Implant survival to 36 months as related to length and diameter

Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study

AIM

To evaluate prospectively the clinical and radiographic outcomes after 2 years of loading of 6 mm long moderately rough implants supporting single crowns in the posterior regions.

MATERIAL AND METHODS

Forty SLActive Straumann short (6 mm) implants were placed in 35 consecutively treated patients. Nineteen implants, 4.1 mm in diameter, and 21 implants, 4.8 mm in diameter, were installed. Implants were loaded after 6 weeks of healing. Implant survival rate, marginal bone loss and resonance frequency analysis (RFA) were evaluated at different intervals. The clinical crown/implant ratio was also calculated.

RESULTS

Two out of 40 implants were lost before loading. Hence, the survival rate before loading was 95%. No further technical or biological complications were encountered during the 2-year follow-up. The mean marginal bone loss before loading was 0.34+/-0.38 mm. After loading, the mean marginal bone loss was 0.23+/-0.33 and 0.21+/-0.39 mm at the 1- and 2-year follow-ups. The RFA values increased between insertion (70.2+/-9) and the 6-week evaluation (74.8+/-6.1). The clinical crown/implant ratio increased with time from 1.5 at the delivery of the prosthesis to 1.8 after 2 years of loading.

CONCLUSION

Short implants (6 mm) with a moderately rough surface loaded early (after 6 weeks) during healing yielded high implant survival rates and moderate loss of bone after 2 years of loading. Longer observation periods are needed to draw more definite conclusions on the reliability of short implants supporting single crowns.

Crown-to-Implant Ratios of Short-Length Implants

Excessive crown-implant ratios have been cited in the literature as being detrimental to long-term implant survival. However, unfavorable crown-implant ratios have not yet been established. The primary aim of this study was to determine the crown-implant ratios of single-tooth implant-supported restorations on short-length implants in a clinical practice, and to evaluate the health of these implants via mesial and distal first bone-to-implant contact levels. Additionally, the relationship between crown-implant ratios and proximal first bone-to-implant contact levels will be evaluated. In this retrospective cohort study, the cohort was composed of 194 patients who possessed at least 1 single 5.7 mm or 6 mm length plateau design implant-supported restoration that had been surgically placed between February 1997 and December 2005. A chart review was performed to acquire the most recent radiographs in which both the entire crown and the implant were visible. The length of the crown and implant was measured directly from the radiographs using consistent magnification to calculate the crown-implant ratio. Mesial and distal first bone-to-implant contact levels were measured using 3 times magnification and were mathematically corrected for distortion. The last available radiograph was used to measure bone levels. Follow-up time was calculated from the day of implant placement to the date of the last available radiograph. Statistical analyses with analysis of variance mixed models were used. Data from 309 single implant-supported fixed restorations were tabulated and included in the study. The mean (SD) follow-up time was 20.9 (23.2) months, with a range of 15.6 to 122.8 months. The mean crown length (SD) was 13.4 (2.6) mm, with a range of 6.2 to 21.7 mm. The mean (SD) crown-implant ratio was 2.0 (0.4) and ranged from 0.9 to 3.2. The average mesial and distal first bone-to-implant contact levels (SD) measured from the radiographs were −0.2 (0.7) mm and −0.2 (0.9) mm, respectively. No statistically significant relationship was observed between increasing crown-implant ratios and decreasing mesial and distal first bone-to-implant contact levels around the implant with P values of .94 and .57, respectively. In this investigation, mesial and distal first bone-to-implant contact levels on short-length implants fall within the established guidelines for success. Also, there are no associations between crown-implant ratios and first bone-to-implant contact levels.

Comparison of panoramic and conventional cross-sectional tomography for preoperative selection of implant size

OBJECTIVE

To compare panoramic and conventional cross-sectional tomography for preoperative selection of implant size for three implant systems (Brånemark, Straumann(®), 3i).

MATERIAL AND METHODS

Presurgical panoramic (Pan) and cross-sectional tomograms (Tomo) of 121 implant sites in 121 patients scheduled for single-tooth implant treatment were recorded; in 70 of the Pans (Pan-B), a metal ball was placed in the edentulous area. By means of dedicated software, an implant with subjectively determined proper dimensions for the respective site was outlined by manually placing four reference points in each image by three observers. Additionally, four reference points corresponding to the margins of the metal ball were manually placed in Pan-Bs. The length and width of the implant were calculated after calibration to the reference ball (true magnification) in Pan-Bs and to a "standard" calibration method in all images (magnification factor 1.25 in Pans and 1.7 in Tomos). Based on the corrected dimensions, the nearest, smaller implant size was selected among those available in each of the three implant systems.

RESULTS

When comparing Pans with Tomos, selected implant size differed in on average 89% of the cases. The length differed in 69% and the width in 66%. Implants planned on Tomos were longer than those planned on Pans in 47% and narrower in 30% (<10% in posterior regions). The Straumann(®) system, with the smallest range of available implant sizes was significantly less affected by the radiographic method compared with the other two systems.

CONCLUSION

The selected implant size differed considerably when planned on panoramic or cross-sectional tomographs.

Use of tilted implants in treatment of the atrophic posterior mandible: a preliminary report of a novel approach

PURPOSE

Restoration of the atrophic partially edentulous posterior mandible with implant retained prostheses has proved to be problematic, with no ideal treatment modality. The purpose of this report is to offer a novel method of treatment using tilted endosseous implants.

MATERIALS AND METHODS

A total of 64 patients with edentulous spans of the mandible and less than 9.5 mm of alveolar bone overlying the inferior alveolar nerve had implants placed. The implants were placed in a bicortical manner with the porous hydroxyapatite placed subperiosteally if more than 1 mm of the apex of the implant was placed beyond the lingual cortex of the mandible. These implants were allowed to osseointegrate for 3 to 5 months and restored using custom-angled abutments.

RESULTS

A total of 196 implants were placed in 64 patients from March 2003 through July 2008. Two implants were lost owing to a lack of osseointegration. No implants were lost because of prosthodontic failure. No damage to the neurovascular structures or permanent paresthesia was noted.

CONCLUSIONS

Our initial results have shown that the use of tilted implants combined with custom abutments is a viable treatment modality for patients with atrophic edentulous mandibular spans that lack the required alveolar height for traditional dental implants.

Effects of the Taper Shape, Dual-Thread, and Length on the Mechanical Properties of Mini-Implants

Objective: To analyze the mechanical effects of the length and the various shapes such as cylindrical shape, taper shape, and dual-thread shape on the insertion and removal torque of mini-implants.

Materials and Methods: Mini-implants (diameter 1.6 mm and length 6 mm and 8 mm) consisting of cylindrical, taper, and dual-thread groups were inserted and removed in Sawbones while measuring the torque and time. Mechanical analysis was done of maximum insertion torque (MIT), maximum removal torque (MRT), torque ratio (TR; MRT/MIT), insertion angular momentum (IAM), removal angular momentum (RAM), and time of MIT. Measurements were statistically evaluated to analyze any differences of shapes and lengths.

Results: The cylindrical shape had the lowest MIT and MRT in each length. Although taper shape showed the highest MIT in each length, dual-thread shape showed significantly higher MRT, TR, and RAM in each length (P &lt; .05). Dual-thread groups showed a gentle increase of insertion torque and a gentle decrease of removal torque in contrast to the other shape groups. However, it had higher IAM and time of MIT. The long length group showed significantly higher measurements except for TR.

Conclusions: Dual-thread shape provided better mechanical stability with high removal torque on the broad range than other shapes. However, dual-thread shape may need improvement for reducing the long insertion time to decrease the stress to the surrounding tissue.

Factors associated with the stability of mini-implants for orthodontic anchorage: a study of 414 samples in Taiwan

PURPOSE

To evaluate failure rates and factors associated with the stability of mini-implants used for orthodontic anchorage.

PATIENTS AND METHODS

We enrolled 166 patients (35 male patients and 131 female patients) who had consecutively received mini-implants for orthodontic anchorage at the Section of Orthodontics and Pediatric Dentistry, Taipei Veterans General Hospital (Taipei, Taiwan) from January 2001 to December 2006. A total of 414 mini-implants with diameters ranging from 1.2 to 2.0 mm were evaluated. Clinical variables for analysis were divided into host-related and implant-related factors. Mini-implants that could be maintained for orthodontic anchorage for more than 6 months were considered to be successful. Statistical analysis was used to evaluate the failure rate in our study cohort and to identify possible associated factors.

RESULTS

The overall failure rate was 10.1% (42 of 414 screws) with orthodontic force loading for more than 6 months. Most failures were due to loosening and occurred within the first 2 weeks. Differences in overall failure rates for the maxilla and mandible (9.3% and 16.3%, respectively) were not statistically significant. A lower failure rate was found for the maxilla with implant diameters equal to or less than 1.4 mm (P = .036). The left side had a lower failure rate than the right (6.7% vs 13.9%, P = .019). Length and type of mini-implants, age, and gender were not associated with mini-implant failure.

CONCLUSIONS

Use of mini-implants for anchorage is reliable. In our study the overall success rate was 89.9%. Careful diameter selection for different locations is essential. In the maxilla an implant diameter equal to or less than 1.4 mm is recommended. In the mandible an implant diameter larger than 1.4 mm is suggested for better orthodontic anchorage. Hygienic care of implantation sites should also be emphasized for long-term success of mini-implant anchorage.

Outcomes of placing short dental implants in the posterior mandible: a retrospective study of 124 cases

PURPOSE

The purpose of this retrospective study was to determine the overall success of short dental implants (8 mm in length) placed in the partially or completely edentulous posterior mandible restored with fixed and removable prostheses.

PATIENTS AND METHODS

A total of 124 patients had 335 8-mm-long implants placed from May 2005 until June 2007. Of the 124 total patients, 35 were men and 89 were women, with a median age of 56 years and an age range of 18 to 80 years at the time of implant surgery. There were 112 patients who were partially edentulous and 12 who were completely edentulous. Of the patients, 32 had a single implant placed whereas the other 92 had multiple implants placed. One patient had the implants immediately provisionally loaded. All of the implants were restored by use of fixed prostheses. Of these fixed prostheses, 245 were splinted together whereas 75 were restored individually.

RESULTS

A total of 335 short dental implants were placed in 124 patients. Of the 335 implants placed, 331 integrated successfully. In the 2 cases that failed, the sites were grafted with porous hydroxyapatite and platelet-rich plasma. The implants were replaced at 5 months after the initial failure in the first patient and at 7 months in the second patient. These replacement implants integrated and have been restored and in function for more than 16 months. There was 1 fracture of an implant with a restoration. The implant had been restored with an individually fabricated fixed restoration, with the fracture occurring at the head of the implant, requiring removal. The implant and restoration had been in function for 10 months before fracture.There were no other fractures of implants or restorative hardware noted in this study. The survival rate for 8-mm implants placed in the mandible was 99% from stage I surgery to a functional prosthesis for up to 2 years.

CONCLUSIONS

Placement of short dental implants is a predictable treatment method for patients with decreased posterior mandibular bone height.

Analysis of association of clinical aspects and vitamin D receptor gene polymorphism with dental implant loss

Osseointegration failure is a complex, multifactorial trait shown to concentrate in some treated populations. There has been shown evidence for genetic contribution to dental implant loss. Genetic polymorphisms have been classically considered as genetic risk factors for several diseases and, more recently, for dental implant loss.

OBJECTIVES

The purpose of this study was to access clinical factors related to failure process, and to investigate the relationship between a vitamin D receptor (VDR) polymorphism (rs731236, TaqI) and dental implant loss.

MATERIAL AND METHODS

Two hundred and seventeen unrelated patients, mean age 51.7+/-11.3 years, were divided into two groups: (i) control group (C), 137 individuals presenting at least one osseointegrated implant in function for 6 months or more and without any implant loss, and (ii) study group (S), 80 individuals presenting at least one implant loss. After DNA collection and purification, VDR TaqI polymorphism analysis was performed by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). Differences between C and S, and between healthy (H; n=1232) and lost (L; n=135) implants were accessed.

RESULTS

Positive evidence of association has been detected between implant loss and the following variables: edentulism, implant position, primary stability, and implant length. Cox's regression model showed that primary stability, surgical technique and bone quantity were related to implant survival over time. No association between genotypes or alleles of VDR TaqI polymorphism and implant loss was found between the groups.

CONCLUSION

It was observed that clinical variables, but not the study polymorphism, were associated with dental implant loss.

Immediate implant loading: current status from available literature

The introduction of osseointegrated implants in dentistry represents a turning point in dental clinical practice. Thanks to their multiple therapeutic possibilities and the high predictability of success, implant therapy is now regarded as an extremely reliable approach to replace missing teeth. The concept of immediate implant loading has recently become popular due to less trauma, reduced overall treatment time, decreased patient's anxiety and discomfort, high patient acceptance and better function and esthetics. Nonetheless, research and understanding in this area are confuse and sometimes contradictory. Hence, it is the purpose of this review to provide rational for immediate implant loading, summarize current available literature, and analyze factors that influencing this newly introduced treatment method. Results from this review indicated that immediate implant loading achieved similar high success rate as that noted in the conventional approach (delayed protocols). However, a careful case selection, proper treatment plan, meticulous surgery and proper design of prosthesis are essential for optimal outcomes when this approach is adopted.

The challenge of implant therapy in the posterior maxilla: providing a rationale for the use of short implants

Rehabilitating patients with a resorbed maxilla presents several challenges when the desired treatment plan involves the placement of endosseous implants. Correct diagnosis requires knowledge on jaw healing patterns, systemic effects, and the impact of bone quality changes on implant success rates. Appropriate treatment planning requires an in-depth understanding of the materials and methods available to the contemporary implant surgeon. The clinician must be able to persist on evidence-based techniques and adhere to those proven methods. Successful surgical placement requires correct use of the available armamentarium and acceptance of the limitations that implant dentistry still presents. Especially challenging is the implant treatment of maxillary molars due to the plethora of complicating factors such as limited bone availability, interarch space challenges, sinus problems, etc. These are just a few of the factors that may lead us to placement of short implants in these sites. An extensive review of the literature that is available for short implants (implants < 10 mm in length) indicates that although they are commonly used in areas of the mouth under increased stress (posterior region), their success rates mimic those of longer implants when careful case selection criteria have been used. The available studies and case-series offer a valid rationale for placement of short implants so long as one understands the limitations, indications, risk factors, and limited studies that actually follow-up success rates of short implants for over 5 years. This review of the literature will provide the reader an in-depth view of the evidence in using short implants as an alternative treatment modality for the maxillary molar region.

Treatment planning complications and surgical miscues

It is critical to have an accurate understanding of the educational limitations of dentists because of a lack of formal training with implants. It is not a unilateral problem, as it can be easily discerned from the cases illustrated in this article. The team must pay attention to specific direction as to the number, location, depth, angulation, spacing, and distribution of implants in their patients. More and more experienced restorative dentists are incorporating implant treatment in their practice. There is more awareness and concern at having simple restorative cases turn into very complex undertakings that require extra chair time and additional laboratory expenses. To avoid treatment planning complications and surgical miscues the following is recommended: 1) always complete a detailed restorative and surgical examination; 2) do not place implants without a restorative prosthodontic workup; 3) refer the patient to an experienced dentist for the workup; 4) insist on a diagnostic wax-up; 5) insist on a radiographic and a surgical stent and use it during placement; 6) determine that the entire treatment team has the knowledge and experience to complete the case; 7) as a surgeon, be sure you understand the exigencies of fixed and removable restorative care; 8) make sure that team members have the same treatment vision; and 9) communicate. Never take anything for granted. Communicate.

Randomized clinical trials in implant therapy: relationships among methodological, statistical, clinical, paratextual features and number of citations

OBJECTIVES

The aim of the present study was to investigate the relationships among reported methodological, statistical, clinical and paratextual variables of randomized clinical trials (RCTs) in implant therapy, and their influence on subsequent research.

MATERIALS AND METHODS

The material consisted of the RCTs in implant therapy published through the end of the year 2000. Methodological, statistical, clinical and paratextual features of the articles were assessed and recorded. The perceived clinical relevance was subjectively evaluated by an experienced clinician on anonymous abstracts. The impact on research was measured by the number of citations found in the Science Citation Index. A new statistical technique (Structural learning of Bayesian Networks) was used to assess the relationships among the considered variables.

RESULTS

Descriptive statistics revealed that the reported methodology and statistics of RCTs in implant therapy were defective. Follow-up of the studies was generally short. The perceived clinical relevance appeared to be associated with the objectives of the studies and with the number of published images in the original articles. The impact on research was related to the nationality of the involved institutions and to the number of published images.

CONCLUSIONS

RCTs in implant therapy (until 2000) show important methodological and statistical flaws and may not be appropriate for guiding clinicians in their practice. The methodological and statistical quality of the studies did not appear to affect their impact on practice and research. Bayesian Networks suggest new and unexpected relationships among the methodological, statistical, clinical and paratextual features of RCTs.

Factors Affecting Outcomes for Single-Tooth Implants and Endodontic Restorations

Initial root canal therapy and implant placement are both common treatment modalities, and, as such, prognostic factors that influence the treatment outcomes of these two restorations should be identified. In a retrospective chart review, 196 implant restorations and 196 matched initial nonsurgical root canal treated (NSRCT) teeth in patients were evaluated for four possible outcomes-success, survival, survival with intervention, and failure. Results showed that smokers had fewer successes and more failures in both groups (p = 0.0001), whereas NSRCT outcomes were affected by periradicular periodontitis (p = 0.001), post placement (p = 0.013), and overfilling (p = 0.003). Outcomes for both groups were not significantly affected by diabetes, age, or gender. Implant group outcomes were not affected by implant length (from 10 to 16 mm), diameter (from 3.25 to 5.5 mm), or an adjacent endodontically treated tooth, nor were NSRCT outcomes affected by the number of appointments for the procedure.

Computer methods for automating preoperative dental implant planning: implant positioning and size assignment

The paper presents computer-aided methods that allocate a dental implant and suggest its size, during the pre-operative planning stage, in conformance with introduced optimization criteria and established clinical requirements. Based on computed tomography data of the jaw and prosthesis anatomy, single tooth cases are planned for the best-suited implant insertion at a user-defined region. An optimum implantation axis line is produced and cylindrical implants of various candidate sizes are then automatically positioned, while their occlusal end is leveled to bone ridge, and evaluated. Radial safety margins are used for the assessment of the implant safety distance from neighboring anatomical structures and bone quantity and quality are estimated and taken into consideration. A case study demonstrates the concept and allows for its discussion.

Reconstruction of the Atrophic Edentulous Maxilla with Free Iliac Crest Grafts and Implants: A 3-Year Report of a Prospective Clinical Study

PURPOSE

The purpose of this study was to perform a longitudinal follow-up study of implant stability in grafted maxillae with the aid of clinical, radiological, and resonance frequency analysis (RFA) parameters.

MATERIALS AND METHODS

The atrophic edentulous maxillae in 29 patients were reconstructed with free iliac crest grafts using onlay/inlay or interpositional grafting techniques. The endpoint of the resorption pattern in the maxilla determined the grafting technique used. Endosteal implants were placed after 6 months of bone-graft healing. Implant stability was measured four times using RFA: when the implants were placed, after 6 to 8 months of healing, after 6 months and 3 years of bridge loading. Individual checkups were performed at the two later RFA registrations after removal of the supraconstructions (Procera Implant Bridge, Nobel Biocare AB, Göteborg, Sweden). Radiological follow up of marginal bone level was performed annually.

RESULTS

Twenty-five patients remained for the follow-up period. A total of 192 implants were placed and with a survival rate of 90% at the 3-year follow up. Women and an implant position with a class 6 resorption prior to reconstruction were factors with significant increased risk for implant failure (multivariate logistic regression). Twelve of the 20 failed implants were lost before loading (early failures). The change in the marginal bone level was 0.3 +/- 0.3 mm between baseline (bridge delivery) and the 3-year follow up. The implant stability quotient (ISQ) value for all implants differed significantly between abutment connection (60.2 +/- 7.3) and after 6 months of bridge loading (62.5 +/- 5.5) (Wilcoxon signed ranks test for paired data, p=.05) but were nonsignificant between 6 months of bridge loading and 3 years of bridge loading (61.8 +/- 5.5). There was a significant difference between successful and failed implants when the ISQ values were compared for individual implants at placement (Mann-Whitney U test, p=.004). All 25 patients were provided with fixed implant bridges at the time of the 3-year follow up.

CONCLUSION

This clinical follow up using radiological examinations and RFA measurements indicates a predictable and stable long-term result for patients with atrophic edentulous maxillae reconstructed with autogenous bone and with delayed placement of endosteal implants. The ISQ value at the time of placement can probably serve as an indicator of level of risk for implant failure.

Pilot Study in the Identification of Stability Values for Determining Immediate and Early Loading of Implants

This pilot study assessed the impact of implant stability criteria on implant loading time. Insertion torque (IT) and baseline implant stability quotients (ISQ) from resonance frequency analysis were recorded for 41 tapered-screw implants placed in the mandibles of 20 patients. Immediate (IL), early (EL) (6 weeks postoperative), or delayed (DL) (12 weeks postoperative) prosthetic loading was performed based on results and study criteria. Postoperative ISQ values were also recorded at 6 time intervals for the IL and EL groups and after healing for the DL group. All implants were definitively restored after 6 weeks of provisionalization. There were no failures, complications, or stability differences based on loading time. At week 12 of follow-up, ISQ values were slightly higher for IL implants compared with EL implants. IL and EL implants showed significantly higher cumulative ISQ values compared with DL implants. High IT and baseline ISQ values in all groups corresponded to high implant survival. Postoperative ISQ values in the IL and EL groups were less certain indicators of implant survival because of fluctuations relative to baseline values. Small sample size and inequitable patient distribution across groups skewed results. More research is needed before definitive results can be drawn. IL and EL were safely performed within the IT and ISQ ranges in this study, but it is unknown whether EL criteria would have also sufficed for IL.

Long-term Clinical Evaluation of Tapered Multi-threaded Implants: Results and Influences of Potential Risk Factors

This prospective study evaluated the long-term performance of tapered screw implants placed in patients with a variety of potentially compromising clinical variables. Sixty patients were treated with 218 implants; each case included one or more potential risk factors associated with increased rates of implant failure, peri-implant bone loss or clinical complications in the dental literature: short implants (23%), comorbid conditions (25%), maxillary implants (61%), immediate loading (88.5%), placement into extraction sockets (91%), and partial edentulism (97%). The implants were restored with a variety of prostheses. Marginal bone changes were calculated utilizing periapical radiographs taken at placement and at all subsequent appointments utilizing a standardized paralleling device and a 1-mm measurement grid. Mean clinical follow-up was 67.5 (range: 1–94) months for implants and 60 (range: 15–74) months for prostheses. Four implants failed to integrate and were immediately replaced by wide-diameter implants. Eight prostheses sustained porcelain fracture (n = 7) or cement failure (n = 1) and were replaced. No peri-implant marginal bone loss was observed for 98% of the implants; the remaining 2% exhibited 1 mm of bone loss. Cumulative survival rates were 98.2% for implants and 96.3% for prostheses after 5 years of clinical loading. Concerns that tapered implant designs may be more prone to crestal bone loss than cylinder designs are unsupported by the results of this study. Tapered implants maintained integration and marginal bone levels despite the presence of one or more potentially compromising variables.

Impact of implant length and diameter on survival rates

INTRODUCTION

Despite the high success rates of endosseous oral implants, restrictions have been advocated to their placement with regard to the bone available in height and volume. The use of short or nonstandard-diameter implants could be one way to overcome this limitation.

MATERIAL AND METHODS

In order to explore the relationship between implant survival rates and their length and diameter, a Medline and a hand search was conducted covering the period 1990-2005. Papers were included which reported: (1) relevant data on implant length and diameter, (2) implant survival rates; either clearly indicated or calculable from data in the paper, (3) clearly defined criteria for implant failure, and in which (4) implants were placed in healed sites and (5) studies were in human subjects.

RESULTS

A total of 53 human studies fulfilled the inclusion criteria. Concerning implant length, a relatively high number of published studies (12) indicated an increased failure rate with short implants which was associated with operators' learning curves, a routine surgical preparation (independent of the bone density), the use of machined-surfaced implants, and the placement in sites with poor bone density. Recent publications (22) reporting an adapted surgical preparation and the use of textured-surfaced implants have indicated survival rates of short implants comparable with those obtained with longer ones. Considering implant diameter, a few publications on wide-diameter implants have reported an increased failure rate, which was mainly associated with the operators' learning curves, poor bone density, implant design and site preparation, and the use of a wide implant when primary stability had not been achieved with a standard-diameter implant. More recent publications with an adapted surgical preparation, new implant designs and adequate indications have demonstrated that implant survival rate and diameter have no relationship.

DISCUSSION

When surgical preparation is related to bone density, textured-surfaced implants are employed, operators' surgical skills are developed, and indications for implant treatment duly considered, the survival rates for short and for wide-diameter implants has been found to be comparable with those obtained with longer implants and those of a standard diameter. The use of a short or wide implant may be considered in sites thought unfavourable for implant success, such as those associated with bone resorption or previous injury and trauma. While in these situations implant failure rates may be increased, outcomes should be compared with those associated with advanced surgical procedure such as bone grafting, sinus lifting, and the transposition of the alveolar nerve.

Risk factors for endosseous dental implant failure

Failures of endosseous dental implants are rare and tend to cluster in patients with common profiles or risk factors. Clinical trials indicate that factors related to implant devices, anatomy, occlusion,systemic health or exposures, microbial biofilm, host immuno-inflammatory responses, and genetics may increase the risk for im-plant complications or loss. In general, factors associated with the patient appear more critical in determining risk for implant failure than those associated with the implant itself. Several risk factors can be modified. For example, the patient can modify smoking and the clinician can modify implant selection, site preparation,and loading strategy. In identifying these factors and making appropriate interventions, clinicians can enhance success rates while improving oral function, esthetics, and patient well-being.

Short Dental Implants in Posterior Partial Edentulism: A Multicenter Retrospective 6-Year Case Series Study

BACKGROUND

Implants <10 mm long in the posterior regions of partial edentulous patients have a higher failure rate in many clinical reports. The purpose of this case series study was to evaluate implant survival when a biomechanical approach was used to decrease stress to the bone-implant interface.

METHODS

A retrospective evaluation of 273 consecutive posterior partially edentulous patients treated with 745 implants. 7 or 9 mm long, supporting 338 restorations over a 1- to 5-year period was reviewed from four private offices. Implant survival data were collected relative to stage I to stage II healing, stage II to prosthesis delivery, and prosthesis delivery to as long as 6 years follow-up. A biomechanical approach to decrease stress to the posterior implants included splinting implants together with no cantilever load, restoring the patient with a mutually protected or canine guidance occlusion, and selecting an implant designed to increase bone-implant contact surface area.

RESULTS

Of the 745 implants inserted, there were six surgical failures from stage I to stage II healing to prosthesis delivery. No implants failed after the 338 final implant prostheses were delivered. A 98.9% survival rate was obtained from stage I surgery to prosthetic follow-up.

CONCLUSIONS

Short-length implants may predictably be used to support fixed restorations in posterior partial edentulism. Methods to decrease biomechanical stress to the bone-implant interface appear appropriate for this treatment.

Maxillary Single-tooth Replacement Utilizing a Novel Ceramic Restorative System: Results to 30 Months

This study reports on the first longitudinal results of an alumina (70%)-zirconia (30%) ceramic restorative system for implant-supported, single-tooth replacement in the anterior maxillary jaw. Eighteen patients (9 men, 9 women, mean age = 42.4 years) were treated with 22 implants placed into 19 extraction sockets and 3 residual ridges. Eight implants were immediately loaded with nonoccluding provisional prostheses. All implants were definitively loaded with fully occluding ceramic restorations after osseointegration and soft tissue maturation. Patients were monitored from 7 to 30 months (mean = 18.1 months) after loading. All implants osseointegrated and were successfully restored. One case of abutment screw loosening occurred because of patient parafunction (bruxing), and another patient reported chewing pain attributed to malocclusion. Both problems were successfully resolved without further incidence. Within the context of this study, single-tooth replacement in the anterior maxillary jaw was successfully achieved with alumina-zirconia ceramic single-tooth restorations with up to 30 months of clinical function.

A distinguishable observation between survival and success rate outcome of hydroxyapatite-coated implants in 5-10 years in function

PURPOSE

To differentiate between the survival and success definitions of functional hydroxyapatite (HA)-coated implant prosthesis.

METHODS

A total of 248 implants (62 patients), 5-10 years in function, were evaluated. The implant distribution length was 8 mm (6.5%), 10 mm (29.4%), 13 mm (30.2%) and 15 mm (33.9%). The diameter was 3.25 mm (60.1%) and 4 mm (39.9%). Probing depth (PD), gingival index (GI), height of keratinized mucosa (KM) and recession (REC) were measured. Periapical radiographs were taken to estimate the amount of crestal bone resorption (BL), mesially and distally, with the aid of a millimetric-scaled magnifying glass (x 8). Only implants that fulfilled the success rate criteria were considered as successful. All other functional implants were assigned to the non-successful group. All functional implant prostheses were defined as survival ones.

RESULTS

The accumulative survival rate after 5 and 10 years was 94.4% and 92.8%, respectively. Accumulative success rates were 89.9% and 54%, respectively. Implants 13 and 15 mm in length (97.9% and 96.4%, respectively) had the highest survival rate, which was higher over implants 8 and 10 mm in length (75%, P<0.01 and 88.2%, respectively). The survival rate of 4 mm diameter implants compared with 3.25 mm was 96.5% and 90.3%, respectively (P=0.019). The average BL was 1.7, 0.92 and 2.79 mm for the survival, successful and non-successful defined implant groups. PD was 3.26, 2.79 and 4 mm and GI was 0.96, 0.75 and 1.57, respectively. These measurements were statistically different between implant groups. KM and REC measurements showed similar scoring for all groups. A correlation was shown between successful and non-successful implants on the score of GI and PD (P<0.001 in both).

CONCLUSION

A distinguishable observation between survival and success rate was noted particularly in long-term observations. Implant length and diameter have an influence on the survival rate. Clinical parameter scores expressed an influence on the defined implant status.

Non-grafted sinus implants in periodontally compromised patients: a time-to-event analysis

This study reports the results of implant therapy involving a sinus membrane lift and of conventional implant therapy in 68 periodontally compromised patients treated between June 1990 and June 2002. Patients had at least two implants inserted, one of which was placed in the maxillary sinus region following fenestration of the lateral sinus wall and lifting of the sinus membrane. Two implant systems were used: a two-stage system (Astra) and a one-stage system (ITI). Annual follow-up visits included recording of plaque, probing pocket depth and measurement of the radiographic distance in millimeter from the implant shoulder to the alveolar crest. Survival analysis showed that the proportion of implants that had not been explanted after 5 years ranged between 88.7% for ITI sinus implants and 97% for ASTRA conventional implants. After 10 years, the proportion of implants remaining in situ ranged between 59% for ITI conventional implants and 97% for ASTRA conventional implants. Cox regression analyses showed that the factors influential for implant explantation were implant type (HR(ITI) = 2.8), implant length (HR(< or = 10 mm) = 3.1), patient being a smoker (HR(smoking) = 2.2) and patient having at least 20 natural teeth (HR(> or = 20 teeth) = 3.8). Our results demonstrate that sinus implants may be inserted with the same success as conventional implants in periodontally compromised patients.

Effect of implant size and shape on implant success rates: a literature review

Understanding and using biomechanical theories that effect endosseous implant design may improve the performance of implants in varying load conditions and allow the clinician to better apply this information with potentially improved success rates. The following article presents information from English peer-reviewed journals identified by a Medline search covering the years from 1974 through 2004, and attempts to integrate information available in the dental literature and address current controversies and issues in selecting diameter, length, and shapes of dental implants.

An evaluation of resonance frequency analysis for the determination of the primary stability of orthodontic palatal implants. A study in human cadavers

BACKGROUND

The primary stability of short orthodontic implants is important for anchorage.

METHODS

For this study 14 cadaveric human heads were used. The stability of orthodontic implants (Straumann) with lengths of 4 and 6 mm and different localization (palatal suture or paramedially) were evaluated. The implants with length of 6 mm were only placed in the suture and primary stability was non-invasively determined with the resonance frequency (Osstell). The invasive method for the analysis of the morphometric parameters of the implant/bone contact was carried out by means of histological and radiological examinations.

RESULTS

The 6 mm implants have significant better primary stability in the palatal suture as 4 mm implants paramedially (P<0.05). No differences were found between 6 and 4 mm implants in the palatal suture and between 4 mm implants in palatal suture to paramedially. The histological and radiological results demonstrate the ability to measure the implant stability by investigation of the bone offer and density around the implant. Bone structure, especially the pore size in the trabecular bone and the precision of placement may influence the stability.

CONCLUSION

This study shows that the short implant gives sufficient bone fixation, independently of placement. The quality of implantation and bone structure are more important than the length of the orthodontic implant.

Comparative evaluation of implant designs: influence of diameter, length, and taper on strains in the alveolar crest

OBJECTIVES

Our aim was to analyze and compare systematically the relative and interactive effects of implant diameter, length, and taper on calculated crestal bone strains.

MATERIAL AND METHODS

Three-dimensional finite-element models were created of a 20-mm premolar section of the mandible with a single endosseous implant embedded in high- or low-density cancellous bone. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic. Perfect bonding was assumed at all interfaces. A two-level factorial statistical design was used to determine the main and interactive effects of four implant design variables on maximum shear strains in the crestal alveolar bone: diameter, length of tapered segment, length of untapered segment, and taper. Implant diameter ranged from 3.5 to 6 mm, total implant length from 5.75 to 23.5 mm, and taper from 0 to 14 degrees , resulting in 16 implant designs.

RESULTS

Increasing implant diameter resulted in as much as a 3.5-fold reduction in crestal strain, increasing length caused as much as a 1.65-fold reduction, whereas taper increased crestal strain, especially in narrow and short implants, where it increased 1.65-fold. Diameter, length, and taper have to be considered together because of their interactive effects on crestal bone strain.

CONCLUSION

If the objective is to minimize peri-implant strain in the crestal alveolar bone, a wide and relatively long, untapered implant appears to be the most favorable choice. Narrow, short implants with taper in the crestal region should be avoided, especially in low-density bone.

A review of selected dental literature on evidence-based treatment planning for dental implants: Report of the Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics

This literature review summarizes research with the aim of providing dentists with evidence-based guidelines to apply when planning treatment with osseointegrated implants. Peer-reviewed literature published in the English language between 1969 and 2003 was reviewed using Medline and hand searches. Topics reviewed include systemic host factors such as age, gender, various medical conditions, and patient habits, local host factors involving the quantity and quality of bone and soft tissue, presence of present or past infection and occlusion, prosthetic design factors, including the number and arrangement of implants, size and coatings of implants, cantilevers and connections to natural teeth, and methods to improve outcomes of implant treatment in each category. The review demonstrated that there is no systemic factor or habit that is an absolute contraindication to the placement of osseointegrated implants in the adult patient, although cessation of smoking can improve outcome significantly. The most important local patient factor for successful treatment is the quality and quantity of bone available at the implant site. Specific design criteria are provided, including guidelines for spacing of implants, size, materials, occlusion, and fit. Limitations in the current body of knowledge are identified, and directions for future research are suggested.

Implant Survival in Periodontally Compromised Patients

BACKGROUND

Relatively little is known on the long-term prognosis of implants inserted in partially edentulous, periodontally compromised patients.

METHODS

A total of 258 conventional implants, 57 two-stage and 201 one-stage implants, which were inserted in 32 and 108 patients, respectively, between June 1988 and June 2002 were followed with respect to their survival, as well as the periodontal parameters bone loss, probing depth, and bleeding on probing. All patients were periodontally compromised who had undergone periodontal surgery and were considered able to maintain a high standard of oral hygiene.

RESULTS

The 5-year survival rates were 97% and 94%, respectively, for the two- and the one-stage implants. The 10-year survival rate remained high at 97% for the two-stage implants, but had dropped to 78% for the one-stage implants. Smoking, short implant length, and insertion during the later period (1995-2002) were found to be associated with an increased failure rate.

CONCLUSIONS

Implants placed in patients with a history of periodontitis have a 5-year survival similar to that observed for implants installed in non-diseased persons. Although the 10-year survival of the one-stage implants was somewhat lower than has been observed for non-diseased patients, implant placement remains a good treatment alternative also for periodontally compromised patients.

AICRG, Part I: A 6-Year Multicentered, Multidisciplinary Clinical Study of a New and Innovative Implant Design

PROBLEM

Repetitive microstrains, which occur at the bone-implant interface during function, can lead to implant loss. In an attempt to improve survival by directing the stresses during function away from the dense cortical bone and toward the resilient trabecular bone, the Ankylos implant was developed with a roughened, progressive thread and a smooth cervical collar. The highly polished collar reduces the stresses in areas of the crestal bone. A precisely machined Morse taper prevents rotation of the abutment on the implant and eliminates the microgap present in many 2-stage implant systems. Clinical studies of other implants at different clinical research centers have demonstrated varying degrees of survival.

PURPOSE

The purpose of this paper was (1) to assess the overall clinical survival of this new implant design and (2) to compare implant stability (ie, Periotest values [PTVs]) over time with other implants.

METHOD

The investigation represented a comprehensive, multicentered, international clinical study conducted over a period of 6 years. It was conducted under an Investigational Device Exemption (IDE) protocol that was reviewed and accepted in the United States by the Food and Drug Administration (FDA). Over 1500 implants were placed and restored, and follow-up data were gathered for a period of up to 3 to 5 years.

RESULTS

Over 44% of the clinical research centers reported no failures (100% survival). A total of 63% of the centers had none or only 1 failure during the study. One center reported 6 failures in 1 patient, which were not related to the implant design. Overall survival for implants in function for 3 to 5 years was 97.5%. Using failure criteria of earlier studies of other implants, 5-year survival was 98.3%. Higher handpiece speeds were associated with an increase in the number of failures. This new design produced a slightly more resilient trabecular bone-implant complex with a difference of about 1 PTV in all bone densities when compared with other implants.

CONCLUSIONS

The following conclusions can be made: (1) the implant design was effective under all clinical conditions; (2) no significant and unexpected complications or risk factors were evident; (3) survival was found to be excellent; and (4) this implant is well suited for use in the restoration of masticatory function and esthetics in patients with missing natural teeth.

Hemorrhaging Associated With Endosseous Implant Placement in the Anterior Mandible: A Review of the Literature

The placement of endosseous dental implants is largely considered a safe surgical procedure. However, upper airway obstruction secondary to severe bleeding in the floor of the mouth has been occasionally reported as a rare but potentially fatal complication of implant surgery. This review presents critical hemorrhagic episodes, related to dental implantation in the anterior segments of the mandible, published to date. Massive internal bleeding in the highly vascularized region of the floor of the mouth is the result of an arterial trauma induced by instrumentation, usually through a perforation of the lingual cortical plate. Depending on the clinical situation, hemorrhage may commence immediately or with some delay after the vascular insult. The progressively expanding lingual, sublingual, submandibular, and submental hematomas have the tendency of displacing the tongue and floor of the mouth to obstruct the airway. Because the course of airway deterioration to complete occlusion may be rapid, ensuring a patent airway is of highest priority. Even though upper airway obstruction is potentially life-threatening, a secure airway was successfully established in all patients without fatal consequences. In most cases, resolution of hemorrhage required a surgical intervention for ligation of the bleeding vessels and hematoma evacuation. To reduce the probability of such a grave complication, preventive and precautionary measures to be taken before, during, and after implant placement in the anterior mandible are presented. Issues related to the level of surgical experience, fine regional arterial anatomy, radiographic and clinical evaluation of the osseous morphology, angulation and length of implants, and timing of hemorrhage onset are discussed. In addition, airway and bleeding management strategies are provided.

Dental implant design and its relationship to long-term implant success

The purpose of this review is to evaluate the effects of the biomechanical aspects of dental implant design on the quality and strength of osseointegration, the bone-implant interface, and their relationships to the long-term success of dental implants. The engineering design of implants is based on many interrelated factors, including the geometry of the implant, mechanical properties, and the initial and long-term stability of the implant-tissue interface. There is no one "optimal" design criterion. However, implants can be engineered to maximize strength, interfacial stability, and load transfer by using different materials, surfaces, and thread designs. Limited information is currently available in addressing how implant thread design influences the overall implant success. Therefore, this article reviews and discusses design elements of various dental implant systems currently in use as they affect the quality of osseointegration and their relationship to overall long-term success patterns.

Success and Failure Rates of 9 mm or Shorter Implants in the Replacement of Missing Maxillary Molars When Restored with Individual Crowns: Preliminary Results 0 to 84 Months in Function. A Retrospective Study

BACKGROUND

The ability to utilize shorter implants in the reconstruction of the posterior maxilla would, theoretically, simplify therapy by lessening the need for augmentation surgery. The purpose of this retrospective study was to assess the success and failure rates of < or = 9 mm or shorter implants in the maxillary posterior regions restored with individual crowns.

METHODS

A total of 979 implants were placed in maxillary molar positions and restored with individual crowns. The implants were followed in function for up to 84 months. The results are discussed in terms of clinical applicability and indications for use.

RESULTS

The cumulative success rates in function were 94.5% for implants in the maxillary first molar positions and 98.7% for implants in the maxillary second molar positions, yielding an overall cumulative success rate of 95.1%, in function for up to 84 months.

CONCLUSION

These findings suggest that non-countersunk implants of 7 to 9 mm in length may be successfully restored with single crowns in the maxillary molar region.

Immediate tooth extraction, placement of a Tapered Screw-Vent implant, and provisionalization in the esthetic zone: a case report

PURPOSE

This clinical report describes an immediate tooth extraction, followed by placement and provisional restoration of a dental implant in the prepared socket of a right maxillary central incisor.

MATERIALS AND METHODS

The tooth was extracted with minimal hard and soft tissue trauma and without flap reflection. A flapless, transmucosal surgical approach was used to prepare the socket and insert a tapered implant. The implant was immediately restored with a provisional abutment and crown without occlusal contacts. An impression was made 22 days after implant insertion, and a definitive, all-ceramic restoration was placed 3 days later.

RESULTS

During the period of provisional progressive loading, no significant soft tissue contraction was observed related to noninvasive operating techniques and the immediate insertion of the provisional restoration. The patient exhibited no clinical or radiologic complications through 8 months of clinical monitoring after loading.

CONCLUSION

The Tapered Screw-Vent implant and all-ceramic restoration provided the patient with immediate esthetics, function, and comfort without any complications during the postloading follow-up period.