Effect of non-thermal plasma treatment and resin cements on the bond strength of zirconia ceramics with different yttria concentrations.

OBJECTIVES: To investigate the effect of different surface treatments and resin cements on the shear bond strength of zirconia ceramics with different yttria concentrations. METHODS: Zirconia blocks characterized by different yttria concentrations [Vita YZ HT (HT), Vita YZ ST (ST) and Vita YZ XT (XT)] were used to prepare disc-shaped specimens (n=252). Specimens prepared to investigate shear bond strength (SBS), water contact angle and surface roughness (Ra) were divided into four subgroups; control (C), sandblasting (S), sandblasting + nonthermal plasma treatment (SNTP) and nonthermal plasma treatment (NTP). For SBS testing, specimens were further divided into two groups (n=108) according to the luting cement used [Panavia F2.0 (P) and Rely X U200 (R)]. The water contact angles were determined by sessile drop technique and Ra was analyzed with optical profilometer. SBS tests were performed in a universal testing machine at a crosshead speed of 0.5 mm/min. The data sets were statistically analyzed with two and three-way ANOVAs followed by post-hoc comparisons (α=0.05). RESULTS: The water contact angle and Ra data were significantly affected by surface treatments. The mean Ra values of ST and XT were significantly lower than HT for the surface treatment groups of C and NTP. The SBS values were significantly different among the groups subjected to different surface treatments. The mean SBS values of surface treatment groups (S, SNTP and NTP) when cemented with R were significantly higher than the groups of C (p<0.05). CONCLUSIONS: For the tested zirconia ceramics with different yttria concentrations, non-thermal plasma activation helps to improve SBS and is a promising tool in practical use.

Prevalence of Proximal Contact Loss between Implant-Supported Prostheses and Adjacent Natural Teeth: An Umbrella Review.

Contact loss between the implant prosthesis and adjacent natural teeth is a clinical complication whose overall prevalence is uncertain. Therefore, the main purpose of this umbrella study was to evaluate the extent of contact loss between implant prostheses and adjacent natural teeth. Electronic database of MEDLINE/PubMed, Cochrane, and Google Scholar was searched until August 2021 without considering language restrictions and according to Preferred Report Items for Systematic and Meta-Analysis guidelines (preferential reporting items for systematic review and meta-analysis). Inclusion criteria were systematic/meta-analysis review articles related to contact loss between implant prostheses and adjacent natural teeth. Inclusion criteria and risk of bias for the selected systematic/meta-analysis review studies were assessed by two or three qualified researchers, and the fourth researcher was used to resolve the ambiguities. From 43 eligible articles, five systematic/meta-analysis review studies were selected for this study. Important information such as the range of contact points, the prevalence, and the location of the contact loss was extracted. Three research studies had a low risk of bias and were considered clinical evidence. Analysis of low-risk studies showed that the superiority of open contact loss was excessive. Prevalence of proximal contact loss was more in mesial contact, especially in the mandibular arch. No significant differences were reported in sex or between the posterior and anterior regions.

An Umbrella Review of Systematic Reviews and Meta-Analyses Evaluating the Success Rate of Prosthetic Restorations on Endodontically Treated Teeth.

MATERIALS AND METHODS: The electronic search was conducted in the MEDLINE/PubMed, Cochrane, and Google Scholar databases until November 2020, regardless of language limitations. The inclusion criterion was as follows: S/M-R regarding prosthetic restorations in endodontically treated teeth. Three qualified researchers evaluated the inclusion criteria and bias risk. The fourth investigator was referred to when facing any doubtfulness. RESULTS: From 43 achieved S/M-R, 14 studies were selected for this inquiry. Primary extracted information included success rate, survival rate, and postendodontic failure rate. Five S/M-R had a moderate risk of bias, and nine S/M-R had a low risk of bias and were considered strong clinical evidence in this examination. According to the low-risk reports, the success rate of fiber posts was higher than that of metal posts; the rate of root fracture in metallic and fiber posts was alike; the failure rate for fiber posts was comparable to fixed partial dentures or single crowns; the construction of endocrowns was likely to perform better than intracanal posts, composite resin, or inlay/onlay restorations. CONCLUSION: It appears that with practice and experience, deciding which type of restoration to choose changes. In dental restorations associated with root canal therapy, the single crowns are likely to be a proper option. Nevertheless, due to the heterogeneity of the studies, more clinical assessments are required to achieve more specific findings in this field.

Investigating the Effect of Nonrigid Connectors on the Success of Tooth-and-Implant-Supported Fixed Partial Prostheses in Maxillary Anterior Region: A Finite Element Analysis (FEA).

OBJECTIVE: This study was designed to assess the effect of nonrigid connectors (NRCs) and their location in the success of tooth-and-implant-supported fixed prostheses in the maxillary anterior region by finite element analysis (FEA). MATERIALS AND METHODS: Three 3D FEA models were designed, presuming maxillary lateral incisor and canine to be extracted. Implant (replacing canine), abutment, bone (spongious and cortical), central incisor (containing dentin, root cement, gutta-percha, and casting post and core), periodontal ligament, and three three-unit cemented PFM prostheses (a rigid one and two nonrigid) were modeled. The NRC was once in the tooth side and once in the implant side. The prostheses were loaded twice: 250N to the incisal edges (0° to the long axis) and 200 N to the cingula (45° to the long axis). The von-Mises stress and vertical displacement were analyzed. RESULTS: Under both vertical and oblique loadings, the rigid model presented the highest stress. Under vertical loading, the NRC caused a significant decrease in the applied stress to the prosthesis, bone, implant, and tooth. Locating the NRC in the tooth side decreased the applied stress to the prosthesis and NRC. Under oblique loading, prosthesis and implant tolerated less stress in the presence of an NRC. Placing the NRC in the tooth side resulted in the least stress in all of the components except for porcelain and patrix. Vertical displacement of the tooth apex was approximately equal in all models. CONCLUSION: Using an NRC on the tooth side is the most efficient method in reducing the applied stress to prosthesis, implant, tooth, and bone. The amount of intrusion is not dependent on using an NRC or not.

Comparison of translucency and opalescence among different dental monolithic ceramics.

STATEMENT OF PROBLEM: Monolithic ceramic restorations designed by computer-aided design and computer-aided manufacturing are increasingly being used by clinicians. With the introduction of new materials, their optical characteristics also need to be investigated. PURPOSE: The purpose of this in vitro study was to compare the translucency and opalescence of lithium disilicate, zirconia-reinforced lithium silicate, presintered zirconia-reinforced lithium silicate, polymer-infiltrated ceramic-network material, and multilayer zirconia. MATERIAL AND METHODS: A total of 50 rectangular plates (14×12×1 mm) of 5 monolithic ceramics were prepared in this in vitro study (n=10). Each zirconia specimen was divided into 3 groups of incisal, middle, and gingival thirds. Each group was then evaluated separately. The color parameters of specimens were measured on 3 backgrounds, white, black, and #3 Ivoclar Natural Die Color material, by using a spectrophotometer. The translucency and opalescence of the specimens were determined by the relevant equations, and between-group comparisons were made. One-way ANOVA and Tamhane post hoc tests were used to compare groups (α=.05). RESULTS: The difference among the groups was significant in translucency (F=137.346, df=6, P<.001), contrast ratio (F=134.148, df=6, P<.001), and opalescence parameters (F=128.028, df=6, P<.001). The 3 zirconia groups (10.87 ±0.54 to 11.88 ±0.26) had a significantly lower translucency than the other groups, and the zirconia-reinforced lithium silicate group (18.14 ±0.74) showed the highest translucency. Zirconia-reinforced lithium silicate (12.36 ±0.42) had the highest opalescence, and the lowest opalescence was found for polymer-infiltrated ceramic-network (5.43 ±0.28) and the incisal third of zirconia (5.45 ±1.06). CONCLUSIONS: The zirconia-reinforced lithium silicate and presintered zirconia-reinforced lithium silicate specimens had the highest translucency and opalescence. The studied multilayer zirconia, which had different cubic phase values from incisal to gingival blank, showed similar translucency over the entire range, and differences among different regions were related to chromatic variables.

Microstructural, physical, and optical characterization of high-translucency zirconia ceramics.

STATEMENT OF PROBLEM: The microstructural, physical, and optical properties of newly available highly-translucent zirconia ceramics have not been thoroughly investigated. PURPOSE: The purpose of this in vitro study was to evaluate the microstructural, physical, and optical properties of current zirconia ceramics with different degrees of translucency and to compare the optical properties with lithium disilicate glass-ceramic at different thicknesses. MATERIAL AND METHODS: Disk-shaped specimens (N=108) were prepared from 3 different monolithic zirconia ceramics: VITA YZ HT (YZ-HT), VITA YZ ST (YZ-ST), and VITA YZ XT (YZ-XT) and lithium disilicate glass-ceramic (IPS e-max CAD LT [IPS]) with a diameter of 14 mm and 3 different thicknesses (0.5, 1.0, and 1.5 mm ±0.02 mm). The microstructural features (grain size, elemental composition, phase identifications, and quantifications), physical properties (Vickers hardness and fracture toughness), and optical properties (translucency parameter and contrast ratio) were investigated. Data were analyzed using 1-way ANOVA, followed by the post hoc Tukey tests or Kruskal-Wallis and Mann-Whitney U tests (α=.05). RESULTS: Differences in grain size, phase assemblages, fracture toughness, translucency parameter, and contrast ratio were found to be significant (P<.05). The average grain size was different for the 3 zirconia specimens with the following order: YZ-XT>YZ-ST>YZ-HT. The fracture toughness of YZ-HT was higher than that of YZ-ST and YZ-XT (P<.05). IPS with 0.5-mm thickness had the highest TP followed by YZ-XT and YZ-ST. The CR values were in the range of 0.54 to 0.91 (YZ-HT), 0.43 to 0.61 (YZ-ST), 0.29 to 0.45 (YZ-XT), and 0.27 to 0.53 (IPS), and all decreased with an increase in thickness. CONCLUSIONS: Based on the results of the present study, the microstructural, physical, and optical properties of zirconia ceramics were affected by the changes in chemical composition and sintering parameters.

Multidisciplinary Management of a Severe Maxillary Midline Diastema: A Clinical Report.

A maxillary midline diastema (MMD) is a common form of incomplete occlusion and often is a primary complaint of patients during dental consultations. MMD is considered to be a multifactorial phenomenon and can therefore be best restored with a multidisciplinary approach. This clinical report presents a multidisciplinary approach to the management of a 4.0-mm MMD by using limited orthodontics combined with periodontal and prosthodontic treatments.