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.     

Long-term performance of posterior InCeram Alumina crowns cemented with different luting agents: a prospective,randomized clinical split-mouth study over 5 years

Objectives

This prospective, randomized clinical split-mouth study investigated the 5-year performance of InCeram Alumina posterior crowns cemented with three different luting cements. 4-META- and MDP-based cements were used for adhesive luting. Glass ionomer cement served as control.

Materials and Methods

Sixty patients were treated with 149 (n?=?62 Panavia F/MDP; n?=?59 SuperBond-C&B/4-META; n?=?28 Ketac Cem/glass ionomer) InCeram Alumina crowns on vital molars and premolars in a comparable position. Follow-up examinations were performed annually up to 5 years after crown placement using the modified United States Public Health Service (USPHS) criteria. Kaplan–Meier survival analysis comprised secondary caries, clinically unacceptable fractures, root canal treatment and debonding. Kaplan–Meier success rate included restorations with minimal crevices, tolerable color deviations (<1 Vitashade), and clinically acceptable fractures. Logistic regression models with a random intercept were fitted.

Results

The 5-year Kaplan–Meier survival probabilities were: SuperBond-C&B 88.7 %, Panavia F 82.8 %, Ketac Cem 80.1 % with no significant difference (p?=?.813). Endodontical treatment was carried out on 7.4 % of all abutment teeth, and 5.4 % revealed secondary caries. Unacceptable ceramic fractures were observed in 7.4 %. Debonding was a rare complication (1.3 %). The 5 year Kaplan–Meier success rate was 91.6 % for SuperBond-C&B-, 87.4 % for Ketac Cem- and 86.3 % for Panavia F-bonded restorations with no significant difference (p?=?.624). All cement types showed significant marginal deterioration over time (p?<?.0001).

Conclusions

Posterior InCeram Alumina crowns showed acceptable long-term survival and success rates independent of luting agent used. Ceramic fractures, endodontical treatments and secondary caries were the most frequent failures.

Clinical relevance

Glass-infiltrated Alumina crowns in combination with adhesive as well as conventional cementation can be considered as a reliable treatment option in posterior teeth.     

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.     

Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns

Objective

The aim of this study was the evaluation of preparations from general dental practitioners for zirconia crowns and their correlation with clinical recommendations using a digital approach.

Material and method

Seventy-five datasets of left first upper molars (FDI 16) prepared for single zirconia crowns by general dental practitioners were analyzed using a computer-aided design software (LAVA^TM Design; 3M ESPE, Seefeld, Germany) and a 3D-inspection software (COMETinspect®plus version 4.5; Steinbichler Optotechnik, Neubeuern, Germany). Evaluated parameters were convergence angle, undercuts, interocclusal reduction, abutment height, and design of preparation margin.

Results

The mean convergence angle was determined to be 26.7°. The convergence angle in the mesiobuccal to distopalatal dimension was significantly the highest (31.7°), and the abutment height showed a mean value of 4.1 mm. Convergence angle and abutment height showed a negative correlation. Seventy-three percent of the evaluated locations revealed a margin design conforming to ceramic restorations. In over 30 % of the cases, the interocclusal reduction was insufficient. Generally, no preparation fulfilled all recommendations. Five (6.66 %) of the preparations fulfilled four criteria, 16 (21.33 %) preparations fulfilled three criteria, 31 (41.33 %) fulfilled two criteria, 17 (22.66 %) preparations fulfilled one criterion, and 6 (8 %) fulfilled no criterion.

Conclusions

Within the limitations of this study, most general dental practitioners seem to have difficulties fulfilling all clinical recommendations given for the preparation of zirconia crowns. The presented digital approach seems to be a useful method to evaluate the preparation geometry.

Clinical relevance

The correct preparation geometry represents an important prerequisite for the success of all-ceramic full crowns. As preparations clearly need to be improved, the approach presented could be the basis of a future tool to increase preparation quality in practice and education by direct objective feedback.     

Retention forces of 14-unit zirconia telescopic prostheses with six double crowns made from zirconia—an in vitro study

Objectives

The aim of this study was to evaluate the retention forces (RFs) of zirconia double-crown systems, with primary and secondary crowns made from zirconia in vitro.

Materials and methods

Ten maxillary models with six abutment teeth were prepared. Sixty inner crowns were fabricated from pre-sintered zirconia with a taper of 0°. Ten 14-unit telescopic prostheses (removable partial dentures, RDPs) were fabricated, using the same computer-aided design/computer-aided manufacturing system as that used for the inner crowns. The removal test was performed in a standardized setup using a universal testing device at a crosshead speed of 10 mm/min. Ten separation cycles were carried out for each single primary crown as well as for each 14-unit RDP in the presence of artificial saliva. The results were imported into a statistic program and analysed by a one-way ANOVA and post hoc tests. The level of significance was set at 5 %.

Results

The mean RFs of the single double-crown systems were in the range of 0.611–2.895 N, whereas the RFs for the whole RDP varied between 8.1 and 13.6 N. RF was dependent on the abutment tooth (p?<?0.001) and on the model (p?<?0.001).

Conclusions

The results of this study indicate that the manufacturing of full-zirconia double-crown systems is possible as well as reproducible. The RFs are comparable to those reported from casted and electroformed double-crown systems.

Clinical relevance

It has been shown that the RFs of the presented telescopic system are comparable to existing double-crown systems.     

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.     

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.     

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.     

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.     

Biomechanical effects of the implant material and implant–abutment interface in immediately loaded small-diameter implants

Objective

Small-diameter implants have been available since the 1990s, but few studies have analyzed their mechanical properties. This study evaluated the effects of the implant material and the implant–abutment connection designs on the primary stability and the marginal bone strain of small-diameter implant subject to immediate loading.

Materials and methods

Insertion torque value (ITV), implant stability quotient (ISQ), and Periotest value (PTV) of three implant systems with four parameters (titanium, titanium alloy, internal and external hexagon connections) were measured after placing implants into artificial type 2 jaw-bone models. Specimens were tested under both vertical and oblique static loads at 190 N. Peak values of the principal bone strain were recorded and analyzed statistically by the Kruskal–Wallis test and multiple-comparisons Bonferroni test.

Results

PTV and ISQ were higher for the NIOSM311 (internal-hex and Ti alloy) and FOSM311 (external-hex and pure Ti) implants, respectively, than for the NOSM311 (external-hex and Ti alloy) implant. Under vertical loading the peak value of peri-implant bone strains did not differ significantly among these three implant systems. However, the peak bone strains were at least 32 % lower for the NIOSM311 and FOSM311 implants than for the NOSM311 implant under lateral loading.

Conclusions

The implant material and the implant–abutment connection design significantly influence the peri-implant bone strain of immediately loaded small-diameter implants, but barely affect their primary stability.

Clinical Relevance

A commercially pure titanium implant with an internal connection has the potential to reduce the risk of implant failure of small-diameter implant related to biomechanical complications.     

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.     

Reliability and failure modes of narrow implant systems

Objectives

Narrow implants are indicated in areas of limited bone width or when grafting is nonviable. However, the reduction of implant diameter may compromise their performance. This study evaluated the reliability of several narrow implant systems under fatigue, after restored with single-unit crowns.

Materials and methods

Narrow implant systems were divided (n = 18 each), as follows: Astra (ASC); BioHorizons (BSC); Straumann Roxolid (SNC), Intra-Lock (IMC), and Intra-Lock one-piece abutment (ILO). Maxillary central incisor crowns were cemented and subjected to step-stress accelerated life testing in water. Use level probability Weibull curves and reliability for a mission of 100,000 cycles at 130- and 180-N loads (90 % two-sided confidence intervals) were calculated. Scanning electron microscopy was used for fractography.

Results

Reliability for 100,000 cycles at 130 N was ～99 % in group ASC, ～99 % in BSC, ～96 % in SNC, ～99 % in IMC, and ～100 % in ILO. At 180 N, reliability of ～34 % resulted for the ASC group, ～91 % for BSC, ～53 % for SNC, ～70 % for IMC, and ～99 % for ILO. Abutment screw fracture was the main failure mode for all groups.

Conclusions

Reliability was not different between systems for 100,000 cycles at the 130-N load. A significant decrease was observed at the 180-N load for ASC, SNC, and IMC, whereas it was maintained for BSC and ILO.

Clinical relevance

The investigated narrow implants presented mechanical performance under fatigue that suggests their safe use as single crowns in the anterior region.

     

Why,when, and how general practitioners restore endodontically treated teeth: a representative survey in Germany

Objective

The purpose of this study was to assess current opinions, applied techniques, and materials for the restoration of endodontically treated teeth (ETT) in a nationwide survey in Germany.

Material and methods

Completed questionnaires from 1,648 dentists were returned (response rate 63 %).

Results

In general, posts were reported to be used more frequently (51 %) for indirect restorations than for direct restorations (21 %). Dentists restored anterior teeth (65 %) more frequently with direct restorations than posterior teeth (48 %). Compared to an earlier survey, fewer dentists stated that posttreatment stabilizes the remaining tooth structure. The ferrule effect as a key success factor was held by the vast majority of dentists (88 %). A trend towards adhesive techniques both for post placement and core build-up was observed. Composite resins (49 %) were reported to be used twice as much as zinc phosphate cement (24 %) for the luting of posts; composite resins were the core build-up material of choice (75 %). Amalgam was rarely used (0.2 %). Irrespective of the final restoration, fiber posts were the most popular post material (46 % for telescopic crowns vs. 69 % for single crowns).

Conclusion

Adhesive composite core build-ups with and without fiber posts were the predominant treatment approach to restore ETT in Germany. There was widespread agreement with the ferrule effect as a key restorative success factor for indirect restorations.

Clinical significance

Today, it is general accepted that ferrule preparation is key. Glass-fiber posts appear to be most popular. Still different systems are used depending on type of final restoration, while the reasons to do so remain unclear.

     

Influence of conventional and digital intraoral impressions on the fit of CAD/CAM-fabricated all-ceramic crowns

Objectives

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

Thirty patients with 30 posterior teeth with a prosthetic demand were selected. Zirconia-based ceramic crowns were made using an intraoral digital impression system (Ultrafast Optical Sectioning technology) (digital group, D) and 2-step silicone impression technique (conventional group, C).To replicate the interface between the crown and the preparation, each crown was cemented on its corresponding clinical preparation using ultra-flow silicone. Each crown was embedded in resin to stabilize the registered interface. Specimens were sectioned in buccolingual orientation, and internal misfit was measured at different areas using stereomicroscopy (×40).Data was analysed using Student’s t test and Mann-Whitney test (α = 0.05).

Results

No statistically significant differences were found (P > 0.05) between two groups. The mean internal misfit and mean marginal misfit were 170.9 μm (SD = 119.4)/106.6 μm (SD = 69.6) for group D and 185.4 μm (SD = 112.1)/119.9 μm (SD = 59.9) for group C.

Conclusion

Ceramic crowns fabricated using an intraoral scanner are comparable to elastomer conventional impressions in terms of their marginal and internal fits. The mean marginal fit in both groups was within the limits of clinical acceptability.

Clinical significance

Impressions based on Ultrafast Optical Sectioning technology can be used for manufacturing ceramic crowns in a normal workflow, with the same results as silicone conventional impressions.

     

Investigation of bone conditions for orthodontic anchorage plates in the anterior mandible

Objectives

The clinical success of orthodontic anchorage plates depends on the stability of the miniscrews used for fixation. For good stability, the application site must provide bone of good quantity and quality. This study was performed to analyze bone quantity for orthodontic anchorage plates in the anterior mandible.

Patients and methods

A total of 51 computed tomography (CT) scans of fully dentate patients (mean age 24.0±8.1 years; 27 men and 24 women) were evaluated. Measurements were taken to analyze the total orovestibular and vestibular cortical thickness of the mandibular jawbone at different anterior locations and levels.

Results

Vestibular cortical thickness is generally thinnest within the incisor area on the apex level. Its thickness increases in basal and distal directions. The total orovestibular thickness is also the least on the level of the anterior mandibular apices, becoming thicker toward more basal levels and the posterior teeth.

Conclusion

We can reasonably assume that the stability of anchorage plates can be optimized by selecting a position well basal to the apices of the lower incisors, as this area offers enhanced cortical and total jawbone thickness.     

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.     

Influence of cusp inclination and curvature on the in vitro failure and fracture resistance of veneered zirconia crowns

Objectives

The aim was to investigate the influence of cusp inclinations and curvatures on the failure behaviour and fracture resistance of veneered zirconia crowns.

Materials and methods

Five groups (n?=?8/group) of zirconia-based molar crowns were fabricated by modifying cusp inclination (S, steep?=?45°; M, medium?=?30°; F, flat?=?10°) and curvature (P, pointed; R, round; O, round-oblate). Combinations MP, MR, SP, SR and FO were investigated. All crowns were fixed on polymethylmethacrylate teeth, thermally cycled and mechanically loaded. Failures were monitored and fracture resistance was determined after ageing. Crowns were fractographically analysed with scanning electron microscopy.

Results

Chipping during thermal cycling and mechanical loading (TCML) was observed in groups MR (1×), SP (6×) and SR (3×). Defect sizes varied between 0.12 mm² (MR) and 17.28 mm² (SP). Failures started from occlusal contacts. Mean fracture varied significantly between 1,354.2?±?360.0 N (SR) and 3,155.8?±?444.4 N (FO).

Conclusions

Cusp inclination and curvature influenced failures during TCML and fracture loads. Crowns with medium cusp inclination and pointed or round curvature are recommended for clinical application as they revealed high resistance to chipping. Steep inclination, especially in combination with pointed curvature, was shown to increase chipping rates and areas and to decrease fracture force.

Clinical relevance

The results show the necessity of considering design parameters of the veneer in order to reduce failures of zirconia-based crowns.     

Accuracy of digital and conventional impression techniques and workflow

Objectives

Digital impression techniques are advertised as an alternative to conventional impressioning. The purpose of this in vitro study was to compare the accuracy of full ceramic crowns obtained from intraoral scans with Lava C.O.S. (3M ESPE), CEREC (Sirona), and iTero (Straumann) with conventional impression techniques.

Materials and methods

A model of a simplified molar was fabricated. Ten 2-step and 10 single-step putty-wash impressions were taken using silicone impression material and poured with type IV plaster. For both techniques 10 crowns were made of two materials (Lava zirconia, Cera E cast crowns). Then, 10 digital impressions (Lava C.O.S.) were taken and Lava zirconia crowns manufactured, 10 full ceramic crowns were fabricated with CEREC (Empress CAD) and 10 full ceramic crowns were made with iTero (Copran Zr-i). The accessible marginal inaccuracy (AMI) and the internal fit (IF) were measured.

Results

For AMI, the following results were obtained (mean?±?SD): overall groups, 44?±?26 μm; single-step putty-wash impression (Lava zirconia), 33?±?19 μm; single-step putty-wash impression (Cera-E), 38?±?25 μm; two-step putty-wash impression (Lava zirconia), 60?±?30 μm; two-step putty-wash impression (Cera-E), 68?±?29 μm; Lava C.O.S., 48?±?25 μm; CEREC, 30?±?17 μm; and iTero, 41?±?16 μm. With regard to IF, errors were assessed as follows (mean?±?SD): overall groups, 49?±?25 μm; single-step putty-wash impression (Lava zirconia), 36?±?5 μm; single-step putty-wash impression (Cera-E), 44?±?22 μm; two-step putty-wash impression (Lava zirconia), 35?±?7 μm; two-step putty-wash impression (Cera-E), 56?±?36 μm; Lava C.O.S., 29?±?7 μm; CEREC, 88?±?20 μm; and iTero, 50?±?2 μm.

Conclusions

Within the limitations of this in vitro study, it can be stated that digital impression systems allow the fabrication of fixed prosthetic restorations with similar accuracy as conventional impression methods.

Clinical relevance

Digital impression techniques can be regarded as a clinical alternative to conventional impressions for fixed dental restorations.     

In vitro comparison of implant- versus gingiva-supported removable dentures in anterior and posterior applications

Objectives

Removable dentures with different denture teeth may provide different performance and resistance in implant and gingival situations, or anterior and posterior applications.

Materials and methods

Two situations of removable dentures were investigated: gingiva (flexible) and implant (rigid) bearing. For simulating the gingiva/jaw situation, the dentures were supported with flexible lining material. For the implant situation, implants (d?=?4.1 mm) were screwed into polymethylenmethacrylate (PMMA) resin. Two commercial (Vita-Physiodens MRP, SR Vivodent/Orthotyp DCL) and two experimental materials (EXP1, EXP2) were investigated in anterior (A) and posterior (P) tooth locations. Chewing simulation was performed, and failures were analyzed (microscopy, SEM). Fracture strength of surviving dentures was determined.

Results

Only EXP1 revealed failures during chewing simulation. Failures varied between anterior and posterior locations, and between implant (P:4x; A:7x) or gingiva (P:1x; A:2x) situations. Kaplan-Meier log-rank test revealed significant differences for implant situations (p?<?0.002), but not for gingiva bearing (p?>?0.093). Fracture testing in the implant situation provided significantly highest values for EXP2 (1476.4?±?532.2 N) in posterior location, and for DCL (1575.4?±?264.4 N) and EXP2 (1797.0?±?604.2 N) in anterior location. For gingival bearing, significantly highest values were found for DCL/P (2148.3?±?836.3 N), and significantly lowest results for EXP1/A (308.2?±?115.6 N). For EXP1?+?EXP2?+?Vita/P and for EXP1/A no significant differences were found between implant- or gingiva-supported situations.

Conclusions

Anterior and posterior teeth showed different material-dependent in vitro performance, further influenced by implant/gingiva bearing. While an implant in anterior application increased fracture strength of two materials, it decreased fracture values of 3/4 of the materials in posterior application.

Clinical relevance

Survival of denture teeth may be influenced by material, oral position, and bearing situation.

     

A prospective 8-year follow-up of posterior resin composite restorations in permanent teeth of children and adolescents in Public Dental Health Service: reasons for replacement

Objectives

The aim of the study was to investigate reasons for replacement and repair of posterior resin composite (RC) restorations placed in permanent teeth of children and adolescents attending Public Dental Health Service in Denmark.

Material and method

All posterior RC placed consecutively by 115 dentists over a period of 4 years were evaluated at baseline and up to 8 years later. The endpoint of each restoration was defined when repair or replacement was performed. The influence of patient, dentist and material factors on reasons for repair or replacement was investigated.

Results

A total of 4,355 restorations were placed. Replacements comprised 406 and repairs 125 restorations. The cumulative survival rate at 8 years was 84 %. Failed restorations were most frequently seen due to secondary caries (57 %), post-operative sensitivity (POS) (10 %) and RC fracture (6 %). POS was observed in 1.5 % of the evaluations and reported more often in girls and from teeth restored with a base material. Older dentists showed lower proportion of replaced restorations due to secondary caries than younger dentists.

Conclusion

Posterior RC restorations in children and adolescents performed in general practice showed a good durability with annual failure rates of 2 %. The main reason for failure was secondary caries followed by post-operative sensitivity and resin composite fracture. A high proportion of replaced/repaired RC restorations were caused by primary caries in a non-filled surface.

Clinical relevance

Secondary caries was the main reason for failure of RC in children and young adults. More teeth with post-operative sensitivity and a shorter longevity of restorations were observed when a base material was used.