Effects of cyclic loading on loss of abutment screw torque of angled screw channel single implant crowns on narrow diameter implants.

STATEMENT OF PROBLEM: Screw access channels that emerge on the facial aspect of anterior screw-retained implant crowns can compromise esthetics. Recently, angled screw channels (ASCs) have been developed that can alter screw access channel angulations to improve esthetics. While ASCs can be used on narrow-diameter implants, information is limited on the loss of abutment screw torque on narrow-diameter implants with ASCs. PURPOSE: The purpose of this in vitro study was to compare the loss of abutment screw torque after thermocycling and the cyclic loading of ASCs from 3 different companies connected to narrow-diameter implants. MATERIAL AND METHODS: A total of 40 narrow-diameter implants (NobelReplace Conical Connection 3.5×11.5 mm) were mounted individually in acrylic resin blocks and divided equally into 4 groups. The first group, NB-0 (Control), consisted of screw-retained zirconia crowns fabricated on ASCs at 0-degree angulation (n=10). The other 3 groups consisted of a total of 30 screw-retained zirconia crowns fabricated on ASCs at 20-degree angulation: NB-20 (Angulated Screw Channel Solutions), ATL-20 (Atlantis Custom Base Solution with angulated screw access), and DA-20 (Dynamic TiBase). Each crown was secured on the mounted implant with its corresponding titanium base insert and screw and then tightened to the manufacturer's recommended torque with a digital torque gauge. The initial reverse torque value (RTVI) was obtained and recorded at baseline. Subsequently, a new set of screws were tightened to recommended values, and each specimen underwent thermocycling and then cyclic loading at 0 to 100 N at 10 Hz for 1 million cycles to simulate 1year of functional loading. After cyclic loading, the final reverse torque values (RTVF) were recorded and compared with the RTVI to evaluate the percentage torque loss (PTLF). Statistical analysis was performed using the Kruskal-Wallis analysis, Rank base analysis of covariance (ANCOVA), and the Tukey HSD post hoc comparisons (α=.05). RESULTS: Significant differences were found for the PTLF among all groups after cyclic loading (P<.001). The PTLF in ATL-20 (51.4%) was significantly higher than in NB-0 (22.2%) (P<.001) and NB-20 (29.2%) (P=.010). No significant difference was found in the PTLF among other groups (P>.05). CONCLUSIONS: The abutment screw torque loss after cyclic loading of the ASCs on narrow diameter implants among the 4 groups did not perform comparably. The largest percentage torque loss was recorded for the ATL-20 group. The NB-20 group demonstrated the lowest percentage torque loss. DA-20 showed percentage torque loss less than ATL-20; however, its RTVF was the lowest.

Evaluation of Marginal and Internal Fit of Ceramic Laminate Veneers Fabricated with Five Intraoral Scanners and Indirect Digitization.

The long-term success of ceramic laminate veneers (CLVs) is influenced by the marginal and internal fit of the restorations. However, studies comparing the fit of CLVs using different intraoral scanners or the indirect digitization technique are lacking. The purpose of this study was therefore to assess the marginal and internal fit of CAD/CAM-milled CLVs using different intraoral scanners and the indirect digitalization technique. An ivorine typodont maxillary left-central incisor was prepared; the tooth and the neighboring teeth were scanned and used as a template to print ninety 3D partial models. Thereafter, ceramic laminate veneers (CLVs) (N = 90) were milled from IPS-Emax CAD blocks and divided into six equal groups (15 specimens each) according to the type of intraoral scanner (IOS), as follows: Omnicam IOS, SC3600 IOS, Trios 3 IOS, Emerald IOS, I500 IOS. Fifteen further CLVs were fabricated using the conventional indirect digitalization technique. After cementation on the resin dies and embedding in clear epoxy resin, specimens were sectioned inciso-gingivally and mesio-distally. At the incisal and cervical positions, the marginal discrepancy was measured and evaluated in addition to the internal gap at six locations using SEM (200×). Differences between gap measurements among the six groups were determined using ANOVA. Games-Howell multiple comparisons for homogenous variances and LSD multiple comparisons for non-homogenous variances were used with 95% confidence intervals. The significance level was set at 0.05. The lowest mean absolute marginal gap at the incisal margins (AMGI) was recorded for Omnicam group (203.28 ± 80.14) µm, while the highest mean absolute marginal gap at the cervical margins (AMGC) was recorded for Omnicam group (147.16 ± 59.78) µm. The mean AMGC was reported to be significantly different between the conventional technique (146.75 ± 38.43) µm and Trios 3 (91.86 ± (35.51) µm; p = 0.001) and between Emerald (112.37 ± (50.31) µm; p = 0.042) and I500 (86.95 ± (41.55) µm; p < 0.001). The mean MGI was found to be significantly different between the conventional technique (114.11 ± (43.45) µm and I500 group (186.99 ± (73.84) µm) only (p = 0.035). However, no significant differences were found in the mean MGI between all types of IOSs. The means of AMG and MG were significantly different at incisal or cervical areas between the conventional technique and IOSs and within the scanner groups (p > 0.05). Marginal gaps were higher in the incisal region compared to the cervical region with both the indirect digitization technique and the IOSs. Ceramic laminate veneers (CLVs) fabricated using IOSs produced overall internal and marginal fit adaptation results comparable to CLVs fabricated from the indirect digitalization method, and both techniques produced clinically acceptable results.

Noncarious cervical lesions: Morphology and progression, prevalence, etiology, pathophysiology, and clinical guidelines for restoration.

PURPOSE: To synthesize the literature regarding noncarious cervical lesions (NCCLs) and propose clinical guidelines when lesion restoration is indicated. MATERIAL AND METHODS: A PubMed search was performed related to NCCL morphology, progression, prevalence, etiology, pathophysiology, and restoration. RESULTS: NCCLs form as either rounded (saucerlike) depressions with smooth, featureless surfaces that progress mainly in height or as V-shaped indentations that increase in both height and depth. Prevalence ranges from less than 10% to over 90% and increases with age. Common locations are the facial surfaces of maxillary premolars. They have a multifactorial etiology due to personal habits such as excessive horizontal toothbrushing and consumption of acidic foods and drinks. Occlusal factors have been identified as contributing to the prevalence of NCCLs in some studies, whereas other studies indicate there is no relationship. The concept of abfraction has been proposed whereby mechanical stress from occlusal loading plays a role in the development and progression of NCCLs with publications supporting the concept and others indicating it lacks the required clinical documentation. Regardless of the development mechanism, demineralization occurs and they are one of the most common demineralization diseases in the body. Treatment should be managed conservatively through preventive intervention with restorative treatment delayed until it becomes necessary due to factors such as lesion progression, impact on patient's quality of life, sensitivity, poor esthetics, and food collection may necessitate restoration. Composite resins are commonly used to restore NCCLs although other materials such as glass ionomer and resin-modified glass ionomer are also used. Sclerotic dentin does not etch like normal dentin and therefore it has been recommended to texture the dentin surface with a fine rotary diamond instrument to improve restoration retention. Some clinicians use mechanical retention to increase retention. Beveling of enamel is used to increase the bonding area and retention as well as enhance the esthetic result by gradually creating a color change between the restoration and tooth. Both multistep and single-step adhesives have been used. Dentin etching should be increased to 30 seconds due to the sclerotic dentin with the adhesive agent applied using a light scrubbing motion for 20 seconds but without excessive force that induces substantial bending of a disposable applicator. Both flowable and sculptable composite resins have been successfully used with some clinicians applying and polymerizing a layer of flowable composite resin and then adding an external layer of sculptable composite resin to provide enhanced resistance to wear. When caries is present, silver diamine fluoride has been used to arrest the caries rather than restore the lesion. CONCLUSIONS: Noncarious cervical lesions (NCCLs) form as smooth saucerlike depressions or as V-shaped notches. Prevalence values as high as 90% and as low as 10% have been reported due to habits such as excessive toothbrushing and an acidic diet. Occlusal factors have been proposed as contributing to their presence but it remains controversial. Publications have both supported and challenged the concept of abfraction. They are one of the most common demineralization diseases in the body. Conservative treatment through prevention is recommended with restorative treatment delayed as long as possible. When treatment is needed, composite resins are commonly used with proposed restorative guidelines including texturing the sclerotic dentin, beveling the enamel, potential use of mechanical retention, 30 seconds of acid etching, and use of either multistep or single-step adhesives in conjunction with a light scrubbing motion for 20 seconds without excessive force placed on disposable applicators.

Additive Manufacturing for Complete Denture Fabrication: A Narrative Review.

PURPOSE: To evaluate and compare the benefits and limitations of additive manufacturing for complete denture fabrication. METHODS: A PubMed and Google Scholar search for topics pertaining to additive manufacturing for complete dentures was performed. The resulting articles were then divided into topics to allow a narrative review. DISCUSSION: Determining how printing compares with conventional and milled dentures is critical for the widespread adoption of this fabrication technique. Physical properties, denture tooth bond strength, denture base adaptation and soft-liner bond strength are discussed to establish how printing compares. CONCLUSIONS: Printing offers many advantages over milled and conventionally processed dentures; however, many questions need to be answered by research. The advantages include reduced cost of most printers compared to milling machines, less material waste, ability to print multiple dentures simultaneously, and complex designs can be fabricated that otherwise could not be milled. Current research has shown flexural strength, fracture toughness, color stability, and denture base adaptation are reduced for printed dentures when compared with milled dentures. Print orientation has been shown to influence accuracy, strength, surface roughness and C. albicans adherence which is not seen with conventional or milled denture materials. These factors do not represent a criticism of printing but rather indicate the need for more research with this new and promising denture fabrication technique. Since printing offers numerous benefits to complete denture fabrication it is likely to have a more significant role in complete denture fabrication in years to come as knowledge increases and materials/techniques continue to advance.

Heat and Sound Generation During Implant Osteotomy When Using Different Types of Drills in Artificial and Bovine Bone Blocks.

The purpose of this study was to compare heat and sound generated during implant osteotomy when different types of drill were used in artificial bone and bovine bone blocks. A total of 80 implant osteotomies were formed using 4 implant drilling systems: N1 (OsseoShaper) (Nobel), NobelActive (Nobel), V3 (MIS), and BLX (Straumann) in both artificial bone and bovine bone blocks. Thermocouple probes were used to record temperature change at the depths of 5.0 mm and 13.0 mm of each implant osteotomy formed by the final drill. In addition, thermographic images, drilling sound, and drilling time were recorded and evaluated. Statistical analyses were performed at α = 0.05. The mean temperature changes as recorded by thermocouple probes and thermocamera were significantly lower in OsseoShaper than most other drill-bone combinations (P < .05). The mean drilling times and sound generation for OsseoShaper were significantly higher and lower than most other drill-bone combinations (P < .05), respectively. Minimal heat and sound generation can be expected when implant osteotomies are performed using OsseoShaper at a low rotational speed (50 rpm) even without irrigation. However, extended drilling time is required.

Reducing the need to maintain fixed complete dentures by providing gold occlusal surfaces: A clinical report.

The excessive occlusal wear of complete-arch implant-supported prostheses made with metal and acrylic resin is a clinical complication that can require repeated maintenance in certain patients. A patient who presented with moderate occlusal wear of the prosthetic teeth and substantial fracture of the maxillary anterior acrylic resin base only 2 years after a previous replacement of the acrylic resin base and denture teeth is described. Because of the patient's history and existing wear, both the maxillary and mandibular prostheses were repaired by replacing the acrylic resin bases and resin denture teeth but with the addition of cast gold occlusal surfaces on the posterior prosthetic teeth. The provided treatment helped this patient, who was likely to need more frequent maintenance visits in the future because of his history of accelerated occlusal wear and increased occlusal force.

Conversion of Digital Dentures for Immediate Loading of Complete Arch Implant Prostheses.

The development and expanded use of digital dentures has led to their use in the immediate loading of complete arch implant prostheses. This paper reviews the prosthetic complications that can occur with immediately loaded conversion prostheses along with the advantages afforded by digital dentures in minimizing or eliminating these complications. The process of using digital dentures in the fabrication of conversion dentures for immediate loading of complete arch implant prostheses is presented as well as the use of digital dentures for definitive prostheses. The described procedures include methods of obtaining clinical records, the fabrication of conversion dentures, the immediate loading procedure using a conversion prosthesis, and use of a conversion denture in the fabrication of a definitive prosthesis.

What Occlusal Scheme Should Be Used with Removable Partial Dentures?

PURPOSE: Multiple clinical studies have been published comparing different philosophies of complete denture occlusion and different types of denture teeth. However, it is unclear whether comparable data are available for occlusal schemes used with removable partial dentures (RPDs). Therefore, this review investigated the dental literature related to occlusal schemes for RPDs. MATERIALS AND METHODS: A PubMed search of English language articles was performed using the term "removable partial denture, occlusion" with 765 results. When the term "occlusion in removable partial prosthodontics" was used there were 784 results. Seventy-four articles were identified using the different search term of "RPD, occlusion" while use of the term "occlusal scheme, with removable partial dentures" listed 18 publications. The term "removable partial denture, occlusion, literature reviews" produced 38 potential publications related to the topic. Using the term "removable partial denture occlusion systematic review" resulted in 2 citations. Using the term "RPD occlusion literature review" resulted in one foreign language manuscript whereas using the term "RPD occlusion systematic review" resulted in one article unrelated to dentistry. The term "clinical studies of RPD occlusion" produced 5 results with none related to the topic. There were 23 results using the term "clinical studies of removable partial denture occlusion" with one potentially related to RPD occlusal schemes. RESULTS: A review of the titles and abstracts revealed 12 articles that appeared to contain specific information about the occlusal scheme used with RPDs. Following a detailed review of those publications, only 4 contained recommendations for RPD occlusion and were included in this review. The available information regarding the recommendations for occlusal schemes in these articles was based on expert opinion. A decision was made to include a hand search of 9 textbooks containing varying amounts of information related to occlusal schemes for RPDs, but no evidence-based references related to RPD occlusal schemes were found in the textbooks. Since this entire review is based on expert opinion, no attempt was made to critique the opinions expressed by these authors but rather to present their perspectives for evaluation by readers. CONCLUSIONS: The occlusion developed with RPDs should be physiologically harmonious, allowing the supporting structures to remain in a good state of health with functional stress distributed among all the occluding teeth. Multiple authors indicate the occlusion in maximum intercuspation/centric occlusion should incorporate bilateral posterior contacts with no deflective occlusal contacts. When most occlusal contacts on natural teeth are missing, it has been proposed that extension base RPDs have their occlusal contacts developed in centric occlusion. Regarding eccentric occlusal relationships, a balanced occlusal scheme has been recommended by multiple authors with one author advocating use of a lingualized balanced. An anterior guided (canine-protected) occlusion has also been recommended when the canines are present and not periodontally compromised. When RPDs oppose a complete denture, several authors indicate a bilateral balanced occlusion should be used to help stabilize the complete denture.

Abutment screw torque changes with straight and angled screw-access channels.

STATEMENT OF PROBLEM: Angle-correcting options allow the use of screw-retained implant prostheses in situations where an implant has been placed with a facial inclination. However, manufacturers have different recommended torque values, and it is unclear whether the performance of these designs is equivalent to that of the traditional screw-retained crowns (SRCs) when subjected to cyclic loading forces. PURPOSE: The purpose of this in vitro study was to compare torque differences between conventional straight-line screw access and angulated access SRCs before and after simulated functional loading. MATERIAL AND METHODS: Five groups consisting of 10 SRCs and implants were formed: Nobel Biocare zirconia crowns with 20-degree access channels (NB-20); Dynamic Abutment Solution zirconia crowns (DA-20) with 20-degree access channels; Core3dcentre angle correction zirconia crowns with 20-degree access channels (C3D-20); Nobel Biocare zirconia crowns with 0-degree access channels (NB-0); and gold alloy crowns cast to Nobel Biocare Gold-Adapt abutments (GA-0). Each specimen underwent thermocycling before cyclic loading. A preload torque based on the manufacturer's recommendation was applied to each crown placed on an implant. Reverse torque measurements were obtained for each specimen before cyclic loading. Each implant-abutment assembly was then cyclic loaded at 0 to 100 N at 10 Hz for 1 million cycles. Reverse torque measurements were obtained after cyclic loading and the percentage difference calculated. RESULTS: No significant percentage torque loss differences were observed between the 0-degree and 20-degree SRCs after cyclic loading. No significant differences were seen among the angulated access channel crowns. DA-20 and C3D-20 specimens had significantly higher torque loss compared with the NB-0 group. The C3D-20 group reported the largest percentage torque loss (34.5%) among the angulated access screw channel groups. The GA-0 group reported the largest percentage torque loss of all the groups (35.9%). No crown mobility or other complications were observed in any of the groups after cyclic loading. CONCLUSIONS: Angulated access channel crowns performed comparably with conventional straight-line screw access SRCs with regard to percentage torque values after cyclic loading. Angulated access channel crowns with lower manufacturer recommended torque values had higher percentage torque differences.

CAD/CAM Complete Denture Systems and Physical Properties: A Review of the Literature.

PURPOSE: CAD/CAM complete dentures have increased in popularity and a wide variety of systems are currently available. These prostheses present many advantages for clinicians, technicians and patients. Subtractive manufacturing is used by most of the available systems while a few manufacturers use an additive manufacturing technique. This article describes the currently available systems and materials available for the fabrication of CAD/CAM complete dentures and reviews the literature relative to their physical properties. METHODS: A comprehensive review of the literature was completed to enumerate the currently available techniques to fabricate CAD/CAM complete dentures and discuss their physical properties. A search of English language peer-reviewed literature was undertaken using MEDLINE and PubMed on research articles published between 2000 and 2019. A hand search of relevant dental journals was also completed. RESULTS: The literature indicates the physical properties of CAD/CAM milled poly(methylmethacrylate) or PMMA as it is commonly described is superior to conventionally processed PMMA for the fabrication of complete dentures. CONCLUSION: The incorporation of CAD/CAM technology into complete denture design and fabrication streamlines the clinical and laboratory processes and provides improved physical properties that enhance denture quality.

Should Digital Complete Dentures Be Part of A Contemporary Prosthodontic Education?

Digital complete dentures should be incorporated into a contemporary dental school education due to factors that include the substantial increase in the number of scientific publications devoted to digital dentures, the increased number of companies producing these prostheses, and the expanded use by practitioners. These factors increased recently due to multiple advantages of digital dentures that are described. Based on positive clinical experiences with such prostheses, preclinical curriculum changes were made with examples presented of both didactic and laboratory courses that now include digital dentures. Perspectives are presented regarding online laboratory procedures where a substantial portion can be performed at home through remote instruction.

An Educational Experiment Resulting from COVID-19: The Use of At-Home Waxing and Webinars for Teaching a 3-Week Intensive Course in Tooth Morphology to First Year Dental Students.

PURPOSE: To report the outcomes of presenting a 3-week intensive course in tooth morphology to first year dental students using "at-home" waxing projects and webinars. MATERIALS AND METHODS: Students were provided with the instrumentation and materials required to complete 5 waxing projects at home during the 3-week course. In the same time period, the didactic content was presented via 11 webinar sessions. A postcourse survey provided student perspectives regarding this new experience. RESULTS: Students were able to effectively complete high-quality waxing projects at home by using step-by-step images and videos but the survey indicated an overwhelming preference for in-person faculty feedback. Webinars based on the students having studied the 3D Tooth Atlas and an instructor reviewing content in the Atlas was effective in teaching the didactic aspect of tooth morphology as evidenced by the student grades and survey results. However, most of the students indicated a preference for physically going to class and being able to interact with faculty and classmates as opposed to online webinars. The condensed 3-week version of the course was part of an expanded 4-week student orientation and worked well, allowing other clinical precursor courses to occur before their usual time in the curriculum, thereby allowing students to begin earlier patient treatment. CONCLUSIONS: The at-home waxing exercises produced very good results by having the students use step-by-step images and videos in the 3D Tooth Atlas. However, the students indicated a strong preference for personal faculty feedback that was not available at home. Students effectively learned the didactic aspects of tooth morphology through the webinars with accompanying use of the 3D Tooth Atlas but again most students prefer physically going to class and being able to interact with faculty and classmates. These preferences for contact with classmates and faculty supports the natural human desire for personal interactions with other human beings.

Does the Stomatognathic System Adapt to Changes in Occlusion? Best Evidence Consensus Statement.

PURPOSE: The purpose of this Best Evidence Consensus Statement was to evaluate the existing literature on the stomatognathic system's ability to adapt to occlusal changes. MATERIALS AND METHODS: The search term stomatognathic system was not useful as it resulted in over 400,000 results nor was the search term temporomandibular joint adaptation with 738 results due to the large number of references not related to the topic. The terms stomatognathic system adaptation to occlusal changes (186 results), teeth flexion (139 results), muscle adaptation to dental occlusion (278 results), and occlusal changes and neuroplasticity (11 results) provided the best selection of articles related to the topic. Limiting the above searches to systematic reviews and randomized controlled clinical trials resulted in multiple publications that were related to the question.9-13 Other literature reviews, data-based publications, and expert opinion resources have been included due to their relationship to the question. RESULTS: From the extensive list of search results, 242 articles were determined to be potentially related to the focus question and were evaluated with 56 being included in this paper. It was determined that the stomatognathic system adapts to occlusal changes through the temporomandibular joint, muscles, teeth and bone. The dynamically modified periosteum on the articulator surfaces of the condyle and fossa has a unique load-bearing morphology with 3 subarticular layers of fibrocartilage that absorb and dissipate both peak (impact) and sustained loads. Adaptability of the TMJs and muscles can be documented through studies where artificially produced occlusal interferences were placed in patients and those study participants with normal temporomandibular joints (TMJs) adapted fairly well whereas those with a previous history of temporomandibular disorders (TMD) did not adapt as well. CONCLUSIONS: Available evidence indicates patients generally adapt to the occlusal change inherent in orthodontic treatment, mandibular advancement surgery, and the use of mandibular advancement devices. The head and neck muscles also adapt to occlusal changes in patients without a history of TMD. The dentition adapts to changes through the bone and periodontal ligaments as well as the ability of teeth to undergo slight flexion under masticatory loading. This article is protected by copyright. All rights reserved.

Evolution of the Temperament Theory and Mental Attitude in Complete Denture Prosthodontics: From Hippocrates to M.M. House.

Some 2,500 years ago Hippocrates developed the "Temperament Theory" of the four humors (fluids) he identified as blood, phlegm, yellow bile, and black bile which then led to the ancient medical concept known as "humorism." In Greco-Roman medicine, these humors were believed to be the influencers of an individual's relative wellness or ill-health, served as a means to classify illnesses, and subsequently guided medical diagnosis and treatment. Centuries later modifications to Hippocrates' hypothesis were suggested for use in dentistry when selecting denture teeth and later as a means to classify the mental status and personality of complete denture patients. This paper examines the historic transition of the terminology, characteristics, and thinking behind the four humors with mention of key thinkers in this journey. Of particular note is the evolution in the application of this theory from its suggested use in medicine, proposed by Hippocrates, to the descriptions of mental attitudes and personalities of complete denture patients first described by Neil and subsequently popularized by M. M. House.

The Temporomandibular Joint: A Critical Review of Life-Support Functions, Development, Articular Surfaces, Biomechanics and Degeneration.

The temporomandibular joint is a highly conserved articulation because it promotes survival and propagation via the essential functions of mastication, communication, and routine mating success (dentofacial esthetics). The temporomandibular joint is a unique secondary joint formed between the endochondral temporal bone and the mandibular secondary condylar cartilage via Indian hedgehog and bone morphogenetic protein signaling that is closely related to ear development. A dynamic epigenetic environment is provided by Spry1 and Spry2 genetic induction of the lateral pterygoid and temporalis muscles. Mechanical loading of the condylar periosteum during fetal development produces a superficial layer of fibrocartilage that separates from the condyle to form the interposed temporomandibular joint disc. The articular surfaces of the condyle and fossa are dynamically modified periosteum that has healing and regenerative capability. This unique tissue is composed of a superficial fibrous layer (synovial surface) with an underlying proliferative (cambium) layer that produces a cushioning layer of fibrocartilage which subsequently forms bone. Prior to occlusion of the first primary (deciduous) molars at about 16 months, facial development is dominated by primary genetic mechanisms. After achieving posterior functional occlusion, biomechanics enhances temporomandibular joint maturation, and assumes control of facial growth, development and adaptation. Concurrently, hypothalamus control of musculoskeletal physiology shifts from insulin-like growth factor IGF2 to IGF1, which affects bone via muscular loading (biomechanics). Three layers of temporomandibular joint fibrocartilage are resistant to heavy functional loading, but parafunctional clenching may result in degeneration that is first manifest as trabecular sclerosis of the mandibular condyle.

Influence of Tooth Preparation Design and Scan Angulations on the Accuracy of Two Intraoral Digital Scanners: An in Vitro Study Based on 3-Dimensional Comparisons.

PURPOSE: To evaluate the accuracy of two intraoral scanners (IOS) in terms of different preparation designs and scan angulation limitation due to the presence of adjacent teeth. MATERIALS AND METHODS: Eight different complete coverage (CC) and partial coverage (PC) tooth preparations were scanned by two IOS, the 3Shape TRIOS (TRI) and the 3M True Definition (TRU). All teeth preparations were scanned in the presence and absence of adjacent teeth. Four groups were established for each IOS; Group 1: PC preparations with adjacent teeth. Group 2: CC preparations with adjacent teeth. Group 3: PC preparations without adjacent teeth. Group 4: CC preparations without adjacent teeth. 3D analysis was performed to examine average absolute discrepancy (AAD) and maximum absolute discrepancy (MAD). A Two-way ANOVA was performed followed by a post-hoc Tukey's test HSD to evaluate the effect of adjacent teeth, preparation design, and the type of IOS used. RESULTS: For TRI, AAD for groups 1, 2, 3, and 4 were 20 ± 1.8 µm, 19.6 ± 2.4 µm, 15.5 ± 2.7 µm, and 12.9 ± 1.4 µm, respectively, whereas MAD for groups 1, 2, 3, and 4 were 109.7 ± 13.5 µm, 93.2 ± 28.9 µm, 85.6 ± 16.1 µm, and 66 ± 20.1 µm, respectively. For TRU IOS, AAD for groups 1, 2, 3, and 4 were 22.0 ± 3.6 µm, 17.9 ± 2 µm, 20 ± 5.9 µm, and 14.9 ± 1.7 µm, respectively, whereas the MAD for groups 1, 2, 3, and 4 were 151.4 ± 38.4 µm, 92.2 ± 17. µm, 92.6 ± 23.6 µm, and 71.4 ± 11.9 µm, respectively. Two-way ANOVA showed statistically significant differences between the AAD and MAD of TRI and TRU (p < 0.001). There were also statistically significant differences for presence or absence of adjacent teeth (p < 0.001), and preparation design (p < 0.001). CONCLUSIONS: PC preparation scans revealed lower accuracy than CC. The presence of adjacent teeth decreased the accuracy of both IOS. TRI gave higher accuracy than TRU for PC, but both IOS showed comparable accuracy for CC groups.

Accuracy of 3D Printed Models Created by Two Technologies of Printers with Different Designs of Model Base.

PURPOSE: To evaluate the accuracy of three-dimensional (3D) printed models manufactured using two different printer technologies with different model base designs. MATERIALS AND METHODS: A maxillary typodont was scanned using a desktop scanner to generate the Standard Tessellation Language (STL) file as a reference scan. After the scanning procedure, the STL file was exported to Model Builder™ for designing the following two types of the model bases: a solid base design and a hollow base design with a 2.0 mm thickness of the external shell. Each design was printed to produce 10 models using a Continuous Liquid Interface Production (CLIP) printer and a Digital Light Processing (DLP) printer. The following four groups were tested: CLIP with solid base (CS); CLIP with hollow base (CH); DLP with solid base (DS); and DLP with hollow base (DH). A total of 40 models were scanned using the same desktop scanner to generate the STL files for evaluation of the accuracy by evaluation of trueness and precision. All STL files were superimposed with the control STL file via surface matching software and a comparison was performed using the 3D color mapping function and a 2D comparison of 48 points selected on the tested model. The data were collected by measuring the deviation between the tested model and the reference scan. Trueness was calculated by using the comparison among four tested groups. The Kruskal-Wallis analysis was conducted to assess the overall statistical significance of differences among the tested groups (α = 0.05). For precision measurement, the evaluation was conducted using Intraclass Correlation Coefficient (ICC) value at 95% confident interval to determine the deviation within the same tested groups. RESULTS: The median values for the deviated distance of the four tested groups were 0.045 (CH), 0.035 (CS), 0.077 (DH), and 0.077 mm (DS). There were no statistically significant differences between the trueness of the two groups when using the same printers regardless of the designs of model base (p > 0.05). However, when comparing the two printers using the same model base design and the two different designs of model base, there were statistically significant differences in trueness (p < 0.05). The 3D printed models created using CLIP technology had higher trueness than the DLP technology printer. Precision of the 3D printed model was displayed in ICC value. The ICC values of four tested groups were 0.968 (CH), 0.981 (CS), 0.969 (DH), and 0.983 (DS). All tested groups were classified as exhibiting an excellent level of precision based on 95% confident interval of the ICC estimation. CONCLUSIONS: The accuracy of 3D printed models was affected by the printer technology regardless of whether the model base was solid or hollow. The CLIP technology printer produced significantly less variation from the reference model than the DLP printer. However, all of the 3D printed models were determined to exhibit a clinically acceptable level of accuracy based on the recorded dimensions being less than 100 µm different than the reference model.

Stainability of acrylic resin materials used in CAD-CAM and conventional complete dentures.

STATEMENT OF PROBLEM: The effect of staining beverages on the color of dentures made with computer-aided design and computer-aided manufacturing (CAD-CAM) is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the stainability of acrylic resins used in CAD-CAM-fabricated complete dentures compared with conventional materials. MATERIAL AND METHODS: Acrylic resin denture teeth from 3 different manufacturers (2 conventional and 1 milled) were obtained (N=45). Denture base acrylic resin specimens were made with 3 different techniques (compression molding, injection molding, and milling) (N=45). Conventional and/or milled acrylic resins were used to make specimens comprising both denture teeth and denture base acrylic resins (4 conventional, 2 milled denture bases with bonded teeth, and 1 all-milled) (N=105). All specimens were then immersed in coffee, red wine, or distilled water as control. The CIELab color differences between before and after immersion were determined by using a VITA Easyshade spectrophotometer. The tooth-denture base interface of the denture blocks was evaluated visually for the presence of stain. The CIELab data were analyzed by using ANOVA, and chi-square test was used for visual assessment (α=.05). RESULTS: Significant interactions were found between each acrylic resin material and each staining solution immersion when compared with distilled water immersion (P<.001). Denture teeth had similar color change after immersion in coffee (P=.149), while the most pronounced color change was observed with Portrait teeth upon immersion in wine (P<.001). Injection-molded denture base specimens exhibited less color change upon staining in wine than compression-molded or milled specimens (P<.001). Upon staining in coffee, milled specimens were not significantly different from injection- (P=.053) and compression-molded specimens (P=.180). The chi-square test showed a significant association between processing technique and stain accumulation at the tooth-denture base interface when evaluated visually (P<.001). Stain accumulation was greatest with compression-molded specimens (58%), followed by injection-molded (43%) and milled specimens with bonded teeth (8%). Monolithic teeth with milled denture base had no stain deposits at the tooth-denture base interface. CONCLUSIONS: The stainability of milled acrylic resins was no better than that of conventional materials. However, CAD-CAM milled denture blocks with teeth and base acrylic resins had greater resistance to stain accumulation at the tooth-denture base interface than those of conventional processing methods.

Selective implant scan body modification to restore severely tilted adjacent implants: A completely digital workflow.

The advancements in computer-aided design and computer-aided manufacturing (CAD-CAM) serve to facilitate the management of clinical challenges in restorative dentistry. This technique article describes the fabrication of implant-supported restorations by using a completely digital workflow to manage a patient with severely tilted implants.

A Comparison of the Flexural and Impact Strengths and Flexural Modulus of CAD/CAM and Conventional Heat-Cured Polymethyl Methacrylate (PMMA).

PURPOSE: The introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) technology to the field of removable prosthodontics has recently made it possible to fabricate complete dentures of prepolymerized polymethyl methacrylate (PMMA) blocks, which are claimed to be of better mechanical properties; however, no published reports that have evaluated mechanical properties of CAD/CAM PMMA. The purpose of this study was to compare flexural strength, impact strength, and flexural modulus of two brands of CAD/CAM PMMA and a conventional heat-cured PMMA. MATERIALS AND METHODS: 45 rectangular specimens (65 mm × 10 mm × 3 mm) were fabricated (15 CAD/CAM AvaDent PMMA specimens from AvaDent, 15 CAD/CAM Tizian PMMA specimens from Shütz Dental, 15 conventional Meliodent PMMA specimens from Heraeus Kulzer) and stored in distilled water at (37  ± 1°C) for 7 days. Specimens (N = 15) in each group were subjected to the three-point bending test and impact strength test, employing the Charpy configuration on unnotched specimens. The morphology of the fractured specimens was studied under a scanning electron microscope (SEM). Statistical analysis was performed using one-way ANOVA and Tukey pairwise multiple comparisons with 95% confidence interval. RESULTS: The Schütz Dental specimens showed the highest mean flexural strength (130.67 MPa) and impact strength (29.56 kg/m2 ). The highest mean flexural modulus was recorded in the AvaDent group (2519.6 MPa). The conventional heat-cured group showed the lowest mean flexural strength (93.33 MPa), impact strength (14.756 kg/m2 ), and flexural modulus (2117.2 MPa). Differences in means of flexural properties between AvaDent and Schütz Dental specimens were not statistically significant (p > 0.05). CONCLUSIONS: As CAD/CAM PMMA specimens exhibited improved flexural strength, flexural modulus, and impact strength in comparison to the conventional heat-cured groups, CAD/CAM dentures are expected to be more durable. Different brands of CAD/CAM PMMA may have inherent variations in mechanical properties.