Preparation of ultrathin translucent zirconia laminate veneers using 3D printing reduction guides.

Minimizing and controlling the amount of tooth reduction during the preparation of ultrathin laminate veneers is a challenge for minimally invasive dentistry. The use of reduction guides is advised to reach the optimal space required for the definitive restoration without excessive reduction. The digital production of a reduction guide used to control tooth preparation for ultrathin laminate veneers is described.

Effect of ceramic materials and tooth preparation design on computer-aided design and computer-aided manufacturing endocrown adaptation and retentive strength: An in vitro study.

OBJECTIVES: To evaluate how various tooth preparation designs impact the adaptation-both at the margins and internally-and the retentive strength of computer-aided design and computer-aided manufacturing (CAD/CAM) produced endocrowns. MATERIALS AND METHODS: 60 extracted human mandibular first molars were endodontically treated and assigned into three groups (n = 20) according to the tooth preparation design: Group N: butt joint design, Group F and F1 received 1- and 2-mm circumferential ferrule preparation, respectively. Endocrowns were milled using either lithium disilicate glass-ceramic (IPS emax ceramic) or monolithic zirconia. The internal and marginal adaptation of the endocrowns were evaluated using the replica technique. After cementation, the endocrowns of all test groups were dislodged axially at 0.5 mm/min using a universal testing machine. A 2-way ANOVA and the independent samples t-test (α = .05) were performed to statistically analyze the data. RESULTS: The effect of changing the design of the tooth preparation (butt joint, ferrule) on the marginal and internal gap was shown to be statistically significant (p < .05); the lower gap values were recorded at the axial followed by cervical, marginal, and pulpal floor walls in both ceramic groups regardless of the teeth preparation design. The ANOVA test revealed similar average removal forces and stresses for the two types of tested ceramic materials. CONCLUSION: IPS emax ceramic adapted better than monolithic zirconia ceramic, regardless of the preparation design. Ferrule preparation design is more retentive than butt joint preparation, regardless of the type of ceramic material used.

Zirconia restoration types, properties, tooth preparation design, and bonding. A narrative review.

OBJECTIVE: The purpose of this review was to provide dental professionals with information regarding the various types of zirconia restorations, their mechanical and optical properties, tooth preparation design, and bonding protocol in an effort to enhance the longevity and durability of zirconia restorations. OVERVIEW: The yttria content of zirconia ceramics determines their classification. The mechanical and optical properties of each type are discussed, with an emphasis on the effect of yttria concentration on the properties of zirconia. The processing and sintering methods are also discussed as they have a direct impact on the properties of zirconia. The design of tooth preparation, specifically occlusal reduction, varies depending on the type of zirconia used in each case. Finally, a protocol for zirconia restoration bonding is described to ensure optimal bonding to the tooth structure. CONCLUSION: Not all zirconia restorations are the same. The selection of zirconia type based on yttria concentration, processing and sintering methods, tooth preparation design, and adherence to the bonding protocol are all critical to the success and longevity of zirconia restorations. CLINICAL SIGNIFICANCE: Zirconia restorations are the most commonly used indirect restorative material. The selection of the most appropriate zirconia type based on its yttria content, which determines its strength and translucency, is critical to the success and the longevity of the restoration. Tooth preparation design also influences the strength and translucency of the zirconia. Air-borne particle abrasion, followed by a ceramic primer and resin cement, can ensure a durable bond to the tooth structure.

Clinical management of vital and non-vital discolored tooth preparation stump shades: A clinical case series.

OBJECTIVE: Traditional and modern-day laboratory techniques can be used to mask vital and non-vital discolored teeth. CLINICAL CONSIDERATIONS: Two clinical case reports are presented showing different treatment approaches to differing clinical scenarios of partial coverage veneer and full coverage crown restorations, respectively. CONCLUSIONS: Feldspathic ceramics should be considered when customization of stump shade correction and equalization is required with minimum facial reduction with veneer restorations. Translucent zirconia (5 mol% Y2 O3 ) can be used to mask metal posts and core restorations on non-vital teeth using an opaquer material that is infused into the intaglio surface in the green state. CLINICAL SIGNIFICANCE: Different clinical scenarios will present to the clinician in regard to discolored stump shades where understanding what laboratory material treatment options are available that will help guide definitive restoration types and ultimately tooth preparation design.

[Non-retentive adhesive restorations]. / Niet-retentieve adhesieve restauraties.

With the advent of adhesive dentistry, tooth preparation can be minimally invasive. An optimal adhesion to the dental tissues is a requirement. Rubberdam isolation, using a gold standard adhesive and bonding to freshly prepared dentin are all factors that improve the adhesion to tooth tissue. For non-retentive restorations, indirect composite and glass-ceramic materials are suitable. To date, several studies have shown a high survival rate of indirect adhesive restorations. The adage "if you can isolate the tooth, you can preserve it" may guide the choice of starting an adhesive procedure.

Simultaneous implantation and tooth preparation technology guided by 3D-printed guide.

Using digital technologies in concurrently performing missing tooth implantation and preparation of remaining teeth is a solution to reduce the number of visits and improve efficiency. This paper proposes a digital process for simultaneously implanting and preparing teeth. It integrates implant surgical guide and 3D-printed tooth preparation guide into a single guide and completes guided implant placement and precise tooth preparation. Based on "repair-oriented" virtual implant planning, the implant surgical guide can improve the efficiency and predictability of implant placement, and its linear accuracy is about 1 mm. The tooth preparation guide precisely guides tooth preparation and restoration space visualization, ensuring the quality of the tooth preparation. The two guides have different design accuracy requirements, and thus their combination improves the overall guiding accuracy requirements. The concurrent application of the two guides minimizes the clinical operation time, number of visits, and economic burden of patients.

Veneer tooth preparation utilizing a novel digital designed workflow: A case report.

OBJECTIVE: This article describes a technique to implement guided tooth preparation where the tooth is virtually prepared in the laboratory and preparation templates are created for chairside use. CLINICAL CONSIDERATIONS: Prior to any tooth preparation, patient records are acquired with an intra-oral scanner, both stump and final shades are selected, and digital photos are taken. These digital records are used in combination with digital laboratory tools to do the virtual preparation first, and then to provide chairside templates for guided tooth preparation. CONCLUSIONS: The traditional approach of tooth preparation has evolved from historically preparing a tooth without any pretreatment guidance to, more currently, preparing the tooth through a mock-up of the desired final restoration. The outcome of these traditional approaches is highly dependent on the operator's skills to produce a successful outcome, and often resulted in more tooth structure removal than necessary. However, CAD/CAM technology now offers a guided tooth approach to tooth preparation which minimizes tooth structure removal and provides an advantage to the beginner dentist. CLINICAL SIGNIFICANCE: This is a unique approach in digital restorative dentistry.

Effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations.

AIM: The aim of the present study was to evaluate the effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations. MATERIALS AND METHODS: Five tooth preparations were constructed, and crowns with different cement gaps and drill offsets were obtained. Then, best-fit alignment was performed on the crowns with the corresponding tooth preparations, and the fit discrepancies were expressed by color-coded difference images and root mean square (RMS) values. The RMS values of each group were analyzed by the rank-based Scheirer-Ray-Hare test (α = 0.05). RESULTS: The color segments in the sharp line angles area of the Sharp line angles group changed significantly before and after the drill offset. The cement gap had a significant effect on the marginal, internal, or overall fit discrepancies of the five design groups (P < 0.001), while the drill offset had a significant effect on the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.001). Additionally, the interaction effect between cement gap and drill offset was significant for the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.01). CONCLUSIONS: The cement gap and drill offset had a significant adverse effect on the marginal or internal fit discrepancies of the crowns designed with the shoulder-lip and sharp line angles designs. Tooth preparation designs with intense curvature changes such as shoulder-lip and sharp line angles should be avoided clinically.

Impact of marginal defects on the accuracy of automated finish line detection in tooth preparation.

AIM: The present study aimed to evaluate the accuracy of automated detection of preparation finish lines in teeth with defective margins. MATERIALS AND METHODS: An extracted first molar was prepared for a full veneer crown, and marginal defects were created and scanned (discontinuity of finish line: 0.5, 1.0, and 1.5 mm; additional line angle: connected, partially connected, and disconnected). Six virtual defect models were entered into CAD software and the preparation finish line was designated by 20 clinicians (CAD-experienced group: n = 10; CAD-inexperienced group: n = 10) using the automated finish line detection method. The accuracy of automatic detection was evaluated by calculating the 3D deviation of the registered finish line. The Kruskal-Wallis and Mann-Whitney U tests were used for between-group comparisons (α = 0.05). RESULTS: The deviation values of the registered finish lines were significantly different according to conditions with different amounts of finish line discontinuity (P < 0.001). There was no statistical difference in the deviation of the registered finish line between models with additional line angles around the margin. Moreover, no statistical difference was found in the results between CAD-experienced and CAD-inexperienced operators. CONCLUSIONS: The accuracy of automated finish line detection for tooth preparation can differ when the finish line is discontinuous. The presence of an additional line angle around the preparation margin and prior experience in dental CAD software do not affect the accuracy of automated finish line detection.

A novel chairside technique to assess the interocclusal clearance and abutment axial walls during tooth preparation.

The importance of a judicious and unerring abutment tooth preparation in the field of prosthodontics has always been paramount. It is not uncommon for many clinicians to face challenges during laboratory fabrication of fixed prostheses, caused due to inappropriate occlusal clearance and over axial wall taper of the abutment tooth. With evolving technologies and methods, the modus operandi for attaining such tooth preparation is varying; however, every technique has its own shortcomings. The technique mentioned in the article is cost-effective as it uses modified Heister mouth gag forceps to achieve the desired objective of evaluating the prepared abutment morphology three-dimensionally with minimum chairside time.

[Prediction, analysis and application of learning curve of tooth preparation for all ceramic crowns of maxillary central incisors].

OBJECTIVE: To predict the learning curve of tooth preparation for all ceramic crowns of maxillary central incisors on phantom head simulators for graduate students participating in standardized dental resident training based on the modified Wright learning curve model, then to analyze and applicate the learning curve. METHODS: Twelve graduate students participating in standardized dental resident training were selected to prepare the resin maxillary central incisors on phantom head simulators for all ceramic crowns 4 times. The results of preparation were evaluated by 3 prosthetic experts with at least 10 years' experience focusing on the reduction, contour, taper, shoulder, finish line, margin placement, adjacent tooth injury, and preparation time for tooth preparation. The learning rate of tooth preparation was calculated by scores of tooth preparation of 4 times. The learning curve of tooth preparation was predicted based on the modified Wright learning curve model. According to the criteria of standardized training skill examinations for dental residents in Beijing, 80 was taken as the qualified standard score. The minimum training times for tooth preparation to satisfy the qualified standard score (80) was calculated, to analyze the characteristics of learning curve and evaluate the effectiveness of tooth preparation. RESULTS: The scores of 4 tooth preparation were 64.03±7.80, 71.40±6.13, 74.33±5.96, and 75.98±4.52, respectively. The learning rate was (106±4)%, which showed the learning curve an upward trend. There were no significant differences between the qualified standard score and the predicted scores of tooth preparation from the 5th preparation to the 13th preparation (P > 0.05). The predicted score of the 14th preparation was higher than the qualified standard score (P < 0.05). CONCLUSION: The trend of the learning curve of tooth preparation for all ceramic crowns of maxillary central incisors on phantom head simulators for graduate students participating in standardized dental resident training is upward, which predicts the minimum training times higher than the qualified standard score is 14 times.

Computer-aided design and 3-dimensional artificial/convolutional neural network for digital partial dental crown synthesis and validation.

The current multiphase, invitro study developed and validated a 3-dimensional convolutional neural network (3D-CNN) to generate partial dental crowns (PDC) for use in restorative dentistry. The effectiveness of desktop laser and intraoral scanners in generating data for the purpose of 3D-CNN was first evaluated (phase 1). There were no significant differences in surface area [t-stat(df) = - 0.01 (10), mean difference = - 0.058, P > 0.99] and volume [t-stat(df) = 0.357(10)]. However, the intraoral scans were chosen for phase 2 as they produced a greater level of volumetric details (343.83 ± 43.52 mm3) compared to desktop laser scanning (322.70 ± 40.15 mm3). In phase 2, 120 tooth preparations were digitally synthesized from intraoral scans, and two clinicians designed the respective PDCs using computer-aided design (CAD) workflows on a personal computer setup. Statistical comparison by 3-factor ANOVA demonstrated significant differences in surface area (P < 0.001), volume (P < 0.001), and spatial overlap (P < 0.001), and therefore only the most accurate PDCs (n = 30) were picked to train the neural network (Phase 3). The current 3D-CNN produced a validation accuracy of 60%, validation loss of 0.68-0.87, sensitivity of 1.00, precision of 0.50-0.83, and serves as a proof-of-concept that 3D-CNN can predict and generate PDC prostheses in CAD for restorative dentistry.

The effect of different tooth preparation finishing procedures and immediate dentin sealing on the scanning accuracy of different intraoral scanners.

PURPOSE: To measure the effect of different tooth preparation finishing procedures (super-coarse grit, fine grit, and air-particle abrasion) and immediate dentin sealing (IDS) on the scanning accuracy of 4 intraoral scanners (IOSs). MATERIAL AND METHODS: A tooth preparation for a full-coverage restoration was performed on an extracted mandibular molar using super-coarse diamond burs. Four groups were created depending on the tooth preparation finishing procedure: super-coarse grit (bur with a grit size of 150 µm) (SCG group), fine grit (bur with a grit size of 30 µm) (FG), air-particle abrasion with 27-µm aluminum oxide particles (APA group), and IDS (IDS group). Each group was divided into 5 subgroups according to the scanning system used to digitize the tooth preparation: laboratory scanner (control subgroup) (T710; Medit), Trios 4 (Trios subgroup), CS 3800 (CS subgroup), i700 wireless (i700 subgroup), and iTero Element 5D Plus (iTero subgroup) (n=20). For each subgroup, the control file was aligned with each experimental scan using the best-fit algorithm and an engineering program (Geomagic Control X). The discrepancy between the control and experimental files of each subgroup was computed by measuring the root mean square (RMS) error. Two-way ANOVA and Tukey tests were used to analyze the data (α=.05). RESULTS: Tooth preparation finishing procedures (P<.001) and the IOS assessed (P<.001) were significant predictors of the trueness and precision values obtained. The highest trueness and precision values were measured in the APA group, while the IDS group had the lowest trueness and precision. Additionally, the i700 subgroup obtained the highest trueness and precision values, while the CS and Trios subgroups had the lowest trueness and precision values. CONCLUSIONS: The different tooth preparations finishing procedures tested influenced on the scanning accuracy of the 4 IOSs considered. The air-particle abrasion procedure obtained the best accuracy values. The trueness discrepancies measured among all the subgroups was 19µm and the precision discrepancies measured among all the subgroups was 4.69 µm. CLINICAL SIGNIFICANCE: The tooth preparation finishing procedure used can reduce the intraoral scanning accuracy of any of the intraoral scanners tested. The air-particle abrasion finishing procedure might be recommended for maximizing the scanning accuracy of the IOSs tested.

Effect of magnifying loupes on tooth preparation of complete coverage crown: A quantitative assessment using a digital approach.

OBJECTIVE: The purpose of this study was to evaluate the use of magnifying loupes (×2.5) on the quality of tooth preparation for complete coverage crowns; performed by predoctoral students using an objective and quantitative digital method. MATERIALS AND METHODS: Forty-two predoctoral students were randomly assigned into 2 groups to perform tooth preparation for a complete coverage crown on a mandibular first molar in a manikin, with and without the use of magnifying loupes. All preparations were digitally evaluated by PrepCheck 3.0 (Dentsply Sirona). Parameters including tooth reduction, total occlusal convergence (TOC), undercut, margin quality and surface quality were assessed. Continuous data were analysed using Paired t-tests or Wilcoxon Signed Ranks tests. Ordinal data were analysed by McNemer's tests. To further detect the majority pattern ( > 50%) in each group (with and without loupes), one-sample t-test or one-sample Wilcoxon Signed Rank test was performed. The level of significance was set at p = .001 after Bonferroni adjustments for multiple testing. RESULTS: No significant differences in the measured outcomes were found between the groups with or without the use of magnifying loupes (p > .002). The majority (>50%) of both groups had no undercuts (99.3% and 99.4% both p < .001) and the preparation type was within tolerance (81.6% and 85.3%, both p < .001) with acceptable margin (86.4% and 86.3%, both p < .001) and acceptable surface quality (99.0% and 99.1%, both p < .001). However, the majority of both groups underprepared occlusally (96.0% and 95.4%, both p < .001) and axially (65.3% and 67%, both p < .001). Only 30.0%-42.1% of the participants achieved the TOC within 0-20°. CONCLUSIONS: Within the limitations of this study, the use of magnification loupes does not appear to significantly improve the quality of tooth preparation for complete coverage crown. The TOC was also found to be overprepared and occlusally underprepared.

Comparison of digital and conventional assessment methods for a single tooth preparation and educational satisfaction.

INTRODUCTION: Digital feedback for tooth preparation can provide dental practitioners with more objective and accurate evaluations compared to conventional methods. This study aimed to evaluate the educational effect and satisfaction of digital feedback compared with those of the conventional putty index method for tooth preparation. MATERIAL AND METHODS: Forty-eight third-grade dental students were selected. All students performed a full-coverage preparation on a right mandibular first molar resin tooth. They were randomly divided into four groups (n = 12)-no guide (control), putty index, digital feedback, and digital and putty index assessment. Three-dimensional analysis was performed using an analysis software (GomInspect 2018, Gom) to evaluate the amount of tooth structure removed. At the end of the practice, the students completed a questionnaire to evaluate the educational satisfaction of the respective methods. RESULTS: There was no statistical significance of the amount of preparation amongst groups in most of the measured areas only except for several specific points. Overall occlusal surface showed 0.99 ± 0.27 mm in the N group (no guide) and 1.15 ± 0.31 mm in the D group (digital feedback), and overall axial surface showed no statistical differences (p > .05). The groups that used digital assessment showed a high level of satisfaction compared with conventional assessment. CONCLUSIONS: It was difficult to confirm that the digital-based feedback promotes accurate tooth preparation compared to conventional feedback within the limitation of this study. However, it improved educational satisfaction and permitted objective evaluation.

Preliminary application and evaluation of digital step-by-step tooth-preparation templates.

STATEMENT OF PROBLEM: Tooth preparation is a fundamental technique, and inaccurate preparation may lead to excessive irreversible tooth removal or insufficient restorative space. The conventional process depends mostly on operator experience, and variable quality is inevitable. Whether a tooth preparation template would be beneficial, especially for inexperienced dentists, is unclear. PURPOSE: The purpose of this preliminary study was to evaluate the application of new digitally designed step-by-step templates to guide tooth preparation. MATERIAL AND METHODS: A laboratory scanner was used to obtain digital scans of dental casts. A 3-dimensional reverse engineering software program was used for the step-by-step digital design. The data for a series of guide templates were imported into a computer-aided manufacturing (CAM) machine for milling. Ten experts and 10 inexperienced dentists prepared teeth on a dentoform in a mannequin head. They were instructed to complete the preparation within 20 minutes both with and without the step-by-step template. The prepared crowns were subsequently scanned with an intraoral scanner, the scans were imported into a preparation evaluation software program, and various indexes were scored. The t test was used to analyze the differences between the 2 methods of tooth preparation in each group (α=.05). RESULTS: No significant differences were found in total scores with and without the guide templates in the expert group (P=.256), but the scores in the inexperienced group differed significantly between the 2 preparation methods (P<.001). In undercut comparisons, the 2 methods of preparation did not differ significantly in the expert (P=.912) or inexperienced groups (P=.601). However, the scores for taper and occlusal reduction were significantly higher in the inexperienced group when using the guide template (P<.001). CONCLUSIONS: The new digitally designed step-by-step tooth preparation guide template significantly improved the efficiency and quality of tooth preparation for inexperienced dentists when preparing multiple teeth.

Reliability of automatic finish line detection for tooth preparation in dental computer-aided software.

PURPOSE: This study aimed to investigate the accuracy of automatic tooth finish line registration compared to manual registration with regard to various finish line configurations and dental computer-aided design (CAD) software. METHODS: Finish line registrations were performed on 15 digital tooth models with different finish line configurations (edge roundness radius = 0 mm, 0.2 mm, and 0.4 mm; edge angle = 30°, 60°, 90°, 120°, and 150°) using automatic and manual methods for designing virtual copings (N = 150). The discrepancies between the registered finish line extracted from the copings and the actual finish line segmented from the digitized tooth model were measured. Three-way analysis of variance (ANOVA) and post-hoc analyses with Bonferroni correction (α = 0.05) were used to analyze the results. RESULTS: The finish line configurations, registration methods, and CAD software interacted with the accuracy of the registered finish line (p = 0.001). The automatic finish line registration method exhibited larger error values than the manual method, especially at high finish line edge roundness and obtuse edge angles for both EXOCAD and R2CAD software (p < 0.001). The difference in dental CAD software affected the registration accuracy in the automatic method (p < 0.001), but not in the manual method (p = 0.676). CONCLUSIONS: Finish line registration errors may occur when the automatic registration method is applied to the indistinct edge of tooth preparation. The accuracy of the automatic finish line registration could differ according to the CAD software program.

A diagnostically and digitally driven tooth preparation protocol by using a patient monitoring tool with an intraoral scanner.

Finding the right balance between the preservation of tooth structure and providing adequate space for the restorative material is a major challenge in prosthetic dentistry. A technique is presented using the patient monitoring tool available in standard software programs of an intraoral scanner to constantly monitor preparation dimensions in relation to the optimal definitive restoration.

Retrospective clinical evaluation of a no-prep porcelain veneer protocol.

STATEMENT OF PROBLEM: Porcelain laminate veneers without tooth preparation (no-prep veneers) might represent a convenient and conservative option for the esthetic rehabilitation of anterior teeth. However, controversy exists about their predictability. PURPOSE: The purpose of this clinical study was to retrospectively evaluate the performance of no-prep porcelain veneers placed as per the recently proposed "CH no-prep" protocol, which claimed to overcome many of the drawbacks of previous no-prep veneer solutions. MATERIAL AND METHODS: One hundred eight no-prep porcelain laminate veneers based on the CH no-prep protocol were placed in 21 patients between 2015 and 2017. All participants were contacted, and 15 received a recall examination: a total of 78 veneers were evaluated as per the Clinical-Photographic-Micromorphologic coding. Plaque and gingival indexes and any increase in gingival recession were recorded. Pulp vitality was verified. A survival rate based on the count of absolute failures and a success rate summarizing the effect of both absolute and relative failures were calculated. RESULTS: The mean observation period was 43.1 months, with an observation interval of 36 to 60 months and a survival rate of 97.4%. From the 5 relative failures (3 minimal fractures or chips and 2 limited marginal discolorations) and the 2 absolute failures (unrepairable fractures), an overall success rate of 91.0% was recorded, with 71 restorations that were judged excellent in terms of clinical acceptance after the recall examination. From the Clinical-Photographic-Micromorphologic evaluation, 5 restorations (6.4%) showed minimal issues for marginal integrity, while a limited porcelain overhang was identified on 2 restorations (2.8%). Micromorphologic analyses confirmed the clinical evaluations. No periodontal recession was observed, and plaque and gingival indexes appeared stable. CONCLUSIONS: Porcelain laminate veneers placed as per the CH no-prep protocol demonstrated excellent performances after 36 to 60 months of clinical service. The achieved outcomes, in terms of color match and overall esthetic and anatomic integration, confirmed that a prepless approach may be safely adopted provided that strict rules for patient selection and finish line placement are adopted.