The Influence of Certain Processing Factors on the Durability of Yttrium Stabilized Zirconia Used As Dental Biomaterial

In dentistry, yttrium partially stabilized zirconia (ZrO2) has become one of the most attractive ceramic materials for prosthetic applications. The aim of this series of studies was to evaluate whether certain treatments used in the manufacturing process, such as sintering time, color shading or heat treatment of zirconia affect the material properties. Another aim was to evaluate the load-bearing capacity and marginal fit of manually copy-milled custom-made versus prefabricated commercially available zirconia implant abutments. Mechanical properties such as flexural strength and surface microhardness were determined for green-stage milled and sintered yttrium partially stabilized zirconia after different sintering time, coloring process and heat treatments. Scanning electron microscope (SEM) was used for analyzing the possible changes in surface structure of zirconia material after reduced sintering time, coloring and heat treatments. Possible phase change from the tetragonal to the monoclinic phase was evaluated by X-ray diffraction analysis (XRD). The load-bearing capacity of different implant abutments was measured and the fit between abutment and implant replica was examined with SEM. The results of these studies showed that the shorter sintering time or the thermocycling did not affect the strength or surface microhardness of zirconia. Coloring of zirconia decreased strength compared to un-colored control zirconia, and some of the colored zirconia specimens also showed a decrease in surface microhardness. Coloring also affected the dimensions of zirconia. Significantly decreased shrinkage was found for colored zirconia specimens during sintering. Heat treatment of zirconia did not seem to affect materials’ mechanical properties but when a thin coating of wash and glaze porcelain was fired on the tensile side of the disc the flexural strength decreased significantly. Furthermore, it was found that thermocycling increased the monoclinic phase on the surface of the zirconia. Color shading or heat treatment did not seem to affect phase transformation but small monoclinic peaks were detected on the surface of the heat treated specimens with a thin coating of wash and glaze porcelain on the opposite side. Custom-made zirconia abutments showed comparable load-bearing capacity to the prefabricated commercially available zirconia abutments. However, the fit of the custom-made abutments was less satisfactory than that of the commercially available abutments. These studies suggest that zirconia is a durable material and other treatments than color shading used in the manufacturing process of zirconia bulk material does not affect the material’s strength. The decrease in strength and dimensional changes after color shading needs to be taken into account when fabricating zirconia substructures for fixed dental prostheses. Manually copy-milled custom-made abutments have acceptable load-bearing capacity but the marginal accuracy has to be evaluated carefully.Siirretty Doriast

Surface Roughness and Streptococcus mutans Adhesion on Metallic and Ceramic Fixed Prosthodontic Materials after Scaling

The aim of this study was to evaluate the surface roughness of fixed prosthodontic materials after polishing or roughening with a stainless steel curette or ultrasonic scaler and to examine the effect of these on Streptococcus mutans adhesion and biofilm accumulation. Thirty specimens (10 x 10 x 3 mm(3)) of zirconia (Zr), pressed lithium disilicate (LDS-Press), milled lithium disilicate glazed (LDS-Glaze), titanium grade V (Ti) and cobalt-chromium (CoCr) were divided into three groups (n = 10) according to surface treatment: polished (C), roughened with stainless steel curette (SC), roughened with ultrasonic scaler (US). Surface roughness values (Sa, Sq) were measured with a spinning disc confocal microscope, and contact angles and surface free energy (SFE) were measured with a contact angle meter. The specimens were covered with sterilized human saliva and immersed into Streptococcus mutans suspensions for bacterial adhesion. The biofilm was allowed to form for 24 h. Sa values were in the range of 0.008-0.139 mu m depending on the material and surface treatment. Curette and ultrasonic scaling increased the surface roughness in LDS-Glaze (p <0.05), Ti (p <0.01) and CoCr (p <0.001), however, surface roughness did not affect bacterial adhesion. Zr C and US had a higher bacterial adhesion percentage compared to LDS-Glaze C and US (p = 0.03). There were no differences between study materials in terms of biofilm accumulation.Peer reviewe

Zirconia single crowns and multiple-unit FDPs—An up to 8 -year retrospective clinical study

Objective: The aim of this retrospective clinical study was to evaluate the survival and the occurrence of technical and biological complications of zirconia crowns and fixed dental prostheses made in the student clinic of Turku University, Finland, between April 2009 and September 2017.Materials and methods: Twenty-seven patients (19 female, 8 male), with zirconia crowns or FDPs, participated in the follow-up investigation. The mean age of patients was 64.6 years. Of the 40 restorations, 17 were single crowns and 23 FDPs. Twenty-seven restorations were anterior and 13 posterior. Restorations were investigated according to modified USPHS criteria.Results: The survival rate of zirconia restorations after 2–8 years (average 5.7 years) of clinical use was 95%. Survival rate of single crowns was 94.2% and of FDPs 95.7%, respectively. The overall complication rate was 26% for FDPs and 5.8% for crowns. One posterior crown was lost due to a vertical root fracture and one FDP showed a framework fracture. Veneering ceramic fractures were detected in 12% of all cases (0% for crowns and 22% for FDPs). Bleeding on probing was present in 38.1% of restored teeth and 13.9% of control teeth. Embrasure space was insufficient in 52% of zirconia FDPs and 81% of these restorations showed elevated BOP values.Conclusions: Zirconia crowns and FDPs survived well in this retrospective follow-up study. Chipping of veneering ceramic and bleeding on probing were the most common complications. Thick connector areas made according to material demands resulted in insufficient embrasure spaces and inflammation of marginal gingiva.</p

Zirconia single crowns and multiple-unit FDPs-An up to 8-year retrospective clinical study

Objective: The aim of this retrospective clinical study was to evaluate the survival and the occurrence of technical and biological complications of zirconia crowns and fixed dental prostheses made in the student clinic of Turku University, Finland, between April 2009 and September 2017. Materials and methods: Twenty-seven patients (19 female, 8 male), with zirconia crowns or FDPs, participated in the follow-up investigation. The mean age of patients was 64.6 years. Of the 40 restorations, 17 were single crowns and 23 FDPs. Twenty-seven restorations were anterior and 13 posterior. Restorations were investigated according to modified USPHS criteria. Results: The survival rate of zirconia restorations after 2-8 years (average 5.7 years) of clinical use was 95%. Survival rate of single crowns was 94.2% and of FDPs 95.7%, respectively. The overall complication rate was 26% for FDPs and 5.8% for crowns. One posterior crown was lost due to a vertical root fracture and one FDP showed a framework fracture. Veneering ceramic fractures were detected in 12% of all cases (0% for crowns and 22% for FDPs). Bleeding on probing was present in 38.1% of restored teeth and 13.9% of control teeth. Embrasure space was insufficient in 52% of zirconia FDPs and 81% of these restorations showed elevated BOP values. Conclusions: Zirconia crowns and FDPs survived well in this retrospective follow-up study. Chipping of veneering ceramic and bleeding on probing were the most common complications. Thick connector areas made according to material demands resulted in insufficient embrasure spaces and inflammation of marginal gingiva.Peer reviewe

Production time, effectiveness and costs of additive and subtractive computer-aided manufacturing (CAM) of implant prostheses: A systematic review

OBJECTIVE To systematically review the dental literature for clinical studies reporting on production time, effectiveness and/or costs of additive and subtractive computer-aided manufacturing (CAM) of implant prostheses. MATERIALS AND METHODS A systematic electronic search for clinical studies from 1990 until June 2020 was performed using the online databases Medline, Embase and Cochrane. Time required for the computer-aided design (CAD) process, the CAM process, and the delivery of the CAD-CAM prostheses were extracted. In addition, articles reporting on the effectiveness and the costs of both manufacturing technologies were included. RESULTS Nine clinical studies were included reporting on subtractive CAM (s-CAM; 8 studies) and additive CAM (a-CAM; 1 study). Eight studies reported on the s-CAM of prosthetic and auxiliary components for single implant crowns. One study applied a-CAM for the fabrication of an implant bar prototype. Time was provided for the CAD process of implant models (range 4.9-11.8 min), abutments (range 19.7-32.7 min) and crowns (range 11.1-37.6 min). The time for s-CAM of single implant crown components (abutment/crown) ranged between 8.2 and 25 min. Post-processing (e.g. sintering) was a time-consuming process (up to 530 min). At delivery, monolithic/veneered CAD-CAM implant crowns resulted in additional adjustments chairside (51%/93%) or labside (11%/19%). CONCLUSIONS No scientific evidence exists on production time, effectiveness and costs of digital workflows comparing s-CAM and a-CAM. For both technologies, post-processing may substantially contribute to the production time. Considering effectiveness, monolithic CAD-CAM implant crowns may be preferred compared to veneered CAD-CAM crowns

Additively and subtractively manufactured implant-supported fixed dental prostheses: A systematic review

AIM To compare and report on the performance of implant-supported fixed dental prostheses (iFDPs) fabricated using additive (AM) or subtractive (SM) manufacturing. METHODS An electronic search was conducted (Medline, Embase, Cochrane Central, Epistemonikos, clinical trials registries) with a focused PICO question: In partially edentulous patients with missing single (or multiple) teeth undergoing dental implant therapy (P), do AM iFDPs (I) compared to SM iFDPs (C) result in improved clinical performance (O)? Included were studies comparing AM to SM iFDPs (randomized clinical trials, prospective/retrospective clinical studies, case series, in vitro studies). RESULTS Of 2'184 citations, no clinical study met the inclusion criteria, whereas six in vitro studies proved to be eligible. Due to the lack of clinical studies and considerable heterogeneity across the studies, no meta-analysis could be performed. AM iFDPs were made of zirconia and polymers. For SM iFDPs, zirconia, lithium disilicate, resin-modified ceramics and different types of polymer-based materials were used. Performance was evaluated by assessing marginal and internal discrepancies and mechanical properties (fracture loads, bending moments). Three of the included studies examined the marginal and internal discrepancies of interim or definitive iFDPs, while four examined mechanical properties. Based on marginal and internal discrepancies as well as the mechanical properties of AM and SM iFDPs, the studies revealed inconclusive results. CONCLUSION Despite the development of AM and the comprehensive search, there is very limited data available on the performance of AM iFDPs and their comparison to SM techniques. Therefore, the clinical performance of iFDPs by AM remains to be elucidated

A minimally invasive two-stage crown lengthening procedure applying a tunneling technique

AIM The purpose of the present retrospective case series was to introduce a minimally invasive two-stage flapless crown lengthening procedure where a gingivectomy was avoided or minimized by reducing the bone height through a tunneling technique. MATERIALS AND METHOD Ten patients (median age 46.6 years, range 26.9 to 71.6 years) were included in the study. The indications for performing a crown lengthening procedure were esthetically short clinical crowns (n = 5), asymmetry of the gingival margin level (n = 2), and both esthetically short clinical crowns and asymmetry of the gingival margin level (n = 3). All the patients presented a thick gingival phenotype, and the mean number of operated teeth per patient was 3.7 (range 2 to 8 teeth). Three patients underwent an additional gingivectomy 6 weeks after the crown lengthening procedure. RESULTS The esthetic and functional outcome of the treatments fulfilled the patients' and dentist's expectations. CONCLUSION A minimally invasive two-stage crown lengthening procedure applying a tunneling technique has the potential to achieve predictable esthetic outcomes without an open-flap approach and an additional gingivectomy. However, prospective clinical studies are needed to validate this technique

Mechanical stability of fully personalized, abutment-free zirconia implant crowns on a novel implant-crown interface

OBJECTIVES: To test the failure load and failure mode of a novel implant-crown interface specifically designed for the fabrication of fully personalized, abutment-free monolithic zirconia CAD-CAM crowns compared to conventional implant-abutment interfaces involving prefabricated or centrally manufactured abutments for zirconia CAD-CAM crowns. METHODS: Implants (N=48) were divided into groups (n=12) according to different implant-abutment interface designs: (1) internal implant connection with personalized, abutment-free CAD-CAM crowns (Abut-Free-Zr), (2) internal conical connection with customized, centrally manufactured zirconia CAD-CAM abutments (Cen-Abut-Zr), (3) prefabricated titanium base abutments from manufacturer 1 (Ti-Base-1), (4) additional prefabricated titanium base abutments from manufacturer 2 (Ti-Base-2). All specimens were restored with a screw-retained monolithic zirconia CAD-CAM molar crown and subjected to thermomechanical aging (1.200.000 cycles, 49 N, 1.67 Hz, 30° angulation, thermocycling 5-50°C). Static load until failure was applied in a universal testing machine. Failure modes were analyzed descriptively under digital microscope. Mean failure load values were statistically analyzed at a significance level of p<0.05. RESULTS: All specimens survived thermomechanical aging. The mean failure loads varied between 1332 N (Abut-Free-Zr) and 1601 N (Ti-Base-2), difference being significant between these groups (p<0.05). No differences between the other groups were seen. The predominant failure mode per group was crown fracture above implant connection (Abut-Free-Zr, 75%), abutment fracture below implant neck (Cen-Abut-Zr, 83%), crown fracture leaving an intact abutment (Ti-Base-1/Ti-Base-2 100%). CONCLUSIONS: Implant-crown interface with fully personalized, abutment-free monolithic CAD-CAM zirconia crowns exhibited similar failure loads as conventional implant-abutment interfaces (except group Ti-Base-2) involving CAD-CAM crowns with prefabricated or centrally manufactured abutment. CLINICAL SIGNIFICANCE: The new implant connection simplifies the digital workflow for all-ceramic implant reconstructions. The specific design of the implant-crown interface allows the fabrication of fully personalized, abutment-free zirconia implant crowns both in-house and in-laboratory without the need of a prefabricated abutment or central manufacturing