Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long‐Term Use In Vivo. Part 2: Metallurgical and Microhardness Analysis

Abstract Purpose: This study involved testing and analyzing multiple retrieved prosthetic retaining screws after long‐term use in vivo to: (1) detect manufacturing defects that could affect in‐service behavior; (2) characterize the microstructure and alloy composition; and (3) further characterize the wear mechanism of the screw threads. Materials and Methods: Two new (control) screws from Nobel Biocare (NB) and 18 used (in service 18–120 months) retaining screws [12 from NB and 6 from Sterngold (SG)] were: (1) metallographically examined by light microscopy and scanning electron microscopy (SEM) to determine the microstructure; (2) analyzed by energy dispersive X‐ray (EDX) microanalysis to determine the qualitative and semiquantitative average alloy and individual phase compositions; and (3) tested for Vickers microhardness. Results: Examination of polished longitudinal sections of the screws using light microscopy revealed a significant defect in only one Group 4 screw. No significant defects in any other screws were observed. The defect was considered a “seam” originating as a “hot tear” during original casting solidification of the alloy. Additionally, the examination of longitudinal sections of the screws revealed a uniform homogeneous microstructure in some groups, while in other groups the sections exhibited rows of second phase particles. The screws for some groups demonstrated severe deformation of the lower threads and the bottom part of the screw leading to the formation of crevices and grooves. Some NB screws were comprised of Au‐based alloy with Pt, Cu, and Ag as alloy elements, while others (Groups 4 and 19) were Pd‐based with Ga, Cu, and Au alloy elements. The microstructure was homogeneous with fine or equiaxed grains for all groups except Group 4, which appeared inhomogeneous with anomalous grains. SG screws demonstrated a typical dendritic structure and were Au‐based alloy with Cu and Ag alloy elements. There were differences in the microhardness of gold alloy screws from NB and SG as well as palladium alloy screws from NB. Conclusions: Significant differences within NB retaining screws and between NB and SG screws were found for microstructure, major alloy constituents, and microhardness

Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long‐term Use in vivo. Part 4: Failure Analysis of 10 Fractured Retaining Screws Retrieved from Three Patients

Purpose: The aim of this study was to perform a failure analysis on fractured prosthetic retaining screws after long‐term use in vivo. Additionally, the study addresses the commonly asked question regarding whether complex repeated functional occlusal forces initiate fatigue‐type cracks in prosthetic retaining screws. Materials and Methods: Ten fractured prosthetic retaining screws retrieved from three patients treated with fixed detachable hybrid prostheses were subjected to a failure analysis. In patients 1 and 2, the middle three retaining screws of the prostheses were found fractured at retrieval time after they had been in service for 20 and 19 months, respectively. In patient 3, the middle three and one of the posterior retaining screws were found to be fractured at retrieval after they had been in service for 18 months. Low power stereomicroscopy and high‐power scanning electron microscopy (SEM) were performed to analyze the fractured surfaces of the retaining screws examining fatigue cracks in greater detail. Results: Typical fatigue failure characterized by ratchet mark formation was revealed by light microscopy and SEM for all examined screws. Using low magnification light microscopy, ratchet marks were visible on the fracture surfaces of only two screws. SEM examination revealed all three classical stages of fatigue failure, and it was possible to see the ratchet marks on the fracture surfaces of all specimens, indicating a fatigue zone. The final catastrophic overload fracture appeared fibrous, indicating ductile fracture. The final overload ductile fracture surfaces showed equiaxed dimples, suggesting tensile overload in all examined screws except in two specimens that showed an elongated dimple pattern indicating shear/tearing overload forces. Conclusions: Fracture of prosthetic retaining screws in hybrid prostheses occurs mainly through a typical fatigue mode involving mostly the middle anterior three screws. Fatigue cracks can grow in more than one prosthetic retaining screw, leading to fracture before the patient or clinician determines that any problem exists

Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long‐term Use In Vivo. Part 3: Preload and Tensile Fracture Load Testing

Purpose: The aim of this study was to determine the preload and tensile fracture load values of prosthetic retaining screws after long‐term use in vivo compared to unused screws (controls). Additionally, the investigation addressed whether the preload and fracture load values of prosthetic retaining screws reported by the manufacturer become altered after long‐term use in vivo. Materials and Methods: For preload testing, 10 new screws (controls) from Nobel Biocare (NB) and 73 used retaining screws [58 from NB and 15 from Sterngold (SG)] were subjected to preload testing. For tensile testing, eight controls from NB and 58 used retaining screws (46 from NB and 12 from SG) were subjected to tensile testing. Used screws for both tests were in service for 18–120 months. A custom load frame, load cell, and torque wrench setup were used for preload testing. All 83 prosthetic screws were torqued once to 10 Ncm, and the produced preload value was recorded (N) using an X–Y plotter. Tensile testing was performed on a universal testing machine and the resulting tensile fracture load value was recorded (N). Preload and tensile fracture load values were analyzed with 2‐way ANOVA and Tukey post‐hoc tests. Results: There was a significant difference between preload values for screws from NB and screws from SG (p \u3c 0.001). The preload values for gold alloy screws from NB decreased as the number of years in service increased. There was a significant difference between tensile fracture values for the three groups (gold alloy screws from NB and SG and palladium alloy screws from NB) at p \u3c 0.001. The tensile fracture values for gold alloy screws from NB and SG decreased as the number of years in service increased. Conclusions: In fixed detachable hybrid prostheses, perhaps as a result of galling, the intended preload values of prosthetic retaining screws may decrease with increased in‐service time. The reduction of the fracture load value may be related to the increase of in‐service time; however, the actual determination of this relationship is not possible from this study alone

Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Long‐term Use In Vivo. Part 1: Characterization of Adhesive Wear and Structure of Retaining Screws

Purpose: The general aim of this study and those presented in Parts 2–4 of this series was to characterize the structure, properties, wear, and fracture of prosthetic retaining screws in fixed detachable hybrid prostheses after long‐term use in vivo. This part of the overall investigation addresses whether there are differences in thread wear between the screws closest to the fulcrum and those that are farthest from the fulcrum in fixed detachable hybrid prostheses. Materials and Methods: The total number of prosthetic retaining screws used in this study was 100 (10 new and 90 used). New screws (controls) from Nobel Biocare (NB) were divided into Group 1 (slotted) and Group 2 (hexed). Ninety used screws (in service 18–120 months) were retrieved from fixed detachable hybrid prostheses in 18 patients (5 screws from each patient, 60 from NB and 30 from Sterngold). The used screws were divided into 18 groups. Additionally, each group was subdivided into A and B categories. Category A contained the middle three prosthetic screws, which were considered the farthest screws from the fulcrum line. Category B contained the most posterior two screws, which were considered the screws closest to the fulcrum line. All 100 screws were subjected to thorough, nondestructive testing. Results: Light and scanning electron microscopic examination of all used screws for each group revealed surface deterioration of the active profile of the screw threads consistent with adhesive wear. The observed thread profile deterioration ranged from mild to severe. The wear was aggressive enough to cause galling, which led to thinning of the threads and, in severe cases, to knife‐edges at thread crests. In ten groups, the most anterior three screws exhibited more wear than the most posterior two screws. In addition to thread wear, severe plastic deformation was detected on the bottom part of each screw for three groups, and a long external longitudinal crack was detected in one screw of Group 2. Conclusions: The findings of this study and those presented in Parts 2–4 demonstrate that different retaining screws from the same manufacturer and/or from different manufacturers have different geometrical design, microstructures, major alloy constituents, and microhardness, and that these differences influence their preload and fractured load values. In this part of the overall investigation, the occurrence of galling as a result of wear involving prosthetic retaining screws appears to be an inevitable and unavoidable consequence of long‐term use in vivo in fixed detachable hybrid prostheses regardless of the intended/original preload value. The galling rate is greater on the middle three screws compared to the most posterior two screws in fixed detachable hybrid prostheses. The wear pattern is consistent with an adhesive wear mechanism; however, this study does not provide enough data to support a definitive analysis

Socio-demographics of Adult Orthodontic Visits in the United States

Introduction: Population-based studies in orthodontics have focused on differences between normative and perceived needs. However, information from national data on the prevalence of orthodontic visits and their associated factors in adults in the United States is scarce. We examined the demographic profile of likely adult users of orthodontic services and whether there is racial and ethnic disparity in orthodontic visits. Methods: We analyzed data from the Medical Expenditure Panel Survey, 2000-2004. Results: Overall, about 1% of the population reported an orthodontic visit. Subjects who made a general dental visit during the current year were significantly more likely to also have an orthodontic visit. Single adults, women, people between 18 and 30 years of age, and those from high-income families were more likely to report an orthodontic visit. There were no indications of racial and ethnic disparity for either black or Hispanic adults compared with white adults after adjusting for other covariates. Conclusions: Substantial racial and ethnic disparity in adult orthodontic usage was not identified. Adults (ages 18-30 years), women, those with higher incomes, and single adults had significantly higher odds of reporting an orthodontic visit. However, additional studies specifically evaluating the association of treatment need among low-income families are required to evaluate whether these adults face significant barriers in accessing orthodontic care

Periodontal-Systemic Disease Education in U.S. and Canadian Dental Schools

Research has proliferated in recent years regarding the relationship of oral disease to systemic conditions. Specifically, periodontal disease has been studied as a potential risk factor for multiple conditions such as cardiovascular disease (CVD) and adverse pregnancy outcomes, while other research focuses on exposures or behaviors associated with oral disease. However, few articles have been published reporting how this information is integrated into schools of dentistry, both in the classroom and clinical curriculum. For our study, a thirty-three-item survey and cover letter were electronically mailed to academic deans at sixty-five accredited dental schools in the United States and Canada in the fall of 2007. The response rate was 77 percent. According to the responses to this survey, the primary topics covered in the didactic curriculum regarding periodontal oral-systemic disease are aging, CVD, diabetes, and tobacco use. Eighty-eight percent of the respondents reported that their students are knowledgeable about the role of inflammation and its impact on oral-systemic conditions. Forty-eight percent of the respondents said they provide formal training for their students in how to discuss or communicate aspects of periodontal oral-systemic disease with patients. Only seven schools reported teaching didactic content to dental students intermixed with other health professions students, and only two schools reported conducting joint projects. Only 9 percent of the respondents said they think nurses and physicians are knowledgeable about oral-systemic disease. The findings indicate that dental schools are confident about the knowledge of their students regarding oral-systemic content. However, much work is needed to educate dental students to work in a collaborative fashion with other health care providers to co-manage patients at risk for oral-systemic conditions

Hmong Adults Self-Rated Oral Health: A Pilot Study

Since 1975, the Hmong refugee population in the U.S. has increased over 200%. However, little is known about their dental needs or self-rated oral health (SROH). The study aims were to: (1) describe the SROH, self-rated general health (SRGH), and use of dental/physician services; and (2) identify the factors associated with SROH among Hmong adults. A cross-sectional study design with locating sampling methodology was used. Oral health questionnaire was administered to assess SROH and SRGH, past dental and physician visits, and language preference. One hundred twenty adults aged 18–50+ were recruited and 118 had useable information. Of these, 49% rated their oral health as poor/fair and 30% rated their general health as poor/fair. Thirty-nine percent reported that they did not have a regular source of dental care, 46% rated their access to dental care as poor/fair, 43% visited a dentist and 66% visited a physician within the past 12 months. Bivariate analyses demonstrated that access to dental care, past dental visits, age and SRGH were significantly associated with SROH (P \u3c 0.05). Multivariate analyses demonstrated a strong association between access to dental care and good/excellent SROH. About half of Hmong adults rated their oral health and access to dental care as poor. Dental insurance, access to dental care, past preventive dental/physician visits and SRGH were associated with SROH

Transfer of Advances in Sciences into Dental Education Periodontal-Systemic Disease Education in U.S. and Canadian Dental Schools

Specifically, periodontal disease has been studied as a potential risk factor for multiple conditions such as cardiovascular disease (CVD) and adverse pregnancy outcomes, while other research focuses on exposures or behaviors associated with oral disease. However, few articles have been published reporting how this information is integrated into schools of dentistry, both in the classroom and clini-cal curriculum. For our study, a thirty-three-item survey and cover letter were electronically mailed to academic deans at sixty-five accredited dental schools in the United States and Canada in the fall of 2007. The response rate was 77 percent. According to the responses to this survey, the primary topics covered in the didactic curriculum regarding periodontal oral-systemic disease are aging, CVD, diabetes, and tobacco use. Eighty-eight percent of the respondents reported that their students are knowledge-able about the role of inflammation and its impact on oral-systemic conditions. Forty-eight percent of the respondents said they provide formal training for their students in how to discuss or communicate aspects of periodontal oral-systemic disease with pa-tients. Only seven schools reported teaching didactic content to dental students intermixed with other health professions students, and only two schools reported conducting joint projects. Only 9 percent of the respondents said they think nurses and physicians are knowledgeable about oral-systemic disease. The findings indicate that dental schools are confident about the knowledge of their students regarding oral-systemic content. However, much work is needed to educate dental students to work in a collabora

An update on novel non-invasive approaches for periodontal diagnosis

For decades there has been an ongoing search for clinically acceptable methods for the accurate, non-invasive diagnosis and prognosis of periodontitis. There are several well-known inherent drawbacks with current clinical procedures. The purpose of this review is to summarize some of the newly emerging diagnostic approaches, namely, infrared spectroscopy, optical coherence tomography (OCT), and ultrasound. The history and attractive features of these new approaches are briefly illustrated, and the interesting and significant inventions related to dental applications are discussed. The particularly attractive aspects for the dental community are that some of these methods are totally non-invasive, do not impose any discomforts to the patients during the procedure, and require no tissue to be extracted. For instance, multiple inflammatory indices withdrawn from near infrared spectra have the potential to identify early signs of inflammation leading to tissue breakdown. Morphologically, some other non-invasive imaging modalities, such as OCT and ultrasound, could be employed to accurately measure probing depths and assess the status of periodontal attachment, the front-line of disease progression. Given that these methods reflect a completely different assessment of periodontal inflammation, if clinically validated, these methods could either replace traditional clinical examinations for the diagnosis of periodontitis or at least serve as attractive complementary diagnostic tools. However, the potential of these techniques should be interpreted more cautiously given the multifactorial character of periodontal disease. In addition to these novel tools in the field of periodontal inflammatory diseases, other alternative modalities like microbiologic and genetic approaches are only briefly mentioned in this review because they have been thoroughly discussed in other comprehensive reviews.Peer reviewed: YesNRC publication: Ye