[Precision of digital impressions with TRIOS under simulated intraoral impression taking conditions].

OBJECTIVE: To evaluate the precision of digital impressions taken under simulated clinical impression taking conditions with TRIOS and to compare with the precision of extraoral digitalizations. METHODS: Six #14-#17 epoxy resin dentitions with extracted #16 tooth preparations embedded were made. For each artificial dentition, (1)a silicone rubber impression was taken with individual tray, poured with type IV plaster,and digitalized with 3Shape D700 model scanner for 10 times; (2) fastened to a dental simulator, 10 digital impressions for each were taken with 3Shape TRIOS intraoral scanner. To assess the precision, best-fit algorithm and 3D comparison were conducted between repeated scan models pairwise by Geomagic Qualify 12.0, exported as averaged errors (AE) and color-coded diagrams. Non-parametric analysis was performed to compare the precisions of digital impressions and model images. The color-coded diagrams were used to show the deviations distributions. RESULTS: The mean of AE for digital impressions was 7.058 281 µm, which was greater than that of 4.092 363 µm for the model images (P<0.05). However, the means and medians of AE for digital impressions were no more than 10 µm, which meant that the consistency between the digital impressions was good. The deviations distribution was uniform in the model images,while nonuniform in the digital impressions with greater deviations lay mainly around the shoulders and interproximal surfaces. CONCLUSION: Digital impressions with TRIOS are of good precision and up to the clinical standard. Shoulders and interproximal surfaces scanning are more difficult.

A novel non-stop mutation in MSX1 causing autosomal dominant non-syndromic oligodontia.

Oligodontia, which is the congenital absence of six or more permanent teeth, excluding the third molars, may contribute to masticatory dysfunction, speech alteration, aesthetic problems and malocclusion. Msh homeobox 1 (MSX1) was the first gene identified as causing non-syndromic oligodontia. In this study, we identified a novel heterozygous non-stop mutation (c.910_911dupTA, p.*304Tyrext*48) in MSX1 in a Chinese family with autosomal dominant non-syndromic oligodontia. This novel mutation substitutes the stop codon with a tyrosine residue, potentially adding 48 amino acids to the C-terminus of MSX1. Further in vitro study found that mutant MSX1 could be expressed but had lost its ability to enter the nucleus. This is the first report indicating that a non-stop mutation in MSX1 is responsible for oligodontia. This study broadens the mutation spectrum for MSX1 and provides a new way to clarify the mechanism of MSX1 in tooth agenesis.

[Association between AXIN2 polymorphism and oligodontia].

OBJECTIVE: To explore the association between AXIN2 polymorphism and oligodontia in Chinese population. METHODS: We employed 97 individuals diagnosed with sporadic non-syndromic oligodontia and 200 healthy control subjects. Their DNA was obtained from the whole blood or buccul swap samples and the genotyping was performed by polymerase chain reaction (PCR). RESULTS: Significant differences were observed in the allele and genotype frequencies of rs145353986 of AXIN2. Distributions of genotypes GG, GC and CC of rs145353986 polymorphism were significantly different between the case group and the control group (P = 0.011) and C allelic frequency was higher in the case group (P=0.002). CONCLUSION: These data demonstrate an association between rs145353986 of AXIN2 and non-syndromic oligodondia in the Chinese population. Furthermore, AXIN2 can be regarded as a marker gene for the risk of tooth agenesis.

[Fracture reliability of zirconia all-ceramic crown according to zirconia coping design].

OBJECTIVE: To study the fracture resistance and characteristics of the bi-layer zirconia all ceramic crowns according to the zirconia coping design using various experimental methods and to compare the results of the in vitro test with the clinical evaluation. METHODS: The bi-layer zirconia all ceramic crowns were fabricated by the same method as used in clinical practice. Two different coping designs with/without zirconia marginal collar were used. All the samples were cemented onto corresponding resin dies. All the specimens were tested in the 2 groups with/without zirconia collar. The fracture load test was performed on 10 crowns from each group. Fracture strength was tested with a universal testing machine. The fracture modes and features of the failed crowns were observed with an integrated microscope and a field emission scanning electron microscope. RESULTS: The zirconia collar group showed higher fracture load than the group without zirconia collar. All the zirconia crowns failed with porcelain failure and without zirconia coping broken. The porcelain fracture modes were crack, chipping and delamination. The distribution of the different fracture modes in the groups was the same. CONCLUSION: The bi-layer zirconia crown with 2 mm zirconia marginal collar showed more fracture strength under once load. The fracture modes of the test specimens were the same as the clinical fracture bi-layer zirconia crowns, showing porcelain chipping and delamination.

[Effects of wearing dentures on sleep breathing among edentulous people: a preliminary study].

OBJECTIVE: To investigate the effects of wearing dentures on sleep breathing among edentulous people. METHODS: Nine edentulous people were recruited to participate in this selfcontrolled case series clinical study. Polysomnogram (PSG) was carried out on two consecutive nights, on one night the patients slept wearing dentures, and on the other without dentures. The indexes such as apnea and hypopnea index (AHI), L-SpO2, and morning blood pressure etc. were compared. RESULTS: Among the nine edentulous people, eight showed a higher AHI when they slept with dentures, and only one showed a lower AHI. The average AHI of the nine edentulous people was 8.82 without dentures and 11.72 with dentures, which meant that AHI was significantly higher when the edentulous people slept with dentures in their mouths (P<0.05). While no significant differences were found in the score of L-SpO2 and morning blood pressures (P>0.05). CONCLUSION: Wearing dentures might lead to an increase of AHI during sleep among edentulous people.

[Effect of early-loaded small diameter implants retained mandibular overdentures on masticatory performance].

OBJECTIVE: To evaluate the clinical effect and masticatory efficiency of two early loaded Small Diameter Implants (SDI) retained mandibular overdentures. METHODS: Eight mandibular edentulous patients received two SDIs insertion between mental foramina. The mandibular overdentures were connected with implants for early loading in the period of 2-4 weeks following implant insertion. The data of visual analogue scale (VAS) of denture satisfaction and masticatory ability were collected at baseline, two weeks, three months and six months following overdenture loading. Masticatory efficiency was evaluated before surgery and six months after overdenture loading. RESULTS: Within the period of six months following overdenture loading, all the 16 implants remained stable. Compared with the baseline, the VAS data of denture satisfaction,stability, masticatory and poltophagy ability two weeks, three months and six months after overdenture loading were significantly improved with 30 degree (P<0.01), especially the masticatory and poltophagy ability of hard and crisp food. The value of masticatory efficiency improved considerably six months after overdenture loading (P<0.01). CONCLUSION: Mandibular overdentures retained by two SDIs can significantly improve patients' denture satisfaction and masticatory efficiency, and provide more rational diet.

[Esthetic evaluation of Cerec 3D anterior crowns].

OBJECTIVE: To observe the short-term effect of clinical application of Cerec 3D anterior crowns. METHODS: A total of 16 patients were restored with 31 Cerec 3D anterior crowns. All restorations were stained before cementation. The evaluation started 1 week after luting. The restorations were examined in accordance with the modified US Public Health Service (USPHS) criteria at baseline and every 6 - 12 months. RESULTS: The observation period of 31 Cerec 3D anterior crowns varied from 8 to 33 months. The mean observation period was 22 months. All restorations scored A or B by modified USPHS standard. And 22 out of 31 restorations scored A for all criteria while 8 restorations scored B in color matching. Slight differences of translucency and chroma could be observed. Between baseline and follow-up examinations, insignificant shift from A-to B-rating occurred. CONCLUSION: Cerec 3D anterior crowns may achieve favorable short-term esthetic effects.

[Influence of experimental palatal plate on mandibular position during continuous [n] phonation in complete denture wearers].

OBJECTIVE: To clarify the influence of an experimental palatal plate on the mandibular position during continuous [n] phonation and at the physiological rest position in complete denture wearers. METHODS: Ten complete denture wears volunteers were investigated. Two kinds of experimental palatal plate with a thickness of 3 mm and 5 mm (from the denture basal surface to denture polished surface) were fabricated and used for each subject. The mandibular position was recorded by a K7 mandibular kinesiograph during continuous [n] phonation and at the physiological rest position under three conditions: wearing a palatal plate with different thickness of 3 mm, 5 mm and without a plate(control). The interocclusal distance both in vertical and anteroposterior direction during continuous phonation and physiological rest position under all three conditions were measured and compared. RESULTS: Under the control condition without wearing of a plate, the mean values of interocclusal distance (IOD) during continuous [n] phonation were (1.69±1.26) mm vertically and (1.74±1.18) mm anteroposteriorly. After insertion of the experimental plates, there was an increase in the IOD during continuous [n] phonation, but this difference from the normal condition was not statistically significant. The mean IOD at the physiological rest position in these 2 directions were (2.91±2.28) mm and (2.56±1.88) mm, respectively. After insertion of the experimental plates, there was a decrease in the IOD, with the 3 mm plate, (2.52±1.88) mm vertically and (2.46±1.64) mm anteroposteriorly; with 5 mm plate, (2.45±1.70) mm vertically and (2.22±1.31) mm anteroposteriorly. No significant differences were found between the control and 2 experimental conditions. CONCLUSION: The mandibular position during continuous [n] phonation was not influenced by the experimental palatal plates and physiological rest position was also not affected by experimental palatal plates.

Time Efficiency of Immediate Loading of Full-arch Implant Reconstructions Using Prefabricated Prostheses Located by an Anchor Pin: a Pilot Study.

OBJECTIVE: To investigate the time efficiency of prefabricated prostheses located by an anchor pin stereolithographic attachment system for immediate loading implant reconstruction of completely edentulous jaws and compare it with the conventional protocol. METHODS: Edentulous patients were recruited and randomly assigned into two groups: the full digital workflow group (digital group) and the conventional workflow group (conventional group). In the digital group, a provisional prosthesis was fabricated before surgery using a fully digital workflow and delivered immediately after implant placement. The positioning of the provisional prosthesis was guided precisely by the anchor pin attachment system. In the conventional group, the provisional prosthesis was fabricated after implant placement using a conventional procedure. Clinical and laboratory time efficiency were recorded, and clinician and patient satisfaction were evaluated. RESULTS: Six patients were enrolled in this pilot study and 57 implants were placed following the guided surgery protocol. Of these, 54 were immediately loaded. The total clinical chair time in the digital workflow group was significantly less than that in the conventional workflow group (digital 60.0 ± 13.2 minutes; conventional 106.7 ± 24.7 minutes) (P = 0.045). The total post-surgery procedure took significantly less time in the digital group than the conventional group (digital 202.5 ± 22.5 minutes; conventional 403.7 ± 55.4 minutes) (P = 0.004). The patients' and clinicians' satisfaction with the provisional prostheses was similar in both groups. CONCLUSION: Time efficiency in immediate loading of implant-supported full-arch fixed restorations was improved with prefabricated prostheses located by the anchor-pin-attachment system. Less postoperative chair time was required in the digital group than in the conventional group.

[Fatigue damage analysis of porcelain in all-ceramic crowns].

OBJECTIVE: To investigate the fatigue damage mechanism of porcelain, and its relation with the microscopic defects in clinically failed all-ceramic crowns. METHODS: Collecting the bilayered all-ceramic crowns failed in vivo. The fractured surfaces and occlusial surfaces of failed crowns were examined by an optical microscope followed by detailed fractography investigations using a field emission scanning electron microscope. When chemical impurities were of concern, energy-dispersive X-ray spectroscopy analysis was performed to examine chemical composition. A standard practice for fractography failure analysis of advanced ceramics is applied to disclose the fracture mode, and damage character. RESULTS: Three types of fracture features are defined as breakdown of the entire crown, and porcelain chipping-off/delamination. Alumina crowns were usually characterized by breakdown of the entire crown, while zirconia crowns by porcelain chipping-off and delamination. The fatigue damage of porcelain was classified into surface wear, cone crack, and porcelain delamination. The observed microscopic defects in this study included air bubbles and impurity particles. CONCLUSION: The multi-point occlusial contacts were recommended in all-ceramic restorations clinically. The thickness of porcelain is important for the anti-fatigue ability of porcelain. Cautions have to be taken to avoid contaminations during the veneering processes.

[Clinical application of computer-aided design and rapid prototyping technique for radioactive seeds contained maxillary device].

OBJECTIVE: To test a new method to manufacture a maxillary applicator containing radioactive seeds for brachytherapy of malignant neoplasms based on computer aided design (CAD) and rapid prototyping (RP). METHODS: Six patients with maxillary malignancy which had eroded the inferior wall of orbit and skull base were included in this study. After excision of the tumors, head CT data of these patients were transmitted into the computer. Three-dimensional digital image of the patient's defected region was then obtained with special software processing based on Mimics 8.11 and Geomagic 7.0 and the resin cast of the defected region was manufactured by rapid prototyping. The elastic obturator was then made on this resin cast which can duplicate the undercut tissue of the defected region. After the obturator was completed, the radiotherapy plan was made. (125)I radioactive seeds were implanted into the tissues, and they were also implanted into the target area of the obturator which was used as a maxillary applicator at the same time. The number of radioactive seeds was then counted and the stability of radioactive seeds was determined by CT examination. All these 6 patients were followed-up for 12 months. RESULTS: All the obturators had good retention and stability and fitted the designed target tissue very well. (125)I radioactive seeds in the form of the obturator applicator were stable. For all patients, the total number of radioactive seeds used was 189. Among them, 105 seeds, 55.6% of the total, were contained in obturator applicators. After the obturator applicators were used, the amount of radioactive seeds irradiating the target regions was significantly increased when compared with that of before. After follow-up of 12 months, there was no recurrence nor severe complications. CONCLUSION: (125)I radioactive seeds contained maxillary applicator made by computer aided design and rapid prototyping can effectively improve the brachytherapy of (125)I when it is used for the post-operation radiotherapy of maxillary malignant tumors.

[Evaluation of clinical application of ACP classification for edentulous patients].

OBJECTIVE: To evaluate clinical application of American College of Prosthodontics classification system for complete edentulism; and to analyze the relationship between clinician's rating of general degree of difficulty of each case and patients' rating of denture satisfaction. METHODS: One hundred and seven edentulous patients were examined clinically using American College of Prosthodontics (ACP) classification for complete edentulism. The least heights of patients' mandible were measured on panoramic radiographs. Clinician rated general degree of difficulty of each case on visual analogue scale. Six month following denture delivery, patients rated their denture using Mcgill satisfaction Visual Analog Scale (VAS). Multivariate linear regression analysis were conducted to analyze the relationship between clinician's rating of general degree of difficulty and mandibular bone height adjusting for confounding factors such as mandibular ridge form, soft tissue quality etc. Pearson correlation analysis was conducted to analyze the correlation between clinician's rating of case difficulty and patients' rating of denture satisfaction. RESULTS: Advanced residual ridge resorption were found in around 80% (83/105) of all the cases. When the least mandibular bone height were measured on panoramic radiographs, intra-examiner reliability was 0.96, inter-examiner reliability was 0.90. Cases were rated as more difficult when patients showed lower mandibular bone height, unfavorate ridge form (knife ridge and irregular ridge), mobile soft tissue and longer period of wearing time of their previous dentures. No significant correlation (r<0.1) was found between clinician's rating of degree of difficulty of each case and patients' rating of denture satisfaction 6 month following delivery of prostheses. Clinician rated cases in which patient's mandibular bone height was lower than 11 mm as 8.8%-16.1% more difficult than those in which patient's mandibular bone height was higher than 11 mm (P<0.05). CONCLUSION: ACP classification for complete edentulism showed good intra- and inter-examiner reliability, and is an useful tool for clinical evaluation of edentulous patients' oral condition. However, there was no significant correlation between clinicians' rating of difficulty of cases and patients' rating of denture satisfaction.

[Patterns of occlusal contacts during unilateral mastication in asymptomatic subjects].

OBJECTIVE: To analyze occlusal contact areas on the working and nonworking sides during unilateral mastication. METHODS: Eighteen subjects without any temporomandibular disorder (TMD) symptoms participated in the present study. The subjects were presented with 3 g gum for right masticating. Chewing movement was simulated using virtual craniofacial movement simulation system. Then occlusal contact areas were calculated at four selected moments during the closing phase in the third chewing cycle: the occurrence of occlusal contact, one third time, two thirds time, the intercuspal occlusion. RESULTS: During the closing phase in the third chewing cycle, the total occlusal contact areas on working side increased from (9.3+/-0.4) mm2 to (39.2+/-1.2) mm2, and that on nonworking side increased from (2.3 +/-0.5) mm2 to (40.3+/-1.2) mm2. At the occurrence of occlusal contacts, occlusal contact areas of the first and second mandibular molars were on average (3.7+/-0.2) mm2 and (3.5+/-0.2) mm2 on working side, and (0.5+/-0.2) mm2 and (1.2+/-0.3) mm2 on nonworking side, respectively. However, when the mandible moved to the intercuspal position, their areas were sharply increased to (14.8+/-0.7) mm2 and (13.9+/-0.4) mm2 on working side, and (13.6+/-0.5) mm2 and (12.1+/-0.5) mm2 on nonworking side, respectively. In addition, nonworking-side contacts were observed for 12 subjects at the occurrence of occlusal contacts, and for all subjects at two thirds time. CONCLUSION: This paper provides a new method useful for analyzing occlusal contacts during functional movements. This study revealed the pattern of occlusal contacts during the closing phase in the chewing cycle. Moreover, it was confirmed that nonworking-side contacts occurred during unilateral mastication.

Occlusal Rehabilitation in a Patient with Oligodontia and Microdontia using Implants and Full-Ceramic Restorations: A Clinical Report.

Oligodontia is the agenesis of six or more permanent teeth, excluding the third molars. Multidisciplinary dental treatments should be performed sequentially due to the restoration requirements for good oral function, aesthetics and self-confidence of patients. In this study, we report a case using dental implants and full-ceramic prostheses to restore the absent and malformed teeth in a patient with agenesis of 18 permanent teeth and with some primary teeth retained. The dental sequential treatments began when she was 16 years old, and she wore removable partial dentures for 4 years with unsatisfying restoration outcome. When she became an adult, dental implants and full-ceramic prostheses were used to restore the absent and malformed teeth. Finally, the patient was very satisfied with the functional and aesthetic outcomes of the prosthetic treatment.

[Short-term and long-term effects of occlusal rehabilitation on the co-contractration patterns of the electromyography of masticatory muscles].

OBJECTIVE: To investigate the short-term and long-term effects of occlusal rehabilitation on the co-contractration patterns of masticatory muscles of patients with extensive tooth wear. METHODS: Twenty-nine patients with severe tooth wear were selected and conducted with occlusal rehabilitation. The surface electromyography (EMG) of masseter (MM), anterior temporalis (TA) and posterior temporalis (TP) at rest position, during clenching and chewing were separately recorded in the stage of pre-treatment, 1 month after temporary restoration, 1 month after permanent restoration and long-term observation (mean 3.5 years). The Asymmetry Indexes (AI) of bilateral muscles, Activity Indexes of MM/TA, MM/TP and TA/TP were compared in each stage. RESULTS: (1) After occlusal rehabilitation, all the AIs of bilateral MM, TA and TP at rest position, during clenching and chewing showed obvious decrements. (2) In every stage of occlusal rehabilitation, all of the Activity Indexes of MM/TA at rest position, during clenching and chewing had no obvious changes. (3) The Activity Indexes of MM/TP and TA/TP during clenching and chewing significantly increased after occlusal rehabilitation. CONCLUSION: The treatment of occlusal rehabilitation can significantly improve the bilateral symmetry of masticatory muscles in patients with extensive tooth wear, and also change the coordinated EMG activity of different masticatory muscles.

[Influence of retention-form design on the retention of resin-bonded fixed partial dentures].

OBJECTIVE: To evaluate the influence of retention-form design of resin bonded fixed partial dentures (RBFPDs). METHODS: Forty-five metal replicas of posterior metal RBFPDs were divided into 3 groups(n=15):C shape(control group), C shape + axial groove, C shape + pin hole. All the replicas were luted with Panavia F cement and subgroup of 5 specimens were subject to 70 N compressive load cycling for 0 cycles, 240,000 cycles , and 1,200,000 cycles respectively .Half of the cycles was on the central fossa of the pontics and half on the buccal inclined surface of the lingual cusp. Forces for dislodgment of the specimens were applied along the long axis of the abutment at a cross head speed of 1.0 mm /min. The separation forces were recorded as maximum retention force at the time of dislodgement. RESULTS: Separation forces of the C shape group (566.82+/-71.59 N)0.05). After 1,200,000 cycles, the retention force of the RBFPDs decreased significantly (P<0.001). CONCLUSION: To compare with axial groove, the design of pinhole retention form was conduced to the improvement of the retention force and durability of RBFPDs.

[Construction of the stable cell line expressing the mouse recombinant enamelin gene].

OBJECTIVE: To construct a mouse recombinant enamelin eukaryocyte expression system, and establish the stable cell line which can produce the protein continuously. METHODS: The mRNA transcript from the 3-day mouse jaw was extracted. and the enamelin gene fragment amplified with RT-PCR techniques. Then the PCR product was cat with two restriction enzymes, and subcloned into the eukaryotic gene expression vector pcDNA3.1TM/mycj His(-)B.The recombinant plasmid was transformed into E.coli DH5alpha bacterial cells, and harvested with plasmid midi kit. The recombinant expression plasmid was transferred to the HEK 293A eukaryocyte cells, cultured selectively with 800 mg/L G418, and examined with SDS-PAGE and Western Blot at the protein level. RESULTS: The mouse enamelin gene was cloned to the eukaryotic expression plasmid successfully by sequence measuring. After the recombinant plasmid was transferred into the HEK 293A cells, about 32,000 enamelin protein was checked out by SDS-PAGE and Western Blot. CONCLUSION: The recombinant eukaryocyte expression plasmid and the stable cell line were established. This is a basic research to obtain high-yeild biologically active enamelin protein, which may facilitate further investigation of its function.

[Research advances in tooth agenesis].

Tooth agenesis constitutes one of the most common developmental anomalies in man. Oligodontia is defined as congenital absence of six or more teeth. Based on the studies of our team in cooperation with Peking University Center for Human Disease Genomics in the past five years, this article reviews the current research progress in clinical phenotypes and case collection, epidemiological investigation and etiological genetic studies of oligodontia. The symptoms of oligodontia were classified into syndromic and non-syndromic according to the occurrence of tooth agenesis with or without systemic developmental defects. As for the advancement of theories and techniques of molecular genetics, a number of gene mutations have been identified to be the direct etiological factors causing some specified diseases, especially those with developmental defects. Here, this article summarized the outcomes of molecular genetic study of some cases we collected. Of the systemic oligondontia patients, a new four-base-deletion mutation in PITX2 was identified in a large kindred with typical symptoms of Rieger Syndrome; four different gene mutations in ED1 casing X-linked hypohidrotic ectodermal displasia were found in five nucleus families. Compared with the former, non-syndromic oligodontia has more genetic heterogeneity rather than some specific virulence gene. PAX9 and MSX1 are the identified genes associated with family tooth agenesis without systemic syndrome. Also, in our research, three gene mutations in CBFA1 were detected in four cleidocranial dysplasia families, which is a systemic developmental disease including the symptoms of tooth eruption abnormality and accessory teeth.

[Biomimetics of crystal texture in dental enamel prism by self-assembly oligopeptide].

OBJECTIVE: To evaluate the possibility of self-assembly oligopeptide(T2) for dental enamel biomimetics, especially for the prism's crystal texture since it could prompt calcium phosphate precipitated in gel carrier. METHODS: SEM (Scanning electron microscope) and TEM (Transmission electron microscope) were used to observe the morphologic presentation and ED(Electron diffraction) to crystal texture comparing with the human molar enamel powder. RESULTS: (a) Flake-like and needle-like octacalcium phosphate precipitated in the gel carrier with self-assemble oligopeptide(T2). They transformed into rod-like hydroxyapatite crystals gradually in the following 2-4 weeks. (b) The rod-like hydroxyapatite may arrange or grow into bundles which are similar to the human enamel prisms in both appearance and size. (c) The rod-like hydroxyapatite showed polycrystal while the enamel prisms showed monocrystal under examination of ED. CONCLUSION: The self-assemble oligopeptide(T2) could regulate the speed of nucleation and crystallization of hydroxyapatite in morphology and crystalline size. Thus, the self-assembly oligopeptide and the gel carrier mineralization system could be primarily applied in biomimetic use for the crystallization of hydroxyapatite in dental prism in vitro.

[Effect of core: dentin thickness ratio on the flexure strength of IPS Empress II heat-pressed all-ceramic restorative material].

OBJECTIVE: To evaluate the effect of core:dentin thickness ratio on the flexure strength, fracture mode and origin of bilayered IPS Empress II ceramic composite specimens. METHODS: IPS Empress II core ceramic, dentin porcelain and bilayered composite specimens with core:dentin thickness ratio of 2:1 and 1:1 were tested in three-point flexure strength. Mean strengths and standard deviations were determined. The optical microscopy was employed for identification of the fracture mode and origin. RESULTS: The flexure strength of dentin porcelain was the smallest(62.7 MPa), and the strength of bilayered composite specimens was smaller than single-layered core ceramic(190.2 MPa). The core: dentin ratio did not influence the strength of bilayered composite specimens. The frequency of occurrence of bilayered specimen delaminations was higher in the group of core: dentin thickness ratio of 1:1 than in the group of 2:1. CONCLUSION: IPS Empress II core ceramic was significantly stronger than veneering dentin porcelain. Core:dentin thickness ratio could significantly influence the fracture mode and origin, and bilayered IPS Empress II ceramic composite specimens showed little influence in the fracture strength.