Purpose: It is over a year since the first case of coronavirus disease (COVID-19) was confirmed in China. This paper reviews and summarizes the characteristics of COVID-19, as understood of December 2020, from a dental perspective.

Study Selection: The PubMed and Scopus online databases were searched using a combination of free words and Medical Subject Headings terms: “dentist” OR “oral care” AND “COVID-19” OR “SARS-CoV-2.”

Results: Older people and those with underlying medical conditions have an increased risk of serious illness due to COVID-19. The virus enters the body by binding to the angiotensin-converting enzyme 2 (ACE2) receptor. It is common for people with COVID-19 to have mild or no symptoms. Moreover, the disease is not contagious in most infected people; it is only highly contagious in some infected people, thereby forming clusters. Due to the large number of virus particles that are shed prior to the onset of symptoms of the disease, retrospective surveys are important. Appropriate personal protective equipment against corona vortices is also important in clinical practice. Although polymerase chain reaction tests are useful for confirming infection in suspected individuals, their reliability is questionable. In addition, concerns regarding long-term sequelae have been reported.

Conclusion: There are few high-quality reports on the implications of COVID-19 in dental practice. However, reports suggest that insufficient oral hygiene may be a risk factor for infection. Reports that ACE2 receptors are abundant in the oral cavity also suggest the importance of oral care.

Purpose: Dental implant therapy is a common clinical treatment for missing teeth. However, the esthetic result is not as satisfactory as expected in some cases, especially in the anterior maxillary area. Poor esthetic results are caused by inadequate preparation of the hard and soft tissues in this area before treatment. The socket shield technique may be an alternative for a desirable esthetic outcome in dental implant treatments.

Study selection: In the present systematic review, PubMed-Medline, Google Scholar, and ScienceDirect were searched for clinical studies published from January 2000 to December 2018.

Results: Twenty studies were included, comprising one randomized controlled trial, two cohort studies, 14 clinical human case reports, and three retrospective case series. In total, 288 patients treated with the socket shield technique with immediate implant placement and follow-up between 3–60 months after placement were included. A quality assessment showed that 12 of the 20 included studies were of good quality. Twenty-six of the 274 (9.5%) cases developed complications or adverse effects related to the socket shield technique. Most studies reported implant survival without the complications (90.5%); most of the cases that were followed up for more than 12 months after implant placement achieved a good esthetic appearance. The failure rate was low without the complications, although there were some failures due to failed implant osseointegration, socket shield mobility and infection, socket shield exposure, socket shield migration, and apical root resorption.

Conclusions: The socket shield technique can be used in dental implant treatment, but it remains difficult to predict the long-term success of this technique until high-quality evidence becomes available.

Purpose: The purpose of this study was to comprehensively review the literature regarding the application of artificial intelligence (AI) in the dental field, focusing on the evaluation criteria and architecture types.

Study selection: Electronic databases (PubMed, Cochrane Library, Scopus) were searched. Full-text articles describing the clinical application of AI for the detection, diagnosis, and treatment of lesions and the AI method/architecture were included.

Results: The primary search presented 422 studies from 1996 to 2019, and 58 studies were finally selected. Regarding the year of publication, the oldest study, which was reported in 1996, focused on “oral and maxillofacial surgery.” Machine-learning architectures were employed in the selected studies, while approximately half of them (29/58) employed neural networks. Regarding the evaluation criteria, eight studies compared the results obtained by AI with the diagnoses formulated by dentists, while several studies compared two or more architectures in terms of performance. The following parameters were employed for evaluating the AI performance: accuracy, sensitivity, specificity, mean absolute error, root mean squared error, and area under the receiver operating characteristic curve.

Conclusion: Application of AI in the dental field has progressed; however, the criteria for evaluating the efficacy of AI have not been clarified. It is necessary to obtain better quality data for machine learning to achieve the effective diagnosis of lesions and suitable treatment planning.

Purpose: To review the current clinical studies regarding the accuracy of implant computer-guided surgery in partially edentulous patients and investigate potential influencing factors.

Study selection: Electronic searches on the PubMed and Cochrane Central Register of Controlled Trials databases, and subsequent manual searches were performed. Two reviewers selected the studies following our inclusion and exclusion criteria. Qualitative review and meta-analysis of the implant placement accuracy were performed to analyze potential influencing factors. Angular deviation, coronal deviation, apical deviation, and depth deviation were evaluated as the accuracy outcomes.

Results: Eighteen studies were included in this systematic review, including six randomized controlled trials, nine prospective studies, and three retrospective clinical studies. A total of 1317 implants placed in 642 partially edentulous patients were reviewed. Eight studies were evaluated using meta-analysis. Fully guided surgery showed statistically higher accuracy in angular (P <0.001), coronal (P <0.001), and apical deviation (P <0.05) compared with pilot-drill guided surgery. A statistically significant difference (P <0.001) was also observed in coronal deviation between the bounded edentulous (BES) and distal extension spaces (DES). A significantly lower angular deviation (P <0.001) was found in implants placed using computer-aided design/computer-aided manufacturing (CAD/CAM) compared to the conventional surgical guides.

Conclusion: The edentulous space type, surgical guide manufacturing procedure, and guided surgery protocol can influence the accuracy of computer-guided surgery in partially edentulous patients. Higher accuracy was found when the implants were placed in BES, with CAD/CAM manufactured surgical guides, using a fully guided surgery protocol.

Purpose: This study comprehensively reviewed the current status of digital workflows in fabricating removable partial dentures (RPDs) using evidence from clinical trials and case reports.

Study selection: We performed a systematic review of the literature on the materials and fabrication of RPDs using digital technologies published in online databases from 1980 to 2020. We selected eligible articles from the search results, retrieved information on digital RPDs from these, and conducted a qualitative analysis. We report evidence from clinical papers and case reports, digital impression-taking methods, and maxillomandibular relationship (MMR) records.

Results: A case report electronically published in 2019 introduced a clasp-retained RPD fabricated via a full-digital workflow without a gypsum definitive cast. Computer-aided design and computer-aided manufacturing of double-crown-retained RPDs with nonmetal materials were described in some case reports. Intraoral scanners were used to obtain digital impressions and MMR records in the fabrication of digital RPDs, which have potential advantages for reducing the number of clinical appointments and simplifying laboratory procedures. Evidence from clinical trials is scarce; a randomized controlled trial reported higher patient satisfaction with digital clasp-retained RPDs than with conventional RPDs.

Conclusions: Full-digital RPDs can be fabricated without a gypsum definitive cast. However, the indication for full-digital RPDs is limited to cases with Kennedy Class III/IV partially edentulous arches with several missing teeth. Challenges in digital impression-taking and MMR recording remain to be solved to extend these indications. More evidence from clinical trials is required to evaluate the efficacy and usefulness of digital RPDs.

Purpose: This study comprehensively reviewed the current status of the digital workflow of removable partial dentures (RPDs) and summarized information about the fabrication methods and material properties of the dental framework, artificial teeth, and denture base.

Study selection: We performed a systematic review of the literature published in online databases from January 1980 to April 2020 regarding RPD fabrication and materials used in the related digital technology. We selected eligible articles, retrieved information regarding digital RPDs, and conducted qualitative/quantitative analyses. In this paper, the computer-aided design/computer-aided manufacturing (CAD/CAM) framework, artificial teeth, and denture base materials are reported.

Results: A variety of materials, such as cobalt-chromium alloy, titanium, zirconia, and polyether ether ketone, are used for dental CAD/CAM frameworks. The mechanical strength of the metal materials used for the CAD/CAM framework was superior to that of the cast framework. However, the fitness and surface roughness of the framework and clasp fabricated using a selective laser melting (SLM) method were not superior to those obtained via cast fabrication. Most material properties and the surface roughness of poly methyl methacrylate (PMMA) discs used for digital RPDs were superior to those of heat-cured PMMA.

Conclusion: The use of a CAD/CAM framework and PMMA disc for digital RPDs offers numerous advantages over conventional RPDs. However, technical challenges regarding the accuracy and durability of adhesion between the framework and denture base remain to be solved. In digital fabrication, human technical factors influence the quality of the framework.

Purpose: To measure the accuracy of the additively manufactured casts with 3 base designs: solid, honeycomb-structure, and hollowed bases.

Methods: A virtual cast was used to create different base designs: solid (S Group), honeycomb-structure (HC group), and hollowed (H group). Three standard tessellation language files were used to fabricate the specimens using a material jetting printer (J720 Dental; Stratasys) and a resin (VeroDent MED670; Stratasys) (n=15). A coordinate measuring machine was selected to measure the linear and 3D discrepancies between the virtual cast and each specimen. Shapiro-Wilk test revealed that all the data was not normally distributed (P<.05). Kruskal Wallis and Mann Whitney U tests were used (α=.05).

Results: The S group obtained a median ±interquartile range 3D discrepancy of 53.00 ±73.25 µm, the HC group of 58.00 ±67.25 µm, and the H group of 34.00 ±45.00 µm. Significant differences were found in the x- (P<.001), y- (P<.001), and z-axes (P<.001), and 3D discrepancies among the groups (P<.001). Significant differences were found between the S and H groups (P=.002) and HC and H groups (P<.001) on the x-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the y-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the z-axis; and S and H groups (P<.001) and HC and H groups (P<.001) on the 3D discrepancy.

Conclusion: The base designs influenced on the accuracy of the casts but all the specimens obtained a clinically acceptable manufacturing range. The H group obtained the highest accuracy.

Purpose: This study aims to evaluate the effects of cement shade, restorative material type, and thickness on the final color of resin-matrix ceramics.

Methods: Ninety A2 shade resin-matrix ceramic specimens were prepared from Vita Enamic, GC Cerasmart, and Lava Ultimate at 0.5 and 1.0 mm thicknesses. Sixty resin cement disks were fabricated from different shades (A1, A3O, B05, and TR) of RelyX Ultimate at 0.1 mm thickness. CIE color coordinates were measured using a spectrophotometer, and color differences (∆E₀₀) were calculated. Data were statistically analyzed (P =0.05).

Results: The ΔE₀₀ values were influenced by the cement shade, restorative material type, thickness, and their interactions (P < 0.05). A3O cement caused clinically unacceptable values for all groups at 0.5 mm thickness and GC at 1.0 mm thickness. A1 and TR cement shades demonstrated visually perceptible but clinically acceptable values, except for VE-A1 and LU-A1 at 0.5 mm thickness. The ∆E₀₀ values of the B05 cement shade were lower than the visually perceptible threshold for both thicknesses except for GC at 0.5 mm thickness.

Conclusion: The shade of the resin cement and the type and thickness of the resin-matrix ceramic material significantly affected the resulting final color. To provide a shade matching with natural dentition and to obtain esthetic restorations, especially for the anterior teeth, the resin cement shade and resin-matrix ceramic material should be carefully selected.

Purpose: Removable dentures are a reasonable option for prosthetic treatment. However, continuous residual ridge resorption and reline procedures are inevitable owing to the strong pressure exerted on the mucosa or inappropriate pressure distribution. This study aimed to elucidate the association between the gonial angle on orthopantomogram (GAO) with occlusal force and reline frequency in removable partial denture wearers.

Methods: Participants were patients who had previously received removable partial denture treatment for a free-end defect. Age, sex, number of remaining teeth, remaining opposing teeth, and occlusal support were investigated. GAO was measured using panoramic radiographs. The mean relining interval was calculated as the mean number of days between denture insertion and the first relining or subsequent relining. The association between the mean relining interval and each factor was investigated.

Results: Sixty-five subjects (33 females) were analyzed. The median value of the mean relining interval was 533.3 days, and the median GAO was 123°. There was a significant positive correlation between the mean relining interval and GAO (rs = 0.335). The number of remaining opposing teeth and occlusal support exhibited weak negative correlations with mean relining interval (rs = -0.187 and -0.214, respectively). Multivariate analysis using a generalized linear model showed that GAO was a significant explanatory variable for the mean relining interval.

Conclusion: Within the limitations of this study, GAO was found GAO was found to contribute to the increased frequency of relining due to ridge resorption in patients with a small GAO.

Purpose: To design an efficient tongue prosthesis with reproducibility and to objectively evaluate improvement in speech function.

Methods: A silicon anatomical artificial tongue (AT) and a flat surface artificial tongue system (FTS) were used in our study. Twenty healthy participants (10 males and 10 females, 26.3 ± 1.8 years) were fitted with a tongue movement suppression appliance (TSA) that fit the dental arch to simulate the glossectomy condition. TSA, TSA + FTS, and TSA + AT simulated the state of glossectomy patients without artificial tongue, with normal artificial tongue, and newly designed artificial tongue, respectively. Three speech intelligibility tests were performed for each of the following conditions: pronouncing 100 Japanese monosyllables, 40 Japanese words, and reading a short story. One-way ANOVA, Wilcoxon signed-rank test, and Tukey-Kramer post-hoc test were used for statistical analyses.

Results: Significant differences were observed for 100 Japanese monosyllables and 40 Japanese words between the TSA + FTS, TSA, and TSA + AT conditions (p < 0.05). Regarding the speech intelligibility test for reading a short story, the TSA + FTS condition resulted in a significantly higher speech intelligibility than the TSA and TSA + AT conditions (p < 0.05).

Conclusion: A flat surface artificial tongue system contributed to the improvement in speech function. This structure can be easily used in cases where conventional artificial tongue are applicable, regardless of variation in the oral condition; thus, making it a widely applicable treatment option for glossectomy patients.

Purpose: The purpose of the present study was to explore the factors related to oral health-related quality of life (OHRQoL) in elderly patients who underwent prosthetic treatment with removable dentures through several objective and subjective examinations and to analyze their interrelationships.

Methods: The current study involved 78 denture wearers, aged 65 years or above, who underwent treatment at the clinic of prosthodontics and undertook routine checkups. The present study used eight age-matched patients with healthy dentition as controls. The following items were evaluated: OHRQoL (Oral Health Impact Profile), main occluding area, maximal occlusal force, masticatory performance, and masticatory ability. Spearman’s rank correlation coefficient was used to assess the correlation between the OHIP score and each item and multiple linear regression analysis with the backward elimination method was used to analyze the factors affecting the OHIP score (α = 0.05).

Results: The OHIP summary score was significantly correlated with the number of occlusal supports, number of remaining teeth, maximal occlusal force, and the masticatory ability score. The multiple regression analysis revealed that the number of occlusal supports, the number of remaining upper teeth, whether the upper main occluding area was the remaining tooth or not, and the masticatory ability score were the significant independent variables that affected the OHIP summary scores.

Conclusion: The present study verified the relationship between the OHRQoL and the occlusion of remaining teeth or the items derived from the main occluding areas. The current results suggest that retaining the maxillary first molar is a key factor in the OHRQoL.

Purpose: The antifungal property of chitosan (Ch) in denture base resin (DBR) was well established. Ch influence on the mechanical properties of DBR is less studied in the literature and is vital for clinical success of denture. This study estimates the effect of different concentrations of Ch on the flexural strength (FS), fracture toughness (FT), impact strength (IS) and surface roughness (Ra) in heat polymerized DBR.

Methods: A total of 160 samples were divided into 4 groups (n =10) by weight percentage - Ch 0, Ch 5, Ch 10, Ch 15. FS and FT were estimated by three-point bending test. IS was determined by Charpy test. Ra was evaluated by non-contact laser surface profilometer. The tested samples were characterized by scanning electron microscope and Fourier transformation infra-red spectroscopy. Data were statistical analyzed with one-way ANOVA and Post hoc Bonferroni test.

Results: FS, FT and IS improved with Ch addition when compared to control group. Ch5 showed higher “FS, FT, IS. (p<0.001)”. Increased Ra was observed in Ch5 and Ch10 with significant statistical differences among the groups. (p <0.001) Ch15 displayed decrease in Ra compared to control group.

Conclusion: The addition of Ch to DBR improved the “FS, FT, IS at 5%wt and Ra at 15%wt” of Ch.

Purpose: The shear bond strength of conventional zirconia (3Y-TZP), translucent zirconia (5Y-PSZ), and titanium alloy (Ti6Al4V) thermocycled using different phosphate monomer resin cements were investigated.

Methods: In this study, 120 specimens of 3Y-TZP, 5Y-PSZ, and Ti6Al4V were cemented to nanocomposite resin cylinders using PANAVIA™ V5 and Rely X™ U200. The bond area and resin cement thickness were controlled as per ISO 29022:2013 and 4049:2009. Each resin cement group was used with/without the Clearfil ceramic primer plus. The shear bond strength of the 12 groups was statistically analyzed using two and one-way ANOVA to determine the properties of the different materials and resin cements (α = 0.05). The mode of failure was observed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

Results: The titanium alloy groups showed better shear bond strength than the zirconia groups (p < 0.05). PANAVIA™ V5 without primer showed significantly lower shear bond strength than other cements in zirconia and titanium alloy specimens (p < 0.05). Titanium alloy with Rely X™ U200 with a Clearfil ceramic primer plus showed the highest shear bond strength (6.37 ± 1.60 MPa). SEM images showed mixed failures in zirconia groups and cohesive failures in titanium alloy groups.

Conclusion: The titanium alloy showed better shear bond strength than zirconia when the Clearfil ceramic primer plus was used. The primer solution containing MDP and resin cement with phosphoric methacrylate ester showed similar shear bond strength with 3Y-TZP and 5Y-PSZ. The resin cement without phosphate monomers demonstrated the least shear bond strength.

Purpose: This retrospective study evaluated the periodontal tissues of the abutment teeth of removable partial dentures (RPDs) with rigid retainers and major connectors in patients with and without type 2 diabetes mellitus (T2D).

Methods: A total of 313 patients who had been treated with RPDs, including rigid retainers and major connectors, were divided into two groups: T2D and non-T2D. The periodontal parameters and radiographic bone heights of the abutment teeth were evaluated at baseline and at a 5-year examination during supportive periodontal therapy (SPT). For patients with accessible standardized radiographs, bone density was analyzed based on the gray level (GL) using digital subtraction radiography (n = 83).

Results: Overall, 739 abutment teeth (86 in the T2D group) of 235 patients (25 in the T2D group) were analyzed, and 95.0% (94.2% in the T2D group, and 95.2% in the non-T2D group) were maintained. The mean probing pocket depth significantly increased in both groups (p < 0.001). There were significant changes in the radiographic bone height (p = 0.038) and GL on the side of the denture base area (p = 0.048) in the T2D group compared to those in the non-T2D group.

Conclusion: Regardless of T2D, RPDs with rigid retainers and major connectors could prevent the progression of periodontal disease and successfully maintain most of the abutment teeth during 5-years of SPT. However, T2D may be significantly associated with loss of bone height reduction and density on the side of the denture base area.

Purpose: Bone morphogenetic protein (BMP)-2 is a potent growth factor that is widely used in the orthopedic and dental fields for bone regeneration. However, recombinant human BMP-2 (rhBMP-2) products have not been legally approved in Japan. Recently, our research group succeeded in producing GMP-grade rhBMP-2 using the E. coli system (E-rhBMP-2) at the industrial level and developed E-rhBMP-2 adsorbed onto β-TCP (E-rhBMP-2/β-TCP) as an alternative material to autogenous bone grafts. Previous studies on the toxicity, pharmacokinetics, and optimal doses of E-rhBMP-2 have confirmed its safety and efficiency. However, comparative studies with standard treatment therapies are still necessary before clinical application in humans. Therefore, in this preclinical study, we compared the bone regeneration ability of E-rhBMP-2/β-TCP and autogenous bone grafts in a canine guided-bone regeneration model.

Methods: Following extraction of the maxillary third premolar, box-type bone defects (10 mmL × 4 mmW × 9 mmH) were created in the extraction socket area and transplanted with E-rhBMP-2/β-TCP or autogenous bone graft in a canine. After 8 weeks, micro-CT and histological analyses were performed.

Results: Transplantation of both E-rhBMP-2/β-TCP and autogenous bone graft significantly promoted bone formation compared to the non-transplantation control group. The bone formation ability of E-rhBMP-2/β-TCP was equal to that of the autogenous bone graft. Histological analysis showed that excessive infiltration of inflammatory cells and residual β-TCP particles mostly were not observed in the E-rhBMP-2/β-TCP transplantation group.

Conclusion: This preclinical study demonstrated that E-rhBMP-2/β-TCP and autogenous bone have equal potential to promote bone regeneration.

Purpose: To compare the effect of 4-META/MMA-TBB resin, which can provide hybrid layer formation, and acid-base cements on survival, complications, and failure risks of full-coverage retainers evaluated for 15 years.

Methods: A total of 1,161 abutment teeth in 260 patients treated with at least one single crown or fixed partial denture were recalled for clinical examination. Survival was defined as not having undergone extraction of abutments or renewal of prostheses. Secondary caries, pulp necrosis, or prosthesis detachment were recorded as complications. Survival and complications rates were analyzed using the Kaplan–Meier method and log-rank test. Multivariable analysis of factors associated with failure or complications using Cox’s proportional hazard regression model was performed (α = 0.05).

Results: Significant differences were observed in survival (p = 0.007), secondary caries (p = 0.000), and prosthesis detachment (p = 0.025) complications between luting agents. The 5-, 10-, and 15-year survival rates for 4-META/MMA-TBB resin were 95.2%, 90.5%, and 90.5%, while those of acid-base cements were 93.2%, 80.6, and 67.4%, respectively. Secondary caries and prosthesis detachment complications for 4-META/MMA-TBB resin were 1.9% and 0.5%, whereas those for acid-base cements were 15.2% and 4.3% respectively. Acid-base cements were associated with a 1.664-, 2.950-, 3.333-, and 4.444-times greater risk of failure, prosthesis renewal, secondary caries, and prosthesis detachment, respectively.

Conclusion: 4-META/MMA-TBB resin has higher long-term survival rate with lesser caries, and prosthesis detachment than acid-base cements. The ability of this resin to create an acid-base resistant hybrid layer may contribute to a life-long function of tooth abutment.

Purpose: To evaluate the effect of three different designs and two monolithic ceramic materials on the durability and fracture resistance of endocrowns on maxillary first premolars, in comparison to post-and-core crowns.

Methods: Fifty-six maxillary premolars were endodontically treated and shortened to a level of 2 mm from the cervical line, and randomly categorized into six endocrown groups and post-and-core crown control group (n=8); E1; endocrowns with flat occlusal table (without ferrule), E2; endocrowns with 1.5 mm circumferential ferrule, E3; endocrowns with 1.5 mm buccal ferrule preparation. Two materials were used for endocrowns: zirconia (4YSZ; Z), and lithium disilicate (L). The control group was restored with zirconia posts, and lithium disilicate crowns. All restorations were bonded using Panavia V5 and its respective primers and underwent thermo-mechanical fatigue with a 10 kg dynamic load for 1,200,000 cycles and thermocycling between 5 and 55 °C. Thereafter all survived specimens were loaded to fracture. The results were statistically analyzed using ANOVA and T-Test.

Results: None of the specimens showed any signs of debonding or fracture caused by the fatigue test. The PC control group showed no statistically significant difference in comparison to groups ZE1, ZE2 and LE2 (p > 0.05). However, it was significantly different from groups LE1, LE3, and ZE3 (p ≤ 0.05).

Conclusions: Preparation designs and materials affected the fracture resistance of endocrowns. The results showed a superiority of the post-and-core crowns, zirconia/lithium disilicate endocrowns with 1.5 mm circumferential ferrule, and zirconia endocrowns with the flat occlusal table.

Purpose: Zirconia cores and frameworks are widely used in restorative dentistry. Although these structures are veneered with porcelain for esthetic reasons, the use of indirect composite resins (ICRs) is expected to increase in the future. The purpose of this study was to investigate the effects of microslits of different dimensions formed by Nd:YVO₄ laser machining on the bond strength between two types of zirconia (3 mol% yttria-partially stabilized zirconia (Y-TZP) and ceria-partially stabilized zirconia/alumina nanocomposite (Ce-TZP/A)) and porcelain or an ICR.

Methods: The zirconia disks were assigned as follows: 1) blasted with alumina particles (AB) and 2–4) surface machined with gridded microslits with a width, pitch, and depth of 50, 75, or 100 µm (MS50, MS75, and MS100, respectively). After the bonding of the veneering materials to the disks, half of the specimens veneered with the ICR were subjected to thermocycling (4–60°C, 20000 cycles). All the specimens were subsequently shear tested (n = 10/group).

Results: There was no significant difference between the groups of the disks bonded to porcelain. On the other hand, for the disks bonded to the ICR, the bond strengths of the MS groups after thermocycling were statistically higher than that of the AB group. However, there was no significant difference in the bond strengths of the disks with different microslits.

Conclusion: Within the study limitations, it can be concluded that, for porcelain, the design of the mechanical retentive structure must be modified. However, for the investigated ICR, a simple gridded pattern can improve the bond strength with zirconia.

Purpose: The lack of occlusal support is an epidemiological risk factor linked to Alzheimer’s disease. This study sought to assess the relationship between amyloid β (Aβ) deposition and the lack of occlusal support in amyloid precursor protein (APP) knock-in mice.

Methods: Sixteen experimental animals were divided into two groups. The upper molars were extracted in the extraction group (group E), and a sham operation was performed in the control group (group C). The Morris water maze test was performed 4 months after the tooth extraction. Aβ immunohistochemical staining and Nissl staining of the hippocampus were performed. Hippocampal plasma corticosterone and Aβ protein levels were measured.

Results: In the maze task, the escape latency was significantly longer in group E than in group C. In the probe trials, the time elapsed in the target quadrant was significantly shorter in group E than in group C. The number of hippocampal neurons decreased in group E. There was no significant difference in the plasma corticosterone levels between the two groups, indicating that there was no effect of chronic stress on the behavioral results. Hippocampal Aβ40 and Aβ42 protein levels and Aβ deposition areas by immunohistochemical staining were not significantly different between the two groups.

Conclusion: Aβ deposition was not increased in the hippocampus of molarless APP knock-in mice. As such, it appears that cognitive impairment due to a lack of occlusal support was not related to Aβ deposition.

Purpose: This study aimed to compare the short-term effects of thermoplastic resin removable partial dentures (TR-RPDs), referred to as non-metal clasp dentures, with those of metal-clasp-retained RPDs (MC-RPDs) on the periodontal health of abutment teeth.

Methods: A randomized cross-over trial was conducted in 28 partially dentate patients. Participants were randomized into two groups and received MC-RPDs followed by TR-RPDs, or vice versa, for 3 months. Periodontal clinical parameters, such as the plaque index, gingival index, probing pocket depth, tooth mobility, and microbiological status of the abutment teeth, were evaluated at the delivery and 3 months after using each RPD.

Results: Of the 28 patients enrolled, 24 (mean age, 67.3 years) completed the trial, and 55 abutment teeth were evaluated. The periodontal condition of the abutment teeth did not deteriorate after 3 months of using both types of RPDs. There was no statistically significant difference in the plaque index, gingival index, probing pocket depth, tooth mobility, and the red complex bacteria between TR- and MC-RPDs (p >0.05). The Periotest value for TR-RPDs was significantly lower than that for MC-RPDs (p <0.05). However, this difference was not clinically significant.

Conclusions: These results suggest that the influence of TR-RPDs on the periodontal health of abutment teeth was limited within 3 months of use.

Purpose: The purpose of this study was to examine the wear of resin materials using two-body wear tests and to verify a selection method for optimal interim restoration materials from findings of a diagnostic occlusal device.

Methods: Specimens were prepared from nine different resins used for diagnostic occlusal devices (soft resin) and interim restorations. Wear tests were conducted using an abrasion testing machine. The resulting wear on resin specimens and antagonist stainless-steel styluses was measured using a laser confocal scanning microscope, and the surface conditions were observed through a scanning electron microscope. The data were analyzed with one-way ANOVA and Tukey’s multiple comparison test. The findings of the previous study on diagnostic occlusal devices were referred to in order to verify the selection method of optimal interim restoration materials.

Results: The maximum wear depth of the soft resin specimens was significantly greater than that of the other specimens (p<0.05) and was equivalent to the wear depth of a diagnostic occlusal device used for 14 nights. The wear of bis-acryl resin material was shallower than that of the other materials (Polymethyl methacrylate and polyethyl methacrylate), and its antagonist stylus was significantly worn (p<0.05).

Conclusion: The findings of the previous and present studies showed a relationship among the parameters of Electromyography, wear depth of the diagnostic occlusal device, and wear of materials used for interim restorations. Findings related to bruxism can guide in the selection of interim restoration material and the determination of a suitable duration of wear.

Patient: A 54-year-old woman presenting with anterior alveolar ridge resorption was submitted to a connective tissue graft (CTG) for esthetic improvement before rehabilitation with a fixed partial denture. Palate-harvested connective tissue was used as a graft after extra-oral removal of the epithelium. Unexpectedly, complete wound healing was not observed. Moreover, 6 months post-surgery, a white discharge was detected at the grafted site. The adjacent tooth showing a root fracture was initially associated with the symptoms and was then extracted. Concomitantly, the unhealed tissue at the grafted site was also excised, leading to temporary symptom resolution. However, the white discharge reappeared after 2 months. The excision area was expanded to remove the grafted tissue entirely, and the wound was completely healed. Since the alveolar ridge resorption had become larger compared to the preoperative condition, the patient was subjected to a second CTG, now using a connective tissue harvested from the palate by a single incision technique. The wound healed uneventfully, and the final prosthesis was delivered 6 months after soft tissue stabilization. The patient has been followed-up for more than 28 months without any recurrence of white discharge.

Discussion: Histopathological and cytological examination detected keratinized epithelial tissues and cells, respectively, in excised tissues and white discharge specimens. Consequently, a possible relationship between white discharge and residual epithelium in the harvested graft was strongly suspected.

Conclusion: Success of the CTG procedure requires careful method selection for tissue transplantation and treatment execution.