Success

The terminology ‘success’ merits discussion. From a biological perspective, success demands evidence of pulp preservation and the absence of developing pulpitis or apical periodontitis (14). One challenge in interpreting the success outcome is that it is a subjective term whose meaning has been applied inconsistently across studies. Traditionally, the measure of treatment success used by VPT researchers has been based on the interpretation of the dental history combined with measurement of several different clinical and radiographic outcomes. These outcomes include responses to sensibility testing, absence of pain or other symptoms indicative of pulpal disease, need for the use of medication (analgesia), evidence of hard tissue bridge formation or continued root development in immature teeth and absence of clinical and radiographic signs of internal resorption and apical periodontitis. The lack of standardization of the term success prohibits accurate comparisons of results from studies already completed. The European Society of Endodontology (ESE) 2019 defined the success of VPT as an asymptomatic tooth with maintenance of vitality after at least one year. There should be an absence of apical periodontitis and root resorption and, in the case of immature teeth, continued root development (15). They stipulated that alongside history taking, both clinical and radiographic findings were required to report outcomes (15).

Pain

The asymptomatic tooth can be considered a tooth that is neither painful nor tender to bite on. Whilst both symptoms are frequently reported, reporting of pain differs across VPT studies. The characteristics of pain suggestive of irreversible pulpal changes are sometimes described (16), but equally, studies may simply report on the presence or absence of pain without further comment on the characteristics which could inform a diagnosis (17). Again, the nuances of pain outcomes can introduce an element of uncertainty in results interpretation. Proxy indicators of pain experience reported in VPT studies include the use of medication such as analgesics in the postoperative period (18) and the incidence of flare‐ups requiring additional intervention (19). Although the use of analgesics links directly to pain, the other indicator does not and so should be interpreted cautiously. Measurement of pain intensity prior to and in response to treatment demands an accurate tool representing a self‐report of the patient’s experience (20). It should, however, be remembered that pain is a subjective sensation subject to individual influences, and so it is difficult to make meaningful comparisons between patients (21–23). Several tools have been proposed for routine use in dentistry including multidimensional tools like the McGill questionnaire (MPQ), through to unidimensional tools including visual analogue scale (VAS), numeric rating scale (NRS) and verbal rating scales (VRS). Multidimensional tools assess the impact of complex or persistent acute and chronic pain on a patient’s activity or mood and as such are rarely used in VPT pain assessment. The unidimensional VAS, NRS and VRS are often used to report pain intensity in VPT studies.

The VAS is a 100 mm line on which a patient indicates a single point on the line representing their pain intensity, from one extreme representing no pain to 100 mm representing the worst pain imaginable (24). The score is awarded based on the distance between 0 (no pain) and the mark on the line placed by the respondent. The VAS is reliable and sensitive to changes in experience of pain so is useful in representing changes in pain pre and post‐VPT. The VAS, however, is not self‐explanatory and is open to interpretation by participants and cannot be administered verbally or on the telephone.

The NRS developed by Downie almost 50 years ago is the numeric representation of the VAS. The line is divided into equal segments, 0–10 (NRS‐11) or 1–10 (NRS‐10), with a verbal descriptor anchor at the two extremes. The respondent selects a whole number that best reflects the intensity of pain they are experiencing (25). NRS is a quick, simple‐to‐use scale that is reliable across most patients and cultures and can be administered verbally or on the telephone. There is good consistency in results between the NRS and VAS (26) (Figure 10.1).

The VRS, also known as the verbal pain scale (VPS), verbal descriptor scale (VDS) or simple descriptor scale (SDS), is both easy to administer and interpret and involves a patient being given adjectives to assess and describe their experience of pain. This may involve the choice of a single adjective through to a short statement. Each adjective is awarded a score providing an ordered categorical scale assessment of pain (Figure 10.2).

Currently, there are no valid tools to measure the proxy measures of pain described earlier including the use of analgesics in the postoperative period, so typically, this data is collected using a self‐administered pain diary or simply having the clinician question the patient at a subsequent visit.

Timing of Measurement of Pain

The outcome of VPT must be measured at a consistent time point after treatment has been completed. This optimizes the likelihood that the effect intended for measurement is what is being measured and the true value of treatment can be assessed. Pain and the use of analgesics in the postoperative period should be measured as a minimum at seven days and for a maximum of three months post‐treatment (27).

Sensibility/Vitality of Pulp

A key indicator of VPT success is pulpal health status. The gold standard in assessing pulpal health is histological assessment (28); however, as the pulp is encased in a rigid structure, histological assessment can only be carried out after commencing endodontic treatment or extraction of the tooth. In the absence of direct observation of tissue, proxy measures of pulpal status are frequently made based on neural responses to stimuli, the sensibility tests. Sensibility testing includes thermal, both cold and heat and electric pulp tests. The movement of dentinal fluid in response to temperature changes leads to odontoblast movement, which in turn mechanically stimulates the nerves within the pulp or direct electrical stimulation of pulp nerve tissue (29). A positive measure of sensibility is a tooth which responds to testing without an exaggerated response. Whilst these tests can be used singularly or in combination, the ESE 2019 recommends both cold and electric pulp sensibility testing are conducted to monitor outcomes of VPT (15). Owing to the nature of the intervention, teeth that have under‐gone VPT may respond differently to sensibility testing and in fact teeth that have under‐gone complete pulpotomy may be unresponsive. A recent study explored the reliability of cold and electric sensibility testing in pulpotomized mature permanent teeth. 95% of the teeth treated by complete pulpotomy responded to electric pulp testing, whereas only 13.5% of the same teeth responded to cold testing (30). This lends weight to the ESE’s recommendation that both thermal and electric tests should be carried out in sensibility measurement.

Whilst routinely used, sensibility testing measures only sensory response without considering that neural tissue is highly resistant to inflammatory changes and can continue to respond after the pulp tissue has degenerated (31). A better measure of pulp health would be the presence of an intact vascular supply in the pulp tissue and tooth vitality. Such tests include laser Doppler and pulse oximetry; however, owing to the more complex nature of measurement and a lack of commercially available machines, vitality outcome is rarely reported in VPT studies.

Timing of Sensibility Testing

Based on the current ESE guidelines, pulp sensibility testing should be conducted at 6‐ and 12‐months post‐treatment, continuing at regular intervals if symptoms persist or when there is doubt about healing (15). The consensus group, however, have suggested that this follow‐up reporting should continue for as long as possible beyond one year in all cases (27).

Absence of Apical Periodontitis, Root Resorption and, in the Case of Immature Teeth, Continued Root Development

Radiographic assessment of the principal endpoint of VPT, pulp preservation in the absence of periapical disease and internal root resorption, with continued root development in immature teeth, demands an assessment of the entire root morphology and surrounding bony tissue. There is acceptance that the quality of digital films is superior to that of traditional films (32), which could improve post‐op evaluation accuracy; however, currently, there is no recommendation regarding the nature of the imaging technique required from the ESE. Several radiographic assessment criteria have been applied to measure VPT outcomes including modified Strindberg (33), and Periapical index (PAI) criteria (16, 34). Strindberg criteria is an established tool in the reporting of endodontic outcomes; however, its rigidity and failure to acknowledge the continuum of the healing process limits its role. Modification of this tool, however, enables its continued and valid use in the reporting of radiographic outcomes in VPT studies. Alternatively, the PAI is a simple, reproducible 5‐point scale used in the reporting of VPT outcomes. The index standardizes the categorization of the radiographic features of apical periodontitis. Conventional radiography, whilst offering cost‐effective imaging with good diagnostic performance and accuracy, is subject to geometric distortion and anatomical noise. Periapical lesions may not be visible until demineralization has reached levels of 30–50% leading to difficulties in assessing early disease (35, 36) and two‐dimensional radiographs may under‐estimate the clinical situation (37). Secondly, root anatomy and any associated pathology may be obscured by neighbouring structures including the maxillary sinus and apical foramen. Cone beam computed tomography (CBCT) has the capacity to overcome these short comings and there has been an increased use of CBCT in endodontics. The PAI scale has been further adapted to allow for this (CBCT‐PAI) and its use has been observed in some VPT studies (38). Despite CBCT offering higher detection rate of periapical and associated pathology, (39) its routine use is not yet recommended in endodontics owing to its higher radiation dosage, cost and the need for additional space and operator training (40).

Timing of Radiographic Assessment

Early periapical changes cannot be visualized on radiographs and so sufficient time must elapse before a radiographic assessment can provide the information necessary to make a valid judgement about treatment outcome. The current recommendation is for radiographic assessment at one year, continuing annually if required for up to four years (15).

Other Outcomes Reported in VPT Studies

Whilst the ESE has defined success under strict outcome criteria, a plethora of outcomes have been reported in VPT studies. As a result of all VPTs sharing a common aim of pulp preservation, there is considerable overlap in the reporting of outcomes across studies (Tables 10.1 and 10.2) (12, 13).