Australian Dental Journal, February, 1978
Volume 23, No. 1
Periodontology and its relevance to clinical dentistry Vincent C. Amerena, M.D.Sc., L.D.S., F.R.A.C.D.S.
ABSTRACT-The important role played by restorations and prostheses in the accumulation of plaque necessitates careful design of all contours to enable proper removal of plaque by the patient. Early diagnosis of impacted teeth is essential as well as careful design of gingival flaps preserving the maximum of attached gingiva where their removal or exposure is planned. Difficulties arising from closed bite and orthodontic treatment, the need for careful consideration to the importance of endodontic therapy, and removable partial dentures in relation to the health of periodontium, are discussed.
Periodontology is the study of the anatomy and physiology of the periodontium plus the prevention and treatment of the diseases of the periodontium. By the periodontium is meant the structures supporting the teeth, i.e. the cementum, the periodontal ligament, the alveolar bone and the soft tissue, the gingivae investing the alveolar bone. This is an extension of the original notion that periodontics was concerned only with the treatment by excision of hyperaemic and hypertrophic inflamed gingivae. Whilst there will always be a need for the specialist periodontist to carry out specific intricate surgical procedures o n individual patients, the future periodontal health of the general public depends on the prevention of periodontal disease and prevention is the realm of the general dentist. As much periodontal disease is iatrogenic in origin the general practitioner must be aware of the periodontal implications of all the clinical procedures he practises. Periodontology may be considered as the hub of the wheel of dentistry in the sense that there is n o clinical procedure carried out on teeth or gums which does not directly or indirectly affect the periodontium. The individual branches of dentistry may be considered as the radiating spokes of the wheel and plaque the offensive mechanism which
threatens the longevity and efficient working of the wheel (Fig. 1). Bacteriological research has elucidated the mechanism of colonization of the tooth surface by bacteria. However, the importance of the mechanical removal of deposits from the teeth has been recognized from the earliest days of dentistry. Promising as is modern research on the chemical control of plaque growth, it must be realized that it is impossible and indeed undesirable to have a sterile mouth. There is a balance between the offensive mechanisms of plaque and the resistance of the host so that the tooth gingiva interface can exist in equilibrium with a certain amount of young plaque. It is well established that plaque plus sucrose leads t o dental caries and Loe, Theilade, and Jensen 19651 have shown definitively in volunteer subjects that if oral hygiene procedures cease, then initially healthy gingivae will show the changes of acute gingival inflammation after five days. Further, if oral hygiene procedures are then instituted, resolution of the inflammation occurs. These macroscopic changes detectable by the eye are the late stages of complex biochemical changes which have been proceeding at a microscopic and
Loe H. Theilade E and Jensen S 8.-Experimental g'ingiJitis in man." J . Period.. '36'3, 177-187 (MayJune) 1965.
Australian Dental Journal, February, 1978 C L I N I C A L DENTISTRY
Fig ].-The interrelation between periodontology and the various branches of dental practice.
sub-microscopic level for some days. Thus, from a periodontal viewpoint plaque older than five days produces gingival inflammation but as a clinical guideline the presence of plaque on teeth, as indicated by disclosing solution should be regarded as the potential for gingivitis. Any plaque control program must be based on the mechanical removal of plaque because clinical experience shows that it is still the most effective and efficient method of controlling plaque growth Using a multi soft type toothbrush with a small head, any method of toothbrushing which removes plaque made visible by disclosing solution is acceptable but vigorous, horizontal scrubbing with the toothbrush must be avoided. Dental floss, interdental stimulators and interdental brushes should be advised according to the needs and manual dexterity of the individual patient. Dietary advice is important for Carlsson, and Egelberg 19652 have shown that high sucrose diets produce rapidly growing soft gelatinous plaque, whilst high protein, low sucrose diets produce thin films of slowly growing plaque. As no specific individual organism can be incriminated as being responsible for gingivitis, the presence or absence of a particular organism cannot be used as an index of the gingivitis potential of a particular plaque. This is in contrast to caries where some authorities believe that Streptococcus mutam can be used as an indicator of caries potential. Thus all plaques when present for two or three days must be regarded as potential gingivitis inducers
'Carlsson, J., and Egelberg. J.-Effect of diet on early plaque formation in man. Odont. Revy. 16: 112-125, 1965.
and any dietary mdifications which will slow the growth of plaque are valuable for the individual patient. Many agents, for example ammonia ureas, dextranases and antibiotics have been investigated in the search for an effective chemical plaque control agent. The most efficient chemical with the least side effects so far discovered is chlorhexidine digluconate. Many studies have shown that chlorhexidine digluconate will arrest the growth of bacterial plaque in individual patients but it is not a panacea for all periodontal ills to be used as a public health measure. Nevertheless, chlorhexidine digluconate is valuabl, 11 the treatment of some acute gingivitis and a i l l help prevent the growth of bacterial plaque in those patients who are unable to carry out normal oral hygiene procedures, e.g. in patients with acute Vincent's infection, acute periodontal abscess or post periodontal surgery. Long term use is inadvisable because of the possibility of changes in oral flora, the emergence of bacterial resistance and the overgrowth of fungi such as candida albicans. However, in 1976 Loe, Schiott, Glavind and Karring3 reported on a study of the use of chlorhexidine in man over two years. They showed that chlorhexidine reduced plaque and gingivitis but tended to stain teeth. In addition the group using chlorhexidine showed a greater amount of supra gingival calculus but there were no other local side effects related to structure and function of the oral mucosa nor any systemic side effects. Fluorides applied topically affect plaque growth. Fluoride in vifro will inhibit many enzymes essential t o cell metabolism and growth. In particular it inhibits enolase which is involved in the glycolithic pathway of energy production. All enolase containing bacteria are susceptible to fluorides SO that in its antibacterial action fluoride is not specific. There is some evidence that fluoride lowers the surface energy of tooth surfaces, thereby making bacterial attachment and plaque formation difficult. This effect is not specific but as gram positive cocci are normally the initial colonizers of plaque they are preferentially discriminated against by topically applied fluoride. As the level of fluoride in water supplies and in fluoride dentifrices is below the effective antibacterial level, daily painting of the teeth with either stannous fluoride or sodium fluoride or acidulated phosphate fluoride is necessary to deliver the requisite amount of fluoride.
H . Schiott C. R., Glavind, L., and Karrin
f w o 'years uAe of chlorhexidine in man. 1. Eeneral design and clinical effects. J . Period. Res.. l 1 : 3 , 135144 -(June) 1976.
Australian Dental Journal. February, 1978 The periodontiurn and restorative procedures It is essential that all gingival tissues be healthy prior t o commencing restorative procedures. Immediate soft tissue damage following operative causes is very dependent on operator care and skill. Trauma may be caused by careless cavity preparation resulting in actual cutting of the tissues by the bur or hand instruments, or by the vigorous placement of matrix bands and interdental wedges. Further, impression taking and the use of gingival retraction cord under pressure can cause damage t o the gingival tissue. Mostly the damage is reversible but the possibility of permanent loss of tissue is increased if the tissues are unhealthy prior to commencing treatment. Whether the presence of a carious lesion actually causes periodontal disease is not clearly e!ucidated. Some studies have shown4 a higher incidence of gingivitis adjacent t o carious lesions than adjacent t o sound teeth, but other studies have shown5 no differences between the two groups. Restorative materials themselves theoretically may affect the periodontal tissues by chemical action, or because of physical characteristics such as surface roughness. Some research workers have found that gold foil is better tolerated by the gingival tissues than either silicate, acrylic resin or amalgam. However, there is little evidence that cast metals and porcelains used for full tooth coverage restorations are intrinsically irritating t o soft tissue. The importance of proper interproximal contacts in the prevention of food impaction is well recognized but, equally important, is the interproximal contour of the restoration. The height of the contour in most teeth is in the cervical third of the crown and the faciolingual dimension at the height of contour is no more than 1 mm greater than at the cemento-enamel junction. In addition the proximal contact is in the occlusal third of the crown except distal t o the maxillary first molar and the proximal contact area is buccal to the central fossa line except between the maxillary first and second molars. Further, there is a larger lingual embrasure than buccal embrasure. Attention to these anatomical contours will minimize plaque retention. However, despite anatomically normal contact relations the contacts between teeth in occlusal interference sometimes open and food impaction occurs. In the short term
food impaction causes periodontal irritation but if allowed to persist bone loss will occur. Nevertheless, open contacts without food impaction are of no periodontal significance (Fig. 2). The most critical periodontal decision in general restorative dentistry is where t o place the gingival margin of a cavity. Many studies have shown that gingival inflammation is associated with subgingival placement of restorations. A. D. Black in 19126 cited faulty margins of fillings and crowns as the cause of gingivitis but G . V. Black's concept of extension for prevention has been the guiding principle for the placement of margins of restorations for many years. Surveys have been carried out on restorations in patients' mouths7,*.9, and it
Fig. 2.-Periodontal pocket associated with poor contour of amalgam restoration.
has been stated that up to 60 per cent of all restorations have overhanging margins and that gingivitis is associated with 80-90 per cent of these. Gilmour and Sheihamlo showed a significantly greater severity of destructive periodontal disease associated with overhanging restorations in posterior teeth than adjacent t o the homologue unrestored tooth surfaces. However, they were unable to demonstrate statistically significant differences in gingivitis around such teeth. This may have been because some overhanging margins were supragingival for the position of the overhanging margin in relation t o the gingival margin is import ant. Subgingival placement of crowns does not afford a reliable protection against new caries and a large percentage of the margins which have been placed subgingivally become supragingival after some
A. D.-Preventive treatment of periodontal disease. Dental Review 26: 861 1912. Harvey, L. C., and Hession, R'. W.-Effects of faulty operative techniques on the periodontal tissues. Austral. D. J. 7:3 228-233 (June) 1962 . I Wrights,' W.' H.-Local factors in periodontal disease. Periodontics, 1: 163, 1963. Newcombe. G . M.-The relationship between the location of subgingival crown margins and gingival inflammation. J. Period., 45:3, 151-154 (Mar.) 1974. l o Gilmour, N., Sheiham, A.-Overhanging dental restorations and periodontal disease. J . Period., 42:k 8-12 (Jan.) 1971.
Russell, A. L.. and White, C. L.-Fluorides and periodontal health. In, Fluorine and dental health; the harmacology and of fluorine. Edits., huhler, J . C., and ~ $ ~ ~ K. ' ~Bloomington, . y University of Indiana, 1959 (pp. 115-127). r. White. C. L., and Russell. A . L.-Some relations between dental caries experience and active periodontal disease in two thousand adults. New York. J. Den., 32:6, 211-215 (June-July) 1962.
Autralian Dental Journal, February, 1978
Gingival inflammation and faulty coronal anatomy. b, Healthy gingival tissues two years after restorations.
years. The gingival inflammation associated with subgingival margins is related to the plaque retention potential of the restorations. Even when subgingival margins appear perfect clinically, scanning electron microscopic studies have shown that there is quite a sizeable gap between the margin of the restoration and the cavity margin. This gap is relatively large compared with the size of bacteria found in the plaque. In addition, the patient is handicapped in his oral hygiene maintenance by this subgingival margin and technically it is much more difficult t o ensure a perfect fit and a perfect finish when working subgingivally. Ideally, when teeth with initial carious lesions a r e to be restored the margin of the cavity should be kept supragingival t o protect the gingival tissues. Caries in the enamel apical to the cavity margin can be prevented by regular applications of topical fluoride and efficient plaque removal with dental floss or interdental brushes. If caries or old restorations extend subgingivally then hypertrophied tissue may be excised with the electrosurge. However, consideration should be given t o the removal of gingival tissue and even some alveolar bone, particularly in elderly patients, in order t o place the cavity margin and the restoration supragingivally. The margins of all crowns must be supragingival whenever possible. Clinically this is possible on the lingual aspect of teeth and often on the buccal aspect of posterior teeth when aesthetics are not important. However, in the anterior region of the mouth aesthetics often demand that the margin of the crown be placed below the free margin of the gingiva. In these instances perfect fit is essential and the subgingival contour of the crown is important. If this is flat then the free marginal gingiva tends to form a roll around the tooth but when the subgingival contour is too thick, because
of excessive bulk of restorative material, gingival inflammation results. Wagmannll believes that the subgingiva! convexity of a tooth or restoration should extend facially or lingually no more than one half of the thickness of the gingiva. Similarly the supragingival contour of the crown is important and one of the commonest faults is over contouring of the restoration. Sometimes this is carried out under the mistaken idea that the extra bulk of the crown gives protection t o the gingiva. However, clinically we find that gingival recession and root abrasion with quite large labial or lingual defects does not result in gingival irritation. Further, whilst deciduous molars have a large buccal bulge, the teeth a r e inclined lingually so that any so-called protective effect of the buccal bulge is obviated. Over contouring of restorations results in plaque retention and gingival inflammation (Fig. 3 ) . In contrast there is no periodontal hazard from increasing the space available for the interproximal papilla. Clinically, there must be a compromise between aesthetics and the ability of the patient to keep the area free of plaque. Ideally, embrasure spaces between crowns and between pontics and crowns should be large enough for the patient to clean either with interdental brushes or floss but for periodontal health it is better t o have wider spaces rather than narrow, inaccessible spaces. Further, pontics should be designed so that they cause minimum plaque retention and they should be clear of the gingival tissue. Histologically, it has been shown that all materials in contact with the alveolar ridge will produce some inflammatory response but this is probably due to the retention of plaque in those areas.
Wagman, S.-The role of coronal contour in gingival health. J. Pros. Dent., 37:3, 280-287 (Mar.) 1977.
Australian Dental Journal, February, I978
Periodontology and Oral Surgery
Whenever a tooth is extracted alveolar bone must be spread and the periodontal ligament ruptured to enable the tooth to be withdrawn from its socket. The pressures exerted during extraction force bacteria in the gingival crevice into the bloodstream, producing a bacteraemia. It has been demonstrated quite conclusively that the more severe the gingivitis and periodontitis in a particular patient, the greater the likelihood and the greater the magnitude of bacteraemia following extraction of teeth. In healthy patients the bloodstream bactericidal factors will effectively kill bacteria within 1-2 minutes but in those patients with valvular lesions, congenital heart disease or prosthetic valve replacements, such a bacteraemia can result in endocarditis. In addition, it is good surgical practice to carry out elective dental extractions only when the periodontal tissues are as healthy as possible. This will minimize bacteraemia, lessen the risk of post-operative haemorrhage and aid post-operative healing. The evidence relating pre-extraction periodontal disease to post-extraction alveolitis is inconclusive.
A complication sometimes following the extraction of unerupted wisdom teeth is the development of a true periodontal pocket on the distal of the remaining second permanent molars. If extraction of impacted third molars is delayed until there is a n unerupted or semi-erupted tooth lying hard against the distal surface of the second molar and if there is already present considerable bone loss and infection, then the extraction of such a tooth inevitably results in the production of a periodontal pocket. In some instances when the wisdom teeth are semi-erupted it is possible to leave buccal and lingual attached gingiva in ~ i t uso that there is a possibility of healing by secondary intention without pocket production. It is important not to tie sutures too tightly in order to minimize the risk of pulling buccinator muscle over the extraction site and reducing the amount of attached gingiva present. From the periodontal viewpoint, early diagnosis of future impaction of unerupted third molars is important. If such a diagnosis can be made at age 13 or 14 years then removal of these teeth often can be carried out without removing the crest of bone immediately distal to the second molar; thus obviating the formation of a periodontal pocket (Fig. 4). In the removal of lower third molars flap design is very important and must be modified according to the difficulties of the extraction of the tooth. However, keeping the distal extension of the incision well to the buccal side of the alveolus will help preserve the attached gingiva. Sometimes the
Fig. 4.-Bone involvement on distal of lower right second molar associated with unerupted and impacted third molar,
envelope type of flap rides up distal to the reniaining second molar and excision of this mass of tissue may result in a lack of attached gingiva post-operatively. Whenever unerupted cuspids or bicuspids are to be surgically exposed t o allow eruption or orthodontic positioning, attached gingiva must be preserved as far as possible. Mere excision of soft tissue usually denudes the impacted tooth of its attached gingiva, thus predisposing to periodontal pocketing. If a full thickness or partial thickness mucosal flap is outlined with its base high in the mucobuccal fold and its apex palatal to the crest of the alveolar ridge then it can be repositioned apically so that the attached gingiva lies immediately over the cervical margin of the exposed crown. Sutures are placed apical to the attached gingiva to fix the flap in this apical positionlz. Periodontology and endodontics
In a root-filled tooth the sealing agent used is in contact with the periodontal ligament and any inflammatory change or irritation first takes place in the periodontal ligament. Histological studies have been reportedl3.14 on the effects of root filling materials and antiseptics on the periodontal tissues. Periapical abscesses following pulp necrosis may drain through the gingival crevice for this is the path of least resistance. When such drainage occurs through the bifurcation or trifurcation of molar teeth, it is often clinically difficult to determine whether the pus is periodontal or periapical
Kincaid, L. C.-Flap design for exposing a labially impacted canine. J . Oral Surg., 34:3, 270-271 (Mar.) 1976. Hand, R . E., Huget, E. F., and Tsaknis, P. J.-Effects of a warm gutta-percha technique on the lateral periodontium. Oral Surg., Oral Med., Oral Path., 42:3, w 5 - m (Sent.) 1976. Tagger,. M.;--Massler M.-Periapical tissue reactions after pulp exposure' in rat molars. Oral Surg., Oral Med., Oral Path., 39:2, 304-317 (Feb.) 1975.
Australian Dental Journal, February, 1978
Fig. 5.-a Periapical abscess on buccal of lower left first molar. b. Silver point in ;inus and area of bone destruction associated with periapical infection. c, Complete resolution of bone 22 months after endodontic therapy.
in origin. If the tooth is non-vital then it is more likely that the lesion is pulpal in causation and competent endodontic therapy will result in resolution. However, it is possible for periapical abscesses t o occur on periodontally involved teeth and usually it is best t o carry out endodontic treatment first. If resolution does not occur in 6-8 weeks then normal periodontal treatment of a bifurcation or trifurcation defect should be carried out. This might involve surgery plus hemisection of the tooth or resection of one root (Fig. 5 ) . The immediate insult to the periodontiurn of rubber dam clamps is usually reversible but if stainless steel bands are placed in order to prevent splitting of crowns, it is important that these should not be left in place for a long period. Gingival inflammation followed by bone loss can result if these bands are in place for several months. The threat t o the periodontium is increased by placing such bands subgingivally, as might occur in the treatment of fractured teeth. The periodontal prognosis of fractured teeth is enhanced if the fracture line can be made supragingiVal. This may be done by excision of tissue and sometimes alveolar bone and in some instances by the orthodontic extrusion of the tooth. Periodontology and Orthodontics
There are few exclusively periodontal reasons
for undertaking orthodontic therapy. The presence of malposed or rotated teeth makes plaque control difficult and there is increased potential for periodontal disease but if a patient has superb oral hygiene, it is possible to maintain a healthy periodontium despite such malocclusionsl~. Overbite and overjet per se produce no ill effects but if the defect is such that the upper anterior teeth are stripping away the periodontal tissues from the labial aspect of the lower anterior teeth, then orthodontic treatment is indicated. Similarly, if there is a closed bite and the lower anterior teeth are contacting the gingival margin lingual t o the upper anterior teeth, orthodontic treatment must be instituted. However, if the lower anterior teeth are biting into the palatal tissues 3-4 mm lingual to the gingival margin, then whilst palatal ulceration and pain might result, no actual damage is done to the periodontal tissues (Fig. 6 ) . When lower anterior teeth are labially placed outside basal bone there is often gingival recession with progressive loss of attached gingiva (Fig. 7 ) . If the tooth is moved bodily into its correct position within the bone there will often be re-growth of alveolar bone and re-growth of gingival tissue. Thus the treatment of such problems is often orthodontic rather than periodontic. A similar defect 1:
Levine S.-The orthodontist, malocclusion and periodontal disease. Aust. Orthod. I., 2: 203-1207 (Feb.) 1971.
Australian Dental Journal, February, 1978
b, Stripping of labial gingiva
is sometimes produced by orthodontic expansion of both arches to give a full look to the smile. In these instances sometimes the lower anterior teeth are brought outside basal bone, producing bone loss and gingival recession. Further, in the treatment of Class 111 malocclusions, when the I.ower anterior teeth are inclined lingually rather than the teeth being moved bodily backwards, then sometimes the roots move forwards and beyond alveolar bone with subsequent loss of gingival tissue.
placed lower right central with mucogingival involvement.
When orthodontic movement of labially placed incisor teeth is not possible, as might occur particularly in some older patients, mucogingiva! surgery is necessary. When mandibular first molars are lost prematurely there is often mesial and lingual tipping of the mandibular second molar. This produces an uneven marginal ridge height with a tendency for food impaction on the mesial and often a deepened gingival crevice results. Occlusal forces will act as
tipping agents on such a tooth and there is also a tendency for balancing side interference to develop on the distobuccal cusp. If such a tooth can be righted orthodontically the pocket depth on the mesial will be reduced considerably. When such a tooth is used as a n abutment for a bridge the mesial wall of the preparation must be such that there is no overlaying of the gingival tissuesls. When orthodontic bands are placed on teeth plaque control must be excellent fiorr the tooth-band interface is an ideal area for plaque growth. As orthodontic treatment is carried out at or about the time of puberty, there is often an exaggerated hormone mediated inflammatory response to minimal plaque deposits. Some gingival irritation is unavoidable during orthodontic repositioning of teeth but it can be minimised by keeping the bands as far away as possible from the gingival margins. However, when tooth crowns are very short incisogingivally, it is sometimes impossible t o avoid placing the bands under the gingival margins. I n these situations consideration should be given to using acrylic brackets bonded to tooth enamel. Following removal of full bands there is often much gingival inflammation and occasionally hypertrophy. Usually the gingival tissues return to normal but if gingival bleeding and loss of contour still persist 3-4 months after removal of orthodontic bands then periodontal consultation should be sought. The periodontal effects of retention appliances must not be ignored. Very often these are removable acrylic type dentures which are tissue born and which are worn 24 hours a day. These can cause intense gingival inflammation and at times severe stripping of tissues from the lingual of
Ramfjord, S. P.-Periodontal aspects of restorative dentistry. J . Oral Rehab., 1: 107-126 (Apr.) 1974.
Australian Dental Journal, February, 1978
teeth. Fixed retention if possible is less hazardous periodontally. Further, when teeth have settled into position following removal of bands consideration should be given to occlusal adjustment by grinding in order to eliminate any lateral forces which might be damaging to the periodontium.
most destructive but also difficult to minimize. Due to elasticity of the denture bearing soft tissue, downward movements occur during mastication; these cause rotational stresses on the abutment teeth which are proportional to the mesio-distal length of the free end saddle (Fig. 8 ) .
Rotated teeth have a marked tendency to return to their original position. It is thought that some of the supra crestal fibres of the periodontium are stretched, and being elastic have a tendency to rotate the tooth back to its original position. Excision of these fibres seems to considerably reduce the rotation of these teeth back to their original positionl7. Periodontology and prosthetics
All partial dentures are potentially harmful to the periodontium for they provide a toothprosthesis interface which is a potential site for plaque growth. Tooth born dentures of skeletal design with occlusal rests and with minimal coverage of gingival tissues are less harmful than tissue born acrylic type partial dentures. Patients must be taught to use disclosing solutions to identify plaque growing on the lingual surfaces of all prosthetic appliances. However, as a toothbrush does not reach all areas on the insides of clasps and occlusal rests it is necessary to use other aids such as cotton buds or interdental brushes.
Prostheses may cause irritation to the periodontium by food impaction but badly designed indirect retainers and clasps may actually impinge on gingival tissues or cause plaque retention. There is an increased incidence and severity of periodontal disease about abutment teeth for prostheses but the damage is greatest in the free end saddle situationls. Free end saddles may move away from the underlying tissue in three directions:1) away fcom tissue as in chewing toffee; 2) towards the tissue as when biting or chewing; 3) in the horizontal plane (backward, forward and sideways to left and right). Upward movements and those in the horizontal plane are controlled by clasps, occlusal rests and maximum tissue coverage, but downward movement of the denture base is not only potentially
tissue damage from partial lower denture.
The load must be distributed over as many teeth as possible, the denture base must be maximal in area and the teeth narrow but-lingually. Stress breakers are often employed but they are sometimes mechanically complex, often expensive and usually fragile. Further resorption of bone underlying the denture base will still occur, necessitating the remodelling of the appliance. The retention of even one endodontically filled root with a gold root cap at the distal end of a saddle area will give some support to the distal end of the prosthesis and lessen periodontal traumal9. Conclusion
All clinical dental procedures directly or indirectly affect the periodontium. Immediate trauma to the gingivae must be minimized during therapy and all restorations and appliances must be designed to minimize plaque retention and to aid plaque removal by the patient. Iatrogenic periodontal disease can be eliminated by a preventive philosophy. Acknowledgements
Walsh E. A.-Pericision: an aid to the reduction of rotaiional relapse in clinical practice? An assessment. Brit. J. Orthod.., 2: 135-140, 1975. 18 Reitz. P. V.. Weiner. M. G.. and Levin. B.-An overdenture survey: preliminary report. J: Pros. Dent., 37:3. 246-258 (Mar.) 1977. 10 Guyer,’ S. ET-&lectively retained vital roots for partial support of overdentures: a patient report. J. Pros. Dent., 33:3, 258-263 (Mar.) 1975. li
Thanks are due to Drs D. Behrend, A. Cattermole, E. Ehrmann, and M. Hase for permission to use the photographs which accompany this paper. 20 Collins Street, Melbourne, Vic., 3000.