Micro-CT Reveals Comparable Outcomes for MTA Compaction in Simulated Root Resorption: Manual, Ultrasonic, and Sonic Endomotor Techniques Examined

Micro-CT Technology Sheds Light on MTA Placement for Root Resorption

When it comes to saving a tooth compromised by internal root resorption (IRR), the choice of filling technique is more than a matter of routine—it’s a clinical crossroads. A recent in vitro study published in BMC Oral Health (Sarıyılmaz et al., 2025) tackled this decision head-on, comparing three methods for placing mineral trioxide aggregate (MTA) in simulated root cavities: manual compaction, indirect ultrasonic activation, and a new sonic-activated endomotor. Using 3D-printed resin teeth and micro-computed tomography (micro-CT), the researchers sought to answer a pressing question: does the choice of technique really matter for the quality of the fill?

Understanding Internal Root Resorption and the Challenge of MTA Placement

IRR is a chronic inflammatory process that eats away at the internal dentin of a tooth. It’s often triggered by trauma or infection, and the resulting cavities are irregular and hard to reach. Achieving a complete and dense fill is essential—not just for sealing the defect but for preventing future infections. Traditional thermoplasticized gutta-percha methods have their merits, but in cases where the cavity communicates with the periodontal tissues, bioactive materials like MTA are preferred for their biocompatibility and sealing ability.

The problem is, MTA is notoriously tricky to handle and compact into these complex shapes. The dental community has debated the best way to deliver it, with some advocating for ultrasonic activation and others for tried-and-true manual techniques. Enter the sonic-activated endomotor—a new device promising to blend sonic vibration and rotary motion for improved adaptation. But does it really outperform the classics?

How the Study Was Designed: Simulated Teeth and Rigorous Testing

To sidestep the variability of natural teeth, the research team created thirty identical, 3D-printed resin teeth with precisely engineered IRR cavities—each 4 mm in diameter, placed 4 mm from the apex, and featuring a 2 mm buccal perforation. This standardization ensured a level playing field for the three compaction techniques.

• Manual Compaction: MTA was placed and pressed into the cavity with hand pluggers.
• Ultrasonic Activation: After manual placement, ultrasonic energy was applied indirectly via a plugger, cycling three times for ten seconds each.
• Sonic-Activated Endomotor: The 812 MT device compacted MTA using alternating clockwise and counterclockwise sonic motions, followed by supplemental manual compaction.

After placement, all samples were incubated under controlled humidity and temperature. The researchers then used high-resolution micro-CT scanning to quantify the volume and distribution of voids inside the filled cavities—a critical measure of how well the material adapted to the challenging internal anatomy.

Results: No Significant Difference in Void Volume Among Techniques

Here’s where the rubber meets the road. The mean void volumes detected by micro-CT were:

• Manual compaction: 6.49 mm³
• Ultrasonic activation: 2.61 mm³
• Sonic-activated endomotor: 3.89 mm³

Despite these numerical differences, statistical analysis (Kruskal-Wallis test, p>0.05) showed no significant difference among the groups. In other words, none of the techniques consistently outperformed the others in terms of reducing voids. This finding echoes results from several previous studies (Keles et al., 2018; Küçükkaya Eren et al., 2019), which also found no clear winner between manual and ultrasonic activation for MTA placement.

The use of micro-CT technology was key: unlike conventional two-dimensional radiographs, micro-CT provides a high-resolution, three-dimensional view, capturing subtle differences in fill quality that might otherwise go unnoticed. This approach allowed the researchers to accurately assess the internal adaptation and detect even minute voids that could compromise clinical outcomes.

Clinical Implications: Operator Preference and Anatomy Guide Technique Choice

From a practical standpoint, the presence of voids in MTA fillings is a concern because they can act as conduits for bacteria, undermining the seal and the long-term success of the treatment. Yet, this study suggests that, in large perforating IRR cavities, the choice of compaction technique may be more about the operator’s comfort, available instruments, and the specifics of the clinical scenario than about expected differences in outcome.

The study also points to potential advantages of ultrasonic and sonic devices in more complex or narrow anatomical regions, where enhanced flow and adaptation of MTA might be more critical. Still, these claims remain largely untested in such settings, and further research is needed to assess their performance in natural teeth and more constricted areas like lateral canals.

Limitations and Future Directions

While the use of standardized resin models ensured consistency, it came at a cost: these models lack the irregular dentin surfaces and biomechanical properties of real teeth. The amount of pressure applied during condensation—another key variable—was not controlled. Finally, the study focused exclusively on void volume, leaving other important factors like dentin adaptation and long-term sealing ability for future investigation.

For clinicians, these findings suggest a nuanced approach. Technique selection should be tailored to the clinical context, with an eye toward ease of use and the unique anatomy of each case. As new devices like the 812 MT endomotor enter the market, ongoing research will be vital to validate their claims and clarify their role in endodontic practice.

Assessment: This study’s rigorous micro-CT analysis provides compelling evidence that, at least in standardized large IRR cavities, manual, ultrasonic, and sonic-activated endomotor techniques are statistically equivalent in reducing voids during MTA placement. The implication is clear: technique choice should be guided by clinical judgment and operator experience, not by presumed superiority in void reduction. As technology evolves, continued research in real-world scenarios will be crucial for refining best practices in endodontic care.