Occlusal Region Research Articles

Effect of build orientation on the fabrication trueness of additively manufactured implant-supported complete arch interim fixed prostheses.

To evaluate how build orientation affects the fabrication trueness of additively manufactured implant-supported complete arch prostheses by comparing them to subtractively manufactured high-impact polymer-based prostheses. An edentulous maxillary model with four implants at canine and first molar regions bilaterally was digitized (ATOS Core 80 5MP) to design a reference implant-supported complete arch prosthesis standard tessellation language file (RF-STL). The STL file was used to manufacture prostheses additively in five different orientations according to the build platform (AM-0, 0-degree; AM-15, 15-degree; AM-30, 30-degree; AM-45, 45-degree; AM-90, 90-degree) or subtractively (SM-HIP, control) (n = 10). The prostheses were digitized with an intraoral scanner (Trios 3) to generate their STLs (TF-STL). After superimposing TF-STLs over the RF-STL with a metrology-grade analysis software program (Geomagic Control X), surface deviations at four regions (overall, occlusal, overall without occlusal, and abutments), linear deviations at each abutment site, and interimplant distance deviations (canine-to-molar, canine-to-canine, and molar-to-molar) were calculated. One-way analysis of variance and Tukey HSD tests were used for the statistical analyses (α = 0.05). AM-90 mostly had the highest surface deviations, while AM-0 had the lowest overall, and lowest overall without occlusal region deviations (p ≤ 0.022). SM-HIP had the lowest occlusal region deviations (p < 0.001). AM-90 had the highest linear deviations (p < 0.001). AM-15 had higher canine-to-molar deviations than SM-HIP (p = 0.042). SM-HIP had the highest canine-to-canine deviations, while AM-90 had higher deviations than AM-0 and AM-30 (p ≤ 0.026). AM-45 and AM-90 had the highest and AM-0 had the lowest molar-to-molar deviations (p ≤ 0.013). AM-0 mostly had higher trueness and AM-90 mostly had lower trueness within tested outcomes. Additively manufactured prostheses mostly had lower canine-to-molar distances and higher molar-to-molar distances, whereas SM-HIP prostheses consistently had higher distances than the design file.

Reliability of the Assessment of Tooth Wear Severity on Dental Hard Tissues and Dental Restorations, Using the TWES 2.0, by Nonexperts.

Tooth wear is a multifactorial process resulting in the loss of dental hard tissues. For its assessment, the tooth wear evaluation system (TWES) 2.0 has been published. Previous studies on the TWES involved well-trained practitioners, rather than nonexperts. The first aim of this study was to investigate the reliability of the assessment of tooth wear severity on dental hard tissues, using the TWES 2.0, by nonexperts. The second aim was to investigate the reliability of assessment of wear severity on dental restorations, using a third scale. Forty-seven dental students evaluated at least 9 of 14 possible patient cases on dental casts and intraoral photographs. Cohen's kappa (agreement with sample solution) and Fleiss' kappa (Inter-rater reliability) were calculated. The agreements of the operators' ratings compared to the sample-solution resulted in Cohen's kappa between 0.02 and 0.9. The agreements were 0.34 for occlusal; 0.43 for vestibular; 0.57 for oral surfaces. Inter-rater reliability (Fleiss' kappa) was 0.35 for occlusal, 0.17 for vestibular and 0.24 for oral assessment. The inter-rater reliability of the ratings on tooth surfaces with restorations was lower with 0.21 (occlusal), 0.14 (vestibular) and 0.39 (oral). The agreement on different restorations differed tremendously. The ability to correctly assess the cases varied considerably between individual examiners. Within the limits of this study, assessment of restorations was slightly more challenging compared to natural teeth, particularly in occlusal regions or when the restorative material is gold. Subsequent studies should address whether enhanced training and improved definition of tooth wear grades result in higher reliability scores.

An innovative evaluation method for clinical comparative analysis of occlusal contact regions obtained via intraoral scanning and conventional impression procedures: a clinical trial

ObjectivesTo compare the occlusal contact regions (OCRs) obtained through an intraoral scanning system and conventional impression procedures via an innovative evaluation method.Materials and methodsFifteen participants with complete dentitions and stable centric occlusion were included. Three groups were created based on the technique used to obtain the OCRs of quadrant posterior teeth at the maximal intercuspal position: 100 μm articulating paper (Control), an intraoral scanner (Test 1, T1) and conventional impression procedure (Test 2, T2). OCRs of control group were digitized by the intraoral scanner, while all conventional impressions were cast and digitized by an extraoral scanner. The virtual occlusal records of the 2 test groups were obtained by buccal bite registration. The OCRs within 100 μm in the 3 groups were three-dimensionally superimposed based on the tooth surfaces and the area of OCRs (SC, ST1, ST2) was calculated. The area of overlapping OCRs (SO) between the test groups and the control group was calculated. In the two test groups, the consistency rate of OCRs (SO/SC) and the positive rate of OCRs (SO/ST) were calculated and compared. For occlusal tightness evaluation, the mean occlusal clearances (OC) as well as minimum OC between the upper and lower models were calculated and compared.ResultsThe consistency rate of OCRs was 0.73 ± 0.17 for T1 group and 0.23 ± 0.13 for T2 group (p < 0.001). The positive rate of OCRs was 0.67 ± 0.15 for T1 group and 0.56 ± 0.23 for T2 group (p = 0.143). The mean OC was 51.32 ± 16.04 μm for T1 group and 68.20 ± 18.15 μm for T2 group (p = 0.024). The minimum OC was − 61.74 ± 35.38 μm for T1 group and 4.09 ± 27.15 μm for T2 group (p < 0.001).ConclusionsFor obtaining occlusal records in the quadrant posterior region, the tested intraoral scanning system was more reliable for recording occlusal contact regions and showed higher occlusal tightness compared with conventional impression procedures.Clinical relevance(1) The evaluation method can assist clinicians in making more objective analysis and comparisons among different sources of virtual occlusal records. (2) Occlusal tightness is a key and indispensable indicator in the evaluation of virtual occlusal records, and it can be quantified by measuring the occlusal clearance utilizing the current evaluation method.

Evaluation of Microstrain in the Regions Surrounding Morse Taper and External Hexagon Implants.

The aim of this study was to compare the Morse taper (MT) + titanium base (Ti-Base) abutment with the external hexagon (EH) + Ti-Base abutment by using the strain gauge method in the mesial, distal, and apical-buccal areas around these types of implants. This study investigated two groups, MT and EH, each comprising five polyurethane samples with a dental implant in the area of artificial tooth 15 (3.75 × 11.5 mm) of a dental manikin. The strain gauges were glued to the mesial, distal, and apical-buccal polyurethane areas of all samples in relation to the implant. Ti-Base nonangled abutments measuring 5.0 × 4.7 × 1.0 mm (DSP, Brazil) were installed on the implants in each group. Ten identical zirconia crowns were constructed by scanning and milling and were subsequently cemented onto the Ti-base abutments with calcium hydroxide cement. Then, an axial load of 100 N was applied to the occlusal region of the zirconia crowns, and strain gauge measurements were taken. Strain gauge data were assessed by a two-way analysis of variance (ANOVA) with "implant connection" and "strain gauge position" factors, followed by the Bonferroni test (p < 0.05). The MT group exhibited a statistically significant reduction in microstrain in the mesial and apical strain gauge measurements compared to the EH group. The MT group exhibited less microstrain in the mesial and apical areas of the polyurethane samples near the implant. Consequently, the MT connection was considered more biomechanically advantageous.

Comparison of Various Commonly Used Luting Cements on the Success of Composite Inlays Assessed by the Levels of the Microleakage-An In vitro Study.

Indirect composite restoration is one of the commonly followed procedures in the posterior teeth. The success of this is dependent on many factors, one being the luting cement. Hence, the current study explores the microleakage of the two luting cements at 2 different times. Eighty extracted human teeth were taken, and class II cavities were made that were to receive the composite inlays. They were grouped as supragingival and subgingival, which for further divided as were further subdivided to be observed for marginal leakage at cervical and occlusal margins, at the end of a day and 1 month. Each group had ten specimens. The luting cements that were evaluated were Variolink N and RelyX Unicem. After the composite inlay restoration was done for all the specimens, the sections were put on slides, and a stereomicroscope was used to measure the amount of dye penetration. Leakage was evaluated and compared using Mann-Whitney U test. At the end of 1 day, there was no significant alteration in the microleakage in the occlusal or cervical regions for either region supragingivally or subgingivally between the two luting cements. Significant difference between the two cements at the cervical borders at the end of a month was seen for both the margins. When compared supragingivally and subgingivally at the end of 1 day or at the end of 1 month, there was not a significant difference for any of the cements. Within the constraints of the current investigation, it can be said that there was similar microleakage for both Variolink N and RelyX Unicem at the conclusion of a day's storage time. After a 1-month storage period, RelyX Unicem showed more cervical microleakage than Variolink N.

Marginal fit of three different nanocomposite inlays fabricated with computer-aided design/computer-aided manufacturing (CAD/CAM) technology: a comparative study.

This study aimed to compare and evaluate the marginal fit of nanocomposite computer-aided design/computer-aided manufacturing (CAD/CAM) inlays. Three types of nanocomposite CAD/CAM blocks (HASEM, VITA Enamic, and Lava Ultimate) were used as materials. Class II disto-occlusal inlay restorations were prepared on a typodont mandibular right first molar using diamond rotary instruments. The inlays were fabricated using CAD/CAM technology and evaluated using the silicone replica technique to measure marginal gaps at five locations on each inlay. The data were analyzed by two-way analysis of variance and Tukey post hoc tests ( α=0.05). There were no significant differences in the marginal gaps based on the type of nanocomposite CAD/CAM inlay used (p=0.209). However, there was a significant difference in the marginal gaps between the measurement regions. The gingival region consistently exhibited a larger marginal gap than the axial and occlusal regions (p<0.001). Within the limitations of this in vitro study, the measurement location significantly influenced the marginal fit of class II disto-occlusal inlay restorations. However, there were no significant differences in the marginal gaps among the different types of CAD/CAM blocks. Furthermore, the overall mean marginal fits of the class II disto-occlusal inlay restorations made with the three types of nanocomposite CAD/CAM blocks were within the clinically acceptable range.

Clinical outcomes of implant-supported and tooth-supported fixed prostheses fabricated from digital versus analogue impression: a systematic review and meta-analysis.

To analyze the clinical outcomes of implant-supported prostheses and tooth-supported fixed prostheses, fabricated from digital and conventional impression. The literature search was carried out on two electronic databases (PubMed and Cochrane Library). Randomized controlled trials (RCT) published from January 2011 to September 2022 were included. The bias risk was evaluated using Cochrane Risk of Bias Tool 2.0. Further screening was done for meta-analysis according to modified Newcastle-Ottawa scoring criteria. Forest plot was generated using a statistical method of inverse variance of random effect with 95% confidence interval. A total of 8 randomized controlled trials were included for systematic review out of which four studies were based on tooth-supported fixed prosthesis and remaining four were based on implant-supported prosthesis. Further screening was conducted and three studies were eligible for meta-analysis. Tooth-supported fixed prosthesis fabricated from digital impression showed no significant difference in the marginal fit in any region measured, except for occlusal region where conventional impression showed more favorable marginal fit. Implant-supported prosthesis fabricated from digital impression showed survival rates ranging from 97.3 to 100% and there was no statistically significant difference in marginal bone loss (p = 0.14). Implant-supported prostheses fabricated from digital and conventional impressions show no significant differences in their clinical outcomes. Tooth-supported fixed prostheses fabricated from digital impression have shown favorable findings in terms of marginal fit. Despite that, there is still lack of clinical trials with larger sample size and longer follow-up periods. Future studies that fulfill these two criteria are deemed necessary.

Effect of different occlusal forces on the accuracy of interocclusal records of loose teeth.

This study aimed to investigate the effect of loose teeth on the accuracy of occlusal records by comparing the differences in the number of occlusal contact points, occlusal contact area, and the center of the occlusal contact region under different occlusal forces in patients with periodontitis. The effects of different occlusal forces on the occlusal contact point (OCP), occlusal contact area (OCA) and the center of occlusal contact region (OCC) of loose teeth. Occlusal training was performed on the thirty patients who completed periodontal serial treatment. One doctor took the occlusal records with silicone rubber and the T-scan system; the patients were digitally scanned intraorally by a technician. The data of the healthy teeth were recorded as the control group, and the data of the loose teeth were recorded as the experimental group. Then we used Image J to measure the numbers of OCP and OCA and Auto CAD to calculate the coordinates of OCC. A paired t-test was used to analyze whether the differences in OCP, OCA, and OCC were statistically significant when the occlusal forces were different. The OCA of all three experimental methods increased under heavy occlusal force (p<.01), and the silicone rubber OCA increased the most. The OCC of all three experimental methods was shifted in the buccal and mesial (p<.01). And the occlusal records obtained by the T-scan system showed a low correlation between the differences of OCA and OCC. Whether the teeth were loose or not, the OCA increased under heavy occlusal forces. For patients with loose teeth, the OCC was shifted toward the buccal under heavy occlusal force.

Digital evaluation of the effect of nanosilica-lithium spray coating on the internal and marginal fit of high translucent zirconia crowns

ObjectivesTo evaluate the effect of a nanosilica–lithium spray coating on the internal and marginal fit of high translucent zirconia crowns using a digital evaluation method. MethodsA three-dimensional analysis model of a zirconia abutment was digitally scanned using a dental scanner, and 30 monolithic high translucent zirconia crowns were designed and fabricated. They were divided into groups (n = 10) according to the surface treatment method: (1) no treatment: as-sintered zirconia; (2) airborne-particle abrasion with 50 μm Al2O3 particles; and (3) nanosilica–lithium spray coating. Three-dimensional data for the abutment, crown, and crown seated on the abutment were obtained using a dental scanner. The three-dimensional seated fit between the crown and abutment was reconstructed using registration technology, and a three-dimensional (3D) deviation analysis was used to evaluate the effect of different modification methods on the internal and marginal fit of the crowns using root mean square (RMS) values. ResultsThe 3D deviation analysis of all groups conformed to a normal distribution (P > 0.05), and the variance was homogeneous (P > 0.05). The different surface treatments had no significant effect on the RMS values in the occlusal, axial, and marginal regions of the high translucent zirconia crowns (P > 0.05). ConclusionsNanosilica-lithium spray coating for the modification of as-sintered zirconia is clinically feasible and does not affect the internal or marginal fit of high translucent zirconia crowns. Clinical significanceNanosilica–lithium spray coating does not affect the adaptation of zirconia crowns and is a clinically feasible surface treatment method for zirconia. It is unnecessary to add the setting values of the internal and marginal fit when fabricating nanosilica–lithium-sprayed zirconia crowns.

How does the occlusal contact region influence the mechanical fatigue performance and fracture region of monolithic lithium disilicate ceramic crowns?

ObjectiveTo characterize the effect of the occlusal contact region on the mechanical fatigue performance and on the fracture region of monolithic lithium disilicate ceramic crowns. Materials and methodsMonolithic lithium disilicate ceramic crowns were machined in a CAD/CAM system and adhesively luted onto glass-fiber reinforced epoxy resin preparations with resin cement. The crowns were divided into three groups (n = 16) according to load application region (cusp tip: restricted to cusp tips; cusp plane: restricted to cuspal inclined plane; or mixed: associating tip cusp and cuspal inclined plane). The specimens were submitted to a cyclic fatigue test (initial load: 200 N; step-size: 100 N; cycles/step: 20,000; loading frequency: 20 Hz; load applicator: 6 mm or 40 mm diameter stainless steel) until observing cracks (1st outcome) and fracture (2nd outcome). The data were analyzed by the Kaplan-Meier + Mantel-Cox post-hoc tests for both outcomes (cracks and fracture). Finite element analysis (FEA), occlusal contact region, contact radii measurements, and fractographic analyzes were performed. ResultsThe mixed group presented worse fatigue mechanical behavior (550 N / 85.000 cycles) compared to the cuspal inclined plane group (656 N / 111,250 cycles) (p < 0.05) for the first crack outcome, while the cusp tip group was similar to both groups (588 N / 97,500 cycles) (p > 0.05). The mixed group had the worst fatigue behavior (1413 N / 253,029 cycles) in relation to the other groups (Cusp tip: 1644 N / 293,312 cycles; Cuspal inclined plane: 1631 N / 295,174 cycles) considering the crown fracture outcome (p < 0.05). FEA showed higher tensile stress concentration areas just below the load application region. In addition, loading on the cuspal inclined plane induced a higher tensile stress concentration in the groove region. The most prevalent type of crown fracture was the wall fracture. Groove fracture was observed in 50% of the loading specimens exclusively on the cuspal inclined plane. ConclusionLoad application on distinct occlusal contact regions affects the stress distribution pattern and consequently the mechanical fatigue performance and fracture region of the monolithic lithium disilicate ceramic crowns. A combination of loading at distinct regions is recommended to promote better evaluation of the fatigue behavior of a restored set.

Micro-CT analysis of 3D printed provisional crowns fitting.

The provisional crowns (PR) play an important role during the course of fixed prosthesis treatment. The fitting of PR varies and depends on various factors. The aim of the study was to evaluate the marginal and internal fit of PR produced by three-dimensional (3D) printing technique and to compare those with PR made by the milling technique by using micro computed tomography (μCT) on three commonly used finish line designs. Ninety study models were made using metal die of #14 tooth (i.e. maxillary 1st premolar molar) prepared for full veneer crown with three different finish line chamfer (C), rounded shoulder (RS) and rounded shoulder with bevel (RSB). PR was fabricated on each study model, using milling (MiL group, n= 45), and 3D printing technique (3D-P group, n= 45). Marginal and internal fit of each study model was measured by micro computed tomography, at 7 Zones Pr-1- Pr-7 on each finish line. Recorded data were statistically analysed by one-way analysis of variance (ANOVA) and using Dunnett t-Test (p> 0.05). The mean gap at margins was minimum for provisional crowns in 3D-P group in any finish line with minimum in rounded shoulder with bevel at zone Pr-1 30.9 ± 5.3 and at zone Pr-7 32.7 ± 5.3. In the axial region, i.e. zone Pr-2, the smallest gap was recorded in the 3D-P group and in the occlusal region, for zone Pr-3, 4 and 5, the maximum gap was recorded in the MiL group. The provisional crowns fabricated by 3D printed technique have better marginal and internal fit than the provisional crowns made by milling technique.

Stress distribution in resin-based CAD-CAM implant-supported crowns.

This study aimed to evaluate the influence of new resin-based CAD-CAM implant-supported materials on posterior crown restoration stress and strain concentrations. A previous 3D implant model was edited to receive a cement-retained posterior crown manufactured with different CAD/CAM materials (Estelite P Block, Estelite Block II or Estelite Layered Block). Each solid model was exported to the computer-aided engineering software and submitted to the finite element analysis of stress and strain. Material properties were assigned to each solid with isotropic and homogeneous behavior according to the manufacturer information. A vertical load of 600N was applied in the occlusal region of the crown, via a simulated food bolus, and stress was calculated in Von Misses (σVM) for the implant, abutment and screw, Maximum (σMAX) Principal Stresses for the crown and microstrain for the bone. All simulated materials showed acceptable stresses levels with a similar stress pattern among the models. At the crown intaglio region and cement layer, however, differences were observed: Estelite P Block showed a lower tensile and shear stresses magnitude when compared to other resin-based materials with lower elastic modulus. The stress effect of different resin-based CAD-CAM implant-supported crowns is predominant in the crown and cement layer, with Estelite P Block showing 7.4% versus 9.3% and 9.2% for Estelite Block II and Estelite Layered Block of crown failure risk.

An assessment of mineral concentration of dental enamel neighbouring hypothetical orthodontic brackets using X-ray microtomography

ObjectivesDifferences in the mineral concentration (MC) level of dental enamel may represent a precursor of white spot lesions adjacent to fixed orthodontic brackets. The aim of the current in vitro study was to compare the MC level central, occlusal and cervical to orthodontic attachments. Methods and MaterialsA total of 16 enamel blocks were obtained from sound human premolar samples extracted for orthodontic reasons. The buccal portion of the dental enamel blocks was divided into central, occlusal, and cervical regions and then imaged and measured to calculate the level of MC using quantitative X-ray microtomography methods (XMT) at each site. ResultsThere was a substantial variation in the mineral concentration with the lowest level being detected in the cervical region when compared with other regions. The MC of the gingival zone was significantly lower than that of the middle zone (P<0.05) and was insignificantly lower than that of the occlusal zone. ConclusionWithin the limitations of the current study, it can be concluded that the cervical region of the permanent enamel had the lowest mineral concentration using XMT. The cervical region may therefore be more vulnerable to the development of white spot lesions (WSLs) adjacent to a fixed orthodontic appliance during orthodontic treatment. Clinical significanceUsing X-ray microtomography lower mineral concentration in the cervical region of the enamel was observed. This may make these areas particularly susceptible to demineralisation during fixed appliance-based orthodontic treatment and may influence the bond strength of fixed orthodontic attachments.

Marginal and Internal Fit and Intaglio Surface Trueness of Temporary Crowns Fabricated with Stereolithography, Digital Light Processing, and Milling Technology.

To evaluate the fit and trueness of temporary crowns fabricated with 3D printing vs milling technologies and to analyze any existing correlations between fit and trueness. Marginal and internal fit and trueness were evaluated. Groups were compared using Kruskal-Wallis H test (α = .05), and correlations were analyzed using Spearman rank correlation analysis (α = .0016). Intaglio surface trueness was partially correlated with the marginal and internal fit (P < .0016). High intaglio surface trueness in the axial and occlusal regions may result in poor marginal fit. In the axial region, high intaglio surface trueness may adversely affect both the marginal and internal fit.

Fracture resistance to fixed partial denture abutments with direct and indirect posts

The objective of this study was to evaluate the resistance to fracture of three-element fixed partial dentof glasstment teeth restored with glass fiber posts (GFP) and cast post-and-core (CPC) retainers. Herein, 60 bovine mandibular incisors were divided into two groups (n = 30) according to the retainer type in: 1) resin composite core reinforced with GFP; and II) CPC (Cu-Al). Each pair of roots consisted of one sample, simulating a three-element fixed partial denture. The structures of the fixed three-element partial dentures were made in Ni-Cr alloy. A conventional dual resin cement (RelyX ARC - 3M Espe, USA) was used for all cementation procedures. Samples were subjected to a compressive load onto an orifice at occlusal contact region of the pontic until collapse or fracture. Normal data distribution was verified by D'Agostino &amp; Pearson normality test. Unpaired t test was used for data analysis (α = 5%). The results showed that the the three-element fixed partial denture abutment teeth restored with composite resin cores retained by GFP presented higher fracture resistance compared to the ones restored with CPC (p=0.0009). In conclusion, the resistance to fracture of three-element fixed partial denture restored with resin composite core reinforced with glass fiber posts was higher to the one restored with post-and-core retainers.

CAD/CAM versus 3D-printing/pressed lithium disilicate monolithic crowns: Adaptation and fatigue behavior

Objectivesthis study aimed to evaluate the adaptation and fatigue behavior of lithium disilicate glass-ceramic (LD) monolithic crowns produced by press (combined with 3D-printing) and CAD/CAM milling (control) techniques. Methodsthirty abutment preparations with a chamfer finish line were produced with a dentin analogue material and scanned with extraoral scanner. Captured images were processed using CAD software to design a premolar. Blocks of LD were milled using CAD/CAM system. For the press technique, crowns were first 3D-printed using a polymeric material and the heat-pressing protocol was performed. Crowns were adhesively cemented to the abutments and scanned using micro-CT. Files were processed and cross-sectional images were analysed in five measuring points: marginal, axial angle, axial, occlusal angle and occlusal. Fatigue test was performed in a MTS universal testing machine (2 Hz, 37°C distilled water) using an anatomic composite piston, following the step-stress method. Failures were detected with an acoustic system and confirmed by transillumination. A cumulative damage-Weibull distribution (95% CI) was used to analyze the fatigue data. Gap thickness data were analyzed using Kruskal-Wallis and Student-Newman-Keuls tests (α=0.05). ResultsCAD/CAM milling resulted in larger gap thickness in the occlusal area and smaller gap thickness in the axial angle and axial area than press (p<0.05). The probability of failure was similar for crowns produced with CAD/CAM milling and press. The most frequent failure mode was radial crack. ConclusionsLD crowns produced using the combination of 3D-printing/press technique showed similar fatigue behavior than CAD/CAM milled control group, and resulted in smaller gap thickness at the occlusal region. Clinical significanceA more controlled process can be achieved by replacing conventional restoration waxing with 3D printing, which in combination with the press technique produces lithium disilicate glass-ceramic monolithic crowns with good adaptation and high fatigue survival.

Three-dimensional fit of self-glazed zirconia monolithic crowns fabricated by wet deposition.

This study evaluated the 3-dimensional (3D) fit of self-glazed zirconia monolithic crowns fabricated by wet deposition, in comparison with milled zirconia and lithium disilicate monolithic crowns. Dual-scan protocol was used to assess the fit of crowns. Root mean squares (RMS) and uniformity index (UI) were calculated to describe the gap size and uniformity. The self-glazed zirconia crowns had significantly lower RMS values for the gaps at axial wall and transition regions than the milled zirconia crowns, and for the gaps at occlusal region than both milled crowns. All 3 types of crowns had comparable RMS values for the gaps at marginal and chamfer regions and comparable UI values for both marginal and internal gaps. The 3D fit of the self-glazed zirconia monolithic crowns was clinically acceptable and they exhibited better fit at occlusal region than the milled crowns.

Gastric emptying rate of a solid meal in patients with anterior open bite malocclusion: A preliminary study

Objectives: The objective of the study was to investigate the relationship between anterior open bite (AOB) malocclusion and digestion by evaluating mastication and gastric emptying (GE) of a solid meal. Material and Methods: We recruited 26 female participants and divided them into two groups according to their occlusion status: The control group with normal occlusion (n = 11; age: 25.2 ± 2.8 years; and body mass index [BMI]: 21.1 ± 1.9 kg/m2) and the AOB group with AOB malocclusion (n = 15; age: 23.2 ± 5.5 years; BMI: 21.0 ± 1.6 kg/m2). GE, chewing, and occlusion were assessed simultaneously. A food questionnaire survey was also administered on the same day. Results: A significant positive correlation was noted between open bite and the occlusal analysis findings. Negative correlations were found between the food questionnaire score and both the open bite and occlusal analysis findings, which confirmed that AOB affects mastication. However, no significant difference in the GE rate parameters was observed between the two groups. Conclusion: Adaptive mechanisms may have a compensatory effect on the GE rate. However, the lack of tooth contact in the anterior occlusal region resulted in reduced masticatory ability. Orthodontic treatment should thus be considered, regardless of the presence of digestive problems, to improve mastication.

Effect of the Sample Preparation and Light-curing Unit on the Microhardness and Degree of Conversion of Bulk-fill Resin-based Composite Restorations.

To evaluate the effect of the sample preparation and light-curing units (LCUs) on the Knoop hardness (KH, N/mm2) and degree of conversion (DC, %) of bulk-fill resin-based composite restorations. Two molds were made using human molar teeth embedded in acrylic resin. One was a conventional tooth mold where the molar received a mesio-occluso-distal (MOD) preparation. In the other, the tooth was sectioned in three slices (buccal, middle, and lingual). The center slice received a MOD preparation similar to the conventional mold. Both tooth molds were placed in the second mandibular molar position in a Dentoform with a 44-mm interincisal opening. Restorations were made using Opus Bulk Fill (FGM) high viscosity bulk-fill resin-based composite (RBC) and light cured using two different lights: VALO Cordless (Ultradent) and Bluephase G2 (Ivoclar Vivadent). The RBC was placed in one increment that was light-cured for a total of 80 seconds (40 seconds at the occluso-mesial and occluso-distal locations). The RBC specimens were then prepared as follows: EmbPol - tooth mold specimen was embedded in polystyrene resin and polished before testing; Pol - tooth mold specimen was not embedded, but was polished before testing; NotPol - sectioned tooth mold, specimen not embedded nor polished before testing. The KH was measured in different depths and regions of the specimens, and the DC was measured using Raman spectroscopy. The results were analyzed using a 2-way analysis of variance (ANOVA) or repeated measures followed by the Tukey post-hoc test (α=0.05). The preparation method (p<0.001), depth of restoration (p<0.001), and the interaction between method and depth (p=0.003) all influenced the KH values. Preparation method (p<0.001), tooth region (p<0.001), and the interaction between method and tooth region (p=0.002) all influenced DC values. The KH values were reduced significantly from the top to the bottom of the restorations and also at the proximal box when compared with the occlusal region. This outcome was most significant in the proximal boxes. The NotPol method was the most effective method to detect the effect of differences in KH or DC within the restoration. A lower DC and KH were found at the gingival regions of the proximal boxes of the restorations. When the KH and DC values were compared, there were no significant differences between the LCUs (KH p=0.4 and DC p=0.317). Preparation methods that embedded the samples in polystyrene resin and polished the specimens reduced the differences between the KH and DC values obtained by different preparation techniques. The NotPol method was better able to detect differences produced by light activation in deeper areas.

Adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3-dimensional gel deposition

Statement of problemA novel monolithic zirconia restoration fabricated by additive 3-dimensional (3D) gel deposition, named as self-glazed zirconia (SGZ), has recently been developed. SGZ crowns exhibit reliable mechanical properties and esthetic appearance, but their adaptation and uniformity are unclear. PurposeThe purpose of this in vitro study was to compare the adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3D gel deposition with that of milled zirconia and lithium disilicate crowns. Material and methodsTen identical resin abutments were made based on the scanning data of an extracted and prepared human mandibular first molar. Three types of monolithic crowns were then fabricated by using 2 different processes: 3D gel deposition zirconia (SGZ), milled zirconia (ZZ), and milled lithium disilicate (EMX) (n=10) through a completely digital workflow. The nondestructive direct-view technique and replica technique were used to measure the marginal and internal discrepancy values individually. The uniformity index was calculated to describe the uniformity of the internal space. The results were analyzed by using 1-way ANOVA and Kruskal-Wallis statistical tests (α=.05). ResultsThe marginal discrepancy of EMX exhibited the highest values among the 3 groups (P=.001). The 2 types of zirconia crowns had comparable marginal discrepancy values (P>.05). The internal discrepancy values of SGZ were significantly lower than those of EMX at the occlusal region and of ZZ at all measured locations (P<.05). All 3 types of monolithic crowns showed comparable good uniformity (P=.056). ConclusionsThe marginal and internal adaptations of novel monolithic zirconia crowns were within clinical requirements. Compared with the zirconia and lithium disilicate crowns fabricated by subtractive milling, monolithic zirconia crowns fabricated by additive 3D gel deposition had comparable uniformity and better internal adaptation.