1st Occlusion Lecture PDF

Faculty Of Dental Medicine Oral Biology Department Lecture: (Occlusion – Part I) Ass. Prof (Fatma Adel Saad) Occlusion I  By Dr. Fatma Adel Saad Associate professor of Oral Biology ARRANGEMENT AND OCCLUSION OF TEETH Curves (curvatures) of arrang...

Faculty Of Dental Medicine Oral Biology Department Lecture: (Occlusion – Part I) Ass. Prof (Fatma Adel Saad) Occlusion I  By Dr. Fatma Adel Saad Associate professor of Oral Biology ARRANGEMENT AND OCCLUSION OF TEETH Curves (curvatures) of arrangement & occlusal planes of Teeth 1- Curves (curvatures) of arrangement of teeth 1- Curves describe arrangement & alignment of teeth Dental arch form (dental arch formation) 2- Curves (curvatures) of occlusal planes of teeth 2- Curves describe the Curved occlusal planes (Compensating curvatures) Mandible moves in a curved path  so, incisal & occlusal surfaces of teeth adapt themselves to these curved planes (paths) 1- Curves of arrangement of teeth / Alignment of teeth / Dental arch formation A- Bonwill triangle. (Lower dental arch) B- Parabolic curve. (Upper & lower dental arches) A- Bonwill triangle (only mandible) 4 inches ,, kk Bonwill triangle (Only mandible) Condyle *Arrangement of lower teeth  form mandibular dental arch which adapts itself to an equilateral triangle of 4 inches in length. *Triangle apex is located at mesial contact areas of both lower central incisors *The angles of the triangle base found at the centers of each condyle.  B- Parabolic curve (maxilla & mandible) *The upper dental arch is somewhat larger than the lower dental arch  On occlusion, upper teeth are outside the lower teeth. *SO, upper teeth overlap lower teeth. * Horizontal distance between upper &lower anterior teeth is named overjet. * Vertical distance between upper &lower anterior teeth is named overbite. Horizontal overlap: Vertical overlap: “overjet” “overbite” *Average of overjet & overbite  2-4 mm *Overjet & overbite prevent the lips and cheeks from being clipped during mastication. Overbite & Overjet 2-4 mm Overjet & overlap  Relationship of Anterior teeth Maxillary anterior teeth overlap mandibular teeth: Horizontal overlap: “Overjet” The incisal edges of maxillary anterior teeth are labial to incisal edges of mandibular teeth. Vertical overlap: “Overbite” The incisal edges of the maxillary anterior teeth extend below the incisal edges of the mandibular anterior teeth. Parabolic curve 4 4 Maxillary jaw 6 6 Mandibular jaw 6 6 4 4 4 4 *Both upper and lower dental arches have a horse - shoe shaped and adapt (conform) to parabolic curves. *The parabolic curves of each dental arch divided into three segments overlapping each other. *Anterior segment: semicircular curve passing along the facial surfaces of anterior teeth & first premolar. *Middle segment: Straight, continuous with anterior segment & overlap it -It passes along facial surfaces of the first, second premolars & mesial half of the first molar. - This line is straight & slightly outside/ slightly deviated buccally. *Posterior segment: -It continuous with middle segment & overlap it. -It passes along the facial surfaces of the first, second and third molars. -It is a straight line which is:  Slightly deviated lingually in upper jaw.  Nearly parallel to the median line in lower jaw.  Why ?? (in parabolic curves) Posterior segment of upper dental arch; outline of buccal surfaces of the upper molars curves toward the midline (slightly deviated lingually) comparing to that in the lower arch Due to: 1- DB convergence of the upper first molar. 2-Second and third maxillary molars are located lingual to the first molar to establish a proper contact. 3- As we go posterior; *The increase of the distal convergence in upper molars. *The decrease of the buccolingual dimension in upper molars. Phases of Development Of Permanent teeth into Dental arches Phases of Eruption of Permanent Teeth 6  1,2  4,5  3,7 8 FIRST PHASE *The first permanent molars erupts at 6 years of age. *They support the deciduous dentition *They increase the chewing efficiency to adapt jaw growth. Second phase *The permanent central and then lateral incisors erupt at first lingual to the deciduous predecessors. *Erupt with 1.6mm crowding in average. particularly in lower incisor segment. *The permanent location and alignment of the incisors cannot be established until dental arch development is completed. Third phase The 1st and 2nd premolars take the places of the deciduous molars. The premolars are significantly smaller in M-D dimensions than primary molars they replaced The difference in size is called Leeway space of Nance with average: 0.9 mm on each maxillary quadrant 1.7 mm on each mandibular quadrant  E D 6 5 4 6 6 5 E  Leeway space of Nance 5 4 2 1 2 1 5 4 Leeway space of Nance is utilized for alignment of permanent incisors as these teeth erupt with an average of 1.6mm of crowding in incisors segment.  Leeway space of Nance The remainder of the space will be utilized by the molars to adjust the proper occlusal relation of maxillary and mandibular permanent molars particularly 1st molar??. Fourth phase The canines (corner stones) force themselves by wedging between the lateral incisors and first premolars in both jaws. Also the second molars erupt distal to the first molars supporting them during the wedging of canines.  Fifth phase Eruption of the wisdom tooth N.B: Permanent dental arch is completed at fourth phase ( end of 12 years with eruption of 3 & 7 )  Primate space *It is noticed during the development of deciduous occlusion. *For maxillary teeth : space  between upper B &C. *For mandibular teeth: space  between lower C & D. *Its function is to preserve a space for the permanent teeth for proper occlusion. C B D C 2- Curves of Occlusal Planes (Compansatory occlusal curvatures) 2- Compensating curvatures / Compansatory curvatures / Curves of curved occlusal planes A- Curve of Spee B- Curve of Wilson C- Curve (Sphere) of Monson  Compensating curvatures of the dental arch (Curved occlusal planes) *The occlusal surfaces of dental arches not follow a flat plane but: *Occlusal surfaces of lower dental arch follow a curved plane (concave). *Occlusal surfaces of upper dental arch follow a curved plane (convex). The two curved planes become identical in centric occlusion. A- Curve of Spee * *  Curve of Spee *In the sagittal plane. *Observed from a point opposite the first molars. *Incisal ridges of anterior teeth & buccal cusps of posterior teeth follow a curve ends at the anterior border of condyle. * *This curve complement the path of the mandibular condyles in the anterio-posterior movements of the mandible.  B- Curve of Wilson *In the coronal plane *For each posterior tooth: The occlusal surfaces of both right & left teeth adapt to a curved plane (convex  upper), (concave  lower). 6 6 6 6 *This curve becomes deeper as we go posterior WHY? the inclinations of posterior teeth becomes greater as we go posterior (molars > premolars). *The crowns of mandibular posterior teeth incline lingually. *The crowns of maxillary posterior teeth incline buccally. *The buccal cusps of mandibular molars and the lingual cusps of maxillary molars appear to be longer. *This curve complement the paths of mandibular condyles in the lateral of movements of the mandible C- Curve (Sphere) of Monson + Sphere of Monson *It is combination of both curve of Spee & curve of Wilson. *Is seen within coronal & sagittal planes. Curve of Wilson Curve of Spee Wilson Curve of Spee  Sphere of Monson *It is a segment of a sphere with a 4 inches radius and the center of the sphere at the glabella. *It is the combination of curve of Spee & curve of Wilson forming a segment of a sphere with a radius of 4 inches & with the center of this sphere at glabella. *As the curvature of occlusal plane is concave for the mandibular arch & convex for the maxillary arch  two curved planes become identical in centric occlusion.  Age changes With age and as a result of attrition, the cusps of the teeth are worn away, so that the curvatures of the occlusal plane are lost and the plane becomes flat. Sample of questions 1-Bonwill described the mandibular dental arch to be adapted to a 4 inches equilateral triangle, its angles are located as follows: a- The angles of the base are located at the anterior border of the condyles while the apex at the mesial contact areas of the lower central incisors. b- The angles of the base at the centers of the condyles while the apex at the mesial contact areas of the lower central incisors. c- The angles of the base at the center of the condyles and the apex at the cingulum of the lower central incisors. d- The angles of the base at the coronoid while the apex at the mesial contact areas of the lower central incisors. 2-The Leeway space occurs during……………of the dental arch development: a- The third phase. b- The sixth phase. c- The fourth phase. d- The fifth phase. 3-Curve of …………Monson…..is the combination of curve of Spee and curve of …Wilson…….it is within the …sagittal………..and…coronal……planes. 4-The phase in the development of the permanent teeth into the dental arches characterized by the eruption of first permanent molars. First phase.