Samer Abi Nader

Hydrogen peroxide whitens teeth by oxidizing the organic structure

OBJECTIVES The mechanism of tooth bleaching using peroxide oxidizers is not fully understood. It is unknown whether peroxide radicals make teeth whiter by deproteinizing, demineralizing, or oxidizing tooth tissues. This study was designed to define the mechanism of tooth bleaching and determine which of tooth enamel chemical components is/are affected by bleaching. METHODS Sixty sound teeth were collected from adult patients. The teeth were divided into 6 equal groups (n=10). Groups 1, 2, 3 and 4 were treated for 4 days with one of the following solutions: deproteinizing (NaOH) that removes organic content, demineralizing (EDTA) that decalcifies the mineral content, oxidizing (H(2)O(2)) and distilled water (control). Group 5 and 6 were pre-treated with either deproteinizing or demineralizing solutions before treating them with oxidizing solutions for 4 days. Changes in enamel elemental ratios, crystallinity index and tooth shade parameters of the treated teeth were examined by means of EDS, Raman spectroscopy and shade-spectrophotometry. The data obtained was analysed with Wilcoxon Signed-Ranks Test, and the statistical significance was set at p<0.05. RESULTS Tooth deproteinization increased the lightness by 4.8 ± 2.7°, tooth demineralization resulted in 8.5 ± 5.6° decrease in the lightness and tooth oxidization induced 19.9 ± 6.5° increase in the lightness. Oxidization of the deproteinized teeth did not influence shade parameters, but oxidation of the demineralized teeth resulted in 10.7 ± 5.8° increase in the lightness. CONCLUSION Hydrogen peroxide does not induce significant changes in tooth enamel organic and inorganic relative contents, and it whitens teeth just by oxidizing their organic matrix. These findings are of great clinical significance since they explain the mechanism of tooth bleaching, and help understanding its limitations and disadvantages.

The role of enamel crystallography on tooth shade.

OBJECTIVES Tooth shade is influenced by a combination of extrinsic-stains that are adsorbed to the enamel surface and by its intrinsic-shade resulting from the interaction of light with tooth structures. This study was designed to investigate how the variations in enamel ultrastructure may affect tooth optical properties. METHODS One-hundred extracted teeth were collected from adult patients attending McGill-Undergraduate Dental Clinics. Shade-spectrophotometry, FTIR and XRD were used to assess tooth shade, enamel chemical composition and crystallography. The data obtained was analysed for Pearson correlation analysis and multiple linear regression analysis. The statistical significance was set at P < 0.05. RESULTS Tooth shade parameters varied dramatically within the studied population. Pearson correlation analysis demonstrated that tooth hue was associated with enamel hydroxyapatite (HA) crystal size (R = -0.358; B = -0.866; P = 0.007), tooth chroma was associated with enamel HA carbonization (R = -0.419; B = -99.06; P = 0.005), and tooth lightness was associated with both enamel HA crystal size (R = -0.313; B = -1.052; P = 0.019) and the degree of HA carbonization (R = -0.265; B=-57.95; P = 0.033). Multiple linear regression analysis demonstrated that the size of enamel HA crystals and the relative content of mineral carbonate were the most important predictors for tooth shade lightness (P = 0.018) and chroma (P=0.008), respectively. In contrast, enamel organic content had no correlation with tooth shade. CONCLUSIONS In the present study we have revealed that the tooth shade is regulated by the size of their HA enamel crystals. On the other hand, variation in the degree of enamel HA carbonization can also affect the tooth shade. These findings are of great relevance in dentistry since it provides better understanding of tooth aesthetics.

Effect of Implant Angulation on Attachment Retention in Mandibular Two-Implant Overdentures: A Clinical Study

PURPOSE Attachment wear can affect the performance of mandibular two-implant overdentures (IODs). This prospective clinical study aimed to investigate the effect of interimplant angulation on the retention achieved by two attachment systems at different time points within 1 year of wearing IODs. MATERIALS AND METHODS Twenty-four patients (mean age = 73.2 years; standard deviation (SD) = 3.1) wearing IODs opposed by conventional maxillary complete dentures were randomly assigned to two groups in two-by-two crossover design. Retentive Anchor (RA) and Locator (LA) were installed in the IODs of both groups for 1 year, sequentially. Coronal and sagittal interimplant angulation were measured on posterior-anterior and lateral cephalometric radiographs. Retention was measured at baseline, 1 week, 3, 6, and 12 months postattachment installation. Data were analyzed using mixed models with α = 0.05. RESULTS Mean coronal and sagittal interimplant angulations were 4.6 (SD = 2.9) and 3.5 (SD = 2.6) degrees, respectively. Only with LAs a statistically significant decrease was found in retention (average 1.1 Newton; standard error = 0.38; p = .007) per 1 degree increased sagittal interimplant angulation. CONCLUSIONS Increased interimplant angulation appears to have higher impact on the retention of LA than of RA attachments. The effect of larger interimplant angulation on the loss of attachment retention and its clinical implications should be further assessed.

Clinical wear of overdenture ball attachments after 1, 3 and 8 years

OBJECTIVES Implant-supported overdentures have become the treatment of choice in restoring complete edentulism, but the types of attachment to assure durable retention are a subject of debate. Ball attachments were reported as a simple treatment, but wear of components was responsible for a decrease in retention. The aim of this retrospective study was to measure the wear of the ball abutment or patrix after three different periods of clinical wear. MATERIAL AND METHODS Sixty-nine specimens of three groups of patrix that were in use for a mean of 12.3 months (group A), 39 months (group B) and 95.6 months (group C) were retrieved from 35 patients and measured on a coordinate measuring machine equipped with a touch trigger probe. Ten unused ball abutments were added as a control (group D). The patrix diameters and any deviation from circularity in different axes were measured. RESULTS The diameters of groups A, B and C were significantly different from that of group D (control). No statistically significant differences were found between diameter and circularity variations between groups B and C. The maximal amount of diameter reduction was limited to approximately 30 μm, and 90% of diameter loss at the equator due to wear was reached in group B. CONCLUSION One, 3 and 8 years of clinical wear reduced significantly the diameters of the ball abutments tested, and the maximal amount of wear was reached after 3 years of clinical use.

Patient satisfaction with laser-sintered removable partial dentures: A crossover pilot clinical trial

Statement of problem: Clinical data regarding newly introduced laser‐sintered removable partial dentures (RPDs) are needed before this technique can be recommended. Currently, only a few clinical reports have been published, with no clinical studies. Purpose: This clinical trial compared short‐term satisfaction in patients wearing RPDs fabricated with conventional or computer‐aided design and computer‐aided manufacturing (CAD‐CAM) laser‐sintering technology. Material and methods: Twelve participants with partial edentulism were enrolled in this pilot crossover double‐blinded clinical trial. Participants were randomly assigned to wear cast or CAD‐CAM laser‐sintered RPDs for alternate periods of 30 days. The outcome of interest was patient satisfaction as measured using the McGill Denture Satisfaction Instrument. Assessments was conducted at 1, 2, and 4 weeks. The participants preference in regard to the type of prosthesis was assessed at the final evaluation. The linear mixed effects regression models for repeated measures were used to analyze the data, using the intention‐to‐treat principle. To assess the robustness of potential, incomplete adherence, sensitivity analyses were conducted. Results: Statistically significant differences were found in patients’ satisfaction between the 2 methods of RPD fabrication. Participants were significantly more satisfied with laser‐sintered prostheses than cast prostheses in regard to general satisfaction, ability to speak, ability to clean, comfort, ability to masticate, masticatory efficiency, and oral condition (P<.05). At the end of the study, 5 participants preferred the laser‐sintered, 1 preferred the cast RPD, and 3 had no preference. Conclusions: The use of CAD‐CAM laser‐sintering technology in the fabrication of removable partial dentures may lead to better outcomes in terms of patient satisfaction in the short term. The conclusion from this pilot study requires confirmation by a larger randomized controlled trial. Clinical Trial: ClinicalTrials.gov. A study about patient satisfaction with laser‐sintered removable partial dentures; NCT02769715.

Wear of matrix overdenture attachments after one to eight years of clinical use

STATEMENT OF PROBLEM Matrices of unsplinted attachment systems are generally reported to be the weak component of implant overdentures, often requiring frequent maintenance. Clinical wear results in reduced retention of the prosthesis, requiring activation or renewal of the matrix to restore the initial level of retention. PURPOSE The purpose of this retrospective study was to measure the wear of the matrix of a ball attachment after various periods of clinical wear. MATERIAL AND METHODS Seventy specimens of 3 groups of matrices of ball attachments that had been in use for mean periods of 12.3 months (1Y group, n=26), 39.0 months (3Y group, n=28) and 95.6 months (8Y group, n=16) were retrieved from 35 patients (2 specimens per patient) and measured on a coordinate measuring machine equipped with a touch trigger probe. Ten unused matrices were used as controls (CTRL group). The external and internal matrix diameters and deviations from circularity were measured. For the various time periods, the decreases in matrix thickness were calculated and compared with controls. Kruskal-Wallis 1-way ANOVA by ranks, followed by the Mann-Whitney post hoc tests, were conducted to test for differences in median values among groups (α =.05). RESULTS For the internal upper diameter of the matrices tested, the Kruskal-Wallis and Mann-Whitney tests revealed significant differences for the 3 groups compared to the controls. For group 1Y, a significant difference (P<.001) of the internal upper diameter was found compared to the CTRL group. Compared to the controls, the nonparametric analyses for groups 3Y and 8Y showed significant differences for the internal upper diameter (P<.001) and deviations from circularity (P<.001). For groups 1Y, 3Y and 8Y, matrix thickness losses were 07, 47 and 70 μm, respectively. CONCLUSIONS Within the limitations of this study, it was observed that one year of clinical wear had limited effect on the ball attachment matrices. Three to 8 years of clinical use resulted in a significant decrease of matrix thickness, especially at the tip of the retentive lamellae.

Case Presentation: Implant-Supported Removable Mandibular Prostheses

Uses of modern dental implants are providing new options for the treatment of complete upper and lower edentulism. Implant-supported removable overdentures have proven to be an effective treatment option, especially for the treatment of patients with severely atrophied residual ridges.

Case Presentation: Implant-Supported Fixed Mandibular Prostheses

This chapter will present a clinical case describing the treatment of a lower edentulous patient with an implant-supported fixed prosthesis. The surgical strategies underlining the placement and the distribution of the dental implants will be highlighted and discussed, as well as the concepts that underscore the design of the final prosthetic outcome.

Case Presentation: Implant Retained Mandibular Prostheses

This chapter will present a clinical case describing the treatment of a lower edentulous patient with an implant-retained prosthesis. The surgical strategies underlining the placement and the distribution of the dental implants to optimize the prosthetic outcome will be highlighted and discussed. The various clinical and laboratory steps starting from the planning to the completion of the prostheses will be presented as well as the criteria for the selection of single attachments for this prosthetic design. This also includes the description and review of the various techniques available to connect the matrix component of the attachment to the denture base. The advantages of each technique will be discussed and their inconveniences highlighted.

Fundamental Surgical and Prosthetic Principles of Mandibular Implant Assisted Prostheses

The introduction of dental implants has dramatically changed the lives of many edentulous patients by providing a mechanism of anchorage that contributes to stabilizing the mandibular denture during function. This has provided a variety of new options for the treatment of complete upper and lower edentulism (Emami et al., Periodontol 66:119–31, 2014).