The influence of bone thickness on facial marginal bone response: stage 1 placement through stage 2 uncovering

BACKGROUND

Various causes of facial bone loss around dental implants are reported in the literature; however, reports on the influence of residual facial bone thickness on the facial bone response (loss or gain) have not been published. This study measured changes in vertical dimension of facial bone between implant insertion and uncovering and compared these changes to facial bone thickness for more than 3,000 hydroxyapatite (HA)-coated and non-HA-coated root-form dental implants.

METHODS

Subjects were predominantly white males, 18 to 80+ years of age (mean 62.9 years), who were patients at 30 Department of Veterans Affairs Medical Centers and two university dental clinics. Alveolar ridges ranged from normal to resorbed with intact basal bone. Following preparation of the osteotomy site, direct measurements with calipers were made of the residual facial bone thickness, approximately 0.5 mm below the crest of the bone. The distance from the top of the implants to the crest of the facial bone was also measured using periodontal probes. Implants were uncovered between 3 to 4 months in the mandible and 6 to 8 months in the maxilla after insertion. Facial bone response was the difference between the height of facial bone at Stage 1 (insertion) and Stage 2 (uncovering).

RESULTS

The mean facial bone thickness after osteotomies were made was 1.7 +/- 1.13 mm. When a mean facial bone thickness of 1.8 +/- 1.41 mm or larger remained after site preparation, bone apposition was more likely to occur. The mean facial bone response for 2,685 implants was -0.7 +/- 1.70 mm. For implants integrated at uncovering, the mean bone response was -0.7 +/- 1.69 mm, and -2.8 +/- 1.57 mm for implants mobile at uncovering. Bone quality-4 had the least facial bone response, -0.5 +/- 2.11 mm. Bone responses were similar for both HA-coated and non-HA-coated implants.

CONCLUSIONS

Significantly greater amounts of facial bone loss were associated with implants that failed to integrate. As the bone thickness approached 1.8 to 2 mm, bone loss decreased significantly and some evidence of bone gain was seen. There was no statistically or clinically significant difference in bone response between HA-coated and non-HA-coated implants.

Variables affecting survival of single-tooth hydroxyapatite-coated implants in anterior maxillae at 3 years

BACKGROUND

The development and expanded use of endosseous dental implants over the last two decades have been remarkably rapid. It is, therefore, imperative that the dental profession closely monitor the performance of root-form implants used in a variety of applications. The Dental Implant Clinical Research Group (DICRG) was established in 1990 by the Department of Veterans Affairs as a forum for conducting prospective, multidisciplinary, multicentered studies in the field of implant dentistry. The DICRG comprised 30 VA medical centers and 2 dental schools at the time of this study. This paper reports on the survival of hydroxyapatite (HA)-coated grooved implants used to replace single missing teeth in anterior maxillae at 3 years post-implant placement.

METHODS

During a 4-year accrual period, a total of 247 single-tooth implant restorations were placed in anterior maxillae. This paper focuses on the survival of 222 implants (149 patients) for which 3-year data were recorded for the period from placement. Survival was examined with respect to patient demographics and health status, implant location, surgical variables, and 2-week post-placement use of chlorhexidine digluconate (0.12%) rinses. Implant stability was recorded using a hand-held probe. Periodontal-type measures were recorded and evaluated, and all complications related to osseointegration were noted. Failure was defined as removal of the implant for any reason.

RESULTS

Establishment and maintenance of osseointegration at 3 years post-placement was 97.3%. During this 3 year period, 6 implants were removed due to either failure to osseointegrate or loss of osseointegration. Implant length correlated positively with 3-year survival (P = 0.003, exact test). The use of preoperative antibiotics was nearly significant to implant survival (P = 0.051. Pearson chi-square). Mean stability values (PTVs) increased incrementally from -4.5 at uncovering to +1.1 at 36 months, indicating a decrease in stability of the bone-implant-prosthesis complex. The most common complication was related to inadequate available bone to fully house implants.

CONCLUSIONS

Three-year post-placement survival data suggest that the use of HA-coated, grooved, endosseous implants to support maxillary anterior single-tooth replacements is a predictable and reliable procedure that can offer significant benefits. Longer implants demonstrated higher survival than shorter implants. The use of preoperative antibiotics was nearly significant to implant survival, and there was an increase in mean PTVs observed over the duration of the study. Further research is needed to assess stability of the hydroxyapatite-bone interface over time.

Three-year post-placement survival of implants mobile at placement

BACKGROUND

Although rigid fixation of endosseous implants at the time of placement is generally thought to be a prerequisite for successful osseointegration, the Dental implant Clinical Research Group (DICRG) of the Department of Veterans Affairs has reported on implants that integrated despite being mobile at placement. The present study examines the frequency of osseointegration and the 36-month post-placement survival of implants mobile at placement in a prospective, multicenter, longitudinal clinical study of more than 3,000 implants conducted by the DICRG.

METHODS

A total of 3,111 implants of 6 different designs were placed in all jaw regions in more than 800 patients at 32 study centers. At the time of this report, 2,770 of these implants had been followed for 36 months post-placement. They included 89 implants that were mobile at placement. Data for demographic variables, implant coating, bone quality, incision type, bone augmentation, and antibiotic usage were recorded. An electronic hand-held probe was used to measure mobility at uncovering and at regular follow-up intervals.

RESULTS

Eighty-nine of 2,770 inserted implants were mobile at placement. Results are reported for two periods: from placement to 36 months and from prosthetic loading to 36 months. The latter method eliminated early failures and resulted in substantially higher scores for both mobile implants at placement (95.9% survival from prosthetic loading to 36 months post-placement versus 79.8% from placement to 36 months) and implants not mobile at placement (98.4% versus 93.4%). Mobility at placement was significant to 3-year survival (P < 0.001). Hydroxyapatite (HA) coating improved the performance of implants mobile at placement (91.8% for HA-coated versus 53.6% for non-HA) and those not mobile at placement (97.2% for HA-coated versus 87.4% for non-HA). Radiographic findings suggested that crestal bone response around implants which were mobile versus immobile at placement was similar.

CONCLUSIONS

Although implant stability at the time of placement is clearly desirable as seen in the superior 3-year survival of stable implants, it may not be an absolute prerequisite to osseointegration or to long-term survival. Several factors may influence the decision to remove or replace a mobile implant. HA-coating significantly improved the performance of both mobile and immobile implants at placement to 3 years post-placement (P < 0.001).

The influence of smoking on 3-year clinical success of osseointegrated dental implants

BACKGROUND

Health risks associated with smoking have been exhaustively documented and include increased incidence of periodontal disease, greater risk of osteitis following oral surgery, and compromised wound healing due to hypoxia. Information related directly to dental implants, although limited, points to higher rates of implant failures among smokers than non-smokers. This paper reports on long-term clinical outcomes of osseointegrated dental implants placed in smokers and non-smokers in a longitudinal clinical study of endosseous dental implants.

METHODS

In 1990, the Dental Implant Clinical Research Group (DICRG) of the Department of Veterans Affairs (DVA) launched an 8-year, randomized, prospective clinical study of more than 2,900 endosseous dental implants in more than 800 patients at 32 study centers. Confounding variables, including smoking patterns, were recorded. For this report, new follow-up data were analyzed for two groups: 1) current smokers and 2) those who never smoked combined with those who quit. Most of the variables recorded for each implant were screened on a univariate basis as possible predictors associated with implant survival/failure. Those with P values less than 0.15 and those likely to be a factor of clinical importance were placed in a logistic regression equation and analyzed for a simultaneous effect on survival. A step-wise procedure was used to eliminate those variables that showed the least significance, until only those variables with a Wald chi-square of significance in the presence of others remained. The effects of clustering within patients and of unbalanced distribution within hospitals were standardized to facilitate analysis of influence of demographic variables. The GEE analysis was performed with the patient as the primary cluster.

RESULTS

Current data do not support earlier findings that smoking contributes to early implant failure (placement to uncovering). A trend of greater failures in smokers appeared between the time after uncovering and before insertion of the prosthesis. Hydroxyapatite (HA)-coated implants had significantly lower failure rates. For the entire 3-year period, overall failures were significantly higher for smokers than non-smokers.

CONCLUSIONS

Results suggest that increased implant failures in smokers are not the result of poor healing or osseointegration, but of exposure of peri-implant tissues to tobacco smoke. Data also suggest that detrimental effects may be reduced by: 1) cessation of smoking; 2) the use of preoperative antibiotics; and 3) the use of HA-coated implants.

Survival and stability (PTVs) of six implant designs from placement to 36 months

BACKGROUND

Numerous new implant designs and materials have become available over the last decade, each with special claims of superiority in restoring complex cases. Differences in existing clinical databases, study designs, and methods of determining failures/survival are seldom standardized, which complicates comparisons of clinical performance of these new designs. Little information is available concerning the changes in stability of various designs and materials following clinical loading.

METHODS

A total of 30 VA medical centers and 2 dental schools combined to form the Dental Implant Clinical Research Group (DICRG). More than 2,900 implants were placed, restored and data gathered from the time of placement to 36 months. Implant stability from uncovering to 36 months and survival from placement to 36 months were determined. Survival was determined using two different approaches--considering all implants removed at any time, regardless of the reason (DICRG approach), and considering only those that were removed following loading of the prosthesis (post-loading approach). Survival was also determined for each of the three phases of implant treatment--phase 1, from the time of placement to uncovering and abutment connection; phase 2, from uncovering to placement and loading of the prosthesis; and phase 3, from loading of the prosthesis to 36 months.

RESULTS

The two approaches to determining survival for each implant design and/or material included in the study showed differences in reported numbers ranging from 1.1% to 21.7%. The largest difference in survival was for the commercially pure titanium screw (used in this study only in the maxillary completely edentulous applications), which showed a 21.7% greater survival rate. With the DICRG approach, the hydroxyapatite (HA)-cylinder had the highest survival (97.5%). When considering the post-loading approach, the titanium-alloy screw had the highest survival (99.4%), with the HA-cylinder having the next highest survival (98.6%). The HA-cylinder did not show increased stability from uncovering to 36 months, and the HA-grooved implant became less stable.

CONCLUSIONS

HA-coated implants demonstrated the highest survival rate; 2) the post-loading analysis approach inflated survival; 3) non-HA implants showed increased stability following loading; 4) HA-coated implants showed a slight decrease or no change in stability; and 5) the clinical significance of the changes in implant stability must be determined for the long-term.

Long-term assessment (5 to 71 months) of endosseous dental implants placed in the augmented maxillary sinus

BACKGROUND

It is not uncommon for the placement of endosseous dental implants in the maxillary posterior jaw region to be complicated by the pneumatization of the maxillary sinus. When this occurs, the residual bone between the floor of the sinus and the crestal ridge is inadequate for the placement of implants. The sinus lift procedure provides a way to increase the amount of available bone and the placement of longer implants.

METHODS

One hundred twenty (120) implants were placed in 45 augmented maxillary sinuses. Patients ranged in age from 34 to 78 years. The implant design included a limited number of non-hydroxyapatite (HA)-coated titanium screws, with the majority of the implants being HA-coated cylinders, grooved cylinders, and screws. The augmentation materials were autogenous bone, allogenic bone (demineralized freeze-dried bone allograft, DFDBA), alloplastic bone (HA), combination grafts of HA and DFDBA, and combination grafts of autogenous bone and DFDBA. All the cases were successfully restored with implant-supported, bar-retained overdentures or fixed partial dentures. The follow-up began at Stage 2 uncovering and ranged from 5 to 71 months, with a mean of 38.2 and standard deviation of 14.6 months.

RESULTS

Three (2.5%) of the 120 implants failed between the period of implant placement and 36 months. Failures appeared to be associated with a history of smoking. Other complications encountered during the study are presented. Implant survival was higher in those placed in grafted sinuses (97.5%) than in those placed in the posterior maxilla without sinus grafting (90.3%).

CONCLUSION

These findings support the use of implants placed in augmented sinuses to support dental prostheses.

Survival of various implant-supported prosthesis designs following 36 months of clinical function

BACKGROUND

The use of endosseous dental implants to replace natural teeth lost to trauma, dental caries, or periodontal disease has become a predictable form of prosthetic treatment since gaining popularity in the early 1980s. While numerous clinical studies have focused on the survival of implants, few address the survival of different prosthesis designs.

METHODS

Beginning in 1991, 882 prostheses supported by more than 2,900 implants (687 patients) were placed by the Department of Veterans Affairs Dental Implant Clinical Research Group (DICRG). These prostheses were divided into five research strata based on arch location. The recommended design for each stratum was: bar-supported overdenture (maxillary completely edentulous); screw-retained hybrid denture (mandibular completely edentulous); screw-retained fixed partial denture (mandibular and maxillary posterior partially edentulous); and cemented single crown (maxillary anterior single tooth). Alternative overdenture designs were utilized in the edentulous arches when the recommended prosthesis could not be fabricated. Prosthesis success rates for the research strata were calculated for an observation time of up to 36 months following prosthesis placement.

RESULTS

Success rates for the maxillary edentulous stratum ranged from 94.6% for the bar-retained overdenture supported by five to six fixtures to 81.8% for the cap-retained overdenture. The mandibular edentulous strata produced success rates of 98.1% for the fixed hybrid prosthesis to 91.7% for the cap-retained prosthesis. Success rates for maxillary and mandibular posterior fixed partial dentures were 94.3% and 92.6%, respectively, while the maxillary anterior single-tooth prosthesis yielded a success rate of 98.1% for the 36-month observation period.

CONCLUSIONS

The recommended prosthesis designs investigated in this study proved to be reliable, with encouraging success rates for an observation period of 36 months following placement.

Implant surface coating and bone quality-related survival outcomes through 36 months post-placement of root-form endosseous dental implants

Survival rates from placement to 36 months were reported for the ongoing Dental Implant Clinical Research Group studies of root-form endosseous dental implants. Failure rates for all implants were similar in bone qualities 1 and 2 (6.2% and 6.7%, respectively) and slightly higher in bone qualities 3 and 4 (8.5% and 8.7%, respectively). Hydroxyapatite (HA)-coated implants had an overall failure rate of 3.9% over 36 months in all bone qualities combined, while non-coated implants had a 13.4% failure rate for the same parameters. For each bone quality, there was a significant difference in implant survival for the non-coated implants (P < 0.01). The highest failure rates for non-coated implants were in bone qualities 3 and 4 (19.1% and 25.5%, respectively). No major difference in survival was found for HA-coated implants placed in each bone quality. Possible reasons for the differences in survival are discussed.

Implant survival in patients with type 2 diabetes: placement to 36 months

BACKGROUND

Because the life expectancy of individuals continues to increase, dentists providing dental implant treatment can expect to see an increasing number of patients with diabetes mellitus. Today, there are little data available concerning the clinical outcomes involving the use of implant treatment for patients with diabetes mellitus. There are three types of diabetes mellitus: Type 1 (insulin dependent), Type 2 (non-insulin dependent), and gestational. Because of possible complications from patients with diabetes mellitus, they are excluded from participation in most clinical studies of endosseous dental implant survival.

METHODS

This study attempted to determine if Type 2 diabetes represents a significant risk factor to the long-term clinical performance of dental implants, using the comprehensive DICRG database. Diabetes was a possible exclusion criterion; however, the final decision on Type 2 patients was left to the dental implant team at the research center. A total of 2,887 implants (663 patients) were surgically placed, restored, and followed for a period of 36 months. Of these, 2,632 (91%) implants were placed in non-diabetic patients and 255 (8.8%) in Type 2 patients. Failures (survival) were compared using descriptive data. Possible clustering was also studied.

RESULTS

A model assuming independence showed that implants in Type 2 patients have significantly more failures (P = 0.020). However, if correlations among implants within the patient are considered, the significance level becomes marginal (P = 0.046). The experience of the surgeon did not produce a clinically significant improvement in implant survival. The use of chlorhexidine rinses following implant placement resulted in a slight improvement (2.5%) in survival in non-Type 2 patients and a greater improvement in Type 2 patients (9.1%); the use of preoperative antibiotics improved survival by 4.5% in non-Type 2 patients and 10.5% in Type 2 patients. The use of HA-coated implants improved survival by 13.2% in Type 2 diabetics.

CONCLUSION

Type 2 diabetic patients tend to have more failures than non-diabetic patients; however, the influence was marginally significant. These findings need to be confirmed by other scientific clinical studies with a larger Type 2 diabetic sample size.

Influence of two different approaches to reporting implant survival outcomes for five different prosthodontic applications

BACKGROUND

Over the years, the definition of implant failure has varied, with some investigators accounting for all implants placed, while others discard failures that occurred before clinical loading. The influence of stresses transmitted to various bone densities, by different prosthetic appliances as well as the method used to determine failures, needs to be clearly understood. This paper reports on the influence of two different methods of determining 36-month survival of implants used to support different dental prostheses.

METHODS

More than 2,900 implants with six different designs were placed in 829 patients at 32 study centers and followed for 3 years. The first method of determining survival accounted for all failures from placement through 36 months, while the second method counted only failures from post-loading of the prosthesis to 36 months. Survival curves were used to determine differences in survival outcomes for the two methods.

RESULTS

For the maxillary single-tooth prosthetic application, implant survival from placement to 36 months was 94.7% when all failures were counted and increased to 98.3% with the post-loading method. For upper completely edentulous applications, implant survival was 85.3% with all failures counted and 95.6% with the post-loading method. This 10.3% difference is clinically important. The survival for implants in lower completely edentulous applications increased by 4.4% simply by using the post-loading approach. Implants used for upper posterior, partially edentulous applications involved only hydroxyapatite (HA)-coated implants, and the survival rates were similar (96.4% for all implants and 98.2% for the post-loading method). The difference in reported survival rates for implants in the lower posterior, partially edentulous application was 5.8%. Since failures tended to occur in the earlier phases of treatment, the post-loading approach always resulted in more favorable survival data. With the post-loading approach, valuable information related to implant performance before loading is lost. In all comparisons, HA-coated implant survival was always better than non-HA implants. Clinical investigators should clearly state the method used for determining failures. For all implants included in the study, survival curves illustrated different failure patterns for each method of determining overall survival.

CONCLUSION

Reporting of implant survival rates based on the post-loading method provides more favorable survival rates; however, accounting for all implants provides a more accurate method of determining survival.

Stability of the bone-implant complex. Results of longitudinal testing to 60 months with the Periotest device on endosseous dental implants

BACKGROUND

Maintenance of the health and integrity of the bone-implant complex (osseointegration) has been shown to be essential for long term success of root-form, endosseous dental implants. If reliable clinical indicators of adequacy of the bone-implant complex existed, they could stimulate new and innovative early intervention research to arrest of reverse early deterioration of the bone-implant complex. In the absence of such indicators, this has been problematic. The Periotest may have the potential to provide this information by indirectly assessing the status of the bone-implant complex. However, little information is available that documents either the capability of the Periotest to reliably assess changes of the bone-implant complex or the "normal variations" in Periotest values (PTVs) for both HA-coated and non-coated implants.

METHODS

The purpose of this paper was to document changes in PTVs as influenced by various implant surfaces, implant designs, and bone densities. The mean PTVs recorded for each visit, for all implant types and bone densities, were combined to provide an overall average PTV (A-PTV). The changes in stability (PTVs) were analyzed using a generalized linear model (GLM) with repeated measures (Hotelling's Trace).

RESULTS

The A-PTV for all implants over all visits was -3.5. The mean PTVs ranged from -4.2 (SD = 2.4) at uncovering to -3.9 (SD = 2.9) at 60 months. All implants in bone qualities 1 and 2 (BQ-1 and BQ-2) became more stable over time, while those in bone quality 3 or 4 (BQ-3 and BQ-4) showed a slight decrease in stability. In BQ-1, the mean PTVs increased from -4.7 at uncovering to -4.9 at 60 months. A similar increase in stability occurred in BQ-2 (-4.1 at uncovering to -4.4 at 60 months). In BQ-3, the stability of the implants decreased over time (-3.6 at uncovering to -2.9 at 60 months), with similar changes recorded for BQ-4 (-2.5 at uncovering to -1.0 at 60 months). When comparing the stability of all HA-coated with all non-coated implants, the HA implants became less stable (-4.4 to -3.4) over time, while non-coated implants showed an improvement in stability (-3.5 to -4.5). The changes in stability found in BQ-1, BQ-2, and BQ-3 were similar, with HA implants becoming less stable and non-coated more stable. HA- and non-coated comparisons were not possible in BQ-4 since there were too few non-coated implants placed in this type of bone. The HA-coated screw showed a decrease in stability when compared to the non-coated screw.

CONCLUSIONS

Conclusions of the study are as follows: 1) PTVs are influenced by bone quality and surface coating of the implant; 2) the PTVs at the time of uncovering provide the best estimate of a clinically acceptable PTV for that bone-implant complex; 3) while the PTVs for any bone-implant complex may fluctuate +/- 1.0 around the uncovering PTV during routine healing and loading of the implant, a consistent shift toward a positive PTV that approaches "0" should be cause for concern that the bone-implant complex may be at risk of failure; 4) HA-coated implants became slightly less stable (more positive PTVs) over time, while the non-coated implants became more stable (more negative PTVs); and 5) until a "critical PTV" can be accurately identified, it is suggested that a consistent shift in recorded PTVs that exceeds the +3.0 value on the PTV scale should be viewed with concern for possible deterioration at the bone-implant complex.

Periodontal-type measurements associated with hydroxyapatite-coated and non-HA-coated implants: uncovering to 36 months

BACKGROUND

While the use of hydroxyapatite (HA)-coated endosseous dental implants has gained in popularity over the past 10 years, the short-term and long-term predictability and indications for their use remain highly controversial. Some reports suggest that the HA coating may separate from the substructure, undergo dissolution in tissue fluids, and/or contribute to rapid osseous breakdown around the implant. Other reports, however, relate favorable responses to HA-coated implants, which include rapid bone adaptation to the HA, greater stability at uncovering, and increased coronal bone growth. These contradictions may be related to differences in chemical composition of the HA on the implant surface. Most clinicians and researchers may agree that long-term, independent, scientific clinical studies are needed to compare HA-coated and non-HA-coated (titanium-alloy and CP-titanium) implants under the same conditions. Concerns appear in the literature that HA-coated implants experience greater breakdown because they are more susceptible to bacterial colonization due to their roughness and hydrophilicity. Some studies suggest that specific putative periodontal pathogens may adhere to the HA, thereby predisposing the implant to greater peri-implantitis than that experienced by non-HA implants.

METHODS

A total of 32 clinical research centers, located in various geographic regions of the United States, were selected to participate in a comprehensive clinical study. More than 2,900 HA-coated and non-HA implants were randomized as to location within one of three jaw regions--maxillary anterior, mandibular anterior, and mandibular posterior--and followed for 36 months. It can be assumed that in each of these jaw regions, the conditions associated with both implant surface types would be similar enough to permit meaningful comparisons of periodontal-type measurements that have not previously been reported. Periodontal-type measurements (gingiva, plaque, suppuration, and calculus indices; probing depth; attachment levels; recession; and keratinized tissue width) for each aspect of each implant (mesial, facial, distal, and lingual) were recorded at 3, 6, 9, 12, 18, 24, and 36 months following implant uncovering. The implant was considered the experimental unit for analysis using generalized estimating equation and repeated measure methods. Data for the four aspects of each implant, as well as measurements over time, were all clustered in the unit of analysis.

RESULTS

The percentages of implants with zeros recorded for the indices was remarkably similar for both HA-coated and non-HA implants. While statistically significant differences were found for some of the measurements associated with HA-coated and non-HA implants under certain conditions, these differences were too small to be considered clinically significant.

CONCLUSIONS

Overall, there was no clinically significant difference between the periodontal-type measurements for HA-coated and non-HA-coated implants followed for a period from 3 through 36 months. The concerns about HA-coated implants being associated with adverse periodontal responses for the HA chemical composition included in this study appear to be unfounded for a period of clinical performance up to 36 months.

The influence of preoperative antibiotics on success of endosseous implants at 36 months

The benefits of prophylactic antibiotics are well recognized in dentistry. However, their routine use in the placement of endosseous dental implants remains controversial. As part of the comprehensive Dental Implant Clinical Research Group (DICRG) clinical implant study, the preoperative or postoperative use of antibiotics, the type used, and the duration of coverage were left to the discretion of the surgeon. These data for 2,973 implants were recorded and correlated with failure of osseointegration during healing (Stage 1), at surgical uncovering (Stage 2), before loading the prosthesis (Stage 3), and from prosthesis loading to 36 months (Stage 4). The results showed a significantly higher survival rate at each stage of treatment in patients who had received preoperative antibiotics.

Implant survival to 36 months as related to length and diameter

BACKGROUND

It is generally accepted that diameter and length of an endosseous dental implant and its stability at placement are critical factors in achieving and maintaining osseointegration. In the event of slight implant mobility at placement, the conventional or accepted treatment is to place a longer implant and/or one of wider diameter. This manuscript presents stability and survival/failure data for implants of different diameters and lengths following 36 months post-placement, as well as crestal bone loss data between placement and uncovering.

METHODS

A subset of the Dental Implant Clinical Research Group's database was used to study the 3-year survival and stability of various implant lengths (7 mm, 8 mm, 10 mm, 13 mm, and 16 mm) and diameters (3 mm+ and 4 mm+). Placement to uncovering crestal bone loss was also determined. The implants were generally representative of those available for clinical use (screws, basket, grooved, hydroxy-apatite-coated, CP-Ti, Ti-alloy). The study protocol specified that the implants be randomized to various jaw regions to accomplish the primary goals of the study--the comparison of each implant design's overall survival. A total of 2,917 implants were placed, restored, and followed. Data for all 3 mm to 3.9 mm diameter implants were pooled into a "3+" group, and the 4 mm to 4.9 mm diameter implants into a "4+" mm group. No attempt was made to look at the influence of any other variables on survival outcomes. The possible influence of clustering on survival was taken into consideration.

RESULTS

The 3+ mm group had a mean stability (PTV) of -3.8 (SD = 2.9), and the 4+ group had a mean PTV of -4.4 (SD = 2.7) (P < 0.05). The PTVs for implant lengths ranged from -2.9 (SD = 2.8) for 7 mm lengths to -3.9 (SD = 2.9) for 16 mm lengths (P < 0.05). Survival to 36 months was 90.7% for the 3+ diameter and 94.6% for the 4+ group (P = 0.01). Survival ranged from 66.7% for the 7 mm implants to 96.4% for 16 mm implants (P = 0.001). Outcomes did not change when clustering was considered, although the P value decreased slightly.

CONCLUSIONS

The results indicate that: 1) shorter implants had statistically lower survival rates as compared with longer implants; 2) 3+ mm diameter implants had a lower survival rate as compared with 4+ mm implants; 3) 3+ mm diameter implants are less stable (more positive PTVs) than 4+ mm implants; and 4) there was no significant difference in crestal bone loss for the two different implant diameters between placement and uncovering.

Characterization of the enzymatic component of Clostridium perfringens iota-toxin

The iota(a) component (i(a)) of Clostridium perfringens ADP ribosylates nonmuscle beta/gamma actin and skeletal muscle alpha-actin. Replacement of Arg-295 in i(a) with alanine led to a complete loss of NAD(+)-glycohydrolase (NADase) and ADP-ribosyltransferase (ARTase); that of the residue with lysine caused a drastic reduction in NADase and ARTase activities (<0.1% of the wild-type activities) but did not completely diminish them. Substitution of alanine for Glu-378 and Glu-380 caused a complete loss of NADase and ARTase. However, exchange of Glu-378 to aspartic acid or glutamine resulted in little effect on NADase activity but a drastic reduction in ARTase activity (<0.1% of the wild-type activity). Exchange of Glu-380 to aspartic acid caused a drastic reduction in NADase and ARTase activities (<0.1% of the wild-type activities) but did not completely diminish them; that of the residue to glutamine caused a complete loss of ARTase activity. Replacement of Ser-338 with alanine resulted in 0.7 to 2.3% wild-type activities, and that of Ser-340 and Thr-339 caused a reduction in these activities of 5 to 30% wild-type activities. The kinetic analysis showed that Arg-295 and Ser-338 also play an important role in the binding of NAD(+) to i(a), that Arg-295, Glu-380, and Ser-338 play a crucial role in the catalytic rate of NADase activity, and that these three amino acid residues and Glu-378 are essential for ARTase activity. The effect of amino acid replacement in i(a) on ARTase activity was similar to that on lethal and cytotoxic activities, suggesting that lethal and cytotoxic activities in i(a) are dependent on ARTase activity.

The efficacy of a counter-rotational powered toothbrush in the maintenance of endosseous dental implants

BACKGROUND

Although most patients with implants have lost their natural teeth because of poor oral hygiene, limited data exist to guide practitioners in their recommendations of home-care regimens for their patients' endosseous dental implants and maintenance of peri-implant soft-tissue health. The authors conducted a study to compare the home-care effectiveness of a counter-rotational powered tooth-brush with that of conventional home-care regimens.

METHODS

Before starting the six-year study, the authors trained 85 clinical investigators at 32 dental research centers across the United States in gathering periodontal data. Data for 2,966 implants were entered into a centralized database. Outcomes were derived from 24-month observations of a subset of the implants studied.

RESULTS

Repeated-measures analysis of the toothbrushing methods used on 2,966 implants showed that the counter-rotational powered toothbrush removed plaque significantly better than manual methods (P < .0001 Wald statistic) from all implant surfaces and at all recall intervals up to 24 months. Similar results were demonstrated for the gingival index.

CONCLUSIONS

The counter-rotational powered brush appears to be well-suited for home-care regimens aimed at maintaining optimal peri-implant soft-tissue health in patients with dental implants.

CLINICAL IMPLICATIONS

The importance of maintaining the health of the peri-implant tissues is well-recognized by the dental profession. The counter-rotational powered toothbrush is an effective tool in meeting the oral hygiene challenges associated with implant prosthesis maintenance.

Clostridium perfringens beta-toxin is sensitive to thiol-group modification but does not require a thiol group for lethal activity

The beta-toxin gene isolated from Clostridium perfringens type B was expressed as a glutathione S-transferase (GST) fusion gene in Escherichia coli. The purified GST-beta-toxin fusion protein from the E. coli transformant cells was not lethal. The N-terminal amino acid sequence of the recombinant beta-toxin (r toxin) isolated by thrombin cleavage of the fusion protein was G-S-N-D-I-G-K-T-T-T. Biological activities and molecular mass of r toxin were indistinguishable from those of native beta-toxin (n toxin) purified from C. perfringens type C. Replacement of Cys-265 with alanine or serine by site-directed mutagenesis resulted in little loss of the activity. Treatment of C265A with N-ethylmaleimide (NEM), which inactivated lethal activity of r toxin and n toxin, led to no loss of the activity. The substitution of tyrosine or histidine for Cys-265 significantly diminished lethal activity. In addition, treatment of C265H with ethoxyformic anhydride which specifically modifies histidyl residue resulted in significant decrease in lethal activity, but that of r toxin with the agent did not. These results showed that replacement of the cysteine residue at position 265 with amino acids with large size of side chain or introduction of functional groups in the position resulted in loss of lethal activity of the toxin. Replacement of Tyr-266, Leu-268 or Trp-275 resulted in complete loss of lethal activity. Simultaneous administration of r toxin and W275A led to a decrease in lethal activity of beta-toxin. These observations suggest that the site essential for the activity is close to the cysteine residue.

Sustained release liquid preparation using sodium alginate for eradication of Helicobacter pyroli

We prepared a new liquid preparation for eradication of Helicobacter pylori (HP), and examined drug release in vitro and in vivo. The liquid preparation mainly consisted of a sodium alginate (AG) aqueous solution containing ampicillin (ABPC), an antibiotic drug, or methylene blue, a dye. Drug release was retarded by Ca pre-treatment (0.10 M, 20 s) of the AG preparation in in vitro drug release studies due to gel-formation at the liquid surface. In in vivo experiments, the AG preparations were administered orally to rats. The rats were divided into two groups, with or without pre-administration of ranitidine hydrochloride (RH, an H2-blocker). The total remaining % of ABPC in the stomach was high in the rats administered the AG preparation compared to the ABPC solution. The AG preparation might float in the stomach without adhering to the gastric wall in the rats without pre-administration of RH. The total remaining % of ABPC at 30 min was almost 100% in the RH pre-administration rats administered the AG preparation, and about 80% of the drug existed in fraction 2 (implying adhesion of the preparation on the gastric mucus). At 60 min, the total remaining % in the AG preparation plus Ca (mean 87%) increased about 2-fold compared to that in the AG preparation alone (mean 44%). In this case, a large portion of the remaining ABPC also existed in fraction 2. This preparation may be useful for eradication of HP.

Factors affecting implant mobility at placement and integration of mobile implants at uncovering

This study examined 1) factors that contributed to implant stability at placement and 2) the likelihood for an implant that was mobile at placement to osseointegrate. Eighty-one (3.1%) of 2,641 implants placed by the Dental Implant Clinical Research Group between 1991 and 1995 were found to be mobile at placement. Seventy-six (93.8%) of the 81 mobile implants were integrated at uncovering compared to 97.5% for the 2,560 immobile implants. Variables that influenced mobility at placement included patient age, implant design and material, anterior-posterior jaw location, bone density, and use of a bone tap. Hydroxyapatite (HA)-coated implants were slightly more likely to be mobile at placement (P = 0.324) than non-hydroxypatite (HA)-coated implants. Of the 54 HA-coated implants that were mobile at placement, all (100%) integrated, while only 17 (81.5%) of the 22 mobile non-HA-coated implants integrated (P = 0.003). Mean electronic mobility testing device values (PTVs) at uncovering for all implants mobile or immobile at placement that integrated were -2.9 and -3.6 respectively. PTVs for HA-coated implants that were mobile (-3.5 PTV) or immobile (-4.0 PTV) at placement differed by 0.5 PTV, whereas non-HA-coated implants exhibited a greater difference of 1.2 PTVs at uncovering. HA-coated implants, regardless of mobility at placement, integrated more frequently and exhibited greater stability than non HA-coated implants.

Hydroxyapatite-coated implants: a case for their use

The information on which this article is based comprises a small fraction of the large database compiled from the DICRG study. These results represent the early performance for HA implants (up to 36 months). The study has been ongoing for 6 years, and there are more than 2,000 implants with 4-year data and 1,500 with 5-year data. These data are similar to the 36-month data, and when they are eventually released, they are likely to reinforce the results reported here. Meanwhile, the evidence presented in this article, along with other corroborating studies cited in the introduction, are sufficient grounds to reach the following conclusion: The ideal implant design and material is one that is easy to use, requires average skills, involves minimal bone trauma, presents a biocompatible contact surface, and produces a high rate of survival in most patients. Based on 36-month survival in the DICRG study, HA-coated implants appeared to satisfy these basic requirements better than the other implants used in the study. HA-coated implants were placed in the most challenging bone types and jaw region, in patients with compromised medical histories, by dentists with different training, skills, and experience, under less than ideal clinical conditions, and still showed the highest survival rates of all implants at every point in the treatment up to 36 months.

Mechanism of membrane damage by Clostridium perfringens alpha-toxin

The effect of Clostridium perfringens alpha-toxin on liposomes prepared from phosphatidylcholine (PC) containing the fatty acyl residues of 18 carbon atoms was investigated. The toxin-induced carboxyfluorescein (CF) leakage and phosphorylcholine release from multilamellar liposomes increased as the phase transition temperature of the phosphatidylcholines containing unsaturated fatty acyl residues decreased. However, there was no difference between the sensitivity of the different phosphatidylcholines solubilized by deoxycholate to the phospholipase C (PLC) activity of the toxin. However, the toxin did not hydrolyze solubilized distearoyl-L-alpha-phosphatidylcholine (DSPC) or phosphatidylcholine containing saturated fatty acyl residue, and caused no effect on liposomes composed of DSPC. These results suggest that the activity of the toxin is closely related to the membrane fluidity and double bond in PC. The N-terminal domain of alpha-toxin (AT1-246) and variant H148G did not induce CF leakage from liposomes composed of dioleoyl-L-alpha-phosphatidylcholine (DOPC). H148G bound to the liposomes, but AT1-246 did not. However, the C-terminal domain (AT251-370) conferred binding to liposomes and the membrane-damaging activity on AT1-246. These observations suggest that the membrane-damaging action of alpha-toxin is due to the binding of the C-terminal domain of the toxin to the double bond in the PC in the bilayer and hydrolysis of the PC by the N-terminal domain.

Assembly of Clostridium perfringens epsilon-toxin on MDCK cell membrane

Clostridium perfringens epsilon-toxin bound to the Madin Darby canine kidney (MDCK) cells and aggregated. The complex of the toxin was formed in a dose- and a time-dependent manner. The formation of the complex increased with a decrease in viable counts of MDCK cells and with increasing K+ release from the cells. The inactivated toxin heated at 100 degrees C did not aggregate under the condition. In addition, the prototoxin dose-dependently bound to the cells, but did not form the complex. Incubation of the toxin with MDCK cell membranes also showed the formation of the complex, but that with membrane preparations prepared from Vero cells or sheep erythrocytes, which are insensitive for the toxin, showed no formation of the complex. Incubation of the toxin with mouse brain homogenates resulted in formation of the complex, but that with brain homogenates heated at 80 degrees C or mouse liver homogenates showed no formation of the complex. These observations show that the complex formation of epsilon-toxin is essential for toxicity of the toxin.

Periotest values of dental implants in the first 2 years after second-stage surgery: DICRG interim report no. 8. Dental Implant Clinical Research Group

In 1991, the Dental Implant Clinical Research Group initiated a long-term clinical study in cooperation with the Department of Veterans Affairs to investigate the influence of implant design, application, and site of placement on clinical performance and crestal bone height. As part of this investigation, Periotest values for 2,212 root from implants were determined at second-stage surgery and during a 24-month follow-up period. Mean Periotest values decreased for implants placed in quality 1 and 2 bone, did not change for implants in quality 3 bone, and increased for implants in quality 4 bone. Implants in the posterior maxilla and single implants in the anterior maxilla had increasing mean Periotest values as compared with decreasing values for implants in other regions. Mean Periotest values for uncoated implants decreased gradually to approach those of hydroxyapatite-coated implants.