The loss of teeth is the most common cause of a physiologic occlusion developing into a non-physiologic occlusion In a healthy complete dentition, there is a an equilibrium of forces from lips, cheeks, tongue, neighboring teeth those help to maintain a relative stability of individual teeth The loss of a single tooth may lead to drifting, tipping, rotation of neighboring teeth, and extrusion of opposite teeth. Tipping Rotation of a molar forward (mesially) or backward (distally) around its body mass axis called Center of Resistance All the teeth are held securely in the jawbone. With no adjacent support the neighboring teeth begin to drift toward the area of the missing tooth Disease, decay or trauma may lead to tooth loss. If a lost tooth is not immediately replaced, the surrounding bone begins to collapse and shrink The amount of bone loss and the pattern of drifting will vary depending on the individual and the location of tooth loss. The drifting of one tooth may lead to the drifting of several teeth, resulting in a significant amount of movement Periodontal disease may begin to form after the teeth have drifted and erupted because it becomes difficult to properly clean the gums and reach all the pockets in those areas. This may lead to tooth decay, receding gums, and further tooth loss. Some potential consequences: 1- Loss of mandibular first molar, meisal tipping of the mandibular second and third molars and the extrusion of the maxillary first molar. 2-Loss of occlusal vertical dimension 3-Opening of proximal contacts 4-Uneven adjacent marginal ridges 5- Development of “Plunger” cusps 6-Food impaction 7-Lack of functional cleansing of teeth These are less predictable because of individual variations Example: Age and time of tooth loss Periodontal conditions Inter cuspation of the teeth adjacent to the lost tooth and their antagonists An epidemiologic study (Zarb et al ., 1978) showed that 20% of patients with tooth loss at an early age had subsequent closure of the ensuing space. Occlusal conditions leading to or resulting from unilateral function represent significant deviations from the criteria of the “ optimal occlusion” Byron : 1969 An optimal occlusion is characterized by – Chewing performed with equal ease on both sides Bilateral stable occlusion contacts on most of the teeth in the intercuspal position Bilateral stable occlusal contacts on posterior teeth in the retrusive range in the retruded contact position and a small distance between intercuspal position and retruded contact position in the mid sagittal plane Even though the ability to adapt with in the masticatory system is great, the loss of even a single tooth may lead to occlusal instability and interferences with unfavorable consequences for occlusal function, chewing habits and oral hygiene The more teeth are lost, the greater the risk of tipping, migration, extrusion, and attrition of remaining teeth and the loss of alveolar bone and occlusal vertical dimension The more depleted the periodontal support, the greater the risk of trauma from occlusion Teeth with markedly reduced periodontal support, occlusal trauma will not cause further destruction of the attachment apparatus, provided the plaque induced periodontal disease has been cured The diverging options about the influence of a reduced dentition on the masticatory system prompted to perform a study on the relationship between shortened dental arches and oral function The results showed two patters of change in oral function. 1. Slow change until four occlusal units are left and then rapid change and 2. Progressive change without sudden change It is probably more accurate to emphasis the neuromuscular and functional sequelae of loss of posterior teeth. In some individuals posterior tooth loss is well compensated by adaptive processes, while in others it may contribute to functional disturbances. Natural Occlusion (organic) • • • Bilateral Posterior Centric Contact Anterior Guidance Mutually Protective Scheme of Occlusion Complete Denture Occlusion Complete denture “dentition” also presents in a variety of forms, but also exhibit certain common characteristics Complete Denture Occlusion • • • Bilateral centric contacts Bilateral eccentric contacts (balance) to provide stability of the denture bases during function Non-balanced monoplane occlusion Complete Denture Occlusion • Because of compromises inherent in restoring the edentulous arch, complete denture tooth forms and arrangements (i.e. occlusion), should be designed to provide function and aesthetics while minimizing denture base tipping (lateral) forces Fundamental differences of natural and complete denture occlusion 1. Sensory feedback mechanism 2. Derivation of : • retention • stability • support 3. Reaction of supporting structures to masticatory forces 1. Sensory Feedback Precision of feedback is significantly compromised following loss of teeth and associated structures (periodontal ligament) 2. Derivation of retention, stability and support for natural occlusion For natural dentition, retention, stability, and support are derived through the periodontium which provides; Sensory feedback mechanism Difference in reaction of supporting structures to masticatory forces Differences in load transfer mechanism and physiology Complete dentures receive their retention, stability, and support from the soft tissues overlying residual bone (ridges, buccal shelf, palate, etc.). Denture Bearing Surface • Retention Resistance to dislodgment forces in a vertical direction away from the bearing surface Denture Bearing Surface • Stability Resistance to laterally oriented dislodgment forces Denture Bearing Surface • Support Factors of the Bearing Surface which resist forces in a vertical direction towards the bearing surface 3. Reaction of supporting structures Natural occlusion Physiologic levels of tension results in alveolar bone apposition (such as that transmitted by loading the periodontal ligament through natural dentition) Complete denture occlusion Non-physiologic compression as may occur under denture bases results in further residual ridge resorption (RRR Summary Denture “Dentition” Natural Dentition • • • • • • • Retained in PDL Units move independently Malocclusion effects not immediate Non-vertical forces affect only teeth involved and usually well tolerated Incising doesn’t affect posteriors Bilateral balance is rare Tactile sensitivity • • • • • • • Mobile bases on mucosa Teeth move as an unit Malocclusion affects entire base immediately Non-vertical forces affect all teeth and are traumatic Incising affects all teeth attached to base Bilateral balance is often desired for base stability Decreased tactile sense A study conducted by Al-Shammari et al., (Journal of Periodontology 2005; 76(11); 1910 – 1918) identified 9 major aspects that influence the condition of tooth loss. They are – 1. 2. 3. 4. Age Male gender Smoking Lack of professional maintenance. 5. Inadequate oral hygiene 6. Diabetes Mellitus 7. Hyper tension 8. Rheumatoid arthritis 9. Anterior tooth type Smoking and Tooth Loss: Another study by M. Ojima et al (BMC Public Health 2008) provide evidence regarding the association between smoking and tooth loss among adults aged 20-39 Smoking rates differed greatly in men (53.3%) and women (15.5%). The overall prevalence of tooth loss was 31.4% (31.8% men and 31.1% women). Tooth loss occurred more frequently among current smokers (40.6%) than former (23.1%) and non-smokers (27.9%). Tooth loss and Social behavior: The loss of many teeth often reduces the quality of life; embarrassment and selfconsciousness limit social interaction and communication. Tooth Loss and general Health: Tooth loss is a significant problem related to general health and the quality of life. Because of chewing problems and decreased masticatory function, a limitation in food selection may occur, resulting in nutritionally poor diets Poor nutrition contributes to an increased risk of several systemic diseases such as cardiovascular diseases and hypertension. F. Bodic et al., Joint Bone Spine 2005(72); 215-221 Alveolar bone play a key role in providing support to the teeth, which are anchored to the bone by desmodontal fibers. Alveolar bone in the maxilla and mandible is subjected to major local loads. This play the leading role in maintaining local bone mass, even in patients with osteoporosis. There is a general agreement that the presence of systemic bone disease influence the rate of alveolar bone resorption after tooth extraction.