Minimal invasive microscopic tooth preparation in esthetic restoration: a specialist consensus

Utilization of magnification devices in Vietnam's dental practice and education: an online survey

Background

Advancements in dental technology have enhanced diagnostic and treatment tools, with magnification devices improving clinical precision and ergonomics. Dental loupes, conventional dental operating microscopes (DOMs), and three-dimensional digital operating microscopes (3D-DOMs) help overcome visual limitations in intricate procedures. Although widely used globally, adoption in Vietnam remains underreported. This study aimed to assess magnification device utilization in Vietnamese dental practice and education, with a pioneering focus on 3D-DOMs.

Methods

An online, questionnaire-based observational survey was conducted from October to December 2024. A total of 108 dentists responded, along with 11 dental education institutions and 5 hospitals (2 specialized, 3 general). The 28-item questionnaire, validated by a subject expert (CVI-S = 0.9), was distributed via email and messaging platforms. Google login ensured one response per participant. Data were analyzed using JASP (version 0.19.3) with descriptive statistics and Chi-square tests (p  < 0.05).

Results

Awareness was high (96.4%), while actual usage was moderate (62.96%). Usage varied by setting: specialized hospitals (100%) and education institutions (80%) showed higher adoption than general hospitals (33.33%). Dental loupes were most common (55.56%), followed by DOMs (25.93%) and 3D-DOMs (5.56%). Future usage intentions were high, particularly for loupes (81.48%). Endodontics was perceived as the specialty benefiting most. Despite cost being the primary barrier, satisfaction was high. Formal training significantly improved self-rated knowledge and satisfaction.

Conclusions

Despite cost and ergonomic barriers, magnification devices—especially 3D-DOMs—show strong potential. With improved training and resource allocation, they could significantly enhance diagnostic precision and clinical outcomes in Vietnamese dentistry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-025-06306-6.

[Geometric position relationship between gingival, preparation, restoration margins and the cementation (adhesive) layer in the marginal area: new classification and scheme for margin position]

The current low quality of fixed restoration margins is highly correlated with the high incidence of margin-related complications. It is also related to the unclear spatiotemporal geometric position relationship among the consensus definitions of the gingival margin (G), preparation margin (P), and restoration margin (R). This paper discusses the existing problem of the existing term "gingival margin" as a surface anatomical landmark; proposes the term "free gingival margin line" that conforms to geometry and measurement and has importance as a surface anatomical landmark; and clarifies the participants that exist in the marginal area. These participants include the P, R, and G; cementation (adhesive) layer; and gingival sulcus. Moreover, this paper discusses the various iatrogenic damages induced by entering the gingival sulcus via the P, R, and cementing (adhesive) layer. Through the discussion of the design deficiencies of the subgingival and biologically oriented preparation technique, the physiological and clinical importance of the concept of gingival sulcus/gingival sulcus fluid + supercrestal tissue attachment (biological width) = first periodontal protective barrier was analyzed. The value of preserving the physiological role of the gingival sulcus is emphasized. Furthermore, the newly defined RPG distance represents the distance between the successive P or R line and free G line and can be measured in the clinical procedure of tooth preparation. The optimal solution is 0-200 µm, that is, RPG200: the P and R are located on the free G line and the distance between these margins is less than 200 µm. This distance not only has the aesthetic effect of invisibility to the naked eye, it also has a minimal effect on the G and gingival sulcus and is convenient for doctors and patients to clean. Furthermore, in accordance with the positional relationship between the three margins and cementation (adhesive) layer, a new classification of marginal positions is proposed. This classification overcomes the problems of incomplete inclusion objects and uncontrolled risk factors in the previous classification. It also has the advantages of strong practicability, good efficiency of main control geometric quantity, and clear risk control points. The new design scheme and classification of the margi-nal position of RPG200 proposed in this paper provide a new understanding for margin design and complication prevention in the future.

Evaluation of mechanical and thermal stress in an endodontically treated cracked premolar with three restorative designs: 3D-finite element analysis

PURPOSE

We aimed to analyze the influence of different designs (inlay, onlay, and crown) on stress distribution and crack propagation in an endodontically treated cracked premolar.

METHODS

Three-dimensional (3D) finite element analysis (FEA) was employed to model an endodontically treated cracked premolar with three different restorations (inlay, onlay, and crown). Six types of loadings (vertical loading of 600 N; hot thermal-600 N vertical coupling loading; cold thermal-600 N vertical coupling loading; oblique loading of 200 N; hot thermal-200 N oblique coupling loading; cold thermal-200 N oblique coupling loading) were applied to simulate the hot and cold food/beverages intake. The Von-Mises Stress (VMS) on the lower margin of the crack surface was measured at 20 points in each model, and the position of the stress concentration on the crack surface was analyzed.

RESULTS

All three restoration types effectively improved stress distribution. The influence of different restorative modalities on the stress distribution at the crack tip exhibited different trends under different loading conditions. Lateral loading and/or hot thermal cycling increased the intensity of VMS, and crown restoration exhibited the highest stress concentration at the crack tip under lateral loading and hot thermal cycling.

CONCLUSIONS

From a mechanical perspective, the outcome of this study suggested that a full crown restoration is not the optimal choice for preventing further crack propagation. Additionally, it is recommended to reduce the consumption of excessively hot foods and beverages daily.

Contemporary Digital Dentistry for Complex Cases in the Anterior Maxilla

OBJECTIVES

To demonstrate how contemporary digitally driven workflow can enhance outcomes for complex esthetic dental cases, focusing on three distinct clinical scenarios involving implant placement, esthetic crown lengthening, and tooth autotransplantation (ATT).

OVERVIEW

Three multidisciplinary clinical cases demonstrate our contemporary digital workflows, integrating diagnosis, treatment planning, patient communication, and guided execution. The first case involves replacing two anterior central incisors using digital planning, guided surgery, prefabricated customized healing abutments, and a digitally driven restorative process. The second case showcases an esthetic crown-lengthening procedure, where Multifunctional Anatomical Prototypes (MAPs) serve as both mock-up and surgical guides, enhancing patient communication on expected outcomes and ensuring precise tissue management to prevent soft tissue rebound. The final case features a tooth ATT, where virtual surgical planning and 3D-printed tooth replica and guides ensure predictability in the therapeutic outcome. These digitally enabled strategies underscore the predictability and customization achievable with contemporary dental technology.

CONCLUSIONS

Dental treatments in the esthetic zone require meticulous planning and precise execution to achieve controlled results that ensure patient satisfaction and long-term stability. Contemporary Digital Dentistry enhances predictability, creating a pathway that leads to success.

Knowledge and practice of dental professionals regarding vertical teeth preparation techniques

BACKGROUND

Vertical preparation techniques (VPTs), particularly the biologically oriented preparation technique (BOPT), have gained prominence in restorative dentistry due to their conservative approach to tooth structure preservation and improved aesthetic outcomes. This study aims to assess the knowledge and clinical practices of VPTs, including BOPT, among dental professionals in Sanaa, Yemen, and explore the barriers to their widespread use.

MATERIALS AND METHODS

An online cross-sectional survey was conducted among general practitioners and specialists in Sanaa, Yemen using a structured, self-administered questionnaire. The survey explored the participants' knowledge, familiarity, and clinical use of VPTs and their perceptions of its advantages and challenges. Data were analyzed using descriptive statistics and Chi-square tests to evaluate associations between professional roles and VPT knowledge and practice. P values < 0.05 indicated statistical significance.

RESULTS

Out of 285 participants, 76.8% were familiar with VPTs but only 11.6% reported using these approaches in clinical practice. The primary source of knowledge acquisition was informal, with 26.3% of the participants citing social media as their main resource. Specialists demonstrated significantly higher proficiency and confidence in applying VPTs compared with general practitioners (p < 0.05). Key challenges identified in clinical adoption were controlling gingival bleeding (32.28%) and achieving precise margins during tooth preparation (34.74%). The majority (55.8%) of participants acknowledged the potential of VPTs as the future of restorative dentistry. Despite these benefits, 36.1% of the respondents emphasized the need for further training and educational programs to enhance proficiency and overcome the perceived complexity of these techniques.

CONCLUSION

This study highlights significant gaps in the knowledge and practice of VPTs, particularly BOPT, among the participants. While these techniques offer promising clinical and aesthetic benefits, their adoption is hindered by inadequate training and perceived complexity. Targeted educational interventions and further research are needed to support the broad implementation of VPTs in clinical practice.

CLINICAL TRIAL NUMBER

Not applicable.

Template-aided and freehand guiding plane preparation for removable partial dentures: A randomized controlled trial

PURPOSE

To evaluate the accuracy of guiding plane preparation for removable partial dentures (RPDs) using 3D-printed templates compared to the freehand method.

MATERIALS AND METHODS

Twenty partially edentulous patients requiring RPDs were randomly divided into two groups: the template-aided group (n = 10) and the freehand group (n = 10). Fifty-six guiding planes were prepared by a single clinician using two different methods. The angle deviation between the prepared guiding plane and the RPD path of placement was measured for both groups. The 3D deviations between the prepared guiding plane and the designed guiding plane were measured for the template-aided group. Patient satisfaction with the RPD was evaluated 2 weeks post-RPD wearing.

RESULTS

The angular deviation observed in the template-aided group (1.77±1.11 degrees) was significantly lower than that (6.29±4.18 degrees) in the freehand group (p < .001). Additionally, the 3D deviation between the prepared guiding plane and the designed guiding plane of the template-aided group was 106.2±40.9 µm. No significant difference in patient satisfaction scores related to RPD wearing was found between the two groups.

CONCLUSIONS

Utilizing the cobalt-chromium (CoCr) alloy template significantly improved the accuracy of guiding plane preparation in the clinic, irrespective of the site of the abutment tooth.

An alternative method for the rapid verification of the three-dimensional adaptation of splinted implant-supported crowns

Fit accuracy is crucial for the clinical success of implant-supported prostheses. Traditionally, radiographs have been used to assess the marginal fit in 2 dimensions. Three-dimensional (3D) evaluation based on optical scanning techniques requires additional software programs and procedural steps. This article describes an alternative workflow for the rapid verification of the 3D fit of splinted implant-supported crowns. First, the abutments and splinted crowns were positioned onto a printed cast and scanned, with the data exported as a reference. Following the intraoral placement of the abutments and the splinted crowns, an additional scan was made and compared with the reference data to calculate deviations directly within the intraoral scanner. This protocol simplifies the fit evaluation process and provides rapid results, thereby enhancing efficiency and saving time.

Masking ability of CAD-CAM resin-matrix ceramics with different translucencies and thicknesses combined with four cement shades against varying background colors when facing veneer restorations

BACKGROUND

To evaluate the comprehensive effect of translucency, thickness, cement shades, and background color on the masking ability of resin-matrix ceramic veneer restorations.

METHODS

Resin-matrix ceramic specimens with 2 translucencies (LT, HT) and 3 thicknesses (0.5, 1.0, and 1.5 mm) were made of Upcera Hyramic (A2 shade). Cement specimens were made of Variolink N in 4 shades (yellow, white, transparent, and bleach XL). Five background specimens were made of IPS Natural Die Material in 5 shades (ND1, ND2, ND3, ND4, and ND5). Color coordinates of 120 subgroups (n = 5) of combined specimens composed of different ceramic, cement, and background specimens were obtained using a spectroradiometer. Color difference (ΔE00) compared with a 4-mm thick specimen of LT and HT ceramics was calculated and four-way ANOVA was used for statistical analysis (α = 0.05).

RESULTS

Translucency, thickness, cement shade, background color, and their interaction had significant effects on ΔE00 (p < 0.001). ΔE00 values of HT groups were always higher than that of LT groups and were greater than 1.8 against all background colors. ΔE00 values of LT groups could be achieved to be less than 1.8 with appropriate thickness and cement shade. ΔE00 value decreased with increasing ceramic thickness. The effect of cement shade on ΔE00 had no obvious regularity, but ΔE00 values of bleach XL cement shade group were always lower than other cement shade groups under ND3 and ND5 background color.

CONCLUSIONS

The masking ability of CAD-CAM resin-matrix ceramics can be simultaneously affected by translucency, thickness, cement shade, and background color. Resin-matrix ceramics with low translucency has a better masking ability than that with high translucency. The masking ability of CAD-CAM resin-matrix ceramics increase with increasing thickness. Cement shade has less impact on the final color of resin-matrix ceramic restorations.

The Effect of Magnification on the Quality of Direct Posterior Composite Restorations and the Adjacent Sound Enamel: An In Vitro Study

Objective This study aimed at comparatively assessing the effect of different magnification levels on the immediate postoperative quality of class I direct posterior composite restorations and the adjacent sound enamel.

Materials and Methods Following the modified Consolidated Standards of Reporting Trails (CONSORT) guidelines for in vitro studies, 30 noncarious maxillary human molars were selected. Standardized class I tooth preparation was done in all the teeth. They were randomly divided into three groups: unaided vision, magnifying loupe (3× magnification), and dental operating microscope (7.5× magnification). Each group underwent direct composite restoration, and the restored samples were evaluated for anatomic contour, surface texture, marginal integrity, excess material, and scratching of the adjacent sound enamel.

Statistical analysis The non-parametric Kruskal-Wallis test, followed by the post-hoc Mann-Whitney test were employed.

Results Statistical analysis revealed no significant differences in anatomic contour, surface texture, marginal integrity, or excess material among the three groups. However, a notable difference was observed in the scratching of adjacent sound enamel, with the unaided vision group exhibiting significantly higher levels than the microscope group (p = 0.022).

Conclusion Direct composite restorations performed without magnification resulted in significantly higher adjacent sound enamel scratching than microscope-assisted procedures. The use of a dental operating microscope may minimize this risk, emphasizing its potential benefits in composite restorations.

A Fluorescence-based Method to Reaccess Root Canals in Endodontically Treated Teeth: A Micro-Computed Tomography Tridimensional Assessment

INTRODUCTION

The aim of this study was to evaluate the volume of dentin removal and the volume of remnants of restorative material after the removal of an esthetic restorative coronal set and cervical barrier in endodontically treated mandibular molars with the aid of different magnification methods using 3-dimensional (3D) micro-computed tomographic (micro-CT) morphometric analysis.

METHODS

A sample of 30 mandibular first molars (N = 30) was used. All teeth were endodontically treated, and the specimens were initially scanned using micro-CT imaging and reconstructed. The molars were filled by a single-cone technique, and immediately the material at the initial 2-mm cervical level was removed. Cervical barriers were confected using ionomer glass cement with fluorescein 0.1%, filling the 2 mm at the cervical level of the canals and an additional 2 mm as the base. The coronal restoration set was performed using esthetic resin composites. A simulated tooth aging process was performed with 20,000 thermocycling cycles. The sample was distributed into the following 3 groups (n = 10) for the removal of the restoration set and cervical barrier with diamond burs based on the magnification aid: no magnification aid (naked eye), operative microscope aid, and REVEAL device (Design for Vision Inc, Bohemia, NY) aid. After removal, the final 3D micro-CT scanning and reconstruction were conducted with the same parameters as the initial scanning, and superposition of the final and initial scanning was performed. Morphometric analysis was conducted using CTAn software (Bruker microCT, Kontich, Belgium) to assess the volume of remnant restorative material (mm³), the volume of dentin removal (mm³), and the direction and site of dentin removal. Data were analyzed using 1-Way analysis of variance (P < .05).

RESULTS

The REVEAL group showed better results regarding the volume of remnant material (3.17 ± 1.65) and the percentage of dentin removal (2.56 ± 1.34). The microscope group showed no statistical difference compared with the REVEAL group regarding dentin removal (3.30 ± 1.48) and was statistically similar to the naked eye group in the volume of remnant material (9.63 ± 4.33). The naked eye group showed the worst results for the volume of remnant material (7.60 ± 2.68) and the percentage of dentin removal (6.60 ± 3.70).

CONCLUSIONS

The use of fluorescence associated with magnification was the method that presented the best results, with lower percentages of dentin removal and smaller volumes of remaining restorative material. This is an innovative technology in endodontics that shows potential to overcome the challenge of reaccessing root canals in the context of endodontic retreatment.

A comparative study of the prognostic outcomes of periodontal soft tissue health in traditional restoration and micro-invasive restoration with the use of microscopy

OBJECTIVE

To compare the treatment efficacy of conventional restoration techniques versus micro-invasive restoration techniques utilizing a microscope in the restorative treatment for dental caries.

METHODS

The clinical information of 84 patients who received restorative treatment for dental caries was retrospectively analyzed. Patients were divided into two groups according to the type of restoration they received. The control group (n=42) underwent traditional restorative treatment, while the observation group (n=42) underwent micro-invasive restoration with the use of a microscope. The restoration effect, marginal fit, periodontal soft tissue health (Oral Health Impact Profile-14 (OHIP-14) score), prognostic outcomes, satisfaction rate, and doctor's posture health were compared between the two groups.

RESULTS

The success restoration rate was 92.86% in the control group and 95.24% in the observation group (P > 0.05). The vertical marginal discrepancy, horizontal marginal discrepancy, and absolute marginal discrepancy values were significantly lower in the observation group compared to the control group (all P < 0.05). There was no significant difference in pre-treatment OHIP-14 scores between the two groups (P > 0.05). However, the post-treatment OHIP-14 score was significantly lower in the observation group compared to the control group (P < 0.05). After a 12-month follow-up, the observation group showed higher proportions of A-level restoration integrity, marginal fit, gingival health, fewer secondary caries, and less food impaction compared to the control group (all P < 0.05). The satisfaction rate in the observation group was significantly higher than that in the control group (95.24% vs. 92.86%, P < 0.05). The posture score of doctors in the observation group was significantly better than that in the control group (P < 0.05).

CONCLUSION

Micro-invasive restoration using a microscope, compared to traditional restoration, offers several advantages. It reduces marginal discrepancies, improves periodontal soft tissue health, and enhances prognostic outcomes for patients, while ensuring a satisfactory restoration effect.

Clinical outcomes of the biologically oriented preparation technique (BOPT) in fixed dental prostheses: A systematic review

STATEMENT OF PROBLEM

The biologically oriented preparation technique is a concept with a vertical tooth preparation, gingitage, an immediate interim restoration preserving the clot, and a specific laboratory technique aiming to adapt the marginal periodontal tissue to a remodeled emergence profile of the crown. However, the published scientific evidence on this subject is limited.

PURPOSE

The purpose of this systematic review was to analyze whether using the biologically oriented preparation technique leads to improved clinical outcomes in terms of probing depth, gingival inflammation index, gingival marginal stability, and fewer mechanical and biological complications.

MATERIAL AND METHODS

Recommendations from the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were used in this systematic review. An electronic search of the MEDLINE/PubMed, EMBASE, Science Direct, Wiley Online Library, Cochrane, and ProQuest databases was made for articles published between March 2010 and July 2021 using keywords. Three reviewers selected and analyzed all articles that mentioned the biologically oriented preparation technique and met the inclusion criteria.

RESULTS

A total of 6 articles met the inclusion criteria: 1 prospective randomized clinical study, 1 randomized clinical study, 1 prospective clinical study, and 3 case series. According to these studies, of all the teeth treated with the biologically oriented preparation technique, probing depth (greater than 3 mm) increased in only 2.3%, gingival inflammation was present in 22.8%, gingival recession occurred in 1.7% (decreased gingival stability), and mechanical and biological failures occurred in 4.4% of the teeth.

CONCLUSIONS

Fixed dental prosthesis treatments performed following the concept of the biologically oriented preparation technique did not increase probing depth and showed a moderate rate of gingival inflammation, lower recession rates, and lower mechanical and biological failures at the 5-year follow-up. The biologically oriented preparation technique appears to be a viable alternative technique for obtaining satisfactory and stable clinical results up to 5 years. Long-term randomized clinical trials are recommended to reach more conclusions about this protocol.

Translucency and colour masking ability of hybrid CAD/CAM materials with different thicknesses: in vitro study

OBJECTIVE

To evaluate effect of material thickness and translucency of two different hybrid CAD/CAM materials on their masking ability.

MATERIALS AND METHODS

40 rectangular-shaped specimens (12 × 14 mm) were obtained from Vita Enamic and Grandio blocks at 0.5 and 1 mm-thick (n = 10/group). Colour parameters of specimens were measured on PMMA tooth-coloured replica backgrounds (A2, C4) and black, white backings using dental spectrophotometer. Translucency parameter (TP) and masking ability (∆E00) values of tested materials with 0.5, and 1 mm thicknesses were calculated. Quantitative variables were compared between groups using student t-test.

RESULTS

TP and ∆E00 significantly decreased as thickness of tested materials increased. Grandio showed significantly higher TP values. There were significantly lower ΔE00 values for Vita Enamic compared to Grandio at 1 mm thickness and inversely insignificant at 0.5 mm. The 0.5 mm-thick ∆E00 of tested materials was above clinical acceptability threshold, whereas, 1 mm-thick did not exceed showing better masking properties.

CONCLUSIONS

Thickness is more effective for colour masking than translucency. In thin thickness, the masking ability is less effective, irrespective of tested materials. Translucency of tested materials was affected by their composition. Both hybrid CAD/CAM materials are promising alternatives for masking dark discolouration at 1 mm-thick.

Digital intraoperative evaluation of restorative space and nontemplate-guided tooth preparation when replacing failed anterior restorations: A dental technique

Assessing the correlation between the current restorative space and the target restorative space is important in determining whether additional tooth preparation is required when replacing failed prostheses. However, existing techniques are not always accurate or efficient. This article describes a digital workflow for the accurate chairside evaluation of the current restorative space and nontemplate-guided tooth preparation. Reference data was obtained from an initial scan of the existing restoration with an intraoral scanner. After removing the existing restoration, a second scan of the tooth was made and compared with the reference data to evaluate the current restorative space. Subsequently, the abutment tooth was prepared and rescanned, with the restorative space being re-evaluated until it met the requirements. This workflow enables the immediate and accurate evaluation of the restorative space, facilitating accurate chairside tooth preparation without the need for silicone indices or other templates, thereby saving time and cost.

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.

Utilization of 3D evaluation for assessing selective caries removal practice in pre-clinical dental students: a pilot study

BACKGROUND

Practicing and assessment of selective caries removal techniques in dental students remain challenges in many dental schools. The aim of this study was to utilize a 3D assessment technique, within a designated acceptable range of deviation, to evaluate the tendency of dental students in performing selective caries removal (SCR). The correlation between 3D assessment results and the conventional rubric rated by an instructor was also determined.

METHODS

Fifth-year dental students (n = 61) performed the SCR task on 3D-printed teeth containing simulated deep caries lesions in occlusal and proximal surfaces. One instructor assessed the results using a conventional analytic rubric. The excavated teeth were additionally evaluated using 3D analysis software with the designated acceptable range of deviations (± 0.5 mm) from the standard cavities. The average root mean square (RMS) value, representing the deviation between student-prepared cavities and the predefined standard cavities, was recorded. A tendency towards over-excavation was defined for RMS values > 0.5 mm, and towards under-excavation for RMS values < 0.5 mm.

RESULTS

The mean (min-max) of RMS was 0.27 (0.18-0.40) for occlusal and 0.29 (0.20-0.57)for proximal cavities. A tendency of dental students toward over-excavation was observed in both occlusal (74%) and proximal cavities (87%). There was a moderate negative correlation between the RMS values and the traditional rubric scores for both occlusal (R2 = 0.148, P = 0.002) and proximal cavities (R2 = 0.107, P = 0.010).

CONCLUSIONS

The 3D evaluation technique effectively revealed specific tendencies in dental students' caries removal skills. The integration of computerized assessments with traditional methods could potentially assist the instructors in delivering more objective and specific feedback to students. Further research is encouraged to investigate the impact of this assessment technique on improving student performance in selective caries removal skills.

Fusion machine learning model predicts CAD-CAM ceramic colors and the corresponding minimal thicknesses over various clinical backgrounds

OBJECTIVES

This study has developed and optimized a machine learning model to accurately predict the final colors of CAD-CAM ceramics and determine their required minimum thicknesses to cover different clinical backgrounds.

METHODS

A total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD-CAM ceramics - IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD - were studied. The CIELab coordinates (L*, a* and b*) of each specimen were obtained over seven different clinical backgrounds (A1, A2, A3.5, ND2, ND7, cobalt-chromium alloy (CC) and medium precious alloy (MPA)) using a digital spectrophotometer. The color difference (ΔE) and lightness difference (ΔL) results were submitted to 39 different models. The prediction results from the top-performing models were used to develop a fusion model via the Stacking integrated learning method for best-fitting prediction. The SHapley Additive exPlanation (SHAP) was performed to interpret the feature importance.

RESULTS

The fusion model, which combined the ExtraTreesRegressor (ET) and XGBRegressor (XGB) models, demonstrated minimal prediction errors (R2 = 0.9) in the external testing sets. Among the investigated variables, thickness and background colors (CC and MPA) majorly influenced the final color of restoration. To achieve perfect aesthetic restoration (ΔE<2.6), at least 1.9 mm IPS ZirCAD or 1.6 mm Upcera TT CAD were required to cover the CC background, while two tested glass-ceramics did not meet the requirements even with thicknesses over 2 mm.

SIGNIFICANCE

The fusion model provided a promising tool for automate decision-making in material selection with minimal thickness over various clinical background.

Scoping review on the association between early childhood caries and responsible resource consumption and production: exploring Sustainable Development Goal 12

BACKGROUND

The Sustainable Development Goal 12 (SDG12) promotes patterns that minimize waste and maximize resource utilization. It is therefore plausible that preventing Early Childhood Caries (ECC) and promoting oral health can contribute to sustainable consumption. In addition, sustainable consumption and production can contribute to the control of ECC. This scoping review aimed to explore the possible evidence on the link between ECC and the SDG12 targets.

METHODS

This scoping review identified articles on the link between resource consumption and production and caries according to the PRISMA-ScR guidelines. Three electronic databases (PubMed, Web of Science, and Scopus) were systematically searched in August 2023, using specific search terms. Studies written in English, with full text available, addressing dental caries and linked with waste minimization and resource utilization maximisation, with results that could be extrapolated to ECC in children less than 6 years of age) were included. Descriptive statistics were planned to summarize the categories of retrieved papers.

RESULTS

The initial search yielded 904 articles, with 863 screened for eligibility after the removal of duplicates. No studies were identified that reported data on an association between responsible consumption and production of resources factors and ECC.

CONCLUSION

This scoping review did not identify any articles published in English on evidence of the direct associations between ECC and SDG12 targets. However, there is a plausibility of such a link using minimum intervention dentistry for ECC management as a waste prevention and resource utilisation maximization strategy.

Accuracy of three digital waxing-guided trial restoration protocols for controlling the depths of tooth preparation for ceramic veneers

STATEMENT OF PROBLEM

The accuracy of digital waxing-guided trial restoration protocols that have been implemented with ceramic veneers has not been reported.

PURPOSE

The purpose of this in vitro study was to evaluate the accuracy of 3 digital trial restorations fabricated from digital waxing for ceramic veneers.

MATERIAL AND METHODS

A uniform 0.3-mm digital waxing added to the facial surface of 30 maxillary central typodont incisors was created in a software program. The trial restorations were fabricated on typodont teeth with autopolymerizing acrylic resin by using a silicone index based on 3-dimensionally printed casts designed from the digital waxing. The 30 maxillary central incisors were divided into 3 groups: the depth cutter (0.5 mm, Komet) (DC) group, the round bur (1.5 mm, Diatech) (RB) group, and the specially designed calibrated depth bur (laser mark of 0.5 mm, Gaofeng) (CD) group. The 3 groups were randomly prepared with a random number table by 2 experienced prosthodontists aiming to produce an even facial clearance of 0.5 mm. The dimensional differences in the standard tessellation language (STL) files between the surfaces of the original teeth, digital waxing, trial restorations, and prepared teeth in the software program were measured and analyzed at the same 9 points on the labial surface. One-way ANOVA with a post hoc test was used to identify significant discrepancies between trial restorations and waxing and differences in the reduction depth of typodont teeth (RDT) and the reduction depth (RD) among the 3 techniques (α=.05). The mean relative differences (MRDs) were calculated to determine the accuracy (%).

RESULTS

The thickness of the trial restorations was significantly greater than that of the digital waxings, with a discrepancy of 0.20 ±0.14 mm, especially at the cervical site. With the use of a trial restoration, the RDTs of the middle (-0.01 ±0.11 mm) and cervical locations (0.09 ±0.20 mm) showed significantly smaller preparation depths than did the other locations. Significant differences in RD were found among the 3 guided techniques (P<.05). Group DC presented the most accurate result of 0.51 ±0.08 mm with an MRD of 2%, whereas the results of 0.57 ±0.10 mm with an MRD of 14% and 0.60 ±0.11 mm with an MRD of 20% were obtained from group RB and group DC, respectively.

CONCLUSIONS

The trial restoration was significantly thicker than its corresponding waxing. The DC technique presented the most accurate reduction result among the 3 protocols examined.

Influence of Augmented Reality Appliances on Tooth Preparation Designs-An In Vitro Study

The aim of this work was to analyze and compare the tooth structure removal between a free-hand preparation technique and a computer-aided preparation technique using an augmented reality appliance for complete-crowns preparation designs and "root mean square" (RMS) alignment value. Ten upper teeth representatives of all dental sectors were selected from a generic model library as "Standard Tessellation Language" (STL-1) digital files and 3D-printed in an anatomically based acrylic resin experimental model. Then these were randomly assigned to the following tooth preparation techniques: Group A: free-hand preparation technique (n = 5) (FHT) and Group B: computer-aided preparation technique using an augmented reality appliance (n = 5) (AR). Experimental models were submitted to a digital impression through an intraoral scan and (STL-2) uploaded into a reverse engineering morphometric software to measure the volumetric reduction in the planned and performed tooth structure (mm3) and RMS using the Student's t-test and the Mann-Whitney non-parametric test. Statistically significant differences were observed between the volumetric reduction in the planned and performed tooth structure (mm3) of the AR and FHT study groups (p = 0.0001). Moreover, statistically significant differences were observed between the RMS of the planned and performed tooth preparations in both the AR and FHT study groups (p = 0.0005). The augmented reality appliance provides a more conservative and predictable complete-crowns preparation design than the free-hand preparation technique.

Toothbrushing effects on the surface roughness and cement volume loss of bonded enamel-ceramic interface

This study evaluated the effect of toothbrushing on enamel-cementing material-ceramic bonded interfaces, using different cementing materials.

MATERIALS AND METHODS

Thirty enamel and thirty ceramic blocks were bonded with cementing materials to produce the samples that were bonded with three types of cementing materials: 1- RelyX Ultimate resin cement (REXU), 2- RelyX Unicem 2 self-adhesive resin cement (REU2) and 3- heated Z100 restorative composite (60°C). Bonded interfaces of the samples were toothbrushed and the surfaces of the 3 cementing materials were evaluated for roughness (RG, in µm), roughness profile (RP, in µm), and volume loss (VL, in µm3) (baseline and after 20,000 and 60,000 toothbrushing cycles). Data were evaluated by Generalized Linear Analysis (two factors: "material" and "toothbrushing cycle") and Bonferroni test (α=0.05).

RESULTS

REXU and Z100 exhibited lower RG than that presented by REU2, except after 60,000 toothbrushing cycles when only Z100 differed from REU2. The increase in toothbrushing cycles increased the RG and RP for all materials. REU2 also showed higher RP than those showed by REXU and Z100 when it was analyzed regarding the enamel. The VL of Z100 was the lowest with 20,000 toothbrushing cycles, regarding the enamel and ceramic. For 60,000 cycles, REXU showed the lowest VL regarding the ceramic, and REU2 had the highest VL regarding the enamel and ceramic.

CONCLUSION

In general, REXU and Z100 showed the best results regarding the evaluations performed and the REU2 exhibited the highest RG, RP, and VL.

Age and sex related change in tooth enamel thickness of maxillary incisors measured by cone beam computed tomography

BACKGROUND

To measure adequate enamel thickness of maxillary incisors in planning enamel reduction for a porcelain laminate veneer restoration in relation to chronological age and sex by using cone beam computed tomography (CBCT) in an Iraqi subpopulation.

METHODS

From 81 CBCT images, 324 maxillary incisors were examined. Enamel thickness was measured at both mesial and distal regions of the tooth in three different levels: cervical, middle, and incisal (occlusal) 1/3 at a sagittal section. Measurements were made for the following tooth areas using CBCT: facial enamel thickness at 1, 3, and 5 mm from the cementoenamel junction (CEJ), palatal enamel thickness at 5 mm from the CEJ (5 mm P), facial and palatal enamel thickness at the incisal edge (IFP), mid incisal enamel thickness (IET), and the incisal edge enamel-pulp distance (IEPD). Relationships of enamel thickness with age and sex were evaluated using Independent t-test, Mann-Whitney U-test and the Pearson correlation coefficient, a simple linear regression analysis used for statistical analysis.

RESULTS

Significant differences (P < 0.05) were found in terms of an inverse association between enamel thickness and chronological age at all measurements above the CEJ and the regression model for the mid-incisal enamel thickness was (R2 of 0.4). In contrast, there was an increase in IFP, palatal, and IPED enamel thickness with age. Also, significant differences were found in enamel thickness between males and females, the enamel being thicker in females in relation to facial enamel thickness, enamel palatal thickness above CEJ and IET, while for IEPD, the enamel thickness was greater in males compared to females.

CONCLUSION

The measurements for enamel thickness outcome variables in relation to chronological age revealed significant differences for each measured distance and there were statistically significant differences in enamel thickness between males and females at all measurements except at IFP. These results demonstrate that CBCT can be used for noninvasive, accurate measurements of enamel thickness in both sex.

Veneer crowns in anterior endodontically-treated teeth: A case report with 1-year follow-up

Key Clinical Message

Veneer crowns can be used in anterior endodontically-treated teeth with light occlusal force and enamel substrate consideration as a more conservative approach instead of conventional all ceramic crowns.

Abstract

All-ceramic anterior crowns and veneers have been used widely in dentistry with high clinical success rate. The development of new reinforced ceramics in recent years has led to more use of extended defect-oriented preparation designs, that is, extended veneers, instead of full crown preparations which are less invasive. A veneer crown is simply a veneer that covers the entire tooth. The preparation preserves remaining enamel and uses a conservative preparation design. Its indication should be carefully raised taking into consideration various factors. The preparation design is crucial to ensure longevity of such restoration. The balance is between sufficient preparation for the material thickness and adequate strength against occlusal load and the enamel preservation. A 24-year-old man referred to the restorative department of the Dentistry School of Tehran University of Medical Sciences complaining from his poor esthetics in the maxillary incisors. In clinical and radiographic evaluation, he had open bite, composite discoloration due to corrosion of the pre-fabricated posts in all four incisors, a periapical lesion in tooth 21 and under-filled root canal therapy in tooth 22. All four posts and composite restorations were removed and teeth 21 and 22 were retreated. Although the amount of remaining tooth tissue was low, it had enough enamel thickness, especially in the buccal area. Taking into consideration this mixed enamel and dentin substrate, endodontics access, esthetics needs and canine guidance occlusion with no parafunction history, bonded lithium disilicate veneer crowns were selected to restore the maxillary incisors. A 12-month follow-up showed promising clinical (healthy gingival tissue and successful restorations) and radiographic (reduced periapical lesion) outcomes.

Accuracy of the preparation depth in mixed targeted restorative space type veneers assisted by different guides: An in vitro study

PURPOSE

Most veneers are mixed targeted restorative space (MTRS)-type restorations that are partially within the original tooth and require inconsistent preparation depths. This study aimed to evaluate the accuracy of the preparation depth for MTRS veneer preparation.

METHODS

MTRS veneer preparation models were developed using the twisted maxillary central incisor (MCI) as the original tooth and the standard MCI as the waxing. Veneer preparations were performed using freehand (MF), silicone (MS), thermoplastic (MT), 3D-printed uniform (MD), and auto-stop (MA) guides. The prepared and original MCI were scanned and superimposed using a custom-made base. The mean absolute differences (MADs) were measured to evaluate the accuracy of the preparation depth. Statistical analysis was performed using the multivariate analysis of variance (MANOVA) test (α=0.05).

RESULTS

The accuracy of the preparation depth was 0.237±0.090, 0.191±0.099, 0.149±0.078, 0.093±0.050, and 0.059±0.040 mm in MF, MS, MT, MD, and MA, respectively. The MADs between the groups were significant (P<0.05). The accuracy of the trial restoration was 0.140±0.081 mm in the MS, and the accuracy of the guiding tube was 0.055±0.033, 0.036±0.011, and 0.033±0.010 mm in the MT, MD, and MA, respectively.

CONCLUSIONS

In MTRS veneer preparation for MCI, tooth preparation guides improved the accuracy of the preparation depth by visualizing the TRS profile and providing clear measurement points. The accuracy of the guide is influenced by its flexibility, and the accuracy of the preparation depth is affected by the accuracy of the measurement points.

Experts consensus on the procedure of dental operative microscope in endodontics and operative dentistry

The dental operative microscope has been widely employed in the field of dentistry, particularly in endodontics and operative dentistry, resulting in significant advancements in the effectiveness of root canal therapy, endodontic surgery, and dental restoration. However, the improper use of this microscope continues to be common in clinical settings, primarily due to operators' insufficient understanding and proficiency in both the features and established operating procedures of this equipment. In October 2019, Professor Jingping Liang, Vice Chairman of the Society of Cariology and Endodontology, Chinese Stomatological Association, organized a consensus meeting with Chinese experts in endodontics and operative dentistry. The objective of this meeting was to establish a standard operation procedure for the dental operative microscope. Subsequently, a consensus was reached and officially issued. Over the span of about four years, the content of this consensus has been further developed and improved through practical experience.

Risk Factors with Porcelain Laminate Veneers Experienced during Cementation: A Review

The clinical success of porcelain laminate veneers (PLVs) depends on many clinical and technical factors, from planning to execution, among which adhesive cementation is of significant importance. This procedure carries many risk factors if not optimally executed. The objective of this study was to document the clinical parameters affecting successful cementation procedures with a focus on the adhesive strength, integrity, and esthetics of the PLVs. A literature search was conducted through MEDLINE, complemented by a hand search using predefined keywords. Articles published in English between 1995 and 2023 were selected. According to this review, the success and longevity of PLVs rely in great part on the implementation of a precise cementation technique, starting from field isolation, adequate materials selection for adhesion, proper manipulation of the materials, the seating of the veneers, polymerization, and elimination of the excess cement. Several clinical steps performed before cementation, including treatment planning, preparation, impression, and adequate choice of the restorative material, could affect the quality of cementation. Scientific evidence suggests careful implementation of this process to achieve predictable outcomes with PLVs. The short- and long-term clinical success of adhesively luted PLVs is tributary to a deep understanding of the materials used and the implementation of clinical protocols. It is also contingent upon all the previous steps from case selection, treatment planning, and execution until and after the cementation.

A micro-computed tomography analysis of internal and marginal fits of fixed partial dentures: Effect of preparation finish line designs on monolithic zirconia and heat-pressed zirconia-reinforced lithium disilicate

PURPOSE

To evaluate the effect of finish line design (chamfer and feather-edge) and ceramic type on the internal and marginal fits of fixed partial dentures on abutment teeth.

MATERIALS AND METHODS

Two typodont mandibular casts, missing right first premolar tooth, received tooth preparation on canine and second premolar abutments (one cast with chamfer finish line and the other cast with feather-edge finish line). The preparation segment of each typodont model was scanned, 3D printed in resin, and then invested and casted in metal to obtain two metal models. Polyvinyl siloxane impressions were made for the metal models and poured in type IV stone. The stone models (n = 40) were randomly assigned into four groups (n = 10): chamfer finish line with heat-pressed zirconia reinforced lithium disilicate fixed partial denture (CL), chamfer finish line with monolithic zirconia fixed partial denture (CZ), feather-edge finish line with heat-pressed zirconia-reinforced lithium disilicate fixed partial denture (FL), and feather-edge finish line with monolithic zirconia fixed partial denture (FZ). After the fabrication of ceramic restoration, micro-computed tomography was used to evaluate the internal and marginal fits of each fixed partial denture. Data were statistically analyzed with three-way ANOVA (α = 0.05).

RESULTS

There were no significant interactions between preparation type, material type, and tooth type at any of the areas assessed. There was significant difference (p = 0.01) between CZ (59.15 ± 4.6 µm) and FZ (73.6 ± 17.1 µm) groups at the finish line area. Regarding the horizontal marginal discrepancy area, there were significant differences between CZ (62.65 ± 10.5 µm) and FZ (90.05 ± 5.6 µm) groups (p < 0.001), CL (77.45 ± 8.1 µm) and CZ (62.65 ± 10.5 µm) groups (p < 0.001), and FZ (90.05 ± 5.6 µm) and CL (77.45 ± 8.1 µm) groups (p < 0.001). At finish line area, there was a significant difference (p = 0.018) between feather-edge with canine (72.75 ± 13.3 µm) and chamfer with canine (59.05 ± 5.8 µm); however, there was no significant difference (p = 0.774) between feather-edge with premolar (69.45 ± 12 µm) and chamfer with premolar (65.1 ± 7.4 µm). Moreover, there was no significant difference (p = 0.886) between feather-edge with canine and feather-edge with premolar.

CONCLUSIONS

The internal and marginal fits of the ceramic fixed partial dentures can be affected by the finish line design and ceramic type. The feather-edge finish line had a negative impact on the marginal and internal fits of ceramic fixed partial dentures at certain measurement points. Regarding the effect of finish line design on abutment teeth, the difference in fit was only detected at the finish line area of the anterior abutment (canine) with the feather-edge finish line.

Research Progress and Clinical Application of All-Ceramic Micro-Veneer

Anterior teeth problems affect the patient's daily eating, communication, social activities, self-confidence, and mental health. The trend in dentistry is to address anterior tooth problems with minimally invasive and aesthetic treatments. With the development of adhesive materials and ceramics, micro-veneers have been proposed as an alternative treatment for enhancing the aesthetic appearance and avoiding unnecessary tooth reduction. A micro-veneer is a veneer that can be cemented to the surface without or with minimal tooth preparation. These benefits include no need for anesthesia, postoperative insensitivity, good adhesion to enamel, reversibility of treatment, and higher patient acceptance. However, the micro-veneer repair is suitable only for specific cases and must be strictly controlled regarding indication. Treatment planning is a crucial step to achieving functional and aesthetic rehabilitation, and following the clinical protocol is helpful for the longevity and success of micro-veneer restorations. However, more precise and predictable tooth preparation methods, such as minimally invasive microscopic tooth preparation and digitally guided veneer preparation, are recommended rather than the traditional free-hand method. Therefore, this paper clarifies micro-veneers and compares them with other restorations to gain a deeper and more comprehensive understanding. The authors also review indications, materials, cementation, and effect evaluation of micro-veneers to provide clinicians with valuable information. In conclusion, micro-veneers are minimally invasive treatments that provide good restoration results when used appropriately and are worthy of promotion for the aesthetic restoration of anterior teeth.

The mechanical properties, tribological behaviors and color stability of a feldspar nanoceramics strengthening extrinsic stain for high-translucent zirconia

The present work is aimed to explore the mechanical properties, tribological behaviors and color stability of nanoceramics and microceramics strengthened extrinsic stain coatings (NS and MS) upon high-translucent zirconia (TZ). The Na-rich feldspar ceramics component, microstructure and particle size of NS and MS were verified. The mechanical properties including elastic modulus and hardness of NS were enhanced compared to MS. Reciprocating wear tests under a ball-on-plate configuration manifested that the reduced coefficient of friction, wear depth and wear volume loss of NS was evaluated after 1 × 10 ⁴ cycles and the wear scar morphology of NS characterized by microcracks while MS featured more delamination and wear debris. Post toothbrushing simulation revealed that the color stability of extrinsic stain coatings was elevated with the addition of feldspar nanoceramics. The feldspar nanoceramics strengthening extrinsic stain exhibited enhanced elastic modulus, hardness, wear resistance and color stability, especially for TZ.

A Scoping Review of Marginal and Internal Fit Accuracy of Lithium Disilicate Restorations

OBJECTIVE

To assess and compare the accuracy of the marginal and internal fit of lithium disilicate crowns and onlays fabricated by conventional and digital methods.

SOURCES

An electronic search was carried out on MEDLINE, Embase, Web of Science and Cochrane Library between 2010 and 2021.

STUDY SELECTION

Seventeen studies published between 2014 & 2021 were included, of which thirteen were in vitro laboratory-based studies; three were in vivo clinical studies and one randomised controlled trial.

DATA

Twelve studies focused on the marginal fit, five focused on the marginal and internal fit. Five studies found that the marginal and internal fit of crowns were more accurate using digital techniques. Five studies noted that there was no difference using either technique and two noted that conventional methods had a more accurate marginal fit.

CONCLUSION

Digital techniques were comparable to conventional methods in terms of accuracy although there was insufficient evidence to indicate that one technique was more accurate than the other with respect to Lithium Disilicate restorations.

CLINICAL SIGNIFICANCE

Digital impressions are reliable and viable alternatives for clinicians compared to conventional impression techniques when restoring teeth with lithium disilicate restorations.

Three-year clinical evaluation of zirconia and zirconia-reinforced lithium silicate crowns with minimally invasive vertical preparation technique

Objectives

Large part of the tooth is required to be removed during crown preparation. A minimally invasive method for preparing single crowns is required to increase the durability of teeth. The aim of this study was to evaluate the clinical performance of two ceramic systems fabricated with minimally invasive vertical preparation.

Materials and methods

Forty endodontically treated maxillary premolars were prepared with vertical preparation and received temporary crowns for a period of 21 days. Twenty zirconia-reinforced lithium silicate (Celtra Duo HT, Dentsply Sirona, Germany) and 20 monolithic high translucency zirconia (Katana HT, Kuarary Noritake, Japan) crowns were fabricated by CAD/CAM and cemented with dual-polymerizing luting resin. The crowns were evaluated clinically and radiographically for 36 months following modified FDI criteria. Statistical analysis was conducted with t Student test (Cochran Q).

Results

Over the follow-up period, there was no need to replace any of the study’s crowns. The overall survival rate of the 40 crowns was 100% according to the Kaplan–Meier survival method. The clinical quality of all crowns and the patient’s satisfaction were high. No caries was detected and no adverse soft tissue reactions around the crowns were observed. Periodontal probing depth was reported to be increased at mesial and distal sites more than the facial one in the 36-month follow-up with no statistically significant difference between both materials (P = 0.186).

Conclusions

Zirconia and zirconia-reinforced lithium silicate could be used as a material for restoration of teeth prepared with vertical preparation technique. Both ceramic materials achieved good esthetic results, promotes healthy and stable soft tissues with no mechanical complications after 3 years of clinical evaluation.

Clinical relevance

Monolithic high translucency zirconia and zirconia-reinforced lithium silicate ceramics can be used for the restorations of minimal invasive vertical preparation in premolar area with 0.5 mm margin thickness.

A case of precise prosthesis under the direction of target restoration space analysis after multidisciplinary combination therapy

Quantitative grinding of abutment teeth is needed in crown and bridge restoration. Accurate quantitative preparation of teeth is one of the goals of minimally invasive restoration. In this paper, a case of congenital loss of upper and lower incisors was reported. Guided by the target restoration space (TRS), a personalized digital guide plate for tooth preparation was built to assist precise tooth preparation after the multidisciplinary combination therapy of orthodontic and periodontal teeth. Finally, the fixed bridge was prepared to meet the integrity, beauty, and function of the maxillary for the patient. In this case, the results suggest that the digital guide plate built under the guidance of TRS can be used to improve the accuracy of dental preparation.

Effects of loupes and microscopes on a dental technician's working posture from ergonomic aspects

OBJECTIVES

This work aimed to study the effects of loupes and microscopes on a dental technician's working posture during practical operation from ergonomic aspects. The technician's working postures under the conditions of the naked eye, loupes, and microscopes were compared. The practical value of loupes and microscopes was assessed based on the evaluation index of working posture from ergonomic aspects.

METHODS

Three dental technicians who were skilled in using loupes and microscopes from West China Stomatology Technology Department of Sichuan University were involved in this prospective rando-mized controlled trial. Before the operation, cameras were installed in the sagittal position, top-view position, and dorsal position of the operation. Each technician made five porcelain veneers of the right maxillary central incisor following the standard process. A chairside computer-aided design and computer-aided manufacturing (CAD/CAM) system was used to mill and layer the ceramic block under the naked eye (A: control group), 3.5× headwear loupes (B: loupe group), and 9× desktop microscopes (C: microscope group). The working posture was recorded by videos throughout the entire process. After each operation, the investigator used OpenPose to recognize the working posture. The joint angles of the arm, elbow, wrist, neck, and trunk, as well as their corresponding rapid upper limb assessment (RULA) scores, were calcula-ted by MATLAB. The working posture was assessed from ergonomic aspects based on the joint angles, RULA scores, and operation time. Statistical analysis was performed using SPSS 26.0.

RESULTS

The RULA score of upper limb joint angles showed that the angles of the arm, elbow, wrist, neck, and trunk under the naked eye were 14.93°±9.44°, 120.19°±2.99°, 23.97°±2.84°, 47.27°±5.72°, and 7.76°±2.30°, respectively. All of the joint angles were significantly different among the three groups (P<0.05). Compared with the control group, the angles of the neck and trunk in the loupe group were reduced by 29.09% and 42.53%, respectively, whereas those in the microscope group were significantly reduced by 43.99% and 87.11%, respectively. Multiple comparisons by LSD for the angles of neck and trunk revealed that the loupe group and the microscope group were significantly different from the control group (P<0.05), and they were also significantly different from each other (P<0.05). The mean RULA scores were 6.24±0.34 in the control group, 5.53±0.35 in the loupe group, and 3.31±0.19 in the microscope group. Compared with the control group, the mean RULA score in the loupe group was lower, and that in the microscope group was significantly lower. The differences between every two groups were statistically significant (P<0.05). The mean RULA score in the microscope group was significantly lower than that in the loupe group (P<0.05). The average operation times of the control group, loupe group, and microscope group were (50.69±36.78), (52.01±34.65), and (59.44±35.81) min, respectively. No significant difference was found among the three groups (P>0.05).

CONCLUSIONS

Use of loupes and microscopes showed an improvement in ergonomics and working posture of dental technicians. Microscopes had a better effect in the ergonomic convenience of the technician than loupes.

8-year multicenter retrospective study on partial laminate veneers

PURPOSE

This retrospective study aimed to evaluate the survival and success rates of ceramic partial laminate veneers. Scanning electron microscopy was used to evaluate fractures and marginal defects.

METHODS

In total, 31 patients received 79 partial laminate veneers on the maxillary anterior teeth. After adhesive luting, restorations were evaluated by calibrated clinicians for up to eight years using modified United States Public Health Service (USPHS) criteria. In addition, epoxy resin replicas were fabricated from silicone impressions and analyzed using scanning electron microscopy. Survival analyses were performed using the Kaplan-Meier and log-rank tests (α = 0.05). Success was analyzed in percentages by comparing the baseline and last follow-up.

RESULTS

The cumulative survival rates were 100% after 1 year; 95.9% (SE 2.8%) after 5 years; and 61.4% (SE 25.3%) after 8 years. No significant differences (P > 0.05) were observed between functional and non-functional restorations. Changes in the USPHS criteria evaluation were only observed for adaptation: 12.5% (SE 4.7%), marginal discoloration: 4.2% (SE 3.0%), color match: 4.2% (SE 3.0%), and fractures: 16.7% (SE 5.3%). Scanning electron microscopy evaluations revealed undetected initial cracks and deficiencies in the restorations.

CONCLUSION

Partial laminate veneers displayed good survival rates during the long-term follow-up. The main problems observed were related to the quality of the margins, color mismatch, and restoration integrity. However, in most cases, restoration replacement was not required.

Diamond particles in toothpastes: in-vitro effect on the abrasive enamel wear

Background

Diamond particles have recently been used as abrasives in toothpastes, which raises questions about its abrasive behaviour towards enamel. This study was carried out to investigate the abrasive enamel wear caused by three diamond-loaded toothpastes (Candida White Diamond: CWD, Swiss Smile Diamond Glow: SSDG, Emoform F Diamond: EFD) and to compare it with a traditional toothpaste with silica abrasive (Colgate Total Original CTO).

Methods

Eighty bovine enamel samples were divided into four groups (n = 20) and brushed for 21,600 cycles (60 cycles/min) for 6 h at 2.5-N brushing force. The abrasive enamel wear was recorded with a contact profilometer. The median and interquartile range (IQR) of the abrasive enamel wear was calculated in each group. Pairwise comparisons were conducted using Wilcoxon signed rank exact test and the p value was adjusted according to Holm. Significance level was set at 0.05.

Results

Diamond-loaded toothpastes caused statistically significantly higher abrasive wear than the traditional toothpaste (p < 0.0001). SSDG caused statistically significantly higher enamel wear (19.0 µm (11.2)) than CWD (8.4 µm (4.6)) and EFD (7.3 µm (3.9)) (p < 0.0001).

Conclusions

Diamond-loaded toothpastes cause higher enamel wear than toothpastes with traditional abrasives and also exhibit different abrasivity behaviour compared to each other.

Do magnification loupes affect the precision of cavity preparations made by undergraduates? A randomized crossover study

BACKGROUND

Evidence on the effect of magnification devices on procedure quality in restorative dentistry is scant. This study therefore aimed to assess, under simulated clinical conditions, if magnification loupes affect the quality of preparations carried out by undergraduate dental students.

METHODS

59 undergraduate dental students underwent two visual acuity tests, based on which they were divided into a "low visual acuity group" (visus < 1) and a "good visual acuity group" (visus ≥ 1). In a randomized crossover experiment, participants performed a two-dimensional S and a three-dimensional O figure preparation with a dental handpiece on standardized acrylic blocs designed for preclinical restorative training. Each participant carried out the preparation tasks twice, once with magnification loupes (2.5×) and once without. Two blinded investigators independently evaluated parameters of preparation precision. Data were analyzed using Spearman rank correlation coefficients, intra-class correlation coefficients, and Wilcoxon rank-sum tests (α = 0.05).

RESULTS

Participants from the "low visual acuity group" did not show a statistically significant improvement in accuracy when they used magnification loupes for the S figure preparation (p ≥ 0.0625). Participants from the "high visual acuity group" obtained a higher level of accuracy (p ≤ 0.0012) when they used magnification loupes for the S figure preparation. The use of magnification loupes had no statistically significant effect on the accuracy parameters of the O figure cavity preparations (p ≥ 0.1865). Participants with high visual acuity achieved only a marginally better accuracy than participants with a visus < 1.

CONCLUSIONS

This study suggests that loupes with 2.5× magnification increase the accuracy of two-dimensional preparations while they have no significant effect, favorable or otherwise, on the accuracy of complex, three-dimensional cavity preparations of untrained dental students.

Masking Ability of the Combined Application of Opaquers and Resin Composite on Discolored Backgrounds

The aim of this study was to evaluate the masking ability of a combined application of opaquers and resin composite over discolored backgrounds: A3, A3.5, C2, C3, and C4. The groups were divided according to the opaquer brand, the number of opaquer coats (one or two), and the thickness of the resin composite layer (0.5 or 1.0 mm). The color measurements were made by a reflectance spectrophotometer (SP60, EX-Rite). The color difference between the opaquer + resin composite + background and a reference background was calculated using the CIEDE2000 formula. ANOVA and Tukey's post hoc test (α=0.05) were used to analyze the ΔE00 mean values. A bivariate analysis was used to determine the association between dependent and independent variables. The masking ability was rated by the ΔE00 visual thresholds of acceptability and perceptibility (Excellent Match: ΔE00 ≤ 0.8; Acceptable Match: 0.8 < ΔE00 ≤1.8; Moderately Unacceptable Mismatch: 1.8 < ΔE00 ≤ 3.6; Clearly Unacceptable Mismatch: 3.6 < ΔE00 ≤ 5.4; Extremely Unacceptable Mismatch: ΔE00 > 5.4). The mean ΔE00 values ranged from 0.5 to 5.52. Masking ability was affected by the opaquer brand, thickness of the resin composite layer, and background shades. Most of the combinations that achieved either excellent or acceptable masking ability were obtained with combinations composed of one or two coats of opaquer and a 1.0-mm-thick resin composite layer for all backgrounds except C4. Acceptable results were also obtained for combinations with 0.5-mm-thick resin composite over C2, A3, and A3.5 backgrounds.

Preparing guiding planes for removable partial dentures: comparison between assisted CAD-CAM template procedure and freehand preparation: An in vitro study

OBJECTIVES

To compare the trueness of computer-aided design and computer-aided manufacturing (CAD-CAM) assisted procedure and freehand procedure for preparing guiding planes for removable partial dentures (RPDs).

METHODS

Forty identical mandibular resin casts were divided into two groups in which the guiding planes of two abutment teeth were prepared freehand (control group, n = 20) and using rigidly constrained templates (test group, n = 20). The template was designed on a digital cast of virtually prepared guiding planes and fabricated by selective laser melting using cobalt-chromium alloy. To assess the 3D trueness, all prepared guiding planes (Test data) were digitized using a laboratory scanner and compared to the virtually designed guiding planes (Reference data). The angle deviation between the Test data and the designed direction of the path of placement was measured for assessing the direction trueness of guiding plane preparation.

RESULTS

The 3D trueness of guiding plane preparation was significantly better in the test group (48.4 ± 12.9 μm) than in the control group (128.5 ± 37.6 μm, p < 0.01). The direction trueness of guiding plane preparation was also significantly better in the test group (1.20 ± 0.55°) than in the control group (7.68 ± 3.00°, p < 0.01).

CONCLUSIONS

The CAD-CAM template assisted procedure can significantly improve tooth preparation of the guiding planes compared to the freehand preparation. The CAD-CAM template could help clinicians prepare parallel guiding planes in a predictable manner.

Consensus on the preparation margin and restoration margin in ceramic esthetic rehabilitation

In esthetic rehabilitation, methods used to enhance the margin quality have always been the focus and difficulty of improving the level of diagnosis and treatment, prevention and treatment of complications, and collaboration between clinicians and technicians. However, it is impeded by the ambiguous definition and classification of margin, unstandardized tooth preparation, manufacturing process of restoration, and lack of reliable means of checking the quantitative requirements of preparation or restoration. The digital technologies that are increasingly applied, such as intra-oral scanner, impression scanner, and computerized numerical control cutting machine, have strict requirements about margin quality. Failure of recognizing margins by these scanners will hinder the digital process of diagnosis and treatment. Even if these sharp and narrow margins are successfully scanned, they cannot be milled accurately. To overcome these problems, this article demonstrated the clear and complete definition of preparation margin and restoration margin, as well as their subclassifications, by analyzing the target restoration space from a geometric perspective. Practical approaches to measuring the margin width and inspecting the margin quality were proposed. The new and full understanding and proposal about preparation margin and restoration margin characterized by measurements will effectively support the thoroughly digitalized process of esthetic rehabilitation using porcelain in fixed prosthodontics, which is based on the guidance of values.

Shear bond strength of ceramic laminate veneers to finishing surfaces with different percentages of preserved enamel under a digital guided method

Background

The purpose of this in vitro study was to evaluate the effect of the percentages of preserved enamel on ceramic laminate veneers’ (CLVs) shear bond strength (SBS).

Methods

Seventy extracted human maxillary central incisors were scanned and reconstructed into three-dimensional models. The extracted teeth were then embedded and randomly divided into seven groups (n = 10 per group). Based on digital analyses of the three-dimensional models, guided tooth preparation and bonding procedures were performed individually to form seven different percentages (100%, 80%, 60% 50%, 40%, 20% and 0%) of remaining enamel thickness on the bonding surface. Finally, the SBS test was performed, and the data were statistically analysed by one-way ANOVA with LSD post hoc test (α = 0.05).

Results

The complete enamel surface exhibited the highest SBS (19.93 ± 4.55 MPa), followed by 80% enamel (19.03 ± 3.66 MPa), 60% enamel (18.44 ± 3.65 MPa), 50% enamel (18.18 ± 3.41 MPa), 40% enamel (17.83 ± 3.01 MPa) and 20% enamel (11.32 ± 3.42 MPa) group. The lowest SBS (9.63 ± 3.46 MPa) was detected in 0% enamel group. No significant difference was observed among the 40–100% enamel groups, while the 20% or 0% enamel group demonstrated a significantly lower mean SBS than the 40% enamel group (p < 0.05).

Conclusion

The SBS value of CLVs bonded to 100% enamel on the finishing surfaces (nearly 20 MPa) was twice that which bonded to 0% enamel (nearly 10 MPa). Bonding to 100% enamel is the most reliable treatment. When dentin exposure is inevitable, enamel should be preserved as much as possible to maintain good bonding. In addition, 40% of preserved enamel on the bonding surface was the minimal acceptable value to fulfil the requirements of good bonding strength.

Recommended clinical practice guidelines of aesthetic dentistry for Indians: An expert consensus

Objective:

Clinical Considerations:

Conclusion:

[Effects of Three Illuminants on the Color of High Translucent Multilayered Zirconia]

OBJECTIVE

To evaluate the effects of three common illuminants on the color of four brands of high translucent multilayered zirconia (HTMZ) ceramics so as to provide reference for clinical practice and dental restoration fabrication, and to reduce the risks for illuminant change causing color mismatch between the natural teeth and the restorations made of HTMZ.

METHODS

Four brands of commonly used HTMZ were selected and ten cuboid samples ( n=10/group) of 12 mm×10 mm×0.8 mm were prepared for each type of HTMZ. The L*, a*, and b* values of the samples were measured under D65, A and F2, three standard illuminants. Then, the L*, a*, and b* values were statistically analyzed by using factors of the type of the illuminant and the brand of the zirconia. Color difference (ΔE) of samples of the same brand under exposure to changed illuminants was also calculated.

RESULTS

When the same samples were exposure to different illuminants, there was no significant difference in the L* value, the a* value for the different iluminants was shown to be illuminant A>illuminant F2>illuminant D65, and the b* value was shown to be illuminant F2>illuminant D65>illuminant A. The L*, a*, and b* values of samples of different brands showed statistically significant difference when they were exposed to the same illuminant ( P<0.0001). Samples of the same brand showed ΔE when they were under the three different illuninants, and all ΔE were clinically acceptable.

CONCLUSION

The types of illuminant used, to a certain degree, affected the hue and chroma of HTMZ. There were colorimetric differences between restorations made of different brands of HTMZ ceramics of the same color. The types of illuminants most common to the daily life of patients and the color characteristics of materials of different brands should be taken into consideration to facilitate the selection of restoration materials and dental restoration fabrication, and to reduce the risks for color mismatch between the restorations and the adjacent teeth caused by the change of illuminants.

Accuracy of Reduction Depths of Tooth Preparation for Porcelain Laminate Veneers Assisted by Different Tooth Preparation Guides: An In Vitro Study

PURPOSE

To evaluate the accuracy (trueness and precision) of reduction depths of guided veneer preparation assisted by four tooth preparation guides.

MATERIALS AND METHODS

Fifty resin artificial teeth were randomly divided into five groups (n = 10): a freehand group (F), silicone guide group (S), thermoplastic guide group (T), 3D printed uniform guide group (D), and 3D printed auto-stop guide group (A). A preparation for a window veneer on the maxillary right central incisor was performed by two surgeons who used tooth preparation guides for assistance. The maxillary right central incisors were scanned before and after the preparation. The reduction depths were measured in the cervical, middle, and incisal thirds of the prepared surface, and depth maps were created using Geomagic Control X software. The accuracy of the reduction depths at each third was evaluated using both trueness and precision values. The trueness of the reduction depths was determined by calculating the mean absolute differences (MADs) compared to the planning depth, and precision was determined by the standard deviation (SD). The collected data were statistically analyzed using one-way ANOVA and the least significant difference test (α = 0.05).

RESULTS

The MAD ± SD values of the reduction depths in the cervical-third region in groups F, S, T, D, and A were 0.19 ± 0.04, 0.12 ± 0.03, 0.09 ± 0.02, 0.07 ± 0.02, and 0.05 ± 0.01 mm, respectively. In the middle-third region, the MAD ± SD values of groups F-A were 0.19 ± 0.05, 0.13 ± 0.02, 0.09 ± 0.01, 0.06 ± 0.01, and 0.05 ± 0.01 mm. In the incisal-third region, the MAD ± SD values were 0.27 ± 0.05, 0.16 ± 0.04, 0.11 ± 0.03, 0.07 ± 0.01, and 0.05 ± 0.01 mm, respectively. Significant differences in trueness and precision values were found across different groups (F = 45.378, p = 0.000), where group F showed higher MADs than the other 4 groups (p = 0.000), and the highest MADs were detected in group S among the 4 groups in all regions (p = 0.000). Group T showed significantly higher MADs than groups D (P = 0.008) and A (p = 0.001), except in the cervical-third region, where no significant difference was observed between groups T and D (p = 0.077). There was no significant difference between groups D and A (p = 0.148). The deviation map showed significant differences among groups (F = 15.963, p = 0.000), group T presented less deviation than group F (p = 0.000) and group S (p = 0.027) and showed more deviation than group A (p = 0.007).

CONCLUSION

Tooth preparation guides provided more accuracy for veneer preparation than freehand preparation. Among the 4 guides, the 3D printed auto-stop guide presented the lowest absolute difference (0.05 mm) and the silicone guide showed the highest absolute difference of preparation (0.12-0.16 mm).

A digital workflow for accurately and rapidly creating an immediate provisional restoration with natural emergence profile using extracted tooth

To describe a digital workflow for creating a provisional restoration by using an extracted tooth rapidly, finally fixing the provisional restoration in the targeted position precisely and preserving the natural emergence profile from the time of provisional restoration to final restoration. CLINICAL CONSIDERATIONS: The use of extracted tooth as an immediate provisional restoration is an effective method for preserving the shape of the emergence profile. However, the existing methods for creating a provisional restoration by using natural tooth are time-consuming and there is no reliable method to precisely attach tooth to temporary abutment. This case demonstrates a new method for using patient's natural tooth as an immediate provisional restoration under a sequence of guides, which significantly reduces the chair-side time and inconvenience for clinicians and patients. Immediate provisional restoration contributes to preserving the soft tissue architecture after post-extraction implant placement, especially when using the patient's tooth as a provisional restoration. Digital technology can help to improve the chair-side clinical efficiency of dentist. CLINICAL SIGNIFICANCE: Maintaining the natural soft tissue architecture is a huge challenge in dental implantology. Use of the extracted tooth as a provisional restoration is likely to achieve an optimal outcome. And digital technology is helpful to the efficiency and accuracy of treatment.

A digital workflow with the virtual enamel evaluation and stereolithographic template for accurate tooth preparation to conservatively manage a case of complex exogenous dental erosion

OBJECTIVE

This article describes a digital workflow using virtual enamel evaluation and a stereolithographic template for accurate tooth preparation for a complex exogenous dental erosion.

CLINICAL CONSIDERATIONS

A 22-year-old man with different degrees of defects on the labial surface in esthetic area was diagnosed as exogenous dental erosion. The residual undamaged enamel area and depth of defect were measured and analyzed accurately by creating a digital virtual patient based on the pretreatment data. According to the different conditions of residual enamel and tooth defect, the treatment plans of porcelain veneer, crown and composite resin were chosen for corresponding involved teeth. Based on the virtual wax-up and the suggested material thickness, a template for tooth preparation was designed and three-dimensional printed. This template together with a special bur indicating the reduction depth accurately guided the teeth preparation and achieved a long-term effect.

CONCLUSIONS

The virtual enamel evaluation contributes to obtaining the appropriate corresponding treatment plan objectively. The stereolithographic template effectively meets the accuracy of tooth preparation, preserving the tooth hard tissue to the greatest extent.

CLINICAL SIGNIFICANCE

The digital workflow described here may provide a quantifiable evaluation method and an accurate tooth preparation method for exogenous dental erosion.

Three-dimensional digital evaluation of thickness accuracy of mock-ups fabricated by silicone matrices: An in vitro study

PURPOSE

Although mock-ups have been widely used in dental esthetic rehabilitation, their accuracy has not been quantitatively evaluated, and the methods of fabricating mock-ups are various. This in vitro study investigated the thickness accuracy of mock-ups fabricated with different silicone matrices.

METHODS

Mock-ups of maxillary anterior teeth were respectively fabricated by 72 silicone matrices that were equally divided into four groups (n=18 for each group) according to two variables of the silicone matrices: labial margin position (equigingival or cover labial gingiva for 1-2 mm) and palatal notches (with or without notches on the palatal side of silicone matrices). The thickness accuracy of the mock-ups was analyzed using 3D scanning and 3D deviation analysis techniques compared with diagnostic waxing. The thickness change ratios of the mock-ups were compared using a two-way analysis of variance (ANOVA). One-way ANOVA and Kruskal-Wallis tests were used to compare differences in thickness change ratios between different teeth in each group.

RESULTS

The thickness accuracy of the mock-ups was significantly affected by the labial margin position and the palatal notches of the silicone matrices, respectively, in the labial area and the incisal area. The most accurate mock-ups were made using silicone matrices with equigingival labial margins and palatal notches. The thickness accuracy of the mock-ups was also inconsistent on different teeth.

CONCLUSIONS

The mock-ups fabricated by silicone matrices were thicker than the diagnostic waxing. The application of silicone matrices to equigingival labial margins and palatal notches was beneficial to the thickness accuracy of mock-ups.

Guided removal of a fractured fiber post and immediate restoration with a digitally prefabricated titanium post-and-core and zirconia crown: A clinical report

A completely digital workflow is described for the immediate restoration of a fractured fiber post with a digitally prefabricated definitive restoration using 3-dimensionally printed guides. The geometric morphology and axis of the root canal were digitally determined by using cone beam computed tomography to localize the 3-dimensional position of the fractured fiber post. A virtual drill modeled on the shape of the fractured post was fabricated and customized for removal of the post by using a guide to facilitate the intraoral transfer of the drilling procedure. A titanium post-and-core and crown had been virtually predesigned and fabricated before the procedure, and 2 digital guides were designed for their placement. All guides were 3-dimensionally printed. By following this workflow, the removal of the fractured fiber post and immediate definitive restoration were completed in 1 visit, facilitating a more efficient, predictable, and straightforward treatment.

Use of auxiliary devices during retreatment of direct resin composite veneers

The removal of direct composite veneers, when the retreatment is necessary, represents a challenge to the clinician, since the healthy dental structure must be preserved. Thus, the aim of this study was to compare the accuracy provided by different auxiliary devices during retreatment of direct composite veneers. Seventy-five bovine teeth were prepared for direct composite veneers, scanned (T1), and restored. Specimens were divided into 5 groups for retreatment: conventional high-speed handpiece without auxiliary device (WD); high-speed handpiece with a white LED (WL); high-speed handpiece with an UV light (UL); electric motor and multiplier 1/5 handpiece (EM); and conventional high-speed handpiece using magnifying loupe (ML). After retreatments, other scanning was performed (T2). Changes on dental wear or composite residues areas, as well as, the average between wear and presence of residues were measured. Data were submitted to Kruskal-Wallis and Dunn’s post-test (p≤ 0.05). There were greater areas of wear for ML, being statistically superior to WD and EM groups. The ML presented smaller residues areas, being statistically lower than the WD and EM groups. Regarding the average between wear and the presence of resin residues, additional wear occurred after re-preparation, regardless of the group. Magnifying loupe promoted greater areas of wear and smaller areas of resin residues than conventional high-speed handpiece and electric motor. Both techniques using light accessories did not differ from other ones.

Impact of Bleaching before or after Veneer Preparation on Color Masking Ability of Laminate Veneers: An In Vitro Study

Purpose

This study evaluates the effect of bleaching before or after veneer preparation and the depth of preparation on color masking ability of laminate veneers. Methods. Sixty extracted premolars were artificially stained to vita shade A4, verified by digital spectrophotometer (Vita Easy Shade V), and then divided into three groups: NB = nonbleached, BBP = bleaching before preparation, and BAP = bleaching after preparation. Based on the preparation depths, each group was further divided into two subgroups: S1 = 0.5 mm and S2 = 1.0 mm. BBP and BAP were subjected to one session of in-office bleaching using 35% hydrogen peroxide. IPS e-max CAD veneers of 0.5 and 1.0 mm thickness (corresponding to the preparation depths) of the same shade and translucency (HT A1) were cemented immediately to the bleached surfaces. Immediately after cementation, the color change ΔE between the baseline (after staining) and the resulted shades was measured using the Vita Easy Shade V digital spectrophotometer and CIELab color system.

Results

Bleached groups exhibited a significant ΔE value compared to the nonbleached group (p < 0.05). BAP showed the highest ΔE value. No significant difference was found between BBP and BAP. S2 revealed a significant ΔE value than S1 (p < 0.05). No significant difference was found between S1of BAP and S2 of NB, BBP, and BAP (p > 0.05). Regarding the color coordinates, the difference between the tested groups was highly significant in lightness (ΔL∗) (p < 0.001), while no significant differences were found in green/red value (Δa∗) and yellow/blue value (Δb∗) (p > 0.05).

Conclusions

In cases of severe tooth discoloration, one session of in-office bleaching before or after veneer preparation and the preparation depth do not influence the color masking ability of laminate veneers.