Abstract
Congenital absence of teeth presents a number of clinical challenges in young patients, and little is known about the success rate of restorative dental treatment in these patients. The aim of this study was to conduct a prospective clinical study of the performance of resin bonded bridges in patients with hypodontia.
Methods
A prospective clinical observation study was undertaken in Cork Dental School and Hospital, Ireland. Forty patients (22 males, 18 females; age range 18–21 years) with a confirmed diagnosis of hypodontia rated as mild (n = 26), moderate (n = 8) or severe (n = 6) participated. Following completion of the orthodontic phase of care, all patients had missing teeth restored with resin bonded bridgework (RBB) using a standardised protocol (48 FF; 17CL design). Patients were followed up for 24 months, with recall visits at 6, 12 and 24 months following provision of RBBs.
Results
65 RBBs were provided, 49 in the maxilla and 16 in the mandible; 43 bridges replaced anterior teeth and 22 replaced posterior teeth. After 24 months, 63 bridges were still in function and deemed to satisfy the preset criteria for success and survival. Two posterior bridges had failed due to repeated debond, and this was attributed to occlusal overload. 20% of the patients demonstrated some evidence of post orthodontic relapse, but this did not require further intervention.
Conclusion
In the short to medium term, resin bonded bridgework provides a reliable and minimally invasive solution for replacing missing teeth in patients with hypodontia.
1
Introduction
Hypodontia is the developmental absence of one or more primary or secondary teeth excluding third molar teeth. Hypodontia is categorized as mild when one to three teeth are absent; moderate when four to six teeth are absent and severe when more than six teeth are absent . Reports on the overall prevalence of missing permanent teeth, excluding third molars, vary substantially, and range from 2% to 10%. In Caucasians, 80% of tooth agenesis cases involve one or two teeth . Leaving aside third molars the mandibular second premolar is the most frequently missing tooth, followed by the maxillary lateral incisor or second premolar . Most studies show that females are affected more often than males by hypodontia. Hypodontia usually presents as an isolated anomaly ( nonsyndromic hypodontia) , but it is known to occur in association with syndromes or inherited disorders (syndromic hypodontia) , many of which have known genetic defects (e.g., Hypohidrotic Ectodermal Dysplasia). In addition to absence of teeth, affected patients quite frequently present with misshapen or small teeth. This causes social embarrassment due to dissatisfaction with appearance, and, problems with chewing food .
The outcome of treatment for patients with the congenital absence of teeth largely depends on early diagnosis and interdisciplinary co-operation, typically between the orthodontist and restorative dentist. The options available for restoration of teeth in young hypodontia patients are essentially those available for the replacement of missing teeth in adults and include removable partial dentures, conventional and adhesive fixed bridges and implant supported prostheses (once growth has been completed). Fixed restorations, specifically resin-bonded bridges and implant supported prostheses, are the preferred treatment for such patients. Removable partial dentures have a place as temporary tooth replacements and space maintainers following completion of orthodontic treatment. The timing and manner of their application must reflect the needs and limitations imposed by a young, growing individual . Adhesive rather than conventional bridgework is generally preferred as this avoids preparation of unrestored teeth, with the large pulp chambers commonly found in young individuals. Short clinical crowns of recently erupted permanent teeth and, in particular, retained primary teeth, can compromise the retention of both adhesive and conventional bridgework. Placement of implant-supported prostheses is unlikely to be considered until clinical signs of growth cessation are present. Implant retained crowns potentially offer a greater degree of predictability, but can be difficult to provide in patients with hypodontia. Bone volume is a major challenge, and the lack of alveolar bone development associated with failure to develop permanent tooth germs often leads to the requirement for alveolar ridge augmentation procedures.
The most conservative fixed option, resin bonded bridgework, has a variable track record in terms of reported outcomes. This is probably a reflection of the variation in approach to designs and techniques reported since the first reports of adhesively retained bridgework over 40 years ago. Pjetursson et al. conducted a systematic review and meta-analysis of the literature and reported an estimated survival rate for resin bonded bridges of 87.7% at 5 years. Debonding was the most common complication with RBBs, and there was no significant difference between anterior and posterior bridgework. However, this review did not specifically assess the impact of framework design on success and survival of RBBs, and a number of studies have compared fixed-fixed and cantilever framework designs. A significant body of work now suggests that outcomes with 2- unit cantilever (CL) designs have a more favourable outcome than 3 unit fixed-fixed (FF) designs. Some researchers have suggested that two-unit cantilever framework designs are less likely to debond than three unit fixed-fixed designs, the logic being that this design is less susceptible to dislodging forces in the mouth related to stress between abutments associated with FF designs. Hussey and Linden have reported a 94% success rate for this design for RBBs with a mean service time of 36.6 months. In a study of 211 two unit cantilever design (CL2) RBBs, Botelho et al. reported a success rate of 84.4% and survival rate of 90% in bridges with a mean service of 9.4 years. In their study, they mentioned the importance of bridge location, and indicated that bridges replacing teeth in mandibular molar region had the highest failure rate. King et al. reported on 5 and 10 year survival rates of 80.8% and 80.4% respectively for 771 RBBs, and stated that best survival rates were for those bridges with minimal tooth preparations (axial wall reduction only, or no preparation). They also reported that the hazard risk for failure of fixed-fixed RBB designs was twice that of cantilever designs. The trend in the literature from long term studies thus strongly suggests that single abutment cantilever bridges are the framework design of choice for resin bonded bridgework. However, there are very limited data in relation to the specific clinical context of hypodontia. In these cases, potentially unfavourable issues include the relatively small size of abutment teeth and use of abutment teeth which have been orthodontically repositioned. A potential issue with the cantilever design in this specific context is relapse of the orthodontically repositioned abutment tooth which is unsplinted. In a retrospective study of survival of 73 RBBs (62 cantilever; 11 fixed-fixed design) placed to restore missing maxillary lateral incisors in patients with hypodontia, Garnett et al. reported a debond prevalence of over 40%, with 20% of debonds attributed to “trauma” of an unspecified nature. They reported that the only significant predictor of survival was the experience of the operator, with more experienced operators achieving significantly better success rates. Framework design was not linked to success, but the authors did place a caveat that there were very few fixed-fixed design bridges in their study. Furthermore, their study did not report on details of fabrication of the bridges or whether rigidity of frameworks was standardised. There are no data from prospective studies specifically focussed on the survival of RBBs in the management of hypodontia, nor the incidence of post orthodontic relapse of abutment teeth retaining RBBs.
The aim of this study was to conduct a prospective clinical study of the performance of resin bonded bridges in patients with hypodontia.
2
Methods
The protocol for this prospective study was approved by the Clinical Research Ethics Committee of the Cork Teaching Hospitals, Ireland ( reference number ECM 5(9) 11/06). Patients with a confirmed diagnosis of non-syndromic hypodontia were recruited for the study from among those attending restorative treatment planning clinics at Cork University Dental School and Hospital, Ireland. Patients were included in the study where restoration of missing teeth with resin bonded bridgework was planned. The inclusion criteria for the study were the following:
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Small edentulous spans (no greater than one premolar size unit) bounded by sound teeth and unrestored teeth.
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Abutment teeth free of caries and periodontal disease.
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Favourable occlusion with minimal vertical overlap (overbite) and sufficient inter occlusal space assessed clinically, on articulated casts.
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Patient willingness to go through the clinical procedures and evaluation recall.
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Had completed a post-orthodontic retention period of a minimum of 6 months.
All patients who met the inclusion criteria for the study received information sheets and the purpose of the study was explained verbally. All participants were assured that their future management would not be affected by their decision on whether or not to participate in the study, and provided written consent to participation.
Diagnosis of congenital absence of teeth was based on clinical examination and confirmed by radiographic assessment. The patient assessment procedure involved a comprehensive clinical and radiographic examination with the formulation of a combined orthodontic and restorative treatment plan. The following demographic details were recorded on a pro-forma for patients who agreed to participate in the study: age, gender, details of treatment stages, and family history. During the course of clinical examination, the number and location of missing teeth was obtained.
2
Methods
The protocol for this prospective study was approved by the Clinical Research Ethics Committee of the Cork Teaching Hospitals, Ireland ( reference number ECM 5(9) 11/06). Patients with a confirmed diagnosis of non-syndromic hypodontia were recruited for the study from among those attending restorative treatment planning clinics at Cork University Dental School and Hospital, Ireland. Patients were included in the study where restoration of missing teeth with resin bonded bridgework was planned. The inclusion criteria for the study were the following:
- •
Small edentulous spans (no greater than one premolar size unit) bounded by sound teeth and unrestored teeth.
- •
Abutment teeth free of caries and periodontal disease.
- •
Favourable occlusion with minimal vertical overlap (overbite) and sufficient inter occlusal space assessed clinically, on articulated casts.
- •
Patient willingness to go through the clinical procedures and evaluation recall.
- •
Had completed a post-orthodontic retention period of a minimum of 6 months.
All patients who met the inclusion criteria for the study received information sheets and the purpose of the study was explained verbally. All participants were assured that their future management would not be affected by their decision on whether or not to participate in the study, and provided written consent to participation.
Diagnosis of congenital absence of teeth was based on clinical examination and confirmed by radiographic assessment. The patient assessment procedure involved a comprehensive clinical and radiographic examination with the formulation of a combined orthodontic and restorative treatment plan. The following demographic details were recorded on a pro-forma for patients who agreed to participate in the study: age, gender, details of treatment stages, and family history. During the course of clinical examination, the number and location of missing teeth was obtained.
3
Treatment protocol for rehabilitation
Upon completion of orthodontic treatment, a standardised clinical protocol was used to provide resin bonded bridgework. As all of the abutment teeth had been orthodontically repositioned, fixed-fixed framework designs were used in all cases restoring a single missing unit. Where spans were longer than a single unit (when both premolar teeth on one side were missing), the cantilever framework designs were used. The rationale for this was to avoid the interabutment stresses associated with long span FF designs. All tooth preparations and subsequent bridge cementation were undertaken by a single operator (LA). Anterior abutment teeth were prepared with palatal/lingual light chamfers and cingulum rests, with 0.5-mm palatal/lingual enamel reduction. Full axial wraparound was extended up to the centre of the inter-proximal contact to obtain maximum coverage, while preserving the proximal contact with the adjacent tooth. A light chamfer finish line was prepared in enamel 1.0 mm supra-gingivally. Proximal grooves were prepared on the mesial surfaces to a depth of 0.5 mm and parallel to the path of insertion. A rest seat was made on the lingual/palatal surface above the cingulum to facilitate accurate seating of the final bridge ( Fig. 1 ).
