Dental occlusion is a static and dynamic relationship between the masticatory surfaces of maxillary and mandibular teeth which is an important variable in the prosthetic rehabilitation.4
In every individual the contact of teeth i.e. maximum intercuspation and disocclusion is a different phenomenon, so every clinician has to diagnose the type of occlusion and disocclusion before the final prosthetic rehabilitation, to achieve functional, comfortable and aesthetic occlusion.5
Canine protection and group function theories are used when describing occlusal schemes during lateral excursion and are widely accepted as types of therapeutic occlusion in natural dentition.2
The character of a therapeutic occlusion is reflected by two well-known concepts: cusp-to-fossa verses cusp- to- marginal ridge area. Both occlusal schemes are prosthetic inventions and have very little, if any substantiated experimental basis. Inspite of the importance of occlusal contacts, little has been presented in the literature regarding the type of tooth contact in sound dentition with normal alignment.7
Hence the aim of this study was to evaluate the prevalence of the occlusion schemes that exists naturally during lateral and protrusive excursion from the intercuspal to the edge-to-edge position in Indian population and also to determine the type of occlusal surface contacts in maximum intercuspation in Angle’s class I molar relation which is important for correct diagnosis and for prosthetic rehabilitation.
6.2 REVIEW OF LITERATURE:
Yaffe A, Ehrlich J, conducted astudy to determine the amount and nature of contact of natural teeth in working movement through the entire range from the intercuspal to the edge-to-edge which was recorded in 72 individuals of age 19-35 years, with normal tooth alignment and Angle’s class I molar and canine relation. The lateral glide movement was divided into three stages to simulate the total range of events in lateral glide movement naturally demonstrated by the patient and shown that lateral glide movement is a complex movement in which the nature of tooth contact was altered in location, direction and number of teeth participating. And consequently it was concluded that the restoration of an occlusion in accordance with the given concept did not always apply to all patients.1
A study was conducted to investigate the relationship between static and dynamic occlusion in 447 school children within a range of 14-17 years with no history of orthodontic treatment or trauma of the teeth and static occlusion was determined for both incisal and molar relationship. Dynamic occlusion was determined in lateral and protrusive movements of the mandible. The majority of the subjects had class I static occlusion for both incisor and molar relationship (45% and 54% respectively). Canine guided occlusion was the dominant type of dynamic occlusion (57%) and most of the subjects had no posterior contact in protrusive movement (78%). There was an association between canine guidance with class II static occlusion. Statistically, a significant relationship was found between the dynamic and static occlusion of the incisor (P< 0.001) but not with the molar (P> 0.05).3
In a study, the location of occlusal contacts in the intercuspal position in 29 young adults of aged 18 to 20 years was described. All participants had Class I essentially normal occlusion. The most striking finding was the high frequency of contacts on the mandibular first molar, which occurred in more than 20.9% of all contacts recorded. Most of the contacts were on cusps; only a few were in central fossae and marginal ridge areas. A surprising finding was the predominance of supracontacts on the second molars when compared to the remains of the dentition. No logical explanation for this finding would be offered. Morphologically good occlusion did not imply maximum contacts since an ideal occlusal contact was not found in any of the participants. Only serial studies showed whether occlusal relationships are stable throughout life or constantly changing.6
A study was conducted byHochman N,Ehrlich J to describe the tooth contact in intercuspal position. On examination the nature and location of occlusal contacts in intercuspal position showed pure cusp to fossa or cusp to marginal ridge area relation, most of the cases showed combination of relationships, including cusp to incline. Class I normal occlusion did not indicate the location and nature of contact of the supporting cusp in maximum tooth intercuspation.7
6.3 OBJECTIVES OF THE STUDY:
1) To evaluate the type of occlusal schemes in lateral and protrusive excursions clinically.
2) To evaluate and compare the type of occlusal schemes by mounting the casts using the condylar and incisal guidance record in lateral and protrusive excursion in Hanau Wide Vue articulator.
3) To evaluate the type of occlusal contact in maximum intercuspation position in Angle’s class I molar relation in permanent dentition.
MATERIALS AND METHOD:
7.1 SOURCE OF DATA:
Dentulous subjects required for the study will be selected from the College of dental sciences, Davangere, within the age group 18-30 years.
7.2 METHOD OF COLLECTION OF DATA (including sampling procedures ,if any) :
- A high quality photographs of the sectioned teeth.
Study will be conducted under the following headings :
a) Determination of type of occlusal scheme in lateral and protrusive excursion.
b) Determination of the type of occlusal surface contact in maximum intercuspation.
A)DETERMINATION OF TYPE OF OCCLUSAL SCHEMES IN LATERAL AND PROTRUSIVE EXCURSION:
i) The subject would be asked to seat in a chair in an upright position and would be instructed to close in maximum intercuspation position.
ii) And the patient would be instructed to slide the mandible laterally to each side, performing a working side movement and photographs will be taken on each working side.
iii) The type of occlusal scheme in working side movement on lateral excursion would be classified into canine-protected or group function.
iv) The canine protected occlusion would be identified when the maxillary and mandibular canines comes in contact and disocclusion in the premolar and molar teeth of the working side.
v) The group function occlusion would be identified when there are multiple tooth contacts on the working side.
vi) From the maximum intercuspal position, the protrusive movement of the mandible would be achieved till the edge -to-edge contact of the anterior teeth to determine posterior disocclusion.
This type of occlusion in lateral and protrusive excursion movements will be confirmed by mounting the casts with the help of facebow transfer, condylar and incisal guidance record on Hanau Wide Vue articulator.
B)DETERMINATION OF THE TYPE OF OCCLUSAL CONTACT IN MAXIMUM INTERCUSPATION:
i) The subject will be asked to swallow and occlude on posterior teeth.
ii) It will be clinically confirmed by examining the contact of the maxillary with the mandibular posterior teeth.
iii) Preliminary impression of maxillary and mandibular dentulous arches are made using elastomeric impression material. Facebow transfer is done to mount the maxillary casts in the Hanau articulator.
iv) First all the anterior teeth are removed in the mounted maxillary and mandibular casts. Starting from the first premolar region each cusp will be halved to mesial and distal parts using the saw, the photographs of mesial and distal occlusal contacts of all the posterior teeth will be taken.
v) Then the articulating paper is placed between each sectioned teeth to confirm the occlusal contacts.
Descriptive summary statistics will be given for all the variables. Difference in proportion will be tested using Chi-square test and Kruskal-Wallies ‘H’ test followed by Mann –Whitney ‘U’ test for intergroup comparison.
7.3 Does the study require any investigations or interventions to be conducted on patients or other humans or animals? If so, please describe briefly.
YES. Evaluation of tooth contact in lateral and protrusive excursion movements and type of occlusal surface contact in maximum intercuspal position and face bow record transfer to the Hanau articulator.
7.4 Has ethical clearance been obtained from your institution in case of 7.3?
LIST OF REFERENCES:
1) Yaffe A, Ehrlich J. The functional range of tooth contact in lateral gliding movements. J Prosthet Dent. 1987 Jun;57(6):730-3.
2) Ogawa T, Ogimoto T, Koyano K.Pattern of occlusal contacts in lateral positions: Canine protection and group function validity in classifying guidance patterns. J Prosthet Dent. 1998 Jul;80(1):67-74.
3) Al-Hiyasat AS, Abu-Alhaija ESJ .The relationship between static and dynamic occlusion in 14 -17 year old school children.J Oral Rehabil. 2004 Jul;31(7):628-33.
4) Wang M, Mehta N. A possible biomechanical role of occlusal cusp-fossa contact relationships. J Oral Rehabil. 2013 Jan;40(1):69-79.
5) Abduo J, Tennant M, Mcgeachie J.Lateral occlusion schemes in natural and minimally restored permanent dentition: a systemic review.J Oral Rehabil. 2013 Oct;40(10):788-802.
6) Ehrlich J, Taicher S. Intercuspal contacts of the natural dentition in centric occlusion.J Prosthet Dent. 1981 Apr;45(4):419-21.