extracted human primary molars which were divided into three groups of 10 teeth in each group. Then the teeth were stored in artificial saliva and incubated at 37°C for 24 h. A load was applied on to the crown and was gradually increased till the crown showed dislodgement, and then the readings were recorded using Instron recorder and analyzed for statistical significance. The surface area of crown was measured by graphical method. The retentive strength was expressed in terms of kg/cm 2 , which was calculated by the equation load divided by area. Retentive strengths of zinc phosphate (ranged from a minimum of 16.93 to amaximum of 28.13 kg/cm 2 with mean of 21.28 kg/cm 2 ) and glass ionomer cement (minimum of 13.69 - 28.15 kg/cm 2 with mean of 20.69 kg/cm 2 ) were greater than that of polycarboxylate cement (minimum of 13.26 - 22.69 kg/cm 2 with mean of 16.79 kg/cm 2 ). Negligible difference (0.59 kg/cm 2 ) of retentive strength was observed between zinc phosphate (21.28 kg/cm 2 ) and glass ionomer cements (20.69 kg/cm 2 ). Glass ionomer cements can be recommended for cementation of stainless steel crowns because of its advantages and the retentive strength was almost similar to that of zinc phosphate cement.     

A comparative study of retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements with stainless steel crowns--an in vitro study

This study was conducted on 30 extracted human primary molars to assess the retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements. The teeth were embedded in resin blocks and were randomly divided into 3 groups of 10 each. The occlusal surfaces of all teeth were reduced uniformly by 1.0 to 1.5 mm. All mesial, distal undercuts were removed and sharp angles rounded. This was followed by cementing pretrimmed and precontoured stainless steel crowns on each tooth with hand pressure and storing in artificial saliva at 37 degrees C for 24 hours. Retentive strength was tested using Instron Universal Testing Machine. The load was applied starting from a zero reading and gradually increased until the cemented stainless steel crowns showed signs of movement and then the readings were recorded. It was found that retentive strengths of zinc phosphate and glass ionomer cements were statistically better (P < 0.05) when compared to the polycarboxylate cement. Negligible difference (0. 59 kg/cm2) was however observed between zinc phosphate and glass ionomer cements.     

Retentiveness of dental cements used with metallic implant components.

There is limited dental literature evaluating the retentive capabilities of luting agents when used between metal components, such as cast metal restorations cemented onto machined metal implant abutments. This study compared the retentive strengths of 5 different classes of luting agents used to cement cast noble metal alloy crowns to 8-degree machined titanium cementable implant abutments from the Straumann ITI Implant System. Sixty prefabricated 5.5-mm solid titanium implant abutments and implants were used; 30 received the standard surface preparation and the other 30 received an anodized surface preparation. Anodized implant components were used to reflect current implant marketing. Sixty castings were fabricated and randomly paired with an abutment and implant. A total of 12 castings were cemented onto the implant-abutment assemblies for each of the 5 different luting agents (zinc phosphate, resin composite, glass ionomer, resin-reinforced glass ionomer, and zinc oxide-non-eugenol). After cementation, the assemblies were stored in a humidor at room temperature prior to thermocycling for 24 hours. Each casting was pulled from its respective abutment, and the force at which bond failure occurred was recorded as retentive strength. A statistically significant difference was found between the 5 cements at P < or = .001. Of the cements used, resin composite demonstrated the highest mean retentive strength. Zinc phosphate and resin-reinforced glass-ionomer cements were the next most retentive, while glass ionomer and zinc oxide-non-eugenol cements demonstrated minimal retention. In addition, retention was not altered by the use of an anodized abutment surface.     

The Retention of Cast Metal Dowels Fabricated by Direct and Indirect Techniques

Purpose: To explore the effect of fabrication technique, cement type, and cementation procedure on retention of cast metal dowels.
Methods and Materials: Eighty intact single-rooted teeth were selected. The clinical crown was removed at the cementoenamel junction level. Each root was prepared to receive a cast metal dowel of 10-mm length and 1.45 mm in diameter. The 80 specimens were divided into two major groups of 40 based on fabrication technique (direct and indirect). Each group was further divided into four subgroups of ten based on the cement type (zinc phosphate and glass ionomer), and cementation procedure (with and without lentulo spiral). The dowels were subjected to a constantly increasing tensile force, in a universal Instron testing machine, at crosshead speed of 5 mm/min until failure.
Results: The most significant factor to affect retention was the cementation procedure, as cementation with lentulo spiral produced greater retention than cementation without the use of lentulo spiral ( p < 0.05); however, there seems to be a close interaction between fabrication technique, cement type, and cementation procedure ( p = 0.051). The least retentive group was the one fabricated by direct technique, cemented with zinc phosphate without the use of lentulo spiral.
Conclusion: Fabrication technique does not affect retention of cast dowels, except when zinc phosphate was the luting agent and placed in the canal space without using a lentulo spiral. The cementation procedure had a significant effect on retention; thus, it is recommended that cementation should be done using the lentulo spiral.     

Effect of Dentin Sealers on Postoperative Sensitivity of Complete Cast Crowns Cemented with Glass Ionomer Cement

Purpose: The purpose of this study was to clinically evaluate the effects of pretreatments with copal/ether varnish and dentin bonding system on postoperative sensitivity of complete cast crowns cemented with glass ionomer cement. Materials and Methods: Three posterior teeth with no pain symptoms were selected from each of 17 patients, totaling 51 teeth, for which a crown was indicated. Rexillium III complete cast crowns were prepared using conventional laboratory techniques. For each patient, the first tooth, which served as the control, received only glass ionomer cement (Ketac‐Cem). Copal/ether varnish (Bosworth Copaliner) was applied to the second tooth preparation prior to cementation. Dentin bonding agent (OptiBond Solo Plus) was used on the third tooth before cementation. Sensitivity to different stimuli (cold, heat) was assessed at 7 days, 1 month, and 6 months following restorative procedures by questionnaire. Results: There were no statistically significant differences between the three groups regarding applied stimulus and day of the study (p > 0.05). No statistically significant differences were found between the postoperative sensitivity responses from 7 days to 1 month, and from 1 month to 6 months (p > 0.05). Conclusions : Postoperative sensitivity resulting from glass ionomer cement with complete cast crowns cannot be completely eliminated with the prior use of a cavity varnish or bonding agent.     

The retention of complete crowns prepared with three different tapers and luted with four different cements

STATEMENT OF PROBLEM: The role of adhesive properties of cements on the retentive strength of crowns with different degrees of taper is not clear. PURPOSE: This study evaluated the retention of full crowns prepared with 3 different tapers and cemented with 2 conventional and 2 adhesive resin cements. MATERIAL AND METHODS: One hundred twenty sound human molar teeth were assigned randomly to 1 of 12 groups, (n=10). The groups represented the 4 cements: zinc phosphate (Fleck's), a conventional glass ionomer (Ketac-Cem); 2 adhesive resin cements (C&B Metabond and Panavia); and 3 tapers of 6-degrees, 12-degrees, and 24-degrees within each cement. Crowns were cast with a high noble alloy. The 6-degree taper was considered the control within each cement group. Retention was measured (MPa) by separating the metal crowns from the prepared teeth under tension on a universal testing machine. Analysis of variance was used to test the main effects on the retentive strength of full crowns, namely cements, tapers, and failure modes. The Fisher's multiple comparison test was used to evaluate the source of the differences. The chi(2) analyses were used to examine the relationships between failure types, cements, and tapers. All statistical tests were conducted at alpha=.05. RESULTS: There was a significant difference in the main effect cement (P<.0001) and taper (P=.0002). The mean retentive strength values of both Fleck's and Ketac-Cem were significantly lower than the mean retentive strength values of both C&B Metabond and Panavia (P<.0001). The retention of crowns prepared with 6-degree taper was not significant from the 12-degree taper (P=.0666). The difference in retention was significant between the 6-degree taper and the 24-degree taper (P<.0001) and between 12-degree taper and 24-degree taper (P=.0178). The types of failure were adhesive in the cement (65%), cohesive in the tooth (31%), and assembly failure (fracture of embedding resin) (4%). The type of failure was dependent on the degree of taper (P<.0001) and on the type of cement (P<.0042). CONCLUSION: Within the limitations of this study, the retentive values of the adhesive resins at 24-degree taper were 20% higher than the retentive values of the conventional cements at 6-degree taper. The use of resin luting agents yielded retention values that were double the values of zinc phosphate or conventional glass ionomer cement.     

Retrievability of implant‐retained crowns following cementation

Objectives: The purpose of this study was to assess the retrievability of cemented implant crowns using two different removal devices. The influence of five cement types and two cement application techniques was evaluated. Methods: Forty copings were cast from a CoCr alloy for 40 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). Twenty copings were modeled as single crowns, whereas 20 copings were modeled with an extension to simulate fixed partial dentures (FPDs). Before cementation, the inner surfaces of the copings were air‐abraded (50 μm Al₂O₃ particles at 2.5 bars), while the abutments were used as delivered with machined surfaces. Copings were cemented with eugenol‐free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (Ketac Cem), polycarboxylate (Durelon) and so‐called self‐adhesive resin (RelyX Unicem) cement. Cement was applied in a thin film band of 1 or 3 mm to the cervical margin of the inner surface of the copings, respectively. After cementation, specimens were stored in saline solution for 24 h. The Coronaflex and a standardized custom‐made removal device were used to remove the copings from the abutments. Results: Using the same cement, no statistically significant influence with regard to the type of restoration (crown/FDP), cement application mode and device was detected (P>0.05). Therefore, data of specimens cemented with the same cement were pooled. Median attempts to remove the copings were: zinc oxide: 3, self‐adhesive resin: 3, zinc phosphate: 5, glass ionomer: 16 and polycarboxylate: 58. Four levels of significance (P<0.0001) were found: (1) zinc oxide/self‐adhesive resin; (2) zinc phosphate; (3) glass ionomer; and (4) polycarboxylate. Conclusions: Zinc phosphate and glass ionomer cement might be suitable for a so‐called ‘semipermanent’ (=retrievable) cementation, while polycarboxylate seems to provide the most durable cementation.     

Microleakage of core materials for complete cast gold crowns

This study evaluated the microleakage patterns of complete cast-gold crowns cemented onto teeth rebuilt with pin-retained cores made from cast gold, amalgam, composite resin, and silver-reinforced glass ionomer by using three different cements (zinc phosphate, glass ionomer, and resin cement). Crowns cemented onto unrebuilt tooth preparations with zinc phosphate cement served as controls. The cemented specimens were thermocycled between 4 degrees and 50 degrees C in waterbaths. They were then embedded in epoxy resin and sectioned. The extent of marginal microleakage was evaluated with a stereomicroscope and scored. The findings indicated that the type of luting agent used appeared to affect microleakage more than the core material. No significant differences in the degree of microleakage were found under crowns cemented onto teeth rebuilt with the four core materials when cemented with the same luting cement.     

Effects of Tooth Preparation Burs and Luting Cement Types on the Marginal Fit of Extracoronal Restorations

Purpose: Although surface roughness of axial walls could contribute to precision of a cast restoration, it is unclear how the roughness of tooth preparation affects marginal fit of the restoration in clinical practice. The purpose of this study was to describe the morphologic features of dentin surfaces prepared by common rotary instruments of similar shapes and to determine their effects on the marginal fit for complete cast crowns. Materials and Methods: Ninety crowns were cast for standardized complete crown tooth preparations. Diamond, tungsten carbide finishing, and crosscut carbide burs of similar shape were used (N = 30). The crowns in each group were subdivided into three groups (n = 10) for use with different luting cements: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac‐Cem), and adhesive resin cement (Panavia 21). Marginal fit was measured with a light microscope in a plane parallel to the tooth surface before and after cementation between four pairs of index indentations placed at equal distances around the circumference of each specimen. Difference among groups was tested for statistical significance with analysis of variance (ANOVA) followed by Ryan‐Einot‐Gabriel‐Welsch Multiple Range Test (α= 0.05). Results: Analysis of measurements disclosed a statistically significant difference for burs used to finish tooth preparations (p < 0.001); however, luting cement measurements were not significantly different (p= 0.152). Also, the interaction effect was not significantly different (p= 0.685). For zinc phosphate cement, the highest marginal discrepancy value (100 ± 106 μm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (36 ± 30 μm) was for tooth preparations refined with finishing burs. For glass ionomer cement, the highest marginal discrepancy value (61 ± 47 μm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (33 ± 40 μm) was for tooth preparations refined with finishing burs. For adhesive resin cement, the highest marginal discrepancy value (88 ± 81 μm) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (19 ± 17 μm) was for tooth preparations refined with finishing burs. Conclusions: Marginal fit of complete cast crowns is influenced by tooth preparation surface characteristics, regardless of the type of luting agent used for cementation. Tooth preparations refined with finishing burs may favor the placement of restorations with the smallest marginal discrepancies, regardless of the type of cement used.     

The influence of ultrasound on the retention of cast posts cemented with different agents

AIM: The aim of this study was to evaluate the influence of ultrasound during the removal of posts cemented with either zinc phosphate cement, glass ionomer cement or resin cement. METHODOLOGY: Eighty-four single-rooted teeth were prepared and after cementation of cast posts, they were randomly divided into six groups of 14. Group 1, 2 and 3 did not receive ultrasonic vibration, whilst groups 4, 5 and 6 received ultrasonic vibration for 10 min. The force necessary for post removal was determined using a universal testing machine. Results were statistically analysed using ANOVA and Tukey tests (5%). RESULTS: The application of ultrasonic vibration reduced the retention provided by zinc phosphate and glass ionomer cements by 39% and 33%, respectively. CONCLUSIONS: A statistically significant reduction in the force necessary to remove posts cemented with zinc phosphate and glass ionomer cements occurred following application of ultrasound. The application of ultrasonic vibration did not influence the retention of cast posts cemented with resin cement.     

Short-term retention properties of cements for retrievable implant-supported prostheses

This in vitro study compared the retentive ability of 11 materials used to cement cast crowns on one implant system. The crowns were cemented to the abutments and the tensile load necessary to remove each casting was measured 30 minutes after cementation in a dry condition at 22 degrees C and after storage for 72 hours in saline solution at 37 degrees C. The results provide a ranking order of the tested materials according to their ability to retain implant restorations. This information, along with studies that better represent the effect of aging, may assist the clinician in selecting a material that is retentive enough to withstand occlusal forces, yet weak enough to allow easy retrieval of cement-retained implant restorations.