Design Requirements for Scientific Clinical Implant Studies

Analysis of 435 screw-vent dental implants placed in 161 patients: software enhancement of clinical evaluation

This paper demonstrates how a computer software program was utilized in a private practice to supplement the clinical evaluation of one implant system. Clinical data were entered into a computer database at the time of implant placement and up to 13 years for follow-up appointments. Data were divided into two groups and subjected to lifetable analyses. The focus group consisted of a machined-titanium, screw-type implant with an internal abutment connection from one manufacturer. The residual database consisted of mixed implant designs with a variety of abutment connections and surfaces from several other manufacturers. Lifetable survival data between the two groups were generated. Cumulative survival rates from 0 to 13 years were 94.2% (n = 435) for the focus group and 90.1% (n = 2339) for the reference group. There were 25 implants lost in the focus group and 11 other implants were deemed "at risk." Survival results from other lifetable analyses are also presented for the two groups. Documentation of empirical clinical data in a computer software database over a period of time can help private practice clinicians better evaluate the dental implant systems used in their practices.

Influence of research center on overall survival outcomes at each phase of treatment

BACKGROUND

Clinical studies of dental implants tend to fall into two broad categories. Efficacy studies apply strict exclusion criteria under carefully controlled conditions to produce a narrow range of results. Effectiveness studies more closely model real-world treatment environments, with a more diverse patient sample and broader range of provider skills. In this multi-center study of more than 2,900 dental implants, study centers were grouped by implant survival scores in an attempt to draw attention to the influence of confounding variables associated with the treatment environment.

METHODS

Thirty-two study centers were ranked by implant survival scores at uncovering and assigned to three performance groups. Centers whose overall scores were within approximately one standard deviation of the mean were placed in the middle (70%) performance group (MPG). The remaining centers were placed in either the top (15%) performance group (TPG) or the lower (15%) performance group (LPG). Overall survival and survival by phase of treatment were recorded for each of six implant designs in each of the three performance groups.

RESULTS

From implant placement to 36 months, the TPG achieved survival rates from 100% (for 3 designs) to 95.5% (for one design), with an average of 97% for all designs. Increased variations in survival (97.2% to 73%) occurred in the MPG, with larger variations (96.4% to 48%) in the LPG. The HA-coated cylinder recorded consistently high survival scores (over 95%) in all performance groups and all phases of treatment. Failures for other designs in the MPG and LPG were concentrated in the healing period (placement to uncovering), except for the commercially pure titanium screw, which had the most failures between uncovering and prosthesis loading.

CONCLUSIONS

Implant design and treatment environment both play an important role in implant survival. Two design characteristics appear to enhance survival: 1) a surgical protocol involving minimal instrumentation at placement, and 2) hydroxyapatite (HA) coating. The HA-coated press-fit cylinder design was the least affected by the center's performance.

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.