Chronic periodontitis is an inflammatory disease of the supporting tissue of the teeth resulting from bacterial inflammation that is characterized by the formation of an alveolar pocket, the progressive loss of the periodontal ligament and alveolar bone, and gingival recession [1]. Periodontal disease is a chronic inflammatory disease initiated primarily by a complex bacterial biofilm in the subgingival niche and is modified by a variety of complicated risk factors including smoking, genetic factors, systemic factors, and psychosocial and behavioral factors [2]. Periodontitis starts most commonly in those aged 20 to 30 years and is classified by the distribution of the affected site and the severity. A cross-sectional study reported that only 10% of the total adult population has healthy periodontal tissue, 80% are affected by moderate periodontal disease, and 10% have severe periodontitis [3].

The treatment of chronic periodontitis involves reconstituting a biocompatible environment through the removal of the subgingival bacterial biofilm and debridement of the mineralized posits on the root surface, with an ultimate goal of preventing inflammatory destruction [4], reducing the periodontal pocket depth, and gaining or maintaining the level of connective tissue attachment. Decreasing the amount or modifying the composition of bacterial biofilm can result in the elimination of gingivitis and reduction of bleeding on probing [5,6].

Periodontal diseases are managed primarily by two modalities: surgical therapy and non-surgical therapy. Non-surgical therapy involves scaling and root planing with hand and/or ultrasonic instruments as well as oral hygiene instruction. Axelsson and Lindhe [7], and Bardersten et al. [8] reported that non-surgical therapy resulted in a significant reduction in pocket depth, a gain in the level of attachment, and a decrease in gingival inflammation. Surgical treatment is scheduled according to the results based on a reevaluation following the non-surgical therapy to further eradicate the remaining pocket and inflammation, to create a healthy environment, and to stimulate regenerative potential of periodontium. Rosling et al. [9] observed that the pocket depth was significantly reduced, the level of attachment was enhanced, and considerable amount of osseous fill was obtained after surgical periodontal therapy.

An in-depth understanding of the prognostic factors affecting the results of periodontal therapy enables dentists to choose an appropriate therapeutic modality for obtaining better results. The relevant factors, such as the patient, tooth, or affected sites on the tooth, may affect the treatment result [2,10,11]. Researchers have listed various prognostic indicators for periodontal therapy including initial probing pocket depth, biofilm or bleeding on probing, existence of furcation, and location of the affected site, smoking, level of plaque accumulation, and shape of the tooth [11-14]. Most recently, Kim et al. [15] in their study on the attachment loss pattern of extracted teeth caused by periodontitis reported that the palatal/lingual surfaces of the maxillary and mandibular premolars and molars showed a significantly higher rate of attachment loss. This indicates that teeth with a higher rate of attachment loss on the palatal/lingual surface may be more liable to a poor prognosis.

In many clinical situations, the reaction to periodontal treatment of a tooth affected by periodontitis may differ according to the attachment loss pattern on the buccal/labial or lingual/palatal surface of a given single tooth. However, there are no previous data reporting the results of periodontal treatment according to the distribution pattern of attachment loss with specific respect to buccal or lingual surface of a given single tooth. Hence, the present study was designed to compare the results of non-surgical periodontal treatment for a single tooth according to the attachment loss pattern on the buccal/labial or the lingual/palatal surface.

The number of target teeth was 113, including 45 teeth of 21 patients in Group I and 68 teeth from 24 patients in Group II.

In the present study, the decrease in the periodontal pocket was 1.00 mm and the gain in the level of attachment was 0.28 mm 6 months after non-surgical periodontal treatment, which was similar to the findings reported by Kaldahl et al. [16] and Kim and Chung [17]. The decrease in periodontal pocket depth in Groups I and II was 1.32 mm and 0.79 mm, respectively, while the gain in the level of attachment in Groups I and II was 0.50 mm and 0.14 mm, respectively. Therefore, Group I patients demonstrated significantly greater amount of pocket depth reduction and attachment gain than Group II patients following the non-surgical periodontal treatment (P<0.01).

Philstrom et al. [18] reported that there was a larger reduction in pocket depth and improvement in the level of attachment with increasing depth after both surgical and non-surgical therapy. However, teeth with an initial pocket depth <3 mm showed little reduction in the pocket depth or gain in the level of attachment. In the present study, the change in pocket depth and the level of attachment was similar to the their results [18], the treatment outcome being increased with increasing initial probing depth.

The decrease in pocket depth and the level of attachment gain in the buccal/labial site of Group I patients was 2.04 mm and 0.93 mm, respectively. However, the decrease in pocket depth and the level of attachment gain in the lingual/palatal site of Group II patients was 1.31 mm and 0.34 mm, respectively. This phenomenon strongly suggests that teeth with a low level of attachment on the lingual/palatal site may respond more poorly to non-surgical treatment than the teeth with a comparable attachment level on the buccal and labial site in a single tooth, which may pose a critical prognostic value.

Many studies have examined the change in tooth mobility after non-surgical periodontal treatment and have reported a significant decrease in tooth mobility [19-23]. Kerry et al. [21] reported greater improvements in the teeth with high mobility than those with low mobility, and Pang et al. [22] reported that the change in mobility was higher when the tooth had a higher initial probing depth, especially in the early stage after surgery. Moreover, Schulte et al. [24] and Demirel et al. [25] reported that tooth mobility is associated with radiographic bone loss and attachment loss. In the present study, there were significant differences between Groups I and II at six months after non-surgical treatment (P<0.01). Groups I and II showed a 0.71±0.51 and 0.22±0.42 decrease in mobility, respectively. Considering the studies of Schulte et al. [24] and Demirel et al. [25], the difference in this study seemed to be associated with the increase in the level of attachment. Therefore, Group I patients, in which there was a greater amount of gain in the level of attachment, showed a better response to non-surgical treatment in terms of tooth mobility than Group II patients. Discomfort on chewing observed at the pre-treatment stage was diminished after non-surgical treatment. However, this result was not significant because only one tooth in Group II showed discomfort on chewing after non-surgical treatment. The changes in the attachment level and tooth mobility might explain why the discomfort on chewing decreased.

The teeth with a greater amount of palatal/lingual attachment loss at baseline examination demonstrated a poorer treatment response than those showing a comparable attachment loss in the buccal/labial aspects. This result can be attributed to many factors, such as crown/root anatomic configurations and angulations, the clinician's accessibility to the area, the ability of the patients to perform optimal oral hygiene, etc. Regarding the anatomical factors, the alveolar bone in the mandible has a thick buccal basal bone in the posterior region while the lingual bony wall is relatively thin, particularly at the level of alveolar crest. In the maxillary molars, the distal root furcation is located at the center of the mesio-distal aspect, while the mesial root furcation is located at two thirds of the palatal aspect. Therefore, if the loss of palatal attachment level is advanced downward, the potential for mesial root furcation involvement increases resulting in a poorer prognosis following nonsurgical therapy [26]. It is possible that the different number of maxillary teeth included in each group might have affected the results because tooth type is also a contributing factor.

Within the context of the present study, it is compelling to define the palatal/lingual attachment loss as one of the prognostic factors that complicates the treatment results. However, a more systematic study would be required to refine the prognostic factors that may influence the outcomes of non-surgical periodontal treatment.

In conclusion, when the treatment outcomes were compared in terms of pocket depth reduction, gain in the attachment level and tooth mobility reduction, the patients demonstrating attachment loss ≥6mm at buccal/labial surfaces responded better to nonsurgical periodontal therapy than those demonstrating comparable attachment loss at the lingual/palatal surfaces.