Written by: Drs. Cherilyn G. Sheets, James C. Earthman, and Gregori M. Kurtzman
Introduction: The Problem and the Solution
Dental diagnostic methods for measuring the structural integrity of teeth and implants have remained largely subjective despite advances in restorative materials and imaging. Often, the only means of assessing a tooth or implant’s structural health is dictated by visually assessed information such as in radiographs, transillumination, or the Miller Scale of tooth mobility. For implants, it is common to listen to the auditory sound made by tapping on the top of an implant. Data gathered through qualitative methods are often variable from clinician to clinician, and even with the same clinician. By the time structural damage is clinically visible, it is often at the end of the cycle of deterioration from fatigue failure, and the clinician has limited remaining restorative options.
The FDA has recently cleared the InnerView System (Perimetrics, Inc), which is based on Quantitative Percussion Diagnostics (QPD), for measuring overall and internal micromobility in teeth and implants. QPD algorithms measure the structural integrity of a site with patented technology.1,2 It provides a radiation-free, fast, objective method of measuring the structural integrity of teeth, implants, and their restorations.
The first cleared algorithm, Mobility, relates to overall micromobility of the site and is influenced by bone quality, bone quantity, and for implants, the osseointegration quality. The second cleared algorithm, Normal Fit Error (NFE), relates to internal mobility generated by micro gap defects that oscillate when percussed. Examples of micro gap defects include cracks in the structures, deteriorating restorations, and restorative adhesive failure. The data is contained in the Energy Return Graph (ERG) derived from the response to percussion. A perfectly shaped bell curve on this graph is the structural fingerprint of a structurally healthy site. The height of the curve indicates the structure’s stability. A curve with irregularities in shape has internal mobility caused by micro gap defects. The greater the irregularities, the greater the damage.
This article reviews the system’s operating principles, clinical applications, and its advantages compared to conventional diagnostic technologies.
Operating Principles: How the System Works
QPD delivers a precisely controlled tap to the buccal surface of the tooth. A disposable smart tip rests flat on the buccal surface of the tooth and is stabilized by a tab placed on the occlusal or incisal surface of the tooth or implant (Figure 1). The handpiece is held horizontally to the floor, and the patient’s head is adjusted to make sure the tip face is flat against the tooth. A sensitive sensor in the rod captures the returning energy waveform, which is then analyzed by the software’s proprietary algorithms. All of the patient’s teeth can be tested in less than 2 minutes, giving a quick structural assessment of the entire mouth without significantly lengthening chairside time. For implants, the test can be performed at any stage of development, including on the finished restoration, to allow lifetime monitoring.
A patient’s initial test results provide 2 benefits: they highlight areas of interest that need further evaluation, as well as providing a baseline for future measurements. Additionally, the system creates a Mobility and NFE trendline providing a structural history that indicates changes over time for every tooth and implant tested.
Mobility scores are on a scale of 0 to 100 and are determined by the height of the peak in the ERG. The higher the peak, the lower the micromobility and the lower the Mobility number. The reverse is also true. Low peaks are caused by high micromobility and have high Mobility scores (Figure 2). Mobility values for teeth are usually found in the 58 to 79 range. Teeth with very low mobility scores are in very dense bone or could have partial or complete ankylosis. Implants with low Mobility scores (below 50) are well integrated as indicated by the low overall micromobility of the fixture.
The Normal Fit Error is determined by the shape of the ERG. The NFE scale is from 0 (associated with an intact structure) to 140+ (indicating severe localized micro-movement). The basics are that the ideal shape of an ERG is the bell-shaped curve. NFE becomes greater as the shape of the ERG deviates more and more from this ideal shape as a result of increased damage in the site (Figure 2).
CLINICAL APPLICATIONS
Crack Detection in Teeth and Detection of Failing Restorations
Cracks within enamel, dentin, or restorations often develop and progress silently and are very difficult to diagnose until pain or a visible fracture occurs. Standard methods, such as transillumination, dyes, or radiographs, detect only surface or gross defects. Percussion tests without measurement are purely subjective and are not clinically helpful in identifying early asymptomatic cracks. Radiographically, the crack needs to be oriented perpendicular to the radiograph sensor and deep enough in the tooth structure to be identifiable radiographically.
Additionally, adhesive breakdown, marginal leakage, or internal voids can develop beneath apparently intact restorations. Explorers and radiographs are limited in detecting subsurface issues and usually reveal deterioration only after recurrent decay or marginal breakdown appears.3,4 QPD detects early structural changes such as these by measuring alterations in oscillation response long before cracks in teeth or restorations are visible.5 By identifying compromised responses early, clinicians can intervene with preventive techniques, conservative restorations, or cuspal coverage before catastrophic tooth failure occurs.
Case Example: Large Existing Amalgam Restoration
A 23-year-old female had an old amalgam filling with minor marginal stains on tooth No. 30 (mandibular right first molar). The tooth had very mild cold sensitivity but showed no recurrent decay on radiographs. QPD testing identified a pre-NFE reading of 65. As the alloy restoration was being removed, a serious fracture was discovered in the alloy restoration extending from the intaglio surface upward that was not yet visible occlusally. Following removal of the restoration, additional problems became visible: microleakage under the restoration, severe undetected decay advancing close to the pulp, and a significant fracture on the pulpal floor that extended from the distal marginal ridge halfway to the mesial. The tooth was restored with a bonded composite restoration and immediately retested within the hour. The post-treatment NFE reading of 19 confirmed that there was improved stability of the tooth. A 6-year followup showed an asymptomatic tooth with an NFE of 21, assuring the patient and dentist that the tooth was still structurally sound, despite the former fracture on the floor of the preparation (Figure 3).
Post-Endodontic Integrity
Endodontically treated teeth restored with posts and cores often fail from post debonding, potentially leading to vertical root fracture. These conditions are rarely detected radiographically until catastrophic failure occurs. Conventional testing methods offer little diagnostic value in identifying these early changes. QPD detects internal oscillation differences that indicate subtle instability within the restored tooth. Recognizing those mechanical weaknesses early enables reinforcement or retreatment before complete failure of the restoration or root structure.
Case Example: Detecting a Loose Post/Core Under a Crown
A female patient was treated 10 years prior with a full-mouth reconstruction. She had recently been seen by a periodontist in another state who noted inflammation around tooth No. 7 and proceeded with pocket elimination surgery. Unfortunately, this created a significant aesthetic defect. The patient was moving back to town and wanted follow-up treatment (Figure 4).
A short-term solution was to place an aesthetic provisional crown to allow final tissue healing. The pretreatment QPD score on tooth No. 7 had predicted a problem (NFE = 145). A high NFE score indicates a structurally unsound tooth with severe internal micromobility (Figure 5). Radiographically, no pathology was noted, but upon removal of the porcelain fused to gold crown, vertical cracks were discovered on the mesial and distal surfaces of the root adjacent to the cast gold post and core (Figure 6).
The patient was shown the data and informed of the vertical root fracture, loose post/core, and the ultimate need for extraction and replacement with an implant. She appreciated the resolution of the source of her problem and moved forward with the treatment plan.
Implant Structural Issues
QPD aids in identifying implant screw loosening, abutment component failure, or fracture in the implant itself by monitoring the NFE Score. When not caught early, increasing levels of damage may result. Undetected screw loosening may lead to a fracture of the screw or damage to the threaded channel at the internal of the implant fixture. Fracture of the implant itself may also occur due to chronic micromovement and is typically not identified until damage or even catastrophic failure results. Also, overtorquing a screw beyond the manufacturer’s recommended torque can have damaging end results.
Implant Stability and Early Loading Decisions
Accurate assessment of implant stability is critical for determining readiness for provisionalization or definitive loading. Clinicians have traditionally relied on insertion torque, reverse torque, tactile evaluation, or resonance frequency analysis (ISQ). Only ISQ provides a measured response, and then with only one metric. While useful, these methods cannot detect micromobility of both overall and internal mobility measurements. QPD directly measures structural response, providing quantifiable data on implant rigidity and early osseointegration (Mobility Score), as well as the stability of all of the individual components being tested (NFE Score).6 Stable readings support immediate or early loading, whereas increased mobility values prompt the clinician to delay restoration or adjust occlusal loading to prevent overloading and potential failure.
Monitoring Osseointegration and Peri-Implant Health
Radiographs and periodontal probing remain the standard for monitoring implants. Both are reactive indicators that reveal bone loss only after significant hard-tissue resorption. Yet, subtle mechanical changes may occur long before radiographic signs appear clinically. By tracking implant mobility trends over time, QPD enables early identification of biomechanical stress or incipient bone loss, allowing early intervention. Deviations in the numerical trendline signal the need for further evaluation of the site for periodontal maintenance or occlusal adjustment before peri-implantitis can develop.7
Case Example: Monitoring Implant Health Over Time
A female patient who had been restored years earlier was being monitored with QPD at her hygiene appointments, including her restored implants at the right maxillary and mandibular right first molars (teeth Nos. 3 and 30). She was symptom-free, and the implants appeared stable both clinically and radiographically. However, during hygiene monitoring testing, QPD revealed elevating NFE scores on her 2 implants over the last 3 visits. She confirmed that increased life stress and the resulting clenching were factors. Based on the data, occlusal protection using a custom nightguard to reduce excessive force on the implants was recommended and provided. Following the occlusal protection intervention, NFE scores significantly decreased over the next 2 hygiene appointments, confirming improved implant stability, validating the effectiveness of occlusal protection in maintaining implant health for this patient (Figure 7).
Case Example: Implant Fracture at its Connector
A patient presented for a new patient examination with no complaints. Her single dental implant in the maxillary left second bicuspid area appeared radiographically and clinically very healthy. However, QPD testing resulted in an NFE reading of 120, and at a follow-up appointment, it was 119. The first thought was that it must be a loose screw causing the internal mobility. But when examined, the screw was very tight. The restoration was removed, and a crack was noted at the base of the implant fixture. A CBCT was taken, confirming the extent of the fracture in the implant. The damage was internal at this point and had not extended to the implant’s outer surface, and the implant was well osseointegrated. Due to these factors, it was possible for the clinician to replace the crown screwed to the manufacturer’s recommended torque and monitor the site in the future with QPD (Figure 8).
The Importance of Hygiene Monitoring with QPD
The dental hygienist in every office sees the patient base more regularly than the dentist due to the recall hygiene program. Therefore, the hygienist can play a critical role not only in preventive and proactive periodontal care, but also in preventive and proactive assessment of the structural health of their patients. Hygienists can discover developing problems for their patients saving them from pain, tooth loss and unnecessary expenses for oral healthcare with just a 2-minute test.
Structural integrity issues are often asymptomatic, and traditional diagnostic aids (radiographs and visual examination) do not identify these problems until late in the damage cycle. “Hygienist initiated QPD testing” can aid in identifying clinical issues during routine recall hygiene appointments. Also, new patients often have asymptomatic developing problems that could benefit from early detection in a quick QPD test as a part of an initial hygiene appointment.
Case Example: The Power of QPD Monitoring During Routine Hygiene Visits
A female patient came for her routine dental hygiene appointment, and the hygienist performed full-mouth testing with QPD. The hygienist quickly noted that one of the teeth had a very high NFE reading and that the numbers for that tooth had increased significantly in 3 consecutive hygiene visits. The doctor was informed, and an x-ray was requested (Figure 9). The patient was asymptomatic, and the tooth was an anterior bridge abutment that had previous endodontic treatment. The radiograph was inconclusive for pathology. A CBCT was then ordered, and the reason for the high NFE became apparent. There were significant bone voids developing around the tooth root. The dentist recommended removing the bridge to confirm the underlying pathology responsible for the bone loss. Upon disassembly of the bridge, it was discovered that there was a vertical root crack on the buccal of tooth No. 13 (Figure 10). The tooth was subsequently extracted, and sites 13 and 14 were grafted for future implant restorations. If the hygienist had not been monitoring all patients, this pending emergency would not have been identified until the infection and bone loss were much greater, and the patient was in pain. Many patients are currently leaving hygiene appointments with undiagnosed structural breakdowns. Routine hygiene monitoring of all patients would greatly reduce this problem.
Case Example: Incorporating QPD Testing Into a New Patient Examination
It is an advantage to share the patient’s QPD results with them prior to a comprehensive dental examination. QPD data shows the areas of structural vulnerability before even looking into the patient’s mouth, creating curiosity among the patient and clinician about the reasons for these findings. The patient then becomes engaged in the examination process.
In the following clinical example of a new patient’s comprehensive examination, the Mobility scores were within the normal range, but the NFE scores showed very elevated readings in the maxillary left and mandibular right quadrants. And yet, at first glance in the mouth, the patient appeared visually healthy, except for tooth No. 30, which had a newly fractured mesial lingual cusp.
The comprehensive examination revealed the reasons for the elevated QPD scores. Tooth No. 16 (NFE = 104) was extruded and was in constant occlusal trauma. Tooth No. 15 (NFE = 77) had an occlusal amalgam with internal micromobility. Tooth No. 14 (NFE = 95) had a large occlusal amalgam that showed gray on the buccal enamel where the walls were thin. Tooth No. 30 (NFE = 51) had a fractured ML cusp and remaining defects (Figures 11 and 12). The mandibular right posterior quadrant had significant bone loss and periodontal disease with elevated NFE readings indicating reduced bone support (Figure 13). Additionally, the patient confirmed he was a clencher/bruxer, chewed ice regularly, and professionally lifted heavy weights with no athletic guard. He had already had 2 crowns due to cracked teeth (Figure 12). Mobility readings showed normal to high bone density, so the majority of his problems were internal mobility issues due to cracks and fractures. With these structural problems highlighted by an initial QPD test as a part of the initial comprehensive examination, it was possible to start connecting his structural problems with his periodontal problems, as a staged treatment plan was developed.
Stage I treatment included periodontal therapy to control his periodontal disease and provide patient education regarding his structural breakdown. Initial therapies also included the extraction of tooth No. 16 and the fabrication of an athletic guard. Tooth No. 30 received a provisional composite restoration while a more comprehensive restorative treatment plan was developed for the future. Ongoing monitoring with QPD during his hygiene visits will help identify areas of improvement and areas that still need treatment as the patient continues his journey toward oral health. Most importantly, the patient was now engaged as an active participant in his care and understood more fully why his teeth kept fracturing and his mouth kept breaking down.
DISCUSSION
Radiographs and physical clinical examination remain essential in diagnosis, but have inherent shortcomings.
As a result, structural failures often progress silently until symptoms arise or visible damage occurs. The QPD technology complements, but does not replace, radiographic and clinical examinations. QPD is a mechanical engineering-based quantitative test based on math and physics. The test results are provided in a format of visual data that enhances the patient’s understanding and trust in this technology and the objective information it creates. Charts, graphs, and numeric scores display the individual metrics on mobility, the NFE trendlines for each site, and the ERG raw data. Presenting this information during examinations allows patients to visualize changes in their mouths that would otherwise be imperceptible, thereby improving treatment planning and patient acceptance.
QPD offers unparalleled objectivity, with its readings interpreted within a full clinical context. A built-in standard of deviation alerts the clinician to automatically repeat any questionable results. However, as with any new technology, training is needed to ensure operator consistency, which is essential for reproducibility. Ongoing studies continue to refine diagnostic thresholds and develop new potential capabilities with the expansion into machine learning and AI.
CONCLUSION
Quantitative Percussion Diagnostics represents a significant advancement in structural assessment for teeth, implants, and their restorations. By quantifying overall and internal micromobility, the technology can identify early biomechanical and adhesive failures that traditional methods cannot detect. Compared with standard diagnostics, which often confirm disease only after it has occurred, QPD enables true prevention with early detection and minimally invasive care. Incorporating this objective data into clinical workflows enhances treatment planning, thereby improving long-term outcomes and ultimately elevating the standard of care in restorative and implant dentistry.
REFERENCES
1. Sheets CG, Wu JC, Earthman JC. Quantitative percussion diagnostics as an indicator of the level of the structural pathology of teeth: Retrospective follow-up investigation of high-risk sites that remained pathological after restorative treatment. J Prosthet Dent. 2018;119(6):928–34. doi:10.1016/j.prosdent.2017.09.013
2. Pandey A. Structural biomechanics in dentistry: Advanced integration of quantitative percussion diagnostics for clinical practice. Arch Med Case Rep Case Stud. 2025;10(2). doi:10.31579/2692-9392/239
3. Sheets CG, Quan DA, Wu JC, et al. An evaluation of quantitative percussion diagnostics for determining the probability of a microgap defect in restored and unrestored teeth: A prospective clinical study. J Prosthet Dent. 2025;133(3):756–63. doi:10.1016/j.prosdent.2023.04.016
4. Sheets CG, Wu JC, Rashad S, et al. In vivo study of the effectiveness of quantitative percussion diagnostics as an indicator of the level of structural pathology of teeth after restoration. J Prosthet Dent. 2017;117(2):218–25. doi:10.1016/j.prosdent.2016.07.010
5. Shen J, Taheri-Nassaj N, Sheets CG, et al. Finite element modeling of an intact and cracked mandibular second molar under quantitative percussion diagnostics loading. J Prosthet Dent. 2024; S0022-3913(24)00601-2. doi:10.1016/j.prosdent.2024.09.003
6. VanSchoiack LR, Shubayev VI, Myers RR, et al. In vivo evaluation of quantitative percussion diagnostics for determining implant stability. Int J Oral Maxillofac Implants. 2013;28(5):1286–92. doi:10.11607/jomi.2779
7. Sheets CG, Hui DD, Bajaj V, et al. Quantitative percussion diagnostics and bone density analysis of the implant-bone interface in a pre- and postmortem human subject. Int J Oral Maxillofac Implants. 2013;28(6):1581–8. doi:10.11607/jomi.3037
ABOUT THE AUTHORS
Dr. Sheets maintains a full-time private practice in Newport Beach, Calif for prosthodontics and aesthetic rehabilitative dentistry. She is an international educator, clinician, author, and researcher. Dr. Sheets has published over 100 peer-reviewed articles, chapters for textbooks, and given lectures/hands-on training to thousands of clinicians. She is the co-founder and co-inventor of Quantitative Percussion Diagnostics, the Periometer Research Instrument, and the Inner
View Clinical System. She can be reached at [email protected].
Dr. Earthman’s research activities include studies of a broad range of deformation and damage mechanisms in both model and advanced materials. His work also involves the development and use of computer-based techniques for investigating the corrosion behavior of metals exposed to molten salts, the nondestructive characterization of surface defects in situ, and the effects of nanobubbles on the stability of materials. He has authored and co-authored more than 120 peer-reviewed research publications, including 2 chapters on biomechanics and materials for tissue engineering. He is an inventor of 19 issued US patents, as well as many international patents and pending US patents. He has also served as editor for 2 books in the fields of materials science and biomedical engineering. He can be reached at [email protected].
Dr. Kurtzman is in private general dental practice in Silver Spring, Md, and a former assistant clinical professor at the University of Maryland in the department of Restorative Dentistry and Endodontics and a former AAID Implant Maxi-Course assistant program director at Howard University College of Dentistry. He has lectured internationally on the topics of restorative dentistry, endodontics, implant surgery and prosthetics, removable and fixed prosthetics, periodontics, and has published more than 920 articles globally, several ebooks, and textbook chapters. Dr. Kurtzman has been honored to be included in the “Leaders in Continuing Education” by Dentistry Today annually since 2006 and was featured on their April 2024 cover. He can be reached at [email protected]
Disclosures: Dr. Sheets and Dr. Earthman are the co-inventors of Quantitative Percussion Diagnostics and the co-founders of Perimetrics. Dr. Sheets is currently the chief clinical officer of Perimetrics, and Dr. Earthman is currently the chief science officer of Perimetrics. Dr. Kurtzman received compensation for his contribution to this article.
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