Partial Ceramic Crowns: Influence of Ceramic Thickness, Preparation Design and Luting Material on Fracture Resistance and Marginal Integrity In Vitro

Long-term performance of ceramic in/-onlays vs. cast gold partial crowns - a retrospective clinical study

OBJECTIVES

To assess the long-term clinical performance of ceramic in-/onlays (CIOs) and cast gold partial crowns (CGPCs) in posterior teeth in terms of success, survival, complications (biological, technical) and quality.

MATERIAL AND METHODS

In a retrospective study, a total of 325 patients were recorded after up to 24.8 years (mean 13.9 ± 3.8 years) having (pre-)molars restored with CIO (Empress I, Ivoclar Vivadent, n = 161) and CGPC (Degunorm, DeguDent, n = 164) by supervised undergraduate students. A total of 296 restorations were assessed clinically and radiologically in healthy and endodontically treated teeth using modified United States Public Health Service (USPHS) criteria. Cumulative success and survival rates of the restorations were calculated using Kaplan-Meier estimates. Biological and technical complications were recorded. Status of oral health comprising caries risk and localized periodontitis were assessed.

RESULTS

The cumulative success rates of CIOs were 92.1% and of CGPCs 84.2% after mean service times of 14.5 years. The annual failure rates of total service times were 0.5% in teeth restored with CIO (n = 155) and 0.7% in teeth restored with CGPC (n = 163). The cumulative survival rates of CIOs were 93.9% after a mean service time of 15.2 years and decreased to 91.7% after 23.5 years. The cumulative survival rates of CGPCs were 92.6% after a mean service time of 14.9 years and 91.8% after 23.5 years. Complications in CIOs (n = 149) were ceramic fracture (6.7%), secondary caries (4.7%), endodontic complication (2.7%) and tooth fracture (1.3%) compared to CGPCs (n = 147) with endodontic complication (8.8%), secondary caries (4.8%) and decementation (2.0%). Endodontically treated teeth restored with CIO or CGPC revealed significantly less often success compared with corresponding vital teeth (p = .02). CIOs and CGPCs revealed clinically and radiographically good and excellent qualities with 71.8% (107/149) and 68% (100/147) without any significant differences regarding type of restoration.

CONCLUSIONS

Both CIOs and CGPCs achieved high survival rates up to 24.8 years when performed by supervised undergraduate students. The longevity of the restorations may benefit from the intraoral repair of accessible defects and, in case of pulp infection or necrosis, an adequate endodontic management.

CLINICAL RELEVANCE

CIOs and CGPCs made by supervised undergraduate students are proper restoration types in posterior teeth in the long-term. An adequate preparation design, meticulous care in the inserting technique and constant biofilm removal due to proper oral hygiene combined with professional maintenance care are substantial. The clinical long-term performance was mostly limited by ceramic fractures in CIOs and endodontic complications in CGPCs.

Thickness and Substrate Effect on the Mechanical Behaviour of Direct Occlusal Veneers

PURPOSE

This study aimed to evaluate the fracture resistance and stress magnitude of occlusal veneers made of conventional or flowable resin composites at different minimal thicknesses bonded on enamel or dentin.

MATERIAL AND METHODS

A total of 120 sound bovine incisors were flattened and used as substrates (enamel or dentin) for the restorations. The teeth were embedded into polymethyl methacrylate and allocated into 4 groups according to the resin composite (Clearfil AP-X PLT and Clearfil Majesty Flow, Kuraray Dental) and substrate. Further, the substrates were randomly subdivided in 12 groups (N = 120, n = 10) according to the occlusal veneer minimal thickness: 0.5, 1.0, or 2.0 mm. The teeth were directly restored with a standardised procedure. Then, the specimens were loaded until fracture in a universal testing machine (Instron 6022, Instron Corp.). A 3-way and a 1-way analysis of variance were used to determine significant differences for each factor. Three-dimensional finite element analysis was carried out following the in vitro boundary conditions to assess the stress magnitude in the restoration during compressive loading.

RESULTS

The fracture loads were recorded into initial load to failure (ILF) and fatal load to failure (FLF). Differences were found in material for ILF and FLF, leading to an overall equal good performance in fracture load and stress distribution for both materials, regardless of the substrate. Differences in thickness were apparent in both ILF and FLF.

CONCLUSIONS

Direct conventional and flow resin composite occlusal veneers present a promising mechanical behaviour when bonded on enamel or dentin. However, caution is advised when preparing 0.5-mm minimal thickness restorations.

Effect of immediate dentin sealing on load-bearing capacity under accelerated fatigue of thin occlusal veneers made of CAD-CAM glass-ceramic and resin composite material

OBJECTIVE

The objective of this study was to assess the influence of immediate dentin sealing (IDS) on the fatigue behavior of laminate occlusal veneers fabricated with CAD/CAM lithium disilicate ceramic and resin composite.

METHODS

Forty sound human molars were prepared and randomly divided into 4 groups (n = 10): RC-IDS+ (IDS and resin composite occlusal laminate veneer); RC-IDS- (resin composite occlusal laminate veneer without IDS); LD-IDS+ (IDS and lithium disilicate laminate veneer); LD-IDS- (lithium disilicate occlusal laminate veneer without IDS). The restorations were obtained using a digital workflow. After surface conditioning and bonding, thermocycling and accelerated fatigue tests (20 Hz, 5000 cycles with an initial load of 300 N, step-size of 100 N for 10,000 cycles, up to 1000 N, and then a step-size of 50 N until failure) were conducted. Fatigue data were recorded for both outcomes (crack or fracture) and statistically analyzed. Fractographic and adhesive interface analysis were conducted.

RESULTS

The indirect resin composite groups showed better fatigue behavior compared to lithium disilicate. IDS only had a positive effect for the survival of resin composite restorations for the 'fracture' outcome. Evident presence of micro-gaps at the adhesive interface in the LD-IDS- group could be noted.

SIGNIFICANCE

Immediate dentin sealing improved fatigue resistance behavior of resin composite occlusal veneers. However, this effect was not observed in lithium disilicate veneers.

Clinical reliability of self-adhesive luting resins compared to other adhesive procedures: A systematic review and meta-analysis

OBJECTIVES

This systematic review aimed to collect and interpret the randomized clinical trials (RCTs) that investigated the outcome of the self-adhesive luting resins (SA) compared to total-etch (TE), selective etch with dentin adhesives (Sle), selective etch without dentin adhesives (SleSA) or self-etch adhesives (SE).

DATA SOURCES

A thorough search of Internet databases was conducted without language restrictions, and the search ran up to and including April 2022. The illegible records citations were checked for more relevant clinical studies.

STUDY SELECTION/RESULTS

The inclusion criteria were randomized controlled trials (RCTs) that compared self-adhesive luting resins with total-etch, selective-etch, or self-etch adhesives regarding postoperative sensitivity, incidences of debonding, and survival rates of indirect restorations. From 1732 records, 9 RCTs met the eligibility criteria. Three RCTs compared total-etch adhesive to self-adhesive luting resin for intracoronal restorations, one RCT compared selective etch to self-adhesive luting resin for inlays, and 5 RCTs compared self-adhesive to other protocols for partial ceramic crowns. Postoperative sensitivity showed a non-statistically significant difference between SA and other adhesive protocols, SA revealed a non-statistically significant difference in debonding and survival to TE, but a lower statistically significant difference to Sle, SleSA, and SE.

CONCLUSIONS

Postoperative sensitivity might not be affected by the adhesive protocol. In relatively short observation, TE revealed comparable survival to SA for intracoronal restorations. SE and Sle exhibited the best clinical outcomes, followed by SleSA. Selective etch, and self-etch adhesives are preferable to self-adhesive resins.

CLINICAL SIGNIFICANCE

The significance of enamel etching and the superiority of self-etching adhesives over self-adhesive luting resins for reliable and durable bonding and improved clinical outcomes. However, long-term RCTs, particularly for total-etch comparison to self-adhesive luting resins, might be recommended to derive further evidence.

A Micro-computed Tomography Analysis of Marginal and Internal Fit of Endocrowns Fabricated from Three CAD/CAM Materials

OBJECTIVE

To assess the marginal and internal misfit of endocrowns fabricated from a resin matrix ceramic (CS), a partially crystallized (EMC), and a fully crystallized (ILS) lithium disilicate glass-ceramic.

METHODS AND MATERIALS

Thirty human premolar teeth restored with endocrowns were investigated. Three CAD/CAM materials were used (n=10 per group): CS, EMC, and ILS. Two-dimensional (2D) analysis of marginal and internal misfit was performed on micro-computed tomography scans before and after adhesive bonding. Further, three-dimensional (3D) analysis was performed to determine the total internal volume discrepancy. Surface roughness of the fitting surfaces of endocrowns was characterized using optical profilometry and scanning electron microscopy.

RESULTS

Adhesive bonding did not significantly affect marginal or internal misfit (p≥0.093). Differences in marginal misfit among the experimental groups were not statistically significant (p≥0.221). However, differences in 2D internal misfit were statistically significant; the CS group exhibited the largest internal misfit (p=0.001), while no significant difference was found between other groups (p=0.123). The largest discrepancies were observed at the pulpal floor and cervical region of all investigated specimens. No statistically significant difference was found in 3D misfit between ILS and EMC groups (p=0.711); however both exhibited statistically lower 3D misfit values compared to the CS group (p≤0.037). ILS endocrowns exhibited the smoothest and most homogenous fitting surface profile (p<0.001). However, there was no significant correlation between 2D internal misfit and the surface roughness (p≥0.082).

CONCLUSIONS

The choice of CAD/CAM material may influence the fitting accuracy of endocrowns. The investigated lithium disilicate glass-ceramics conferred superior internal fit for endocrowns compared to resin matrix ceramic.

Fracture Resistance and Failure Mode of Mandibular Molar Restored by Occlusal Veneer: Effect of Material Type and Dental Bonding Surface

This study assesses the effect of the material type (lithium disilicate, zirconia, and polymer-infiltrated ceramic) and dental bonding substrates (dentin, dentin with intra-coronal cavity, and dentin with composite filling) on the fracture resistance and failure mode of molars restored by occlusal veneers. Methods: Ninety occlusal veneers, fabricated from either lithium disilicate, zirconia, or polymer-infiltrated ceramic, were adhesively bonded to teeth prepared with either dentin, dentin with intra-coronal cavity, or dentin with composite filling. All specimens were thermally aged (5000 cycles), then load cycled (120,000 cycles). Each specimen was subjected to a compressive load through fracture, then was examined (×20) to identify the fracture type. Data were statistically analyzed. Results: Material type and dental substrate had no significant effect on the fracture resistance of adhesively retained occlusal veneer restorations. For each material, no significant differences were found between veneers bonded to dentin, dentin with intra-coronal cavity, and dentin with composite filling. Additionally, within each bonding substrate, there were no significant differences between lithium disilicate, zirconia, and polymer-infiltrated ceramic veneers. The adhesive failure was recorded mainly with zirconia occlusal veneer restorations. Conclusions: Considering the fracture results, lithium disilicate, zirconia, and polymer-infiltrated ceramic occlusal veneers perform well whatever the type of dental bonding surface. When the dental bonding surface varies, different occlusal veneer materials should be considered. Occlusal veneers bonded to dentin, dentin with composite filling, or dentin with an intra-coronal cavity exhibited a fracture resistance exceeding the average human masticatory forces in the molar area.

Bacterial translocation and microgap formation at a novel conical indexed implant abutment system for single crowns

OBJECTIVES

A conometric concept was recently introduced in which conical implant abutments hold the matching crown copings by friction alone, eliminating the need for cement or screws. The aim of this in vitro study was to assess the presence of microgap formation and bacterial leakage at the Acuris conometric restorative interface of three different implant abutment systems.

MATERIAL AND METHODS

A total of 75 Acuris samples of three implant-abutment systems (Ankylos, Astra Tech EV, Xive) were subjected to microbiological (n = 60) and scanning electron microscopic (SEM) investigation (n = 15). Bacterial migration into and out of the conical coupling system were analyzed in an anaerobic workstation for 48, 96, 144, and 192 h. Bacterial DNA quantification using qrt-PCR was performed at each time point. The precision of the conometric coupling and internal fit of cemented CAD/CAM crowns on corresponding Acuris TiN copings were determined by means of SEM.

RESULTS

qrt-PCR results failed to demonstrate microbial leakage from or into the Acuris system. SEM analysis revealed minute punctate microgaps at the apical aspect of the conometric junction (2.04 to 2.64 µm), while mean cement gaps of 12 to 145 µm were observed at the crown-coping interface.

CONCLUSIONS

The prosthetic morse taper connection of all systems examined does not allow bacterial passage. Marginal integrity and internal luting gap between the ceramic crown and the coping remained within the clinically acceptable limits.

CLINICAL RELEVANCE

Conometrically seated single crowns provide sufficient sealing efficiency, relocating potential misfits from the crown-abutment interface to the crown-coping interface.

Monolithic Zirconia Partial Coverage Restorations: An In Vitro Mastication Simulation Study

PURPOSE

To evaluate the survival rate (fatigue resistance), bonding efficiency and marginal integrity of monolithic zirconia partial and full coverage single restorations adhesively bonded to the tooth structure using air-particle abrasion, a primer with 10-methacryloyloxydecyl dihydrogen phosphate and a composite-resin cement (APC) protocol.

MATERIALS AND METHODS

Extracted human premolars (N = 32) were randomly divided into four groups of eight specimens each. Premolars were prepared for the following restorations: full crown (group 1, control), mesial-occlusal-distal-facial onlay (MODF, group 2) preserving 2 mm facio-lingual functional cusp width, mesial-occlusal-distal-lingual onlay (MODL, group 3) preserving 2 mm facio-lingual nonfunctional cusp width, mesial-occlusal-distal-buccal-lingual onlay (MODBL, group 4), overlay preparation. All restorations were milled from monolithic 3 mol% yttria (3Y) zirconia blocks (ZirCad, A1 LT, Ivoclar Vivadent) with CAD/CAM software presets at minimum occlusal and axial thicknesses of 1 mm. The intaglio surface of the restorations was air-particle abraded (50 µm Al₂ O₃ , 2-Bar pressure, 15 s, 10 mm distance) and primed. An adhesive cement system was used to bond the restorations. Each group was subjected to thermomechanical loading for 1.2 million cycles (force = 70 N, 1.4 Hz) with simultaneous thermocycling (5-55°C, 30 s dwell time) using a mastication simulator. All specimens were examined under scanning electron microscope (SEM) analysis (30, 100, and 150×) to evaluate cracks and marginal defects. Fracture of restoration and/or fracture within tooth structure, and debonding were considered modes of failure.

RESULTS

One specimen from group 2 debonded at 632,000 cycles. None of the specimens failed due to fracture. SEM analysis at 30× indicated marginal integrity issue of the remaining seven intact specimens of group 2 in the area of antagonist contact. No specimens from group 1, 3, and 4 demonstrated marginal integrity issue at 30×. None of the specimens demonstrated any microcrack at 100× and150×.

CONCLUSIONS

Due to its fatigue resistance, 3Y-zirconia is a viable option for partial and full coverage single restorations. Following a strict bonding protocol, zirconia demonstrated durable adhesion to the tooth structure. Occlusal contact on restoration margins should be avoided.

Development of a Weight-Drop Impact Testing Method for Dental Applications

For evaluating the impact strength of dental materials, the Izod test or Charpy test has been used, but specimen preparation for these tests is difficult due to the adjustment of a notch on them. By contrast, a weight-drop impact test does not require notched specimens. Therefore, it might be possible to measure the impact strength more accurately than conventional methods. This study aimed to establish appropriate conditions for applying the weight-drop impact test on small specimens of acrylic resin. To determine the most reliable impact fracture energy of acrylic resins, different diameters and thicknesses of PMMA resin specimens, diameters and weights of the striker, and diameters of the supporting jig were compared. For all specimen thicknesses, when the striker diameter was 6–10 mm, the impact fracture energy was constant when the inner diameter of the specimen-supporting jig was 8–10 mm. In addition, the measured E_50% value was mostly equal to the median value of the impact fracture energy. Thus, for the weight-drop impact test, this method was effective for material testing of small specimens, by clearly specifying the test conditions, such as the thickness of disc-shaped specimens, the diameter of the striker, and the inner diameter of the specimen-supporting jig.

Influence of the Fabrication Technique on the Marginal and Internal Adaptation of Ceramic Onlays

This study aimed to evaluate the marginal and internal adaptation of partial coverage crowns (ceramic onlays) fabricated with Press, CEREC BlueCam, and CEREC OmniCam systems, using two preparation designs and evaluating the internal discrepancies at different locations. Two phantom maxillary premolars (master teeth) received different preparation designs, with (BX) and without (NB) a modified occlusal box with round internal angles. Sixty IPS e-max ceramic restorations were fabricated with three systems: Press (n=20), CEREC BlueCam (n=20), and CEREC OmniCam (n=20). Both marginal and internal discrepancy width were measured by using a stereomicroscope at ×25 magnification. The data were evaluated statistically using analysis of variance followed by Tukey's Honestly Significant Difference test (α=0.05). The ceramic restorations fabricated with the Press system presented significantly smaller marginal and internal disadaptations than the BlueCam and OmniCam CEREC systems (p&lt;0.0001). Regarding the preparation designs, preparation BX presented the smallest marginal discrepancies for all fabrication systems and larger internal discrepancies than for restorations fabricated with the Press system. The occlusal location presented a larger internal discrepancy compared with the axial locations. Although the three systems resulted in the fabrication of restorations within a clinically acceptable adaptation with marginal discrepancies below 100 μm, the Press system presented the smallest marginal and internal discrepancies. An improved marginal adaptation was observed in the preparation design with a modified occlusal box with rounded internal angles.

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

OBJECTIVE

The fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects.

METHODS

Eighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3mm IPS Empress CAD and 0.3 and 0.5mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100N. Kaplan-Meier survival curves and log-rank tests were used for data analysis.

RESULTS

All highly standardized and 0.3/0.5mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks.

SIGNIFICANCE

Ultrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin-enamel defects.

Influence of bonding surface and bonding methods on the fracture resistance and survival rate of full-coverage occlusal veneers made from lithium disilicate ceramic after cyclic loading

OBJECTIVES

The purpose of this laboratory study was to evaluate the influence of bonding method and type of dental bonding surface on fracture resistance and survival rate of resin bonded occlusal veneers made from lithium disilicate ceramic after cyclic loading.

METHODS

Fourty-eight extracted molars were divided into three groups (N=16) depending on the preparation: within enamel, within dentin/enamel or within enamel/composite resin filling. Lithium disilicate occlussal veneers were fabricated with a fissure-cusp thickness of 0.3-0.6mm. Restorations were etched (5% HF), silanated and adhesively luted using a dual-curing luting composite resin. Test groups were divided into two subgroups, one using a only a self-etching primer, the other additionally etching the enamel with phosphoric acid. After water storage (37°C; 21d) and thermocycling (7500 cycles; 5-55°C), specimens were subjected to dynamic loading in a chewing simulator (600,000 cycles; 10kg/2Hz). Surviving specimens were loaded until fracture using a universal testing machine.

RESULTS

All specimens survived artificial aging, several specimens showed some damage. ANOVA revealed that enamel etching provided statistically significantly (p≤0.05) higher fracture resistance than self-etching when bonding to enamel and dentin. Self-etching provided statistically significant (p≤0.05) higher fracture resistance for the enamel-composite group than for the enamel group. Enamel etching provided statistically significant (p≤0.05) higher fracture resistance for the enamel and dentin group than for groups enamel and enamel-composite.

SIGNIFICANCE

Etching enamel improved the fracture resistance of occlusal veneers when bonding to dentin and enamel and increased the survival rate when bonding to enamel.

Influence of preparation designs on marginal adaptation and failure load of full-coverage occlusal veneers after thermomechanical aging simulation

OBJECTIVES

To evaluate the fracture resistance and marginal quality of maxillary molars restored using lithium disilicate glass-ceramic (LDG) occlusal veneers with two preparation designs.

METHODS

Sixteen extracted maxillary molars were assigned to two groups (n = 8). In group 1 (G1), the teeth received a preparation for a conservative full-coverage occlusal veneer restoration with a 90° rounded shoulder margin. In group 2 (G2), the teeth underwent a 1-mm cusp reduction with a marginal chamfer. LDG restorations (IPS e.max CAD) were obtained with the Cerec 3 CAD/CAM system and luted with Variolink II cement. After thermomechanical aging (1 250 000 cycles), the specimens were loaded to fracture. A semiquantitative marginal seal evaluation was performed observing resin replicas of the specimens at the scanning electron microscope. Cement thickness was assessed at the stereomicroscope on sectioned specimens. Collected data were statistically analyzed by parametric and nonparametric tests.

RESULTS

The maximum load to fracture was 2395.01 ± 150.96 N in G1 and 2408.39 ± 112.66 N in G2. Most of the observed specimens exhibited restorable fractures and continuous margins. Cement thickness was 132 ± 38 μm in G1 and 150 ± 41 μm in G2. No differences between the groups emerged.

CONCLUSION

This study demonstrated similar satisfactory performance of the two considered preparations designs for occlusal veneer with LDG.

CLINICAL SIGNIFICANCE

A new minimally invasive occlusal veneer preparation with marginal chamfer exhibited promising fracture resistance and marginal adaptation that were comparable to those of a standard conservative preparation for the restoration of molars with CAD/CAM lithium disilicate occlusal veneers.

Influence of Preparation Reconstruction on the Compressive Strength of CAD/CAM Ceramic Inlays

The aim of this study was to evaluate whether the compressive strength of lithium dissilicate ceramic inlays is influenced by the substrate (dentin or composite resin build-up) and to compare it to nonrestored teeth. Thirty freshly extracted human maxillary third molars were selected and randomly ascribed to three groups (n=10). Standardized Class II MOD preparations were made (bucco-palatal width = 2/3 of the intercuspal width and 2/3 of the width at the tooth equator for the proximal boxes), varying the extension of the preparations (Group 2: preparation limited to tooth structure; Group 3: pulpal floor of the preparation rebuilt with composite resin, IPS Empress Direct, restored with lithium dissilicate CAD/CAM ceramic inlays (e.max CAD) and cemented with a resin cement (Variolink II)). All groups were subjected to compressive strength test (1mm/min crosshead speed). The results showed that the fracture strength of G1 (control group) was significantly higher than G2 and G3, while within these groups there were no statistically significant differences. Both groups restored with lithium dissilicate restorations did not reach the fracture strength of the sound teeth but were statistically equivalent and sufficient to withstand physiologic masticatory forces.

Hoffa fracture of the femoral condyle: Injury mechanism, classification, diagnosis, and treatment

BACKGROUND

Hoffa fractures are coronal-plane fractures of the femoral condyle, which are rarer than sagittal-plane condylar fractures. This study aimed to systematically review the clinical knowledge base of Hoffa fractures to facilitate the diagnosis and management of such injuries.

METHODS

We searched Medline, Embase, Cochrane Library, Google Scholar, China National Knowledge Infrastructure, and China Biology Medicine disc, using the terms "Hoffa fracture" and "coronal fracture of femoral condyle."

RESULTS

One hundred five articles on Hoffa fractures were reviewed, and the clinical knowledge base was summarized. High-energy trauma is a common cause of a Hoffa fracture, although low-energy trauma and iatrogenic injury can also lead to these fractures. Commonly used classifications include the Letenneur classification, a computed tomography (CT) classification, the AO classification, and modified AO classification. Radiography can reveal fracture lines. If radiographic findings are negative in questionable cases, CT and magnetic resonance imaging (MRI) should be performed. Nondisplaced fractures can be managed conservatively; however, they involve a high risk of redisplacement. Open reduction and internal fixation are preferred. For young patients with good compliance, simple medial or lateral condylar fractures can be treated via a medial or lateral parapatellar approach. After fracture exposure, headless compression screws can be inserted perpendicularly to the fracture line from posterior to anterior. For bicondylar fractures, a median parapatellar incision can be used. For complex fractures in patients with osteoporosis or a high body mass index, cannulated screws with antigliding plate fixation should be used.

CONCLUSION

Here, we summarized the injury mechanism, diagnosis, classification, and treatment options of Hoffa fractures.

Comparison of digital intraoral scanners by single-image capture system and full-color movie system

BACKGROUND

The use of dental computer-aided design/computer-aided manufacturing (CAD/CAM) restoration is rapidly increasing.

OBJECTIVE

This study was performed to evaluate the marginal and internal cement thickness and the adhesive gap of internal cavities comprising CAD/CAM materials using two digital impression acquisition methods and micro-computed tomography.

METHODS

Images obtained by a single-image acquisition system (Bluecam Ver. 4.0) and a full-color video acquisition system (Omnicam Ver. 4.2) were divided into the BL and OM groups, respectively. Silicone impressions were prepared from an ISO-standard metal mold, and CEREC Stone BC and New Fuji Rock IMP were used to create working models (n=20) in the BL and OM groups (n=10 per group), respectively. Individual inlays were designed in a conventional manner using designated software, and all restorations were prepared using CEREC inLab MC XL. These were assembled with the corresponding working models used for measurement, and the level of fit was examined by three-dimensional analysis based on micro-computed tomography.

RESULTS

Significant differences in the marginal and internal cement thickness and adhesive gap spacing were found between the OM and BL groups.

CONCLUSIONS

The full-color movie capture system appears to be a more optimal restoration system than the single-image capture system.

Effect of Preparation Depth on the Marginal and Internal Adaptation of Computer-aided Design/Computer-assisted Manufacture Endocrowns

The aim of the study was to evaluate the effect of preparation depth and intraradicular extension on the marginal and internal adaptation of computer-aided design/computer-assisted manufacture (CAD/CAM) endocrown restorations. Standardized preparations were made in resin endodontic tooth models (Nissin Dental), with an intracoronal preparation depth of 2 mm (group H2), with extra 1- (group H3) or 2-mm (group H4) intraradicular extensions in the root canals (n=12). Vita Enamic polymer-infiltrated ceramic-network material endocrowns were fabricated using the CEREC AC CAD/CAM system and were seated on the prepared teeth. Specimens were evaluated by microtomography. Horizontal and vertical tomographic sections were recorded and reconstructed by using the CTSkan software (TView v1.1, Skyscan).The surface/void volume (S/V) in the region of interest was calculated. Marginal gap (MG), absolute marginal discrepancy (MD), and internal marginal gap were measured at various measuring locations and calculated in microscale (μm). Marginal and internal discrepancy data (μm) were analyzed with nonparametric Kruskal-Wallis analysis of variance by ranks with Dunn's post hoc, whereas S/V data were analyzed by one-way analysis of variance and Bonferroni multiple comparisons (α=0.05). Significant differences were found in MG, MD, and internal gap width values between the groups, with H2 showing the lowest values from all groups. S/V calculations presented significant differences between H2 and the other two groups (H3 and H4) tested, with H2 again showing the lowest values. Increasing the intraradicular extension of endocrown restorations increased the marginal and internal gap of endocrown restorations.

Cementation of Glass-Ceramic Posterior Restorations: A Systematic Review

Aim. The aim of this comprehensive review is to systematically organize the current knowledge regarding the cementation of glass-ceramic materials and restorations, with an additional focus on the benefits of Immediate Dentin Sealing (IDS). Materials and Methods. An extensive literature search concerning the cementation of single-unit glass-ceramic posterior restorations was conducted in the databases of MEDLINE (Pubmed), CENTRAL (Cochrane Central Register of Controlled Trials), and EMBASE. To be considered for inclusion, in vitro and in vivo studies should compare different cementation regimes involving a “glass-ceramic/cement/human tooth” complex. Results and Conclusions. 88 studies were included in total. The in vitro data were organized according to the following topics: (micro)shear and (micro)tensile bond strength, fracture strength, and marginal gap and integrity. For in vivo studies survival and quality of survival were considered. In vitro studies showed that adhesive systems (3-step, etch-and-rinse) result in the best (micro)shear bond strength values compared to self-adhesive and self-etch systems when luting glass-ceramic substrates to human dentin. The highest fracture strength is obtained with adhesive cements in particular. No marked clinical preference for one specific procedure could be demonstrated on the basis of the reviewed literature. The possible merits of IDS are most convincingly illustrated by the favorable microtensile bond strengths. No clinical studies regarding IDS were found.

Effect of Ceramic Thickness and Composite Bases on Stress Distribution of Inlays - A Finite Element Analysis

The purpose of this study was to determine the effect of cavity depth, ceramic thickness, and resin bases with different elastic modulus on von Mises stress patterns of ceramic inlays. Tridimensional geometric models were developed with SolidWorks image software. The differences between the models were: depth of pulpal wall, ceramic thickness, and presence of composite bases with different thickness and elastic modulus. The geometric models were constrained at the proximal surfaces and base of maxillary bone. A load of 100 N was applied. The stress distribution pattern was analyzed with von Mises stress diagrams. The maximum von Mises stress values ranged from 176 MPa to 263 MPa and varied among the 3D-models. The highest von Mises stress value was found on models with 1-mm-thick composite resin base and 1-mm-thick ceramic inlay. Intermediate values (249-250 MPa) occurred on models with 2-mm-thick composite resin base and 1-mm-thick ceramic inlay and 1-mm-thick composite resin base and 2-mm-thick ceramic inlay. The lowest values were observed on models restored exclusively with ceramic inlay (176 MPa to 182 MPa). It was found that thicker inlays distribute stress more favorably and bases with low elastic modulus increase stress concentrations on the internal surface of the ceramic inlay. The increase of ceramic thickness tends to present more favorable stress distribution, especially when bonded directly onto the cavity without the use of supporting materials. When the use of a composite base is required, composite resin with high elastic modulus and reduced thickness should be preferred.

Influence of preparation design on fit and ceramic thickness of CEREC 3 partial ceramic crowns after cementation

OBJECTIVE

This study investigated the influence of preparation design on the marginal and internal gap and ceramic thickness of partial ceramic crowns (PCCs) fabricated with the CEREC 3 system.

MATERIALS AND METHODS

Sixteen extracted human mandibular molars were prepared according to two different preparation designs (n = 8): a retentive preparation design with traditional cusp capping (Group I) and a non-retentive preparation design with horizontal reduction of cusps (Group II). PCCs were fabricated from IPS Empress CAD with the CEREC 3 system. The parameters for luting space and minimum occlusal ceramic thickness were set to 30 μm and 1.5 mm, respectively. The fabricated PCCs were cemented to their corresponding teeth with self-adhesive resin cement and were then scanned by micro-computed tomography. The marginal and internal gaps were measured at pre-determined measuring points in five bucco-lingual and three mesio-distal cross-sectional images. The ceramic thicknesses of the PCCs were measured at the measuring points for cusp capping areas.

RESULTS

Group II (167.4 ± 76.4 μm) had a smaller overall mean gap, which included the marginal and internal gap measurements, than that of Group I (184.8 ± 89.0 μm). The internal gaps were larger than the marginal gaps, regardless of preparation design. Group I presented a thinner ceramic thickness in the cusp capping areas than the minimum occlusal ceramic thickness parameter of 1.5 mm. CONCLUSION. Preparation design had an influence on fit, particularly the internal gap of the PCCs. Ceramic thickness could be thinner than the minimum ceramic thickness parameter.

Coronal plane fracture of the femoral condyles: anatomy, injury patterns, and approach to management of the Hoffa fragment

OBJECTIVE

The purpose of this article is to provide a review of coronal fractures of the femoral condyles, known as Hoffa fractures. This includes a review of the normal anatomy of the femoral condyles, examples of the injury, and postoperative imaging findings after surgical treatments.

CONCLUSIONS

Knowledge of anatomy with related pathology, orthopedic trends, imaging findings, and complications, is important in assessing Hoffa fractures.

Marginal and internal fit of heat pressed versus CAD/CAM fabricated all-ceramic onlays after exposure to thermo-mechanical fatigue

OBJECTIVES

The aim of the study was to evaluate the marginal and internal fit of heat-pressed and CAD/CAM fabricated all-ceramic onlays before and after luting as well as after thermo-mechanical fatigue.

MATERIALS AND METHODS

Seventy-two caries-free, extracted human mandibular molars were randomly divided into three groups (n=24/group). All teeth received an onlay preparation with a mesio-occlusal-distal inlay cavity and an occlusal reduction of all cusps. Teeth were restored with heat-pressed IPS-e.max-Press* (IP, *Ivoclar-Vivadent) and Vita-PM9 (VP, Vita-Zahnfabrik) as well as CAD/CAM fabricated IPS-e.max-CAD* (IC, Cerec 3D/InLab/Sirona) all-ceramic materials. After cementation with a dual-polymerising resin cement (VariolinkII*), all restorations were subjected to mouth-motion fatigue (98 N, 1.2 million cycles; 5°C/55°C). Marginal fit discrepancies were examined on epoxy replicas before and after luting as well as after fatigue at 200× magnification. Internal fit was evaluated by multiple sectioning technique. For the statistical analysis, a linear model was fitted with accounting for repeated measurements.

RESULTS

Adhesive cementation of onlays resulted in significantly increased marginal gap values in all groups, whereas thermo-mechanical fatigue had no effect. Marginal gap values of all test groups were equal after fatigue exposure. Internal discrepancies of CAD/CAM fabricated restorations were significantly higher than both press manufactured onlays.

CONCLUSIONS

Mean marginal gap values of the investigated onlays before and after luting as well as after fatigue were within the clinically acceptable range. Marginal fit was not affected by the investigated heat-press versus CAD/CAM fabrication technique. Press fabrication resulted in a superior internal fit of onlays as compared to the CAD/CAM technique.

CLINICAL RELEVANCE

Clinical requirements of 100 μm for marginal fit were fulfilled by the heat-press as well as by the CAD/CAM fabricated all-ceramic onlays. Superior internal fit was observed with the heat-press manufacturing method. The impact of present findings on the clinical long-term behaviour of differently fabricated all-ceramic onlays warrants further investigation.

Clinical performance of a new biomimetic double network material

BACKGROUND

The development of ceramics during the last years was overwhelming. However, the focus was laid on the hardness and the strength of the restorative materials, resulting in high antagonistic tooth wear. This is critical for patients with bruxism.

OBJECTIVES

The purpose of this study was to evaluate the clinical performance of the new double hybrid material for non-invasive treatment approaches.

MATERIAL AND METHODS

The new approach of the material tested, was to modify ceramics to create a biomimetic material that has similar physical properties like dentin and enamel and is still as strong as conventional ceramics.

RESULTS

The produced crowns had a thickness ranging from 0.5 to 1.5 mm. To evaluate the clinical performance and durability of the crowns, the patient was examined half a year later. The crowns were still intact and soft tissues appeared healthy and this was achieved without any loss of tooth structure.

CONCLUSIONS

The material can be milled to thin layers, but is still strong enough to prevent cracks which are stopped by the interpenetrating polymer within the network. Depending on the clinical situation, minimally- up to non-invasive restorations can be milled.

CLINICAL RELEVANCE

Dentistry aims in preservation of tooth structure. Patients suffering from loss of tooth structure (dental erosion, Amelogenesis imperfecta) or even young patients could benefit from minimally-invasive crowns. Due to a Vickers hardness between dentin and enamel, antagonistic tooth wear is very low. This might be interesting for treating patients with bruxism.

Load-bearing properties of minimal-invasive monolithic lithium disilicate and zirconia occlusal onlays: finite element and theoretical analyses

OBJECTIVE

The aim of this study was to test the hypothesis that monolithic lithium disilicate glass-ceramic occlusal onlay can exhibit a load-bearing capacity that approaches monolithic zirconia, due to a smaller elastic modulus mismatch between the lithium disilicate and its supporting tooth structure relative to zirconia.

METHODS

Ceramic occlusal onlays of various thicknesses cemented to either enamel or dentin were considered. Occlusal load was applied through an enamel-like deformable indenter or a control rigid indenter. Flexural tensile stress at the ceramic intaglio (cementation) surface-a cause for bulk fracture of occlusal onlays-was rigorously analyzed using finite element analysis and classical plate-on-foundation theory.

RESULTS

When bonded to enamel (supported by dentin), the load-bearing capacity of lithium disilicate can approach 75% of that of zirconia, despite the flexural strength of lithium disilicate (400MPa) being merely 40% of zirconia (1000MPa). When bonded to dentin (with the enamel completely removed), the load-bearing capacity of lithium disilicate is about 57% of zirconia, still significantly higher than the anticipated value based on its strength. Both ceramics show slightly higher load-bearing capacity when loaded with a deformable indenter (enamel, glass-ceramic, or porcelain) rather than a rigid indenter.

SIGNIFICANCE

When supported by enamel, the load-bearing property of minimally invasive lithium disilicate occlusal onlays (0.6-1.4mm thick) can exceed 70% of that of zirconia. Additionally, a relatively weak dependence of fracture load on restoration thickness indicates that a 1.2mm thin lithium disilicate onlay can be as fracture resistant as its 1.6mm counterpart.

In vitro marginal fit of three all-ceramic crown systems before and after cementation

STATEMENT OF THE PROBLEM

Full-coverage all-ceramic restorations are widely used. The impact of various classifications of luting agent on marginal discrepancies is not well understood.

PURPOSE

The purpose of this study was to evaluate the cervical fit of all ceramic crowns (IPS e.maxPress, Cergogold, and In Ceram) on bovine teeth with two luting agents before and after cementation.

MATERIALS AND METHODS

Ninety bovine incisors were embedded in resin. The coronal portions of the teeth were prepared to receive full-coverage crowns. Thirty crowns of 7.0 ± 0.5 mm height, 8.0 mm cervical diameter, and 4.2 mm incisal diameter were fabricated for each ceramic system. The crowns were seated on the teeth, and the marginal discrepancy was measured using a measuring microscope. Then, 15 crowns of each ceramic system were luted on the teeth with resin cement (Variolink II) or resin-modified glass ionomer cement (Rely X luting), and the marginal discrepancy was measured. The results were submitted to analysis of variance, t test and Tukey's test (p<0.05).

RESULTS

The three ceramic systems showed cervical fits after cementation statistically inferior to cervical fits before cementation for the two cements. The IPS e.maxPress showed values for cervical fit statistically superior to Cergogold before cementation. No statistically significant difference was found between IPS e.maxPress and In Ceram and In Ceram and Cergogold. After cementation, no statistically significant difference was found for the three ceramics systems when luted with resin or resin-modified glass ionomer luting agents.

CONCLUSIONS

Within the limitations of this study, it can be concluded that both cements studied increase the marginal discrepancy between the crown and the preparation for the three ceramic systems evaluated.

Protective Effect of Resin Coating on the Microleakage of Class V Restorations Following Treatment with Carbamide Peroxide In Vitro

Carbamide peroxide treatment increased the microleakage of Class V conventional glass-ionomer cement and resin modified glass-ionomer cement restorations. The resin coating is an effective method to avoid bleaching-induced microleakage without affecting the bleaching outcome.

Ceramic inlays and partial ceramic crowns: influence of remaining cusp wall thickness on the marginal integrity and enamel crack formation in vitro

No information is currently available about what the critical cavity wall thickness is and its influence upon 1) the marginal integrity of ceramic inlays (CI) and partial ceramic crowns (PCC) and 2) the crack formation of dental tissues. This in vitro study of CI and PCC tested the effects of different remaining cusp wall thicknesses on marginal integrity and enamel crack formation. CI (n = 25) and PCC (n = 26) preparations were performed in extracted human molars. Functional cusps of CI and PCC were adjusted to a 2.5 mm thickness; for PCC, the functional cusps were reduced to a thickness of 2.0 mm. Non-functional cusps were adjusted to wall thicknesses of 1) 1.0 mm and 2) 2.0 mm. Ceramic restorations (Vita Mark II, Cerec3 System) were fabricated and adhesively luted to the cavities with Excite/Variolink II. The specimens were exposed to thermocycling and central mechanical loading (TCML: 5000 x 5 degrees C-55 degrees C; 30 seconds/cycle; 500000 x 72.5N, 1.6Hz). Marginal integrity was assessed by evaluating a) dye penetration (fuchsin) on multiple sections after TCML and by using b) quantitative margin analysis in the scanning electron microscope (SEM) before and after TCML. Ceramic- and tooth-luting agent interfaces (LA) were evaluated separately. Enamel cracks were documented under a reflective light microscope. The data were statistically analyzed with the Mann Whitney U-test (alpha = 0.05) and the Error Rates Method (ERM). Crack formation was analyzed with the Chi-Square-test (alpha = 0.05) and ERM. In general, the remaining cusp wall thickness, interface, cavity design and TCML had no statistically significant influence on marginal integrity for both CI and PCC (ERM). Single pairwise comparisons showed that the CI and PCC of Group 2 had a tendency towards less microleakage along the dentin/LA interface than Group 1. Cavity design and location had no statistically significant influence on crack formation, but the specimens with 1.0 mm of remaining wall thickness had statistically significantly more crack formation after TCML than the group with 2.0 mm of remaining cusp wall thickness for CI. The remaining cusp wall thickness of non-functional cusps of adhesively bonded restorations (especially for CI) should have a thickness of at least 2.0 mm to avoid cracks and marginal deficiency at the dentin/LA interface.

Marginal Fit of Heat-pressed vs CAD/CAM Processed All-ceramic Onlays Using a Milling Unit Prototype

The marginal fit of all-ceramic restorations has an important influence on the clinical performance and lifetime of adhesively luted restorations. In proximal boxes, an average marginal gap of less than 100 μm is claimed. These clinical requirements are fulfilled by both processing procedures.