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1.

Statement of problem

The degree of mandibular bone atrophy can guide and determine the choice of prosthetic treatment. Although several methodologies have been proposed for classifying atrophy, the clinical and radiographic parameters considered for the classification of mandibular bone atrophy should be standardized.

Purpose

The purpose of this clinical study was to evaluate the influence of methodologies of mandibular bone atrophy categorization on the masticatory function in complete denture (CD) wearers and to verify the relationship between these parameters according to the retention and stability of the mandibular CD.

Material and methods

CD wearers were radiographically and clinically evaluated to determine the mandibular bone atrophy levels. Three classifications were adopted: the Cawood and Howell criteria, the Wical and Swoope criteria, and the Kapur classification. CD retention and stability were scored based on the Sato et al method. The masticatory function was evaluated by the multiple sieve method using optical test food to determine the masticatory performance (MP) indexes (median particle size, MP X50; homogeneity index, MP B) and the masticatory efficiency (sieves 4 and 2.8).

Results

In this sample of 63 individuals (mean age of 67.4 years), atrophic participants presented significant differences in all radiographic parameters (Mann–Whitney test, P<.05) with both the Cawood and Howell and Wical and Swoope methodologies. No differences in masticatory function were found, except for atrophic participants classified by Wical and Swoope criteria, who had worse MP X50 (P=.047) than nonatrophic participants, with a medium effect size of 0.7. The retention of the mandibular CD significantly affected the masticatory outcomes, with higher values for MP X50 (P=.012) and MP B (P=.040) and lower values for masticatory efficiency, 2.8 (P=.008) for atrophic participants. The presence of mandibular bone atrophy showed an association with poor retention (P=.04) and poor stability (P=.002) when the Cawood and Howell criteria were adopted (Fisher exact test, P<.05).

Conclusions

The Kapur classification confirmed the clinical condition of the participants' atrophy, and the most clinically atrophic participants showed poor retention and stability of the mandibular CD. Only the poor retention directly affected the masticatory function. Radiographic evaluations alone did not provide sufficient data to determine the predictability of CD treatment regarding the participants' masticatory function. Radiographically, atrophic participants with poor retention had impaired mastication.  相似文献   

2.
Restoring a single darkened central incisor can be challenging. Both direct and indirect options may be acceptable to mask discoloration and achieve functional requirements. This report describes placement of a modified feldspathic porcelain veneer to reproduce the appearance of a maxillary central incisor discolored after trauma.  相似文献   

3.

Statement of problem

Clinical evidence on the best chemical protocol for the disinfection and removal of biofilm from complete dentures is lacking.

Purpose

The purpose of this crossover randomized clinical trial was to assess the effectiveness of various chemical hygiene clinical protocols in reducing the microbial viability of biofilm formed on complete dentures.

Material and methods

In this triple-blind (participants, dentist, and outcome evaluator) study, complete denture wearers without candidiasis were randomly divided into 4 groups (n=40) according to the chemical hygiene protocol: water (placebo), 0.5% sodium hypochlorite solution, 0.12% chlorhexidine gluconate solution, and 5% sodium bicarbonate solution. The biofilm formed on the palate intaglio and denture teeth was collected and assessed in each experimental phase for quantitative microbial viability at the seventh and 14th day after using the chemical protocol.

Results

Two participants were lost. Data were analyzed by MANOVA and Tukey HSD tests. Soaking dentures was not effective in decreasing Candida albicans, C. non-albicans, and lactobacillus counts. The use of sodium hypochlorite and chlorhexidine decreased total microorganisms and Streptococcus mutans counts for both palate and teeth compared with water and sodium bicarbonate. The intaglio of the dentures always presented higher microbial counts than did the denture teeth.

Conclusions

The use of sodium hypochlorite and chlorhexidine and mechanical cleansing with a toothbrush decreased microbial viability in healthy complete denture wearers.  相似文献   

4.
PurposeThis systematic review and meta-analysis aimed to evaluate the difference in longevity of tooth-supported ceramic prostheses designed by conventional and computer-aided design/computer-aided manufacturing (CAD/CAM) techniques.Study selectionTwo reviewers searched the Web of Science, PubMed, SCOPUS and LILACS databases between 1966 and October 2017. Clinical studies that compared the survival rate of CAD/CAM against conventional restorations were included.ResultsEleven randomized controlled trials and three prospective studies were included, n = 14. Three types of tooth-supported restorations were searched in the included studies: single crown, multiple-unit and partial ceramic crown. The follow-up of patients in the studies ranged from 24 to 84 months. A total of 1209 restorations had been placed in 957 patients in the included trials, and failures were analyzed by type and material restoration. From a total of 72 restoration failures, the CAD/CAM system resulted in a 1.84 (IC95%: 1.28–2.63) higher risk than conventional manufacturing of ceramic restoration. Nevertheless, when drop-outs were included as a failure risk, the CAD/CAM system resulted in a risk of 1.32 (IC95%: 1.10–1.58). Multilevel analysis of tooth-supported ceramic restorations, considering drop-outs as successes, resulted in rates of 1.48 and 2.62 failures per 100 restoration-years for the controls and CAD/CAM groups, respectively. Considering drop-outs as failures, we found rates of 4.23 and 5.88 failures per 100 restoration-years for the controls and CAD/CAM groups, respectively.ConclusionsThe meta-analysis results suggest that the longevity of a tooth-supported ceramic prostheses made by CAD/CAM manufacturing is lower than that of crowns mad by the conventional technique.  相似文献   

5.

Statement of problem

Ceramic restorations are popular because of their excellent optical properties. However, failures are still a major concern, and dentists are confronted with the following question: is sleep bruxism (SB) associated with an increased frequency of ceramic restoration failures?

Purpose

The purpose of this systematic review and meta-analysis was to assess whether the presence of SB is associated with increased ceramic restoration failure.

Material and methods

Observational studies and clinical trials that evaluated the short- and long-term survival rate of ceramic restorations in SB participants were selected. Sleep bruxism diagnostic criteria must have included at least 1 of the following: questionnaire, clinical evaluation, or polysomnography. Seven databases, in addition to 3 nonpeer-reviewed literature databases, were searched. The risk of bias was assessed by using the meta-analysis of statistics assessment and review instrument (MAStARI) checklist.

Results

Eight studies were included for qualitative synthesis, but only 5 for the meta-analysis. Three studies were categorized as moderate risk and 5 as high risk of bias. Clinical and methodological heterogeneity across studies were considered high. Increased hazard ratio (HR=7.74; 95% confidence interval [CI]=2.50 to 23.95) and odds ratio (OR=2.52; 95% CI=1.24 to 5.12) were observed considering only anterior ceramic veneers. Nevertheless, limited data from the meta-analysis and from the restricted number of included studies suggested that differences in the overall odds of failure concerning SB and other types of ceramic restorations did not favor or disfavor any association (OR=1.10; 95% CI=0.43 to 2.8). The overall quality of evidence was considered very low according to the GRADE criteria.

Conclusions

Within the limitations of this systematic review, the overall result from the meta-analysis did not favor any association between SB and increased odds of failure for ceramic restorations.  相似文献   

6.

Statement of problem

The success of single, anterior, implant-supported restorations relies on mechanical and esthetic outcomes. Titanium has been the most commonly used material for abutments, but zirconia is increasingly chosen for its appearance despite its unclear mechanical performance. Today, manufacturers market prefabricated, computer-aided design and computer-aided manufacturing (CAD-CAM) custom and zirconia abutments with titanium connections.

Purpose

The purpose of this study was to systematically review the mechanical and esthetic outcomes of implant zirconia abutments used in the anterior region, considering the design changes of the past 5 years.

Material and methods

An electronic search was conducted in Medline (PubMed) for studies on zirconia abutments. All clinical studies with at least a 1-year follow-up and case series (>5 abutments) published after 2013 were included. Mechanical and esthetic outcomes were collected.

Results

Of the 231 retrieved studies, 20 remained for quantitative analysis. Twelve described mechanical outcomes, and 15 focused on esthetics, using mainly the pink esthetic score. Five articles reported abutment fractures and no chipping. No difference was found between prefabricated and custom abutments or internal and external implant connections regarding fractures or screw loosening. All authors reported “good to excellent” esthetic integration in terms of restorations and soft-tissue color and the presence and height of papillae. The most difficult esthetic parameters to achieve were root convexity, soft-tissue color, and texture and level of mucosa.

Conclusions

Esthetics remain the major advantage of zirconia abutment when compared with titanium, despite reservations concerning the risk of mechanical complications. Data are lacking for zirconia abutments with titanium inserts, although the prospects for this design are promising.  相似文献   

7.

Statement of problem

No knowledge synthesis exists concerning when to use a direct restoration versus a complete-coverage indirect restoration in posterior vital teeth.

Purpose

The purpose of this systematic review was to identify the failure rate of conventional single-unit tooth-supported restorations in posterior permanent vital teeth as a function of remaining tooth structure.

Material and methods

Four databases were searched electronically, and 8 selected journals were searched manually up to February 2015. Clinical studies of tooth-supported single-unit restorative treatments with a mean follow-up period of at least 3 years were selected. The outcome measured was the restorations’ clinical or radiological failure. Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines, the Cochrane Collaboration procedures for randomized control trials, the Strengthening the Reporting of Observational Studies in Epidemiology criteria for observational studies, 2 reviewers independently applied eligibility criteria, extracted data, and assessed the quality of the evidence of the included studies using the American Association of Critical Care Nurses’ system. The weighted-mean group 5-year failure rates of the restorations were reported according to the type of treatment and remaining tooth structure. A metaregression model was used to assess the correlation between the number of remaining tooth walls and the weighted-mean 5-year failure rates.

Results

Five randomized controlled trials and 9 observational studies were included and their quality ranged from low to moderate. These studies included a total of 358 crowns, 4804 composite resins, and 303 582 amalgams. Data obtained from the randomized controlled trials showed that, regardless of the amount of remaining tooth structure, amalgams presented better outcomes than composite resins. Furthermore, in teeth with fewer than 2 remaining walls, high-quality observational studies demonstrated that crowns were better than amalgams. A clear inverse correlation was found between the amount of remaining tooth structure and restoration failure.

Conclusions

Insufficient high-quality data are available to support one restorative treatment or material over another for the restoration of vital posterior teeth. However, the current evidence suggests that the failure rates of treatments may depend on the amount of remaining tooth structure and types of treatment.  相似文献   

8.

Statement of problem

The accuracy of the virtual images used in digital dentistry is essential to the success of oral rehabilitation.

Purpose

The purpose of this systematic review was to estimate the mean accuracy of digital technologies used to scan facial, skeletal, and intraoral tissues.

Material and methods

A search strategy was applied in 4 databases and in the non–peer-reviewed literature from April through June 2017 and was updated in July 2017. Studies evaluating the dimensional accuracy of 3-dimensional images acquired by the scanning of hard and soft tissues were included.

Results

A total of 2093 studies were identified by the search strategy, of which 183 were initially screened for full-text reading and 34 were considered eligible for this review. The scanning of facial tissues showed deviation values ranging between 140 and 1330 μm, whereas the 3D reconstruction of the jaw bone ranged between 106 and 760 μm. The scanning of a dentate arch by intraoral and laboratorial scanners varied from 17 μm to 378 μm. For edentulous arches, the scanners showed a trueness ranging between 44.1 and 591 μm and between 19.32 and 112 μm for dental implant digital scanning.

Conclusions

The current digital technologies are reported to be accurate for specific applications. However, the scanning of edentulous arches still represents a challenge.  相似文献   

9.
Harmony among the teeth, lips, and facial components is the goal of prosthodontic treatment, whether performed by conventional or digital workflow methods. This clinical report describes a facial approach to planning computer-guided surgery and immediate computer-aided designed and computer-aided manufactured (CAD-CAM) interim complete-arch fixed dental prostheses on immediately placed dental implants with a digital workflow. A single clinical appointment for data collection included dentofacial documentation with photographs and videos. On these photographs, facial reference lines were drawn to create a smile frame. This digital smile design and sagittal cephalometric analysis were merged with 3-dimensional scanned casts and a cone beam computed tomographic file in virtual planning software, thus guiding virtual waxing and implant positioning. Computer-guided implant surgery and CAD-CAM interim dental prostheses allowed esthetic and functional rehabilitation in a predictable manner and integrated with the patient’s face.  相似文献   

10.

Statement of problem

Consensus is lacking regarding the optimal number of implants for supporting complete-arch prostheses with good survival rates and lower prosthetic complications and marginal bone loss.

Purpose

The purpose of this systematic review was to evaluate the influence of the number of implants used for complete-arch prostheses with at least 5 years of follow-up.

Material and methods

A search was performed in the PubMed/MEDLINE, Scopus, and Cochrane Library databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria and was registered in The International Prospective Register of Systematic Reviews (CRD42016048468). The following was the population, intervention, comparison, outcome (PICO) question: Does the number of implants influence the longevity of complete-arch prostheses?

Results

Nineteen studies including 1006 patients with a mean age of 61.44 years were selected for evaluation. The number of implants per jaw ranged between 2 and 9 in the maxilla, mandible, or both jaws. For implant survival rate in complete-arch prostheses with fewer than 5 implants per jaw, the pooled weighted event rate was 1.4% (I2=25.26%; P=.211) and 4.2% (I2=81.35%; P<.001) for complete arches with more than 4 implants per jaw. For the prosthesis survival rate, the pooled weighted event rate for a complete-arch with fewer than 5 implants per jaw was 1.5% (I2=0%; P=.677) and 9% (I2=17.33%; P=.304) for complete arches with more than 4 implants per jaw. For prosthesis complications for complete arches with fewer than 5 implants per jaw, the pooled weighted event rate was 19.9% (I2=93.5%; P<.001) and 24.5% (I2=88.89; P<.001) for complete arches with more than 4 implants per jaw. The mean marginal bone loss for complete arches with fewer than 5 implants per jaw was 1.22 ±0.49 mm (I2=99.46; P<.001) and 1.46 ±0.46 mm (I2=99.6; P <.001) for more than 4 implants per jaw.

Conclusions

The current systematic review indicated no relationship of the number of implants used to support a complete-arch prosthesis with implant survival rate, prosthesis survival rate, prosthesis complications, or marginal bone loss in studies with follow-up periods of between 5 and 15 years.  相似文献   

11.

Statement of problem

Whether microthreads in the crestal portion can reduce the amount of marginal bone loss (MBL) around implants has not yet been determined.

Purpose

The purpose of this systematic review was to investigate the marginal bone loss around dental implants with and without microthreads in the neck.

Material and methods

This review was based on the PRISMA guidelines. An electronic search with no restrictions on language was performed from inception to August 19, 2015, in PubMed, Cochrane Central Register of Controlled Trials, EMBASE, Web of Sciences, and AMED (Ovid) databases. A manual search was also performed. Randomized clinical trials (RCTs) that compared the MBL between implants with and without microthreads in the neck were included. Qualitative synthesis and meta-analysis were performed. MBL was measured by using the mean difference (MD). Review Manager v5.3 software was used for meta-analysis (α=.05).

Results

Five articles were included in the qualitative synthesis, and 3 articles were included in the meta-analysis. Four studies found that a microthread design can significantly reduce MBL under functional loading, whereas 1 study found no signi?cant difference. The homogeneity test of meta-analysis confirmed acceptable heterogeneity among the 3 studies (I2=0.49). A random-effects model was used. The result shows that MBL around implants with microthread design can be reduced signi?cantly (P=.030; MD: ?0.09; CI: ?0.18 to ?0.01).

Conclusions

Meta-analysis showed that microthread design in the implant neck can reduce the amount of MBL; however, RCTs included in the review were few and the difference was small. In clinical practice, an implant with a roughened surface and microthreaded neck could be selected to maintain bone level.  相似文献   

12.

Statement of problem

The decision to splint or to restore independently generally occurs during the planning stage, when the advantages and disadvantages of each clinical situation are considered based on the proposed treatment. However, clinical evidence to help clinicians make this decision is lacking.

Purpose

The purpose of this systematic review and meta-analysis was to assess the marginal bone loss, implant survival rate, and prosthetic complications of splinted and nonsplinted implant restorations.

Material and methods

This study was designed according to the Cochrane criteria for elaborating a systematic review and meta-analysis and adopted the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. Also, this review was registered at the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42017080162). An electronic search in the PubMed/MEDLINE, Cochrane Library, and Scopus databases was conducted up to November 2017. A specific clinical question was structured according to the population, intervention, comparison, outcome (PICO) approach. The addressed focused question was “Should the restoration of adjacent implants be splinted or nonsplinted?” The meta-analysis was based on the Mantel-Haenszel and inverse variance methods to assess the marginal bone loss, implant survival, and prosthetic complications of splinted and nonsplinted implant restorations.

Results

Nineteen studies were selected for qualitative and quantitative analyses. A total of 4215 implants were placed in 2185 patients (splinted, 2768; nonsplinted, 1447); the mean follow-up was 87.8 months (range=12-264 months). Quantitative analysis found no significant differences between splinted and nonsplinted restorations for marginal bone loss. The assessed studies reported that 75 implants failed (3.4%), of which 24 were splinted (99.1% of survival rate) and 51 were nonsplinted (96.5% of survival rate). Quantitative analysis of all studies showed statistically significant higher survival rates for splinted restorations than for nonsplinted restorations. Ceramic chipping, screw loosening, abutment screw breakage, and soft tissue inflammation were reported in the selected studies. The quantitative analysis found no statistically significant difference in the prosthetic complications of splinted and nonsplinted restorations.

Conclusions

Within the limitations of this systematic review and meta-analysis, it was concluded that there was no difference in the marginal bone loss and prosthetic complications of splinted and nonsplinted implant restorations; this is especially true for restorations in the posterior region. However, splinted restorations were associated with decreased implant failure.  相似文献   

13.

Statement of problem

Contamination with salivary fluids or blood during the treatment process changes the preload, remaining torque, and removal torque of retained screws, which ultimately affects the resistance to screw loosening. In previous studies, no consensus has been reached as to whether contamination can be used as a lubricant.

Purpose

The purpose of this 3-dimensional (3D) finite element analysis study was to compare the preload, remaining torque, and removal torque under different frictional conditions in the processes of tightening, waiting period, and removal of abutment screws using a numeric method and finite element analysis.

Material and methods

Three-dimensional finite element models of a single implant restoration including a crown, dental implant, abutment, and abutment screw, along with the surrounding bone, were constructed. The geometry of all threaded interfaces was designed as a threaded helix. The Abaqus software was used to perform the dynamic simulation of 3 steps such as tightening, waiting period, and removal. Three static and kinetic friction conditions were considered to determine the effect of different frictional conditions. The values of preload at the tightening step, remaining torque at the waiting period, and removal torque at the removal step were evaluated and compared with theoretically predicted values.

Results

The amount of removal torque required to loosen the abutment screw was smaller than the insertion torque for all frictional conditions. By decreasing the coefficient of friction, the remaining torque and the preload increased, and the torsional relaxation and removal torque decreased.

Conclusions

Although the value of the removal torque decreased by decreasing the coefficient of friction, the resistance to screw loosening increased with the increase of the preload and the increase of the remaining torque in the implant complex assembly. Considering the biological complications of fluid lubricants, clinicians may contaminate the abutment screw with lubricants. Gold-coated screws should also be preferred to noncoated screws.  相似文献   

14.

Statement of problem

Nonthermal argon plasma may increase the surface energy of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) dental ceramics. However, studies that evaluated the effect of increased plasma treatment times on the bond strength of resin cements to Y-TZP ceramics are lacking.

Purpose

The purpose of this in vitro study was to evaluate the effect of different nonthermal argon plasma (NTAP) treatment times on the surface energy and bond strength of a self-adhesive resin cement to Y-TZP ceramic.

Material and methods

Forty-eighty Y-TZP plates were divided into 2 groups (n=24): as-sintered (AS) and airborne-particle abrasion (APA) with 50-μm Al2O3, which were subdivided into 4 groups (n=6) according to the time of NTAP treatment: 0, 20, 60, and 120 seconds. The surface energy was evaluated with a goniometer. Forty Y-TZP blocks submitted to the same surface treatments (8 groups; n=5) were cemented to composite resin blocks, using a self-adhesive resin cement. After storage in distilled water at 37°C for 24 hours, the Y-TZP-composite resin blocks were cut into beams and submitted to a microtensile bond strength (μTBS) test. Data were analyzed using 2-way ANOVA and the Tukey honestly significant differences test (α=.05).

Results

Treatment with NTAP increased the surface energy for AS and APA groups (P<.05). For both groups, the μTBS was as follows: 0 seconds < 20 seconds < 60 seconds = 120 seconds (P<.05). Only after 120 seconds of NTAP treatment was the μTBS of APA higher than that of AS (P<.05).

Conclusions

Treatment with NTAP improved the surface energy and increased the μTBS of self-adhesive resin cement to Y-TZP ceramic, with higher times of plasma treatment resulting in higher bond strength.  相似文献   

15.
The multidisciplinary teams involved in the treatment of individuals with cleft lip and palate are challenged when implants are indicated in the cleft area. Difficulties include obtaining a healthy peri-implant area and, especially, obtaining the natural-looking papilla essential for esthetic success. The area affected by the cleft has a bone deficiency, which is typically augmented with an alveolar bone graft at adolescence. Guidelines for the 3-dimensional placement of implants at the cleft area are presented based on clinical reports. The patients were followed up for at least 1 year. Adoption of the proposed guidelines enables satisfactory esthetic and functional outcomes in patients with cleft lip and palate.  相似文献   

16.

Statement of problem

Spark erosion is a fit corrective technology that can be used even after the veneering material has been applied. The framework does not require sectioning, thus preserving its mechanical resistance. However, the spark erosion effect on veneered Co-Cr fixed complete denture (FCD) frameworks has not been investigated.

Purpose

The purpose of this in vitro study was to evaluate whether spark erosion is effective in improving marginal fit on screw-retained Co-Cr FCD frameworks veneered with different materials. A comparison between ceramic applications and simulated ceramic firing cycles was also investigated.

Material and methods

Forty FCD frameworks were fabricated with a Co-Cr alloy. Four groups (n=10) were obtained according to the veneer material used on frameworks: HR (heat-polymerized resin); LR (light-polymerized resin); C (ceramic); and SC (simulated ceramic firing cycle). The spark erosion process was conducted for all groups. The marginal fit was analyzed according to the single-screw test protocol, and the measurements were performed at 3 evaluation times: initial, after veneer material application, and after spark erosion process. The results were submitted to a 2-way repeated measures ANOVA and the Tukey honest significant differences test (α=.05).

Results

Poorer marginal fit (in micrometers) was noted after veneer material application, where the HR and C groups presented the worst values (HR: 170; LR: 72; C: 165; SC: 86; P<.05). The spark erosion process was effective in improving the fit for all groups (HR: 109; LR: 52; C: 110; SC: 60; P<.05).

Conclusions

Spark erosion improved the fit of Co-Cr FCD frameworks veneered with different materials. An actual ceramic application should be used to assess distortions generated by veneer material application instead of using only simulated ceramic firing cycles.  相似文献   

17.

Statement of problem

The effects of coping and veneer thickness on the color of zirconia-based restorations are unknown.

Purpose

The purpose of this in vitro study was to evaluate the influence of coping and veneer thickness on the color of zirconia-based restorations on different implant abutment backgrounds and to define minimum coping and veneer thicknesses for the backgrounds investigated to achieve a target color.

Material and methods

Thirty zirconia disk specimens with thicknesses of 0.4, 0.6, and 0.8 mm and 30 veneering ceramic disk specimens with thicknesses of 0.8, 1.0, and 1.2 mm were fabricated. Three backgrounds were prepared: titanium alloy, zirconia ceramic, and base metal alloy. The zirconia specimens were placed on the backgrounds, and the veneering ceramic specimens were located on the zirconia specimens. Spectrophotometric measurements were made to determine CIELab values. Color difference (ΔE) values were calculated to measure color differences between the specimens and the A2 VITA classical shade tab. ΔE values were compared with a perceptibility threshold (ΔE=2.6). Repeated measures ANOVA, Bonferroni test, and 1-sample t test were used to analyze data (α=.05).

Results

Mean ΔE values ranged from 2.0 to 9.8. Coping thickness, veneer thickness, and their combination significantly affected ΔE (P<.001).

Conclusions

To achieve the target color with zirconia-based restorations, regardless of the backgrounds tested, the minimum thickness of zirconia coping should be 0.6 mm, and the minimum thickness of veneering ceramic should be 1.2 mm.  相似文献   

18.
Statement of problemRestorative materials are cemented on different types of substrates, such as dentin, metal, and glass-fiber posts with composite resin cores.PurposeThe purpose of this in vitro study was to evaluate the failure behavior after cycling fatigue of a polymer-infiltrated ceramic network material (PICN; VITA ENAMIC) cemented on different supporting substrates.Material and methodsPICN plates (N=80) were obtained from computer-assisted design and computer-assisted manufacturing (CAD-CAM) blocks and cemented with a resin cement to 4 different supporting substrates (n=20): (1) human dentin (PICNDen); (2) dentin analog (PICNDenAn); (3) nickel-chromium alloy (PICNNiCr); and (4) composite resin plus fiberglass post (PICNRc). For comparison, the fracture behavior of a feldspathic ceramic (FelDenAn; VITABLOCS Mark II) and an indirect composite resin (ResDenAn; Opallis LAB Resin) cemented to the DenAn substrate was investigated (n=20). Thus, specimens were composed of the restorative material layer (1-mm thick) resin cemented (0.1-mm-thick layer) to a 2-mm-thick supporting substrate. All specimens were subjected to mechanical cycling (MC) using a pneumatic cycling machine (500 000 cycles, 2 Hz, 50 N). Specimens that did not fracture during cycling were tested under compression using a universal testing machine at a cross-head speed of 0.5 mm/min until the sound of the first crack was detected using an acoustic system. Failure data were statistically evaluated using Weibull distribution. Failures were classified as radial crack, cone crack, combined, and catastrophic fracture.ResultsAll FelDenAn specimens were fractured during MC. Only 4 PICNRc specimens survived MC, so their fracture load data were not statistically analyzed. PICNNiCr showed the greatest characteristic load (L0) value, followed by ResDenAn. Groups PICNDenAn and PICNDen showed lower and similar L0 but statistically different Weibull modulus (m). There was a significant relationship between experimental group and failure mode (P<.001). FelDenAn and PICNRc had a higher frequency of radial cracks, whereas PICNNiCr failed from cone cracking.ConclusionsThe supporting substrate influenced the failure behavior of PICN. When the substrate had a higher elastic modulus than the restorative material, better mechanical behavior was observed.  相似文献   

19.

Statement of problem

Cement-retained implant-supported prostheses eliminate screw loosening and enhance esthetics. However, retrievability and the possibility of removing extruded excess cement (EEC) have been problematic.

Purpose

The purpose of this systematic review was to analyze the effects of modifying the screw access channel (SAC) on the amount of EEC and the retention of cement-retained implant-supported prostheses.

Material and methods

PubMed, Web of Science, Scopus, and Google Scholar databases were searched with appropriate key words. Related titles and abstracts published up to June 2017 were screened and selected on the basis of defined inclusion criteria. Full texts of all studies were read and subjected to quality assessments. After the initial search, 1521 articles were included in the study. Of these, 11 studies were subjected to critical appraisal, and 10 of them were reliable enough in methodology to be systemically reviewed.

Results

All the studies were in vitro and described a total of 260 specimens. According to the interpreted results, closed SACs caused lower retention with a higher amount of EEC, whereas open SACs caused the reverse. Also, as the abutment height decreased, retention decreased.

Conclusions

Extending the crown’s margin into the SAC, leaving the SAC open, and using internal vents in the SAC space are possible methods of modifying the SAC to gain higher retentive values. Also, the use of internal vents in the SAC system and open or partially filled SAC space reduce the amount of EEC.  相似文献   

20.
The facial masks commercially available for noninvasive positive pressure ventilation therapy for children with clinical conditions of hypoventilation are limited by size and hardness. The present report describes a straightforward method of developing a nasal mask from a room-temperature vulcanizing silicone elastomer for daily contact with the nasal mucosa of babies during noninvasive positive pressure ventilation. The fabrication of the silicone mask with nasal tubes is based on maxillofacial prosthesis techniques, with retention with steel prongs and elastics.  相似文献   

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