Prevalence and radiological characteristics of palatogingival groove: A retrospective cone-beam computed tomography study in an Indian cohort.

Aim: This study aims to investigate the prevalence of palatogingival groove (PG) in anterior maxillary teeth in an Indian cohort using cone beam computed tomography (CBCT) scans. Study Design: Retrospective study. Materials and
Methods: Analysis of 119 CBCT scans (64 males, 55 females, and mean age 31.6 ± 13.5 years) was performed. The data of 636 anterior maxillary teeth (220 canine, 212 lateral incisor, and 204 central incisor teeth) were studied for PG's presence. Demographic details of patients and characteristics of PG, i.e., location, extension, depth, and type were recorded.
Results: Out of the 636 anterior maxillary teeth studied, PGs were detected in 12 (1.88%) teeth (3 [1.47%] central incisors, 9 [4.2%] lateral incisors, and 0 canines). All the teeth were categorized as having either type I (Seven teeth) or type II (Five teeth) radicular groove. Two of the 12 PGs were present in the mesial, six in the mid-palatal, and four were present in the distal portion of the palatal surface of the teeth. Conclusions: The prevalence of PG in maxillary incisors in this Indian cohort is 2.88%. Maxillary lateral incisors are the most affected teeth. Copyright:

INTRODUCTION

Successful clinical management of teeth with anatomic variations has incessantly been a daunting challenge for the dentist. Thorough knowledge of anatomic complexities is critical for accurate diagnosis and proper treatment planning to ensure favorable treatment outcome. Palatogingival groove (PG) represents one such dental anomaly often overlooked and results in endodontic treatment failure. Black was the first to described it as a radicular groove (RG) in 1908.[1] This developmental anomaly is present as a funnel-shaped depression on the palatal surface of the maxillary incisors. It typically originates near the cingulum and extends apically toward the cementoenamel junction (CEJ) and the root surface.[1] Several terms have been traditionally used to describe PG, i.e., distolingual groove, radicular lingual groove, RG, and syndesmocorono RG.[2345] Multiple angulated periapical radiographs can reveal the presence of a radiolucent parapulpal line.[4] The etiology is presently unclear, but mechanisms proposed for PG's development include infolding of the inner enamel epithelium and epithelial sheath of Hertwig or an attempt to form a supernumerary root.[23678] The maxillary incisors are the most commonly affected teeth with greater predilection for lateral incisors.[46] It can present as an isolated entity or coexist with other developmental anomalies such as dens invaginatus or dens evaginatus. The reported prevalence of PG ranges from 0.5% to 18% in various populations.[9] The prevalence of dental anomalies can vary appreciably according to the specific ethnicity of the population being studied, necessitating an in-depth analysis with particular emphasis on different races or region. The prevalence of PG in the Indian population has not been reported in the past. Therefore, the present retrospective study was designed to investigate the prevalence, radiological characteristics, and type of PG in an Indian cohort of patients undergoing cone beam computed tomography (CBCT) scans for various dental indications in a tertiary care center.

MATERIALS AND METHODS

This is a retrospective analysis of 119 CBCT scans done from January 2019 to December 2019 at the CBCT facility of a tertiary care dental institute. The study was reviewed and approved by the Institutional Ethical Board of the institute (IEC-522/05.06.2020, RP-22/2020). All the scans had been referred from various departments for implant planning or evaluation of periapical pathology. All subjects had already been informed about the harmful effects of radiation at the time of their CBCT scan and had consented that the scans may be used for teaching and research purposes as per our CBCT requisition form. The requisition form for CBCT has been prepared according to the American Academy of Oral and Maxillofacial Radiology position statement which includes guidelines based on volume, dose consideration, patient selection criteria, patient consent, interpretation, and protection of patients and office personnel for CBCT examination.[10] All CBCT scans were performed with the i-CAT™ 3D imaging system (Imaging Sciences International Inc., Hatfield, PA, USA). CBCT images were viewed using a personal computer running Windows Embedded Standard software (i- CAT with a 22-inch LCD screen with a resolution of 1920 × 1080 pixels. Consecutive CBCT scans with fields of view 8 cm × 8 cm, and voxel sizes 0.3, 0.2, 0.125 mm were analyzed.

Only CBCT scans with good image quality of permanent maxillary anterior teeth, devoid of metal (prosthesis, restorations, endodontic filling materials/posts, implants), and motion artefacts were included in the analysis. Any permanent maxillary anterior teeth with coronal/root fractures, caries, internal/external resorption, impaction, displacement from normal alveolar bone position in the scans were excluded from analysis. A total of 636 permanent maxillary anterior teeth (central incisor (204), lateral incisor (212), and canine(220) were screened for the presence of the PG. Only grooves extending up to or beyond the CEJ onto the radicular portion were included as PGs in this study. The initial screening was done in axial view to confirm the presence of groove while the corresponding sagittal view was used to confirm the extent of groove in relation to CEJ of the involved tooth [Figure 1]. Once confirmed as PG the location (distal/mesial/central) was determined by orienting the longitudinal plane along an imaginary line perpendicular to the midpoint of the incisal edge of the involved anterior tooth and the center of the cingulum. The groove's length was determined as the vertical distance between the groove's start and endpoint on the tooth. The starting and ending point was located on the axial view, and the corresponding sagittal view was used to determine the vertical length. The groove's depth was determined by scrolling through the axial sections of the tooth to determine the deepest point of invagination of the groove toward the pulp cavity. A horizontal distance from the imaginary outer circumference of the tooth to this deepest point was taken as the depth of the groove and the conformation was described as shallow/flat (<1 mm), deep (>1 mm), or a closed tube that forms a tunnel-like channel.[5] The groove's length and depth were taken together further to classify the groove's complexity and severity. The labial and palatal alveolar bone plate's height was measured from the CEJ to the alveolar crest in the sagittal plane passing through the PG. Any involved tooth with alveolar crest height at >2 mm from CEJ was taken as loss of alveolar bone height. Any periapical pathology seen in tooth involved with PG was evaluated in all three planes (axial, sagittal, and coronal) to determine the lesion's maximum dimension in the anteroposterior, mediolateral, and superoinferior direction. All observations and measurements were made by two calibrated observers (Oral Maxillofacial Radiologist and Endodontist) individually, verified by a senior oral and maxillofacial radiologist, on two separate occasions, 2 weeks apart. The length and depth of the PG were the mean value of all the observations for the particular tooth.

Figure 1

Palatogingival groove evident in the axial section at the level of cementoenamel junction demonstrated in the corresponding sagittal section

Statistical analysis

The data were analyzed using Stata 15.0 software (StataCorp LP, Texas, USA). Descriptive statistics were used to determine the distribution of the demographic attributes of the patients, presence, complexity, and severity of the PGs and loss of alveolar bone height. The frequency distribution of PG between different gender and tooth type was evaluated using Pearson's Chi-squared test. The difference between the proportion of PGs present at different location and presence of associated periapical pathology was calculated using Fisher's exact test. Cohen's kappa statistic was used to determine the inter- and intra-observer reliability for CBCT scan interpretation.

RESULTS

This study included CBCT scans of 119 patients, 55 (46%) females and 64 (54%) males. The mean age of patients was 31.6 ± 13.5 years. The Cohen's kappa coefficient values for the intra and inter-rater reliabilities for CBCT scan assessment were 0.90 and 0.88, respectively. PGs were detected in 3 (1.47%) central incisors and 9 (4.2%) lateral incisors. No PG was detected in any of the canine teeth in the study [Table 1]. There was a statistically significant difference among the different tooth types in terms of PGs' presence (P = 0.05). The combined prevalence of PG in maxillary anterior teeth and incisor teeth was 1.88% and 2.88%, respectively. Bilateral PG was detected only in one patient in central incisors; the rest were unilateral. PGs' frequency in males (n = 7) was higher than in females (n = 4) [Table 2]; however, the difference between gender distribution was not statistically significant (P = 0.491). Out of the 12 PGs, two were present in the mesial, six were present in mid-palatal, and four were present in the distal aspect of the teeth' palatal surface [Table 2]. This difference of proportion for PG based on the location was statistically significant (P = 0.000). When the depth of the groove was measured, eight PGs were shallow (<1 mm) and four were deep (>1 mm). All the teeth were categorized as having either Type I (seven teeth) or type II (five teeth) RG [Table 2]. Periapical pathology was evident in only four (33%) teeth with PGs. There was a statistically significant difference between the presence or absence of associated periapical pathology in teeth with PGs. Alveolar bone loss on the palatal aspect was evident in all teeth (100%) with PGs.

Table 1

Frequency distribution of palatogingival groove

Tooth type	Total number	Teeth with PG (%)	Unilateral PGs	Bilateral PGs
Permanent maxillary central incisor	204	3 (1.47)	1	2
Permanent maxillary lateral incisor	212	9 (4.2)	9	0
Permanent maxillary canine	220	0	0	0

PGs: Palatogingival grooves

Table 2

Characteristics of palatogingival grooves in the study

Patient	Age (years)	Gender	Tooth number	Location of PG	Degree of invagination towards pulp cavity	Goon’s classification	Gu’s classification	Classification system for root canal anomalies	Alveolar bone loss (mm)	Periapical pathology
1	33	Male	11	Distal	Deep	Moderate	Type II	(PGGII) 111	2.2	Not detected
			21	Midpalatal	Shallow	Mild	Type I	(PGGI) 121	1.5	Not detected
2	28	Male	12	Mesial	Deep	Mild	Type I	(PGGI) 112	1.3	Not detected
3	23	Male	12	Midpalatal	Shallow	Moderate	Type II	(PGGII) 112	1.2	Not detected
4	34	Female	12	Distal	Shallow	Mild	Type I	(PGGI) 112	2.3	Not detected
5	23	Female	21	Midpalatal	Deep	Mild	Type I	(PGGI) 121	1.8	Not detected
6	25	Male	12	Midpalatal	Deep	Moderate	Type II	(PGGII) 112	6.3	Present
7	23	Male	22	Mesial	Shallow	Moderate	Type II	(PGGII) 122	1.8	Present
8	30	Male	12	Midpalatal	Shallow	Moderate	Type II	(PGGII) 112	1.75	Present
9	23	Female	12	Distal	Shallow	Mild	Type I	(PGGI) 112	1.5	Present
10	55	Female	22	Distal	Shallow	Mild	Type I	(PGGI) 122	2.3	Not detected
11	27	Male	22	Midpalatal	Shallow	Mild	Type I	(PGGI) 122	1.75	Not detected

PG: Palatogingival groove

DISCUSSION

Prevalence represents existing cases of a disease and can be seen as a measure of disease status, i.e., the proportion of people in a population having a disease. Various techniques have been used in literature to assess the prevalence of PGs. These involve microscopic examination or micro-computed tomographic analysis of extracted teeth, in vivo clinical observation, and retrospective radiological data analysis.[61112] There is limited value of in vivo clinical inspection for PGs' identification because the overlying alveolar bone and gingival tissue can obscure the information whereas the cross-sectioning of teeth for microscopic analysis is an invasive procedure. In addition, research using extracted teeth to determine the incidence of dental PG has a biased sample as most of anterior teeth are extracted because of periodontal reasons.[4] Two-dimensional radiographs are associated with inevitable geometric distortion and anatomical noise and do not allow accurate examination of PGs. The three-dimensional (3-D) imaging modalities offer a noninvasive tool for assessment of anatomic structures. CBCT scan is the most commonly used 3D imaging technique in dentistry. It precisely captures craniofacial hard tissues' internal and external anatomy and allows qualitative and quantitative assessment of tooth characteristics. CBCT is the only modality which gives an in vivo assessment of location, length, depth, severity, complexity, and associated alveolar bone loss with PG at lower radiation dose than conventional CT. Therefore, in the present study, the pre-existing CBCT scans from the patient's database were utilized.

This is the first study to investigate PGs' prevalence in Indian subjects. The combined prevalence of PGs in anterior maxillary teeth in this Indian cohort that have undergone CBCT scans was found to be 1.88%. This may not be a true reflection of the prevalence of PG in an Indian population because of the retrospective nature of the study and selection/referral bias. However, the present study results are in uniformity with the previous studies that reported the prevalence of PGs in maxillary anterior teeth between the ranges of 0.05% and 18% among various populations. In the international literature, the prevalence of PGs in maxillary lateral and central incisors was reported to be 2.3% and 0.6%, 4.4% and 0.28%, and 30.2% and 5.9%, respectively, in Turkish, American, and Chinese population.[6913] A similar trend of the highest occurrence of PGs in the maxillary lateral incisors was also observed in the present study, where CBCT scans revealed presence of PGs in 4.2% lateral incisors and 1.46% central incisors. Analogous to the reports by Arslan et al., Aksoy et al., the PG could not be identified in any of the canine tooth in this study.[1314] However, this was contrary to 2.4% prevalence of PGs in canines for Nepalese population.[15] This disparity in prevalence rates among studies could be attributed to the use of different diagnostic criteria, examination methodologies and ethnic/racial differences in the study population.

Significant variations in position, depth, extension, and termination of PG have been documented and several classifications have been proposed to categorize the anomaly. Mostly the PG originates coronal to cingulum and extends onto the root surface in a disto-apical direction.[4] Bacić et al. had detected 45% of PGs positioned on the distal aspect, 40% on midpalatal aspect and 15% on the mesial aspect.[11] In a study by Pinheiro et al., 70% of PGs were positioned along the distal root surface of the palatal side, followed by 20% in the central, and 10% in the mesial sides.[16] However, in the present study, 50% of the grooves were present in the mid-palatal surface of the teeth, 33% on distal aspect and 17% on the mesial aspect. Similar findings were reported by Hou and Tsai where 42.5% of PGs were positioned in the midpalatal surface, 30.1% on the distal aspect and 27.4% on the mesial aspect.[9] Based on the degree of severity assessed on the analysis of microcomputed tomography scans of teeth with RGs, it has been classified as type I, II and III.[17] In a study by Arslan et al., type I, type II, and type III RGs were detected in 68.4% of the teeth with RG, 15.7% and 15.7% teeth, respectively.[13] Aksoy et al. reported that all the teeth with PGs in their study had Type I RG.[14] In the current study, PGs were classified as type I in 58% teeth and type II in 42% of teeth.

The PGs extending on the root surface are inaccessible to the oral hygiene efforts of the patients leading to the accumulation of plaque and bacteria. These teeth are reported to exhibit higher gingival and plaque index scores.[11] Therefore, the PG is considered as a predisposing factor for localized periodontal breakdown. This information was reiterated by the findings of the present study where alveolar bone loss was observed on the palatal aspect of all teeth. However, this finding was in contrast to the incidence of periodontal pocket in 52% teeth with RG as reported by Pécora and da Cruz Filho. This could be attributed to the inclusion of patients of ages between 7 and 15 years in their study where the periodontal problems may not have yet accentuated.[12]

The data on prevalence and characteristics of PG obtained from this study will increase knowledge and understanding of the clinicians regarding this anomaly. The dentist can be more attentive and expect the presence of PG in maxillary incisors and associated periodontal pockets during clinical evaluation. Patients with PG can be educated about oral hygiene practice and importance of periodic dental visits to prevent periodontal breakdown.[12] The presence of PG should be suspected in a nonvital maxillary anterior tooth without any signs of caries/crack and absence of history of traumatic dental injury.

The management of teeth with PGs often requires a multidisciplinary approach and should be done with the aim of eliminating the causative pathologic factor to achieve a favorable outcome.[18] In the present study, periapical pathology was evident in only four teeth with PG. The identification of etiology of pulp necrosis in teeth with PG is a challenge. The accessory foramina and lateral canals opening in the groove can act as a channel for bacterial invasion, leading to the pulp's secondary involvement.[19] A primarily infected root canal (because of trauma or caries) can result in a severe periodontal defect. The pulpal and periodontal lesions can also be unrelated and have distinct etiologies. In teeth with endodontic-periodontal lesions, the endodontic treatment is recommended first. A CBCT scan can be expedient in determining canal morphology, associated anomaly and the amount of dentine between root canal space and external root surface near the groove. Lateral root perforation during root canal or post space preparation can jeopardize the treatment outcome.

The prognosis for PGs is mainly determined by the severity of the periodontal problem and the extent, depth, and accessibility of the groove.[20] Elevation of mucoperiosteal flap is required to gain access to the PGs extending beyond the CEJ, i.e., moderate and complex types. The shallow grooves can be eliminated or corrected by odontoplasty while the deep grooves require sealing. Various materials used in the literature to seal the groove includes, glass ionomer cements (GIC), composite resin, mineral trioxide aggregate (MTA), and newer calcium silicate-based cements. Composite resins do not allow fibroblast attachment and causes gingival inflammation. MTA has prolonged setting time and difficult handling characteristics. GIC and newer calcium silicate cements, such as Biodentine, are the materials of choice for sealing PG due to excellent handling properties, faster setting and biocompatibility.[18] The presence of alveolar bone loss around PG necessitate application of combined application of bone graft and guided tissue regeneration (GTR) membrane.[21] Although both nonresorbable (polytetrafluoroethylene) and resorbable (collagen and platelet-rich fibrin) membranes have been used successfully for periodontal regeneration around teeth with PGs the application of resorbable GTR membrane is advantageous as it obviates the need for second surgery.[212223] Intentional re-implantation is another treatment modality suggested for the management of complex PG where the access is difficult from palatal surgical approach, but it is associated with the risk of external root resorption and ankylosis.[2425] Consideration must be given during the prosthetic rehabilitation of teeth with PGs. The margins should be appropriately positioned to avoid leaving unsupported enamel and the use of teeth with PG as abutment for fixed partial dentures should be avoided.

CONCLUSIONS

The knowledge of intricate tooth morphology in the local population can provide reliable guidance for management and enhancing success rate of the treatment. The prevalence of PG in maxillary incisors in an Indian cohort is 2.88%. Maxillary lateral incisors are the most affected teeth, and the majority of PGs are located on the midpalatal surface. Alveolar bone destruction is invariably present adjacently to the PG.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.