Roy Judge

Fracture resistance of titanium and zirconia abutments: an in vitro study.

STATEMENT OF PROBLEM Little information comparing the fracture resistance of internal connection titanium and zirconia abutments exists to validate their use intraorally. PURPOSE The purpose of this study was to determine the fracture resistance of internal connection titanium and zirconia abutments by simulating cyclic masticatory loads in vitro. MATERIAL AND METHODS Twenty-two specimens simulating implant-supported anterior single crowns were randomly divided into 2 equal test groups: Group T with titanium abutments and Group Z with zirconia abutments. Abutments were attached to dental implants mounted in acrylic resin, and computer-aided design/computer-aided manufacturing (CAD/CAM) crowns were fabricated. Masticatory function was simulated by using cyclic loading in a stepped fatigue loading protocol until failure. Failed specimens were then analyzed by using scanning electron microscopy (SEM) and fractographic analysis. The load (N) and the number of cycles at which fracture occurred were collected and statistically analyzed by using a 2-sample t test (α=.05). RESULTS The titanium abutment group fractured at a mean (SD) load of 270 (56.7) N and a mean (SD) number of 81 935 (27 929) cycles. The zirconia abutment group fractured at a mean (SD) load of 140 (24.6) N and a mean (SD) number of 26 296 (9200) cycles. The differences between the groups were statistically significant for mean load and number of cycles (P<.001). For the titanium abutment specimens, multiple modes of failure occurred. The mode of failure of the zirconia abutments was fracture at the apical portion of the abutment without damage or plastic deformation of the abutment screw or implant. CONCLUSIONS Within the limitations of this in vitro study, 1-piece zirconia abutments exhibited a significantly lower fracture resistance than titanium abutments. The mode of failure is specific to the abutment material and design, with the zirconia abutment fracturing before the retentive abutment screw.

Implications of implant framework misfit: a systematic review of biomechanical sequelae.

PURPOSE The objective of this study was to review all biomechanical investigations that have evaluated the implications of implant framework misfit with fixed prostheses. MATERIALS AND METHODS A detailed electronic search was conducted of PubMed (MEDLINE), Google Scholar, and Cochrane Library with the aid of Boolean operators to combine relevant key words. The search was confined to articles published in English through April 2013. The literature search was enlarged by manual searches of the peer-reviewed literature and the reference lists of the selected articles. RESULTS A total of 633 articles were retrieved from the initial search; however, only 28 articles met the determined inclusion criteria of the review. According to the study design, the selected articles were classified into two categories: laboratory studies (finite element analyses, actual model analyses, and screw stability analyses) and animal studies. The studies evaluated the effects of alterations in the magnitude and configuration of misfit, framework rigidity, type of retaining screws, and implant loading time. In addition to a lack of clear criteria of what constitutes an accurate implant framework fit, the biomechanical implications of framework misfit are unclear. CONCLUSIONS Although implant framework misfit alters the biomechanical situation, negative biomechanical sequelae could not be confirmed from the included studies. Biologically, bone resorption cannot develop as a result of framework misfit. From a mechanical perspective, the framework stresses and screw stresses and instability increase with misfit, but the clinical significance of this remains unclear.

In vitro bone strain analysis of implant following occlusal overload

OBJECTIVES To enumerate peri-implant bone strain pattern under quantified occlusal load and verify the bone response through comparison with the critical strain thresholds defined by Frosts bone mechanostat theory. MATERIAL AND METHODS Mandibular unilateral recipient sites in two greyhound dogs were established with posterior teeth extractions. After 6 weeks, four titanium implants were placed in each dog mandible. Following 12 weeks of healing, successfully osseointegrated implants were placed in supra-occlusal contact via screw-retained non-splinted metal crowns. Plaque control and a dental health enhancing diet were prescribed. A bite force detection device was used to quantify in vivo occlusal load as the dogs functioned with supra-occlusal contact. After 8 weeks, the dogs were sacrificed. In vitro peri-implant bone strain under quantified occlusal load was measured using bonded stacked rosette strain gauges. RESULTS The average and peak in vivo occlusal load measured were 434 and 795 newton (N). When individually and simultaneously loaded in vitro (≤476 N), absolute bone strains up to 1133 and 753 microstrains (με) were measured at implant apices, respectively. Bone strain reaching 229 με was recorded at distant sites. For bone strain to reach the pathological overload threshold defined by Frosts bone mechanostat theory (3000 με), an occlusal load of 1344 N (greater than peak measured in vivo) is required based on the simple linear regression model. CONCLUSION Under the in vivo and in vitro conditions investigated in this study, peri-implant bone was not found to be under pathological overload following supra-occlusal contact function. Strain dissipation to distant sites appeared to be an effective mechanism by which implant overload was avoided.

Diamond as a scaffold for bone growth

Diamond is an attractive material for biomedical implants. In this work, we investigate its capacity as a bone scaffold. It is well established that the bioactivity of a material can be evaluated by examining its capacity to form apatite-like calcium phosphate phases on its surface when exposed to simulated body fluid. Accordingly, polycrystalline diamond (PCD) and ultrananocrystalline diamond (UNCD) deposited by microwave plasma chemical vapour deposition were exposed to simulated body fluid and assessed for apatite growth when compared to the bulk silicon. Scanning electron microscopy and X-ray photoelectron spectroscopy showed that both UNCD and PCD are capable of acting as a bone scaffold. The composition of deposited apatite suggests that UNCD and PCD are suitable for in vivo implantation with UNCD possible favoured in applications where rapid osseointegration is essential.

Evaluation of the fit of CAD/CAM abutments.

PURPOSE This study aimed to compare the fit of computer-aided design/computerassisted manufacture (CAD/CAM) abutments provided by a single system with proprietary prefabricated abutments on various implant systems. MATERIALS AND METHODS Titanium CAD/CAM abutments were compared with prefabricated abutments on five different implant types. The samples were embedded in epoxy resin, sectioned longitudinally, and polished. Scanning electron microscopy was used to measure the gap between the implants and abutments at the connecting flanges and internal features. Independent t tests were used to compare data. RESULTS A mean difference of 1.86 μm between the gold synOcta and CAD/CAM abutments on the Straumann Standard Plus implant was observed to be statistically significant (P = .002). Less than 0.4 μm of difference was found between the CAD/CAM and prefabricated abutments for the remaining implant types, and statistical significance was not observed. Mean differences of 34.4 μm (gold) and 44.7 μm (titanium) were observed between the CAD/ CAM and prefabricated abutments on the Straumann Standard Plus implants, which were statistically significant (P < .001). A mean difference of 15 μm was also observed between the CAD/CAM and prefabricated abutment on the NobelReplace implant, which was statistically significant (P = .026). All other groups had less that 4 μm of difference, and statistical significance was not observed. CONCLUSION The CAD/CAM abutments appeared to have a comparable fit with prefabricated abutments for most of the systems evaluated. Design differences between the abutment connections for both Straumann implants were observed that affected the fit of internal components of the implant-abutment connections.

Description of a photoelastic coating technique to describe surface strain of a dog skull loaded in vitro

There are several methods of determining strain in the facial skeleton on loading in vitro. This article describes an alternative photoelastic coating technique adapted from the commonly accepted method used by engineers to study surface strains in objects. In applying this method to the stomatognathic system, because the masticatory apparatus is loaded by muscular contraction an opposite reaction load should be distributed throughout the skeletal structure. This load distribution should slightly deform the bones to which the muscles of mastication are attached. An understanding of the resulting strain generated in the facial skeleton is important because strain distribution on loading reflects how the loads applied during mastication are partially dissipated. Preliminary descriptive results are presented, suggesting that anatomic structures influence the distribution of strain on loading. The technique described should allow in vitro investigation of the mechanical environment into which osseointegrated implants are placed and may aid in understanding their behavior.

Strategies for restoration of single implants and use of cross‐pin retained restorations by Australian prosthodontists

BACKGROUND Implant supported restorations (ISRs) for the single implant may be cement retained or screw retained. Limited scientific evidence exists to support the superiority of a retention type for either implant or prosthetic success. The aim of this study was to assess preferences of Australian prosthodontists when restoring single implants. In particular, clinical practices for cross-pin retained implant supported restorations for a single implant were investigated. METHODS A written questionnaire comprised of seven questions, some of which had multiple parts and of both open- and closed-format, was sent to 124 Australian prosthodontists. The questionnaire asked recipients to identify: (1) their preference for retention choice when restoring a single implant; (2) the frequency of use; and (3) clinical practice when restoring a cross-pin retained restoration. RESULTS Seventy-seven per cent of respondents indicated that direct to fixture (DTF) retention was their first preference. DTF retention was also the most frequently employed restoration for single implants. Respondents indicated that cross-pinned ISRs are employed to maintain retrievability or when DTF is not possible. The majority of respondents indicated they always or sometimes use a gasket with cross-pin retained restorations, though gasket type varied. Thirty-eight respondents (31%) indicated that they would never use a cross-pinned retained restoration for a single ISR. CONCLUSIONS Australian prosthodontists prefer, and more frequently restore single implants, using DTF retention. Queensland prosthodontists prefer cement retained ISRs. In comparison, cross-pinned restorations tend to be the least favoured and least used retention type. In addition, variation in opinion exists regarding the need for a gasket and type of gasket to be placed.

Fracture force of cantilevered zirconia frameworks: an in vitro study.

STATEMENT OF PROBLEM Little evidence is available showing the effect of connector dimension and cantilever length on the ultimate fracture force of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia implant frameworks. PURPOSE The purpose of the study was to determine the impact of variations in the cross-sectional dimension of connector sites and variations in the effective cantilever length (load point) on zirconia implant frameworks. This would allow verification of the fracture force with 2 proposed mathematical models. MATERIAL AND METHODS Forty zirconia implant-supported frameworks with 12-mm distal cantilevers were divided into 4 equal test groups (n=10). Connector dimensions (3×5 mm, 3×4 mm) and cantilever loading distance (7 mm, 10 mm) were tested for ultimate fracture force. A 2-way analysis of variance (ANOVA) was used to examine the ultimate fracture force and examine the relationship between connector dimension and ultimate fracture force. The data obtained from all 4 groups were compared and verified with calculations from 2 theoretical mathematical models. RESULTS Two-way ANOVA revealed significant effects for cross-sectional area connector dimension on fracture force (P<.001) and cantilever length (P=.009). No statistically significant interaction was observed between the 2 factors (P=.229). The observed data were consistent with the data from the proposed mathematical models, with group comparisons showing no statistical significance. The largest difference between the mathematical results and mathematical models was in the 7 mm 3×5 mm group of the fixed cantilever bending model (P=.032). The predominant mode of failure was fracture of the zirconia framework, without damage or plastic deformation of the abutment screws or implant analogs. The 10 mm 3×5 mm specimens fractured at a mean load of 923.7 ±234.5 N; the 10 mm 3×4 mm specimens at a mean load of 474.8 ±122.9 N; the 7 mm 3×5 mm specimens at a mean load of 1011.7 ±185.3 N; and the 7 mm 3×4 mm specimens at a mean load of 700.9 ±152.4 N. CONCLUSIONS Zirconia implant frameworks loaded 7 mm from the distal abutment failed at higher fracture loads than specimens loaded 10 mm from the distal abutment. Zirconia implant frameworks with cross-sectional area connector dimensions of 3×5 mm failed at higher fracture loads than specimens with cross-sectional area connector dimensions of 3×4 mm. No statistically significant interaction was observed between the cross-sectional connector area dimension and cantilever length. Calculations from the mathematical models closely approximated the observed data, which supports the use of the mathematical models as a predictor of fracture force.

A 5-Year Retrospective Assay of Implant Treatments and Complications in Private Practice: The Restorative Complications of Single and Short-Span Implant-Supported Fixed Prostheses.

PURPOSE This report aims to describe the restorative outcome of 5,491 implant-supported single crowns, fixed partial dentures, and splinted restorations that were prescribed or had implants placed during the study period. Timing of the complications and the relationship between the complications and different factors (practitioner, patient, and restoration) are examined. MATERIALS AND METHODS Dental clinicians qualified in or before December 2004, registered in Victoria, and placing and/or restoring implants in private practice were invited to participate in the study. Data extraction was conducted by two trained and calibrated research assistants with specific training in implant terminology and previous research experience extracting data from dental records. Prostheses average time observed/in function was calculated using the difference between the definitive restoration date and the patient record examination date or the date of implant/restoration lost. Both descriptive statistics and generalized linear mixed modeling were used to describe the restorative complications. RESULTS Over the study period a total of 499 mechanical complications were recorded. Single-implant crowns had the largest sample size (n = 4,760) and a recorded complication rate of 2.56 per 100 prostheses per year. The majority of screw loosenings recorded in this study were inadequately described. In single-implant crowns, abutment screw loosening occurred at a rate of 0.07 per 100 per year while unspecified screw loosening occurred at a rate of 0.53. Lateral screw loosening was more common in lateral screw-retained implant crowns (1.06) than decementation was in cement-retained implant crowns (0.57). Esthetics (0.25), veneer chipping or fracture (0.41), and food packing/contact point issues (0.53) also represent significant portions of the restorative complications. Each type of complication presented with a slightly different timing profile. Clustering within the first year was common. The ratio of screw loosening between the group who prescribed between 1 and 100 during the study period and those who prescribed more than 501 implant restorations was 1:0.15 (P = .005). Patients with operator-reported attrition had double the rate of veneer fracture (P = .005). Contact point issues were approximately three times more common in the posterior segment (P = .001). CONCLUSION During the period of January 2005 to December 2009, screw loosening, lateral screw loosening, decementation, esthetic complication, veneer chipping or fracture, and food packing/contact point issues were recorded at different rates for different types of prostheses in the private practices included in this study. Clusters of several complications within the first year were observed. For single-implant crowns, screw-loosening complications were less frequent in the more experienced group. Operator-reported attrition was related to higher rate of veneering material fracture. More contact point complications were found in the posterior regions of the oral cavity.

Five-Year Retrospective Assay of Implant Treatments and Complications in Private Practice: Restorative Treatment Profiles of Single and Short-Span Implant-Supported Fixed Prostheses.

PURPOSE The aim of this study was to describe and analyze the restoration profiles of 5,491 implant-supported single crowns, fixed partial dentures (FPDs), and splinted restorations prescribed between January 2005 and December 2009. MATERIALS AND METHODS Dental clinicians qualified in or before December 2004, registered in Victoria, and placing and/or restoring implants in private practice were invited to participate in the study. Data was extracted by two trained and calibrated research assistants from dental records. Cross tabulation was carried out in SPSS (IBM) to provide descriptive statistics on clinician profiles, patient demographics, and restoration information. RESULTS A total of 34 practitioners participated in the study: 25 general dentists and 9 specialists. Clinicians that graduated between 1970 and 1989 (16 to 40 years of experience) prescribed most of the prostheses (82.0%). Female patients were present in higher numbers across most age and restoration groups. Of the implant-supported prostheses, 5,491 fit the criteria for simple basic restorations and were included in this report. The majority of the prostheses (86.7%) were single-tooth restorations. Metal-ceramic was the material of choice for the majority of the restorations (3,382/5,491). The use of single implant-supported crowns in the anterior mandible was rare. More than 65% of the implant-supported restorations in this study were screw retained directly to the implant. The specialist clinicians in this study largely used the screw-retained method to retain single implant-supported crowns (82.0%). General dentists provided 1,066% more cement-retained single implant-supported crowns compared with other practitioners. CONCLUSION This report showed that during the period of January 2005 to December 2009, private practice clinicians in Victoria, Australia favored porcelain-fused-to-metal material over all-ceramic for implant restorations. Most implant restorations were single crowns. More female patients received implant-supported restorations in the posterior region of the mouth. The clinicians included in this study, particularly the specialists, generally favored a retrievable design in choosing the retention method for the prostheses.