Browsing by Subject "Dentistry"

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3-year survival estimates of short (less than or equal to 6 mm) length implants and the relationship to crown-to-implant ratios.
(2011-12) Saldarriaga, Augusto V.
INTRODUCTION: The literature regarding survival of short implants is conflicting. Furthermore, excessive crown-to-implant ratios have been cited in the literature as being detrimental to implant survival. Hence, the purpose of this study was to determine the 3- year survival estimates, and the relationship between crown-to-implant ratios and survival of short, roughened, plateau-design implants. Additionally, risk factors for failure were evaluated. MATERIAL AND METHOD: This retrospective cohort study involved 341 patients who possessed at least 1 single ≤6mm length plateau-design implant supported restoration that had been surgically placed between August 2000 and June 2007. An electronic chart review was conducted to acquire data on patient demographics, implant location, bone density, length of time in function and/or implant failure, as well as the most recent digital periapical radiographs in which the entire crown and implant were visible. Data analysis was conducted utilizing appropriate univariate and multivariate regression statistics, as well as non-parametric Kaplan-Meier survival analysis in order to determine the overall 3-year survival rate. RESULTS: Data from 573 single implant-supported fixed restorations were tabulated and included in the study. 13 implants failed overall. The 3-year Kaplan-Meier survival analysis adjusted for clustered observations was found to be 93.9%. The average (SD) crown-to-implant ratio of implants that were in function was 2.06 (0.4), and the average (SD) crown-to-implant ratio of those that failed was 2.02 (0.3). This difference was not statistically significant. Results from the multivariate model found quality of bone, and history of adjacent endodontically treated teeth to be statistically associated with implant failure, with hazard ratios of 13.2 and 2.7 respectively (P ≤ 0.05). CONCLUSIONS:The results of this study suggest that the survival of short, roughened, plateau-design dental implants is comparable to implants of traditional lengths, which suggests that these implants are a clinically acceptable option where alveolar bone height is limited or anatomic limitations exist.
Anatomic investigation of the roots of second mandibular molars using micro CT.
(2011-08) Barsness, Sara A.
An understanding of tooth anatomy is an important cornerstone in providing successful endodontic treatment. Detailed images of tooth anatomy using microcomputed tomography allow measurements of pulpal floor anatomy, canal configurations, canal dinemsions, root wall thickness, presence of calcifications, and apical anatomy. The aim of this study of eighteen mandibular second molars using micro CT was to investigate various aspects of tooth anatomy. The most frequently found mesial root canal configuration was Vertucci Type 7 (1-2-1-2) in 33% of samples. Distal canals were most frequently Vertucci Type 1(1), with 61% of samples showing this configuration. 11% of samples had two canals, 44% of samples had three canals, 33% of samples had four canals, and 11% of samples had five canals at some point along the root. On average, root wall thickness between the mesiobuccal root and the furcation was the thinnest at 1.23 mm. The mesiolingual canal root wall thickness was on average 1.29 mm, and the distal was 1.41 mm. 78% of samples had calcifications present in both the pulp chamber and within the canals; 17% of samples were free from calcification in both the pulp chamber and within the canals; one (6%) sample had calcification in the chamber only. Other reported data included canal dimensions at one millimeter increments along the root, pulpal floor anatomy, and apical anatomy.
An anatomical investigation of the mandibular first molar using micro-computed tomography.
(2011-08) Harris, Samantha P.
Abstract summary not available
Asymmetry assessment using cone-beam CT: a class I and class II patient comparison
(2010-06) Sievers, Matthew Michael
Introduction: Asymmetry assessment is an important component of orthodontic diagnosis and treatment planning. Before the advent of three-dimensional imaging, orthodontists relied on two-dimensional headfilms to diagnose asymmetry. Cone beam computed tomography (CBCT) allows for assessment of asymmetry on a dimensionally accurate volumetric image. This study aims to determine if there is a difference in skeletal asymmetry between patients with a skeletal class I ANB angle compared to patients who have a skeletal class II using CBCT images. Methods: CBCT images were examined from 70 consecutive patients who presented for routine orthodontic care and fit inclusion criteria. Asymmetry was analyzed using an asymmetry index developed by Katsumata et al.18 Anatomic landmarks were defined and reference planes were established to determine the variance of the landmarks using a coordinate plane system. 30 randomly selected patients were reanalyzed to assess reliability of the method. Results: Statistical analysis demonstrated no significant relationship between asymmetry and ANB angle for any of the landmarks. Asymmetry index scores were reproducible within a certain range of agreement for each landmark. Conclusions: Based on this study, the differential in jaw proportion common for class II skeletal patterns results in no more skeletal asymmetry than class I skeletal patterns. Altman-Bland agreement plots suggest that some modification may be indicated to the system proposed by Katsumata et al18 to improve asymmetry diagnosis.
Bone Morphogenetic Protein-2 (BMP2) upregulates osteoclast gene expression.
(2009-11) Espe, Kelly Christine
Bone Morphogenetic Proteins (BMPs) induce bone formation by osteoblasts, but their direct role in bone resorption by osteoclasts remains to be characterized. Twisted Gastrulation (Twsg1) is a secreted BMP binding protein that inhibits BMPs from binding to their receptors. Mice lacking the Twsg1 gene (Twsg1-/-) exhibit an osteopenic skeletal defect. Previous studies indicate that the osteopenic phenotype in Twsg1-/- mice is due to increased osteoclastogenesis and not due to reduced osteoblast function. This study hypothesizes that treatment of wild-type osteoclasts with BMP2 will increase osteoclast gene expression and that this gene expression will decrease with the addition of the known BMP inhibitor, Noggin. The results of this investigation show that the addition of BMP2 to RANKL upregulates Cathepsin K, Nfatc1, Acp5, DCSTAMP, and ATP6v6d02 gene expression levels. The addition of the more well understood BMP inhibitor, Noggin, downregulates these gene expression levels. These results indicate a possible direct mechanism of action for BMP2 on osteoclast activation.
CAD/CAM lithium disilicate crown performance cemented extraorally and delivered as a screw-retained implant restoration
(2015-03) Lassle, Michael Jon
Purpose: To determine if a novel technique combining the attributes of a cement-retained implant restoration fabricated extraorally and delivered to the patient as a screw-retained implant restoration has the necessary strength to provide a clinically acceptable and predicable restoration.Materials and Methods: Thirty specimens were fabricated and tested in this novel implant restoration technique, in which stock abutment was scanned using a bench top laboratory scanner and 30 lithium disilicate full contour crowns were designed and milled. In the first experimental group, the occlusal access channel was prepared in a pre-sintered crown using new high-speed diamond burs in a high-speed handpiece with ample irrigation as to keep the specimen cool. The access channel was prepared by the same operator for every specimen and the diameter was recorded. The specimens were allowed to air dry for 48 hours prior to being glazed, fired and finished. In the second experimental group, the screw access channel was prepared after the crown was fired and finished. In the control group, no screw access channel was prepared. Each finished crown intaglio surface was silinated per manufacturer specifications and luted with self-adhesive resin cement to its corresponding stock abutment. The cement was allowed to cure for at least 24 hours before testing. Each specimen was individually mounted in a custom-fabricated testing fixture and tested to failure on a servo-hydraulic testing system for static and dynamic tests. Each specimen was vertically loaded at a dynamic rate of 0.100 mm/min until failure and the highest force reached at the point of failure was recorded. Statistical analysis was performed by consultants from the Biostatistical Design and Analysis Center. Results: A total of thirty CAD/CAM lithium disilicate crowns were fabricated and tested to failure. The first experimental group had a mean failure of 990.64N. The second experimental group had a mean failure of 1167.65, and the control group had a mean failure of 188.68N. A two-sample t-test was used to compare the load among the three groups and because there are 3 comparisons, Bonferroni method is applied to adjust p-values for multiple comparisons. The results show that experimental group #1, experimental group #2 and the control group are statistically significantly different from each other. The diameter of the screw access channel did not make a statistically significant difference, most likely because the difference among the diameter wasn't that great between samples.Conclusions: The null hypothesis stated there will be no difference in the axial force required to fracture a lithium disilicate crown with and without a screw access channel prepared. The results of this study support rejecting the null hypothesis and accepting the alternative hypothesis. The preparation of a screw access channel in a lithium disilicate crown has statistical significance and reduces the axial load capacity from a crown without occlusal access. The diameter of the screw access channel did not make a statistically significant difference, most likely because the difference among the diameter wasn't that great between samples.
Class II subdivision malocclusions treated non extraction with symmetrical forces.
(2012-07) Caballero, Carlos
Non-extraction treatment of Class II subdivision malocclusion, with symmetrical forces has not been described in the literature. This study evaluated the use of symmetrical forces with face-bow therapy in conjunction with full fixed appliances of 47 patients (28 females and 19 males) that were treated by the same practitioner. The pretreatment and post-treatment records were taken at an average age of 12.3 and 14.4 years respectively. The results showed that the Caballero index (The distance from the tip of the mesio-buccal cusp of the upper first molar to the mesio-buccal groove of the lower first molar on the class II side.) decreased from 1.86 to 0.12 mm, making this statistically significant. The midline showed a distinctive improvement having a pretreatment value of 1.33 mm and a post treatment value of 0.29 mm. Arch length had a modest gain of 1.15 mm with the left side having the biggest contribution. The maxillary intermolar position remained stable with a 0.3 mm net change. The ANB angle decreased from 3.5 to 2.1 degrees. The upper incisor in relation to S-N and lower incisor inclination increased by 3.3 degrees. Finally, the mandibular plane angle increased in value from 31.2 degrees to 32.2 post treatment. Within the limits of this study and based on the test of equivalence, it is concluded that when symmetrical forces are used in non extraction therapy for Class II subdivision growing patients, the class II malocclusion is corrected, but some asymmetry in the molar position remains.
Comparing the oral health related quality of life in four orofacial pain conditions
(2014-11) Shueb, Sarah
Objectives: Pain is known to reduce quality of life. Concurrently, it is believed that orofacial pain reduces the oral health-related quality of life (OHRQoL). While the impact that painful temporomandibular disorders (TMD) have on OHRQoL has been well described, little has been reported about the impact of acute dental pain (ADP). Moreover, the impact of trigeminal neuralgia (TN) and persistent dentoalveolar pain disorder (PDAP) on OHRQoL has not been reported yet. The aim of this study was, therefore, to compare the OHRQoL impairment among four orofacial pain conditions, i.e., participant with TMD, ADP, TN, and PDAP and compare the results with people without orofacial pain. Methods: OHRQoL was measured using the OHIP-49 questionnaire, using a convenience sample of four orofacial pain conditions (pain groups with TMD (n=30), ADP (n=27), TN (n=21), PDAP (n=16)). To provide a frame of reference for pain-related OHRQoL impairment, we also included a group of pain-free control participants (n=20). The mean OHIP-49 summary score, with its 95% confidence interval (95% CI), described the level of impact. The differences in mean values across the four pain conditions were analyzed using Analysis of Variance (ANOVA). The second part of the analysis was performed by comparing the OHIP-49 mean score of each condition and the OHIP mean score of the control group using Student's two sample t-test. Finally the absolute score differences between groups were judged according to: the Minimal Important Difference (MID) and the Effect sizes (ES).Results: OHRQoL was measured using OHIP-49 in a convenience sample of four conditions (patient groups with orofacial pain; TMD (n=30), acute dental pain (n=27), TN (n=21), PDAP (n=16)). Our results showed significant impairment in the OHRQoL for the four conditions compared to the control group. The mean OHIP-49 score (95% CI) was 60.8 (48-74) for TMD, 61 (48-74) for ADP, 58 (41-75) for TN, and 66 (46-86) for PDAP. For comparison purposes, the mean OHIP-49 score (95% CI) was 8 (3-13) for the pain free group. The difference was statistically significant and clinically relevant between pain groups and the control group (all comparisons: P<0.001). Each of the four orofacial pain conditions had similar levels of impact on the OHRQoL when compared to each other. Using the Minimum Important Deference (MID) there was a clinical significance between chronic conditions (TMD, TN, PDAP) and the ADP (11 (-6 to 28), 8.4 (-11 to 28), and 17(-4 to 37)) respectively, also a clinical significance between the four orofacial conditions and the control group was detected. A moderate effect size was detected between participants with PDAP and ADP (ES=0.5, 95%CI (-0.1 to 1.1)). Conclusion: Our data supported the hypothesis that orofacial pain conditions have a substantial impact and adversely affect the quality of life of participants with four orofacial pain conditions as compared to those with no pain.
Comparison of initial Implant stability placed using bi-cortical fixation, indirect sinus lift and uni-cortical fixation
(2014-07) Hsu, Andrea Raquel, D.M.D
Purpose: This study aim was to determine if self-threading dental implants placed using stopper drills so to bi-cortically engage both the alveolar crest and sinus floor (bi-cortical fixation) achieved comparable primary and/or secondary stabilities to that of short implants only engaging alveolar crest cortical bone (uni-cortical fixation) or implants engaging both crest and sinus floor but via greenstick fracture and grafting (indirect sinus lift).Material and Methods: Thirty-eight patients exhibiting 7 - 11 mm of bone coronal to the sinus floor as confirmed by pre-operative CBCT were recruited. Forty-five implants were randomly assigned to one of the placement techniques. No patient received more than two implants, which were placed in opposite sides of the maxilla while using different surgical techniques. An Osstell ISQ was employed immediately after implant placement to measure stability 6 times in a buccal/lingual dimension. Secondary stability was measured at 2nd stage surgery after a 3- to 6-month healing period. Results: The greatest primary implant stability was achieved via indirect sinus lift. However, no statistical significant difference was found among the three surgical techniques (P = 0.13; bi-cortical fixation: 71.4 [SE 2.1], uni-cortical fixation: 69.6 [2.1], indirect sinus lift: 75.9 [2.3]). The three techniques had similar secondary stability (P = 1.0; respectively 79.9 [1.2], 80.0 [1.2], 80.0 [1.3]). Baseline residual ridge height measured on CBCT was similar (P = 0.1; respectively 8.8 mm, 9.9 mm, 9.4 mm) but implant diameter and length placed in the maxilla differed (P = 0.03/P < 0.001; respectively 4.7/11.4 mm, 4.3/8.1 mm, 4.7/11.8 mm). Primary implant stability was significantly correlated to CBCT bone density (r = 0.37). Conclusion: Primary and secondary implant stabilities of bi-cortical fixation did not differ significantly from those of uni-cortical fixation and indirect sinus lift. However, use of the bi-cortical fixation technique is warranted since it is simpler and more economical than the indirect sinus lift plus allows for longer implants than the unicortical fixation while yielding similar secondary implant stability.
Comparisons of the shaping abilities of three NiTi file systems using rotational versus reciprocal movements
(2014-08) Peterson, Tyler Blaine, DDS
Introduction: The purpose of this study was to determine if there were any differences in shaping abilities between three NiTi file systems when using rotational versus reciprocal movements in simulated S-shaped canals, as well as compare the time required to complete canal preparations.Methods: One hundred twenty S-shaped canals were filled with ink and pre- instrumentation images were obtained using a stereomicroscope. Experimental canal preparations where completed using K3XF in rotary movement, K3XF in reciprocal movement, Twisted File (TF) in rotary movement, TF in reciprocal movement, ProTaper Next (PTN) in rotary movement, and PTN in reciprocal movement. Pre-instrumentation and post-instrumentation images were superimposed, and standardized for area difference measurements. Pre-instrumentation and post-instrumentation area differences were measured in seven defined regions and the mean differences were compared between the experimental instrumentation groups. Time required to complete canal preparations was recorded for each group for comparisons.Results: Statistical analysis showed there were significant differences between NiTi file systems, instrumentation movement type, as well as time to complete canal preparations. The TF file system performed better in shaping abilities than the PTN file system followed by the K3XF file system in a majority of the defined areas measured. The TF file system performed the best in reciprocal motion in all defined regions compared to the TF in rotary motion. Reciprocal motion was better in shaping ability compared to rotary motion in a majority of the defined areas measured. The K3XF file system in reciprocal motion completed canal preparations quicker than the K3XF file system in rotary motion. Conclusions: Differences were found between K3XF, TF, and PTN file systems in regards to shaping abilities, rotatory versus reciprocal motions, and canal preparation times.
Cone beam computed tomography-anatomic analysis of mandibular posterior teeth: impact on endodontic microsurgery
(2014-08) Chiona, Dafni, DDS.
Purpose: The purpose of this study was to use cone beam computed tomography (CBCT) measurements to investigate the root thickness (B-L) of the mandibular posterior teeth at the root end resection level, the thickness of the buccal and lingual bone at both the resection level and the mandibular canal (MC) level, the dimension of the mandibular canal, the relative location of the mandibular canal to the tooth, and the possible differences between males and females.Methods: CBCT scans from 106 patients were used to evaluate measurements from 801 teeth and respective tooth areas. Bone and root thickness were measured at the preferred root resection level of 3mm from root apex, and at the level of the mandibular canal. Also, the dimension and the relative location of the mandibular canal (MC) to the apices of the posterior teeth were evaluated. Results: Buccal bone was thinnest over the root of the 1st premolar (2.08 mm) and thickest over the distal root of the 2nd molar (6.35 mm). Bone thickness averaged 2.19 mm over the root of the 2nd premolar, 2.3 mm over the mesial root of the 1st molar, 3 mm over the distal root of the 1st molar, and 5.16 mm over the mesial root of the 2nd molar, respectively. Root thickness (B-L) at the resection level averaged 4.58mm, 5.42mm, 5.28mm, 5.77mm, 4.39 mm and 4.3mm for the 2nd molar distal root, 2nd molar mesial root, 1st molar distal root, 1st molar mesial root, 2nd premolar and 1st premolar, respectively. Mandibular bone thickness lingual to the root was more consistent, ranging from the thinnest area over the distal root of the 2nd molar (2.42 mm) to the thickest over the root of the 2nd premolar (4.5mm). The mandibular canal (MC) location in relation to the individual tooth roots was most often seen to the buccal in the area of the 2nd molar distal root (58%) while it was most often seen to the lingual of the root at the level of the mesial root of the 1st molar (31.5%). The MC was inferior to roots of posterior teeth in 38-58% of the time. Conclusions: Knowledge of the mandibular posterior tooth dimension for apical resection is beneficial to the endodontist. The depth of the root below buccal bone, its relative position in the mandible as well as to the mandibular canal can aid the surgeon performing the root resection and this data contributes to a knowledge base for the practicing endodontist.
Correlation Between Patient Reported Jaw Activities with Self-Reported Pain Ratings and Dentists’ Clinical Findings
(2022-06) Al-Taee, Anas
This study aims to investigate the relationship between the Jaw Functional Limitation Scale (JFLS8) with the orofacial pain instruments of TMD screener, persistent tooth pain (PP) questions as well as dentists’ clinical findings. It is based on pre-existing dataset from the National Dental Practice-Based Research Network. A statistical analysis is performed for 1,306 participants who received root canal treatment. TMD and PP questionnaires are found to be moderately correlated (ρ=0.47) with JFLS8 using Spearman’s correlation analysis. On the other hand, the dentists’ clinical examination for tenderness to palpation, percussion, and biting did not correspond with JFLS8 (ρ=0.07, ρ=0.19, and ρ=0.23 respectively). Additionally, the JFLS8 is neither sensitive nor specific enough to clinically determine the presence of TMD or PP (AUC=0.72 and AUC=0.64 respectively). The JFLS8 correlates with TMD screener and PP questionnaire. Clinical endodontic examination, on the other hand, does not correlate with jaw functional limitations.
Dentists' Attitudes and Perspectives on Viewing Cone-beam Computed Tomography of Impacted Teeth in Virtual Reality
(2024-06) Liu, Deborah
Introduction: Three-dimensional (3-D) radiographic imaging has transformed the dental field since its inception by giving clinicians a wealth of data impossible to glean from two-dimensional (2-D) imaging. However, current viewing modalities were designed for 2-D and analog data, with no way to view 3-D imaging in its natural 3-D state, such as the case with cone-beam computed tomography (CBCT). Virtual reality (VR) has become increasingly widespread in recent years and poises itself as a new potential tool for viewing volumetric datasets.Aim: The aim of this study is to evaluate dentists’ attitudes and perspectives on using VR medical imaging application Medicalholodeck to view CBCT of impacted teeth using Oculus Quest 2 immersive VR headsets. This study also aims to investigate whether viewing 3-D data in VR allows for improved visualization and/or efficiency compared to 2-D viewing modalities. Methods: CBCT datasets of three patients with impacted teeth were uploaded to Quest 2 headsets. Participants underwent a VR tutorial and viewing session to become familiar with navigating 3-D data in VR and then completed a survey on their experience. As a proof-of-concept study, data were descriptive in nature and no statistical hypotheses were tested. Results: Results revealed varying perceptions of visualization and/or accuracy for impacted teeth and their surrounding craniofacial structures when viewed in VR. For many factors that oral surgeons, orthodontists, and periodontists consider in treating cases with impacted teeth, clinicians found VR to be beneficial, especially when used in conjunction with traditional 2-D viewing modalities. Clinicians perceived VR to provide heightened global visualization with its immersive capabilities, to be easy to use, and highly enjoyable. Current shortcomings of VR include its accompanying learning curve, mediocre resolution, and decreased ability to visualize small structures. Conclusions: Few studies have been completed thus far evaluating VR as a tool for viewing 3-D data in dentistry. Data from this study showed VR has promise for enhanced viewing of CBCT images, despite not currently being perceived to improve clinicians’ efficiency. Dentists believed VR provided improved visualization for certain morphological characteristics and will likely be most useful as an adjunctive tool for complex cases. As this study was descriptive in nature, further in-depth research is needed to provide additional insight on the clinical utility of viewing 3-D data in VR.
Dosimetry of a next generation i-CAT CBCT machine as compared to a digital panoramic and lateral cephalogram in patient diagnosis and treatment at the University of Minnesota Division of Orthodontics.
(2010-11) Schieck, Jacquelyn Rae Kolbeck DDS
Background: Three-dimensional cone-beam computed tomography (CBCT) has rapidly gained prominence and exposure in the dental community over the last few years, and is quickly becoming the routine imaging modality for many orthodontic clinics. However, questions remain about the amount of radiation patients are exposed to during the multiple scans needed for the associated advanced diagnostic and treatment techniques. Objective: To determine the amount of radiation potentially absorbed by a patient during routine orthodontic imaging with the Next Generation i-CAT® cone-beam computed tomography machine with various scan settings. Also, to evaluate the amount of radiation patients at the University of Minnesota Division of Orthodontics are exposed to during a routine two-year treatment including cone-beam scans for diagnosis and for SureSmile® treatment. Methods: Twenty-four thermoluminescent dosimeters placed at anatomic sites inside a RANDO® phantom were scanned using various scan protocols on a Next Generation i- CAT machine and digital panoramic and cephalometric xray machine. Effective doses were calculated using the 2007 International Commission on Radiological Protection recommended tissue weighting factors. Results: The effective doses ranged from 108-129mSv for standard resolution CBCT scans at various voxel size and field of view settings; 196-212mSv for enhanced or highresolution full field of view scans; and measured 252mSv for a high-resolution landscape scan as would be used for SureSmile® therapy. Digital panoramic xray dose was 39mSv and lateral cephalogram was 25mSv. Discussion: Cone-beam CT, while providing proven diagnostic and therapeutic benefits, also exposes patients to a higher level of radiation than with standard digital 2D examinations. It is important for the clinician to weigh the benefits against the risks when determining their imaging protocol.
The effect of surgical guide design and surgeon’s experience on the experience on the accuracy of implant placement.
(2010-05) Hinckfuss, Simon Robert
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 volunteer surgeons were recruited to participate in this study. They were divided equally 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) utilizing 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 were 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, 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 volunteer surgeons were recruited to participate in this study. They were divided equally 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) utilizing 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 were 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 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 volunteer surgeons were recruited to participate in this study. They were divided equally 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) utilizing 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 were 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 degrees in the mesial-distal and buccal-lingual angulations respectively with an overall range of 0.01 to 9.7 degrees. 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. Key Words: Surgical guide, implant placement
The effect of tenofovir on bone remodeling.
(2011-08) Dowd, Elizabeth Ann
With the introduction of Highly Active Anti-Retroviral Therapy (HAART), HIVinfected patients have had long-term survival rates increase dramatically. A significant sequela from HIV-infection and side effect from some HAART medications is the loss of bone mineral density. The purpose of this study was to investigate the effects of a common HAART medication, tenofovir, on bone cells. It was hypothesized that tenofovir alters the gene expression of osteoblasts and osteoclasts, which creates an imbalance in the bone remodeling system and skeletal change. To test this, mice were treated with tenofovir, then serum was obtained to determine changes in osteocalcin, osteopontin, and carboxyl telopeptides of type I collagen activity. Furthermore, changes in osteoclast numbers were obtained by tartrate resistant acid phosphatase staining of mouse femurs. While other studies have shown that gene expression is altered in tenofovir treated cells, the present study did not find a significant difference in osteocalcin, osteopontin or carboxyl telopeptide of type I collagen activity for tenofovir mice. However, tenofovir decreased the number of osteoclasts in tartrate resistant acid phosphatase stained sections in mice. Given that HIV patients taking tenofovir medication have an increase in osteoporosis and the results of this study indicate tenofovir alone creates osteopetrotic effect, further studies are needed to determine the relationship between HIV infection and tenofovir.
The effectiveness of suresmile technology to achieve predicted treatment outcome
(2011-08) Vaubel, Christopher John
INTRODUCTION: The present study evaluated the effectiveness of SureSmile technology when used as an adjunctive tool in orthodontic treatment. The study was designed to evaluate the effectiveness of SureSmile archwires to produce the final tooth position prescribed by the SureSmile virtual treatment plan. METHODS: Digital models of the SureSmile virtual treatment plan and final treatment outcome were digitally superimposed to determine areas of discrepancy. Discrepancy less than 0.5 mm with respect to mesial-distal, facial-lingual, vertical dimensions, and discrepancy less than 2 degrees for crown torque, crown tip, and crown rotation were considered to be clinically acceptable. RESULTS: Discrepancy was within clinically acceptable limits with respect to the mesial-distal dimension for all teeth except upper 2nd molars and upper lateral incisors. In the facial-lingual dimension, clinically acceptable results were observed for upper canines and lateral incisors, lower 1st molars, lower 1st and 2nd premolars, and lower canines. Discrepancy in the vertical dimension was minimal with only lower 2nd molars exceeding clinically acceptable limits. Discrepancy exceeded clinically acceptable levels for crown torque, crown tip, and crown rotation with the exception of crown torque on lower 2nd premolars and crown tip on lower 1st molars and lower 2nd premolars. CONCLUSION: The effectiveness of SureSmile treatment to achieve predicted final tooth position is highly variable for tooth type and dimension of movement.
The effects of taper size on the fracture resistance of root fracture.
(2012-09) Nguy, Tom Hai-Tam.
The purpose of this study was to investigate the effects of taper sizes on fracture resistance in root sections and determine if there is a difference in the fracture resistance of different regions within the same root. Thirty-six single-rooted mandibular premolars were divided into three groups for three different taper sizes (.02, .04, and .06). The specimens were instrumented and sectioned. Each section was photographed and the net average surface area was calculated using the ImageJ software (NIH, Bethesda, MD). Each individual root section was then subjected to a load to fracture test using the MTS 858 machine (MTS, Eden Praire, MN). A ratio of the load to fracture and average surface area was calculated. Statistical analysis was conducted using ANOVA, Tukey-Kramer, Pairwise Spearman, and Random Intercept Models. It was determined that fracture resistance increase with larger taper size and was higher in the apical region.
Evaluation of software developed for automated segmentation of digital dental models.
(2012-03) Moon, Joe Min
Introduction: The use of digital models for simulation of orthodontic treatment is currently hampered by time-consuming manual segmentation processes which rely on the user to manually define tooth boundaries for separation into individual tooth objects. A new software tool has been developed that almost completely automates the segmentation process requiring little input from the user. The software combines novel methods to analyze the 3D mesh curvatures that make up a digital model, identify the gingival margin for separation of the teeth from the gingival tissues, repair the gingival margins, and then identify the high curvature vertices on the gingival margins to determine segmentation boundaries between teeth. Methods: Thirty pretreatment models (15 upper, 15 lower) with varying amounts of crowding and spacing were digitally scanned using an R700 digital model scanner (3Shape, Copenhagen, Denmark). Each digital model was then segmented using the newly developed software tool and then visually evaluated for segmentation accuracy. To determine inter- and intra- operator repeatability, two different examiners participated in this study. To use as a comparison, the same 30 digital models were also segmented using 3Shape’s OrthoAnalyzer® and evaluated for segmentation accuracy in the same manner. Results: Of the 387 possible separators on the 30 models tested, 380 were correctly placed by the new software tool (98.2% accuracy, 5 omitted separators, 2 misplaced separators). On a tooth by tooth basis, a total of 77 errors were observed on 417 teeth; 67 being minor errors that did not affect the segmentation of the models and 10 being major errors that did affect the segmentation of the models (83.0% success in accurate tooth anatomy reproduction after segmentation). Both inter- and intra- operator repeatability was high. Using OrthoAnalyzer® to segment the same 30 digital models, all 387 separators were correctly placed and there were 14 tooth anatomy reproduction errors. Conclusions: Initial results indicate that mesh segmentation algorithms can be developed to accurately segment digital dental models in most situations while requiring little user time. Further development of these algorithms could provide the orthodontic practitioner fast, easy treatment simulation for help in treatment planning.
Evaluation of stress distribution patterns on short implants with differing crown heights: a three dimensional finite element analysis
(2010-12) Ritkajorn, Tanawat
Statement of problem: The use of short dental implants is usually confined to areas of the mouth with limited vertical bone height. As a result, longer implant crowns are required to restore the occlusion with the opposing arch, leading to a disproportionate crown-to-implant ratio (C/I ratio). Purpose: The purpose of this study was to evaluate the stress distribution patterns on crestal bone of short implants plateau-designed connected with different crown heights, and to compare these findings with those of regular implants. Material and Methods: Two implant designs (∅5 mm×6 mm and ∅5 mm×11 mm) and abutments (∅5 mm×9 mm and ∅5 mm×5 mm) were scanned using a micro-CT scanner. STL surface models were subsequently extracted to generate surfaces. All models were imported to Abaqus CAE for three-dimensional non-linear finite element analysis. For each implant model, loadings of 100, 200, and 700 N were simulated in 2 directions: pure vertical and at an oblique angle of 15 degrees. Results: At 100 and 200 N oblique loads, peak compressive and tensile stresses ranged from 18.30 to 53.57 MPa and 7.39 to 43.95 MPa, respectively. At 700 N oblique loads, the ∅5 mm×6 mm implant with long abutment model exceeded the compressive and tensile strength of cortical bone, at 193.4 and 158.6 MPa correspondingly. For 700 N oblique loads, increasing crown height increased peak compressive stress by 28.6 % and peak tensile stress by 28.4 %. Stress distribution patterns showed the highest amounts of stress located at the implant crest module in cortical bone. Conclusion: Stress distribution patterns for the oblique loads of 100 and 200 N were similar in all models, regardless of the C/I ratios. All peak stresses were within physiological tolerance. At 700 N loads, increasing crown height resulted in bone failure.

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