In vitro fracture load of monolithic lithium disilicate ceramic molar crowns with different wall thicknesses

Objectives

The objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns.

Material and methods

Forty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (d?=?0.5, 1.0, and 1.5 mm; n?=?16 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000 cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2 million cycles, Willytec CS3, SD Mechatronik, F _max?=?108 N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0.

Results

Crowns with d?=?1.0 and 1.5 mm wall thickness did not crack during artificial aging whereas two of the crowns with d?=?0.5 mm wall thickness did. The loads to failure (F _u) of the crowns without aging (with aging) were 470.2?±?80.3 N (369.2?±?117.8 N) for d?=?0.5 mm, 801.4?±?123.1 N (889.1?±?154.6 N) for d?=?1.0 mm, and 1107.6?±?131.3 N (980.8?±?115.3 N) for d?=?1.5 mm. For aged crowns with d?=?0.5 mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with d?=?1.0 mm and d?=?1.5 mm wall thickness were not significant.

Conclusions

Fracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (F _u?<?500 N) to guarantee a low complication rate in vivo, whereas all crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances F _u?>?600 N.

Clinical relevance

The wall thickness of posterior lithium disilicate crowns might be reduced to 1 mm, thus reducing the invasiveness of the preparation, which is essential for young patients.     

Fracture resistance of different primary anterior esthetic crowns

Purpose

Investigate and compare fracture resistance of four commercially available esthetic crowns.

Fracture resistance of cingulum rest seats in CAD-CAM tooth-colored crowns for removable partial denture abutments

Statement of problem

The prevalent use of computer-aided design and computer-aided manufacturing (CAD-CAM) for tooth-colored ceramic materials has led to several case reports and retrospective clinical studies of surveyed crowns used to support removable partial dentures. How the specific contour of a cingulum rest seat affects the fracture resistance of these CAD-CAM tooth-colored materials is unknown.

Clinical results of lithium-disilicate crowns after up to 9 years of service

Objectives

The purpose of this prospective study was to evaluate the clinical outcome of anterior and posterior crowns made of a lithium-disilicate glass–ceramic framework material (IPS e.max Press, Ivoclar Vivadent).

Materials and methods

A total of 104 single crowns were placed in 41 patients (mean age, 34?±?9.6 years; 15 male, 26 female). Eighty-two anterior and 22 posterior crowns were inserted. All teeth received a 1-mm-wide chamfer or rounded shoulder preparation with an occlusal/incisal reduction of 1.5–2.0 mm. The minimum framework thickness was 0.8 mm. Frameworks were laminated by a prototype of a veneering material combined with an experimental glaze. Considering the individual abutment preconditions, the examined crowns were either adhesively luted (69.2 %) or inserted with glass–ionomer cement (30.8 %). Follow-up appointments were performed 6 months after insertion, then annually. Replacement of a restoration was defined as failure.

Results

Four patients (10 crowns) were defined as dropouts. For the remaining 94 crowns, the mean observation time was 79.5 months (range, 34–109.7 months). The cumulative survival rate according to Kaplan–Meier was 97.4 % after 5 years and 94.8 % after 8 years. Applying log rank test, it was shown that the location of the crown did not significantly have an impact on the survival rate (p?=?0.74) and that the cementation mode did not significantly influence the occurrence of complications (p?=?0.17).

Conclusions

The application of lithium-disilicate framework material for single crowns seems to be a reliable treatment option.

Clinical relevance

Crowns made of a lithium-disilicate framework material can be used clinically in the anterior and posterior region irrespective of an adhesive or conventional cementation when considering abutment preconditions.     

Fracture behavior of zirconia implant abutments is influenced by superstructure-geometry

Objectives

The purpose of this in vitro study was to evaluate the influence of the superstructure-geometry on the fracture behavior of zirconia abutments (Compartis, DeguDent GmbH, Hanau, G).

Materials and methods

Four different groups (n?=?8) representing anterior single crown replacement were prepared. In groups 1 and 2, the implants were restored with customized all-ceramic abutments and anatomically shaped crowns (chromium cobalt alloy). Groups 3 and 4 received crowns with a geometry according to the international standard ISO 14801 (dynamic fatigue test for endosseous dental implants) with a spherical contact area. Groups 2 and 4 were subjected to mechanical aging in a chewing simulator (50 N?×?1,200,000 cycles). Static loading until fracture was performed using a universal testing device at an angle of 30° to the implant axis. Fracture patterns were analyzed using SEM.

Results

In group 2, only one specimen survived mechanical aging. In group 4, one specimen fractured during the chewing simulation. Groups 1 and 2 showed significantly lower load-bearing capacity than groups 3 and 4. Artificial aging did not influence the fracture resistance. The SEM analysis revealed fatigue-related fracture patterns in those specimens, which failed during artificial aging.

Conclusions

Drawing conclusions from ISO testing concerning clinical performance appears to be critical as anatomic superstructure geometries induce different fracture behaviors.

Clinical relevance

ISO testing of zirconia abutments should be accompanied by load-bearing capacity testing under simulated clinical conditions to predict clinical performance.     

Adhesive restoration of anterior endodontically treated teeth: influence of post length on fracture strength

Objectives

This study aims to evaluate the fracture resistance of endodontically treated anterior teeth restored with crowns made of composite or ceramic and retained without the use of a post (endocrowns) or with posts of 5 mm (short) and 10 mm in length (long).

Material and methods

Forty-eight intact maxillary incisors were selected for the study. After endodontic treatment, the crowns were sectioned 2 mm coronally to the cementoenamel junction provided with a ferrule of 2 mm. The roots were randomly divided into six groups (n?=?8) according to the post length and type of coronary restoration. The crowns were fabricated with the chairside economical restoration of esthetic ceramics system. Group 1 was restored with a 10-mm glass fiber post, composite core, and a full-coverage ceramic crown (LPCer); group 2, with a 5-mm glass fiber post, composite core, and a full-coverage ceramic crown (SPCer); group 3, with a 10-mm glass fiber post, composite core, and a full-coverage composite crown (LPCpr); group 4, with a 5-mm glass fiber post, composite core, and a full-coverage composite crown (SPCpr); and groups 5 (EndoCer) and 6 (EndoCpr) were restored with ceramic and composite endocrowns, respectively. The teeth were then thermomechanically loaded in a chewing machine. After fatigue, the specimens were loaded to fracture. Data were analyzed with ANOVA and chi-square test. Mode of failure was defined as repairable or non-repairable.

Results

Presence of post, post length, and crown material had no significant effect on the fracture resistance. Groups restored with endocrowns presented a higher number of repairable fractures in respect to the other groups.

Conclusions

Presence of a post had no effect on the restorations’ fracture strength.

Clinical relevance

Although this in vitro study has some limitations in respect to its clinical relevance, the restoration of largely destroyed anterior teeth with the use of an endocrown or a short glass fiber post might have advantages over a large glass fiber post.     

Chair-side generated posterior lithium disilicate crowns after 4 years

Objectives

The objective of this prospective clinical study was to evaluate the performance of chair-side generated crowns after 48 months.

Materials and methods

Forty-one posterior full contour crowns made of a machinable lithium disilicate ceramic (e.max CAD LT) were inserted in 34 patients applying a chair-side CAD/CAM technique. One crown per patient was randomly selected for evaluation at baseline, after 6, 12, 24, 36, and 48 months according to modified US Public Health Service criteria.

Results

After a mean observation time of 51 months (min, 48 months; max, 56 months; SD?±?2.3 months), 29 crowns were available for re-examination. Within the observation period, one failure occurred due to a crown fracture after 2.8 years. Four abutment teeth revealed signs of biological complications: Two abutment changed sensibility perception from positive to negative within the first 13 month. Two abutment teeth showed secondary caries below the crown margin, one after the 24, and another after the 48 month recall. Both abutments received cervical adhesive composite fillings. The failure-free rate was 96.3 % after 4 years according to Kaplan–Meier (CI: upper bound, 4.4 years; lower bound, 4.7 years).

Conclusions

Due to the fact that the secondary caries was not caused as a result of an inaccuracy of the crown margins and the endodontic complications were in a normal range, the clinical performance of the crowns was completely satisfying.

Clinical relevance

The chair-side application of lithium disilicate crowns can be recommended.     

Postoperative tooth sensitivity with a new self-adhesive resin cement—a randomized clinical trial

Objectives

This study evaluated and compared sensitivity of teeth after cementation of full-coverage crowns with a new self-adhesive resin cement (SARC). A resin-modified glass ionomer cement (RMGIC) served as control.

Materials and methods

Eighty-eight full-coverage crowns were cemented to vital teeth with either the self-adhesive cement iCem (Heraeus Kulzer; n?=?44) or the RMGIC GC Fuji PLUS (GC, n?=?44). Before preparations, patients were questioned for sensitivity (patient sensitivity, PS). In addition, air was blown for 2 s onto the buccal cementoenamel junction (air sensitivity, AS), and ice spray was applied in the cementoenamel junction area (ice sensitivity, IS). Patient responses were recorded with a visual analog scale. After cementation of the crowns, patients were recalled for follow-up (f/u) visits at 1 day, 1 week, and 3 weeks. PS, AS, and IS were recorded during each visit. Data were analyzed with Mann–Whitney U tests.

Results

The two groups revealed comparable sensitivity scores at baseline. SARC showed significantly lower PS sensitivity scores at 1 day (p?=?0.02) and significantly lower AS scores at 1-week follow-up (p?=?0.01). IS generally produced the highest sensitivity scores with SARC revealing significantly lower scores at all follow-up visits.

Conclusion

Cementation of crowns with the SARC tested in this study resulted in overall lower postoperative sensitivity than with the RMGIC.

Clinical relevance

Among other clinical advantages, some self-adhesive resin cements seem to lower postoperative sensitivity of crowned teeth.     

Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns

The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments (ZirDesign?; Astra Tech, Mölndal, Sweden) supporting anterior single crowns (SCs). Four different test groups (n?=?8) representing anterior SCs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (left central incisor) from a prosthetic point of view, which allows for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position, requiring an angulated (20°) abutment. OsseoSpeed? implants (Astra Tech) 4.5 mm in diameter and 13 mm in length were used to support the abutments. The SCs (chromium cobalt alloy) were cemented with glass ionomer cement. Groups 2 and 4 were thermomechanically loaded (TCML?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. All samples tested survived TCML. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the groups with straight abutments or the groups with angulated abutments. The restorations that utilized angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1, 280.25?±?30.45 N; group 2, 268.88?±?38.00 N; group 3, 355.00?±?24.71 N; group 4, 320.71?±?78.08 N). This difference in load-bearing performance between straight and angulated abutments was statistically significant (p?=?0.000) only when no artificial aging was employed. The vast majority of the abutments fractured below the implant shoulder.     

Retention and surface changes of zirconia primary crowns with secondary crowns of different materials

Objectives

To evaluate zirconia as a substitute for gold alloy in primary crowns facing secondary crowns manufactured with different materials, in terms of long-term retention force changes, wear, and phase transformation was aimed.

Materials and Methods

A total of 12 groups, each containing six samples, consisting of gold alloy primary crown-electroformed gold secondary crowns (AA), zirconia primary crown-electroformed gold secondary crowns (ZA) and zirconia primary crown-casted non-precious alloy secondary crowns (ZC) with conus angles of 0°, 2°, 4°, and 6° were evaluated. Samples were subjected to 10,000 insertion–separation cycles in artificial saliva and retention force was measured. X-ray diffraction and scanning electron microscope analysis were performed on the sample surfaces.

Results

The highest retention forces were obtained from ZC-0° group (72.09–71.26 N) and the lowest were obtained from ZA-4° (12.73–19.44 N) and ZA-6° (5.36–19.73 N) groups in the beginning and after 10,000 cycles, respectively. Retention force increased as the conus angle decreased. The monoclinic phase ratio of the zirconia primary crowns decreased after the experiments. No wear was observed in zirconia primary crowns except for the ZC-0° and ZC-2° groups. The use of zirconia primary crowns resulted in a less excursive retention force.

Conclusions

A more predictable and less excursive retention force can be obtained using a hard and rigid primary crown material like zirconia.

Clinical Relevance

Despite a lack of knowledge about the aging of zirconia without a veneer layer in the oral environment, zirconia primary crowns are more advantageous in terms of retention force development and wear.     

Survival rate of approximal-ART restorations using a two-layer technique for glass ionomer insertion

Objective

Good survival rates (SR) have been reported for occlusal-atraumatic restorative treatment (ART) restorations but not for approximal-ART restorations. The high-viscosity consistency of the glass ionomer cement (GIC) may lead to its incorrect adaptation into the cavity and thus to failure of the restoration. Because the use of a flowable GIC layer seemed to improve its adaptation in approximal restorations in vitro, we evaluated whether the use of an intermediate flowable GIC layer would improve the SR of approximal-ART restorations.

Methods

A total of 208 children (6–7 years old) with at least one occluso-proximal carious lesion in a primary molar were selected and randomly allocated to two groups: G1, conventional technique, one-layer GIC (powder/liquid ratio 1:1); and G2, two-layer technique, consisting of a first layer of GIC with a flowable consistency (powder/liquid ratio 1:2) and a second layer of a regular consistency. Restorations were made by final-year students and evaluated after 1, 6, 12 and 18 months. Restoration survival was evaluated using Kaplan–Meier survival and logrank test. Poisson regression analyses (α?=?5) were used to verify the influence of factors such as insertion technique, restoration surface and operators.

Results

The overall SR of the restorations after 18 months was 68 %. There was no difference in SR between the techniques, neither did the other factors influence the SR.

Conclusions

Over 18 months, the use of an intermediate flowable GIC layer in approximal-ART restorations does not improve the restoration survival.

Clinical relevance

This study suggests that the two-layer technique is not the answer for increasing approximal-ART restoration longevity.     

Concentrations of amoxicillin and clindamycin in teeth following a single dose of oral medication

Objectives

The main purpose of this study is the detection of amoxicillin and clindamycin concentrations in teeth.

Materials and methods

Eleven patients received 2 g of amoxicillin, and 11 patients received 600 mg of clindamycin in a single dose of oral medication at least 60 min prior to tooth extraction due to systemic diseases. The concentrations were determined in crowns and roots separately using liquid chromatography–tandem mass spectrometry (LC-MS-MS).

Results

Amoxicillin (13 samples) and clindamycin (12 samples) were detected in the samples of the root and crown preparations of the extracted teeth. The mean concentration of amoxicillin was 0.502 μg/g in the roots and 0.171 μg/g in the crowns. The mean concentration of clindamycin was 0.270 μg/g in the roots and 0.064 μg/g in the crowns.

Conclusions

A single dose of oral amoxicillin and clindamycin leads to concentrations of both antibiotics in teeth which exceed the minimal inhibition concentration of some oral bacteria.

Clinical relevance

The proof of antibacterial activity in dental hard tissue after oral single-dose application is new. The antimicrobial effect of amoxicillin and clindamycin concentrations in roots of teeth may be of clinical relevance to bacterial reinfection from dentinal tubules.     

Wear behavior of different double-crown systems

Objectives

The aim of this study was to evaluate aging effects on the retentive forces (RFs) of different double-crown systems. The effects of abutment height, inner- and outer-crown-material, taper angle, and artificial aging were analyzed.

Material and methods

Inner (IC) and outer crowns (OC) (240), divided into four groups, 60 specimens each, were manufactured: A: IC?=?zirconia, OC?=?electroformed; B: IC?=?non-precious alloy, OC?=?electroformed; C: IC?=?precious alloy, OC?=?electroformed; D: IC?=?precious alloy, OC?=?conventionally cast (control group). Ten specimens each with three different abutment heights and two different tapers were used. Ten thousand separation cycles were performed for each specimen, and the RFs were measured at baseline, 5,000, and 10,000 cycles in the presence of artificial saliva. Data were imported into a statistical software (SPSS, V18) and analyzed by a multivariate ANOVA test. Significance level was set at 5 %.

Results

Group D showed highest RFs (baseline: 4.0 N; 5,000 cycles: 3.9 N; 10,000 cycles: 3.9 N) compared to A, B, and C (baseline: 2.6/3.5/2.6 N; 5,000 cycles: 2.5/3.4/2.5 N, 10,000: 2.5/3.3/2.5 N). RF was dependent on material (p?<?0.001). The RF of groups A, B, and C were dependent on abutment height (p?<?0.001), taper angle (p?<?0.001), and artificial aging (p?<?0.001). Group D showed no correlation between retentive force and abutment height (p?=?0.550).

Conclusions

Wear caused loss of RF in all evaluated groups. However, the material used exhibited significant influence. Conventionally, cast DCs can provide higher RFs, and electroformed DCs can provide more predictable results.

Clinical relevance

In clinical cases with few and short abutment teeth, conventionally cast DCs can rather provide the necessary RF than electroformed DCs.     

Does an intracanal composite anchorage replace posts?

Objectives

This study aims to assess the effectiveness of an intracanal composite anchorage to replace conventionally cemented titanium or bonded glass fibre posts.

Materials and methods

Post space preparation was performed up to depths of 6 mm (groups 1 and 2) and 3 mm (group 3) in root filled mandibular premolars. In group 1, titanium posts were cemented with zinc phosphate cement. Glass fibre posts were adhesively cemented in group 2 using a dual-cure composite resin. In group 3, intracanal anchorage was solely performed with a dual-cure composite. All teeth were restored with standardised direct composite crowns without a ferrule. After thermo-mechanical loading, static load was applied until failure. Fracture patterns were assessed, and a microscopic analysis was performed to analyse the occurrence of additional cracks.

Results

Group 2 revealed a significantly higher median fracture value (408 N) than groups 1 and 3, while no difference was detected between group 1 (290 N) and group 3 (234 N) (p?=?.1417). In group 3, the more favourable fracture patterns were observed. However, the majority of teeth within this fracture category revealed additional minor cracks of the root.

Conclusions

Within the limitations of this study, adhesive intracanal anchorage to a depth of 3 mm with resin composite only has the same fracture resistance as titanium posts conventionally cemented to a depth of 6 mm. Even teeth with repairable main fractures exhibited additional dentinal cracks on the root.

Clinical relevance

Additional dentinal root cracks in the teeth with repairable main fractures may considerably impair their longevity.     

Radiotherapy does not impair dentin adhesive properties in head and neck cancer patients

Objectives

This study evaluated the influence of radiotherapy on the dentin bond strength of teeth extracted from patients who had undergone head and neck radiotherapy.

Materials and methods

A total of 36 samples were divided into two experimental groups: group I (control group, n?=?18) and group II (in vivo irradiated group, n?=?18). Groups I and II were further separated into three subgroups (six specimens per subgroup), which were further assigned to the three adhesive system protocols employed: Single Bond 2 (SB) (3M ESPE), Easy Bond (EB) (3M ESPE) and Clearfil SE Bond (CSE) (Kuraray). The adhesive systems were applied to the prepared surface according to the manufacturers’ instructions and restored using composite resin (Filtek Supreme, 3M ESPE). After 24 h in deionised water (37^oC), teeth were horizontally and vertically cut to obtain beam specimens with a cross-section area of 0.8?±?1.0 mm². Specimens were tested in tension using a universal testing machine at a cross-speed of 0.5 mm/min. Fracture patterns were observed under SEM. Data was analysed by two-way analysis of variance (p?≤?0.05).

Results

No statistically significant difference was found between the irradiated (R/SB?=?44.66?±?10.12 MPa; R/EB?=?41.48?±?12.71 MPa; and R/CSE?=?46.01?±?6.98 MPa) and control group (C/SB?=?39.12?±?9.51 MPa; C/EB?=?42.40?±?6.66 MPa; and C/CSE?=?36.58?±?7.06 MPa) for any of the adhesive systems. All groups presented a predominance of mixed fracture modes.

Conclusion

Head and neck radiotherapy did not affect dentin bond strength for the adhesive materials tested in this study.     

Comparison of biogenerically reconstructed and waxed-up complete occlusal surfaces with respect to the original tooth morphology

Objectives

Recently, it has become possible to reconstruct complete occlusal surfaces using the biogeneric tooth model. This study aimed to mathematically assess and compare the morphologic agreement between original morphology and CAD-reconstructed, waxed-up and CAM partial crowns.

Materials and methods

Thirty-nine intact first permanent molars (39 participants) were included. Impressions, bite registrations and three gypsum replicas were made. Preparations for CAD/CAM partial crowns were performed and scanned. The restorations were biogenerically reconstructed (CEREC® v3.80) and milled. Wax-ups of these preparations were scanned as well as the milled restorations and original teeth. Discrepancies were evaluated by matching the scans with the original morphologies (Match3D, output: volume/area, z difference) and by contact patterns. The discrepancies were compared between CAD-reconstructions and either wax-ups or milled restorations (paired t test, α?=?0.025 for two multiple tests).

Results

The mean differences between natural tooth morphology (triangular stabilisation 71.8 %) and biogeneric reconstructions, wax-ups and milled restorations (triangular stabilisation 87.2 %) were: 184?±?36 μm (volume/area), 187?±?41 μm (z difference); 263?±?40 μm (volume/area), 269?±?45 μm (z difference) and 182?±?40 μm (volume/area), 184?±?41 μm (z difference). Differences associated with biogeneric reconstructions were significantly less than those of wax-ups (volume/area and z difference, p?<?0.0001), but not significantly different than those of milled restorations (p?=?0.423 (volume/area), p?=?0.110 (z difference)).

Conclusions

CAD software enables a closer reconstruction of teeth than do wax-ups, even when no cusps remain. The milling device is precise enough to transfer CAD into the final restoration.

Clinical relevance

This study shows that state of the art CAD/CAM can effectively produce natural tooth morphology and may be ideal for fixed partial dentures.     

Clinical evaluation comparing the fit of all-ceramic crowns obtained from silicone and digital intraoral impressions

Objectives

The aim of this study is to compare the fit of all-ceramic crowns fabricated from conventional silicone impressions with the fit of all-ceramic crowns fabricated from intraoral digital impressions.

Methods

Twenty patients with 26 posterior teeth with a prosthetic demand were selected for the study. Two crowns (Straumann-Zerion) were made for each preparation. One crown was fabricated from an intraoral digital impression system (IDI group; Cadent-iTero), and the other crown was fabricated from a conventional one-step silicone impression (CI group; Express Penta Putty and Body Light). To replicate the interface between the crown and the preparation, each crown was cemented on its corresponding clinical preparation with ultra-flow silicone (Express Ultra Light Body). Each crown was embedded in resin to stabilize the registered interface, cut in 2-mm-thick slices in a buco-lingual orientation. Internal misfit was measured in microns using stereomicroscopy with a magnification of ×40. Measurements were taken at different landmarks: margin, chamfer angle, axial, crest, and occlusal fosse. After checking for normality, data was analyzed using paired Student’s t test (α?=?0.05).

Results

Fit values were significantly affected by the impression technique (p?=?0.000). Mean internal misfit and mean marginal misfit were 111.40 μm (SD?=?54.04)/80.29 μm (SD?=?26.24) for the crowns of the IDI group and 173.00 μm (SD?=?92.65)/133.51 μm (SD?=?48.78) for the CI group.

Conclusion

All-ceramic crowns fabricated from intraoral digital impressions with parallel confocal technology demonstrated a clinically acceptable internal and marginal fit as conventional impression.

Clinical significance

Intraoral digital impressions as initial step to the digital workflow could further improve the marginal adaptation of all ceramic single crowns.

Trial registration

http://www.isrctn.com/ISRCTN16111844

     

Fluoride release and mechanical properties after 1-year water storage of recent restorative glass ionomer cements

Objectives

The objective of this study was to evaluate the relationships between fluoride release and mechanical properties after 1-year water storage of five recent restorative glass ionomer cements (GICs).

Materials and methods

Five GICs, FujiIX GP EXTRA (FEX), FujiIX GP (FIX), GlasIonomer FX-II (GFX), Ketac Molar Easymix (KME), and Riva Self Cure (RSC), were examined. Cumulative fluoride release, compressive strength, and surface hardness were measured up to 1-year storage (n?=?5), and analyzed with one-way or two-way ANOVA and Tukey HSD test (α?=?0.05). Elemental compositions before and after 1-year storage were also examined (n?=?3).

Results

The amounts of fluoride release were significantly different among the products. The highest amount of fluoride release occurred during the first day. Then, the amount of fluoride release rapidly decreased and still continued until 1-year storage. Compressive strengths indicated that two main factors were significant (GFX?<?FEX?=?RSC?<?FIX?<?KME; 1 day?<?1 week?=?1 month?=?3 months?=?6 months?=?1 year), but surface hardness showed a slightly different tendency (GFX?=?RSC?<?FEX?=?FIX?=?KME; 1 year?<?1 day?<?1 week?=?1 month?=?3 months?=?6 months). Significant correlation was found between decrease of silicon and decrease rate of the surface hardness.

Conclusions

Fluoride releases were detected up to 1-year storage, but the mechanical properties slightly decreased due to decrease of Si after 1-year storage. Elution of Si instead of fluoride release was considered more critical to deteriorate the mechanical properties of GICs.

Clinical relevance

Fluoride released for 1-year water storage will contribute to secondary caries prevention. The amount of fluoride release did not affect these mechanical properties. These results indicate the usefulness of these GICs.     

Are implants more reliable than severely compromised endodontically treated teeth as abutments for zirconia-based FPDs?

Objectives

The aim was to study the impact of the defect size of endodontically treated incisors compared to dental implants as abutments on the survival of zirconia two-unit anterior cantilever-fixed partial dentures (2U-FPDs) during 10-year simulation.

Materials and methods

Human maxillary central incisors were endodontically treated and divided into three groups (n?=?24): I, access cavities rebuilt with composite core; II, teeth decoronated and restored with composite; and III as II supported by fiber posts. In group IV, implants with individual zirconia abutments were used. Specimens were restored with zirconia 2U-FPDs and exposed to two sequences of thermal cycling and mechanical loading. Statistics: Kaplan–Meier; log-rank tests.

Results

During TCML in group I two tooth fractures and two debondings with chipping were found. Solely chippings occurred in groups II (2×), IV (2×), and III (1×). No significant different survival was found for the different abutments (p?=?0.085) or FPDs (p?=?0.526). Load capability differed significantly between groups I (176 N) and III (670 N), and III and IV (324 N) (p?<?0.024).

Conclusion

Within the limitations of an in vitro study, it can be concluded that zirconia-framework 2U-FPDs on decoronated teeth with/without post showed comparable in vitro reliability as restorations on implants. The results indicated that restorations on teeth with only access cavity perform worse in survival and linear loading.

Clinical relevance

Even severe defects do not justify per se a replacement of this particular tooth by a dental implant from load capability point of view.     

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PURPOSE

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method.

MATERIALS AND METHODS

An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture.

RESULTS

The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly.

CONCLUSION

The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.