Non-photorealistic rendering of virtual implant models for computer-assisted fluoroscopy-based surgical procedures

Surgical navigation systems visualize the positions and orientations of surgical instruments and implants as graphical overlays onto a medical image of the operated anatomy on a computer monitor. The orthopaedic surgical navigation systems could be categorized according to the image modalities that are used for the visualization of surgical action. In the so-called CT-based systems or 'surgeon-defined anatomy' based systems, where a 3D volume or surface representation of the operated anatomy could be constructed from the preoperatively acquired tomographic data or through intraoperatively digitized anatomy landmarks, a photorealistic rendering of the surgical action has been identified to greatly improve usability of these navigation systems. However, this may not hold true when the virtual representation of surgical instruments and implants is superimposed onto 2D projection images in a fluoroscopy-based navigation system due to the so-called image occlusion problem. Image occlusion occurs when the field of view of the fluoroscopic image is occupied by the virtual representation of surgical implants or instruments. In these situations, the surgeon may miss part of the image details, even if transparency and/or wire-frame rendering is used. In this paper, we propose to use non-photorealistic rendering to overcome this difficulty. Laboratory testing results on foamed plastic bones during various computer-assisted fluoroscopybased surgical procedures including total hip arthroplasty and long bone fracture reduction and osteosynthesis are shown.

Early implant placement with simultaneous guided bone regeneration following single-tooth extraction in the esthetic zone: a cross-sectional, retrospective study in 45 subjects with a 2- to 4-year follow-up

BACKGROUND: The concept of early implant placement is a treatment option in postextraction sites of single teeth in the anterior maxilla. Implant placement is performed after a soft tissue healing period of 4 to 8 weeks. Implant placement in a correct three-dimensional position is combined with a simultaneous guided bone regeneration procedure to rebuild esthetic facial hard and soft tissue contours. METHODS: In this retrospective, cross-sectional study, 45 patients with an implant-borne single crown in function for 2 to 4 years were recalled for examination. Clinical and radiologic parameters, routinely used in implant studies, were assessed. RESULTS: All 45 implants were clinically successful according to strict success criteria. The implants demonstrated ankylotic stability without signs of a peri-implant infection. The peri-implant soft tissues were clinically healthy as indicated by low mean plaque (0.42) and sulcus bleeding index (0.51) values. None of the implants revealed a mucosal recession on the facial aspect as confirmed by a clearly submucosal position of all implant shoulders. The mean distance from the mucosal margin to the implant shoulder was -1.93 mm on the facial aspect. The periapical radiographs showed stable peri-implant bone levels, with a mean distance between the implant shoulder and the first bone-implant contact of 2.18 mm. CONCLUSIONS: This retrospective study demonstrated successful treatment outcomes for all 45 implants examined. The mid-term follow-up of 2 to 4 years also showed that the risk for mucosal recession was low with this treatment concept. Prospective clinical studies are required to confirm these encouraging results.

The influence of non-matching implant and abutment diameters on radiographic crestal bone levels in dogs

BACKGROUND: It has been shown that different implant designs and different vertical implant positions have an influence on crestal bone levels. The aim of the present study was to evaluate radiographic crestal bone changes around experimental dental implants with non-matching implant-abutment diameters placed submucosally or transmucosally at three different levels relative to the alveolar crest. METHODS: Sixty two-piece dental implants with non-matching implant-abutment diameters were placed in edentulous spaces bilaterally in five foxhounds. The implants were placed submucosally or transmucosally in the left or the right side of the mandible. Within each side, six implants were randomly placed at three distinct levels relative to the alveolar crest. After 12 weeks, 60 crowns were cemented. Radiographs were obtained from all implant sites following implant placement, after crown insertion, and monthly for 6 months after loading. RESULTS: Radiographic analysis revealed very little bone loss and a slight increase in bone level for implants placed at the level of the crest or 1 mm above. The greatest bone loss occurred at implants placed 1 mm below the bone crest. No clinically significant differences regarding marginal bone loss and the level of the bone-to-implant contact were detected between implants with a submucosal or a transmucosal healing. CONCLUSIONS: Implants with non-matching implant-abutment diameters demonstrated some bone loss; however, it was a small amount. There was no clinically significant difference between submucosal and transmucosal approaches.

[Effects of tobacco use on systemic health: relevant information for dentistry (II)--part 2: cardiovascular diseases and public health issues]

This is the sixth and concluding part of a series of publications from the Swiss task force named "Smoking - Intervention in the private dental office" on the topic "tobacco use and dental medicine". The focus of this review is the effects of smoking for the development of atherosclerosis as pathohistological correlate for acute coronary syndrome (ACS), arterial occlusive disease, and cerebrovascular diseases (stroke). Additionally, a causal relationship between tobacco use and an increased rate for complications during pregnancy and child birth will be discussed. Next to causal therapy of local and systemic diseases in general, an emphasis must be given to tobacco use prevention and cessation. Finally, important public health issues concerning smoking and tobacco use will be demonstrated, and options to improve the current situation will be presented.

[Effects of tobacco use on general health: relevant information for dentistry (I)--part 1: pulmonary diseases and other malignancies]

This fifth part of a series of publications from the Swiss task force named "Smoking--Intervention in the private dental office" on the topic "tobacco use and dental medicine" focuses on the effects of tobacco use on general health. A significant increase of tobacco use associated morbidity and mortality for many cardiovascular and pulmonary diseases has been well documented in the literature. In this review, the epidemiologic background as well as the pathophysiological fundamentals for tobacco-mediated pulmonary diseases is presented, focusing especially on chronic obstructive pulmonary disease (COPD) and lung cancer. In addition, a causal relationship between nicotine abuse and an increased carcinoma incidence for other malignancies but lung cancer will be discussed. Regarding the evidence in the present literature, it is undisputable that smoking is the most preventable cause for COPD and lung cancer.

Bone apposition around two different sandblasted and acid-etched titanium implant surfaces: a histomorphometric study in canine mandibles

PURPOSE: The aim of this study was to evaluate bone apposition to a modified sandblasted and acid-etched (SLA) implant surface (modSLA) in the canine mandible as compared with the standard SLA surface. MATERIAL AND METHODS: In this experimental study, all mandibular premolars and first molars were extracted bilaterally in five foxhounds. After a healing period of 6 months, each side of the mandible received six randomly assigned dental implants alternating between the standard SLA and modSLA surface. The dogs were sacrificed at 2 weeks (n=2) or 4 weeks (n=3) after implant placement. Histologic and histomorphometric analyses were then performed for each implant. RESULTS: The microscopic healing patterns at weeks 2 and 4 for the two implant types with the standard SLA and modSLA surfaces showed similar qualitative findings. New bone tissue had already established direct contact with implant surfaces after 2 weeks of healing. The mean percentage of newly formed bone in contact with the implant (BIC) was significantly greater for modSLA (28.2+/-7.9%) than for SLA (22.2+/-7.3%) (P<0.05). This difference was no longer evident after 4 weeks. An increase in BIC for both implant surface types occurred from weeks 2 to 4. This increase was statistically significant when compared with SLA at 2 weeks (P<0.05), but not when compared with modSLA at 2 weeks. CONCLUSION: The data from the present study demonstrate significantly more bone apposition for the modSLA surface than the standard SLA surface after 2 weeks of healing. This increased bone apposition may allow a further reduction of the healing period following implant placement for patients undergoing early loading procedures.

Implant Failure Predictors in the Posterior Maxilla: A Retrospective Study of 273 Consecutive Implants

Background: The goal of this study was to retrospectively analyze a cohort of 136 patients who underwent dental implant placement in the posterior maxilla at the University of Connecticut Health Center to assess and identify predictors for implant failure in the posterior maxilla. Methods: Data were retrieved from patient charts to identify subjects older than 21 years of age who received dental implant(s) in the posterior maxilla. Patients without a postoperative baseline radiograph were excluded. A recall radiograph was taken 3 to 6 months after implant placement. If there was no recall radiograph, the subject was contacted for a recall visit that included a clinical evaluation and radiographs to determine the implant status. Based on a univariate screening, variables considered potential implant failure predictors included gender, diabetes, smoking, implant length, implant diameter, membrane use, sinus-elevation technique, and surgical complications. These parameters were further assessed, and a multivariable logistic regression was performed with implant failure as a dependant variable. All tests of significance were evaluated at the 0.05 error level. Results: Two hundred seventy-three implants were placed in the posterior maxilla. Fourteen implants failed (early and late failures combined), resulting in a 94.9% overall survival rate. The survival rates for the sinus-elevation group and native bone group were 92.2% and 96.7%, respectively (P = 0.090). Based on the multivariable analysis, sinus floor-elevation procedures were not associated with increased risk for implant failure (P = 0.702). In contrast, smoking and surgical complications had a statistically significant effect on implant failure; the odds ratios for implant failure were 6.4 (P = 0.025) and 8.2 (P = 0.004), respectively. Conclusion: Sinus-elevation procedures with simultaneous or staged implant placement do not increase the risk for implant failure, whereas smoking and surgical complications markedly increase the risk for implant failure.

Zirconia for teeth and implants

This case series reports on the use of nonsilica-based high-strength full ceramics for different prosthetic indications. Fifty-two consecutive patients received tooth- or implant-supported zirconia reconstructions during a 2-year period. The observation period for reexamination was 12 to 30 months. The most frequent indications were single crowns and short-span fixed partial dentures. A few implant superstructures were screw-retained, whereas all remaining restorations were cemented on natural teeth or zirconia implant abutments. Clinical examination included biologic (probing depths, bleeding on probing) and esthetic (Papilla Index) parameters, as well as technical complications. No implant was lost or caused any problems, but two teeth were lost after horizontal fracture. Overall, the periodontal parameters were favorable. Fractures of frameworks or implant abutments were not observed. Abutment-screw loosening occurred once for one premolar single crown. Furthermore, five implant crowns in the posterior region exhibited chipping of the porcelain veneering material. With regard to esthetics, no reconstructions were considered unacceptable, but three crowns were remade shortly after delivery. In this short-term study, it was observed that biologic, esthetic, and mechanical properties of zirconia were favorable, and the material could be used in various prosthetic indications on teeth or implants.

Measurement of dental implant stability by resonance frequency analysis and damping capacity assessment: comparison of both techniques in a clinical trial

PURPOSE: Two noninvasive methods to measure dental implant stability are damping capacity assessment (Periotest) and resonance frequency analysis (Osstell). The objective of the present study was to assess the correlation of these 2 techniques in clinical use. MATERIALS AND METHODS: Implant stability of 213 clinically stable loaded and unloaded 1-stage implants in 65 patients was measured in triplicate by means of resonance frequency analysis and Periotest. Descriptive statistics as well as Pearson's, Spearman's, and intraclass correlation coefficients were calculated with SPSS 11.0.2. RESULTS: The mean values were 57.66 +/- 8.19 implant stability quotient for the resonance frequency analysis and -5.08 +/- 2.02 for the Periotest. The correlation of both measuring techniques was -0.64 (Pearson) and -0.65 (Spearman). The single-measure intraclass correlation coefficients for the ISQ and Periotest values were 0.99 and 0.88, respectively (95% CI). No significant correlation of implant length with either resonance frequency analysis or Periotest could be found. However, a significant correlation of implant diameter with both techniques was found (P < .005). The correlation of both measuring systems is moderate to good. It seems that the Periotest is more susceptible to clinical measurement variables than the Osstell device. The intraclass correlation indicated lower measurement precision for the Periotest technique. Additionally, the Periotest values differed more from the normal (Gaussian) curve of distribution than the ISQs. Both measurement techniques show a significant correlation to the implant diameter. CONCLUSION: Resonance frequency analysis appeared to be the more precise technique.

Prosthetic considerations

Implants have changed prosthodontics more than any other innovation in dentistry. Replacement of lost teeth by a fixed or removable prosthesis is considered to be a restitutio ad similem, while implants may provide a feeling of restitutio ad integrum. Implant prosthodontics means restoring function, aesthetics, and providing technology; biology and technology are combined. Placement of implants is a reconstructive, preprosthetic surgical intervention and is therefore different from most goals in oral surgery that consist of tooth extraction, treating infection and removing pathology from soft or hard tissues. Thus, implants are part of the final prosthetic treatment which encompasses functional, aesthetic and social rehabilitation. The patient's needs and functional status determine the goal of prosthetic treatment. Treatment outcomes in implant prosthodontics are survival of implants and prostheses, impact on physiological and psychological status, oral health-related impact on quality of life, and initial and maintenance costs. A variety of prosthetic solutions are available to restore the partially and completely edentulous jaw and more recently specific methods have been developed such as computer guided planning and CAD-CAM technologies. These should allow more uniform quality and passive fit of prostheses, and simultaneously enables processing of biologically well-accepted materials.

Effects of diabetes mellitus on periodontal and peri-implant conditions: update on associations and risks

OBJECTIVES: To review the evidence for the association between diabetes and periodontal and peri-implant conditions and the impact of periodontal therapy in subjects with diabetes. MATERIAL AND METHODS: A search of MEDLINE-PubMed was performed up to and including December 2007. The search was limited to clinical studies published in English. Publications on animal studies were excluded. The selection criteria included all levels of available evidence. RESULTS: Evidence on the association between diabetes and periodontitis supports the concept of increased severity but not extent of periodontitis in subjects with poorly controlled diabetes. Subjects with controlled diabetes do not show an increase in extent and severity of periodontitis. Periodontitis is associated with poor glycaemic control and diabetes-related complications. It is inconclusive that periodontal therapy with or without the use of antibiotics results in improvements of glycaemic control and of markers of systemic inflammation. Evidence is lacking to indicate that implant therapy in subjects with diabetes yields long-term outcomes comparable with those of non-diabetic subjects. CONCLUSIONS: Poorly controlled diabetes may be considered a risk factor for increased severity of periodontitis. The effects of periodontal therapy on glycaemic control and systemic inflammation is not proven beyond doubt and need to be confirmed in large-scale randomized-controlled clinical trials.

Immediate transmucosal implant placement in molar extraction sites: a 12-month prospective multicenter cohort study

AIM: To assess the clinical and radiographic outcomes of immediate transmucosal placement of implants into molar extraction sockets. STUDY DESIGN: Twelve-month multicenter prospective cohort study. MATERIAL AND METHODS: Following molar extraction, tapered implants with an endosseous diameter of 4.8 mm and a shoulder diameter of 6.5 mm were immediately placed into the sockets. Molars with evidence of acute periapical pathology were excluded. After implant placement and achievement of primary stability, flaps were repositioned and sutured allowing a non-submerged, transmucosal healing. Peri-implant marginal defects were treated according to the principles of guided bone regeneration (GBR) by means of deproteinized bovine bone mineral particles in conjunction with a bioresrobable collagen membrane. Standardized radiographs were obtained at baseline and 12 months thereafter. Changes in depth and width of the distance from the implant shoulder (IS) and from the alveolar crest (AC) to the bottom of the defect (BD) were assessed. RESULTS: Eighty-two patients (42 males and 40 females) were enrolled and followed for 12 months. They contributed with 82 tapered implants. Extraction sites displayed sufficient residual bone volume to allow primary stability of all implants. Sixty-four percent of the implants were placed in the areas of 36 and 46. GBR was used in conjunction with the placement of all implants. No post-surgical complications were observed. All implants healed uneventfully yielding a survival rate of 100% and healthy soft tissue conditions after 12 months. Radiographically, statistically significant changes (P<0.0001) in mesial and distal crestal bone levels were observed from baseline to the 12-month follow-up. CONCLUSIONS: The findings of this 12-month prospective cohort study showed that immediate transmucosal implant placement represented a predictable treatment option for the replacement of mandibular and maxillary molars lost due to reasons other than periodontitis including vertical root fractures, endodontic failures and caries.

A retrospective analysis of patients referred for implant placement to a specialty clinic: indications, surgical procedures, and early failures

Purpose: This retrospective study analyzed the pool of patients referred for treatment with dental implants over a 3-year period in a referral specialty clinic. Materials and Methods: All patients receiving dental implants between 2002 and 2004 in the Department of Oral Surgery and Stomatology, University of Bern, were included in this retrospective study. Patients were analyzed according to age, gender, indications for implant therapy, location of implants, and type and length of implants placed. A cumulative logistic regression analysis was performed to identify and analyze potential risk factors for complications or failures. Results: A total of 1,206 patients received 1,817 dental implants. The group comprised 573 men and 633 women with a mean age of 55.2 years. Almost 60% of patients were age 50 or older. The most frequent indication for implant therapy was single-tooth replacement in the maxilla (522 implants or 28.7%). A total of 726 implants (40%) were inserted in the esthetically demanding region of the anterior maxilla. For 939 implants (51.7%), additional bone-augmentation procedures were required. Of these, ridge augmentation with guided bone regeneration was performed more frequently than sinus grafting. Thirteen complications leading to early failures were recorded, resulting in an early failure rate of 0.7%. The regression analysis failed to identify statistically significant failure etiologies for the variables assessed. Conclusions: From this study it can be concluded that patients referred to a specialty clinic for implant placement were more likely to be partially edentulous and over 50 years old. Single-tooth replacement was the most frequent indication (> 50%). Similarly, additional bone augmentation was indicated in more than 50% of cases. Adhering to strict patient selection criteria and a standardized surgical protocol, an early failure rate of 0.7% was experienced in this study population