Stock Versus CAD/CAM Customized Zirconia Implant Abutments - Clinical and Patient-Based Outcomes in a Randomized Controlled Clinical Trial.

BACKGROUND: Single-tooth replacement often requires a prefabricated dental implant and a customized crown. The benefits of individualization of the abutment remain unclear. PURPOSE: This randomized controlled clinical trial aims to study potential benefits of individualization of zirconia implant abutments with respect to preservation of marginal bone level and several clinical and patient-based outcome measures. MATERIAL AND METHODS: Fifty participants with a missing premolar were included and randomly assigned to standard (ZirDesign, DentsplySirona Implants, Mölndal, Sweden) or computer aided design/computer aided manufacturing (CAD/CAM) customized (Atlantis, DentsplySirona Implants, Mölndal, Sweden) zirconia abutment therapy. Peri-implant bone level (primary outcome), Plaque-index, calculus formation, bleeding on probing, gingiva index, probing pocket depth, recession, appearance of soft tissues and patients' contentment were assessed shortly after placement and one year later. RESULTS: No implants were lost and no complications related to the abutments were observed. Statistically significant differences between stock and CAD/CAM customized zirconia abutments could not be demonstrated for any of the operationalized variables. CONCLUSION: The use of a CAD/CAM customized zirconia abutment in single tooth replacement of a premolar is not associated with an improvement in clinical performance or patients' contentment when compared to the use of a stock zirconia abutment.

Impact of periodontal maintenance on tooth survival in patients with removable partial dentures.

AIM: Removable partial dentures (RPDs) may have a negative impact on oral health and have the potential to cause further tooth loss, especially of abutment teeth. However, no evidence indicates the effective interval of regular periodontal maintenance after RPD provision. This practice-based cohort study aimed to examine the impact of regular periodontal maintenance visits on survival of RPD abutment teeth. MATERIALS AND METHODS: One hundred and ninety-two patients had been previously provided with 304 new clasp-retained RPDs at Osaka University Dental Hospital, Japan. Using the Kaplan-Meier method and log-rank test, 1094 abutments were analysed to illustrate survival curves and to compare each curve. According to the frequency of periodontal maintenance, study samples were divided into three groups; every 3-6 months (3-6M) group, 1-year (1Y) group and no-maintenance (NM) group. RESULTS: Seven-year cumulative survival rates were 83.7% (3-6M), 75.5% (1Y) and 71.9% (NM) respectively. Survival of abutment teeth in the 3-6M group was significantly better than both 1Y (p = 0.005) and NM (p < 0.001) groups. CONCLUSION: These longitudinal clinical data indicates that periodontal maintenance at least once in 6 months had the most favourable outcome. Frequent periodontal maintenance after RPD provision could be effective in preventing further tooth loss.

Contribution of the palate to denture base support: an in vivo study.

The aim of this study was to examine the contribution of the palate to denture base support. Four subjects with tooth- or implant-supported maxillary overdentures were enrolled. Recordings (strain values converted to load values) were performed using miniature strain gauges and force transducers for the following conditions: metal framework only (A), denture base with full palatal coverage (B), and denture base without palatal coverage (C). The palatal-supporting ratio (PSR) was calculated using the equation PSR = (B - C) / A. The PSR values were less than 10% in all subjects, suggesting that the palate plays a minimal role in denture base support.

Effects of abutment and screw access channel modification on dislodgement of cement-retained implant-supported restorations.

This study investigated the influence of implant abutment and screw access channel modification on the retention of copings. Titanium abutment access openings were either left open or modified by placing two vent holes 3 mm from the occlusal edge and 180 degrees apart. Access openings sealed with a resin material were used as controls. Metal copings were cemented and subjected to tensile testing until failure. Access openings with two vent holes resulted in significantly higher mean retention values compared to the opened or sealed screw access groups (P < .05). Cement flow was affected by the internal vent, which increased the area of cementabutment contact.

Provisional prostheses during ridge augmentation and implant dentistry.

Recent advancements in ridge augmentation and bone regeneration have expanded the pool of patients that could benefit from dental implants. However, providing the patient with a temporary prosthesis during the wound healing phase without impairing the process is a challenging task. This article summarizes available information pertaining to provisional prostheses, both tooth-supported and soft tissue-supported, that may meet the patient needs. The advantages and disadvantages of each class of prosthesis, along with indications and contraindications, were taken into consideration to aid the restorative dentist in choosing the optimal provisional for their patients.

A review of implant abutments--abutment classification to aid prosthetic selection.

With an increase in the availability of implant restorative components, the selection of an appropriate implant abutment for a given clinical situation has become more challenging. This article describes a classification system that will help the practitioner understand the different implant abutments available and therefore be able to understand the selection of abutments for single and multiple unit fixed implant prosthesis.

Frictional telescopic crowns in severely reduced dentitions: a 5-year clinical outcome study.

Clinical outcomes for frictional telescopic crowns supporting removable prostheses in patients with severely reduced dentitions with one to three remaining teeth per arch have been inadequately documented. Seventy-four patients with severely reduced dentitions received 82 telescopic removable partial dentures that were supported by 173 frictional telescopic crowns. The recorded individual telescopic abutment survival rate over a 60-month period was 80.6%. This observation was significantly influenced by sex and tooth vitality and mobility (Kaplan-Meier). The risk of loss of telescopic crowns was significantly influenced by sex, arch, vitality, and abutment tooth distribution (Cox regression). Telescopic removable partial dentures were proven to be a favorable treatment concept for severely reduced dentitions in the selected group of patients.

Regular and platform switching: bone stress analysis varying implant type.

PURPOSE: This study aimed to evaluate stress distribution on peri-implant bone simulating the influence of platform switching in external and internal hexagon implants using three-dimensional finite element analysis. MATERIALS AND METHODS: Four mathematical models of a central incisor supported by an implant were created: External Regular model (ER) with 5.0 mm × 11.5 mm external hexagon implant and 5.0 mm abutment (0% abutment shifting), Internal Regular model (IR) with 4.5 mm × 11.5 mm internal hexagon implant and 4.5 mm abutment (0% abutment shifting), External Switching model (ES) with 5.0 mm × 11.5 mm external hexagon implant and 4.1 mm abutment (18% abutment shifting), and Internal Switching model (IS) with 4.5 mm × 11.5 mm internal hexagon implant and 3.8 mm abutment (15% abutment shifting). The models were created by SolidWorks software. The numerical analysis was performed using ANSYS Workbench. Oblique forces (100 N) were applied to the palatal surface of the central incisor. The maximum (σ(max)) and minimum (σ(min)) principal stress, equivalent von Mises stress (σ(vM)), and maximum principal elastic strain (ε(max)) values were evaluated for the cortical and trabecular bone. RESULTS: For cortical bone, the highest stress values (σ(max) and σ(vm) ) (MPa) were observed in IR (87.4 and 82.3), followed by IS (83.3 and 72.4), ER (82 and 65.1), and ES (56.7 and 51.6). For ε(max), IR showed the highest stress (5.46e-003), followed by IS (5.23e-003), ER (5.22e-003), and ES (3.67e-003). For the trabecular bone, the highest stress values (σ(max)) (MPa) were observed in ER (12.5), followed by IS (12), ES (11.9), and IR (4.95). For σ(vM), the highest stress values (MPa) were observed in IS (9.65), followed by ER (9.3), ES (8.61), and IR (5.62). For ε(max) , ER showed the highest stress (5.5e-003), followed by ES (5.43e-003), IS (3.75e-003), and IR (3.15e-003). CONCLUSION: The influence of platform switching was more evident for cortical bone than for trabecular bone, mainly for the external hexagon implants. In addition, the external hexagon implants showed less stress concentration in the regular and switching platforms in comparison to the internal hexagon implants.

Diferentes sistemas de pilares protésicos sobre implantes: [revisión] / Differents dental implant abutment systems: [review]

El presente artículo de revisión hace referencia a los distintos sistemas de pilares que existen hoy en día en el mercado, mencionando su clasificación, criterios para seleccionarlos y sus características principales e indicaciones. Se incluyen estudios comparativos entre los diferentes sistemas de pilares, resaltando cuáles son sus ventajas y desventajas. Además se hace mención al sistema CAD-CAM como una alternativa de alta confiabilidad y menor tiempo clínico para la confección de estos aditamentos.

The present article reviews the different systems of abutments that exist nowadays in the market, their classification, selection criteria, and their basic characteristics and indications. Comparative studies between the different systems of abutments are included, focusing on their advantages and disadvantages. Also, the CAD-CAM system is mentioned as an alternative of high reliability and less clinical time for the fabrication of these components.

Comparison of 3 luting agents on retention of implant-supported crowns on 2 different abutments.

BACKGROUND: For fixed prostheses, retention is one of the most important factors for clinical success. It is unknown whether grooves that increase surface area of implant abutment while retaining the diameter and wall height provide greater uniaxial retention force. The purpose of this study was to determine the retention of 3 different cements on 2 implant abutments with different surface configurations. MATERIALS AND METHODS: Thirty samples on 2 different abutments (a total of 60 crowns) with different margin and axial walls configuration and surface area were used. Metal crowns were fabricated on the abutment and cemented with 3 different (zinc-phosphate [ZP], glass ionomer [GI], or eugenol-free zinc oxide [ZO]) cements. After cementation, implant-abutment-casting assemblies were thermal cycled 1000 times with 1-minute dwell-time between 5°C and 55°C then subjected to tensile test with universal testing machine until decementation occurred. The mean force required to dislodge castings from abutment was determined. RESULTS: The luting agents influenced retention of castings on implant abutments, whereas different surface configurations and total surface area of the abutments did not influence the uniaxial retention forces. Among the cements tested, ZP exhibited higher values of retention, followed by GI and eugenol-free ZO. CONCLUSIONS: The increase in surface area of abutment did not result in improved retention. The present results suggest using ZP rather than GI and eugenol-free ZO in implant-supported crowns to provide higher retention.

Partial edentulism and removable partial denture design in a dental school population: a survey in Greece.

OBJECTIVES: To investigate the pattern of partial edentulism and the most frequent designs of cobalt-chromium removable partial dentures (RPDs), constructed at the Dental School of Athens, Greece. METHODS AND MATERIALS: Five hundred and fifty-three patients, between 42 and 81 years old, mostly males, treated by undergraduate dental students, were included. The survey was based on visual evaluation of master casts and work authorisation to dental technicians. Aspects examined were: Kennedy Classification, modification areas, major connectors, clasping, placement of rest seats and indirect retention. RESULTS: Kennedy Class I was the most common encountered in the maxilla (50.5%) and in the mandible (70%). The most frequent major connectors were the lingual bar (92.6%) and the U-shaped palatal strap (54%). The most common clasp was the Roach (69.2%) in Class I and Class II. In Class III and IV, the most common was the occlusally approaching clasp (55% and 70%). The most frequent location of the rest was mesial of abutment teeth. On the average, 39.5% of Class I RPDs and 58.6% of Class II RPDs had indirect retainers. CONCLUSION: A combination of the two major philosophies of RPD design (biomechanical and hygienic) was evident in the RPDs examined in our study.

Critical bending moment of four implant-abutment interface designs.

PURPOSE: Critical bending moment (CBM), defined as the bending moment at which the external nonaxial load applied overcomes screw joint preload and causes loss of contact between the mating surfaces of the implant screw joint components, was measured for four different implants and their single-tooth replacement abutments. MATERIALS AND METHODS: CBM at the implant-abutment screw joint for four implant-abutment test groups was measured in vitro at 80%, 100%, and 120% of the manufacturers' recommended torque levels. Regular-platform implants with their corresponding single-tooth abutments were used. Microstrain was measured while known loads were applied to the abutment at known distances from the implant-abutment interface. Strain instrumentation was used to record the strain data dynamically to determine the point of gap opening. All torque applications and strain measurements were repeated five times for the five samples in each group. RESULTS: For the Branemark/CeraOne assemblies, the mean CBMs were 72.14 Ncm, 102.21 Ncm, and 119.13 Ncm, respectively, at 80%, 100%, and 120% of the manufacturer's recommended torque. For the Replace/Easy assemblies, mean CBMs were 86.20 Ncm, 109.92 Ncm, and 120.93 Ncm; for the Biomet 3i/STA assemblies, they were 67.97 Ncm, 83.14 Ncm, and 91.81 Ncm; and for the Lifecore/COC assemblies, they were 58.32 Ncm, 76.79 Ncm, and 78.93 Ncm. Two-way analysis of variance revealed significant effects for the test groups and torque levels. Subsequent tests confirmed that significant differences existed between test groups and torque levels. CONCLUSION: The results appear to confirm the primary role of the compressive preload imparted by the abutment screw in maintaining screw joint integrity. CBM was found to differ among implant systems and torque levels. Torque levels recommended by the manufacturer should be followed to ensure screw joint integrity.

Two-year prospective follow-up of implant/tooth-supported versus freestanding implant-supported fixed partial dentures.

The aim of this study was to compare the prosthetic outcomes of implant/tooth-supported three-unit fixed partial dentures (FPDs) with those of freestanding implant-supported FPDs after 2 years of function. Twenty-nine partially edentulous patients presenting with unilateral or bilateral distal-extension edentulous areas received FPDs and were followed for a minimum of 24 months. In all, 49 FPDs were fabricated. In 34 FPDs, implants were connected to teeth and thus the FPDs were categorized as mixed (m-FPDs), whereas 15 FPDs were supported by freestanding terminal implants (fs-FPDs). Evaluation of prosthetic parameters including mechanical complications was performed. Changes in marginal bone level (DeltaMBL) around implants in both treatment groups were measured on digitalized periapical radiographs. Neither loss of osseointegration of an implant nor intrusion of abutment teeth was recorded. All FPDs were functioning after 24 months. Mean DeltaMBLs of posterior implants supporting m-FPDs and fs-FPDs at 24 months were 0.189 mm and -0.285 mm, respectively, representing a significant difference (P < .05). Mean DeltaMBLs at the mesial and distal surfaces of anterior and posterior implants supporting fs-FPDs were similar (P > .05). In the treatment of short-span distal-extension edentulous areas, similar clinical outcomes may be obtained for implant- and tooth/implant-supported three-unit FPDs in the early stages of function.

A classification system to measure the implant-abutment microgap.

PURPOSE: A large microgap at the implant-abutment interface has been reported to result in adverse effects, including screw loosening, abutment rotation, and abutment fracture. However, a standardized classification of the implant-abutment interface has not been established. The purposes of this investigation were (1) to propose a classification system based on the horizontal and vertical microgap of the implant-abutment interface and (2) to compare the implant-abutment interface in 4 groups of abutments. MATERIALS AND METHODS: Forty-eight randomly selected external hexagonal implants were paired with (1) machined titanium abutments, (2) premachined palladium abutments cast-on with palladium alloy, (3) plastic burnout abutments cast with nickel chromium alloy, and (4) plastic burnout abutments cast with cobalt chromium alloy. A comparison of the horizontal and vertical microgaps at the implant-abutment interface was completed at 8 locations on each specimen to the nearest micrometer using an optical microscope with a magnification of 150x. Group means and significant differences between groups were determined by analysis of variance and Tukey multiple-comparisons post-hoc analysis. P < .05 was the threshold for statistical significance. RESULTS: There was no significant difference between groups with respect to vertical misfit. For horizontal misfit, machined titanium abutments presented significantly higher horizontal misfit compared to other groups (P < .001). Premachined cast-on abutments had significantly higher horizontal misfit than cast NiCr abutments (P < .001). In the proposed classification system, 23% of all sites measured at the implant-abutment interface had an ideal relationship, 34% had a horizontal discrepancy only, 4% had a vertical discrepancy only, and 39% had both vertical and horizontal discrepancies. CONCLUSION: The proposed implant-abutment classification system demonstrated a way to characterize and compare the microgap at the implant-abutment interface.

The pier abutment: a review of the literature and a suggested mathematical model.

Many clinicians consider the prosthetic restoration of missing posterior teeth by means of a 5-unit fixed partial denture with a pier abutment a non-favorable situation. The present article assesses the validity of the pier abutment by means of a critical review of the literature and mathematical analysis of the forces generated within a fixed partial denture of this design. Few studies are available, and none substantiate the theory that the pier abutment serves as a fulcrum. A mathematical model suggests that debonding may occur in the anterior abutment, but not due to the teetering of the fixed partial denture around the pier abutment.

A 16-year study of the microgap between 272 human titanium implants and their abutments.

A microgap has been described at the level of the implant-abutment connection. This microgap can be colonized by bacteria, and this fact could have relevance on the remodeling of the peri-implant crestal bone and on the long-term health of the peri-implant tissues. The authors report on 272 implants with screw- or cement-retained abutments retrieved from humans for different causes during a 16-year period. In the implants with screw-retained abutments, a 60-microm microgap was present at the level of implant-abutment connection. In some areas the titanium had sheared off from the surface and from the internal threads. The contact between the threads of the implant and those of the abutment was limited to a few areas. Bacteria were often present in the microgaps between implant and abutment and in the internal portion of the implants. In implants with cement-retained abutments, a 40-microm microgap was found at the level of the implant-abutment connection. No mechanical damage was observed at the level of the implant or of the abutment. All the internal voids were always completely filled by the cement. No bacteria were observed in the internal portion of the implants or at the level of the microgap. The differences in the size of the microgap between the two groups were statistically significant (P < .05). In conclusion, in screw-retained abutments the microgap can be a critical factor for colonization of bacteria, whereas in cement-retained abutments all the internal spaces were filled by cement. In these retrieved implants, the size of the microgap was markedly variable and much larger than that observed in vitro.

Ideal gingival form with computer-generated permanent healing abutments.

Implant fixture positioning and inclination problems that result from poor osseous height, width, and ridge configuration have created difficult prosthetic tooth replacement scenarios. Options for ameliorating poor angulation are limited to the use of preangled and custom abutments. Overcoming poor angulation has been simplified by using custom vs preangled abutments because preangled abutments are limited by their standardization to a few random angles. Custom abutments can be more predictably formed to re-create the desired supporting preparation orientation and morphology. This facilitates the formation of anatomical gingival topography and coronal contours for prosthetic replacement. Cast, ceramic, and machine-milled titanium abutments have several advantages and disadvantages. A new custom abutment system that uses computer-guided manufacturing technology to machine mill custom abutments from commercially pure titanium is described. These abutments are anatomically correct, have the proper emergence anatomy, proper spatial design at the cervical margins, necessary occlusal reduction, and the proper axial angulation of ideal tooth preparations. A clinical case that illustrates implementation, with respect to the principle of stage 2 guided tissue healing, is presented.

Generic terminology for endosseous implant prosthodontics.

Implant dentistry has become an integral treatment modality in the restoration of the complete and partially edentulous patient. Most practitioners have been educated by manufacturer-sponsored courses oriented to the use of a specific implant system. The ever-increasing number of implant systems has made the names of many implant components product-unique and confusing. Fortunately, a prosthetic continuity exists between most implant systems. A generic terminology for endosseous root-form prosthodontics is presented that allows effective communication between members of the profession.