Advancing Dental Diagnostics with Integrity-Focused Technologies

Diagnostic radiographs remain central to restorative and preventive decision-making; however, their inherent two-dimensional, density-based limitations frequently delay identification of early caries, incomplete fractures, and subclinical restoration failure. While radiographs are indispensable for identifying advanced pathology, they often fail to detect disease until significant biological or mechanical compromise has already occurred. This article examines the limitations of conventional radiography in the diagnosis of caries, cracks, and restoration failure; reviews the biological, mechanical, and restorative advantages of early detection; and expands upon the role of integrity-based diagnostic technologies—including Quantitative Percussion Diagnostics (QPD®) and InnerView® (Perimetrics, Redmond, Washington)—as complementary tools that assess functional structural integrity rather than mineral density alone. When integrated into routine clinical workflows, these technologies support minimally invasive treatment strategies, enhanced diagnostic confidence, and improved long-term outcomes.

Introduction

Intraoral radiographs have long served as the cornerstone of diagnostic dentistry. This has provided essential information regarding caries, periapical status, alveolar bone levels, and the integrity of existing restorations.¹ Despite those advantages, radiographs represent a 2D view of complex 3D structures, thus relying primarily on differences in tooth (dentin and enamel) and bone density to generate diagnostic contrast. This fundamental limitation reduces their sensitivity for detecting early or subclinical disease. Cone-beam computed tomography (CBCT) has improved those diagnostics but exposes the patient to greater levels of radiation exposure than standard 2D radiographs and investment by the practice in that technology which is a significant cost. Additionally, CBCT is not recommended for routine evaluations on patients not presenting with a clinical problem.

In routine clinical appointments such as recall prophylaxis, the diagnostic limitations of radiographs becomes most apparent in two highly prevalent clinical scenarios: incomplete tooth fractures, and early restoration failure. In each of these conditions, degradation or mechanical fatigue typically precedes radiographic changes.^2-5 As a result, dentists are often forced to make treatment decisions only after the problem has progressed to a stage that it is clinically apparent requiring more invasive intervention. Early recognition of this diagnostic gap underscores the need for adjunctive technologies capable of identifying compromised teeth and restorations at an earlier, more manageable stage.

Radiographic diagnosis of dental caries is fundamentally dependent on the degree of mineral loss within enamel and dentin. Numerous investigations have demonstrated that there needs to be approximately a 30% to 40% demineralization of enamel lost before a carious lesion becomes apparent radiographically.^1,2 Consequently, dentinal caries often progresses undetected beneath an apparently intact crown or restoration due to the opaque nature of the restoration that obscures the radiographic view, in addition to the need for extensive mineral loss prior to radiographic detection. It is the micromobility of the deteriorating restoration seal or cement that allows percolation of fluids beneath the intaglio surface of the restoration and allows carious breakdown to initiate. These factors highlight the need for a structural assessment of the tooth in addition to radiographic assessment.

Limitations of Radiographs in Detecting Dental Caries

The InnerView system recently received FDA clearance for the objective measurement of overall and internal mobility in teeth and implants, providing a quantitative assessment of structural integrity at the site. The system is based on a patented technology known as Quantitative Percussion Diagnostics (QPD).^6,7 QPD offers a rapid, radiation-free, and objective method for evaluating the structural health of restorations, natural teeth, and dental implants. In less than two minutes, the clinician can obtain quantitative data related to micro-mobility within the patient’s dentition or implant system. Data acquisition is accomplished through generation of an Energy Return Graph (ERG®), which is subsequently analyzed using two distinct algorithms.

The first algorithm, the loss coefficient, is a standard engineering calculation used to generate a mobility scale that quantifies overall mobility at the site. Overall mobility reflects factors such as bone quality, bone quantity, and in the case of implants, the degree and quality of osseointegration. The second algorithm, the normal fit error (NFE), evaluates internal mobility by identifying oscillatory behavior associated with microgap defects within the structure, including cracks, adhesive degradation, and deteriorating restorations. By identifying these internal structural changes, the InnerView system enables detection of restorative adhesive failure, crack initiation, and other forms of structural compromise well before overt clinical signs or symptoms become evident. This article reviews the operating principles of the InnerView system, its clinical applications, and its advantages relative to conventional diagnostic technologies.

How InnerView and QPD Function

The InnerView system utilizes QPD to deliver a precisely controlled 2.5-millisecond mechanical impulse through a disposable smart tip positioned flush against the buccal surface of the tooth or implant. Proper stabilization is achieved using a positioning tab placed on the occlusal or incisal surface (Figure 1). The sensor embedded within the percussion rod delivers a gentle, standardized tap while simultaneously capturing the returning energy waveform generated by the structure under evaluation. This waveform is transmitted to the software platform, where it is analyzed using proprietary algorithms developed by Perimetrics.

A full-mouth scan can be completed in less than two minutes, enabling comprehensive assessment of the dentition without extending chairside time. Importantly, both restored teeth and implants can be evaluated without removal of crowns, bridges, or implant prostheses, eliminating the need for disassembly and simplifying clinical workflow.

Initial testing serves two primary purposes. First, it identifies sites of interest that may warrant further diagnostic evaluation. Second, it establishes a quantitative baseline against which future measurements can be compared. The system also generates a monitoring report that longitudinally tracks both overall mobility and internal mobility (NFE) values, effectively creating a structural health record for each tooth and implant. When incorporated into routine hygiene recall visits, this brief assessment adds objective data to ongoing patient monitoring and frequently identifies early structural breakdown in asymptomatic sites. Early detection of these subclinical changes allows for timely preventive or proactive intervention, reducing the risk of patient discomfort, financial burden, and loss of tooth or supporting bone structure.

Overall mobility is reported on a numerical scale ranging from 0 to 100, with average values for natural teeth typically falling between 58 and 79. Higher values indicate increased micromobility, while lower values are associated with denser supporting bone. Extremely low mobility scores may suggest ankylosis. The mobility score is derived from the height of the primary peak on the ERG; a higher peak corresponds to lower micromobility. A smooth, symmetrical bell-shaped curve represents the structural fingerprint of a stable, healthy site.

NFE is determined by analysis of the ERG waveform morphology and reflects internal structural integrity. The NFE scale ranges from 0 (associated with an intact structure) to values exceeding 140 (which indicates severe localized micromovement) (Figure 2). Tooth-specific geometry ranges are provided to guide clinical interpretation. In general, a single well-defined bell-shaped curve is indicative of structural integrity, whereas multiple peaks, irregular oscillations, and prolonged decay times are characteristic of increasing structural damage.

Clinical Benefits of Early Detection

Early identification of structural compromise provides substantial biological, mechanical, and restorative advantages. From a biological perspective, limiting bacterial ingress at the tooth-restoration interface reduces pulpal inflammation and decreases the likelihood of irreversible pulpal pathology.^8,9 Mechanically, early intervention preserves favorable stress distribution within the tooth, reducing crack initiation and propagation that may otherwise lead to catastrophic fracture.¹⁰ 

From a restorative standpoint, early detection of small defects supports repair-based and minimally invasive treatment strategies. Restoration repair and localized intervention preserve significantly more tooth structure than full replacement and have demonstrated survival rates comparable to newly placed restorations.¹¹ This preservation-first approach reduces cumulative structural loss over successive treatment cycles and improves long-term tooth survival, as long as the intaglio surfaces are still structurally sound and not experiencing microleakage.

Integrity-Based Diagnostics: A Functional Perspective

Integrity-based diagnostic technologies address the limitations of density-based imaging by evaluating the functional mechanical behavior of the tooth-restoration complex. Rather than relying on mineral density changes or visual cues, these systems assess how teeth respond to controlled mechanical stimulation, generating quantitative data related to stiffness, damping, and mobility.^12-14 QPD and InnerView technology identify alterations in mechanical response that occur early in the disease process, enabling detection of subsurface demineralization, internal debonding, and incomplete fractures before radiographic changes become apparent.

Radiographic Challenges in Diagnosing Cracks

Incomplete fractures and cracked tooth syndrome represent some of the most diagnostically challenging entities in restorative dentistry. Most clinically relevant cracks propagate in a mesiodistal orientation and are microscopic in width, rendering direct visualization on conventional intraoral radiographs uncommon.^5,15 Instead, radiographs more often reveal indirect or secondary signs, such as periodontal ligament space widening, periapical radiolucency, or localized alveolar bone loss—findings that typically reflect advanced structural compromise rather than early crack formation.

While CBCT may assist in selected cases, particularly when vertical root fracture is suspected, its routine use for crack detection is constrained by voxel resolution limits, scatter from existing restorations, and motion artifacts.^15,16 As a result, reliance on radiography alone often delays diagnosis until crack propagation has compromised tooth prognosis.

As a clinical example, a patient treated with crowns on the maxillary anterior teeth 10 years earlier was evaluated by a periodontist, who observed inflammation around tooth No. 7. Surgery had eliminated the pocket but created an esthetic problem. The patient returned to discuss replacement of the crown on tooth No. 7 to correct the esthetic concerns (Figure 3). A provisional crown was suggested to close the spaces resulting from bilateral papilla loss until a final restoration could be performed. Radiographically no pathology was noted. Pre-treatment InnerView testing showed normal mobility (Figure 4) but very high NFE (145) on that tooth (Figure 5). Following crown removal, a loose cast gold post/core was noted. Examination noted a vertical fracture on the mesial and distal proximal surfaces of the tooth (Figure 6). An ERG demonstrated a very structurally unsound tooth with multiple peaks oscillating over a long-time span (Figure 7). The patient was informed that the vertical root fracture was caused by the loose cast post/core, and extraction followed by implant placement was recommended.

Radiographs and Early Restoration Failure

Radiographs are effective for identifying gross restorative defects, including overhangs, open margins, and advanced recurrent caries. However, the earliest stages of restoration failure are frequently radiographically silent. Contemporary adhesive restorations often fail internally through adhesive degradation, fatigue-related microfracture, or loss of interfacial integrity before marginal breakdown becomes clinically or radiographically evident.^17,18

Radiopaque restorative materials may further obscure underlying pathology, complicating interpretation and masking early secondary caries.¹⁹ As a consequence, radiographic diagnosis often lags behind the biological and mechanical processes that ultimately compromise restoration longevity and tooth survival.

As a clinical example, a patient had recently begun noticing light cold sensitivity on her right mandibular first molar (Figure 8). Radiographic examination did not note any pathology (Figure 9). QPD testing noted an elevated NFE of 65 (Figure 10, left). It was decided with the patient to remove the restoration even though there was no visible problem. During restoration removal, a significant crack appeared in the restoration which then easily fractured away exposing significant decay due to micro leakage at the restoration’s margins. Upon removal of the entire amalgam, the decay covered the entire pulpal floor, extending deep into the tooth structure (Figure 11). A crack in the pulpal floor was visible extending halfway from the distal to the mesial. Caries was removed and the tooth was restored with a bonded composite restoration (Figure 12). Following restoration, the tooth was tested again and the post treatment NFE had lowered from 65 to 19 (Figure 10, right). Six years after restoration, testing of the tooth showed that the NFE remained low at 21. The patient reported that the tooth had remained asymptomatic.

QPD and InnerView Technology for Detection of Failing Crowns

The long-term success of indirect restorations depends not only on restorative material selection and cementation protocols, but also on the clinician’s ability to identify early biomechanical failure before clinical symptoms or radiographic changes become evident. Conventional diagnostic methods such as visual inspection, tactile assessment, and radiography remain limited in their ability to detect subclinical crown failure, particularly when breakdown occurs at the adhesive interface or within the underlying tooth structure. Consequently, many crowns are not identified as failing until debonding, fracture, recurrent caries, or patient discomfort occurs.²⁰ 

QPD delivered through the InnerView system provides an objective, data-driven method for evaluating crown stability and structural integrity. Unlike subjective percussion testing or radiographic interpretation, QPD measures how the crown-tooth complex responds biomechanically to a precisely controlled mechanical impulse, allowing detection of instability that precedes overt clinical failure.²¹ The proprietary algorithms of InnerView analyze this response to generate quantitative metrics reflecting overall mobility and internal structural integrity. In well-bonded crowns, energy dissipation is consistent and repeatable, whereas crowns affected by cement degradation, micro-movement, adhesive failure, or underlying dentinal cracks demonstrate altered waveforms indicative of biomechanical compromise.²²

A primary clinical advantage of QPD is its ability to identify failing crowns before catastrophic events occur. Early cement breakdown or loss of retention may present without clinical or radiographic signs yet still compromise restoration longevity.²³ QPD enables detection at a stage when conservative intervention, such as recementation or occlusal adjustment, may be possible rather than full crown replacement. Additionally, testing is noninvasive, requires no crown removal, is unaffected by restorative material, and can be completed in seconds, making it well suited for incorporation into routine recall examinations. Baseline QPD measurements establish a biomechanical reference for each crown, allowing longitudinal monitoring over time. Progressive deviation from baseline values serves as an early warning indicator of developing failure, even in asymptomatic patients. This capability supports a predictive and preventive restorative model, improving diagnostic confidence, patient communication, and long-term restorative outcomes.²⁴ 

A patient presented with sensitivity on the mandibular right first premolar that had a distal occlusal cast gold inlay (Figure 13). Clinically and radiographically (Figure 14) nothing was noted related to the restoration’s margins. But QPD testing noted a consistently high NFE (Figure 15). NFE testing noted a decrease following removal of the gold inlay (Figure 16). Recurrent decay was noted clinically and was removed the preparation (Figure 17).

Discussion

The diagnostic limitations of conventional radiography highlight a fundamental gap between disease initiation and disease detection. Integrity-based diagnostics help bridge this gap by providing objective, reproducible measures of structural integrity that complement traditional visual and radiographic examination. When integrated into clinical workflows, these technologies reduce reliance on subjective interpretation and support earlier, evidence-based decision-making.

Importantly, structural integrity-based diagnostics align closely with contemporary principles of minimally invasive dentistry. By identifying compromised teeth earlier, clinicians can prioritize monitoring, preventive intervention, or restoration repair rather than replacement. This strategy is consistent with evidence demonstrating that cumulative tooth structure loss is a primary determinant of long-term tooth survival. Continued longitudinal research is warranted to further correlate integrity-based diagnostic metrics with clinical outcomes.

Clinical Takeaways / Chairside Implications

Radiographs remain essential for identifying advanced pathology but should not be relied upon as the sole diagnostic modality when evaluating early caries under restorations, suspected cracks, or restoration integrity.

Early caries activity associated with microleakage, incomplete fractures, and adhesive restoration failure frequently progress beneath radiographic detectability thresholds or are blocked by radiopaque pre-existing restorations; absence of radiographic findings does not equate to structural health.

Structural integrity-based diagnostics provide objective, reproducible data that assess functional structural behavior rather than mineral density alone, improving diagnostic confidence in equivocal clinical scenarios.

Early identification of compromised teeth supports minimally invasive strategies such as monitoring, remineralization, restoration repair, or selective intervention—reducing unnecessary replacement and preserving tooth structure.

Incorporating structural integrity-based diagnostics into routine workflows enhances patient communication by allowing clinicians to demonstrate objective findings, support treatment recommendations, and monitor structural changes over time.

A combined diagnostic approach—integrating clinical examination, radiography, and structural integrity-based assessment—offers the most comprehensive strategy for long-term tooth preservation and restorative success.

Conclusion

Radiographs remain indispensable for identifying advanced dental pathology; however, they are insufficient as stand-alone tools for early diagnosis of caries associated with microleakage under existing restorations, cracks, and restoration failure. Structural integrity-based diagnostic technologies provide a biologically and mechanically relevant adjunct by evaluating functional structural integrity rather than mineral density alone. Their integration into routine practice supports earlier intervention, conservative treatment planning, and improved long-term clinical outcomes.

Figures and Images

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Cherilyn G. Sheets, DDS

James C. Earthman, PhD

Gregori M. Kurtzman, DDS

Figure 1

The device must be held horizontal to the floor. The handpiece tab is placed on the incisal or occlusal surface with the face of the tip flush against the buccal surface of the tooth.

Figure 2

Color scale showing the increasing severity as the normal fit error (NFE) score increases.

Figure 3

Tooth No. 7 following periodontal surgery and prior to removing the crown.

Figure 4

InnerView testing demonstrating normal mobility on the teeth.

Figure 5

NFE testing noted a very high reading on tooth No. 7 compared to the adjacent natural teeth.

Figure 6

Following removal of crown, a vertical fracture on the mesial and distal adjacent to the cast post/core is seen.

Figure 7

The Energy Return Graph (ERG) indicated a structurally unsound tooth, with four peaks oscillating over an extended time period.

Figure 8

Clinical appearance of the molar with a large occluso-mesiallingual (OML) amalgam restoration.

Figure 9

Large molar amalgam restoration with cold sensitivity and no radiographic issues.

Figure 10

The pre-NFE of 65 indicated problems (left) and the immediate composite restoration measured a post-NFE reading of 19 (right) and symptoms quickly abated.

Figure 11

Following removal of the amalgam the crack can be seen running across the pulpal floor.

Figure 12

The molar following replacement of the amalgam restoration with a bonded direct composite.

Figure 13

Clinical appearance of the cast gold inlay on the mandibular first premolar.

Figure 14

Radiograph with no noted marginal issues on the first premolar’s cast inlay.

Figure 15

No clinical or radiographic pathology was noted, but a consistently high NFE presented.

Figure 16

NFE testing noted a decrease following removal of the gold inlay.

Figure 17

The first premolar following removal of the cast inlay and recurrent decay that was not observable clinically and radiographically before removal of the inlay.

Cherilyn G. Sheets, DDS

Private practice, Newport Beach, California

James C. Earthman, PhD

Professor Samueli School of Engineering, University of California Irvine, California

Gregori M. Kurtzman, DDS

Private practice, Silver Spring, Maryland