Effect of scan body designs and internal conical angles on the 3-dimensional accuracy of implant digital scans.

STATEMENT OF PROBLEM: Axial displacement is inevitable when connecting scan bodies to implants for digital scans using intraoral scanners, and axial displacement may reduce implant position accuracy in digital casts. However, studies assessing scan body type and accuracy are lacking. PURPOSE: The purpose of this in vitro study was to assess the linear and angular displacements of implants in digital casts using 2 scan body types with or without a vertical stop to minimize the axial displacement and 2 internal conical connection implants (ICCIs) with different internal conical angles. MATERIAL AND METHODS: Two identical reference casts were fabricated from epoxy resin by duplicating a partially edentulous mandibular dentiform. Each cast received 3 implants in the left first premolar, first molar, and second molar regions. One cast received an ICCI with a 7-degree internal conical angle (7-degree ICCI), and the other received an ICCI with an 11-degree internal conical angle (11-degree ICCI). A 10-mm polyetheretherketone (PEEK) cube was attached to the buccal area of the mandibular second premolar of each reference cast. A vertical stop was used in the experimental scan bodies to minimize the axial displacement, and conventional scan bodies were hand tightened to the implants in the reference casts. An intraoral scanner was used to fabricate 4 digital cast groups (2 implant types and 2 scan body types; each group had 10 casts). A coordinate measuring machine and digital inspection software program were used to measure the implant platform centroids (x, y, z) and projection angles (θXY, θYZ, θZX) of implant long axes in the reference and digital casts, respectively. One-way analysis of variance (ANOVA) and linear mixed model both with Tukey post hoc and 2-way ANOVA tests were performed to assess the significance of linear and angular displacements between groups (α=.05). RESULTS: Significant differences were noted in all linear displacement variables among the 4 digital cast groups, except for Δx in the left first premolar implant. For the 7-degree ICCI, the linear displacement was statistically similar in the experimental and conventional scan bodies. However, for the 11-degree ICCIs, the experimental scan body group resulted in significantly smaller Δy, Δz, and Δd (Δd2=Δx2+Δy2+Δz2) than the conventional scan body group (P<.05). Overall, the 11-degree ICCIs demonstrated a significantly greater linear displacement than the 7-degree ICCI, regardless of the scan body type (P<.05). Significant differences between the test groups were observed for 10 of the 12 angular displacement variables (P<.05). CONCLUSIONS: The 11-degree ICCIs demonstrated significantly greater linear displacements in Δy, Δz, and Δr than the 7-degree ICCIs. The experimental scan bodies with a vertical stop demonstrated significantly smaller linear displacements in the 11-degree ICCIs.

An esthetic clinical approach for the management of an infrapositioned implant-retained maxillary incisor crown.

Infrapositioning of implants in the maxillary anterior region can cause esthetic complications, including soft tissue problems. These complications commonly occur in implants placed in young adults. However, there are many clinical reports of implant infrapositioning in the maxillary anterior region after the fourth decade of life. This clinical report describes a case of infrapositioning of the maxillary central incisor wherein esthetic results were obtained through surgical and prosthetic approaches. The surgical approach improved the gingiva shape using the tunnel technique, and the prosthetic approach increased gingiva thickness by adjusting the shape of the abutment, resulting in a shape similar to the natural teeth.

Comparative Analysis of Bone Regeneration According to Particle Type and Barrier Membrane for Octacalcium Phosphate Grafted into Rabbit Calvarial Defects.

This animal study was aimed to evaluate the efficacy of new bone formation and volume maintenance according to the particle type and the collagen membrane function for grafted octacalcium phosphate (OCP) in rabbit calvarial defects. The synthetic bone substitutes were prepared in powder form with 90% OCP and granular form with 76% OCP, respectively. The calvarial defects were divided into four groups according to the particle type and the membrane application. All specimens were acquired 2 weeks (n = 5) and 8 weeks (n = 5) after surgery. According to the micro-CT results, the new bone volume increased at 2 weeks in the 76% OCP groups compared to the 90% OCP groups, and the bone volume ratio was significantly lower in the 90% OCP group after 2 weeks. The histomorphometric analysis results indicated that the new bone area and its ratio in all experimental groups were increased at 8 weeks except for the group with 90% OCP without a membrane. Furthermore, the residual bone graft area and its ratio in the 90% OCP groups were decreased at 8 weeks. In conclusion, all types of OCP could be applied as biocompatible bone graft materials regardless of its density and membrane application. Neither the OCP concentration nor the membrane application had a significant effect on new bone formation in the defect area, but the higher the OCP concentration, the less graft volume maintenance was needed.

Impact of profile angle of CAD-CAM abutment on the marginal bone loss of implant-supported single-tooth posterior restorations.

STATEMENT OF PROBLEM: Although the emergence angle has been related to marginal bone loss, information regarding the relationship between the transmucosal configuration of a computer-aided design and computer-aided manufacturing (CAD-CAM) abutment at specific subgingival levels and the amount of marginal bone loss is lacking. PURPOSE: The purpose of this retrospective clinical study was to evaluate the influence of CAD-CAM abutment profile angles, measured at different subgingival positions, on the marginal bone loss of posterior single-tooth implant-supported restorations. MATERIAL AND METHODS: A total of 260 posterior single-tooth implant-supported restorations using CAD-CAM abutments were analyzed in 206 patients. All implants had internal conical seal connections with a platform-switched design. The following data were extracted using digital periapical radiography: emergence profile, profile angle at distance ranges of 0 to 1 mm, 1 to 2 mm, and 2 to 3 mm from the implant-abutment junction, and peri-implant marginal bone loss (MBL). The MBL was measured from the time of delivery of the restorations up to 7 years or more. A linear mixed model was applied to investigate whether there was a significant difference in MBL based on the emergence profile and time, followed by the Bonferroni correction post hoc test. A Pearson correlation analysis was used to analyze the correlation between the profile angle and MBL at each distance range. The cut-off points for each distance range were determined by using the c-index, and independent t tests were conducted based on these cut-off values to evaluate the statistical differences (α=.05 for all statistical analyses). RESULTS: The convex emergence profile exhibited greater MBL than the concave and straight profiles at each follow-up visit (P<.001). A significant correlation was found between the profile angle and MBL in the 0 to 1 mm, 1 to 2 mm distance ranges. However, no significant correlation was found between the profile angle and MBL in the 2 to 3 mm distance range (P>.05). The cut-off points were 34 degrees at the mesial and 28 degrees at the distal in the 0 to 1 mm range, and 33 and 20 degrees at the mesial and distal in the 1 to 2 mm range. CONCLUSIONS: The profile angle near the implant-abutment junction and the type of emergence profile of the CAD-CAM abutment were closely associated with MBL in implants with internal conical seal connection with a platform switch design.

Digital mounting accuracy of 2 intraoral scanners with a single anterior or bilateral posterior occlusal scan: A three-dimensional analysis.

STATEMENT OF PROBLEM: Although intraoral scanners (IOSs) are popular, few studies have evaluated the accuracy of digital mounting by using IOSs. PURPOSE: The purpose of this in vitro study was to compare the accuracy of digital mounting by using 2 IOSs and 2 occlusal scanning methods. MATERIAL AND METHODS: Fourteen Ø5-mm zirconia balls were attached approximately 5 mm apical to the free gingival margin of both second molars, second premolars, and canines and between the central incisors in maxillary and mandibular epoxy casts. A polyetheretherketone hexagonal cube with a 10-mm-long edge was attached to the buccal side of the missing mandibular right first molar area, and the cube was used to set a part coordinate system. Two IOSs (TRIOS 3, Primescan) were used to assess the intra-arch and interarch accuracies. For intra-arch assessment, each IOS was used to digitally scan the mandibular epoxy cast 15 times and fabricate 15 datasets. The deviation of each zirconia ball centroid was statistically compared between the IOSs. For interarch assessment, each IOS was used to digitally scan the maxillary and mandibular epoxy casts, and the data were digitally mounted by using a single anterior occlusal scan (A) or bilateral posterior occlusal scan (P). Both occlusal scans were performed 15 times; therefore, 4 groups (15 datasets per group) of mounted digital datasets were assigned. The deviation of each maxillary zirconia ball centroid, as well as the interarch distance between the corresponding maxillary and mandibular zirconia ball centroids, were compared among the 4 groups. For statistical analysis, the Mann-Whitney U test and Kruskal-Wallis test with Bonferroni correction were used (α=.05). RESULTS: Primescan had less deviation than TRIOS 3 in the complete arch scan. When the zirconia balls were close to the origin, the bilateral posterior occlusal scan produced less deviation of their centroids. Primescan produced decreased interarch distance in the anterior and posterior dentition, while TRIOS 3 produced increased interarch distance in the anterior dentition and decreased interarch distance in the posterior dentition. CONCLUSIONS: A significant difference was noted in intra-arch accuracy between the IOSs, and the difference influenced the digital mounting accuracy. The type of occlusal scan and IOS significantly influenced the accuracy of digital mounting. Both IOSs produced decreased interarch distances in the second molar area.

Up to a 15-Year Survival Rate and Marginal Bone Resorption of 1780 Implants with or without Microthreads: A Multi Center Retrospective Study.

The effect of microthreads at the implant neck on the amount of marginal bone resorption is controversial. This multicenter retrospective study compared the implant survival rate and amount of marginal bone resorption between two platform-switching internal connection implant systems with or without microthreads. Patient-related (age and sex), surgery-related (implant installation site, type, diameter, and length), and prosthesis-related (prosthesis type) data were collected from patient charts from the implant placement surgery to the final recall visit. A total of 1780 implants, including 1379 with microthreads and 401 without microthreads, were placed in 804 patients. For implants with and without microthreads, the longest follow-up period after prosthesis delivery was 15 and 6 years, respectively. Twenty implants failed during the 15-year follow-up period (98.8% survival rate) due to failed osseointegration, peri-implantitis, implant fractures, and non-functioning implants. The mean marginal bone loss was < 0.1 mm for both implant systems at the 1-year follow-up and 0.18 mm and 0.09 mm at the 4-year follow-up for implants with and without microthreads, respectively, without statistical significance. Microthreads did not significantly affect the amount of marginal bone loss or the implant survival rate for implants with an internal connection with a platform-switching design.

Implant-retained overdenture delivery in 2 visits with a digital workflow.

The conventional method of fabricating implant-retained overdentures involves multiple steps and patient visits. However, the duplication of existing complete dentures could decrease the number of visits and increase patient satisfaction. An existing maxillary implant-retained overdenture was replaced for a 78-year-old man; the existing implant-retained overdenture and his face were scanned at the first visit. The scanned intaglio image was inverted to obtain a virtual maxillary cast and used to fabricate the metal framework of the replacement implant-retained overdenture. Prefabricated artificial teeth were arranged on a 3-dimensional trial denture created from the scan data of the existing implant-retained overdenture. The replacement implant-retained overdenture was fabricated on the metal framework by using the injection molding technique. By using these digital techniques, a stable and esthetic implant-retained overdenture was delivered in 2 visits.

Advancements in Methods of Classification and Measurement Used to Assess Tooth Mobility: A Narrative Review.

Evaluating tooth mobility is clinically significant, not only for diagnosing periodontal tissues but also in determining the overall periodontal treatment plan. Numerous studies related to tooth mobility have been conducted over the years, including the proposal of various classifications as well as the development of electronic devices for objective measurement. However, there is still no consensus on the measurement methods and criteria for assessing tooth mobility. In this study, we provide a comprehensive review of past and current tooth mobility classification and measurement methods. In order to propose a new method to intuitively evaluate tooth mobility based on previous studies, a digital approach capable of recording tooth micromovements induced by dynamic load should be considered.

Accurate detection for dental implant and peri-implant tissue by transfer learning of faster R-CNN: a diagnostic accuracy study.

BACKGROUND: The diagnosis of dental implants and the periapical tissues using periapical radiographs is crucial. Recently, artificial intelligence has shown a rapid advancement in the field of radiographic imaging. PURPOSE: This study attempted to detect dental implants and peri-implant tissues by using a deep learning method known as object detection on the implant image of periapical radiographs. METHODS: After implant treatment, the periapical images were collected and data were processed by labeling the dental implant and peri-implant tissue together in the images. Next, 300 images of the periapical radiographs were split into 80:20 ratio (i.e. 80% of the data were used for training the model while 20% were used for testing the model). These were evaluated using an object detection model known as Faster R-CNN, which simultaneously performs classification and localization. This model was evaluated on the classification performance using metrics, including precision, recall, and F1 score. Additionally, in order to assess the localization performance, an evaluation through intersection over union (IoU) was utilized, and, Average Precision (AP) was used to assess both the classification and localization performance. RESULTS: Considering the classification performance, precision = 0.977, recall = 0.992, and F1 score = 0.984 were derived. The indicator of localization was derived as mean IoU = 0.907. On the other hand, considering the indicators of both classification and localization performance, AP showed an object detection level of AP@0.5 = 0.996 and AP@0.75 = 0.967. CONCLUSION: Thus, the implementation of Faster R-CNN model for object detection on 300 periapical radiographic images including dental implants, resulted in high-quality object detection for dental implants and peri-implant tissues.

The Neutral Zone Approach with CAD-CAM Record Bases.

Lack of adequate retention, support, and stability in the complete denture can be attributed to a poor fit or incorrect shape of the polished surfaces. This article presents a case using the neutral zone technique effectively with the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) record bases in an edentulous patient with severely resorbed alveolar ridges and discusses the overall treatment steps and clinical implications of this technique. A stable neutral zone and an accurate jaw relation were recorded using CAD-CAM record bases and stability of complete denture was optimized by arranging denture teeth and reforming polishing surfaces in the neutral zone. A new complete denture was fabricated for a patient with atrophic alveolar ridges by a technique utilizing the neutral zone with CAD-CAM record bases.

Effect of Acid Mixtures on Surface Properties and Biaxial Flexural Strength of As-Sintered and Air-Abraded Zirconia.

The aim of this work was to evaluate the effects of application time of an acid mixture solution on the surface roughness, phase transformation, and biaxial flexural strength of 3Y-TZP after sintering or air abrasion. For the biaxial flexural strength measurement, 220 3Y-TZP disk-shaped specimens were prepared after as-sintering or air abrasion. The etching solution comprised a mixture of hydrofluoric acid, sulfuric acid, hydrogen peroxide, methyl alcohol, and purified water. The samples were divided into 11 subgroups according to the etching times (Control, 1, 2, 3, 5, 8, 10, 12, 15, 20, and 30 min). The results showed that acid treatment on both as-sintered and air-abraded 3Y-TZP surfaces increased the surface roughness. However, it had no significant effects on the monoclinic phase or flexural strength of as-sintered zirconia. The monoclinic phase and flexural strength of air-abraded zirconia increased sharply after air abrasion; however, they gradually decreased after acid treatment, to a similar level to the case of the untreated surface. Surface treatment with acid mixture increased the roughness, but the lack of increase of monoclinic phase is thought to be because the loose monoclinic particles remaining on the surface were removed through the etching process.

The efficacy of convenient cleaning methods applicable for customized abutments: an in vitro study.

BACKGROUND: The demand for implant dentistry, which includes customized abutments, is increasing. A lot of pollutions are generated on the customized abutment surface following milling procedure. This study evaluated the surface topography and cleanliness of customized abutments after cleaning procedures, which are simply applicable in the dental clinic. METHODS: Thirty computer-aided design and computer-aided manufacturing internal connection type titanium abutments were produced, milled, and randomly divided into 3 groups: steam cleaning (control group), chlorhexidine (CHX) scrubbing (test group 1), and ultrasonic cleaning with CHX solution, acetone, and ethyl alcohol (test group 2). Each group was evaluated using microscopic and microbial analysis. RESULTS: Foreign bodies were observed on the abutment surfaces in control group and test group 1, but not in test group 2. Bacteria were observed on 40% of the agar plates following steam cleaning; most of the colonies consisted of Bacillus cereus and Staphylococcus warneri. Colony growth was absent following test group 1 and 2. CONCLUSION: For customized abutments, cleaning with steam is ineffective. CHX scrubbing effectively eliminates only bacteria. Ultrasonic cleaning with CHX solution, acetone, and ethyl alcohol successfully removes both foreign bodies and bacteria. Thus, the ultrasonic cleaning method is conveniently applicable in the dental clinic for eliminating contamination of the customized abutment surface.

Conventional open-tray impression versus intraoral digital scan for implant-level complete-arch impression.

STATEMENT OF PROBLEM: The best-fit method is frequently used to evaluate the accuracy of different implant impression techniques. However, the method includes inherent superimposition errors, which may accumulate and become more exaggerated in complete-arch impressions. PURPOSE: The purpose of this in vitro study was to evaluate and compare the trueness and precision of conventional open-tray impressions and intraoral digital scans at the implant level in an edentulous maxillary model with 6 implant replicas without superimposition. MATERIAL AND METHODS: A master model was fabricated using epoxy resin by duplicating a maxillary edentulous cast that had 6 implant replicas in the right first molar, right first premolar, right lateral incisor, left lateral incisor, left first premolar, and left first molar positions. The conventional open-tray, splinted-coping impression technique was used to fabricate 10 definitive casts (group CI). Intraoral digital scans were performed, after which scan bodies were connected to each implant replica to fabricate 10 digital models (group IOS). For the master model and group CI, a computerized coordinate-measuring machine was used to determine the 3D spatial orientation of the implant replicas. For group IOS, the scan bodies were converted to implant replicas using a digital library, and an inspection software program was used to measure the implant replicas. To compare the accuracies of different impression techniques, a 3D part coordinate system was set to compute the centroid and projection angles of each implant replica. The changes in the centroid coordinates (linear displacement: Δx, Δy, Δz, and ΔD; ΔD=Δx2+Δy2+Δz2) and projection angles onto XY and ZX planes (angular displacement: ΔθXY and ΔθZX) were statistically compared (α=.05). RESULTS: Group CI gave more accurate trueness values than group IOS for overall Δx (P<.001), Δy (P =.029), Δz (P<.001), and ΔD (P<.001). Furthermore, group CI had more accurate precision values for Δx, Δy, and Δz. Group IOS exhibited a statistically greater angular displacement in the ZX plane (P=.002), but the difference was only 0.24 degrees. No differences were found between the 2 groups for the angular displacement in the XY plane (P=.529). CONCLUSIONS: Conventional open-tray impressions produced significantly smaller linear displacements than the digital scan obtained using an intraoral scanner at the implant level in a complete-arch model.

Regenerated Bone Pattern Around Exposed Implants with Various Designs.

PURPOSE: The design and surface features of dental implants substantially affect the healing and remodeling of adjacent bones. This study aimed to investigate the impact of design and surface on bone regeneration using implants of two different pitches, each with three different surface features. MATERIALS AND METHODS: Custom-manufactured titanium implants (length, 10 mm; diameter, 3.5 mm) were divided along the major axis into two sections: one with 0.6-mm pitch and the other with 0.4-mm pitch. They were processed by turned, blasting and etching, and anodic oxidation surface treatments and implanted into rabbit tibia. The upper 4 mm of the inserted implants was exposed, and bone regeneration was induced around the exposed area using a titanium chamber (height: 4 mm) containing particulate autogenous and bovine bone. After a 12-week healing period, the quantity and quality of bone regeneration around the implants were evaluated. Thirty specimens-10 specimens each from the turned, blasting and etching, and anodic oxidation surface groups with 0.6- and 0.4-mm pitch sizes- were evaluated by histomophometric analysis. RESULTS: The vertical height and width of regenerated bone around blasting and etching and anodic oxidation surfaces were significantly greater than those around turned implants (P < .05); the vertical heights of regenerated bone around the 0.4-mm-pitch sections of blasting and etching and anodic oxidation surfaces were significantly greater than those around the 0.6-mm-pitch sections (P < .05). Both blasting and etching and anodic oxidation surfaces exhibited significantly greater bone-to-implant contact and bone volume at the implant thread than turned implants (P < .05). However, there was no significant difference between the 0.6- and 0.4-mm-pitch sections. CONCLUSION: The findings of this study indicate that blasting and etching and anodic oxidation surfaces with a 0.4-mm-pitch design result in greater vertical ingrowth of regenerated bone than those with a 0.6-mm-pitch design.

Effect of the number of splinted abutments on the accuracy of zirconia copings.

STATEMENT OF PROBLEM: Splinting periodontally or structurally compromised abutments is a common procedure. However, studies that investigated the effect of splinting on the accuracy of zirconia copings are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the magnitude of marginal and internal gaps of zirconia copings based on the number of splinted abutments and digital scan technique. MATERIAL AND METHODS: Four maxillary acrylic resin incisors were prepared for ceramic restorations. Epoxy resin master models were fabricated by duplicating the acrylic resin model. An intraoral scanner was used to build 40 digital models (direct digital scan group [DD]); an additional 40 digital models were constructed by scanning 40 maxillary definitive casts using a laboratory scanner (indirect digital scan group [ID]). During computer-aided design, the DD and ID groups were subdivided into 4 groups; single unit (group SU); 2-unit splinted (group 2S); 3-unit splinted (group 3S), and 4-unit splinted (group 4S). Zirconia copings were then fabricated. Using the replica technique, marginal, axial, and occlusal gaps were measured and statistically evaluated (α=.05). RESULTS: In DD, group 4S exhibited larger marginal gaps than groups SU, 2S, and 3S (P<.001). In ID, group SU exhibited smaller marginal and occlusal gaps than group 4S (P<.001). Group 4S exhibited significantly greater axial gaps than groups SU, 2S, and 3S (P<.001). CONCLUSIONS: As the number of splinting units increased, the magnitude of the marginal gap tended to increase; however, the differences were less than 5 µm, which is clinically insignificant. Axial gaps in the ID group demonstrated a significant difference (>35 µm) among the groups.

Effect of number of pontics and impression technique on the accuracy of four-unit monolithic zirconia fixed dental prostheses.

STATEMENT OF PROBLEM: Because of their relatively small scanning area, intraoral scanners may result in less accurate fixed dental prostheses (FDPs) than do laboratory scanners. PURPOSE: The purpose of this in vitro study was to evaluate the accuracy of monolithic zirconia FDPs with different numbers of pontics fabricated with different impression techniques. MATERIAL AND METHODS: The mandibular right premolars and molars of an acrylic resin model were prepared to receive 4-unit FDPs. Three master models were fabricated with epoxy resin: model NP, no pontic; model 1P, 1 pontic; and model 2P, 2 pontics. Each master model was scanned by using direct (DD) and indirect digitalization (ID). Four-unit monolithic zirconia FDPs were fabricated and divided into 3 groups (groups NP, 1P, and 2P) and then subdivided according to the digitalization technique (group DD and ID; n=10). The FDPs were also evaluated based on the presence (Po) or absence (NPo) of an adjacent pontic. The marginal, axial, and occlusal gap widths of each FDP were measured, and statistical analyses were performed to evaluate and compare the amount of gap present (α=.05). RESULTS: For direct digitalization, group 2P had significantly greater marginal (69.4 µm versus 60.9 µm or 62.3 µm; P<.001) and axial gap widths (127.1 µm versus 108.9 µm or 110.4 µm; P<.001) than group NP or 1P. Group DD resulted in significantly smaller gaps compared with group ID at marginal (64.8 µm versus 73.6 µm), axial (114.8 µm versus 124.3 µm), and occlusal (172.6 µm versus 184.1 µm) measurement locations (P<.001). Greater marginal and axial gaps were noted in group Po than NPo (P<.001). CONCLUSIONS: The length of the edentulous area significantly influenced the extent of the marginal and internal gap with the use of direct digitalization. Direct digitalization resulted in significantly smaller gap widths in all measurement areas than indirect digitalization; however, the mean differences were less than 12 µm, which is considered clinically insignificant. The presence of an adjacent pontic had a significant effect on the adjacent marginal and axial gap widths.

The effect of different cooling rates and coping thicknesses on the failure load of zirconia-ceramic crowns after fatigue loading.

PURPOSE: The purpose of this study was to evaluate the influence of different coping thicknesses and veneer ceramic cooling rates on the failure load of zirconia-ceramic crowns. MATERIALS AND METHODS: Zirconia copings of two different thicknesses (0.5 mm or 1.5 mm; n=20 each) were fabricated from scanning 40 identical abutment models using a dental computer-aided design and computer-aided manufacturing system. Zirconia-ceramic crowns were completed by veneering feldspathic ceramics under different cooling rates (conventional or slow, n=20 each), resulting in 4 different groups (CONV05, SLOW05, CONV15, SLOW15; n=10 per group). Each crown was cemented on the abutment. 300,000 cycles of a 50-N load and thermocycling were applied on the crown, and then, a monotonic load was applied on each crown until failure. The mean failure loads were evaluated with two-way analysis of variance (P=.05). RESULTS: No cohesive or adhesive failure was observed after fatigue loading with thermocycling. Among the 4 groups, SLOW15 group (slow cooling and 1.5 mm chipping thickness) resulted in a significantly greater mean failure load than the other groups (P<.001). Coping fractures were only observed in SLOW15 group. CONCLUSION: The failure load of zirconia-ceramic crowns was significantly influenced by cooling rate as well as coping thickness. Under conventional cooling conditions, the mean failure load was not influenced by the coping thickness; however, under slow cooling conditions, the mean failure load was significantly influenced by the coping thickness.

Long-term Stability of Autotransplanted Premolars as a Substitute for Molars in Adults.

Autotransplantation is a viable treatment option for tooth replacement when a suitable donor tooth is available. This case report presents 2 cases that describe successful treatment outcome and prognosis after autotransplantation of a mature premolar as a missing molar. The first premolar was extracted for orthodontic purposes and transplanted to the missing first molar site in the mandible. The transplanted tooth was monitored up to 7 years. The transplant was functional and maintained a normal bone level throughout the follow-up period. Clinical examination showed normal physiologic movement without any signs of ankylosis and root resorption. Autotransplantation of a mature premolar to a molar site is a viable treatment option showing successful results. The selection of a functional donor tooth, adequate surgical procedures, and timely application of orthodontic movement may have positively contributed to the favorable prognosis.

Critical appraisal of implant impression accuracies: A systematic review.

STATEMENT OF PROBLEM: Different assessment methods have been used to measure the accuracy of implant impression techniques; therefore, the readers should understand the benefits and limitations of each assessment method used. PURPOSE: The purpose of this systematic review was to classify the implant impression studies by the assessment methods and techniques used and to understand the characteristics of each assessment method. The results of published studies were also analyzed to draw meaningful conclusions about the accuracy of the implant impressions. MATERIAL AND METHODS: An electronic search of the MEDLINE/PubMed database was performed in February 2013 using specific search terms and predetermined criteria to identify and assess laboratory studies of the accuracy of implant impression techniques. A final list of articles deemed to be of interest was comprehensively reviewed by 2 reviewers to ensure that these were suitable for the purpose of this review. The results of the current review were also compared with results from a previous systematic review. RESULTS: A total of 56 studies met the inclusion criteria for this review. Thirty-seven studies measured the amount of linear distortion, and 17 studies compared the angular change to assess the accuracy. Most linear or angular distortions were only measured in 2 dimensions, and 3-dimensional analysis was rare. More than 80% of the studies compared nonsplinting versus splinting, direct versus indirect techniques, and different impression materials. CONCLUSIONS: In recent publications, the direct or splint technique showed more accurate results than the indirect or nonsplinted technique. In contrast to external connection implants, inconsistent results were reported for internal connection implants.

Catastrophic failure of a monolithic zirconia prosthesis.

Recently, monolithic zirconia restorations have received attention as an alternative to zirconia veneered with feldspathic porcelain to eliminate chipping failures of veneer ceramics. In this clinical report, a patient with mandibular edentulism received 4 dental implants in the interforaminal area, and a screw-retained monolithic zirconia prosthesis was fabricated. The patient also received a maxillary complete removable dental prosthesis over 4 anterior roots. At the 18-month follow-up, all of the zirconia cylinders were seen to be fractured, and the contacting abutment surfaces had lost structural integrity. The damaged abutments were replaced with new abutments, and a new prosthesis was delivered with a computer-assisted design and computer-assisted manufacturing fabricated titanium framework with denture teeth and denture base resins. At the 6-month recall, the patient did not have any problems. Dental zirconia has excellent physical properties; however, care should be taken to prevent excessive stresses on the zirconia cylinders when a screw-retained zirconia restoration is planned as a definitive prosthesis.