Statement of problem
Despite the high prevalence of posterior cracked teeth, questions remain regarding the best course of action for managing these teeth.
The purpose of this clinical study was to identify and quantify the characteristics of visible cracks in posterior teeth and their association with treatment recommendations among patients in the National Dental Practice-Based Research Network.
Material and methods
Network dentists enrolled patients with a single, vital posterior tooth with at least 1 observable external crack. Data were collected at the patient, tooth, and crack levels, including the presence and type of pain and treatment recommendations for subject teeth. Frequencies according to treatment recommendation were obtained, and odds ratios (ORs) comparing recommendations for the tooth to be restored versus monitored were calculated. Stepwise regressions were performed using generalized models to adjust for clustering; characteristics with P <.05 were retained.
A total of 209 dentists enrolled 2858 patients with a posterior tooth with at least 1 crack. Mean ±standard deviation patient age was 54 ±12 years; 1813 (63%) were female, 2394 (85%) were non-Hispanic white, 2213 (77%) had some dental insurance, and 2432 (86%) had some college education. Overall, 1297 (46%) teeth caused 1 or more of the following types of pain: 1055 sensitivity to cold, 459 biting, and 367 spontaneous. A total of 1040 teeth were recommended for 1 or more treatments: restoration (n=1018; 98%), endodontics (n=29; 3%), endodontic treatment and restoration (n=20; 2%), extraction (n=2; 0.2%), and noninvasive treatment, for example, occlusal device, desensitizing (n=11; 1%). The presence of caries (OR=67.3), biting pain (OR=7.3), and evidence of a crack on radiographs (OR=5.0) were associated with over 5-fold odds of recommending restoration. Spontaneous pain was associated with nearly 3-fold odds; pain to cold, having dental insurance, a crack that was detectable with an explorer or blocked transilluminated light, or connected with a restoration were each weakly associated with increased odds of recommending a restoration (OR<2.0).
Approximately one-third of cracked teeth were recommended for restoration. The presence of caries, biting pain, and evidence of a crack on a radiograph were strong predictors of recommending a restoration, although the evidence of a crack on a radiograph only accounted for a 3% absolute difference (4% recommended treatment versus 1% recommended monitoring).
Various posterior tooth characteristics affect the clinician’s decision to monitor versus treat a cracked tooth. When the decision is made to treat the tooth, most commonly because of the practitioner’s concern about the integrity of the tooth or because the patient experienced pain, dentists and patients will usually opt for restorative treatment. The restorative treatment of choice for posterior cracked teeth is a complete crown.
Teeth with cracks are a common occurrence in adults, with prevalence rates of up to 70%, depending on the tooth type and location. The diagnosis and treatment of cracked teeth have been challenging for dentists and patients, and the outcomes can be consequential, with the need for a major restoration, root canal therapy, or extraction. As a result, finding the best treatment option for cracked teeth is a priority. Various procedures have been suggested either to aid in the diagnosis or treatment of a cracked tooth, including occlusal adjustment, sedative interim restorations, placement of orthodontic bands, interim crowns, direct or indirect composite resin restorations, complex and bonded amalgam restorations, and partial and complete indirect crowns.
In a practice-based study in which 1777 dentists were presented with various clinical scenarios, the presence of a crack or fracture was the factor most likely to result in the dentist recommending a crown. Another study presented 95 dentists (generalists, prosthodontists, and endodontists) with 4 different clinical cracked tooth scenarios and asked what treatment they would recommend. Treatment suggestions were wide-ranging and were not related to the practitioners’ specialty. A variety of factors contribute to the decision to restore versus monitor a tooth, including caries, the quality of the remaining tooth structure, presence of a visible fracture line, sealing the tooth against bacterial ingress, protecting cusps against flexure under function, presence of an existing restoration, and whether or not the patient has dental insurance. Evidence-based guidelines are needed for the treatment of cracked teeth. The purpose of this clinical study was to contribute to this evidential foundation by identifying and quantifying characteristics at the patient, tooth, and crack levels and their association with treating posterior teeth with visible cracks among patients enrolled in the National Dental Practice-Based Research Network.
Material and methods
A detailed report of the study procedures, including enrollment and data collection, has been provided in a previous publication. In brief, the study used a convenience sample of participants between the age of 19 and 85 years enrolled by dentists in the National Dental Practice-based Research Network. To be eligible, participants were required to have at least 1 single, vital posterior tooth with at least 1 observable external crack. Participating dentists were asked to select 1 of these teeth in each patient and to characterize this tooth for 20 eligible participants or as many as they could enroll in 8 weeks, whichever came first. The study was reviewed and approved by the institutional review board of the lead investigators (T.J.H., J.L.F.), as well as by the various institutional review boards that oversee the 6 regions of the network. Informed consent was obtained for all participants enrolled into the study. There were 2 phases to enrollment: a pilot phase with 183 patients from 12 practices from April through July 2014, and a main launch phase that occurred from October 2014 through April 2015. The study instruments were evaluated in the pilot phase to address understandability, coverage, and ease of form completion and were revised for full-study implementation based on feedback from pilot practitioners.
Dentists and their designated practice personnel were trained in data collection using a training manual developed and approved by the study principal investigators (PIs). Data including the presence and type of pain, as well as data on treatment recommendations for participant teeth, were collected at the patient, tooth, and crack levels. Data forms are publicly available at nationaldentalpbrn.org/study-results/cracked-tooth-registry.php . Confirmation of tooth vitality of enrolled teeth was with cold (for example, refrigerant or ice), although other methods were used such as air, air-water spray, or electric pulp testing. Spontaneous pain information was obtained from patient report; sensitivity to cold was ascertained using refrigerant, ice, or air-water spray; and pain upon biting was verified by having the patient occlude on a device or instrument placed on the occlusal surface of the cracked tooth. To help patients discriminate between pain (an increased response to the cold or bite assessment) and an ordinary response, dentists were asked to also perform these tests on an unaffected (for example, the contralateral) tooth. Practitioners indicated reason(s) why they recommended the study teeth for treatment from a list of 9 options (with the instruction to check all that apply, plus the option to write in an additional reason). If a practitioner recommended a tooth for restoration, they were asked to specify restoration type (intracoronal, partial crown, or complete crown), placement technique (direct or indirect), and adhesive bonding (yes or no).
Frequencies according to treatment recommendation were obtained, and odds ratios (ORs) were calculated for recommendations of treatment versus monitoring. As the validity of a statistical test depends on independent observations and the model and as the test must reflect the correlation structure of the data to yield valid estimates of variance and valid statistical tests, patients within a practice represent clusters that are often correlated to the outcome being studied. Clustering typically reduces precision of estimation, yielding lower statistical power and wider confidence intervals than studies of equal sample size but without clusters. In a univariable fashion, each patient-, tooth-, and crack-level characteristic was entered into a logistic regression model that used generalized estimating equations (GEEs) adjusted for clustering of patients within the practice and implemented using the SAS procedure for generalized models, with an exchangeable compound symmetric correlation matrix (PROC GENMOD in SAS with the CORR=EXCH option). This approach specified a model in which observations on individual patients seen by a particular practitioner are allowed to be correlated, whereas those from different practitioners are assumed to be independent. This approach removed variability caused by differences among practitioners from the tests for association between the predictor variable and the outcome variable and so uses the appropriate estimate of standard error for statistical tests.
To identify independent associations for recommending that a study tooth be restored versus monitored, all characteristics with P <.05 after adjusting only for clustering of patients within the practice were entered into a full model, followed by backward elimination to remove all variables for which P was ≥.05, using GEE to adjust for clustering. After fitting the final model, all interaction terms were tested for significance at the 5% level. To assess the robustness of findings, regressions were repeated, comparing all definitive treatment recommendations (extraction, endodontics, and restorations) to monitoring only. All ORs and P values were adjusted for clustering of patients treated by the same practitioner with GEE. All analyses were performed using statistical software (SAS v9.4; SAS Institute Inc).
A total of 2858 patients with a posterior cracked tooth were enrolled by 209 practitioners. The mean/median was 14.8/15 patients per practice, and the range was 1 to 20. The distribution of the characteristics that study dentists took into consideration when deciding whether to restore versus monitor a cracked tooth is presented in Figure 1 .
A total of 1040 teeth (36%) were recommended for the following treatments: restoration only (998; 96%), endodontic treatment only (9; 0.1%), endodontic treatment and restoration (20; 2%), extraction (2; 0.2%), or noninvasive treatment (for example, occlusal device, desensitizing [11; 1%]). The disposition of the 1018 cracked teeth recommended for restoration is as follows—type of restoration: 357 (35%) intracoronal, 34 (3%) partial crown, and 623 (61%) complete crown; type of placement: direct 452 (45%) and indirect 562 (55%); bonded: yes 624 (62%) and no 380 (38%) ( Fig. 2 ).
Virtually all those teeth recommended for indirect placement were to receive complete crowns (N=534; 95%), and the majority of those teeth recommended for direct placement were to receive an intracoronal restoration (N=355; 79%). Similarly, the majority of restorations not recommended for bonding were complete crowns (N=315; 83%). Approximately equal numbers of intracoronal restorations and complete crowns were recommended as bonded restorations.
The mean age ±standard deviation of the practitioners was 53 ±10; the median age (interquartile range) was 56 (45 to 60) years, with a range from 27 to 73 years. Of the 209 dentists participating in the study, 153 (73%) practitioners were male and 173 (83%) were non-Hispanic white. Two practitioners were periodontists, and the other 207 were general practitioners. Over half (N=118; 56%) were solo, private practitioners, with almost another third being either owners of non–solo private practice settings (N=46; 22%) or associates in private practices (N=17, 8%). Thirteen (6%) were in large group practices offering preferred care (HealthPartners or Permanente Dental Associates), and 6 (3%) were in academic centers.
The age range of patients was 19 to 85 years, with a mean age ±standard deviation of 54 ±12 years and a median age (interquartile range) of 55 (46 to 62) years. Of the 2858 patients enrolled in the study, 1813 (63%) were female, 2394 were non-Hispanic white (83%), 2213 had some dental insurance (77%), and 2432 had some college education (85%). Two-thirds of the patients (N=1900, 66%) reported clenching, grinding, or pressing their teeth together, and 2190 of 2690 main launch participants (81%) reported feeling at least some stress, with over one-third reporting feeling stressed at least weekly (N=1048, 39%). Data on stress were not obtained in the pilot phase. A total of 1297 (45%) teeth were symptomatic. Pain was noted from cold stimuli (N=1055; 81%) and biting (N=459; 35%); spontaneous pain was also reported (N=367; 28%), and 409 (35%) had more than 1 type of symptom.
The age was inversely associated with a tooth being recommended for restoration (OR=0.86 per 10 years, P <.001). A patient who had dental insurance (OR=1.4, P <.001), cold pain (OR=2.8, P <.001), biting pain (OR=9.0, P <.001), and spontaneous pain (OR=5.6, P <.001) were likely to be recommended to receive a restoration rather than monitoring.
Most cracked teeth were molars (N=2332; 82%), and more than half of these were in the mandibular arch (N=1675, 59%). The vast majority of external cracks, N=2640 (92%), were on a tooth with a restoration: N=2041 (71%) of cracked teeth had 1 restoration, N=547 (19%) had 2 restorations, and N=52 (2%) had 3 or 4 restorations. Slightly more than one-third (N=1018; 36%) of teeth had 1 external crack, 759 (27%) had 2, 507 (18%) had 3, and 574 (20%) had 4 or more. Of the total, 638 (22%) had some root exposure, 676 (24%) presented with at least 1 wear facet through enamel, and 254 (9%) had a noncarious cervical lesion. Only 53 (2%) had evidence of a crack on a radiograph. Of 302 (11%) teeth with caries, only 6 (<1%) were on a tooth that practitioners recommended for monitoring.
The presence of caries was strongly associated with a tooth being recommended for restoration rather than monitoring (OR=54.8, P <.001). Evidence of a crack on a radiograph was also strongly associated with a restoration recommendation (OR=4.9, P <.001), whereas a crack on a molar (OR=1.6, P <.001), multiple external cracks (OR=1.3, P =.006), and the presence of a wear facet through the enamel (OR=1.4, P <.001) were each modestly associated with a recommendation for restoration. Cracked teeth with exposed roots were inversely associated (OR=0.8, P =.018) with a restoration recommendation ( Table 1 ).
|Tooth-Level Characteristic||Monitor (N=1818)||Restore (N=1018)|
|N a||Col% b||N||Row% c|
|Cluster-adjusted OR d||OR=1.6|
|Cluster-adjusted P e||P <.001|
|2 or more external cracks||680||37||691||50|
|1 external crack||1138||63||327||22|
|Cluster-adjusted P||P =.006|
|Wear facet through enamel||385||21||286||43|
|No wear facet through enamel||1433||79||732||34|
|Cluster-adjusted P||P <.001|
|No exposed roots||1391||77||812||37|
|Cluster-adjusted P||P =.018|
|No caries present||1812||100||723||29|
|Cluster-adjusted P||P <.001|
|No NCCL present||1649||91||935||36|
|Cluster-adjusted P||P =.122|
|Evidence of crack(s) on radiograph||12||1||41||77|
|No evidence of crack(s) on radiograph||1806||99||977||35|
|Cluster-adjusted P||P <.001|