• Accuracy of Dynamic Virtual Articulation: Trueness and Precision

      Hsu, Michael; Masri, Radi, 1975- (2020)
      Purpose: To study the effects of altering condylar settings and pin openings on the trueness and precision of virtual articulators versus mechanical articulators. Materials and Methods: Maxillary and mandibular typodonts with fiducial markers were mounted on a mechanical Artex-CR articulator and the mandibular teeth were prepared to allow guidance solely by the posterior determinants of the articulator and the incisal table. The relationship of the mounted typodonts was preserved digitally by scanning using manufacturer transfer plate adaptors. On the mechanical articulator, pattern resin was allowed to set between the maxillary and mandibular occlusal surfaces (area #25-30) at the endpoints of dynamic movements at three different condylar inclinations (SCI): 10°, 30°, and 45°, n=12/inclination, or at three different incisal pin openings (2, 5, and 10 mm, n=12/opening). All other articulator settings were kept constant. Resin specimens attached to the typodonts were scanned within five minutes of setting, then removed and the articulated typodonts rescanned. FDPs #25-30 were designed on the virtual articulator using identical parameters to the mechanical articulator. Dynamic virtual movements were used to sculpt the design and a file of the design was saved. The files of both types of samples were aligned and overlaid. Interocclusal separation was measured in triplicate at the indentation created by the mesiolabioincisal point angle on the incisal edge of #8 and the mesiobucco-occlusal point angle of #3. Trueness and precision of both types of articulators were calculated and compared using one-way ANOVA, followed by the Tukey HSD test (α=.05). Results: There was no statistically significant difference at altered pin openings in either trueness (F<.202, p>.37) or precision (F<3.134, p>.09) for the majority of measurements. The only significant difference was in the precision between the two types of articulators at 5mm incisal opening, and only at the anterior measurement point (F=15.134, p=.0008). However, these differences were less than 100 μm. When the SCI was altered, there was no statistically significant difference (F< 3.624, p>.05) between the virtual and mechanical articulators in trueness for 5 of the 6 measurements obtained (F<3.624, p>.07) or for all of the precision measurements (F<3.529, p>.07). The one trueness measurement that was significantly different (F=9.237, p=.006 ) occurs at SCI of 10º, and it was less than 100 μm. Conclusions: Dynamic movements on the virtual articulator were shown to be as true and precise as to the mechanical articulator. When there were deviations, these deviations were less than 100 μm and thus, these deviations may not be clinically relevant.
    • Alcohol-Induced Migraine: An Animal Model

      ALABWAH, YAQOUB; Masri, Radi, 1975-; 0000-0002-5952-9182 (2015)
      Migraine is a recurring moderate to severe, unilateral, disabling headache that can result in a progressive, chronic disease state. Migraine attacks can be triggered by factors or events, which precede the attack. Multiple trigger factors have been reported including alcohol intake. In this research project, we developed an animal model of chronic migraine, in which signs of migraine can be triggered by alcohol administration. In this animal model, repeated administration of potassium chloride to the dura, sensitizes dural afferents and renders animals susceptible to alcohol-induced ongoing pain, and hyperalgesia. Unlike most of the animal models of migraine headaches that relied exclusively on reflexive measures of evoked pain, we tested for the presence of ongoing pain after repeated potassium chloride administration to the dura. We used the conditioned place preference paradigm and the rat grimace scale tests to test the ongoing pain. Our results show that repeated potassium chloride administration to the dura caused aversion of rats to potassium chloride paired chamber. Following Alcohol IV administration, the rats present with a significant, time dependent increase in orbital tightening score, which suggest that the animals develop pain, a sign of migraine headache. Our results suggest a probable association between alcohol and development of ongoing pain in animals receiving repeated administration of potassium chloride. This model can be used to investigate the pathophysiology of alcohol-induced migraines and how it is initiated.
    • Bacterial Adhesion to Various Implant Surfaces

      Khatra, Navpreet Kaur; Masri, Radi, 1975- (2018)
      Dental implants provide a major course of treatment for patients who are partially or completely edentulous. These implants are biocompatible metal anchors that are surgically positioned in the jawbone to support the prostheses where natural teeth are missing. However, the use of dental implants has some disadvantages, which can result in complications. Once the clean implant surface is exposed in the oral cavity, it is immediately coated with salivary pellicle and subsequently colonized by oral microbial species. In fact, microbial adhesion and accumulation on implants are considered to play major roles in the pathogenesis of peri-implant mucositis and peri-implantitis. The physico- chemical characteristics of specific material surface are known to significantly influence the bacterial adhesion process. Therefore, the surface characteristics of dental implants have been refined and restructured over a period of time to improve the interaction of implants with host cells and tissues. Hence, investigating the microbiological aspects related to implant surfaces will provide important insights relevant to expectations of treatment outcome. To that end, in this study, we aimed to comparatively evaluate microbial adherence and accumulation on five different types of implants. Specimens were provided by Dental Implant Systems, Biodenta Group and implant surfaces included: .3- .5 μm anodized surface, 1 μm BST surface, .8- 1.0 μm anodized surface, 1.6μm SLA surface and .3- .4 μm machined surface. To assess microbial adherence, the cariogenic bacterial species Streptococcus mutans and the bacterial pathogen Staphylococcus aureus were studied. Results from these studies were analyzed using analysis of variance (ANOVA) and significant differences were further analyzed by Tukey’s Honestly Significant Difference (HSD) test. Pearson’s r was also used to evaluate the association between surface roughness and bacterial accumulation. The present study has demonstrated that not only surface roughness but other physicochemical properties such as surface charge, energy, wettability and biological factors such as host immune response and oral hygiene influence bacterial adhesion and accumulation around implant surfaces.
    • CAMBRA and its effect on surface roughness of various restorative materials

      Bolding, Lauren Mills; Masri, Radi, 1975-; Driscoll, Carl F. (2012)
      Purpose: The purpose of this study was to investigate the effect of various anti-caries agents on the surface roughness of three different restorative materials. Materials and Methods: Sixty-four specimens of each material (porcelain, base metal and titanium alloy) were prepared and separated into four groups for soaking in anti-caries agents (Prevident, ACT, chlorhexidine and water). A profilometer was used to measure surface roughness before and after soaking for two years simulated usage. The change in surface roughness for each specimen was calculated. Statistical analysis was completed using a factorial analysis of variance (two-way ANOVA) followed by Tukey's HSD test. A p value ≤0.05 was considered significant. Results: The results demonstrate that there was no significant difference in mean change in surface roughness between the three materials, porcelain, base metal, and titanium. The results further demonstrate that there was a significant difference in mean change in surface roughness between Prevident Dental Rinse and chlorhexidine gluconate. There was no significant difference between water, ACT, and chlorhexidine gluconate. There was also no significant difference between Prevident Dental Rinse, water, and ACT. There was a significant interaction between Prevident Dental Rinse and chlorhexidine within the porcelain samples. Prevident Dental Rinse produced a negative change in surface roughness while chlorhexidine gluconate produced a positive change in surface roughness. Conclusion: Within the limitations of this study, it can be concluded that Prevident Dental Rinse and chlorhexidine gluconate may cause a change in surface roughness of porcelain when used for a period of two years. Prevident Dental Rinse may cause an increase in surface roughness of porcelain while chlorhexidine gluconate may cause a decrease in surface roughness of porcelain.
    • Comparative Microbial Adherence to Various Implant Dental Restorative Materials

      Alshehri, Malek Rofidi A; Masri, Radi, 1975- (2018)
      The oral cavity contains the most complex microbial community of the body, which has more than 700 bacterial species. These microbial species colonize different habitats in the oral cavity. The biological interaction between dental restorative materials and the encompassing oral microbes is one of the most important factors for their clinical prognosis. Many studies have shown that there are distinctive interactions between the rate of microbial formation and the restoration material itself. Currently, there are several Implant Dental Restorative Materials on the market like poly-methyl methacrylate, feldspathic porcelain, dental zirconia, and dental composite resin. The purpose of this study was to comparatively evaluate initial adherence for C. albicans and S. aureus on five different implant dental restorative materials. Ten samples/group were constructed as 5mm x 5mm x 2.5 mm rectangles and were fabricated as per the manufacturer's instructions for each groups. Five groups were made from different types of materials: Polymethyl methacrylate denture material processed with the compression molding technique (PMMA), computer-aided design and computer-aided manufactured dental acrylic (CAD/CAM PMMA), feldspathic porcelain, dental zirconia, and pink dental composite resin. There was a significant difference between the five groups for C. Albicans (F=891.16, p=.0005). CFUs/ml for the pink dental composite resin were significantly higher than the other four groups. However, The dental zirconia group showed the lowest CFUs/ml for initial adherence between all the groups. For S. aureus, CFUs/ml for the pink dental composite resin was significantly higher than the other four groups. Heat polymerized PMMA and the CAD/CAM PMMA group showed significantly higher CFUs/ml than Feldspathic porcelain and dental zirconia groups. In conclusion, there was a significant difference between the five groups for initial adherence of C. albicans and S. aureus. The dental zirconia group showed the lowest initial adherence and the pink dental composite resin group showed the highest initial adherence for both microbes. Within limitation for this study, understanding what is the best for final dental restorative material from aspect of how much it could harbor microbes is an important factor in the final success of treatment and this study investigated this aspect under control conditions.
    • Dimensional Stability of CAD/CAM Patterns: A Longitudinal Study

      Byun, Shane S.; Masri, Radi, 1975- (2020)
      The goal of this study was to investigate the accuracy, over time, of computer-aided design and computer-aided manufactured (CAD/CAM) dental patterns in two different materials (resin and wax) using two different fabrication methods (subtractive and additive manufacturing). The intaglio surface of the patterns (n=48/time period) were evaluated at five predetermined time periods (zero minutes, 20 minutes, 24 hours, one week, and two weeks) relative to fabrication time. Intaglio surface scans of the generated samples were aligned with the Best Fit alignment to the design file (.stl) and compared with 3D Compare on Geomagic Control X to obtain the deviations as a root mean square (RMS). Trueness of the patterns were compared at all time points using three-way Analysis of Variance (ANOVA) (=.05). Accuracy of dental patterns deteriorated over time. When materials were considered, wax had better dimensional stability than resin. When fabrication method was considered, milled patterns had better dimensional stability than printed patterns. Time, material type, fabrication method, and all their interactions, showed a significant effect, however, the differences were very small (ranging from <1 m to 20 m). Thus, both resin and wax CAD/CAM patterns fabricated by additive and subtractive manufacturing can be used to produce dental restorations with acceptable accuracy.
    • The Effect of Bar Design and Repetitive Loading on the Reverse Torque Values of Lateral Set Screws

      Yahya, Jenin Hilmi; Masri, Radi, 1975- (2015)
      Statement of problem: Utilizing set screws allows easy retrieval of the prostheses with minimum cost and satisfies esthetic requirements. Set screws use is mostly governed by retrospective, anecdotal and clinical reports. The purpose was to investigate the difference in reverse torque values of fatigued one set screw or two set screws used to retain straight or curved implant prostheses in vitro. Materials and methods: Milled substructures (straight and curved) and cast superstructures retained by one or two set screws were used. There were four groups (n=8). Set screws were tested for changes in reverse torque values after simulated chewing of six months. Data (Ncm) was analyzed using 2-way ANOVA (p≤0.05). Results: No statistically significant difference in the reverse torque values between prostheses retained by one set screw and two set screws (F = 0.18, p = 0.67) or between prosthesis retained on curved bars and straight bars (F = 0.42, p = 0.52). No significant interaction was found in the reverse torque values between the number of set screws and substructure design (F = 0.32, p = 0.58). Conclusions: Under functional loading the reverse torque values are not affected by the design of the prosthesis or the number of set screws used to retain the prosthesis.
    • The Effect of CAMBRA Agents on Fracture Strength of Lithium Disilicate Crowns

      Sinada, Naif Ghazi; Masri, Radi, 1975- (2017)
      The Caries Management By Risk Assessment (CAMBRA) protocol outlines an approach in which certain agents can be used to serve as protective factors toward the management of dental caries. In this study, the effects of particular CAMBRA agents on the fracture strength of lithium disilicate ceramics (commonly used in dentistry) are studied. While Chlorhexidine exhibited no effects on the fracture strength of these ceramics, Prevident showed a decrease in the fracture strength of all the ceramics studied. These results indicate that clinicians should proceed with caution when using these CAMBRA agents in patients restored with lithium disilicate ceramics. Further studies on the particular mechanisms whereby this reduction in fracture strength occurs are indicated.
    • The Effect of CAMBRA Recommended Anti-Caries Agents on Surface Roughness of Lithium Disilicate Ceramics

      Ghunaim, Dima Hanna; Masri, Radi, 1975-; Driscoll, Carl F. (2014)
      Purpose: The purpose of this study was to explore the clinical importance of the effect of Prevident and chlorhexidine on the surface roughness of three commonly utilized lithium disilicate ceramics: pressed (Press), milled (CAD), milled and veneered with fluorapatite (CAD/CERAM). Methods and Materials: Seventy-six rectangular specimens in each group of Press, CAD, and CAD/CERAM were fabricated. A profilometer was used to measure the surface roughness prior to and after soaking. The samples were immersed in the assigned anti-caries solution in an airtight plastic container. For the simulation of 2 years use the samples were soaked in chlorhexidine for 3 hours, Prevident, 6% alcohol and distilled water for 12 hours. Statistical analysis was completed using a two-way ANOVA followed by Tukey's HSD test. A p value ≤.05 was considered significant. Results: The results demonstrated that Press samples became significantly rougher. In addition to that, the surface roughness of CAD and CAD/CERAM was significantly decreased. However, CAD was significantly less rough than CAD/CERAM. Water did not significantly change the surface roughness of ceramics, while 6% alcohol, Prevident, and chlorhexidine significantly decreased the roughness of the ceramics. There was no significant difference in the increase of surface smoothness among the three solutions. A significant interaction was found only with water, the control. Conclusion: Within the limitations of this study, it can be concluded that Prevident and chlorhexidine can change the surface roughness of lithium disilicate ceramics when used for a period of 2 years. The surface roughness of Press increased, while that of CAD and CAD/CERAM decreased.
    • The Effect of Cementation Techniques on Marginal Seal of Porcelain Veneers

      Okasha, Ismail; Masri, Radi, 1975- (2013)
      Today's society has embarked on a quest for the latest and greatest tools to help enhance esthetics and function. More specific to the realm of dentistry, the demand for treatment of unaesthetic anterior teeth is rapidly growing. The advancement of material science and cementation techniques have paved the way for restorations, such as veneers, as a reasonable alternative to the durable and predictable full coverage crowns that have been used for many years. There is little data, however, in the literature comparing different adhesive cementation techniques and their effect on the marginal integrity. The aim of this study is to measure the marginal discrepancy of porcelain veneers adhesively cemented using four different techniques: fully polymerized with Griptab carrier, partially polymerized with Gribtab carrier, fully polymerized with finger pressure and partially polymerized with finger pressure. Using a micoscope, measurements were taken before and after cementation at four different locations for each fabricated porcelain veneer. The differences in measurements were taken and statistically analyzed. Within the limitations of this study, no significant difference was found among the four test groups and the values of the marginal gap were within clinically acceptable limits. Since the results of the different groups do not deviate between them, clinically, the operator should choose among the above techniques depending on their personal preference.
    • The Effect of Disinfectants on Shade Tabs

      Huang, Peterson Yi-Jen; Masri, Radi, 1975- (2014)
      Statement of problem: Dental shade guides are used to evaluate tooth color prior to restorative and prosthodontic procedures and are subjected to disinfection after use. The effect of disinfection on shade guides has not been thoroughly investigated. Purpose: The purpose of this project was to study the effect of disinfectants on changes in color of shade tabs. Materials and Methods: Changes in color (Delta E) of Vita Classic Shade Guide tabs were measured with a Vita Easyshade spectrophotometer and calculated after being subjected to Cavicide, Asepticare TB, Sporicidin, and distilled water (control) over a simulated two-years period. Statistical analysis was accomplished by a two-way analysis of variance followed by Tukey's HSD test (p<0.05) Results: There was a significant difference in the degree of shade tab color change depending on the type of disinfectant used (F=153.2, p=0.0005). There was no significant difference in the amount of shade tab color change that occurred after disinfection between the different shade tabs used (F=0.611, p=0.87) nor a significant interaction between the type of disinfectant and the different shade tabs used (F=0.7, p=0.92). Aspecticare TB showed the least significant amount of change (Delta E=0.401), Sporicidin (Delta E=0.889) and the control (Delta E=0.969) showed significantly more color change than Asepticare TB but less color change than Cavicide (Delta E=1.198). Conclusion: It has been reported that human observers can be expected to detect color differences of 1 Delta E unit under standardized laboratory conditions (Kuehni 1979). In the oral cavity, however, an average change of 3.7 Delta E units could still allow teeth to be matched as having the same color (Johnson 1989). Therefore, while the results are significant, they may not be clinically important.
    • Effect of drug-eluting nanoparticles (prednisolone) on injured pulp, in vivo

      Choi, Seung Kee; Masri, Radi, 1975- (2017)
      Treatment of irreversible pulpitis is focused on removing the affected tooth structure including the pulp. Pharmacologic treatments may only help control symptoms of pulpitis. This study evaluated the effect of prednisolone-eluting nanoparticles on inflamed pulp in rat teeth. 48 adult rat molar teeth received cavity preparations. After 2 weeks of exposure, only one half of the group received prednisolone. Pulp tissues were harvested at 2, 4, and 24 weeks for PCR to obtain levels of TNF-α, IL-1β, PDGF-α, and TGF. The results were compared at the three time points with 2-way ANOVA and Tukey's HSD test. A p ≤ 0.05 was considered significant. Prednisolone-eluting nanoparticles significantly reduced the level of TGF (F = 4.435, p ≤ .041) but did not significantly affect the levels of TNF-α, IL-1β, and PDGF-α.
    • The effect of electrical stimulation on success of bone grafts: an in vivo study

      Talwar, Garima Kaur; Masri, Radi, 1975-; Driscoll, Carl F. (2012)
      Purpose: Bone grafting is often unpredictable and is associated with reduced success rate, extended healing times and morbidity. Methods that expedite healing and increase predictability will contribute to the overall success of reconstructive efforts. In this project, the effect of electrical stimulation on bone graft healing in rat calvaria was examined. Materials and Methods: Fifteen adult male Sprague-Dawley rats were used. A 7 mm diameter bone defect at the midline of the calvarium was grafted using freeze-dried mineralized bone. Bipolar platinum stimulating electrodes were overlaid on top of the periosteum on the center of the graft. Animals were divided randomly into two groups. The experimental group (n=8) received electrical stimulation (3 times/day for 10 days) and the control group (n=7) received no stimulation. At 6 weeks, the grafted areas together with the surrounding bone were harvested from the cranium. Tissue sections (5-7 μm) were prepared and stained using hematoxylin and eosin. Mounted slides were analyzed and for each animal, the grafted area was marked and the percent of new bone, remaining graft material and connective tissue was calculated. Data was analyzed using ANOVA. A p≤.05 was considered significant. Results: There were statistically significant differences between the experimental and control group. The electrical stimulation group had significantly more (p=0.034) bone (3.81+3.6 %) compared to the control group (0.47+0.52%). The amount of remaining graft material was also significantly higher (p=0.024)in the control group (26.11+6.54%) compared to the stimulation group (16.64+5.28%). No significant difference (p=0.15) was found between the 2 groups in the amount of connective tissue (stimulation: 79+5.47%; control: 73.2+6.82%). Conclusion: In this animal model of bone graft healing, electrical stimulation resulted in significantly more bone formation and less remaining graft material. These findings suggest that electrical stimulation expedites bone graft healing.
    • The effect of grooves on the load to dislodgement of Procera crowns

      Parekh, Monica; Masri, Radi, 1975- (2011)
      Statement of Problem: The objective of this study was to investigate the effect of grooves on a tooth preparation for a full coverage zirconia Procera restoration on the load to dislodgement of Procera zirconia crowns. Methods: Three standardized stainless steel dies were used to simulate a mandibular molar crown preparation with inadequate retention and resistance forms. The first die resembled a preparation with no grooves (control). The second die resembled a preparation with two grooves placed on the mid-mesial and distal walls. The third die resembled a preparation with two grooves as above; however, the grooves were placed after the dies were scanned. The stainless steel dies were scanned to fabricate zirconia abutments. After the addition of porcelain to the copings, the crowns were cemented with zinc phosphate cement. The load to dislodgement was tested via a universal load-testing machine. Data was analyzed using a one-way ANOVA statistical test followed by Tukey's HSD test. Results: There was a significant difference between the three experimental conditions (F = 213.69, p < 0.0001). Procera crowns cemented on the stainless steel dies with grooves prepared before scanning had a significantly higher load to dislodgement than all other groups (3850 ± 370 N). Procera crowns cemented on the stainless steel dies with grooves prepared after scanning exhibited the second highest load to dislodgement (2610 ± 250 N). The lowest value of load to dislodgement was when no grooves were present (2260 ± 300 N). Conclusion: Grooves placed before scanning of dies provided the most improvement load to dislodgement of Procera zirconia crowns.
    • The effect of implant angulation and impression technique on impression accuracy of NobelActive implants.

      Hazboun, Gillian Brewer Alexander; Masri, Radi, 1975- (2013)
      Purpose: The purpose of this study was to measure the accuracy of implant impression techniques in vitro, using closed and open tray impression techniques, for NobelActive implants placed at various angulations. Materials and Methods: Six NobelActive implants were placed in a master cast as follows: 0 degrees of angulation to a line drawn perpendicular to the occlusal plane in the molar area, 15 degrees of angulation to a line drawn perpendicular to the occlusal plane in the premolar area, and 30 degrees of angulation to a line drawn perpendicular to the occlusal plane in the incisor area. Twelve open tray and twelve closed tray impressions were made. Occlusal, lateral and frontal view photographs of the resulting casts were taken and analyzed in Adobe Photoshop. Linear displacement was measured in micrometers and angular displacement was measured in degrees. Statistical analysis was performed using a factorial analysis of variance (two-way ANOVA) and Tukey's Honestly Significant Difference test. A p value of ≤ 0.05 was considered significant. Results: There was no significant difference found in the accuracy of impressions made of NobelActive implants using the open or closed tray technique when measured in micrometers or degrees. In addition, there was no significant difference found in the accuracy of impressions made of NobelActive implants placed at 0, 15 or 30 degrees of angulation to a line drawn perpendicular to the occlusal plane when measured in micrometers or degrees. Finally, there was no significant interaction found between impression technique and implant angulation on NobelActive implants. Conclusions: Within the limitations of this study, impression technique (open vs. closed tray) and implant angulation (0, 15, and 30 degrees to a line drawn perpendicular to the cast) did not have a significant effect on the accuracy of in vitro impressions made of NobelActive implants.
    • The Effect of Impression Technique, Connection Type and Implant Angulation on Impression Accuracy

      Kempler, Joanna; Masri, Radi, 1975- (2011)
      Purpose: To measure the accuracy of implant impression techniques in vitro, using open and closed tray techniques with internal and external connection implants at various angulations. Materials and Methods: Three internal connection implants and three external connection implants were placed in an acrylic master cast as follows from posterior to anterior: 90, 15 and 30 degrees. Twenty-four open tray and closed tray impressions were made and the resulting casts were analyzed using digital photography. The following measurements were performed (1) horizontal displacement; (2) vertical displacement; (3) angulation displacement in the lateral view; (4) angulation displacement in the frontal view. Statistical analysis was completed by using a factorial analysis of variance (three-way ANOVA). A p value ≤0.05 was considered significant. Tukey's HSD test was used to analyze significant differences for the angulation variable. Results: (1) The results show that there was no difference in the impression accuracy when open vs. closed tray impression techniques were used except in the horizontal plane where the closed tray produced more accurate impressions than the open tray. (2) External connection implants produced a significantly larger horizontal displacement compared to the internal connection implants. (3) The results did not follow a particular pattern for the effect of implant angulation on impression accuracy. (4) The interactions observed between connection type, implant angulation and tray type and the resulting discrepancy in the horizontal plane showed that implants placed at 90 degrees produced the largest horizontal displacement. In the vertical plane, internal connection implants placed at 15 degrees when an open tray technique was used produced the largest vertical displacement. Conclusion: Clinically, the results from this study suggest that when encountering full arch implant restorations it is most beneficial to have the implants as parallel to each other as possible and to remove the custom tray along the same path as the implant angulation. The splinted open tray technique is time consuming and it might not result in a more accurate master cast. Open or closed tray techniques can be used, however, the master cast should always be verified before fabricating the final prosthesis.
    • The Effect Of Locator Abutment Height On The Retentive Values Of Pink Locator Attachments: An In Vitro Study.

      Sia, Priscilla Kia Suan; Masri, Radi, 1975-; 0000-0002-4799-8707 (2015)
      Purpose of this study was to evaluate the effect of different Locator abutment heights on the retention of overdentures. This study was conducted using four sets of edentulous mandible analogs with implants positioned at different depths relative to each other (N=40). Two implant-retained overdenture set-ups with Locator attachments at different vertical levels of 0, 2, 4, 6 mm to each other were tested for changes in peak load-to-dislodgement after simulated chewing of six months. Varying heights of Locator abutments had a significant effect on the retentive values of the pink Locator attachments. The results of ANOVA and Tukey HSD showed that the retention of Groups 0 mm and 2 mm was significantly lower than Group 6 mm. In conclusion, a difference in Locator abutment heights between the two implants did not adversely affect retention, therefore clinicians should choose Locator abutments according to the tissue thickness for implants at different levels.
    • The effect of number and distribution of maxillary implants on the load on the palate under implant-retained overdentures

      Damghani, Sahar; Masri, Radi, 1975- (2011)
      Purpose: to evaluate the effect of the number and distribution of dental implants on the occlusal pressure transmitted to the palate. Material and Methods: eight implant analogs were placed in a replica of maxilla in the areas of teeth number 3, 4, 5, 6, 11, 12, 13 and 14. Locator attachments were attached to the implant analogs. The distances between the centers of implant analogs on each side were 8 mm. Fifteen denture bases with occlusal rims were fabricated to fit on the maxillary replica. Under a load of 245 N, pressure on the palate was measured under each denture base in six different designs of Locator insertions: No Locators, 2 Locators, 4 Locators with distances of 8, 16, and 24 mm and 8 Locators. Data was analyzed using One-Way ANOVA and Tukey's HSD test. A p value of ≤0.05 was considered significant. Results: Pressure transmitted to the palate ranged from 20.67 +/- 16.06 N (mean +/- SD) for overdentures supported by 8 Locators to 85.61 +/- 27.94 N for a conventional denture (control). The amount of pressure transmitted to the palate when the overdentures were supported by 4 Locator attachments, was significantly lower than when no, or when two Locator attachments were used. However, they were not significantly different from each other. When the overdentures were supported by 8 locator attachments, the pressure transmitted to the palate was significantly lower than that of conventional dentures, overdentures supported by 2 Locator attachments and overdentures supported by 4 Locator attachments when the distance between the anterior and posterior implants was 8 mm. Conclusion: Using 4 Locator attachments produced significantly less pressure on the palate, compared to when zero or two Locators were used. When the distance between the 4 Locators was 16 or more mm, the pressure was not significantly lower than 8 Locator design, suggesting that the palate of a 4 implant-retained overdenture with a distance of 16 mm or more, does not contribute significantly to the pressure distribution under the overdenture. Considering the static nature of the load, the results of this study should be interpreted clinically with caution.
    • Effect of Simulated Loading on the Locator Attachment System: A Comparison Between the Retentive Values of Locator Attachments With Initially Placed Nylon-Inserts and Replacement Nylon-Inserts: An In-Vitro Study

      Greenbaum, Daniel Seth; Masri, Radi, 1975- (2011)
      Purpose: This study examined the retentive values of Locator attachments (Zest Anchors, Escondido, CA) with initially placed nylon-inserts, as compared to Locator attachments with replacement nylon-inserts. Materials and Methods: Five test samples simulated implant retained overdentures utilizing Locator attachments. Each attachment was tested with the initially placed pink nylon-insert (Group 1, n=5), and with a replacement nylon-insert (Group 2, n=5). Both groups were tested for 2920 cycles. The results were used to compare Group 1 with Group 2 at three time intervals. A one-way analysis of variance (ANOVA) with a p value of ≤0.05 was considered significant. Results: No significant differences were found between the retentive values of both groups (initial p=0.70, middle p = 0.41, and final p=0.09). The retentive values at the three time intervals were plotted in terms of cycles. A best-fit linear regression showed the rate of degradation. The slope of Group 2 was double that of Group 1. Conclusions: No significant differences in retentive values were found between the attachments with the initial nylon-inserts, and the attachments with replacement nylon-inserts for the time intervals studied. However, the attachments with replacement nylon-inserts lost retention at twice the rate of the attachments with initially placed nylon-inserts.
    • Fracture Strength of Repaired Midline Fractures of Maxillary Denture

      TAN, YINGHAN; Masri, Radi, 1975- (2013)
      Statement of problem: Denture fracture is a frequent clinical problem faced by the dentist. Denture repair should be simple to perform, cost-effective and quick. Unfortunately, the current methods of repair do not meet all of these requirements. Cyanoacrylate is a conveniently available adhesive material and it has been used by some patients to temporarily repair dentures before they get new ones. It is easy to use and relatively inexpensive. However, there is no literature that lists cyanoacrylate as a type of denture repair material. Purpose: This study investigated the transverse fracture strength of denture bases repaired with cyanoacrylates (Loctite Superglue Liquid, Loctite Superglue Liquid Professional). This was compared with denture bases repaired with auto-polymerizing acrylic resin (Lucitone 199 Repair Material). Material and methods: Thirty maxillary denture specimens were prepared and tested. They were divided into 3 different groups. Each of them was prepared with a clean midline fracture, repaired with Loctite Superglue Liquid, Loctite Superglue Liquid Professional or Lucitone 199 Repair Material and tested using the Universal Testing Machine. Data were analyzed using 1-way ANOVA and Tukey's HSD test, α=0.05. Results: There was a significant difference among the 3 types of repair materials. There was no significant difference in transverse fracture strength between Loctite Superglue Liquid Professional (107.16 ±20.57 MPa) and Lucitone 199 Repair Material (128.90 ±22.08 MPa). Loctite Superglue Liquid (53.79 ±19.05 MPa) had significant less transverse fracture strength than the other 2 types of material. Conclusion: Within the limitations of this study, cyanoacrylate containing methyl methacrylate polymer (Loctite Superglue Liquid Professional) is an inexpensive and readily available material which can be used as a temporary measure to repair dentures with a clean fracture. However, further studies are required to investigate the long term cytotoxicity and intraoral stability of the material.