Preparation Techniques Used to Make Single-Unit Crowns: Findings from The National Dental Practice-Based Research Network.

PURPOSE: To: (1) determine which preparation techniques clinicians use in routine clinical practice for single-unit crown restorations; (2) test whether certain practice, dentist, and patient characteristics are significantly associated with these techniques. MATERIALS AND METHODS: Dentists in the National Dental Practice-Based Research Network participated in a questionnaire regarding preparation techniques, dental equipment used for single-unit crown preparations, scheduled chair time, occlusal clearance determination, location of finish lines, magnification during preparation, supplemental lighting, shade selection, use of intraoral photographs, and trimming dies. Survey responses were compared by dentist and practice characteristics using ANOVA. RESULTS: Of the 2132 eligible dentists, 1777 (83%) responded to the survey. The top two margin configuration choices for single-unit crown preparation for posterior crowns were chamfer/heavy chamfer (65%) and shoulder (23%). For anterior crowns, the most prevalent choices were the chamfer (54%) and the shoulder (37%) configurations. Regarding shade selection, a combination of dentist, assistant, and patient input was used to select anterior shades 59% of the time. Photographs are used to communicate shade selection with the laboratory in about half of esthetically demanding cases. The ideal finish line was located at the crest of gingival tissue for 49% of respondents; 29% preferred 1 mm below the crest; and 22% preferred the finish line above the crest of tissue. Average chair time scheduled for a crown preparation appointment was 76 ± 21 minutes. Practice and dentist characteristics were significantly associated with margin choice including practice type (p < 0.001), region (p < 0.001), and years since graduation (p < 0.001). CONCLUSIONS: Network dentists prefer chamfer/heavy chamfer margin designs, followed by shoulder preparations. These choices were related to practice and dentist characteristics.

Clinical Performance of CAD/CAM Tooth-Supported Ceramic Restorations: A Systematic Review.

Owing to an increased demand for safe and esthetically pleasing dental materials, ceramics have been developed and optimized to rehabilitate anterior and posterior teeth. This evolution in ceramic materials is directly related to the development of sophisticated processing technologies and systems for use in dental medicine, particularly computer-aided design/computer-assisted manufacture (CAD/CAM) technology. This study is a systematic review outlining long-term clinical survival rates of single-tooth restorations fabricated with CAD/CAM technology with a minimum follow-up of 3 years. A bibliographic search up to September 2016 was performed using two databases: MEDLINE (PubMed) and Embase. Selected keywords and well-defined inclusion and exclusion criteria guided the search of relevant results. All articles were first reviewed by title, then by abstract, and subsequently by a full text reading. Data were assessed and extracted through a standardized form. The pooled results were statistically analyzed, and the overall failure rate was calculated by random effects model. Reported failures were analyzed by CAD/CAM system, type of restoration, restorative material, and luting agent. From a total of 2,916 single-tooth restorations with a mean exposure time of 7.0 years and 351 failures, the failure rate was 2.17% per year, estimated per 100 restoration years (95% confidence interval [CI]: 1.35% to 3.51%). The estimated total survival rate after 5 years was 89.7% (95% CI: 88.1% to 91.1%). The overall survival rate of single-tooth ceramic restorations fabricated with CAD/CAM technology was similar to those conventionally manufactured.

Impression Techniques Used for Single-Unit Crowns: Findings from the National Dental Practice-Based Research Network.

PURPOSE: To: (1) determine which impression and gingival displacement techniques practitioners use for single-unit crowns on natural teeth; and (2) test whether certain dentist and practice characteristics are significantly associated with the use of these techniques. MATERIALS AND METHODS: Dentists participating in the National Dental Practice-Based Research Network were eligible for this survey study. The study used a questionnaire developed by clinicians, statisticians, laboratory technicians, and survey experts. The questionnaire was pretested via cognitive interviewing with a regionally diverse group of practitioners. The survey included questions regarding gingival displacement and impression techniques. Survey responses were compared by dentist and practice characteristics using ANOVA. RESULTS: The response rate was 1777 of 2132 eligible dentists (83%). Regarding gingival displacement, most clinicians reported using either a single cord (35%) or dual cord (35%) technique. About 16% of respondents preferred an injectable retraction technique. For making impressions, the most frequently used techniques and materials are: poly(vinyl siloxane), 77%; polyether, 12%; optical/digital, 9%. A dental auxiliary or assistant made the final impression 2% of the time. Regarding dual-arch impression trays, 23% of practitioners report they typically use a metal frame tray, 60% use a plastic frame, and 16% do not use a dual-arch tray. Clinicians using optical impression techniques were more likely to be private practice owners or associates. CONCLUSIONS: This study documents current techniques for gingival displacement and making impressions for crowns. Certain dentist and practice characteristics are significantly associated with these techniques.

Impression evaluation and laboratory use for single-unit crowns: Findings from The National Dental Practice-Based Research Network.

BACKGROUND: Objectives were to determine the likelihood that a clinician accepts an impression for a single-unit crown and document crown remake rates. METHODS: The authors developed a questionnaire that asked dentists about techniques used to fabricate single-unit crowns. The authors showed dentists photographs of 4 impressions and asked them to accept or reject each impression. The authors correlated answers with dentist and practice characteristics. Other questions pertained to laboratory use and crown remake rates. RESULTS: The response rate was 83% (1,777 of 2,132 eligible dentists). Of the 4 impressions evaluated, 3 received consistent responses, with 85% agreement. One impression was more equivocal; 52% accepted the impression. The likelihood of accepting an impression was associated significantly with the clinician's sex, race, ethnicity, and practice busyness. Clinicians produced 18 crowns per month on average, and 9% used in-office milling. Most dentists (59%) reported a remake rate of less than 2%, whereas 17% reported a remake rate greater than 4%. Lower remake rates were associated significantly with more experienced clinicians, optical impressions, and not using dual-arch trays. CONCLUSIONS: Although dentists were largely consistent in their evaluation of impressions (> 85%), nonclinical factors were associated with whether an impression was accepted or rejected. Lower crown remake rates were associated with more experienced clinicians, optical impressions, and not using dual-arch trays. PRACTICAL IMPLICATIONS: These results provide a snapshot of clinical care considerations among a diverse group of dentists. Clinicians can compare their own remake rates and impression evaluation techniques with those in this sample when developing best practice protocols.

Survey on the use of CAD-CAM technology by UK and Irish dental technicians.

Statement of the problem Digital workflows (CAD/CAM) have been introduced in dentistry during recent years. No published information exists on dental technicians' use and reporting of this technology.Purpose The aim of this cross sectional survey was to identify the extent digital technology has infiltrated the workplace and to investigate the factors affecting the use of CAD-CAM technology by dental laboratory technicians within Ireland and the UK.Materials and methods A web-based questionnaire was composed (Opinio, Object Planet Inc. Oslo, Norway) and distributed to UK and Irish dental technicians. Answers to all questions were anonymous and grouped such that general information was gathered initially, followed by branching of the survey into two sections depending on whether or not the respondent worked with CAD-CAM technology. Results were compiled and statistical analysis (Fisher's Exact test, SPSS, IBM, Armonk, New York, USA) was performed in order to investigate any correlation between various demographic variables and the answers provided.Results The survey was distributed to 760 UK technicians and 77 Irish technicians. The total number of completed surveys was 105, which yielded a total response rate of 14%. Most technicians reported using some form of CAD/CAM aspect in the workflow, and this was more significant for technicians working in large laboratories. Most training received was company-led. Large laboratories were also significantly correlated with less outsourcing of CAD/CAM work and a change in dental material use leading to the increase of zirconia and the decrease of noble alloys. Dental technicians did not report any significant change in working relationships and staffing as a result of CAD/CAM incorporation. High initial investment cost was the most common reason quoted from non-users, along with the lack of such technology in their working environment.

Evaluation of Ultrashort and Longer Implants with Microrough Surfaces: Results of a 24- to 36-Month Prospective Study.

PURPOSE: The aim of this prospective study was to establish if ultrashort implants are a reliable therapeutic solution by evaluating their effect on mean crestal bone loss and assessing their survival and success rates. MATERIALS AND METHODS: Patients were treated using 6-, 9-, and 11-mm-long implants with sandblasted and acid-etched surfaces and fitted with fixed partial prostheses. Clinical and radiographic examinations were scheduled yearly. Data collected included the implant positioning site, implant length and diameter, peri-implant bone loss (PBL), and clinical and anatomical C/I ratios. RESULTS: One hundred eleven implants (6-mm-long, 30.6%) were positioned; two implants were lost before loading. During the 36-month followup, no other implants were lost (98.2% survival rate, 100% from loading), but four implants did not meet the criteria for success, due to excessive crestal bone loss, resulting in a 94.6% success rate, 96.3% from loading. Success rates and peri-implant bone loss were not significantly different among implants with different lengths. No correlation was observed between implant length and bone resorption. CONCLUSION: Six-millimeter-long implants did not show different results in comparison with 9- and 11-mm-long implants. They can be considered a reliable solution for implant prosthetic rehabilitation and a dependable and minimally invasive therapeutic option in areas showing severe bone resorption.

The Accuracy of Fit of Crowns Made From Wax Patterns Produced Conventionally (Hand Formed) and Via CAD/CAM Technology.

OBJECTIVE: The aim of this study was to compare the marginal and internal fit accuracy of crowns constructed using three different wax production methods; conventional, milled, and 3D printed and utilizing three different cement gap thicknesses. METHODS: 15 identical stone dies were made for each method. Wax patterns were produced and then cast into metal crowns, which were assessed for differences in accuracy of both marginal and internal fit. Measurement points were 4 points per crown; occlusal, axial, marginal gap, and marginal discrepancy points. A silicone impression technique and conventional cementation technique were employed to facilitate the measurements. RESULTS: There was no significant difference (p > 0.05) in accuracy between the digitally and manually produced crowns, with the 3D printed crowns being slightly more accurate. Whereas, statistically significant differences were noticed between the conventional versus printed groups, in occlusal and marginal gap points (p < 0.05). CONCLUSION: The marginal and internal fit of 3D printed wax patterns is more accurate than the other two production methods. The milling of wax crowns is as accurate as the conventional hand carved production in terms of internal and marginal fit. The manufacturer recommended offset/die-spacer of 30 µm produced the most accurate internal and marginal fits.

Evaluation of reliability and validity of three dental color-matching devices.

PURPOSE: To assess the repeatability and accuracy of three dental color-matching devices under standardized and freehand measurement conditions. MATERIALS AND METHODS: Two shade guides (Vita Classical A1-D4, Vita; and Vita Toothguide 3D-Master, Vita), and three color-matching devices (Easyshade, Vita; SpectroShade, MHT Optic Research; and ShadeVision, X-Rite) were used. Five shade tabs were selected from the Vita Classical A1-D4 (A2, A3.5, B1, C4, D3), and five from the Vita Toothguide 3D-Master (1M1, 2R1.5, 3M2, 4L2.5, 5M3) shade guides. Each shade tab was recorded 15 continuous, repeated times with each device under two different measurement conditions (standardized, and freehand). Both qualitative (color shade) and quantitative (L, a, and b) color characteristics were recorded. The color difference (ΔE) of each recorded value with the known values of the shade tab was calculated. The repeatability of each device was evaluated by the coefficient of variance. The accuracy of each device was determined by comparing the recorded values with the known values of the reference shade tab (one sample t test; α = 0.05). The agreement between the recorded shade and the reference shade tab was calculated. The influence of the parameters (devices and conditions) on the parameter ΔE was investigated (two-way ANOVA). Comparison of the devices was performed with Bonferroni pairwise post-hoc analysis. RESULTS: Under standardized conditions, repeatability of all three devices was very good, except for ShadeVision with Vita Classical A1-D4. Accuracy ranged from good to fair, depending on the device and the shade guide. Under freehand conditions, repeatability and accuracy for Easyshade and ShadeVision were negatively influenced, but not for SpectroShade, regardless of the shade guide. CONCLUSION: Based on the total of the color parameters assessed per device, SpectroShade was the most reliable of the three color-matching devices studied.

Effectiveness of Implant Therapy Analyzed in a Swedish Population: Prevalence of Peri-implantitis.

Peri-implantitis is an inflammatory disease affecting soft and hard tissues surrounding dental implants. As the global number of individuals that undergo restorative therapy through dental implants increases, peri-implantitis is considered as a major and growing problem in dentistry. A randomly selected sample of 588 patients who all had received implant-supported therapy 9 y earlier was clinically and radiographically examined. Prevalence of peri-implantitis was assessed and risk indicators were identified by multilevel regression analysis. Forty-five percent of all patients presented with peri-implantitis (bleeding on probing/suppuration and bone loss >0.5 mm). Moderate/severe peri-implantitis (bleeding on probing/suppuration and bone loss >2 mm) was diagnosed in 14.5%. Patients with periodontitis and with ≥4 implants, as well as implants of certain brands and prosthetic therapy delivered by general practitioners, exhibited higher odds ratios for moderate/severe peri-implantitis. Similarly, higher odds ratios were identified for implants installed in the mandible and with crown restoration margins positioned ≤1.5 mm from the crestal bone at baseline. It is suggested that peri-implantitis is a common condition and that several patient- and implant-related factors influence the risk for moderate/severe peri-implantitis (ClinicalTrials.gov NCT01825772).

A long-term retrospective analysis of survival rates of implants in the mandible.

PURPOSE: To retrospectively analyze the survival rate of endosseous dental implants placed in the edentulous or partially edentulous mandible over a long-term follow-up period of 10 years or more. MATERIALS AND METHODS: The charts of patients who underwent mandibular implant placement at a private prosthodontics practice and received follow-up care for 10 years or more were included in this study. Implants were examined according to the following study variables: patient sex, patient age, degree of edentulism (fully vs partially edentulous), implant location, time of loading (delayed vs immediate), implant size and type, bone quality, prosthesis type, and the presence of other implants during placement. RESULTS: The study sample was composed of 2,394 implants placed in 470 patients with 10 to 27 years of follow-up. Of these 2,394 implants, 176 failed, resulting in an overall cumulative survival rate (CSR) of 92.6%. A total of 1,482 implants were placed in edentulous mandibles, and 912 implants were placed in partially edentulous mandibles, with CSRs of 92.6% and 92.7%, respectively. Comparisons of the study variables with respect to CSR were largely nonsignificant. However, there were significant differences in CSRs between anterior vs posterior locations and rough- vs smooth-surfaced implants in addition to some prosthesis types, ages, and bone qualities. The overall CSR of 92.6% in the present study is high and comparable to survival rates observed in previous long-term analyses of mandibular implants. The significant differences observed between implant locations, patient age groups, bone qualities, and prostheses were not suggestive of any remarkable trends. CONCLUSION: Patient sex, age, degree of edentulism, implant location, time of loading, implant size and type, bone quality, prosthesis type, and the presence of multiple implants did not result in any significant effect on long-term implant survival. The CSR observed after 10 to 27 years of follow-up in a single private prosthodontic center was high (92.6%) and supports the use of endosseous dental implants as a long-term treatment option for the rehabilitation of the edentulous and partially edentulous mandible.

Critical appraisal of implant impression accuracies: A systematic review.

STATEMENT OF PROBLEM: Different assessment methods have been used to measure the accuracy of implant impression techniques; therefore, the readers should understand the benefits and limitations of each assessment method used. PURPOSE: The purpose of this systematic review was to classify the implant impression studies by the assessment methods and techniques used and to understand the characteristics of each assessment method. The results of published studies were also analyzed to draw meaningful conclusions about the accuracy of the implant impressions. MATERIAL AND METHODS: An electronic search of the MEDLINE/PubMed database was performed in February 2013 using specific search terms and predetermined criteria to identify and assess laboratory studies of the accuracy of implant impression techniques. A final list of articles deemed to be of interest was comprehensively reviewed by 2 reviewers to ensure that these were suitable for the purpose of this review. The results of the current review were also compared with results from a previous systematic review. RESULTS: A total of 56 studies met the inclusion criteria for this review. Thirty-seven studies measured the amount of linear distortion, and 17 studies compared the angular change to assess the accuracy. Most linear or angular distortions were only measured in 2 dimensions, and 3-dimensional analysis was rare. More than 80% of the studies compared nonsplinting versus splinting, direct versus indirect techniques, and different impression materials. CONCLUSIONS: In recent publications, the direct or splint technique showed more accurate results than the indirect or nonsplinted technique. In contrast to external connection implants, inconsistent results were reported for internal connection implants.

Cross-sectional study on the prevalence and risk indicators of peri-implant diseases.

PURPOSE: To evaluate the prevalence of peri-implant diseases in a university patient sample and to analyse possible risk variables associated with their occurrence. MATERIALS AND METHODS: One hundred and eighty-six patients with 597 implants were examined clinically and radiographically. The mean period of function was 5.5 years (range 1 to 16.5 years). A subgroup analysis was performed for implants with a minimum function time of 5 years. Outcome measures were implant failures, prevalence and risk indicators of peri-implant diseases. In order to identify statistically significant risk indicators of peri-implant mucositis and peri-implantitis multi-level logistic regression models were constructed. RESULTS: The prevalence of peri-implantitis and peri-implant mucositis on patient levels were 12.9% (13.3% for ≥ 5 years) and 64.5% (64.4% for ≥ 5 years), respectively. Multi-level analysis showed that a high plaque score (OR = 1.365; 95% CI: 1.18 to 1.57, P < 0.001) was a risk indicator for periimplant mucositis, while augmentation of the hard or soft tissue at implant sites had a protective effect (OR = 0.878 95% CI: 0.79 to 0.97, P = 0.01). It was also shown that the odds ratio for having peri-implant mucositis increased with the increase of plaque score in a dose-dependent manner. With respect to peri-implantitis, loss of the last tooth due to periodontitis (OR = 1.063; 95% CI: 1.00 to 1.12, P = 0.03) and location of the implants in the maxilla (OR = 1.052, 95% CI: 1.00 to 1.09, P = 0.02) were identified as statistically significant risk indicators. CONCLUSIONS: Within the limitations of this study, the history of periodontal disease was the most significant risk indicator for peri-implantitis and the level of oral hygiene was significantly associated with peri-implant mucositis.

Analysis of implant-failure predictors in the posterior maxilla: a retrospective study of 1395 implants.

The aim of this study was to analyze predictors for dental implant failure in the posterior maxilla. A database was created to include patients being treated with dental implants posterior to the maxillary cuspids. Independent variables thought to be predictive of potential implant failure included (1) sinus elevation, (2) implant length, (3) implant diameter, (4) indication, (5) implant region, (6) timepoint of implant placement, (7) one-vs. two-stage augmentation, and (8) healing mode. Cox regression analysis was used to evaluate the influence of predictors 1-3 on implant failure as dependent variable. The predictors 4-9 were analyzed strictly descriptively. The final database included 592 patients with 1395 implants. The overall 1- and 5-year implant survival rates were 94.8% and 88.6%, respectively. The survival rates for sinus elevation vs. placement into native bone were 94.4% and 95.4%, respectively (p = 0.33). The survival rates for the short (<10 mm), the middle (10-13 mm) and the long implants (>13 mm) were 100%, 89% and 76.8%, respectively (middle-vs. long implants p = 0.62). The implant survival rates for the small- (<3.6 mm), the middle- (3.6-4.5 mm) and the wide diameter implants (>4.5 mm) were 92.5%, 87.9% and 89.6%, respectively (p = 0.0425). None of the parameters evaluated were identified as predictor of implant failure in the posterior maxilla.

Comparison of accuracy and reproducibility of casts made by digital and conventional methods.

STATEMENT OF PROBLEM: Little peer-reviewed information is available regarding the accuracy and reproducibility of digitally fabricated casts compared to conventional nondigital methods. PURPOSE: The purpose of this in vitro study was to compare the accuracy and reproducibility of a digital impression and cast fabrication with a conventional impression and cast fabrication. MATERIAL AND METHODS: Conventional impressions were made via a 1-step single viscosity technique with vinyl siloxanether material of a typodont master model, and conventional casts were cast from dental stone. Digital impressions were obtained with a digital scanner, and digital stereolithographic models were printed. The typodont and fabricated casts were digitized with a structured light scanner and saved in surface tessellation language (STL) format. All STL records were superimposed via a best-fit method. The digital impression and cast fabrication method was compared with the conventional impression and cast fabrication method for discrepancy, accuracy, and reproducibility. The Levene test was used to determine equality of variances, and a 1-way ANOVA was conducted to assess the overall statistical significance of differences among the groups (n=5, α=.05). RESULTS: No significant statistical difference was found between the digital cast and conventional casts in the internal area or finish line area (P>.05). In addition, there was no statistically significant difference between these 2 techniques for a fixed dental prosthesis or single crown (P>.05). However, statistically significant differences were observed for overall areas of the casts in terms of accuracy (P<.01) and reproducibility (P<.001). Digital impression and cast fabrication were less accurate and reproducible than conventional impression and cast fabrication methods. CONCLUSIONS: No statistically significant difference was found between the digital cast and conventional cast groups in the internal and finish line areas. However, in terms of the reproducibility and accuracy of the entire cast area, the conventional cast was significantly better than the digital cast.

Understanding dental CAD/CAM for restorations--accuracy from a mechanical engineering viewpoint.

As is the case in the field of medicine, as well as in most areas of daily life, digital technology is increasingly being introduced into dental practice. Computer-aided design/ computer-aided manufacturing (CAD/CAM) solutions are available not only for chairside practice but also for creating inlays, crowns, fixed partial dentures (FPDs), implant abutments, and other dental prostheses. CAD/CAM dental practice can be considered as the handling of devices and software processing for the almost automatic design and creation of dental restorations. However, dentists who want to use dental CAD/CAM systems often do not have enough information to understand the variations offered by such technology practice. Knowledge of the random and systematic errors in accuracy with CAD/CAM systems can help to achieve successful restorations with this technology, and help with the purchasing of a CAD/CAM system that meets the clinical needs of restoration. This article provides a mechanical engineering viewpoint of the accuracy of CAD/ CAM systems, to help dentists understand the impact of this technology on restoration accuracy.

Effectiveness of implant therapy analyzed in a Swedish population: early and late implant loss.

Treatment outcomes in implant dentistry have been mainly assessed as implant survival rates in small, selected patient groups of specialist or university clinical settings. This study reports on loss of dental implants assessed in a large and randomly selected patient sample. The results were aimed at representing evaluation of effectiveness of implant dentistry. Using the national data register of the Swedish Social Insurance Agency, 4,716 patients were randomly selected. All had been provided with implant-supported restorative therapy in 2003. Patient files of 2,765 patients (11,311 implants) were collected from more than 800 clinicians. Information on patients, treatment procedures, and outcomes related to the implant-supported restorative therapy was extracted from the files. In total, 596 of the 2,765 subjects, provided with 2,367 implants, attended a clinical examination 9 y after therapy. Implant loss that occurred prior to connection of the supraconstruction was scored as an early implant loss, while later occurring loss was considered late implant loss. Early implant loss occurred in 4.4% of patients (1.4% of implants), while 4.2% of the patients who were examined 9 y after therapy presented with late implant loss (2.0% of implants). Overall, 7.6% of the patients had lost at least 1 implant. Multilevel analysis revealed higher odds ratios for early implant loss among smokers and patients with an initial diagnosis of periodontitis. Implants shorter than 10 mm and representing certain brands also showed higher odds ratios for early implant loss. Implant brand also influenced late implant loss. Implant loss is not an uncommon event, and patient and implant characteristics influence outcomes (ClinicalTrials.gov NCT01825772).

A 3-dimensional accuracy analysis of chairside CAD/CAM milling processes.

STATEMENT OF PROBLEM: Milling is a central and important aspect of computer-aided design and computer-aided manufacturing (CAD/CAM) technology. High milling accuracy reduces the time needed to adapt the workpiece and provides restorations with better longevity and esthetic appeal. The influence of different milling processes on the accuracy of milled restorations has not yet been reviewed. PURPOSE: The purpose of this study was to investigate the influence of different milling processes on the accuracy of ceramic restorations. MATERIAL AND METHODS: Four groups of partial crowns were milled (each n = 17): Three groups in a 4-axial milling unit: (1) 1-step mode and Step Bur 12S (12S), (2) 1-step mode and Step Bur 12 (1Step), (3) 2-step mode and Step Bur 12 (2Step), and (4) one group in a 5-axial milling unit (5axis). The milled occlusal and inner surfaces were scanned and superimposed over the digital data sets of calculated restorations with specialized difference analysis software. The trueness of each restoration and each group was measured. One-way ANOVA with a post hoc Tukey test was used to compare the data (α = .05). RESULTS: The highest trueness for the inner surface was achieved in group 5axis (trueness, 41 ± 15 µm, P<.05). The 4-axial milling unit exhibited trueness at settings ranging from 61 µm (2Step) to 96 µm (12S). For the occlusal surface, the highest trueness was achieved with group 5axis (trueness, 42 ± 10 µm). The 4-axial milling unit exhibited trueness at settings ranging from 55 µm (1Step) to 76 µm (12S). CONCLUSIONS: Restorations milled with a 5-axial milling unit have a higher trueness than those milled with a 4-axial milling unit. A rotary cutting instrument with a smaller diameter results in a more accurate milling process. The 2-step mode is not significantly better than the 1-step mode.

The influence of rehabilitation characteristics in the incidence of peri-implant pathology: a case-control study.

PURPOSE: To investigate the influence of rehabilitation characteristics in the incidence of peri-implant pathology (P-iP). MATERIALS AND METHODS: A total of 1350 patients (270 with P-iP matched for age, gender, and time of follow-up with 1080 controls without P-iP) rehabilitated with dental implants were included. The effect of the independent variables [Implant length in millimeters (IL); implant diameter in millimeters; implant surface (IS); presence of cantilevers; implant:crown ratio (ICR), type of abutment (TA); abutment height; fracture of prosthetic components (FPCs); type of prosthetic reconstruction (TPR); type of material used in the prosthesis (TMUP); loosening of prosthetic components (LPCs); and passive misfit (PM) diagnosed within the previous year] was evaluated through bivariate analysis (chi-square), with level of significance of 5%. Crude odds ratios (OR) with 95% confidence intervals and the attributable fraction (AF) were calculated for the independent variables individually identified as factors associated with the incidence of peri-implant pathology. RESULTS: The following variables were identified as risk factors: machined IS (p = 0.015; OR = 1.46), 17° TA (p = 0.000; OR = 3.06), completely edentulous TPR (p = 0.000; OR = 2.49), TMUP (p = 0.000; metal-acrylic OR = 2.29; acrylic OR = 4.90; metal-ceramic OR = 8.43), 1:1 ICR (p = 0.002; OR = 1.54), FPC (p = 0.000; OR = 3.01), LPC (p = 0.000; OR = 4.15), and PM (p = 0.002; OR = 20.36). The attributable fraction rendered the following theoretical potential reductions in the cases if the exposure to the variables was removed: IS (31.5%), TA (67.3%), TMUP (5.4% to 73.3%), ICR (35%), FPC (66.8%), LPC (73.8%), and PM (95.1%). CONCLUSIONS: Within the limitations of this study, machined implant surfaces, 17° abutments, completely edentulous reconstructions, the type of metal used in the prosthesis, 1:1 implant:crown ratio, fracture of prosthetic components, loosening of prosthetic components, and passive misfit emerged as risk factors for the incidence of P-iP. Eliminating the exposure to these variables would, in theory, result in a significant reduction in the incidence of P-iP.

Implant diameter and length influence on survival: interim results during the first 2 years of function of implants by a single manufacturer.

OBJECTIVES: The aim of the present study was to evaluate the influence of implant length and diameter on implant survival. METHODS: A retrospective cohort of 787 consecutive patients from 2 private practices between the years 2008 and 2011 had been evaluated. Patient demographics, site and implant characteristics, and time of follow-up were recorded from the medical files. RESULTS: Overall, 3043 implants were investigated. Overall survival rate was 98.7% with 39 implant failures recorded. Survival rates for narrow- (<3.75 mm), regular- (3.75-5 mm), and wide- (>5 mm) diameter implants were 98.2%, 98.7%, and 98.5%, respectively (P = 0.89). Survival rates of short (<10 mm) and regular (10 mm and above) implants were 97% and 98.7%, respectively (P = 0.22). CONCLUSIONS: Implant length and diameter were not found to be significant factors affecting implant survival during the first 2 years of function in the present investigation of this specific implant system by a single manufacturer. Further long-term follow-up studies are warranted because 2-years are only interim short-term results when dealing with dental implants.

Comparative evaluation of osseointegrated dental implants based on platform-switching concept: influence of diameter, length, thread shape, and in-bone positioning depth on stress-based performance.

This study aimed to investigate the influence of implant design (in terms of diameter, length, and thread shape), in-bone positioning depth, and bone posthealing crestal morphology on load transfer mechanisms of osseointegrated dental implants based on platform-switching concept. In order to perform an effective multiparametric comparative analysis, 11 implants different in dimensions and in thread features were analyzed by a linearly elastic 3-dimensional finite element approach, under a static load. Implant models were integrated with the detailed model of a maxillary premolar bone segment. Different implant in-bone positioning levels were modeled, considering also different posthealing crestal bone morphologies. Bone overloading risk was quantified by introducing proper local stress measures, highlighting that implant diameter is a more effective design parameter than the implant length, as well as that thread shape and thread details can significantly affect stresses at peri-implant bone, especially for short implants. Numerical simulations revealed that the optimal in-bone positioning depth results from the balance of 2 counteracting effects: cratering phenomena and bone apposition induced by platform-switching configuration. Proposed results contribute to identify the mutual influence of a number of factors affecting the bone-implant loading transfer mechanisms, furnishing useful insights and indications for choosing and/or designing threaded osseointegrated implants.