An IN VITRO Comparison of the Computerized Tomography/CAD-CAM and Direct Bone Impression Techniques for Subperiosteal Implant Model Generation

An in vitro comparison of the computerized tomography/CAD-CAM and direct bone impression techniques for subperiosteal implant model generation

1. Scientific Reference

• Study Title: An in vitro comparison of the computerized tomography/CAD-CAM and direct bone impression techniques for subperiosteal implant model generation
• Authors: A. Norman Cranin, Michael Klein, John P. Ley, John Andrews, Robert DiGregorio
• Journal: Journal of Oral Implantology
• Year of Publication: 1998
• DOI: Not specified in the provided material.

2. Scientific Background

The fabrication of subperiosteal implants has traditionally relied on a two-stage surgical protocol involving a direct impression of the exposed bone. While this approach has long been regarded as the reference method for achieving an accurate fit, it requires an additional surgical procedure. The introduction of computed tomography (CT) combined with computer-aided design and computer-aided manufacturing (CAD/CAM) represented an important technological advance by enabling implant framework fabrication from radiographic data, potentially reducing treatment to a single surgical intervention.

As digital workflows emerged in implant dentistry, questions arose regarding whether CT-derived anatomical models could reproduce osseous structures with the same level of accuracy as direct bone impressions. Since passive adaptation is essential for subperiosteal implant stability, validating the precision of these manufacturing techniques became clinically relevant. This study addresses that issue through an in vitro comparison using human cadaver jaws, providing objective data on the anatomical fidelity of both fabrication methods.

3. Study Objective

The purpose of this investigation was to compare the accuracy of bone models produced by two different fabrication techniques used for subperiosteal implant construction: the conventional direct bone impression method and a CT/CAD-CAM workflow.

The authors sought to determine whether digitally generated models could reproduce maxillary and mandibular anatomy with sufficient precision for the fabrication of clinically acceptable subperiosteal implant frameworks.

4. Methodology

This research was designed as an in vitro experimental study using seven human cadaver jaw specimens, including two maxillae and five mandibles.

Each specimen underwent both fabrication protocols. Direct bone impressions were taken using custom trays and polysulfide impression material before stone casts were poured. The same specimens were subsequently scanned using computed tomography according to a standardized acquisition protocol, and the imaging data were used to manufacture CAD/CAM-generated models.

For every model, chromium-cobalt-molybdenum analytical grids representing subperiosteal implant frameworks were fabricated. The adaptation of each grid to its corresponding bony specimen was quantitatively evaluated through a custom measurement system that calculated an inaccuracy index based on the length and magnitude of misfitting framework segments. Statistical comparisons between both techniques were performed using the chi-square test.

5. Main Findings

The investigation demonstrated measurable differences in model accuracy between the two fabrication methods.

All seven models produced from direct bone impressions were considered clinically acceptable. In comparison, five of the seven CT/CAD-CAM-generated models achieved an acceptable level of adaptation.

The largest discrepancies were observed in the two maxillary specimens, where digitally generated models exhibited substantially greater inaccuracy than their conventionally produced counterparts. Statistical analysis showed a significant overall difference between the two techniques (p = 0.001), with the maxillary subgroup also demonstrating significant differences. Conversely, no statistically significant differences were identified among the mandibular specimens.

The authors suggest that these inaccuracies may be related to procedural variables, specimen handling, or technical limitations associated with CT/CAD-CAM technology available at the time of the investigation rather than representing a universal limitation of digital workflows.

6. Clinical Analysis

This study offers valuable insight into the early development of digital manufacturing techniques for subperiosteal implant fabrication. Rather than simply comparing two laboratory procedures, it evaluates whether a less invasive digital workflow could achieve anatomical accuracy comparable to the long-established direct bone impression technique.

The findings indicate that conventional bone impressions produced consistently accurate models under the experimental conditions tested, whereas CT/CAD-CAM demonstrated greater variability, particularly in maxillary specimens. The authors propose several possible explanations, including specimen dehydration, subtle movement during CT acquisition, and the difficulty of reproducing complex maxillary anatomy using late-1990s imaging and manufacturing technologies.

From a clinical perspective, these observations should be interpreted within their historical context. The CT scanners, image reconstruction software, and CAD/CAM systems evaluated in this study differ substantially from contemporary digital technologies. Consequently, the reported limitations should not be directly extrapolated to current digital implant workflows.

Nevertheless, the study highlights a principle that remains highly relevant today: successful fabrication of patient-specific subperiosteal implants depends on precise anatomical replication. Accurate digital acquisition remains a fundamental requirement for passive framework adaptation, regardless of ongoing technological improvements.

7. Clinical Applications

The results are primarily applicable to the manufacturing process of custom subperiosteal implants and the evaluation of digital workflows used in implant dentistry.

The study may be relevant for:

• assessing the accuracy of patient-specific implant fabrication techniques;
• understanding the evolution of CAD/CAM technology in implant dentistry;
• evaluating digital planning protocols for complex edentulous cases;
• appreciating the importance of anatomical accuracy during framework fabrication.

Because this investigation focused exclusively on laboratory model accuracy, it does not provide evidence regarding long-term clinical outcomes, implant survival, or patient-centered treatment effectiveness.

8. Level of Evidence, Limitations, and Transparency

This publication represents an in vitro experimental study, corresponding to preclinical evidence.

Several methodological limitations should be considered. The investigation included only seven anatomical specimens, with only two maxillae, limiting subgroup interpretation. The study was performed on preserved cadaver specimens rather than living patients, restricting direct clinical generalization.

The authors also acknowledge that factors such as specimen dehydration, possible movement during CT acquisition, and technological limitations of contemporary imaging systems may have influenced model accuracy.

Regarding transparency, the acknowledgements indicate material and technical support from Techmedica Corporation, Aim-Park Dental Laboratories, and the Department of Radiology at Orange Memorial Hospital. No explicit conflict of interest statement is reported in the provided article.

9. Key Study Points

• Study design: In vitro experimental study
• Level of evidence: Preclinical
• Study population: Seven human cadaver jaw specimens (2 maxillae, 5 mandibles)
• Number of patients: Not applicable
• Follow-up: Not applicable
• Primary outcome: Accuracy of bone models generated by direct bone impression versus CT/CAD-CAM
• Main finding: Direct bone impression produced clinically acceptable models in all seven cases, whereas CT/CAD-CAM achieved acceptable accuracy in five of seven specimens.
• Scientific conclusion: Conventional direct bone impression demonstrated superior overall accuracy under the experimental conditions, with most discrepancies occurring in maxillary models.
• Main limitations: Small sample size, limited number of maxillary specimens, cadaver-based design, and evaluation of technologies available in the late 1990s.

10. Scientific Impact

This study represents one of the earliest quantitative comparisons between conventional and digital manufacturing techniques for subperiosteal implant model generation. Beyond comparing fabrication methods, it introduces a reproducible analytical approach for objectively measuring discrepancies between implant frameworks and the supporting bone.

Its findings contributed to the scientific discussion surrounding the reliability of early CT/CAD-CAM technology during a period when digital implant workflows were still emerging. While the study identified limitations in the digital approach—particularly for maxillary anatomy—it also demonstrated that CT-based manufacturing was capable of producing clinically acceptable models in most mandibular specimens.

Although modern imaging technologies have evolved considerably since this investigation, the study remains historically significant because it established the importance of objectively validating digital manufacturing accuracy before widespread clinical adoption. It also helped identify anatomical situations where further technological refinement was required, ultimately contributing to the evolution of contemporary digital implantology.

11. Editorial Conclusion

This preclinical investigation provides an important historical benchmark in the evolution of digital implant manufacturing. Under the experimental conditions evaluated, direct bone impressions produced more consistently accurate anatomical models than the CT/CAD-CAM workflow, with the greatest differences observed in maxillary specimens. While these findings reflect the capabilities of late-1990s imaging technology rather than current digital systems, the study reinforces a principle that remains fundamental today: precise anatomical reproduction is essential for the successful fabrication of patient-specific subperiosteal implants.