Auto-Segmentation and Quantification of Non-Cavitated Enamel Caries Imaged with Swept-Source Optical Coherence Tomography.

(1) Background: OCT imaging has been used to assess enamel demineralization in dental research, but it is not yet developed enough to qualify as a diagnostic technique in clinics. The current capabilities of most commercial acquisition software allow for visual and qualitative assessments. There is a need for a fast and verified batch-processing algorithm to segment and analyze demineralized enamel. This study suggests a GUI MATLAB algorithm for the processing and quantitative analysis of demineralized enamel. (2) Methods: A group of artificially demineralized human enamels was in vitro scanned under the OCT, and ROI frames were extracted. By using a selected intensity threshold colormap, Inter- (Ie) and Intra- (Ia) prismatic demineralization can be segmented. A set of quantitative measurements for the average demineralized depth, average line profile, and integrated reflectivity can be obtained for an accurate assessment. Real and simulated OCT frames were used for algorithm verification. (3) Results: A strong correlation between the automated and known Excel measurements for the average demineralization depth was found (R2 > 0.97). (4) Conclusions: OCT image segmentation and quantification of the enamel demineralization zones are possible. The algorithm can assess the future development of a real-time assessment of dental diagnostics using an oral probe OCT.

Displacement of a Dental Implant into the Pterygoid Fossa: A Clinical Report.

The placement of dental implants in the pterygomaxillary region can be advantageous in maxillary complete arch fixed implant-supported prosthetic rehabilitations to avoid bone grafting and sinus elevation surgeries. Pterygomaxillary implants improve implant biomechanics by eliminating distal cantilevers and increasing the anteroposterior spread with reported mean implant survival rates comparable to traditional implant sites. Although only minor surgical complications have been reported in the literature with the placement of dental implants in the pterygomaxillary region this clinical report describes a major surgical complication involving the displacement of a dental implant into the pterygoid fossa.

Postmortem evaluation of mandibular implant-supported fixed complete denture after 30 years of service.

A postmortem evaluation of a 5-implant-supported mandibular fixed complete denture that had successfully opposed a maxillary conventional complete denture for 30 years was undertaken. Before embalming, radiographs, implant stability measurements, push-in failure load tests, and histomorphometric analyses were performed on the implants and the mandible. Evaluation of this cadaver suggests that an edentulous mandible restored with an implant-supported fixed prosthesis can function successfully for over 30 years with few complications.

Comparison of the correlation of photoelasticity and digital imaging to characterize the load transfer of implant-supported restorations.

STATEMENT OF PROBLEM: Whether splinting or not splinting adjacent implants together can optimize the stress/strain transfer to the supporting structures remains controversial. PURPOSE: The purpose of this study was to compare the photoelasticity and digital image correlation (DIC) in analyzing the stresses/strains transferred by an implant-supported prosthesis. MATERIAL AND METHODS: A polymethylmethacrylate model was made with a combination of acrylic resin replicas of a mandibular first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and nonsplinted (G2/G4) metal-ceramic screw-retained crowns were loaded with (G1/G2) and without (G3/G4) the presence of the second molar. Vertical static loads were applied to the first molar implant-supported crown (50 N-photoelasticity; 250 N-DIC). The resulting isochromatic fringes in the photoelastic models were photographed, and a single-camera 2-dimensional DIC system recorded the deformation at the surface of the resin models. RESULTS: Residual stresses were present in the photoelastic model after screw fixation of the crowns. The following average photoelastic stress results (MPa) were found around the loaded implant: G1 (20.06), G2 (23.49), G3 (30.86), G4 (37.64). Horizontal strains (εxx, %) between the molars averaged over the length of the loaded implant were found by DIC: G1 (0.08 ± 0.09), G2 (0.13 ± 0.10), G3 (0.13 ± 0.11), G4 (0.16 ± 0.11). Splinted crowns transferred lower stresses to the supporting bone when the second molar was absent. The second molar optimized the stress distribution between the supporting structures even for nonsplinted restorations. CONCLUSIONS: Both methods presented similar results and seemed capable of indicating where issues associated with stress/strain concentrations might arise. However, DIC, while apparently less sensitive than photoelasticity, is not restricted to the use of light-polarizing materials.

Validation of finite element models for strain analysis of implant-supported prostheses using digital image correlation.

OBJECTIVES: A validated numerical model for stress/strain predictions is essential in understanding the biomechanical behavior of implant-supported dental prostheses. The digital image correlation (DIC) method for full-field strain measurement was compared with finite element analysis (FEA) in assessing bone strain induced by implants. METHODS: An epoxy resin model simulating the lower arch was made for the experimental test with acrylic resin replicas of the first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and non-splinted (G2/G4) metal-ceramic screw-retained crowns were fabricated and loaded with (G1/G2) or without (G3/G4) the second molar that provided proximal contact. A single-camera, two-dimensional DIC system was used to record deformation of the resin model surface under a load of 250N. Three-dimensional finite element (FE) models were constructed for the physical models using computer-aided design (CAD) software. Surface strains were used for comparison between the two methods, while internal strains at the implant/resin block interface were calculated using FEA. RESULTS: Both methods found similar strain distributions over the simulant bone block surface, which indicated possible benefits of having splinted crowns and proximal contact in reducing bone strains. Internal strains predicted by FEA at the implant-resin interface were 8 times higher than those on the surface of the model, and they confirmed the results deduced from the surface strains. FEA gave higher strain values than experiments, probably due to incorrect material properties being used. SIGNIFICANCE: DIC is a useful tool for validating FE models used for the biomechanical analysis of dental prosthesis.

Comparison of push-in versus pull-out tests on bone-implant interfaces of rabbit tibia dental implant healing model.

PURPOSE: This study aimed to investigate whether push-in and pull-out tests measure mechanical properties of the bone-implant interface differently, and which test is more sensitive to changes over the healing period. MATERIALS AND METHODS: Two identical self-threading dental implants (3.3×8.5mm) were placed in medial surface of the proximal condyles of left and right tibias of 20 rabbits (40 implants total). Five rabbits each were sacrificed after 1, 4, 8, and 12 weeks of healing. Push-in test was performed on one side's tibia implant and pull-out on the other side's implant, at a rate of 6mm/min. Primary and secondary implant stabilities and tibia weight were measured on all implants. RESULTS: The push-in test generated significantly higher failure load (p=.0001; 530N vs 279N), lower displacement at failure (p=.0003; 0.436mm vs 0.680mm), and higher interface stiffness (p<.0001; 1,641N/mm vs 619N/mm) than pull-out test. Failure load, stiffness, and secondary implant stability were significantly higher for longer compared with shorter healing periods, while displacement, tibia weight, and primary stability were not. Failure load and stiffness differed significantly for four healing times for the push-in but not for the pull-out test. Failure load was significantly correlated with secondary implant stability for both push-in (r=0.66) and pull-out (r=0.48) tests, but stiffness was significantly correlated with secondary stability only for the push-in test (r=0.72; pull-out test r=0.40). CONCLUSION: The push-in test appeared more sensitive than pull-out to changes in mechanical properties at bone-implant interfaces during healing in rabbit tibia model.

Prevalence of sinus augmentation associated with maxillary posterior implants.

Pneumatization of the maxillary sinus limits the quantity of alveolar bone available for implant placement and may result in a lack of primary stability and difficulty in achieving osseointegration. The purpose of this study was to retrospectively analyze a group of patients who had implants placed in the posterior maxilla, calculate the prevalence of sinus augmentation, and identify factors related to sinus augmentation. With institutional review board approval, dental records from a population of patients who had implants placed in the maxillary posterior region between January 2000 and December 2004 were used to create a database. Independent variables were classified as continuous (age of the patient at stage 1 implant surgery [S1], time between extraction and S1, time between extraction and sinus augmentation, and time between sinus augmentation and S1) and categorical (gender, implant failure, American Society of Anesthesiologists system classification, smoking, osteoporosis, residual crestal bone height, implant position, implant proximity, prostheses type, and implant diameter and length). The dependent variable was the incidence of a sinus augmentation procedure. Simple logistic regression was used to assess the influence of each factor on the presence of sinus augmentation (P < .05). The final database included 502 maxillary posterior implants with an overall survival rate of 93.2% over a mean follow-up period of 35.7 months. Of 502 implants, 272 (54.2%) were associated with a sinus augmentation procedure. Among variables, residual crestal bone height (P < .001), implant position (P < .001), implant proximity (P < .001), prosthesis type (P < .001), implant failure (P < .01), and implant diameter (P < .01), were statistically associated with sinus augmentation. Within the limitations of this retrospective study, the results suggest that more than half (54.2%) of the maxillary posterior implants were involved with a sinus augmentation procedure. The prevalence of sinus augmentation increased with decreased residual crestal bone height, more posterior implant locations, and complete or partial edentulism. Sinus augmentation was significantly associated with implant failure and wide implants.

Effect of surgical guide design and surgeon's experience on the accuracy of implant placement.

Implant position is a key determinant of esthetic and functional success. Achieving the goal of ideal implant position may be affected by case selection, prosthodontically driven treatment planning, site preparation, surgeon's experience and use of a surgical guide. The combined effect of surgical guide design, surgeon's experience, and size of the edentulous area on the accuracy of implant placement was evaluated in a simulated clinical setting. Twenty-one volunteers were recruited to participate in the study. They were divided evenly into 3 groups (novice, intermediate, and experienced). Each surgeon placed implants in single and double sites using 4 different surgical guide designs (no guide, tube, channel, and guided) and written instructions describing the ideal implant positions. A definitive typodont was constructed that had 3 implants in prosthetically determined ideal positions of single and double sites. The position and angulation of implants placed by the surgeons in the duplicate typodonts was measured using a computerized coordinate measuring machine and compared to the definitive typodont. The mean absolute positional error for all guides was 0.273, 0.340, 0.197 mm in mesial-distal, buccal-lingual, vertical positions, respectively, with an overall range of 0.00 to 1.81 mm. The mean absolute angle error for all guides was 1.61° and 2.39° in the mesial-distal and buccal-lingual angulations, respectively, with an overall range of 0.01° to 9.7°. Surgical guide design had a statistically significant effect on the accuracy of implant placement regardless of the surgeon's experience level. Experienced surgeons had significantly less error in buccal-lingual angulation. The size of the edentulous sites was found to affect both implant angle and position significantly. The magnitude of error in position and angulation caused by surgical guide design, surgeon's experience, and site size reported in this study are possibly not large enough to be clinically significant; however, it is likely that errors would be magnified in clinical practice. Future research is recommended to evaluate the effect of surgical guide design in vivo on implant angulation and position error.

Dental students choosing licensure path give more consideration to career flexibility rather than ethical dilemmas.

Although a patient-based clinical licensure examination (CLE) has been used in the United States for many decades to evaluate an individual's competency to practice dentistry, there continue to be validity, reliability, and ethical issues of concern to the profession. As a result of a 2009 decision by the Minnesota Board of Dentistry, dental students from the University of Minnesota School of Dentistry, beginning with the Class of 2010, are eligible for initial licensure in Minnesota by passing the nonpatient-based National Dental Examining Board of Canada Examination. Surveys were distributed to 101 senior dental students to assess what factors students used to decide whether or not to register for a patient-based CLE. The response rate to the survey was 84.2% (85/101). The opportunity to apply for a license in multiple states after passing a patient-based CLE was the primary factor in influencing the students to register for a patient-based CLE. Regarding the use of live patients in a CLE, students were most concerned with having to operatively restore teeth that could be treated more conservatively and for other reasons outside of their control, such as the patient failing to show up, patient not being accepted by the examiners, and procedural issues during the examination.

Digital image correlation analysis of the load transfer by implant-supported restorations.

This study compared splinted and non-splinted implant-supported prosthesis with and without a distal proximal contact using a digital image correlation method. An epoxy resin model was made with acrylic resin replicas of a mandibular first premolar and second molar and with threaded implants replacing the second premolar and first molar. Splinted and non-splinted metal-ceramic screw-retained crowns were fabricated and loaded with and without the presence of the second molar. A single-camera measuring system was used to record the in-plane deformation on the model surface at a frequency of 1.0Hz under a load from 0 to 250N. The images were then analyzed with specialist software to determine the direct (horizontal) and shear strains along the model. Not splinting the crowns resulted in higher stress transfer to the supporting implants when the second molar replica was absent. The presence of a second molar and an effective interproximal contact contributed to lower stress transfer to the supporting structures even for non-splinted restorations. Shear strains were higher in the region between the molars when the second molar was absent, regardless of splinting. The opposite was found for the region between the implants, which had higher shear strain values when the second molar was present. When an effective distal contact is absent, non-splinted implant-supported restorations introduce higher direct strains to the supporting structures under loading. Shear strains appear to be dependent also on the region within the model, with different regions showing different trends in strain changes in the absence of an effective distal contact.

Retrospective cohort study of the predictors of implant failure in the posterior maxilla.

PURPOSE: The purpose of this study was to retrospectively analyze a cohort of patients who had implants placed in the posterior maxilla and assess and identify the predictors of implant failure. MATERIALS AND METHODS: With institutional review board approval, dental records from a population of patients who had maxillary posterior implants placed were used to create a database. Independent variables were divided into continuous (age of the patient at stage-one implant surgery [S1], time between extraction and S1, time between extraction and sinus augmentation, time between sinus augmentation and S1, time between S1 and stage-two implant surgery [S2], and the time between S2 and restoration of the implant) and categorical (gender, American Society of Anesthesiologists [ASA] status, current smoking status, implant position, implant proximity, residual crestal bone height, implant length and diameter, and sinus augmentation technique and materials). The dependent variable was implant failure, which was defined as complete removal of the implant. Simple logistic regression was used to assess the influence of each of the predictors on implant failure (P < .05). RESULTS: The final database included 504 maxillary posterior implants with an overall survival rate of 93.2% over a mean follow-up period of 35.7 months. For the continuous variables, the age of the patient at S1 was statistically associated with implant failure (P = .028), as was the time between extraction and S1 (P = .014). For the categorical variables, ASA status (P < .001), implant proximity (P = .043), residual crestal bone height (P < .001), implant diameter (P = .050), sinus augmentation technique (P = .002), and sinus graft materials (P < .001) were statistically associated with implant failure. CONCLUSION: Within the limitations of this retrospective study, the results suggest that there are risk factors associated with maxillary posterior implant failure. Implants placed in areas with inadequate residual crestal bone height that required sinus augmentation were statistically associated with implant failure.

Potential damage to bone-implant interface when measuring initial implant stability.

BACKGROUND: An electronically controlled mechanical tapping device (MTD) to measure implant stability has been studied extensively for its ability to measure initial stability at the time of surgical placement and predict an implant's survival prognosis, with few reported complications. METHODS: Initial stability data, measured repeatedly with a resonance frequency analysis device and the MTD, for seven of 28 implants placed in jawbones of four fresh human cadavers and the histologic images of bone-implant interfaces are presented as evidence for potential damage to the bone-implant interface using these techniques. RESULTS: A progressive increase in mobility from stable (-1) to less stable (4) and eventually to visibly mobile (999) was observed after three measurements with the MTD. Corresponding histologic images revealed that the buccal threads in the coronal half of the implants were displaced lingually and apically from the bony indentations that were created during insertion of the self-threading implants, subsequent to repeated MTD measurements in the buccal and axial directions. The histologic images and changes in MTD values indicated that repeated MTD measurements at the time of implant placement surgery may damage the bone-implant interface, and a stable or borderline implant may become mobile after repeated MTD measurements. CONCLUSIONS: Histologic images showed potential damage to the bone-implant interface during repeated initial implant-stability measurements using the MTD. Initial implant-stability measurements using the MTD should be performed with caution, and they may be contraindicated for implants placed in low-quality bone.

Internalized discoloration of dentin under porcelain crowns: a clinical report.

This clinical report describes the situation of a patient who was concerned about the appearance of porcelain crowns that were placed on the maxillary incisors 4 years prior. The mechanicochemical gingival retraction technique combining the use of ferric sulfate and knitted retraction cord is described as a possible etiology of internalized discoloration of the dentin in this situation. The hypothesis is explained by the high acidity of gingival retraction fluids (GRFs) and the high affinity of iron for hard tooth tissues, resulting in an interaction with bacterial byproducts and precipitation of insoluble ferric sulfide in the porous demineralized dentin. A prospective clinical trial is warranted to track the effects of GRFs on tooth structure. This article describes the treatment of internalized discoloration of dentin under porcelain crowns.

Accuracy of friction-style and spring-style mechanical torque limiting devices for dental implants.

STATEMENT OF PROBLEM: Accurate delivery of torque to implant prosthetic screws is critical to generate ideal preload in the screw joint and offer protection against screw loosening. Mechanical torque limiting devices (MTLDs) are available in 2 different styles that have not been compared for accuracy. PURPOSE: The purpose of this study was to determine the accuracy of friction-style and spring-style MTLDs in delivering target torque values. MATERIAL AND METHODS: Five MTLDs from each of 6 different implant manufacturers (n=30) were selected to determine their accuracy relative to their target torque values. All MTLDs were new; 3 types were of the friction style while 3 were of the spring style. To measure the output of each MTLD, a digital torque gauge with a 3-jaw chuck to hold the driver was used. Force was applied to the MTLD until either the friction style released at a precalibrated torque value or the spring style flexed to a precalibrated limit. The peak torque value registered by the digital torque gauge was recorded and the procedure was repeated 50 times for each MTLD. Statistical analysis used repeated-measures ANOVA (alpha=.05) to assess the accuracy of the MTLDs in delivering target torque values. RESULTS: Both the mean absolute difference (ABSDIFF) and the mean percentage deviation (PERDEV) between measured torque values and target torque values differed significantly (P<.001) for the friction-style MTLDs (3.83 Ncm, 13.74%) and for the spring-style MTLDs (0.82 Ncm, 2.36%). CONCLUSIONS: Within the limitations of this study, MTLDs that use spring-style components are significantly more accurate than those that use friction-style components in achieving their target torque values.

Fractures related to occlusal overload with single posterior implants: a clinical report.

This clinical report describes 2 patient situations in which fractures related to occlusal overload occurred with a single posterior implants. The initial clinical presentation of both patients appeared to be screw loosening, but upon further examination, implant and abutment fractures were identified. Several factors are described that have been implicated in the etiology of implant fractures, including occlusal overload, implant location, inadequate fit of the prosthesis, design of the prosthesis, progressive bone loss, metal fatigue, implant diameter, manufacturing defects, and galvanic activity. This article describes the management of implant and abutment fractures and discusses possible mechanisms of failure for the patient situations presented. Careful treatment planning and execution of implant therapy is necessary to minimize the risk of implant and component fractures.

Current ceramic materials and systems with clinical recommendations: a systematic review.

STATEMENT OF PROBLEM: Developments in ceramic core materials such as lithium disilicate, aluminum oxide, and zirconium oxide have allowed more widespread application of all-ceramic restorations over the past 10 years. With a plethora of ceramic materials and systems currently available for use, an overview of the scientific literature on the efficacy of this treatment therapy is indicated. PURPOSE: This article reviews the current literature covering all-ceramic materials and systems, with respect to survival, material properties, marginal and internal fit, cementation and bonding, and color and esthetics, and provides clinical recommendations for their use. MATERIAL AND METHODS: A comprehensive review of the literature was completed seeking evidence for the treatment of teeth with all-ceramic restorations. A search of English language peer-reviewed literature was undertaken using MEDLINE and PubMed with a focus on evidence-based research articles published between 1996 and 2006. A hand search of relevant dental journals was also completed. Randomized controlled trials, nonrandomized controlled studies, longitudinal experimental clinical studies, longitudinal prospective studies, and longitudinal retrospective studies were reviewed. The last search was conducted on June 12, 2007. Data supporting the clinical application of all-ceramic materials and systems was sought. RESULTS: The literature demonstrates that multiple all-ceramic materials and systems are currently available for clinical use, and there is not a single universal material or system for all clinical situations. The successful application is dependent upon the clinician to match the materials, manufacturing techniques, and cementation or bonding procedures, with the individual clinical situation. CONCLUSIONS: Within the scope of this systematic review, there is no evidence to support the universal application of a single ceramic material and system for all clinical situations. Additional longitudinal clinical studies are required to advance the development of ceramic materials and systems.