Misfit of implant prostheses and its impact on clinical outcomes. Definition, assessment and a systematic review of the literature.

BACKGROUND AND AIM: Compromised fit between the contact surfaces of screw-retained implant-supported fixed dentures (IFDs) is thought to create uncontrolled strains in the prosthetic components and peri-implant tissues, thus evoking biological and technical complications such as bone loss, screw loosening, component fractures and, at worst, loss of implants or prostheses. The aim of this systematic review was to evaluate the impact of marginal misfit on the clinical outcomes of IFDs, and to elucidate definition and assessment methods for passive fit. MATERIALS AND METHODS: A systematic review of the literature was conducted with a PICO question: "For partially or complete edentulous subjects with screw-retained IFDs, does the marginal misfit at the implant-prosthesis interfaces have an impact on the clinical outcomes?". A literature search was performed electronically in PubMed (MEDLINE) with the help of Boolean operators to combine key words, and by hand search in relevant journals. English written in vivo studies published before August 31, 2016 that reported on both clinical outcome and related implant prosthesis misfit (gap, strains, torque) were selected using predetermined inclusion criteria. RESULTS: The initial search yielded 2626 records. After screening and a subsequent filtering process, five human and five animal studies were included in the descriptive analysis. The selected studies used different methods to assess misfit (linear distortion, vertical gap, strains, screw torque). While two human studies evaluated the biological response and technical complications prospectively over 6 and 12 months, the animal studies had an observation period < 12 weeks. Four human studies analysed retrospectively the 3 to 32 years' outcomes. Screw-related complications were observed, but biological sequelae could not be confirmed. Although the animal studies had different designs, bone adaptation and implant displacement was found in histological analyses. Due to the small number of studies and the heterogenic designs and misfit assessment methods, no meta-analysis of the data could be performed. CONCLUSIONS: The current literature provides insufficient evidence as to the effect of misfit at the prosthesis-implant interface on clinical outcomes of screw-retained implant-supported fixed dentures. Marginal gaps and static strains due to screw tightening were not found to have negative effects on initial osseointegration or peri-implant bone stability over time. Based on two clinical studies, the risk for technical screw-related complications was slightly higher. While the degree of tolerable misfit remains a matter of debate, the present data do not imply that clinicians neglect good fit, but aim to achieve the least misfit possible. Conflict of interest statement: The authors declare no conflict of interest. The review was conducted as part of the 2016 Foundation of Oral Rehabilitation Consensus Conference on "Prosthetic Protocols in Implant-based Oral Rehabilitation".

Patient-specific gingiva-colored abutments: a case series.

The purpose of this report is to present a case series of gingiva-colored abutments utilized to meet patients, esthetic needs. The color of the abutment was determined by evaluating the color of the patients, marginal gingiva using a digital shade guide. Thereafter, anodic oxidation was performed on computer-aided design/computer-assisted manufacture abutments. The baseline digital color information was compared with the color of the gingiva after 1.5 years in three patients. The gingival colors as well as the marginal bone and soft tissue levels after 1.5 years were comparable to the baseline values. Thus, the gingiva-colored abutments obtained by anodic oxidation provided improved esthetics, especially for patients with thin gingival biotypes.

Effect of thermomechanical aging on bond strength and interface morphology of glass fiber and zirconia posts bonded with a self-etch adhesive and a self-adhesive resin cement to natural teeth.

STATEMENT OF PROBLEM: Information regarding the effect of thermomechanical aging (TMA) on the bond strength of luting cements to root canal dentin and endodontic posts is limited. PURPOSE: The purpose of this study was to investigate the effect of TMA on the bond strength of fiber and zirconia posts bonded to root canal dentin with 2 different resin cements with microtensile and scanning electron microscopic evaluation. MATERIAL AND METHODS: Eighty extracted single-rooted human premolars were endodontically treated and restored with either a glass fiber post (FP) or a zirconia post (ZP) with 2 commercially available resin luting cements. The teeth were divided into 2 main groups. In the first group, posts (n=40) were bonded with a self-etch adhesive cement (SEAC). In the second group (n=40), posts were bonded using a self-adhesive cement (SAC). During the first aging phase, all specimens in each group were stored in distilled water for 30 days at 37°C. During the second phase, half of the specimens in each group were subjected to the TMA. The test groups were as follows: FP/SEAC, FP/SEAC+TMA, ZP/SEAC, ZP/SEAC+TMA, FP/SAC, FP/SAC+TMA, ZP/SAC, and ZP/SAC+TMA. The bond strength was measured with a microtensile test. Data were analyzed by 3-way analysis of variance and the Tukey honest significant different test (α=.05). RESULTS: FP/SEAC at 30 days was higher than in the other groups. However, bond strength values were significantly reduced in this group after TMA (P<.001). CONCLUSIONS: Bond strength values and physical properties of SEAC with higher filler content were more affected by the TMA than those of SALC. According to scanning electron microscopic observation, TMA also affected the micromorphologic interface between the posts and the resin cements as well as between the resin cements and the root canal dentin.

A retrospective survey on long-term survival of posterior zirconia and porcelain-fused-to-metal crowns in private practice.

OBJECTIVES: This retrospective survey assessed the clinical survival of zirconia-based crowns (PFZ) and conventional porcelain- fused-to-metal (PFM) crowns on posterior teeth in private practice. METHOD AND MATERIALS: A print survey of 13 private practitioners was conducted to assess the long-term survival of previously placed full-coverage crowns. The practitioners reported a total of 2,182 premolar (n = 881) and molar (n = 1,301) full-coverage single crowns, 1,102 PFZ and 1,080 PFM, fabricated by one dental laboratory (Cusp, Boston) and followed over 7.4 years. All post-cementation complications (eg, porcelain fractures and chippings) were recorded as failures. In the PFZ group, one veneering porcelain (CZR, Kuraray Noritake) was used in combination with three coping systems (Lava, 3M ESPE; Procera, Nobelbiocare; Katana, Kuraray Noritake). Kaplan-Meier survival analysis was used for statistical analyses. RESULTS: The probability of survival of posterior crowns investigated over the period of study (7.4 years) was 99.3% for PFM and 99.2% for PFZ restorations. There was no statistically significant difference (P = .614) between PFZ and PFM groups. In the PFZ group, probability of survival was 97.7% for Lava, 100% for Procera, and 99.5% for Katana. There were no statistically significant differences (P = .34) between the three PFZ systems or the location of the crowns (premolar or molar; P = .454). CONCLUSION: PFZ crowns fabricated with CZR and three commercial zirconia coping systems revealed excellent long-term success rates. Survival times and survival probabilities of posterior PFZ crowns did not differ from PFM crowns and were independent of type of coping system and location (molar or premolar teeth).

Clinical outcome of single porcelain-fused-to-zirconium dioxide crowns: a systematic review.

STATEMENT OF PROBLEM: The increasing demand by patients for esthetic and metal-free restorations has driven the development of ceramic restorations with good esthetic and mechanical stability. Recent clinical studies have investigated the use of zirconium dioxide as a core material for complete crowns and computer-aided-design/computer-aided-manufacturing fabricated restorations. PURPOSE: The aim of this systematic review was to evaluate the clinical survival rates of porcelain-fused-to-zirconia (PFZ) single crowns on anterior and posterior teeth and to compare them with metal ceramic (MC) crowns. MATERIAL AND METHODS: A systematic search was conducted with PubMed and manual research to identify literature written in English that refers to in vivo studies published from January 1, 1950 through July 1, 2011. Clinical trials that evaluated PFZ and MC single crowns on natural teeth were selected for further analysis. Titles and/or abstracts of articles identified through the electronic searches were reviewed and evaluated for appropriateness. In addition, a hand search of relevant dental journals was peformed, and reference lists of culled articles were screened to identify publications. RESULTS: The search resulted in a total of 488 initial matches. Nineteen studies with a total of 3621 crowns met the inclusion criteria. The survival rates of PFZ crowns (total 300) ranged from 92.7% to 100% for a follow-up time of 24 to 39 months, whereas those of MC crowns (total 3321) ranged from 70% to 100% for a follow-up time of 12 to 298 months. Studies that reported long-term results were found only for the MC crown group. CONCLUSIONS: The scientific clinical data available to compare PFZ and MC crowns are limited. The survival rates may well be influenced by the selection and appropriate use of the veneering ceramic, and, therefore, additional prospective long-term clinical trials are necessary to draw reliable conclusions.

Relative bone width of the edentulous maxillary ridge. Clinical implications of digital assessment in presurgical implant planning.

BACKGROUND: Healthy, well-structured mucosa may clinically disguise atrophic jawbone in preimplant diagnosis. PURPOSE: To analyze bone width in relation to the complete ridge thickness comparing the anterior with the posterior edentulous maxilla. MATERIALS AND METHODS: Data of 52 patients (mean age 62 ± 9 years) who were edentulous for at least 1 year and who received implant treatment were analyzed. Computed tomography (CT) scans were obtained and virtually analyzed in perpendicular sections of 12 maxillary positions (central and lateral incisors, canines, premolars, and first molars) using an implant planning software. Absolute thickness of complete jaw, bone, and mucosa were digitally measured at crestal and basal ridge levels allowing for relative bone width (B-rel) calculation. RESULTS: Mean B-rel at crestal levels was lower than at basal levels (38.6% vs 51.5%, p < .001). Bone width increased significantly (p < .001) in the posterior maxilla at both levels, whereas the thickness of palatal and buccal mucosa was considerably stable. Mean basal B-rel ranged from 49% (6.2 ± 2.0 mm) at incisors to 59% (9.0 ± 2.3 mm) at first molars (p < .001). Mean proportion of regions showing B-rel < 50% were 43% at basal and 80% at crestal levels. CONCLUSIONS: The osseous volume of a large edentulous ridge might be clinically overestimated in preimplant diagnosis, as the relative bone width was generally lower than 50%. Clinicians can use the present results of the virtual bone and mucosa measurements to have a better first estimation of the osseous proportion depending on the maxillary area. However, up to date implant therapy for the edentulous maxilla requires CT-based prosthetically driven implant planning and preferably combination with guided implant placement by transferring planning information to a surgical template.

Type 2 diabetes impairs implant osseointegration capacity in rats.

PURPOSE: The effect of type 2 diabetes mellitus (adult-onset non-insulin-dependent), which is the most common form of diabetes in humans, on osseointegration capacity has not been addressed in an appropriate animal model. This study histologically and histomorphometrically examines bone healing around titanium implants in the type 2 diabetes rat model. MATERIALS AND METHODS: Titanium implants with a chamber were placed into the femurs of normal male rats and genetically modified male rats with a close symptomatic resemblance to human type 2 diabetes, as characterized by late-onset hyperglycemia and obesity. Cross-sectional histology for the tissue grown into the implant chamber was examined. RESULTS: Bone volume around implants was consistently (from weeks 4 to 8 postimplantation) smaller for the diabetes group than for the control group in the cortical area, while the bone volume in the marrow area was not affected by the diabetes. Bone-implant contact percentage was considerably lower for the diabetes group in both the cortical and marrow areas, with the week 4 bone-implant contact in the cortical area being 12% for the diabetes group and 61% for the control group. A 2-fold difference remained at week 8. Bone morphogenesis in the diabetic rats was characterized by fragmented bone tissues and extensive soft tissue intervention. CONCLUSIONS: Type 2 diabetes mellitus impaired osseointegration capacity disproportionally between the cortical bone and bone marrow areas. The reduction of the bone quantity in the cortical area and the bone-implant contact in both the cortical and marrow areas was remarkable.