|Year : 2015 | Volume
| Issue : 2 | Page : 101-104
Validity of intraoral soft tissue landmarks as reference points for orientation of occlusal plane in natural dentition: A clinical study
Shefali Singla1, Manu Rathee2
1 Department of Prosthodontics, Dr. HSJ Institute of Dental Sciences and Hospital, Punjab University, Chandigarh, India
2 Department of Prosthodontics, Post Graduate Institute of Dental Sciences, Pt. B. D. Sharma University of Health Sciences, Rohtak, Haryana, India
|Date of Web Publication||2-Mar-2016|
Department of Prosthodontics, Post Graduate Institute of Dental Sciences, Pt. B. D. Sharma University of Health Sciences, Rohtak - 124 001, Haryana
Source of Support: None, Conflict of Interest: None
Introduction: Occlusal plane is the average plane established by incisal and occlusal surfaces of teeth. Various anatomic landmarks are used to determine this missing component of occlusion which is lost with the loss of teeth. However, variation has been observed in the orientation of occlusal plane determined clinically with different anatomical landmarks as references.
Objective: This study was undertaken to determine the relation of intraoral anatomic soft tissue landmarks, namely, retromolar pad and parotid papilla with occlusal plane in natural dentition.
Materials and Methods: Irreversible hydrocolloid impressions of 100 edentulous individuals (50 males and 50 females) were made to get the models. A 16 gauge wire was extended from mandibular occlusion plane posteriorly up to retromolar pad to establish their relationship. Furthermore, vertical distance of apex of parotid papilla to maxillary molar cusp tip it opposed (distobuccal cusp of maxillary first molar or mesiobuccal cusp of maxillary second molar), and mandibular molar cusp tip (to which parotid papilla apposed) was measured when the teeth were in maximal intercuspal position.
Results: This study determined that the natural occlusal plane is oriented posteriorly at the level corresponding with the lower third of retromolar pad. Mean distance of parotid papilla above the corresponding maxillary cusp tip (while in occlusion) was 5.048 mm, and mean distance of Parotid papilla above the corresponding mandibular molar cusp tip (while in occlusion) was determined to be 3.602 mm. The difference in observed means between males and females or between right and left side was not statistically significant.
Keywords: Occlusal plane, parotid papilla, retromolar pad
|How to cite this article:|
Singla S, Rathee M. Validity of intraoral soft tissue landmarks as reference points for orientation of occlusal plane in natural dentition: A clinical study. Saint Int Dent J 2015;1:101-4
|How to cite this URL:|
Singla S, Rathee M. Validity of intraoral soft tissue landmarks as reference points for orientation of occlusal plane in natural dentition: A clinical study. Saint Int Dent J [serial online] 2015 [cited 2021 Apr 19];1:101-4. Available from: https://www.sidj.org/text.asp?2015/1/2/101/177938
The significance of occlusal plane lies in the fact that this plane determines the spatial orientation of occlusal surfaces of teeth in relation to bases of skull and maxillary bones. According to the glossary of prosthodontic terms, occlusal plane is defined as the average plane established by incisal and occlusal surfaces of teeth.  Inclination of occlusal plane is one of the key factors governing occlusal balance, phonetics, and esthetics.
Precise establishment and orientation of the plane of occlusion is very important during rehabilitation of the completely edentulous subjects and is one of the important factors, which determines the prognosis of the case. It is desirable that the occlusal plane lost in edentulous patients should be relocated in prosthesis to conform to natural occlusal plane of the patient. Faulty orientation of occlusal plane in the prosthesis will jeopardize the interaction between tongue and buccinator muscle in placement of food bolus on the occlusal table. If the plane is too high, it would cause collection of food in the sulcus, and if it is too low, it would result in biting of cheek or tongue. Occlusal plane is an important factor of stability, critical in mounting on articulators, has a bearing on health and function of temporomandibular joint and is also of vital importance for articulate speech in a complete denture patient.
Different schools of thought exist regarding the method of orienting the occlusal plane based on intraoral and extraoral landmarks during complete denture fabrication. These include ala-tragus line, anterior nasal spine and hamular notch, lateral border of tongue, buccinator grooves, and commissure of lips and positioning the occlusal plane midway between the ridges. , Lingual frenum has also been related to occlusal plane.  Absolute clarity is lacking regarding orientation of the occlusal plane.
This study was undertaken to determine the relation of certain intraoral anatomic landmarks with the occlusal plane. Patients with normal occlusions were examined to determine the relationship between these anatomic landmarks, namely, retromolar pad and the parotid papilla, and the occlusal plane. Parotid papilla is a small mucosal fold on which the orifice of Stensen's duct normally opens and is located in the cheek at the level of crown of maxillary first molar tooth.  Retromolar pad is a triangular soft elevation of mucosa that lies distal to mandibular third molar.
| Materials and Methods|| |
Hundred edentulous individuals, 50 males and 50 females, in the age range of 18-50 years with Angle's Class-I molar relation and full complement of teeth in normal alignment, irrespective of the status of the third molar, were included in the study. Subjects with history of orthodontic treatment, facial trauma, and surgical intervention, and those with attrition of teeth were excluded from the study. Mandibular impressions using irreversible hydrocolloid were made and poured immediately using dental stone (Apexion India,Calicut,India) to get the casts.
Location of plane of occlusion in relation to retromolar pad on the cast
A 16 gauge wire was placed on tip of the mandibular cuspid and posteriorly extended to the distolingual cusp tip of second or third molar and further till the retromolar pad. The vertical height of the retromolar pad was divided into three parts, namely, lower, middle, and upper third. The relationship of the plane of occlusion to retromolar pad was determined by the intersection of wire and pad.
Location of plane of occlusion in relation to parotid papilla on the cast as well as intraorally
Light, intermittent, external pressure was applied to the cheek while the apex of papilla was located and marked with an indelible pencil. The relation of apex of parotid papilla to the maxillary molar cusp tip it opposed (distobuccal cusp of maxillary first molar or mesiobuccal cusp of maxillary second molar) was determined, and its vertical distance (X) to the cusp tip in maximum intercuspation position was recorded using the geometrical divider. These measurements were recorded both for the right and left sides.
For the determination of relation of apex of parotid papilla to mandibular molar cusp tip, a point corresponding to cusp tip, to which parotid papilla apposed, was marked on cervical margin of mandibular molar. The vertical distance (a) of apex of parotid papilla to this point was recorded while teeth were in maximum intercuspation. Then cervicoincisal length (b) of mandibular molar (from the marked point to cusp tip) was recorded. The vertical distance (Y) of mandibular molar cusp tip to apex of parotid papilla was calculated by subtracting value b from a, i.e. Y = a − b.
Mean, standard deviation, standard error, and coefficient of variation were calculated for both male and female groups for the right and left sides for all the parameters. Since data obtained was normally distributed, Student's t-test for paired observations was used for studying the level of significance.
| Results|| |
Relation of occlusal plane with retromolar pad
Analysis of data obtained indicated that the occlusal plane, as determined by a line from mandibular cuspid tip to the distolingual cusp tip of distal most mandibular molar, terminated in the lower third area of the retromolar pad in 58%, in middle third in 34%, and in upper third in 8% male subjects. In female subjects, the percentage was 66%, 20%, and 14%, respectively. The difference between male and female subjects was not statistically significant at 5% level. The overall percentages of subjects having occlusal plane at the level of lower, middle, and upper third of retromolar pad were 62%, 27%, and 11%, respectively [Table 1].
Relation of occlusal plane with parotid papilla
With maxillary molar cusp tip as reference point, the mean distance (X) of parotid papilla was 4.939 mm on the right side and 4.998 mm on the left side in males. The difference in the value of X between right and left side was not statistically significant at 5% level as t = 0.246, i.e. <1.96. The overall mean value (X) for males was 4.966 mm, with range being 2.0-7.9 mm.
In females, the distance was 5.15 mm on the right side and 5.11 mm on the left side, the difference was not significant statistically as t = 0.181. Overall mean value (X) for females was 5.13 mm, range being 3.1-7.3 mm. The difference in value of X for males and females on the right side as well as on the left side was not statistically significant. Parotid papilla was found to be adjacent to distobuccal cusp of maxillary first molar in 45 subjects and adjacent to mesiobuccal cusp of maxillary second molar in 55 subjects.
With mandibular molar cusp tip as a reference point, the mean distance (Y) in males was 3.610 mm on the right side and 3.648 mm on the left side, with overall value being 3.624 mm. The difference in value between right and left side was not statistically significant as t = 0.703.
In females, the mean distance (Y) of parotid papilla above the occlusal plane was 3.68 mm on the right side and 3.48 mm on the left side with overall mean being 3.58 mm. The difference between right and left side was not statistically significant, " t" being 0.870. Difference in the value of Y for males and females on the right side as well as on the left side was not statistically significant [Table 2] and [Table 3].
|Table 2: Distance of parotid papilla from corresponding maxillary molar cusp tip (X) and from corresponding mandibular molar cusp tip (Y) in males on both sides |
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|Table 3: Distance of parotid papilla from corresponding maxillary molar cusp tip (X) and from corresponding mandibular molar cusp tip (Y) in females on both sides |
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| Discussion|| |
The occlusal plane position is the foundation of clinical treatment in oral rehabilitation and one of the most important criteria to judge the degree of treatment success. The results of the current study regarding retromolar pad were consistent with those of Lundquist and Luther, who reported that in 75% of their subjects, occlusal plane terminated in area of lower half of retromolar pad.  Ismail and Bowman  found it to be at level of middle third of retromolar pad, whereas Boucher, Pound, Yasaki, Hall, Wright, and Piermatti concluded in their studies that the retromolar pad could be used as a landmark wherein posterior plane terminated at distal part of retromolar pad. ,,,,, Boucher found that the occlusal surfaces of lower last molars were nearly parallel with the soft tissues immediately distal to the teeth. Authors chose a wider age group in a larger sample from a different population. Criteria of selection of subjects for these studies and technique used differed from those of this study. The distolingual cusp tip of mandibular distal molar has a closer anatomic relationship to the retromolar pad than does the distobuccal cusp. For this reason, the distolingual cusp was used as the distal reference point in this study. A higher percentage of occlusal planes would have been related to the upper half of the retromolar pad, if the distobuccal cusp had been used, due to the lingual inclination of mandibular molars.
According to glossary of prosthodontic terms, the plane of occlusion is defined as "an imaginary surface that is related anatomically to the cranium and that theoretically touches the incisal edges of the incisors and tips of occluding surfaces of posterior teeth. It is not a plane in true sense of the word but represents the planar mean of the curvature of these surfaces."  The curve of occlusion defined therein as "Curved occlusal surface that makes simultaneous contact with the major portion of the incisal and occlusal prominences of existing teeth." A paradox was immediately apparent, i.e., whether both maxillary and mandibular teeth had a plane of occlusion with teeth separated or there was a single plane of occlusion when the teeth were in centric occlusion. With the teeth in centric occlusion, the two planes did not coincide, particularly in the anterior region. Posteriorly, the cusp tips represented the plane of occlusion by definition. However, in centric occlusion, the maxillary plane is inferior to the mandibular plane by height of its cusps. Thus, the plane of occlusion should exist only when the teeth are in centric occlusion.
These results in this study are consistent with those in a study by Lundquist and Luther where mean superior distance of parotid papilla above corresponding maxillary molar cusp tip was 4.2 mm, and papilla was adjacent to maxillary second molar in 57.5% of subjects and to maxillary first molar in 42.5%. Furthermore, similar observations were made in a study by Foley and Latta, who found mean distance of parotid papilla above corresponding mandibular molar to be 3.3 mm. However, only white population showed a statistically significant difference between right and left sides. 
| Conclusion|| |
This study determined that the natural occlusal plane coincided posteriorly with lower third of retromolar pad in majority of cases. The parotid papilla could also assist in the determination of vertical location of the plane of occlusion. An additional finding was that gender and the side (right or left) differences were not statistically significant. On the basis of the results obtained in this study, it is recommended that a fairly constant relationship exists between parotid papilla and occlusal plane. It is also recommended that retromolar pad could be used as a landmark to assess the posterior plane of occlusion, wherein the posterior plane coincided with lower third area of retromolar pad. However, the location of occlusal plane depends on mature clinical judgment of the individual dentist and must satisfy esthetics, denture stability, function, and comfort.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]