Success of non‐surgical periodontal therapy in adult periodontitis patients: A retrospective analysis

Abstract Objective To evaluate the results of active non‐surgical treatment in patients diagnosed with adult periodontitis treated in a specialized clinic for periodontology. Material & Methods In total, 1182 patients with adult periodontitis received active non‐surgical therapy, which involved professional oral hygiene instruction, scaling and root planing, supragingival polishing and elective systemic antimicrobial medication. The results of this therapy were based on a full‐mouth periodontal chart as assessed at the time of evaluation. Successful treatment as periodontal pocket depth (PPD) ≤5 mm was the main outcome parameter with bleeding on pocket probing as secondary outcome. Patient‐related factors such as smoking and severity of periodontitis at baseline and site‐related factors such as tooth type, furcation involvement and endodontic treatment were analysed. Possible relations with assessed parameters and the success of active periodontal therapy were evaluated. Results Overall 39% of the patients reached the successful treatment objective and a mean bleeding on pocket probing tendency of 14%. Treatment success appeared to be dependent on tooth type where the results at single‐rooted front teeth (85%) and premolar teeth (78%) were more successful than at molar teeth (47%). Analysis revealed that in 55% of the cases furcation involvement at molars was associated with the absence of success. Endodontic treatment was associated with absence of success in 8%‐11% of the cases. Smoking negatively influences successful treatment outcome (P < 0.001). Conclusion Active non‐surgical periodontal therapy in patients with adult periodontitis resulted in approximately one third of the cases in the success endpoint of PPD ≤ 5mm. Sub‐analysis showed that the outcome appeared to be dependent on tooth type, furcation involvement, severity of periodontal disease at intake and smoking status.


| INTRODUC TI ON
The goal of periodontal therapy is to preserve, improve and maintain the natural dentition. 1 Therapy includes manual, sonic and/ or ultrasonic instrumentation in conjunction with supragingival plaque control. 2 A systematic review of the literature evaluated the effect of subgingival debridement in terms of bleeding on probing, pocket depth and probing attachment level in patients with chronic periodontitis. Subgingival debridement was found to be an effective treatment in reducing probing pocket depth and improving the clinical attachment level. 3 Treatment results in a pocket depth reduction due to recession of the gingiva and gain in clinical attachment level. When a pocket depth smaller or equal to 5mm is reached, the treatment can be considered successful. 4 Various factors have an impact on the success of the active nonsurgical periodontal therapy. 5 Patient-associated factors such as severity of the disease and smoking status have a negative effect on periodontal therapy. 6 Sitespecific factors, for example tooth type and endodontic treatment, may also have an impact on the outcome. With respect to tooth type, there is a difference between single-rooted and multi-rooted teeth with possible furcation involvement, which is a complication for the successful treatment of molars. 7 The aim of the present study was to evaluate the success of active non-surgical periodontal therapy in patients with adult periodontitis. Successful treatment was considered to be an intra-oral condition with residual pockets not deeper than 5mm at the point of evaluation.

| MATERIAL & ME THODS
This report was prepared according to the guidelines suggested by the STROBE 8,9 and RECORD 10,11 checklists. These checklists recommend items that should be included in reports of observational studies and studies using routinely collected observational data. All data were procured retrospectively from the treatment records. Involved patients had provided permission in advance that their treatment outcome could be used for analysis. Approval by the Institutional Review Board of the Academic Centre for Dentistry Amsterdam (ACTA) was provided for this study under number 2017026.

| Subjects
Patients involved in the study had been referred because of periodontal problems by their general dentist. They were treated within 12 months following their intake appointment at the specialist Clinic for Periodontology, Utrecht, The Netherlands, from 2013 up to 2016. The clinical diagnosis before active periodontal treatment was moderate-to-severe adult periodontitis. 12,13 The first appointment included intra-and extra-oral assessment, full-mouth periodontal charting and a complete set of radiographs. The parameters that were collected included probing pocket depth (PPD; measurements were rounded off to the nearest millimetre), bleeding on pocket probing (BOPP scored as absent or present) and furcation involvement (using a PQ0W6 pocket probe and PQZNM furcation probe, Hu-Friedy, Hu-Friedy ® Inc). PPD and BOPP were recorded at six sites (mesio-buccal, buccal, disto-buccal, mesio-lingual, lingual and disto-lingual). Based upon these parameters, in relation to age (>35 years old) and in combination with the information as obtained from the radiographs the responsible periodontist came to the clinical diagnosis of (semi) generalized adult periodontitis. 12,13 Following the intake appointment, the active phase of non-surgical periodontal therapy was started. Dental hygienists were responsible for the professional tooth debridement and oral hygiene instructions.
All patients received 2 to 5 one-hour sessions of thorough supra-and subgingival scaling and root planing of all teeth involved. If necessary, because of individual needs of the patient, this was performed under local anaesthesia. Elective systemic antimicrobial medication consisting of a combination of amoxicillin (375 mg) and metronidazole (250 mg) three times daily for seven days was provided after the treatment sessions at the indication of the periodontist responsible for the treatment. For instrumentation, a piezoelectric ultrasonic unit (Piezon Master, EMS ® ) at a moderate setting and with the appropriate tips for initial therapy (A, P, PS, PL1-5, EMS ® ) was used. In addition, where deemed appropriate by the dental care professional, hand instruments were utilized (204SD, 12/13 11/14 Hu-Friedy; Hu-Friedy ® Inc). At each appointment, the level of oral hygiene of the patients was evaluated and if necessary reinforced in case of inadequate plaque control. Patients were scheduled for the interim evaluation, about 6 weeks later by the same dental hygienist. At this appointment, the oral hygiene of the patients was reinforced if after disclosing remaining plaque was made visible. Subgingival debridement was carried out where necessary (ie, PPD > 3mm), and a professional prophylaxis was provided. Approximately two and a half months later, a final evaluation was carried out and PPD, BOPP and furcation involvement were assessed again as described above by the same periodontist.

| Data extraction and analysis
The summary data as used for this study were extracted from the patients' files by the periodontist who was responsible for the provided therapy and entered anonymously into a computer database (Microsoft Excel). Data extracted were age, bone loss ≥50%, 12,13 presence of pockets ≥9mm, 14 smoking status at intake and the absence or presence of a residual pocket depth at the evaluation appointment not deeper than 5 mm. The latter was also separated by tooth type being front, premolar and molar teeth. The percentage of endodontic treatment was recorded in relation to each of the three tooth types, and for premolars and molars, additionally the presence of furcation involvement was recorded. Furthermore, the percentage BOPP at the evaluation appointment was extracted. Normal distribution of BOPP was tested by Kolmogorov-Smirnov and Shapiro-Wilk. Accordingly, statistical analyses were performed using the chi-square test and the independent-samples t test. P-values of < 0.05 were considered to be an indicator of statistical significance.

| Demographics
In total 1182 patients included in this study were treated for adult periodontitis between 2013 and 2016. The mean age at intake was 52.6 ± 9.8 years (range 36-86), and 28.6% of the patients were smokers. The average time of treatment between intake and evaluation was 7.3 ± 1.9 months (range 3-12).

| Treatment success
In total, 39% of the patients ended with pockets not deeper than 5 mm at the evaluation appointment. The success at the front teeth was higher (85%) than at molar teeth (47%). At evaluation, the mean percentage of BOPP at patient level was 13.9 ± 11.1 (Table 1). This was not normally distributed (P > 0.0001), and the median BOPP was 11%. If, as proposed by Chapple et al, 15 a threshold for bleeding on probing of <10% is used for defining a clinical case of health, 44% (n = 515) could be considered as a successfully treated periodontitis patient. When ≤5 mm probing pocket depth is combined with <10% BOPP only in 19% of the patients (n = 226), success was achieved.

| Non-treatment success
If the treatment outcome was not successful, that is the presence of residual pockets deeper than 5 mm, tooth-related factors were evaluated. Endodontic treatment was associated with the absence of success ranging from 8% to 11% of the cases. At the premolar teeth in 10% of the patients, the presence of pockets deeper than 5 mm was associated with furcation involvement. In molar teeth, this was 55% ( Table 2).
The level of success was associated with the severity of periodontal disease at intake (P < 0.001; Table 3a,b). In patients treated successfully, 26% had pockets ≥9 mm at intake as compared to 55% in those that were unsuccessful. Reversely successful treatment was associated with 74% of the patients with pockets <9 mm at intake as compared to 45% in those without success. This difference was significant (P < 0.001; Table 3a). Similarly in 80% of the patients without success, the severity of bone loss at intake was higher (as defined by the presence of >50% bone loss). In 49% of the patients treated successfully, the bone loss at intake was ≤50% (P < 0.001; Table 3b). At a patient level, the severity of the disease at the intake appointment as assessed based on the presence of pockets ≥9 mm was not associated with the smoking status (P = 0.334; Table 3a). There was however a significant relationship between smoking status and severity of bone loss at intake (Table 3b). In smokers, the percentage of patients with bone loss >50% was 77.5% as compared to 66% for nonsmokers, which was a significant difference (P < 0.001; Table 3b).
At a patient level, non-smoking was associated with a higher percentage of success than outcome of treatment in patients that did smoke (Table 4). In smokers, treatment in 71% of the cases was unsuccessful. In non-smokers, treatment was successful in 43% of the patients and unsuccessful in 57%. Non-smokers therefore showed a significantly better treatment success than smokers (P < 0.001). The mean level of BOPP in smokers (15%) at the evaluation appointment was significantly different among smokers and non-smokers (13%) (P = 0.004).

| Summary of our findings
The purpose of this retrospective study was to evaluate successfulness of active non-surgical therapy in adult periodontitis patients.
These results represent real-life situations of a specialized clinic restricted to periodontal therapy. Overall 39% of the patients finished with the predefined level of success being overall with pockets ≤5 mm. Treatment success was more frequently obtained in the front teeth region (85%) and the premolar region (78%). Smoking status, severity of disease and molar furcation involvement appeared to be factors that negatively interfered with success.

| Success percentage
The prediction of success of periodontal treatment would be of great benefit for clinicians treating cases of periodontitis, as well as for the patients to allow them to take informed decisions.
Conclusions regarding the effect of periodontal therapy are based on the definition of treatment response. In this study, it was chosen TA B L E 1 Success of active non-surgical periodontal treatment N = 1182 as assessed at the evaluation appointment defined as no residual pockets deeper than 5 mm overall separated by tooth type. In addition, the mean percentage of sites that showed bleeding on pocket probing (BOPP) is given Consequently if in one of the tooth types the treatment is not successful (residual pocket depth >5 mm at evaluation) than the treatment is considered to be unsuccessful. On the other hand, if one considers the results in relation to tooth type a higher success rate can be predicted in single-rooted teeth. Other researchers have also pointed out that if a satisfactory treatment result is obtained the number of successfully treated individuals is much lower than the successfully treated sites. Success rates at site level are higher than the overall success rate due to the fact that many subjects exhibited a mixture of both diseased and healthy sites. 26 The results of a clinical study with a follow-up of 36 months after active therapy show that based on a construction of clinical parameters to define success 26% of the individuals exhibited "perfect" periodontal health and were considered to be successfully treated. 26 In the light of this, the success rate of 39% in the present study could also be seen as an acceptable success.

| Relation between tooth type and the effect of active non-surgical periodontal therapy
The results of the present study show a higher percentage of success in single-rooted teeth (front teeth: 85%) as compared to molar teeth (47%) ( Table 1). This is in agreement with a study where changes in clinical parameters in single-and multi-rooted teeth were evaluated.
More positive outcomes were observed by single-than by multirooted teeth with respect to the change of initial probing depth to the probing depth at evaluation. 27  One of these influencers is furcation involvement where outcomes from clinical trials showed that molars with furcation involvement responded less favourably to non-surgical therapy as compared to molars without furcation involvement. 28,33 Complete debridement of molars will be rarely obtained because of the complex morphology in the furcation area. 34,35 Therefore, non-surgical therapy is recommended for teeth with shallow furcation defects (furcation not probeable or the root trunk coronal to the furcation entrance probeable). Non-surgical periodontal therapy of advanced furcation involvement (furcation entrance probeable >3 mm in horizontal direction or entrance is "through-and-through") usually leads to disease progression in the furcation area with a risk of eventual loss of teeth. 37 A wide range of alternative treatment modalities have been proposed in the literature based on the depth of the furcation involvement. 38 A systematic review which has evaluated various therapeutic approaches followed by a period of maintenance care indicates a good survival rate of multi-rooted teeth with furcation involvement. 39

| Effect of endodontic treated teeth on active non-surgical therapy
At a site level, endodontic treatment may have an effect on the outcome of periodontal therapy. Patients with teeth that have been endodontically treated show more bone loss compared to contralateral teeth without an endodontic treatment. 40 In sites with greater bone loss, a poorer treatment response has been reported regarding probing pocket depth reduction. 5 Also, periodontal disease (pockets > 5 mm) around endodontically treated teeth appears to be an extra risk factor, which can affect tooth survival. 41,42 In the present study, patients that did not have a successful treatment response had endodontic treatment, which varied between 8% and 11% dependent on tooth type (Table 2). This therefore did not provide a clear explanation why treatment was unsuccessful. Concern about endodontic treatment with respect to treatment success may also be less because Pretzl et al 43 have shown that it is feasible to retain endodontically treated teeth in periodontitis patients in combination with active and supportive periodontal therapy for more than 10 years.
However, after active periodontal therapy, endodontic treatment appeared to be a strong risk factor for tooth loss of molars.

| Effect smoking status and non-surgical periodontal therapy
Smoking has proven to be a major risk factor in the prevalence, extent and severity of periodontitis. 44,45 Van der Weijden et al 48 reported that cigarette smoking is a factor associated with deeper periodontal pockets. As is apparent from Table 3 in the present study, no significant difference was found between smokers and non-smokers with respect to the presence of initially deep pockets (>9 mm; P = 0.334) (Table 3a). The reason for this is unclear but may be related to the relatively high cut-off of 9 mm that was chosen to discern between moderate and deep pockets.
Duane 49 shows that there is a strong association between chronic smoking and bone loss which is in agreement with the present study. Table 3b shows that smokers presented more often with bone loss (>50%) than non-smokers (P < 0.001). Several studies have also shown that smokers have a poorer response to non-surgical periodontal therapy than non-smokers. 50,51 This also is in agreement with the results of the present study where treatment in non-smokers was more successful than in smokers (P < 0.001, Table 4). Similarly, Renvert et al (1998) 52 have shown that the treatment response in non-smokers was better than in smokers. They observed following non-surgical periodontal therapy in non-smokers a pocket depth reduction of 2.5mm as compared to a reduction in smokers of 1.9mm. Other authors have observed that smoking cessation promoted an additional benefit in the reduction of probing pocket depth. 53,54 With respect to bleeding scores, Renvert et al 52 observed a higher level of residual inflammation with a full-mouth bleeding score in smokers of 37% as compared to 23% in non-smokers. The present study did not find such a large difference in mean percentage bleeding scores between smokers (15%) and non-smokers (13%) ( Table 4).
However, smoking has a detrimental effect on the incidence and progression of periodontitis. Tobacco smoking, therefore, is important information that should be assessed along with other risk factors for periodontitis. 55

| Severity of periodontitis and treatment success
According to the literature, all severities of periodontitis can be treated well and should show a positive effect following the non-surgical periodontal therapy. 56,57 In the present study, severity of periodontitis is determined by bone loss >50% (yes/no) and initial pocket depth ≥9 mm (yes/no). These two factors have a significant negative impact on the treatment outcome (Tables 3 and 4). Some authors have provided guidelines for the daily practice to address the "critical probing depth". 58 In sites with initial probing depths above the "critical probing depth" value, a better result occurred following periodontal surgery than following non-surgical periodontal therapy. 59 Their data also disclosed that the level of oral hygiene maintained by the patients during healing and maintenance was more critical for the resulting probing depths and attachment levels than the mode of initial therapy used.

| Treatment facility
The present study is to some extent limited by the records of the Clinic for Periodontology, which rely on data from clinicians' and patient-reported data regarding smoking habits. It has however been shown that treatment provided in the private periodontal clinic showed significantly less progression of periodontitis and tooth loss as compared to treated in an academic setting. 60 A recent retrospective study evaluated the effect of supportive periodontal treatment from the same periodontal practice as the present study. It showed that after 10 years on average 2.6 teeth were lost. 61 Based on a recent systematic review, it appears that specialist periodontal maintenance is effective in sustaining periodontal stability following active specialist intervention. There is some evidence that primary dental care provides the same level of care. The limited comparative data available suggest that outcomes could be slightly worse in primary dental care. 62

| Limitations
Baseline pocket depth was not entered into the database. In retro- The number of teeth present at intake and those extracted during non-surgical periodontal therapy were not taken from the individual patient records. This would have provided related information.
The level of oral hygiene is a factor related to presence of residual pockets after therapy. These data were not analysed. However, individual oral hygiene instructions and reinforcement were part of the treatment protocol.

| CON CLUS ION
This present study shows that active non-surgical periodontal therapy in patients with adult periodontitis resulted in approximately one third of the cases in the success endpoint of no pockets deeper than 5 mm. Sub-analysis showed that the outcome appeared to be dependent on different factors, such as tooth type, furcation involvement and smoking. Treatment success was higher at single-rooted teeth than at molar teeth, especially in those with furcation involvement. Success rate was also related to the severity of periodontal disease at intake and to the smoking status.

| Scientific rationale for the study
Periodontitis is primarily treated with non-surgical periodontal therapy. When a probing pocket depth (PPD) ≤5 mm is reached, the treatment can be considered as successful. In this retrospective study, the results of active non-surgical periodontal therapy in a clinic restricted to periodontology are evaluated.

| Principal findings
Active non-surgical periodontal therapy in patients with adult periodontitis resulted in approximately one third of the cases in "success" (PPD ≤ 5 mm).

| Practical implications
Success following active non-surgical periodontal therapy in patients with adult periodontitis is limited. Especially in molar teeth, it is difficult to reach pockets ≤ 5 mm. Dental care professionals should consider this when they estimate the prognosis of teeth and molars.

ACK N OWLED G EM ENTS
The authors would like to thank the team of the Clinic for Periodontology, Utrecht, for their help in filling the database. Thanks are also extended to Diyar Kamal for his help with the primary analysis of the database.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflicts of interest.

AUTH O R CO NTR I B UTI O N
All authors gave final approval and agreed to be accountable for all aspects of work ensuring integrity and accuracy. GAW contributed to conception and design, analysis and interpretation, and drafted the manuscript. GJD contributed to analysis and interpretation, and