Effect of material and antagonist type on the wear of occlusal devices with different compositions fabricated by using conventional, additive, and subtractive manufacturing.

STATEMENT OF PROBLEM: Additive (AM) and subtractive (SM) manufacturing have become popular for fabricating occlusal devices with materials of different chemical compositions. However, knowledge on the effect of material and antagonist type on the wear characteristics of occlusal devices fabricated by using different methods is limited. PURPOSE: The purpose of this in vitro study was to evaluate the effect of material and antagonist type on the wear of occlusal devices fabricated by using conventional manufacturing, AM, and SM. MATERIAL AND METHODS: Two-hundred and forty Ø10×2-mm disk-shaped specimens were fabricated by using heat-polymerized polymethylmethacrylate (control, CM), AM clear device resin fabricated in 3 different orientations (horizontal [AMH], diagonal [AMD], and vertical [AMV]), SM polymethylmethacrylate (SMP), and SM ceramic-reinforced polyetheretherketone (SMB) (n=40). Specimens were then divided into 4 groups based on the antagonists: steatite ceramic (SC); multilayered zirconia (ZR); lithium disilicate (EX); and zirconia-reinforced lithium silicate (ZLS) used for thermomechanical aging (n=10). After aging, the volume loss (mm3) and maximum wear depth (µm) were digitally evaluated. Data were analyzed with 2-way analysis of variance and Tukey honestly significant difference tests (α=.05). RESULTS: The interaction between the device material and the antagonist affected volume loss and maximum depth of wear (P<.001). AMH had volume loss and depth of wear that was either similar to or higher than those of other materials (P≤.044). When SC was used, CM had higher volume loss and depth of wear than AMV, and, when EX was used, AMD had higher volume loss and depth of wear than SMP (P≤.013). SC and ZR led to higher volume loss of CM and AMH than EX and led to the highest depth of wear for these materials, while ZR also led to the highest volume loss and depth of wear of AMD and AMV (P≤.019). EX led to the lowest volume loss and depth of wear of AMV and SMP and to the lowest depth of wear of AMH (P≤.021). Regardless of the antagonist, SMB had the lowest volume loss and depth of wear (P≤.005). CONCLUSIONS: AMH mostly had higher volume loss and depth of wear, while SMB had the lowest volume loss, and its depth of wear was not affected by the tested antagonists. ZR mostly led to higher volume loss and maximum depth of wear, while EX mostly led to lower volume loss and maximum depth of wear of the tested occlusal device materials.

Evaluation of enamel wear by 3 occlusal splint materials: An in vitro study.

STATEMENT OF PROBLEM: Occlusal devices used to manage bruxism have been commonly fabricated from polymethyl methacrylate with the powder-liquid technique. More recently, Vertex ThermoSens (VTS) and the biocompatible high-performance polymer (BioHPP), an optimized material having polyetheretherketone (PEEK) as its basis, have been used, but little is known about the wear of these materials on human enamel. PURPOSE: The purpose of this in vitro study was to assess via a mastication simulation test how 3 occlusal device materials affected the wear and roughness of enamel antagonists. MATERIAL AND METHODS: A noncontact 3D optical profilometer was used to measure the enamel surface roughness (Ra) against 3 occlusal device materials: vertex regular, VTS, and PEEK high-performance polymer (BioHPP). A dual-axis mastication simulator was used to perform a 2-body wear test on specimens from each group. The test consisted of 10 000 cycles with a 70-N force and 5 to 55 °C thermocycling. Following simulated mastication, the weight of each specimen and the Ra change were compared with the Kolmogorov-Smirnov test, paired specimens t test, Wilcoxon signed-rank test, and 1-way analysis of variance (α=.05). RESULTS: The polyamide group caused the lowest amount of enamel wear (P<.05), while the heat-polymerized acrylic resin group induced the largest amount of enamel wear (P<.05). For polyamide and PEEK, the change in enamel surface roughness exhibited a smooth texture, whereas it found a rougher surface for the heat-polymerized acrylic resin. CONCLUSIONS: According to this study, surface roughness and wear on human enamel were not correlated. PEEK is a promising material for the fabrication of occlusal devices.

Three-dimensional microscopic comparison of wear behavior between immature and mature enamel: an in vitro study.

BACKGROUND: Dental enamel, the hardest outermost layer of a human tooth, is subjected to occlusal forces throughout life during different oral function as talking, mastication etc. Due to this continuous stress, wear causes the loss of this protective shell. This study aimed to detect microscopic differences in enamel's wear behavior among different age groups of adolescents and adults. AIMS AND METHODS: Enamel specimens from immature open-apex and mature closed-apex premolars were subjected to simulated occlusal wear of impact and sliding wear test ISWT. Upper and lower enamel specimens were made to come in contact under controlled conditions. The enamel specimens' surfaces were examined using different microscopes. The upper and lower specimens were subjected to the following tests; pre-test light microscopy examination, enamel specimens' preparation for ISWT, scanning laser confocal microscopy of upper specimens, three-dimensional (3D) colored laser microscope and a Profilometer imaging of the lower specimens. RESULTS: Wear characteristics, including wear areas, crater depths, and relation to enamel microstructures, differed among different age groups. Immature enamel from the upper specimens was more resistant to chipping than mature enamel with no statistically significant wear area difference. The immature enamel craters from the lower specimens were wider and deeper than those in the mature enamel; the wear areas in the mature enamel in the lower specimens were almost flat and smooth. The wear areas in the immature enamel in the lower specimens were significantly larger than those in the mature enamel. CONCLUSIONS: Wear characteristics of the immature enamel are different from those of the mature enamel. Hence, it should be repaired using restorative materials with compatible wear properties.

Linear and volumetric wear of conventional and milled denture teeth.

OBJECTIVE: The purpose of this study was to compare the linear and volumetric wear of conventional and milled double-cross-linked polymethyl methacrylate, nano-composite, and nano-ceramic infused resin posterior denture teeth. METHODS: Double-cross-linked polymethyl methacrylate (PMMA) premolar teeth were scanned and used to mill denture teeth from a double-cross-linked PMMA resin disc and a nano-composite with nano-ceramic infused resin disc. The specimens (n = 8: conventional double-cross-linked PMMA resin teeth-DCL, milled double-cross-linked PMMA resin teeth-DCL-CAM, conventional nano-composite infused resin teeth with four layers composed of composite and PMMA resin teeth-NC, and milled nano-composite and nano-ceramic infused resin teeth-NC-CAM) underwent chewing simulation in the biaxial fatigue testing machine at 1.53 Hz frequency, thermocycling between 5 and 55°C, and 49 N force against a Ø6mm steatite. After 250,000 cycles, the linear changes on the occlusal surfaces of the specimens were analyzed with pairwise comparison with Bonferroni post hoc test, and the volumetric changes of the specimens were analyzed with a one-way ANOVA with Bonferroni post hoc test (p < 0.05). RESULTS: The linear wear of the conventional and milled denture teeth was linearly correlated with the number of cycles between 50,000 and 250,000 cycles. After 250,000 cycles, NC had significantly more linear and volumetric wear (0.52 ± 0.10 mm and 4.29 ± 0.94 mm3 ) than DCL (0.18 ± 0.03 mm and 0.74 ± 0.14 mm3 ; p < 0.001) and NC-CAM (0.15 ± 0.03 mm and 0.35 ± 0.21 mm3 ; p < 0.001). DCL-CAM and NC-CAM had linearly and volumetrically equivalent wear to DCL (p > 0.05). NC-CAM had significantly less linear and volumetric wear (0.15 ± 0.03 mm and 0.35 ± 0.21 mm3 ) than DCL-CAM (0.24 ± 0.07 mm and 1.22 ± 0.61 mm3 ; p < 0.05). CONCLUSIONS: The conventional NC wore more than DCL, DCL-CAM, and NC-CAM. Both milled denture teeth wore an equivalent amount to conventional DCL. The wear between the conventional and milled DCL was equivalent. CLINICAL SIGNIFICANCE: Denture teeth selection can prolong the retreading process and decrease the occurrences of prosthetic complications. Milled denture teeth are good alternatives to conventional denture teeth with regards to their wear resistance.

Effects of occlusal splint therapy on opposing tooth tissues, filling materials and restorations.

BACKGROUND: Little is known about the effect of the type of splint material, heat-cured PMMA (HC) or chemical-cured PMMA (CC) on the wear of opposing tooth surfaces. OBJECTIVE: The aim of this in vitro study was to evaluate two-body wear of dentin, enamel, glass-ceramic or one of four resin composites when opposing splint materials, namely ProBase HC and CC. METHODS: The two-body wear of bovine dentine, bovine enamel, glass-ceramic IPS e.max CAD (EMAX) and four composites (Filtek Z250 [Z250], Clearfil AP-X [AP-X], Clearfil Majesty Posterior [CMP], Filtek Supreme XTE [FSE]) opposing three antagonists (HC and CC and stainless steel as control) were evaluated in the ACTA wear machine. In addition, all the surfaces were evaluated with scanning electron microscopy. RESULTS: The highest average wear was observed in the case of dentin. The lowest average wear was found EMAX. In every case-except for EMAX-the wear rate was higher with HC than with CC (all differences being statistically significant). CONCLUSIONS: The level of wear of enamel, dentin and various resin composites was higher in contact with HC than in CC, the wear of dentin being the highest. In the case of a patient with no or little tooth wear or whose teeth are restored with composite material or glass-ceramic, the splint HC might be preferred because of its better durability. However, when the splint is in contact with opposing dentin preservation of the dentin, CC might be the best choice.

Evaluation of the wear of glazed and polished zirconia crowns and the opposing natural teeth: A clinical pilot study.

STATEMENT OF PROBLEM: Clinical studies on the wear properties of different zirconia surfaces are lacking. Selecting a surface that causes and undergoes minimal wear will help improve clinical outcomes. PURPOSE: The purpose of this clinical study was to evaluate and compare the wear over 1 year use of glazed zirconia (GZ) and polished zirconia (PZ) crowns opposing natural enamel and the wear of natural enamel opposing PZ and GZ crowns. MATERIAL AND METHODS: This prospective, split mouth, randomized clinical trial included 14 participants requiring complete coverage crowns on first molars, bilaterally, in a completely dentate mandibular arch. GZ and PZ crowns were cemented according to a randomization chart. Polyvinyl siloxane impressions were made immediately and 1 year after the cementation of the crowns. The respective casts were scanned by using a 3D scanner and a software program to measure the amount of linear wear of zirconia crowns and opposing natural teeth. Wear was observed in 8 groups: PZ crowns, GZ crowns, natural enamel opposing natural enamel in the molar and premolar regions (NE-M and NE-PM), natural enamel opposing PZ crowns in the molar region (NE-PZ-M), natural enamel opposing GZ crowns in the molar region (NE-GZ-M), natural enamel opposing PZ crowns in the premolar region (NE-PZ-PM), and natural enamel opposing GZ crowns in the premolar region (NE-GZ-PM). A descriptive analysis was followed by comparison between groups by using a repeated-measure ANOVA with post hoc adjustments (α=.05). RESULTS: The mean wear (µm) observed was as follows (in ascending order): PZ crowns (13 ±3), NE-PM (13 ±1), GZ crowns (27 ±9), NE-M (34 ±3), NE-PZ-PM (44 ±18), NE-PZ-M (63 ±22), NE-GZ-PM (69 ±21), NE-GZ-M (113 ±33). Wear of GZ and PZ crowns was less than wear of NE-M. The difference was statistically significant when comparing PZ with NE-M (P<.001, CI=-17 to -24). Wear of NE-GZ-M and NE-PZ-M was higher than wear of NE-M, with a statistically significant difference (P<.001, CI=-49 to -107 and P =.004, CI=-8 to -49, respectively). Wear of NE-GZ-M was more than that of NE-PZ-M, and the difference was statistically significant (P<.001, CI=-68 to -32). Wear of NE-PZ-PM and NE-GZ-PM was also more than the wear of NE-PM, and the difference was statistically significant (P<.001, CI=-17 to -43 and P<.001, CI=-39 to -70). CONCLUSIONS: PZ and GZ crowns wear substantially with time, with lesser wear observed in PZ crowns. PZ and GZ crowns also cause more wear in opposing natural enamel than natural enamel antagonists, with the highest wear caused by GZ crowns.

Quantitative analysis on the wear of monolithic zirconia crowns on antagonist teeth.

BACKGROUND: The present study aimed to quantitate the wear of the highly transparent Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramic monolithic zirconia crown on the enamel in vivo and discuss the prone position of the wear and the underlying mechanism. METHODS: A total of 43 patients with 43 posterior teeth were selected for full zirconia crown restoration and examined immediately, at 6 months, and at 1 year after restoration. During the follow-up visit, the fine impression of the patients' monolithic zirconia crowns, the antagonist teeth, the corresponding contralateral natural teeth, the super plaster cast, and epoxy resin model was ontained. The model of epoxy resin was observed under a stereo microscope, and the microstructure parts were observed under a scanning electron microscope. RESULTS: After 1 year, the mean depth and volume of wearing of the monolithic zirconia crown were the smallest (all P < 0.01), while those of the antagonist teeth were significantly larger than those of the natural teeth (P < 0.0001), and no significant difference was found among the natural teeth (P = 0.3473, P = 0.6996). The amount of wear after one year was remarkably higher than that at 6 months (P < 0.0001). The microscopic observation revealed the tendency of wearing of the monolithic zirconia crown on the antagonist teeth at the protruding early contact points. Electron micrographs of tooth scars showed that the wearing mechanism of the monolithic zirconia crown on natural teeth was mainly abrasive and fatigue wear. CONCLUSIONS: Although the self-wearing is insignificant, the monolithic zirconia crown can cause wear of the antagonist teeth via occlusal or early contact significantly; the amount of wearing is higher than that of natural teeth and increases over time. The wearing mechanism is mainly abrasive and fatigue wear.

Wear Resistance of 3D Printed and Prefabricated Denture Teeth Opposing Zirconia.

PURPOSE: To evaluate the wear resistance of a recently developed three-dimensional (3D) printed denture teeth resin compared to three commercially available prefabricated denture teeth. MATERIALS AND METHODS: A total of 88 maxillary first molar denture teeth were evaluated: C (Classic; Dentsply Sirona, York, PA), DCL (SR Postaris DCL; Ivoclar Vivadent, Schaan, Liechtenstein), IPN (Portrait IPN; Dentsply Sirona, York, PA), and F (Denture Teeth A2 Resin 1 L; Formlabs, Somerville, MA). The 3D printed denture tooth specimens were fabricated from a methacrylate-based photopolymerizing resin using stereolithography (SLA). Denture teeth were subjected to a three-body wear test with a poly(methylmethacrylate) (PMMA) abrasive slurry. A Leinfelder-style four station wear apparatus with custom bullet-shaped milled zirconia styli was utilized with a load force of 36-40 N at 1.7 Hz for 200,000 cycles. Maximum depth of wear was measured using a lab grade scanner and analyzing software program. Data were analyzed using a one-way ANOVA followed by the Tukey's Multiple Comparisons post hoc test (α = 0.05). RESULTS: A statistically significant difference in depth of wear was found between denture tooth materials (p < 0.001). The mean vertical depth of wear for the 3D printed denture teeth (0.016 ± 0.010 mm) was statistically significantly less than the prefabricated denture teeth. The highly cross-linked denture teeth, DCL (0.036 ± 0.011 mm) and IPN (0.035 ± 0.014 mm), exhibited statistically significantly less wear than the conventional acrylic denture teeth. The conventional acrylic denture teeth demonstrated the greatest wear (0.058 ± 0.014 mm). No significant difference in depth of wear was found between DCL and IPN (p > 0.001). CONCLUSIONS: Denture tooth material significantly influences the depth of wear. The 3D printed denture teeth demonstrated superior wear resistance compared to the commercially available prefabricated denture teeth when opposed to zirconia. Denture teeth fabricated with SLA technology may have a promising future in prosthetic dentistry.

Speech changes in patients with a full rehabilitation for severe tooth wear, a first evaluation study.

OBJECTIVE: The aim of this study was to evaluate changes in speech characteristics and self-perceived quality of speech in tooth wear patients, after occlusal rehabilitation. MATERIALS AND METHODS: Patients with tooth wear were included in this study after informed consent. The amount of tooth wear was scored with Tooth Wear Evaluation System (TWES). To assess the perspective of the patient, the Dutch Speech Handicap Index was used (SHI). Acoustic analysis was performed to evaluate changes with the use of voice recordings. These were made before treatment, T0; directly after treatment, T1; 1 month after treatment, T2. With the use of PRAAT software, the spectral characteristic centre of gravity (COG) was evaluated for the sounds /s/, /f/, /v/, /d/, /t/, /m/. RESULTS: Recordings of 17 patients (14 men, 3 women, mean age 41.2 ± 10.4 years) were included. SHI scores did not change significantly between T0 and T2 (p = 0.054). A multiple regression model showed that for all sounds the intercept was negative, but statistically significant only for /s/ and /f/ between T0 and T1. The effect of the initial change (between T0 and T1) on the change between T1 and T2 was clearly negative for all sounds (p < 0.001), showing a rebound effect ranging between 29 and 68% of the initial change. CONCLUSION: Tooth wear patients perceive improvement in speech function after treatment. CLINICAL SIGNIFICANCE: Clinicians may explain to patients that speech is likely to alter for a short period due to treatment but that there will be a good adaption to the new situation.

Wear of resin teeth opposing zirconia.

STATEMENT OF PROBLEM: The use of dissimilar materials for opposing complete-mouth implant-supported prosthesis has become popular, especially when one arch is made from anatomical contour zirconia. However, the amount of wear zirconia causes on resin and other denture tooth materials is largely unknown. PURPOSE: The purpose of this in vitro study was to determine the volumetric wear of 4 commercially available resin materials used for denture teeth in complete-arch implant-supported prostheses opposed by zirconia. MATERIAL AND METHODS: A total of 32 maxillary central incisor denture teeth were evaluated (n=8): double crosslinked polymethyl methacrylate (PMMA) (DCL), nanohybrid composite resin (PHO), and computer-aided design and computer-aided manufacturing (CAD-CAM)-fabricated teeth made from crosslinked PMMA (TEL) and acrylate polymer (ZCAD). Antagonist cone-shaped specimens were milled from zirconia. Specimens were mounted in acrylic resin, polished to a flat surface by using 1200-grit SiC paper, and stored in water (37 °C for 24 hours) before exposure in a custom dual-axis wear simulator for 200 000 cycles with a vertical load of 20 N, a horizontal slide of 2 mm, and a frequency of 1 Hz. Volumetric wear was measured by using a noncontact profilometer and a superimposition software program. Data were analyzed with a 1-way analysis of variance (ANOVA) and the Tukey Honestly Significant Difference (HSD) post hoc test (α=.05). RESULTS: A statistically significant difference in volumetric wear was found between groups (P<.001), with PHO (4.3 ±1.0 mm3)

Wear resistance of 3D-printed denture tooth resin opposing zirconia and metal antagonists.

STATEMENT OF PROBLEM: Additive manufacturing technology can be used for denture bases and also denture teeth. Therefore, the mechanical properties of 3D-printed resin denture teeth should be evaluated. PURPOSE: The purpose of this in vitro study was to compare the wear resistance of 3D-printed denture tooth resin with that of conventionally prefabricated denture teeth. MATERIAL AND METHODS: Eighty substrate specimens were prepared with 5 kinds of resin denture teeth: 3D-printed denture tooth resin (DENTCA denture tooth resin; DENTCA, Inc), Artic 6 (Kulzer GmbH), Preference (Candulor AG), Premium 6 (Kulzer GmbH), and Surpass (GC Corp). The 3D-printed denture tooth specimens were made of methacrylate-based photopolymerized resin by stereolithography 3D printing. Antagonistic surfaces were made from zirconia by milling and from cobalt-chromium (Co-Cr) alloy by 3D printing and casting. The specimens were loaded at 49 N for 30 000 cycles under thermocycling conditions in a mastication simulator. Wear resistance was measured by calculating the volume of substance lost. Wear surface characteristics were observed by using a scanning electron microscope (SEM). Two-way ANOVA was used to analyze the data (α=.05). RESULTS: The influence of the resin denture teeth and the type of antagonist were both statistically significant. The wear volume loss of the 3D-printed denture tooth resin was higher than that of Artic 6 and Preference when opposing the zirconia and the metal antagonists (P<.05). The 3D-printed denture tooth resin did not show a significant difference from Premium 6 with the zirconia and the metal antagonists or Surpass with the zirconia antagonist. From the SEM images, the specimens of the 3D-printed denture tooth resin showed a relatively smooth surface with the zirconia antagonist and exhibited cracks when opposed by the metal antagonist. CONCLUSIONS: The results suggest that 3D-printing by using resin materials provides adequate wear resistance for denture tooth use.

Two-body Wear and Hardness of New Generation Artificial Resin Teeth.

The purpose of this study was to evaluate two-body wear and hardness of new generation artificial resin teeth. Ten specimens of four different artificial resin teeth (nanofill composite, nanohybrid composite, microfiller reinforced acrylic and highly modified acrylic) were prepared. Specimens were thermodynamically loaded in a dual-axis chewing simulator (50N, 240,000 cycles, 1.6 Hz, 5/55°C thermocycle). The wear loss was analyzed by using plaster replicas and 3D laser scanner. Vickers hardness was determined before and after thermodynamic loading. Mean Vickers hardness values of highly modified acrylic resin teeth were statistically significantly lower than nanohybrid composite (p⟨0.001), nanofilled composite (p⟨0.001) and microfiller reinforced acrylic resin teeth (p⟨0.001). Mean wear loss of highly modified and microfiller reinforced acrylic resin teeth were statistically significantly lower than nanohybrid composite (p⟨0.001) and nanofilled composite (p⟨0.001) resin teeth. There was a statistically significant difference in wear among the materials. The correlation between hardness and wear was not statistically significant.

Limited Evidence Supports Polished Monolithic Zirconia as Less Likely to Cause Antagonist Enamel Wear Compared to Other Prosthetic Materials.

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION: Antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns in vivo: A systematic review. Gou M, Chen H, Kang J, Wang H. J Prosthet Dent 2019;121:598-603. SOURCE OF FUNDING: This study was funded by the authors. TYPE OF STUDY/DESIGN: Systematic review and meta-analysis.

Wear of direct resin composites and teeth: considerations for oral rehabilitation.

Little is known about the wear rate of enamel and dentin opposing resin composite following restoration of the occlusal surface in patients with tooth wear. Hence, the aim of this in vitro study was to evaluate the wear of enamel and dentin surfaces when opposing each of three resin composites in a two-body and three-body wear test. The two-body and three-body wear of dentin, enamel, and three resin composites (Clearfil AP-X, Filtek Z250, and Filtek Supreme) opposing four antagonists (stainless steel and three resin composites) were evaluated using the ACTA wear machine. In addition, all the surfaces were evaluated with scanning electron microscopy. The results showed the lowest wear rate in enamel and the highest in dentine, with the composite showing intermediate wear rates. The three-body wear results were not affected by the antagonist and showed pure wear caused by the abrasive food medium. The in vitro enamel/composite wear ratio was 2.5. The results show that tooth wear accelerates as soon as enamel disappears and dentin is exposed to composite resin. Therefore, it is important to protect dentin with a restorative material.

Enamel wear and aging of translucent zirconias: In vitro and clinical studies.

STATEMENT OF PROBLEM: Zirconia is a widely used restorative material. However, phase transformation on clinical application of zirconia has not yet been studied. PURPOSE: The purpose of this study was to evaluate the wear, surface roughness, and aging associated with polished translucent zirconia in both in vitro and clinical experiments. MATERIAL AND METHODS: In vitro experiments were performed with Rainbow and Katana zirconia blocks and natural tooth enamel as the control. They were subjected to 100 000 loading cycles with a maxillary premolar antagonist. All specimens were analyzed for wear, and the zirconia specimens were evaluated for surface roughness and monoclinic phase (m-phase) transformation by X-ray diffractometry before and after cyclic loading. The clinical study included participants who required single-crown implant-supported restorations replacing the first or second molar. The participants received Rainbow or Katana zirconia prostheses (n=15, each). For wear analysis, impressions of each prosthesis, antagonist, and adjacent tooth were made at 1 week and 6 months after crown delivery. The occlusal relationship of the crowns in maximum intercuspation was evaluated by using the T-Scan 8 occlusal diagnostic system. The degree of transformation of zirconia to the m-phase was measured by using X-ray diffractometry of the crowns after 6 months of use. RESULTS: Zirconia induced significantly greater enamel wear than the natural tooth control. Katana specimens exhibited significantly greater wear and surface roughness than the Rainbow specimens. The degrees of antagonistic wear and zirconia phase transformation in the clinical experiment were significantly greater than those in the in vitro experiment. The Katana groups showed significantly higher m-phase levels than the Rainbow groups. CONCLUSIONS: Phase transformation of zirconia occurs within 6 months of clinical use, and the wear and degrees of phase transformation varied according to the zirconia product used.

In Vitro Effect of Mastication on the Retention and Wear of Locator Attachments in a Flat Mandibular Ridge Model.

PURPOSE: The effect of masticatory loads on the retention of overdenture attachments is poorly documented. The aim of this in vitro study is to assess the effect of simulated mastication on the retentive properties and dimensions of Locator inserts. MATERIALS AND METHODS: 30 specimens simulating nonanatomic edentulous flat ridges with two implant replicas each were fabricated. Overdenture units were connected to the implants with Locator attachments and 3 types of inserts: transparent (Group T; n = 10 pairs), pink (Group P; n = 10 pairs), and blue (Group B; n = 10 pairs). The overdenture units were subjected to simulated bi-axial masticatory loads of 68.6 N. Locator retention was assessed using axial dislodging forces at baseline (T0) and following 100,000 (T1) and 200,000 (T2) masticatory cycles. The inner diameter of the insert (XY) and the diameter of the central core (AB) were measured under stereomicroscope at T0 and T2. Retention changes and dimensional variations of the inserts were statistically analyzed. RESULTS: The 3 groups showed significantly different retentions with the highest values recorded for group T followed by group P, and finally group B at T0, T1, and T2. Groups T and P were not affected by loading while group B showed a significant mean retention loss from T0 to T1. XY and AB were significantly different between the 3 color-coded inserts at baseline and at T2. No correlation could be established between retention changes and dimensional variations of the 3 types of inserts. CONCLUSIONS: Within the limitations of this in vitro study, simulated mastication seems to significantly affect the extra-light blue Locator inserts but not the more-retentive ones. The transparent and pink inserts may require less frequent replacements and could therefore be recommended under clinical conditions.

Assessment of Antagonist Enamel Wear and Clinical Performance of Full-Contour Monolithic Zirconia Crowns: One-Year Results of a Prospective Study.

PURPOSE: To assess the clinical performance and survival of full-contour monolithic zirconia (MZ) crowns and enamel wear produced over a 1-year period. MATERIALS AND METHODS: 60 patients requiring full-coverage restorations for endodontically treated posterior teeth opposed by healthy unrestored antagonistic teeth were selected. MZ crowns were fabricated. Vinyl polysiloxane impressions of the antagonist teeth were made, and the stone casts were digitized using a 3D laser scanner. Wear of the opposing natural teeth was evaluated at baseline (1 week), 6 months, and 1 year after crown cementation. Superimposition of the follow-up scans on the baseline scans were performed to evaluate wear. Survival and function of the restorations were evaluated by the modified USPHS rating criteria at the same timeframes. RESULTS: Comparison of the baseline and the follow-up wear values was statistically tested using the paired t-test. Statistical significance was noted between the wear values at 6 months (15.5 µm) and at 12 months (16.3 µm) (p < 0.05). The Wilcoxon signed rank sum test was performed to evaluate each parameter of the modified USPHS criteria and to analyze the change in the follow-up scores of the restorations. The survival rate for the crowns was 100%. Results were classified as "excellent" over a 1-year follow up. CONCLUSIONS: MZ crowns showed promising results related to antagonist enamel wear and survival/clinical performance.

In Vitro evaluation of the wear of primary tooth enamel against different ceramic and composite resin materials.

BACKGROUND: Although there are several studies on permanent tooth wear caused by dental materials, studies concerning primary teeth are limited. AIM: To evaluate the wear of primary tooth enamel against different ceramic and composite resin materials. SETTINGS AND DESIGN: In vitro study. Materials and Methods: We assessed five materials (n = 10 per group): monolithic zirconia (group Z), lithium disilicate glass ceramic (group L), resin nanoceramic (group R), nanohybrid composite resin (group C), and primary tooth enamel (group E). The mesiopalatal cusps of primary maxillary second molars were used as antagonists. Wear tests were performed in a dual-axis chewing simulator, and the volume loss in the antagonist tooth was evaluated using a laser scanner and three-dimensional profiling system. STATISTICAL ANALYSIS USED: Data were statistically analyzed using one-way analysis of variance with Tukey's post hoc tests (P < 0.05). Results: The maximum antagonist tooth wear was observed in group L (3.84 ± 0.7 mm3), followed by groups C (3.68 ± 0.76 mm3), R (3.48 ± 0.71 mm3), Z (2.66 ± 0.65 mm3), and E (1.66 ± 0.42 mm3). Volume loss was significantly lesser in group Z than in groups L and C (P < 0.05), whereas there were no significant differences among groups L, C, and R. CONCLUSION: Within the limitations of this in vitro study, our findings suggest that zirconia should be used for full coronal coverage in primary tooth restorations because it causes lesser antagonist tooth wear than does lithium disilicate, resin nanoceramic, and nanohybrid composite resin.

Study of Two-Body Wear Performance of Dental Materials.

INTRODUCTION: The purpose of this study was to evaluate the two-body wear resistances of natural enamel and four dental materials in vitro. METHODS: The testing machine was modified to form a type of pin-on-disk wear test apparatus. Four dental material specimens (Au-Pd alloy, Ag-Pd alloy, FiltekTMP60 and FiltekTMZ350 composite resins) and enamel were used as the pins, and a steatite ceramic grinding wheel was used as the abrasive counter face. The wear volume loss and the rigidity value was measured. The worn surface and the element analysis of the debris were analyzed. RESULT: The wear volume loss of Au-Pd alloy and its steatite antagonists were the nearest to those of the dental enamel. SEM microphotographs showed that, the main wear mechanism of the dental materials was abrasive and adhesive wear. CONCLUSIONS: Au-Pd alloy had good wear resistance and was more suitable for dental applications than other three dental materials.

Comparison of wear between occlusal splint materials and resin composite materials.

Tooth wear in bruxing patients often results in a need for treatment with composite restorations. In some cases, bruxing patients receive an occlusal splint as a protective means as well. However, the wear between these opposing materials has not been investigated yet. The aim of this in vitro study was to assess the wear of different splint materials against resin composite materials. A two-body wear test was conducted using the ACTA wear machine. The materials selected for this study were three composites used for direct restorations (Filtek Z250, CLEARFIL AP-X, and Filtek Supreme XT) and four occlusal splints materials, viz. a polyamide resin (ThermoSens) an conventional (hand-processed), milled and printed polymethylmethacrylate (PMMA). As antagonistic materials, stainless steel, Filtek Supreme XT and CLEARFIL AP-X were used. The wear rate of the seven materials was determined after 200 000 cycles, using a profilometry. The rates were analysed using two-way ANOVA and post hoc Tukey's tests. The wear rates were significantly higher for the conventional and milled PMMA materials than for all other materials (P < .001). The wear rates of printed PMMA and the polyamide resin were comparable to composite wear rates. The antagonist materials have minor or no influence on the amount of wear of the various splint materials (P < .001). In conclusion, different splint materials yielded different wear rates for all antagonist materials tested. Keeping in mind that this study is an experimental in vitro study, this finding enables practitioners to choose the splint material necessary according to their patients' needs.